Essay: Three-Phase Active Front End Rectifier Using Dsp Tms320F2812

Current harmonics, which are injected in the utility by non-linear loads, cause major problems that tend to deteriorate the power quality at mains. In power electronic systems, especially diode and thyristor rectifiers are commonly applied in the front end of dc-link power converters as an interface with the ac line power (grid).They are non-linear in nature and consequently, generate harmonic currents in ac line power. The high harmonic content of the line current and resulting low power factor of the load cause a number of problems such as voltage distortion and electromagnetic interference affecting the other users of power system increasing volt ampere ratings of the power system equipment (generators, transformers, transmission lines, etc). This problem is mitigated by employing a PWM rectifier. The most widely used PWM schemes are carrier-based sinusoidal PWM (SPWM) and space vector PWM (SVPWM). There is an increasing trend of using SVPWM because of their easier digital realisation and better dc bus utilization. Here, space vector PWM control scheme is employed. Using the instantaneous reactive power theory, the mathematical models in three-phase static and two-phase rotary coordinate system are built. Based on this theory and voltage-oriented vector control’s idea, introduces a dual-channel closed loop control strategy with current-inner-loop and voltage-outer-loop. This AFE rectifier can achieve unity power factor, sinusoidal current on AC side and constant output voltage on DC side. Using DSP TMS320F2812, the proposed algorithm is implemented. It is a 32-bit fixed point processor which offers 150 million instruction per second which is well suited for performing complex calculations very quickly. Open loop and close loop simulation of proposed strategy is being carried out using MATLAB/SIMULINK. Simulation of three-phase active front-end rectifier is verified under different loads and simulation results presented. The result shows the legitimacy of this model having UPF, constant DC output voltage and about 1% THD of input AC current.

Table of Contents

Abstract”””””””””””””””’.ii
Table of Content”””””””””””””’iii
List of Figures””””””””””””””..vi
List of Tables”””””””””””””’…….ix
Abbreviations””””””””””””””’x
Nomenclature””””””””””””””. xi
1 Introduction””””””””””’…………..2
1.1 Basic Idea’ ‘..4
1.2 Problem Identification 4
1.2.1 Problems Faced In Diode Rectifiers 5
1.3 Active Front End Rectifier 7
1.3.1 Active-front-end converter also called regenerative converter 8
1.3.2 Goals: 9
1.3.3 Functions: 9
2 Active Front End Rectifier”””””””’ ’11
2.1 Classification of Rectifiers 11
2.1.1 Simple Boost Type 12
2.1.2 Diode Rectifier with PWM Regenerative Braking Rectifier 12
2.1.3 Diode Rectifier with PWM Active Filtering Rectifier 13
2.1.4 Vienna Rectifier (3-Level Converter) 13
2.1.5 PWM Reversible Rectifier (2-Level Converter) 14
2.2 Key Features of Active Front End Rectifier 14
2.3 Block Diagram of Active Front End Rectifier 16
2.4 Operation of the Active Front End Rectifier. 17
2.4.1 Mathematical Description of the Active Front End Rectifier 19
2.5 Advantages of Active Front End Rectifier 21
2.6 Disadvantages of Active Front End Rectifier 21
2.7 Applications 21
3 Control Strategies for PWM Rectifier””””’..23
3.1 Introduction. 23
3.1.1 D-Q Theory 24
3.2 Voltage Oriented Control (VOC) 26
3.2.1 Decoupled Current Controller 28
3.3 Direct Power Control (DPC) 29
3.4 Pulse Width Modulation (PWM) Techniques 31
3.4.1 Sinusoidal Pulse Width Modulation (SPWM) 31
3.4.2 Space Vector Pulse Width Modulation (SVPWM) 32
4 Design of Parameters ”””””””””’35
4.1 General 35
4.2 Technical Specification 35
4.2.1 Output Specification 35
4.2.2 Design of AC-DC Converter 35
5 Simulation Model and Results”””””””.39
5.1 Open Loop Active Front End Rectifier Using SPWM 39
5.1.1 Block Diagram of Open Loop Active Front End Rectifier Using SPWM 39
5.1.2 Simulation Model of three phase Open loop Active Front End Rectifier Using SPWM 40
5.1.3 Simulation Results 41
5.2 Open Loop Active Front-End Rectifier Using SVPWM 43
5.2.1 Block Diagram of Open Loop Active Front End Rectifier Using SVPWM 43
5.2.2 Simulation Model of three phase Open loop Active Front End Rectifier Using SVPWM 43
5.2.3 Simulation Results 45
5.3 Closed Loop Active Front End Rectifier Using SVPWM 46
5.3.1 Block Diagram of Closed Loop Active Front End Rectifier Using SVPWM 46
5.3.2 Simulation Model of three phase closed loop Active Front End Rectifier Using SVPWM 47
5.3.3 SVPWM Generation Block 51
5.3.4 Ideal and simulated pulses of PWM generation block 54
6 Hardware Design and Results”””””””..56
6.1 Hardware Block Diagram 56
6.2 AC Inductor Design 57
6.3 Sensor Circuit Design 57
6.3.1 AC Sensors 57
6.3.2 DC Sensor 60
6.3.3 Hardware of Sensing Circuits 61
6.4 DSP TMS320f2812 61
6.4.1 Description of DSP 320F2812 62
7 Conclusion And Future Scope”””””””’64
7.1 Conclusion. 64
7.2 Future Scope 64
APPENDIX A”””””””””””””’…65
APPENDIX B””””””””””””””66
APPENDIX C””””””””””””””67
References””””””””””””””’..68
List of Figures
Figure 1.1: Most Popular Three-Phase Harmonic Reduction Techniques of Current. 2
Figure 1.2: Two Basic Topologies of PWM Rectifier 3
Figure 1.3: Multipulse Diode Rectifiers with Input Current 6
Figure 1.4: Typical Waveforms of Current At Mains And Characteristic Harmonic 7
Figure 1.5: Active Front End System 8
Figure 1.6: DC distributed power system 8
Figure 2.1: Simple Boost Type Converter 12
Figure 2.2: Diode Rectifier with PWM Regenerative Braking Rectifier 12
Figure 2.3: Diode Rectifier with PWM Active Filtering Rectifier 13
Figure 2.4: Vienna Rectifier (3-Level Converter) 13
Figure 2.5: PWM Reversible Rectifier (2-Level Converter) 14
Figure 2.6: Block Diagram of Active Front End Rectifier 16
Figure 2.7: Simplified Representation of Three-Phase PWM Rectifier 17
Figure 2.8: Phasor Diagram for the PWM Rectifier 17
Figure 2.9: Switching State of Active Front-End Rectifier 18
Figure 2.10: Relationship Between Vectors of The Active Front-End Rectifier 19
Figure 3.1: Relationship between control of PWM rectifier and PWM inverter ‘ fed IM 23
Figure 3.2: Classification of control methods for PWM rectifier 24
Figure 3.3: three-phase (abc) to two-phase (??-??) stationary reference frame and stationary to rotating (d-q) reference frame (Park transformation) 25
Figure 3.4: Block diagram of the voltage oriented scheme (VOC) 26
Figure 3.5: Vector diagram of VOC transformation from ??-?? tod-q coordinates 27
Figure 3.6: Decoupled current control of PWM rectifier 28
Figure 3.7: Block diagram of DPC with PLL generator 29
Figure 3.8: Selection of region in DPC 30
Figure 3.9: Sinusoidal PWM waveforms 31
Figure 3.10: Space voltage vectors representation 32
Figure 5.1: Block Diagram of Open Loop 3 Phase Active Front End Rectifier 39
Figure 5.2: Simulation Model of three phase Open loop Active Front End Rectifier Using SPWM 40
Figure 5.3: Waveform of Output Voltage 41
Figure 5.4: Waveform of Output Current 41
Figure 5.5: Waveform of Input Voltage and Current 41
Figure 5.6: Switching Pulses generated by comparison of Carrier Signal and Reference Signal 42
Figure 5.7: FFT Analysis of Input Current 42
Figure 5.8: Block Diagram of Open Loop 3 Phase Active Front End Rectifier 43
Figure 5.9: Simulation Model of three phase Open loop Active Front End Rectifier Using SVPWM 44
Figure 5.10: Waveform of Output DC Voltage 45
Figure 5.11: Waveform of Output DC Current 45
Figure 5.12: Block Diagram of Closed Loop Active Front End Rectifier 46
Figure 5.13: Simulation Model of Active Front End Rectifier with R Load 47
Figure 5.14: Output Voltage Waveform of Closed Loop AFE Rectifier with R Load 48
Figure 5.15: Output Current Waveform of Closed loop AFE Rectifier with R Load 48
Figure 5.16: input Voltage and Current Waveform of Closed loop AFE Rectifier with R Load 48
Figure 5.17: FFT Analysis of Input Current of AFE Rectifier with R Load 49
Figure 5.18: Simulation Model of Active Front End Rectifier with RL Load 49
Figure 5.19: Output Voltage Waveform of Closed Loop AFE Rectifier with RL Load 50
Figure 5.20: Output Current Waveform of Closed Loop AFE Rectifier with RL Load 50
Figure 5.21: Input Voltage and Current Waveform of Closed Loop AFE Rectifier with RL Load 50
Figure 5.22: FFT Analysis of Input Current of AFE Rectifier with RL Load 51
Figure 5.23: SVPWM Generation Block 51
Figure 5.24: Ideal and Practical Switching Pattern For Each Sector 54
Figure 6.1: Block Diagram of Hardware Implementation 56
Figure 6.2: Inductor 57
Figure 6.3: Voltage sensing circuit 58
Figure 6.4: Hardware Result for AC Voltage Sensor (sensed AC voltage after shifting) 58
Figure 6.5: Hardware Result for AC Voltage (CH1: sensed AC voltage after shifting, CH2: Single Phase AC Voltage- 230 V.) 58
Figure 6.6: current sensing circuit 59
Figure 6.7: Hardware Result for AC current sensor 59
Figure 6.8: DC Voltage Sensing Circuit 60
Figure 6.9: Hardware Results of DC Voltage Sensor 60
Figure 6.10: Hardware of Sensing Circuit 61
Figure 6.11: Hardware Kit for DSP320F2812 61

List of Tables
Table 1: Features of Three-Phase Rectifiers 15
Table 2: Specification Used In Simulation of Open Loop AFE Rectifier Using SPWM 40
Table 3: Specification Used In a Simulation of Open Loop AFE Rectifier Using SVPWM 44
Table 4: Specification Used In a Simulation of Closed Loop AFE Rectifier Using SVPWM 47
Table 5: Sector Identification 52

Abbreviations
ADC””””””””””…’Analog to Digital Converter AFE””””””””””””’.’Active Front End ALC”””””””””””’.Active Line Conditioner CSI””””””””””””Current Source Inverter DPC””””””””””””..Direct Power Control DPF”””””””””””.Displacement Power Factor DSP”””””””””””’..Digital Signal Processor EMI””””””””””’.Electro Magnetic Interference FFT””””””””””””Fast Fourier Transform FOC””””””””””””Field Oriented Control IGBT”””””””””..’Insulated Gate Bipolar Transistor OPAMP””””””””””’…’Operational Amplifier PLL”””””””””’..”””Phase Locked Loop PWM”””””””””””’Pulse Width Modulation SPWM””””””””…’Sinusoidal Pulse Width Modulation SVM”””””””””””’Space Vector Modulator SVPWM””””””””Space Vector Pulse Width Modulation THD”””””””””””..Total Harmonic Distortion UPF””””””””””””..’Unity Power Factor VOC””””””””””’….’Voltage Oriented control VSI””””””””””””Voltage Source Inverter

Nomenclature
””””””””””””””””??..angle””””””””””””””””?? phase ”””””””””””’??…….”.angular frequency f”””””””””””””’…supply frequency fs””””””””””””’….switching frequency M”””””””””””””’modulation index kp, ki’…””””””’proportional control part, integral control part V””””””””””””??.”..alpha axis voltage V”””””””””””’??.””beta axis voltage Va””””””””””””””a phase voltage Vb”””””””””””””..’.b phase voltage Vc”””””””””””””’….c phase voltage Vd””””””””””””’…d axis active voltage Vq”””””””””””’..’..q axis reactive voltage Sa, Sb, Sc””””’..”””.”’switching state of the converter ur””””””””””’..”’.input voltage of rectifier X, Y, Z””””””””””””.universal variables T”””””””””””..”””switching time

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CHAPTER 1
INTRODUCTION

Introduction
A nonlinear load, is a source of current harmonics, which produce increase of reactive power and power losses in transmission lines. The harmonics also cause electromagnetic interference and, sometimes, dangerous resonances. Moreover, nonlinear loads and non-sinusoidal currents produce non-sinusoidal voltage drops across the network impedances, so that a non-sinusoidal voltage appears at several points of the mains.
Restrictions on current and voltage harmonics maintained in many countries through IEEE 519-1992 in the USA and IEC 61000-3-2/IEC 61000-3-4 in Europe standards, are associated with the popular idea of clean power.
Many of harmonic reduction method exist [1]. These techniques based on passive components, mixing single and three-phase diode rectifiers, and power electronics techniques as: multipulse rectifiers, active filters and PWM rectifiers Figure 1.
They can be generally divided as:
A) Harmonic reduction of already installed non-linear load;
B) Harmonic reduction through linear power electronics load installation

Figure 1.1 Most Popular Three-Phase Harmonic Reduction Techniques of Current.
Power electronics equipments become more widely used. Unfortunately the standard diode or thyristor bridge rectifiers at the input side cause several problems like: low input power factor, high value of harmonic distortion of AC line currents and harmonic pollution on the grid.
The PWM rectifier is preferred choice for providing a DC voltage source for DC loads or voltage source fed drives, due to its capacity of input power factor regulation, line current harmonic mitigation, DC voltage control and bidirectional power flow.
The interesting current harmonic reduction technique is a PWM (active) rectifier, which is shown in Figure 1.2 Two types of PWM converters, with a voltage source output (Figure 1.2(a)) and a current source output (Figure 1.2(b)) can be used. First of them called a boost rectifier (increases the voltage) works with fixed DC voltage polarity, and the second, called a buck rectifier (reduces the voltage) operates with fixed DC current flow.

Figure 1.2: Two Basic Topologies of PWM Rectifier:
Boost with Voltage Output b) Buck with Current Output
The main features of PWM rectifier are:
Bi-directional power flow,
Nearly sinusoidal input current,
Regulation of input power factor to unity,
Low harmonic distortion of line current (THD below 5%),
Adjustment and stabilization of DC-link voltage (or current),
Reduced capacitor (or inductor) size due to the continues current.
Furthermore, it can be properly operated under line voltage distortion and notching, and line voltage frequency variations.
The PWM rectifier has a complex control structure; the efficiency is lower than the diode rectifier due to extra switching losses. A properly designed low-pass passive filter is needed in front of the PWM rectifier due to EMI concerns.
This technique is most promising thanks to advances in power semiconductor devices (enhanced speed and performance, and high ratings) and digital signal processors, which allow fast operation and cost reduction. It offers possibilities for implementation of sophisticated control algorithm.
Basic Idea
In this report, an Active Front-End Rectifier For reactive power compensation is analyzed. The vector control method is used for high performance control of any type of load (e.g. induction motor Drive). To achieve better dynamic performance the decoupled control is also used in the line-side. The Space Vector Pulse Width Modulation (SVPWM) scheme is used to control IGBT switches in rectifier bridges.
The system model is obtained using D-q rotating frame theory. The line currents are decomposed into iq and id components. The iq component is used to control the reactive power. The Id component is used to control the DC-link voltage and also to supply active power required by the motor. A high gain feedback with input-output linearization control is presented to remove coupling between iq and id currents. A load power feed-forward loop is added to the DC-link voltage controller for fast dynamic response.
Using dynamic d-q model, the Drive performance is analyzed to define system specifications. The simulation model is built in a MATLAB/SIMULINK. The complete system hardware comprising of switches, line inductors, DC-link capacitor bank and the load is implemented in a MATLAB/SIMULINK.
Problem Identification
In power electronic systems, especially, diode and thyristor rectifiers are applied in the front end of dc-link power converters as an interface with the ac line power (grid). The rectifiers are nonlinear in nature and, consequently, generate harmonic currents in the ac line power. The affects on the electrical parameters at input side.
Current
The current drawn from AC supply system is not a pure sinusoidal as the active converters creates the phase displacement of current with respect to voltage. To regulate the DC link voltage, the controlled rectifier is required which creates very high distortion in the current especially when operated at lower firing angle.
Power factor
The major drawback of the controlled rectifier is that it creates a lagging input displacement power factor at the lower firing angles. The high harmonic content of the line current and the resulting low power factor of the load cause a number of problems in the power distribution system:
a. Voltage distortion and electromagnetic interface (EMI) affecting other users of the power system
b. Increasing volt-ampere ratings of the power system equipment (generators, trans- formers, transmission lines, etc.)
Problems Faced In Diode Rectifiers
Method is simple but suffers from the demerits due to Cost of transformer Size and weight
Poor dynamic response
Poor input power factor
High % THD on source side
Unidirectional power flow does not allow regeneration
[2]. There are guidelines for harmonic regulation such as the IEEE STD 519 recommendations. Some techniques can be used to reduce the harmonic currents such as:
Passive filters:
If the passive filters are connected at the input side, the LC circuit is excited by the harmonic voltages already present due to the other non-linear loads. Because utility power supply having the low line resistance, the LC resonance circuit may not be sufficiently damped and oscillations and over voltages may occur. This may destroy the rectifier components.
Multipulse Rectifier:
[3]Here, the cascade connection of 6 pulse 3 phase diode rectifiers with the use of phase shifting transformer to feed the rectifiers. The characteristic harmonics generated by these rectifiers are cancelled by the harmonics generated by others sets of rectifiers.
This mitigation is performed by the appropriate design of the phase shifting transformer with multipulse secondary.

In a multipulse rectifier, the generated characteristic harmonics are given by:
h= P.n ?? 1
Where: n – An integer (1, 2, 3, 4 …’)
h – Harmonic order,
P – The number of pulses of the rectifier.
Figure 1.3Shows multipulse Diode rectifier with their input current at primary of phase shifting transformers Figure 1.3(a) Shows 6 pulse Diode rectifier ,it uses two secondary transformers which are connected in delta/why connection. Figure 3(b) shows 12 pulse rectifier, it uses three secondary transformers, which are connected in delta/delta, delta /+20??,delta/-20?? deltta while Figure 1.3(c) shows 18 pulse rectifier with their input currents[4].

Figure 1.3: Multipulse Diode Rectifiers with Input Current

Figure 1.4 Typical Waveforms of Current At Mains And Characteristic Harmonic
For 6/12/18 Pulse Diode Rectifier

Figure 1.4 shows typical waveforms of current at mains and characteristic harmonic for 6/12/18 pulse Diode Rectifier.
It is possible to meet all IEEE STD 519 requirements with an 18 pulse diode rectifier. On the other hand, the drawbacks of this configuration is that they are using low voltage power cells in series or cascade connection at the inverter section and they have to supply each power cell separately, so they use a transformer with more isolated secondaries. A disadvantage for this strategy is that the transformer must be located close to the VSD because the voltage drops and the excessive number of cables and connections. The costs involved for cooling and space requirements should be considered in this case. The phase shifting transformer should be designed to allow the additional losses introduced by the input rectifier harmonic currents.
Active Front End Rectifier
The term Active Front End Rectifier refers to the power converter system consisting of the Line’side converter with active switches such as IGBTs, the dc-link capacitor bank, and the load. This converter, during regeneration it can also be operated as an inverter, feeding power back to the line. Active Front End Rectifier is popularly referred to as a PWM rectifier. This is due to fact that, with active switches, the rectifier can be switched using suitable pulse width modulation technique. The PWM rectifier basically operates as a boost chopper with AC voltage at the input, But the DC voltage at the output. The intermediate voltage should be higher than the peak of supply voltage [1]. This is required to avoid saturation of the PWM controller due to insufficient DC link voltage, resulting in line side harmonics. The required DC-link voltage needs to be maintained constant during operation. The ripple in DC-link voltage can be reduced using an appropriately sized capacitor bank. The Active Front-End Rectifier for any type of load is shown in Figure 1.5. The configuration uses 6 controllable switches. The inductor is needed for boost operation of the line side converter.

Figure 1.5: Active Front End System
For a constant DC-link voltage, the IGBTs are switched to produce three-phase PWM voltages at a, b, and c input terminals. The PWM voltages, generated in this way, control the line currents to the desired value. When DC-link voltage drops below the reference value, the feedback diodes carry the capacitor charging currents, and bring the DC-link voltage back to reference value.
Active-front-end converter also called regenerative converter
Replacing the diode or SCR rectifier bridge for turn-on / turn-off controlled switches it is possible to implement an Active Front End (AFE) converter also called regenerative converter, which can also be used to reduce the harmonic components of the input current.

Figure 1.6 DC distributed power system
However, the obtained THD with these converters is close to an 18 pulse solution. Active Front-End converters are more suitable for applications where motor repetitive braking is needed and the economy obtained, regenerating the energy back to the power supply, justifies the investment of this solution [1].
Figure 1.6 shows the typical example of this. The line-side converter operates as a rectifier in forward energy flow, and as an inverter in reverse energy flow. In further discussion assuming the forward energy flow as the basic mode of operation the line-side converter will be called a PWM rectifier. The ac side voltage of the PWM rectifier can be controlled in magnitude and phase so as to obtain sinusoidal line current at unity power factor (UPF). Although such a PWM rectifier/inverter (ac/dc/ac) system is expensive, and the control is complex, the topology is ideal for four-quadrant operation. Additionally, the PWM rectifier provides dc bus voltage stabilization and can also act as an active line conditioner (ALC) that compensates harmonics and reactive power.
Goals:
Low harmonic distortion of AC (mains) current
Unity power factor
Obtain the system dynamic model and present effective decoupling control strategies for better transient performance.
Functions:
Complete control of harmonics
Complete control of reactive power
Complete control of DC bus bar voltage
Completely energy reversibility

CHAPTER 2
ACTIVE FRONT END RECTIFIER
Active Front End Rectifier
Classification of Rectifiers
An Active Front End Rectifier can categorically be classified in different ways as follows:

Converter Based.

VSI

CSI

Supply system based classification.

Single -‘

Three – ‘

Topology Based.

Simple Boost-type Rectifier

Diode Rectifier with PWM Regenerative braking Rectifier

Diode Rectifier with PWM active filtering Rectifier

Vienna Rectifier (3-level converter)

PWM Reversible Rectifier (2-level converter).

Simple Boost Type

Figure 2.1: Simple Boost Type Converter
The circuit of Simple Boost Type Converter is shown in Figure 2.1. This type of PWM rectifiers presents a simple solution of boost-type converter with the possibility to increase dc output voltage. This is an important feature for ASD’s converters giving maximum motor output voltage. The main drawback of this solution is stress on the components and low-frequency distortion of the input current.
Diode Rectifier with PWM Regenerative Braking Rectifier

Figure 2.2: Diode Rectifier with PWM Regenerative Braking Rectifier
The Circuit of Diode Rectifier with PWM Regenerative Braking Rectifier is shown in Figure 2.2.This topology used PWM rectifier modules with a very low current rating. Hence they have a low cost potential and provide only the possibility of regenerative braking mode. It can not improve the input power quality and power factor.
Diode Rectifier with PWM Active Filtering Rectifier

Figure 2.3: Diode Rectifier with PWM Active Filtering Rectifier
The circuit of Diode Rectifier with PWM Active Filtering Rectifier is shown in Figure 2.3. This topology is similar to (b) so use PWM rectifier modules with a very low current rating .Hence they have a low cost potential and provide active filtering ,line side power conditioning and improving power factor. The feedback of regenerative energy is not possible in it.
Vienna Rectifier (3-Level Converter)

Figure 2.4: Vienna Rectifier (3-Level Converter)
The circuit of Vienna Rectifier (3-Level Converter) is shown in Figure 2.4. This topology presents a Three-level converter called a Vienna rectifier. The main advantage is low switch voltage, provides the active filtering, line side power conditioning and improving power factor, but non-typical switches are required.

PWM Reversible Rectifier (2-Level Converter)

Figure 2.5: PWM Reversible Rectifier (2-Level Converter)
The circuit of PWM Reversible Rectifier (2-Level Converter) is shown in Figure 2.5. This topology presents the most popular topology used in UPS and more recently as a PWM rectifier. This universal topology has the advantage of using a low-cost three-phase module with a bidirectional energy flow capability. The line side converter is popularly referred to as a PWM rectifier. This is due to fact that, the rectifier can be switched using suitable pulse width modulation technique. This PWM rectifier basically operates as a boost chopper with AC voltage at the input, but DC voltage at the output.
Key Features of Active Front End Rectifier
Regenerative capabilities: Normally power flows from supply-side to the motor. The line-side converter operates as rectifier, whereas load side converter operates as an inverter. During regenerative braking mode, their respective roles are reversed. The system can continuously regenerate power if the machine is generator, such as in wind generation system.

Unity power factor Operation: With the line currents in phase with the line voltages, the unwanted reactive currents are eliminated. Since regeneration is also possible at unity power factor, the overall power quality is improved significantly. The converter will be able to supply the same active power but at reduced current ratings. Thus an increased cost of the converter on account of using active power switches can be justified for high power applications.

Reactive power Compensation: Alternatively, the KVA ratings saved due unity power factor operation can be used to provide reactive power compensation to the utility system.

Line supply voltage fluctuations are compensated

Interface between Distributed Energy source and utility: The line side converters are applicable whenever a DC bus is to be connected to the AC grid. Usually this is the case for distributed energy sources such as fuel cells, micro turbines, or variables speed wind energy plants employing a DC link. The PWM rectifier facilitates the flow of power from distributed sources to the utility at a fixed frequency and at desired power factor.

Extremely high drive dynamic performance

Sinusoidal line currents [5], [6].

Table 1: Features of Three-Phase Rectifier

Block Diagram of Active Front End Rectifier

Figure 2.6: Block Diagram of Active Front End Rectifier
Block diagram Of Active Front End Rectifier is shown in Figure 2.6. The overall system contains 3 paths 1) Forward path, 2) Feed-Forward path and 3) Feed-Back path; hence Active Front-end Rectifier is a Dual Close Loop System
Forward path goes from Source to load through input resister and inductor, 6 IGBT Bridge, output capacitor. Feed-Forward path starts from sensing of three phase input voltage and current to Decoupled controller via abc to dq transformation. Feed-Back path senses output Dc link voltage and compare that with desired reference voltage and transfers error to Decoupling Block. Overall system operation can be understood from the points given below.
From the supply mains, the AC power feed to the active fronted rectifier which produces the DC output with the help of SPWM signal generation block.
Here, three phase to two phase transformation is done with the help of Clarke and Park transformation.
The output voltage is compared with the reference voltage produce an error.
This error and dq components of input voltage is given to decoupling controller.
Output of decoupling controller is transformed into alpha-beta components via dq to alpha-beta transformation.
These alpha-beta components are given to Space Vector PWM generation (SVPWM) block and generate gating pulses for 6 Switches (IGBT). This gating pulses controls switching of IGBTs and gives Unity Power Factor as well as Sinusoidal input current.
Operation of the Active Front End Rectifier.
Figure 2.7(b) Shows a single-phase representation of the rectifier circuit presented in Figure 2.7(a). L and R represent the line inductor. uL is the line voltage and uS is the bridge converter voltage controllable from the DC-side. Magnitude of uS depends on the modulation index and DC voltage level.

Figure 2.7: Simplified Representation of Three-Phase PWM Rectifier
For Bi-Directional Power Flow
Main Circuit, B) Single Phase Representation of Rectifier Circuit
Inductors connected between input of rectifier and lines are integral part of the circuit. It brings current source character of input circuit and provide boost feature of converter. The line current iL is controlled by the voltage drop across the inductance L interconnecting two voltage sources (line and converter).

Figure 2.8: Phasor Diagram for the PWM Rectifier A) General Phasor Diagram
Rectification at Unity Power Factor C) Inversion at Unity Power Factor
It means that the inductance voltage uI equals the difference between the line voltage uL and the converter voltage uS. When we control phase angle ?? and amplitude of converter voltage uS, we control indirectly phase and amplitude of line current. In this way average value and sign of DC current is subject to control what is proportional to active power conducted through converter. The reactive power can be controlled independently with shift of fundamental harmonic current IL in respect to voltage UL.
Figure 2.8presents general phasor diagram and both rectification and regenerating phasor diagrams when unity power factor is required. The figure shows that the voltage vector uS is higher during regeneration (up to 3%) then rectifier mode. It means that these two modes are not symmetrical
Main circuit of bridge converter (Figure 2.7(a) consists of three legs with IGBT transistor or, in case of high power, GTO thyristors.
The bridge converter voltage can be represented with eight possible switching states Figure 2.9 six-active and two-zero) [7] described by equation:

u_(k+1) = 2/3 u_dc e^(jk’??3) for k=0…5 (2.1)
0

Figure 2.9: Switching State of Active Front-End Rectifier
Mathematical Description of the Active Front End Rectifier
The basic relationship between vectors of the Active Front End Rectifier is presented in Figure 2.10
Description of line voltages and currents
Three phase line voltage and the fundamental line current is
U= E_m cos’??t (2.2a)
U_b= E_m cos'(??t+2??/3) (2.2b)
‘ U’_c= E_m cos'(??t-2??/3) (2.2c)
‘ i’_a= I_m cos'(??t+??) (2.3a)
‘ i’_b= I_m cos'(??t+2??/3+??) (2.3b)
i_c= I_m cos”(??t-2??/3+??) ‘ (2.3c)
where Em (Im) and ”are amplitude of the phase voltage (current) and angular frequency, respectively, with assumption
ia + ib + ic = 0 (2.4)

Figure 2.10: Relationship Between Vectors of The Active Front-End Rectifier
Description of input voltage in Active Front End rectifier

Line to line input voltages of PWM rectifier can be described with the help of
Figure 2.7 as:[8]
U_a=L di_a/dt+Ri_a+U_ra
‘ U’_b=L di_b/dt+Ri_b+U_rb (2.5)
U_c=L di_c/dt+Ri_c+U_rc
Line to line input voltages of PWM rectifier can be described with the help of Figure 15 as:
Ura =[Sa- 1/3 (S_a+S_b+S_c ) ] U_dc
Urb =[Sb- 1/3 (S_a+S_b+S_c ) ] U_dc (2.6 )
Urc =[Sc- 1/3 (S_a+S_b+S_c ) ] U_dc

Description of Active Front End rectifier

Model of three-phase PWM rectifier

The voltage equations for balanced three-phase system without the neutral connection
can be written as (Figure 2.7)):
uL = uI + uS (2.7 )
U_L=Ri_L+L di_L/dt+U_S (2.8 )
”(U_a@U_b@U_c )’ = R”(i_a@i_b@i_c )’+ L d/dt ”(i_a@i_b@i_c )’+ ”(U_sa@U_sb@U_sc )’ (2.9) additionally for currents
C(dV_dc)/dt = Saia + Sbib + Scic – iL (2.10)
Model of Active Front-End rectifier in synchronous rotating coordinates (d-q)

The equations in the synchronous d-q coordinates are obtained using the park coordinate transformation[12].
P=2/3 [‘(cos’??&cos'(??-2′??3)&cos'(??+2′??3)@sin’??&sin'(??-2′??3)&sin'(??+2′??3)@1/2&1/2&1/2)] (2.11)
L (di_d)/dt = u_d-Ri_d+??Li_q-u_rd
L (di_q)/dt = u_q-Ri_q+??Li_d-u_rd (2.12)
C (dV_dc)/dt=3/2 (S_d i_d+S_q i_q )-V_dc/R_L
Where: S_d=S_?? cos”??t+S_?? sin’??t ‘; S_q=S_?? cos”??t-S_?? sin’??t ‘
u_(rd=) S_(d.) U_dc; U_(rq=) S_q ‘.V’_dc
urd ,urq, and Sd , Sq are input voltage of rectifier, switch function in synchronous rotating d-q coordinate, respectively. ud, uq and id, iq are voltage source, current in synchronous rotating d-q coordinate, respectively. ?? is angular frequency[9].
Advantages of Active Front End Rectifier
Four quadrant operation
Unity power factor
The PWM rectifier also acts as an active line conditioner (ALC) that compensates harmonic and reactive power.
Operating cost is simultaneously reduced due to lower reactive power and losses.
It provides DC bus voltage stabilization.
Disadvantages of Active Front End Rectifier
Active Front-End rectifier’s capital cost is high but it eliminates power factor correction system and harmonic filters.
Complex control
Applications
Converter for solar and wind power plant
Converter in variable speed drive with regenerative braking
Converter in wind and water turbines.
Cranes and elevator system
Paper and rolling mill system
Traction (mainly single phase)

CHAPTER 3
CONTROL STATEGIES FOR
PWM RECTIFIER

Control Strategies for PWM Rectifier
Introduction
Various control strategies have been proposed in recent works on this type PWM converter. Although these control strategies can achieve the same main goals, such as the high power factor and near-sinusoidal current waveforms, their principles differ. Particularly, the Voltage Oriented Control (VOC) which guarantees high dynamic and static performance via an internal current control loops, has become very popular and has constantly been developed and improved. Consequently, the final configuration and performance of the VOC system largely depends on the quality of the applied current control strategy [10].

Figure 3.1: Relationship between control of PWM rectifier and PWM inverter ‘ fed IM
Another control strategy called Direct Power Control (DPC) is based on the instantaneous active and reactive power control loops. In DPC there are no internal current control loops and no PWM modulator block, because the converter switching states are selected by a switching table based on the instantaneous errors between the commanded and estimated values of active and reactive power. Figure 3.1shows the relationship between control of PWM rectifier and inverter.
The main advantages of VOC over DPC is low sampling frequency for good performance, cheaper A/D converter and fixed switching frequency so design of input inductor is easier. There are some disadvantages of VOC like coupling occurs between active and reactive component but it can be resolved by a decoupling controller.

Figure 3.2: Classification of control methods for PWM rectifier
The control techniques for PWM rectifier can be generally classified as voltage based and virtual flux based, as shown in Figure 3.2. The virtual flux based method corresponds to direct analogy of IM control [1].
D-Q Theory
A system of three-phase, sinusoidal, time varying voltages can be represented by an equivalent two-phase system. Consider a balanced, 3-??, Y-connected voltages Va, Vb, Vc, which are 120 degree apart. It is assumed that there is no neutral connection. Consider a stationary, two-axis coordinate system, where the ??-axis is aligned with Va, and ??-axis is orthogonal to the ??-axis as shown in Figure 3.3 [11]. The 3-?? voltages have component on both ?? and ?? axis. The ?? ‘ ?? axis components can be expressed in matrix form as,
[ ‘(V_??@V_?? ) ]= [ ‘(1&-1/2&-1/2@0&’3/2&-‘3/2) ] [ ‘(V_a@V_b@V_c ) ]
However, in order that the two coordinate systems are equivalent, the instantaneous power in both coordinate systems should be equal.
Pdq = Pabc
where, Pabc is power in 3-?? circuit, and Pdq is power in equivalent 2-?? system. To meet this requirement, the transformation matrix needs to be multiplied by a factor ‘2/’3 . The new transformation matrix C1 is,
C_1= ‘2/’3 [ ‘(1&-1/2&-1/2@0&’3/2&-‘3/2) ] ; C_1^(-1)= ‘2/’3 [ ‘(1&0@-1/2& ‘3/2@-1/2&-‘3/2) ]
The equation 3.1 can be rewritten as (Clark transformation),
[ ‘(V_??@V_?? ) ]= ‘2/’3 [‘(1&-1/2&-1/2@0&’3/2&-‘3/2)] [ ‘(V_a@V_b@V_c ) ]
and inversely,
[ ‘(V_a@V_b@V_c ) ]= ‘2/’3 [‘(1&0@-1/2& ‘3/2@-1/2&-‘3/2)] [ ‘(V_??@V_?? ) ]
Note that parameters V??, V?? in 2-?? stationary reference frame are still time-varying. Because most of the electric circuits are associated with inductances, the time varying parameters such as sinusoidal currents and voltages tends to make the system model complex and system response is often sluggish.
R. H. Park proposed in 1920 [12] to transform these variables to a fictitious reference frame rotating at some angular speed. If this speed of operation is same as the angular frequency of time varying parameters, then all the parameters in this reference frame become time invariant or DC quantities. Because the effect of inductances associated with varying currents and voltages is removed, the system model is relatively simple and system can be sufficiently fast. Figure 3.3 illustrates clark and park transformation.

Figure 3.3: three-phase (abc) to two-phase (??-??) stationary reference frame and stationary to rotating (d-q) reference frame (Park transformation)
The voltages on the ?? ‘ ?? axis can be converted into the d ‘ q frame as follows (Park transformation):
[‘(V_d@V_q )]= [‘(cos”??_e ‘&sin”??_e ‘@-sin”??_e ‘&cos”??_e ‘ )] [‘(V_??@V_?? )]
and inversely,
[ ‘(V_??@V_?? ) ]= [ ‘(cos”??_e ‘&’-sin”’??_e ‘@sin”??_e ‘& cos”??_e ‘ ) ] [ ‘(V_d@V_q ) ]
The Park’s transformation matrix is referred to as C2,
C_2 = [ ‘(cos”??_e ‘&sin”??_e ‘@-sin”??_e ‘&cos”??_e ‘ ) ]; C_2^(-1) = [ ‘(cos”??_e ‘&-sin”??_e ‘@sin”??_e ‘& cos”??_e ‘ ) ]
Note that both the matrices C1 and C2 are orthogonal matrices such that,
C_1^T C_1= C_1 C_1^T=I and C_2^T C_2= C_2 C_2^T=I
where, I represents an identity matrix.

Voltage Oriented Control (VOC)
Similarly to FOC of an induction motor, voltage oriented control (VOC) for line side PWM rectifier is based on coordinated transformation between stationary ??-?? and synchronous rotating d-q reference systems. This strategy guarantees fast transient response and high static performance via an internal current control loops [1].

Figure 3.4: Block diagram of the voltage oriented scheme (VOC)
The conventional control system uses closed loop current control in a rotating reference frame, the Voltage Oriented Control (VOC) scheme is shown in Figure 3.4.
A characteristic feature for this current controller is the processing of the signals in two coordinated systems. The first is the ”? and the second is the synchronously rotating d-q coordinate system. Three-phase measured values are converted into stationary two phase system (??-??) and then into rotating coordinate system (d-q) as shown in equation 3.6 and 3.7.
For both coordinate transformations the angle of the voltage vector ??ul is defined as,
sin”??_ul ‘= U_l??/'((U_l??^2+ U_l??^2 ) )
cos”??_ul ‘= U_l??/'((U_l??^2+ U_l??^2 ) )
In voltage oriented d-q coordinates, the ac line current vector iL is split into two rectangular components iL = [iLd, iLq] as shown in Figure 3.5. The component iLq determines reactive power, whereas iLd decides active power flow. Thus the reactive and the active power can be controlled independently [13].

Figure 3.5: Vector diagram of VOC transformation from ??-?? tod-q coordinates
The UPF condition is met when the line current vector iL is aligned with the line voltage vector vL. By replacing the d-axis of the rotating coordinates on the line voltage vector a simplified dynamic model can be obtained. The voltage equations in the d-q synchronous reference frame are as follows,
u_Ld=Ri_Ld+L (di_Ld)/dt+ u_Sd- ??Li_Lq
u_Lq=Ri_Lq+L (di_Lq)/dt+ u_Sq- ??Li_Ld

As in Figure 3.4, the q-axis current is set to zero in all condition for unity power factor control while the reference current iLd is set by the DC link voltage controller and controls the active power flow between the supply and DC link. For R = 0 the above equation can be reduced to:
u_Ld=L(di_Ld)/dt+ u_Sd- ??Li_Lq
0=L (di_Lq)/dt+ u_Sq- ??Li_Ld
Assuming that the q-axis current is well regulated to zero,
u_Ld=L(di_Ld)/dt+ u_Sd
0=u_Sq+ ??Li_Ld
As the current controller, the PI-type can be used. However, the PI current controller has no satisfactory tracing performance especially for the coupled system described by above equations.
Decoupled Current Controller
For a high performance application with accuracy current tracking at a dynamic state the decoupled controller diagram for the PWM rectifier should be applied, as shown in Figure 3.6.

Figure 3.6: Decoupled current control of PWM rectifier
In the reference frame, the component id corresponds to active power while the component iq represents the reactive power so named active power control channel and reactive power control channel respectively. Active power channel stabilize the DC side voltage (outer voltage loop) and reactive power channel can regulate PF (inner current loop) [14].
u_Sd= ??Li_Lq+ u_Ld+ ‘u_d
u_Sq= -??Li_Ld+ ‘u_q
where, ?? are the output signals of the current controllers:
‘u_d= k_p (i_d^*- i_d )+ k_i ”(i_d^*- i_d ) dt
‘u_q= k_p (i_q^*- i_q )+ k_i ”(i_q^*- i_q ) dt
The output signals from PI controllers after d-q transformation are used for switching signal generation by a space vector modulator (SVM).

Direct Power Control (DPC)
The main idea of DPC proposed is similar to the direct torque control (DTC) for the induation motors [malino]. Instead of torque and stator flux the instantaneous active (p) and reactive (q) powers are controlled as shown in Figure 3.7.

Figure 3.7: Block diagram of DPC with PLL generator
The commands of reactive power qref (set to zero for unity power factor) and active power (delivered from the outer PI-DC voltage controller) are compared with the estimated q and p values in reactive and active power hysteresis controllers, respectively.
The digitized output signal of the reactive power controller is defined as:
d_q=1 for q<q_ref-H_q
d_q=0 for q>q_ref+H_q
And similarly that of the active power controller as
d_p=1 for p<p_ref-H_p
d_p=0 for p<p_ref+H_p
where, Hq and Hp are the hysteresis bands.
The digitized variables dp, dq and the voltage vector position ??ul = arctg (UL?? / Ul??) or flux vector position ‘?l = arctg (??L?? / ??L??) form a digital word,which by accessing the address of the lookup table selects the appropriate voltage vector according to the switching table described in Figure 3.8. The region of the voltage or flux vector position is divided into 12 sectors, as shown and sectors can be numerically expressed as:
(n-2) ??/6 ‘ ??_n <(n-1) ??/6 ; where n=1,2,’12
Note that the sampling frequency has to be a few times higher than the average switching frequency. This very simple solution allows precise control of instantaneous active and reactive power and errors are limited only by the hysteresis band. No transformation into rotating coordinates is needed and the equation are easily implemented. This method deals with instantaneous variables: therefore, estimated values contain not only a fundamental but also harmonic components. This feature also improves the total power factor and efficiency [1].

Figure 3.8: Selection of region in DPC
This guarantees sector that is very stable and free of disturbances, even under operation with distorted and unbalanced line voltages.
Pulse Width Modulation (PWM) Techniques
The three-phase switch-mode rectifier with six switches has gained increasing interest among researches. Each switch requires an additional driving circuit for its control, which makes the control scheme more complicated. However, the switch-mode rectifier is a promising solution because the use of PWM technology which allows to obtain sinusoidal three-phase input current. More advantages of PWM are mentioned below:
Improvement of the supply current harmonic content in the presence of multiple nonlinear loads
Improvement of the displacement power factor (DPF)
The power flow is bilateral, allowing a four-quadrant active rectifier operation.
A PWM rectifier can operate as a static VAR compensator, adjusting the power factor of any loads, filtering harmonic contents on power lines and improving significantly power quality on the power-distribution system.
There are many different PWM modulation techniques, such as sinusoidal PWM (SPWM), space vector PWM (SVPWM), delta modulation techniques [15].
Sinusoidal Pulse Width Modulation (SPWM)
Sinusoidal modulation is based on triangular carrier signal. By comparison of common

Figure 3.9: Sinusoidal PWM waveforms
carrier signal (Vcr) with three reference sinusoidal signals Va, Vb, Vc (moved in phase of 120 degree), which defines switching instants of power switch are generated [8]. The frequency of triangular wave is higher than sinusoidal reference wave. Figure 3.9 shows the sinusoidal PWM waveforms. The width of the pulses (and output voltage) are varied by changing the amplitude of the reference signal (Vr) or the modulation index (M) from 0 to 1. The modulation index, M is Ar/Ac. Figure 3.9 also shows that the pulse widths are not uniform as it changes with time.
Advantages:
Simpler to implement
More flexible
Lower order harmonics are reduced.
Disadvantages:
Switching losses are higher compare to other PWM strategies.
The extension of SPWM in the over-modulation range is difficult.
Space Vector Pulse Width Modulation (SVPWM)
Space vector is a vector which varies with time according to its angle while magnitude remains the same. Space vector modulation is one of the preferred real time modulation technique and is widely used for digital control of PWM converters. Basic tasks for SVPWM controlled rectifier are given below [8],
To provide a constant and adjustable DC link voltage with respect to the load changes and supply network imperfection
To ensure possibility of regeneration
To minimize line side harmonics injected by the rectifier switching
To provide UPF at the point of common coupling.

Figure 3.10: Space voltage vectors representation
Figure 3.10 shows a space voltage diagram for three-phase PWM rectifier. Depending on the switching state on the circuit, the bridge rectifier leg voltage can assume 8 possible distinct states, represented as voltage vectors (V0 to V7) in the ??-?? coordinates. V1 to V6 are six fixed non-zero voltage vectors and V0, V7 are two zero voltage vectors. The non-zero vectors are all of the same magnitude, equal the DC bus voltage.
Three phase voltage can be treated as a voltage vector Vr. For example, the reference vector shown in Figure 3.10 with magnitude Vr and angle ?? in sector I, is realized by applying the active vector 1, the active vector 2 and the zero vector.
Advantages:
SVPWM scheme gives more fundamental voltage and better harmonic performance compared to SPWM scheme.
Very low switching losses because only one switch change its state from sector to other.
Higher values of output voltage can be obtained by an additional over-modulation range.
Disadvantages:
It requires sector identification and lookup tables to determine the timing for various switching vectors in all the sectors. This makes the implementation of SVPWM scheme quite complicated
Increase the computational time.
SVPWM (space vector PWM) technique is used to get the required waveforms for active front end topology.

CHAPTER 4
DESIGN OF PARAMETERS
Design of Parameters
General
The Design mainly includes the selection of device ratings, design of Inductor and Capacitor. The design procedure mainly divides according to power processing stage.
Technical Specification
Output Specification
Output Power (Po) = 22.5 KW
DC-link voltage for Active Front End can be calculated from following equation

U_DCmin > U_(Ph(rms)) ?? ‘3 ?? ‘2
= 2.45 ?? U_(Ph(rms))

= 2.45 ?? 240

= 588 ‘ 600
Output DC Voltage (Vo) = 600 V
Design of AC-DC Converter
This design includes inductor design and capacitor design and selection of switch. The main task of this design is to make high efficient Inductor
Design Specification
Input AC Voltage (rms) Vi = 415 V (3-‘)
Output DC Voltage (Vo) = 600 V
Output Power (Po) = 22.5 KW
Switching Frequency (fs) = 10 KHz
Rating of Switch
Switching Frequency = 10 KHz
Voltage rating = 1200 V
Current rating = 40 A
Input side Parameter Design
Input AC Voltage (rms) Vi = 415 V (3-‘)
We have use three single-phase voltage source
Input Voltage (rms) (Vin) = 240 V (1-‘)
Peak Input Voltage (Vip) = 340 V (1-‘)
Assume 4% Loss in a system
Efficiency (??) = 96%
Efficiency (??) =(Output Power (Po))/(Input Power (PIn))
‘ Input Power (Pin) = (Output Power (Po))/(Efficiency (??) )
= 22500/(96%)
= 22500/0.96
= 23437.5
= 23.4375 KW
Input Power (Pin) = 23.4375 KW (4.1)
Fundamental line current (IL1) = (Input Power (Pin))/(3v_ph )
= 23437.5/(3??240)
= 32.55 A
Fundamental line current (IL1) = 32.55 A (4.2)

(Switching Frequency (fs)of IGBT = 10 KHz)
Peak Switching Current Limited to 2% of Fundamental Current (Peak) [37.5′??2]
(4??( 600)’2)/?? ?? 1/(2??f_s L) ?? 1/(37.5′??2) = 0.02
L = 5.7315?? ’10’^(-3)
L ‘ 6 ?? ’10’^(-3)
Input Inductor (L) = 6 mH (4.3)
Output Side Parameter Design
DC bus Voltage = 600 V (dc)
DC Link Current / Output Current (I0) = 22500/600
= 37.5 A
DC Link Current / Output Current (I0) = 37.5 A (4.4)
DC link 2nd Harmonic (Peak) = 0.25 ?? DC link Current
= 0.25 ?? 37.5
= 9.375 A
DC link 2nd Harmonic Current (Peak) = 9.375 A (4.5)
For DC Link Capacitor
DC link 2nd Harmonic (Peak) ?? 1/(2C_d ??) ?? 1/600 = 0.03
DC link 2nd Harmonic (Peak) ?? 1/(2C_min ??) ?? 1/600 = 0.03
C_d= 8.29 ?? ’10’^(-4) F
DC Link Capacitor'(C’_min) = 829 ??F (4.6)
Take any value which is greater than and practically workable for DC link Capacitor
For design specification calculation

CHAPTER 5
SIMULATION MODEL
AND RESULTS
Simulation Model and Results
Open Loop Active Front End Rectifier Using SPWM
Block Diagram of Open Loop Active Front End Rectifier Using SPWM

Figure 5.1: Block Diagram of Open Loop 3 Phase Active Front End Rectifier
Using SPWM
Figure 5.1 describes the Block diagram of open loop 3 Phase SPWM rectifier. It is a close loop system. In a forward path, supply voltage is given to 6 Pulse IGBT bridge rectifier and output voltage is measured across the load. In a Feed-forward path the system senses the input voltage and gives them to SPWM generation block.
The operation of SPWM generation block can be understood as following.
Three phase sinusoidal input voltage are sensed by sensing circuit, which is given to SPWM generation block. These sinusoidal signal are reference signal, which are compared with repeating triangular signal and provides switching pulses to IGBT switches
Simulation Model of three phase Open loop Active Front End Rectifier Using SPWM
The simulation model is built using MATLAB/SIMULINK to test the performance of open loop VS AFE rectifier described by the proposed model. The whole system behavior is simulated as a discrete control system. The specification used in simulation is presented in a Table 2. In the circuits, the ac source is three-single phase voltage source of 100 V with frequency of 50HZ.
Table 2: Specification Used In Simulation of Open Loop
AFE Rectifier Using SPWM

Variable Description Value
Vp Peak of line voltage 100 V
Vo Output voltage 160 V
Po Output power 5 kW
Li Input inductor 1 mH
Co Output capacitor 4700 ??F
RL Load resistor 5 ‘
LI Load inductor 1 mH
fs Switching frequency 10 kHz

Simulation Model is shown in Figure 5.2.

Figure 5.2: Simulation Model of three phase Open loop Active Front End Rectifier Using SPWM
Simulation Results
Resulting Waveforms
Waveforms of simulation results are shown as below. The waveform of output DC voltage is shown in Figure 5.3, waveform of output DC current is shown in Figure 5.4. The input voltage and input current are shown in Figure 5.5.The resultant output voltage is 160V and output current is 32 A. waveform of input voltage and current is sinusoidal but they are not in phase with each other.

Figure 5.3: Waveform of Output Voltage

Figure 5.4: Waveform of Output Current

Figure 5.5: Waveform of Input Voltage and Current
Simulated Results of Sinusoidal PWM
In Sinusoidal PWM Triangular wave (Carrier Signal) and Sinusoidal Signals (Reference Signal) are compared. By this comparison PWM pulses are generated. These generated switching pulses are shown in Figure 5.6 Simulation model triangular waveform of frequency 10 KHZ is used.

Figure 5.6: Switching Pulses generated by comparison of Carrier Signal and Reference Signal
FFT analysis of Input Current
According to IEEE 519 standards, THD should be less than 5%. In FFT analysis of input current, THD obtained is 0.85% which is nearly sinusoidal. FFT analysis of input current is shown in Figure 5.7.

Figure 5.7: FFT Analysis of Input Current
Open Loop Active Front-End Rectifier Using SVPWM
Block Diagram of Open Loop Active Front End Rectifier Using SVPWM

Figure 5.8: Block Diagram of Open Loop 3 Phase Active Front End Rectifier
Using SVPWM
Figure 5.8 describes the Block diagram of open loop 3 Phase SPWM rectifier. It is a close loop system. In a forward path, supply voltage is given to 6 Pulse IGBT bridge rectifier and output voltage is measured across the load. In a Feed-forward path the system senses the input voltage and gives them to SVPWM generation block.
This Block generates Controlled Switching pulses for IGBT switches. IGBT turns on and off by these switching pulses and generates output voltage across it.
Simulation Model of three phase Open loop Active Front End Rectifier Using SVPWM
The simulation model is built using MATLAB/SIMULINK to test the performance of open loop VS AFE rectifier described by the proposed model. The whole system behaviour is simulated as a discrete control system. The specification used in simulation is presented in a Table 3. In the circuits, the ac source is three-single phase voltage source of 380 V with frequency of 50HZ.

Simulation Model is shown in Figure 5.9

Table 3: Specification Used In a Simulation of
Open Lop AFE Rectifier Using SVPWM
Variable Description Value
Vp Peak of line voltage 380 V
Vin RMS input line voltage 268.7 V
Vo Output voltage 600 V
Po Output power 5 kW
Li Input inductor 1 mH
Co Output capacitor 4700 ??F
RL Load resistor 72 ‘
fs Switching frequency 10 kHz

Figure 5.9: Simulation Model of three phase Open loop Active Front End Rectifier Using SVPWM

Simulation Results
Waveform of Output voltage and Current
Waveforms of simulation results are shown as below. The waveform of output DC voltage is shown in Figure 5.10, waveform of output current is shown in Figure 5.11

Figure 5.10: Waveform of Output DC Voltage

Figure 5.11: Waveform of Output DC Current

Closed Loop Active Front End Rectifier Using SVPWM
Block Diagram of Closed Loop Active Front End Rectifier Using SVPWM

Figure 5.12: Block Diagram of Closed Loop Active Front End Rectifier
Using SVPWM
Block diagram of close loop Active Front End Rectifier is shown in Figure 5.12. The overall system contains 3 paths 1) Forward path, 2) Feed-Forward path and 3) Feed-Back path. Overall system operation can be understood from the points given below.
From the supply mains, the AC power feed to the Active Front End Rectifier which produces the DC output with the help of SVPWM (Space Vector Pulse Width Modulation) generation block.
Three phase to two phase transformation is done with the help of Clarke and Park transformation.
This is compared with the error taken by the output side and the reference values and final voltage outputs is made, again this will be transform two phase to three phase using Inverse Clarke and Park transformation.
The final a, b, c outputs are given to the Space Vector Pulse Width Modulation controller which gives the gate pulses to the IGBT bridge rectifier according to its switching frequency.
By controlling the switching frequency the PWM signal generation block provides the control signal for proper switching of the Active Front-End rectifier that gives unity power factor.
Simulation Model of three phase closed loop Active Front End Rectifier Using SVPWM
The simulation model is built using MATLAB/SIMULINK to test the performance of VS PWM rectifier described by the proposed model. The whole system behaviour is simulated as a discrete control system. The specification used in simulation is presented in a Table 4. In the circuits, the ac source is three-single phase voltage source with frequency of 50HZ and line to line voltage is 415 V. The simulation model is shown in Figure 5.13.
Table 4: Specification Used In a Simulation of
Closed Loop AFE Rectifier Using SVPWM
Variable Description Value
Vp Peak of line voltage 340 V
Vin RMS input line voltage 240 V
Vo Output voltage 600 V
Po Output power 22.5 kW
Li Input inductor 6 mH
Co Output capacitor 6300 ??F
RL Load Resistor 16 ‘
fs Switching frequency 10 kHz

Simulation Model of Active Front End Rectifier with R Load

Figure 5.13: Simulation Model of Active Front End Rectifier with R Load
Simulation Results with R Load
The waveform of output DC voltage is shown in Figure 5.14 and of output DC current is shown in Figure 5.15. In this model reference output voltage is set to 600 V DC. Resultant input voltage and input current waveform are shown in Figure 5.16. Input current obtained is sinusoidal. The current and voltage on line side are in phase with each other and it has unity power factor (UPF).

Figure 5.14: Output Voltage Waveform of Closed Loop AFE Rectifier with R Load

Figure 5.15: Output Current Waveform of Closed loop AFE Rectifier with R Load

Figure 5.16: input Voltage and Current Waveform of Closed loop AFE Rectifier with R Load
FFT Analysis of Input Current of AFE Rectifier with R Load
According to IEEE 519 standards, THD should be less than 5%. In FFT analysis of input current, THD obtained is 1.09% which is nearly sinusoidal. FFT analysis of input current is shown in Figure 5.17.

Figure 5.17: FFT Analysis of Input Current of AFE Rectifier with R Load
Simulation Model of Active Front End Rectifier with RL Load
The Specifications used in a simulation are the same as they were in simulation model with R load. The simulation model is shown in Figure 5.18. Except that the load is RL and Values of that are: R=16 ‘ and L=5 mH.

Figure 5.18: Simulation Model of Active Front End Rectifier with RL Load
Simulation Results with RL Load
The waveform of output DC voltage is shown in Figure 5.19 and of output DC current is shown in Figure 5.20. In this model reference output voltage is set to 600 V DC. Resultant input voltage and input current waveform are shown in Figure 5.21. Input current obtained is sinusoidal. The current and voltage on line side are in phase with each other and it has unity power factor (UPF).

Figure 5.19: Output Voltage Waveform of Closed Loop AFE Rectifier
With RL Load

Figure 5.20: Output Current Waveform of Closed Loop AFE Rectifier
With RL Load

Figure 5.21: Input Voltage and Current Waveform of Closed Loop AFE Rectifier
with RL Load
FFT Analysis of Input Current of AFE Rectifier with RL Load
According to IEEE 519 standards, THD should be less than 5%. In FFT analysis of input current, THD obtained is 1.13% which is nearly sinusoidal. FFT analysis of input current is shown in Figure 5.22.

Figure 5.22: FFT Analysis of Input Current of AFE Rectifier with RL Load
SVPWM Generation Block
The Space Vector PWM (SVPWM) Generation Block which is used in Simulation of Closed Loop AFE Rectifier has been built up by using logic which is explained below. Basically SVPWM generation block takes alpha-beta components as inputs and generates switching pulses. SVPWM generation block is shown in a Figure 5.23.This SVPWM generation block is made of four subsystems. The operations of these subsystems are explained as below:

Figure 5.23: SVPWM Generation Block
To generate Space Vector PWM first need is to find sector number which can be obtained by simple logic which is given in a Table 5.
Table 5: Sector Identification
Sector
Number Angle
Greater Than or Equal to Less Than
1 0 60
2 60 120
3 120 180
4 180 240
5 240 300
6 300 360/0

Subsystem: 1
This block generates three universal time variables (X, Y, Z)by taking alpha-beta components (Ualpha, Ubeta), switching time (T) and DC reference voltage (Udc) in its input. The logic is explained below .
Ts=1/10000, Udc=600 v
The expression for universal variables:
X=’3(Ts/Udc)*Vs??
Y=??(‘3(Ts/Udc)*Vs?? +’3(Ts/Udc)*Vs??)
Z= ??(‘3(Ts/Udc)*Vs?? 3(Ts/Udc)*Vs??

Subsystem: 2
This Block takes universal time variables(X, Y, Z), switching time (T) and Sector number (N) as inputs and generates Time period T1 and T2 in Output. This logic is explained.

When Sn=1 ‘ T1= -Z, T2 = X
When Sn=2 ‘ T1 = Z , T2 = X
When Sn=3 ‘ T1 = X, T2 = -Y
When Sn=4 ‘ T1 = -X, T2 = Z
When Sn=5 ‘ T1 = -Y, T2 = -Z
When Sn=6 ‘ T1 = Y, T2 = -X
T0 = TS – T1 ‘ T2

Subsystem: 3
From subsystem 2 time periods T1 and T2 are obtained. As these time periods are two and IGBT Bridge have 3 legs so that needed to generate 3 time periods. This block Generates time periods for 3 legs of bridge from time periods T1, T2, sector number (N) and switching time (T). Logic is explained below.
Ta = (Ts-T1-T2)/4
Tb= Ta+??T1
Tc=Tb+??T2
Sn = 1 Sn = 4
Tcm1=Ta Tcm1=Tc
Tcm2=Tb Tcm2=Tb
Tcm3=Tc Tcm3=Ta
Sn = 2 Sn = 5
Tcm1=Tb Tcm1=Tb
Tcm2=Ta Tcm2=Tc
Tcm3=Tc Tcm3=Ta
Sn = 3 Sn = 4
Tcm1=Tc Tcm1=Ta
Tcm2=Ta Tcm2=Tc
Tcm3=Tb Tcm3=Tb

Subsystem: 4
This block generates switching pulses for IGBTs. Pulse generation block uses Tcm1, Tcm2, Tcm1 and compares with Triangular repeating pulses generates switching pulses. Functioning of this block is explained below.

Ideal and simulated pulses of PWM generation block
SVPWM generation block generates switching pulses. These resultant switching pulses and ideal switching pulses which should be generated by SVPWM generation is shown below. Switching pulses for each sector is shown.
Switching Pattern for Sector: 1

Switching Pattern for Sector: 2

Switching Pattern for Sector: 3

Switching Pattern for Sector: 4

Switching Pattern for Sector: 5

Switching Pattern for Sector: 6

Figure 5.24: Ideal and Practical Switching Pattern For Each Sector
CHAPTER 6
HARDWARE DESIGN AND RESULTS

Hardware Design and Results
Hardware Block Diagram

Figure 6.1: Block Diagram of Hardware Implementation
Block Diagram of hardware implementation is shown in Figure 6.1.The input is sent to bridge rectifier via ac sensors and bridge is connected to load via DC sensors in a forward path.
A Closed loop model contains 2 types: 1) Feed forward path, 2) Feedback path. In a Feed forward path the input has been taken from AC mains by using ac sensors. This three phase quantity is converted with the help of Clarke and park transformation. In a feedback path ,The Output DC voltage of rectifier is been compared with desired output signal , which is taken by using DC sensor that gives an error signal. Now these both signals for closed loop are sent to the Decoupled controller which generates d-q components which are decoupled from each other. After that with the help of inverse park transformation alpha beta components is converted into alpha-beta components. These alpha-beta components are sent to SVPWM generation block, which generates switching pulses and are given to the Active Front End Rectifier. This whole closed loop control is done using DSP.
In this section, AC-DC sensor designs, results are given.

AC Inductor Design
Designing of an inductor for AC-DC converter configuration for the following specifications
Input AC voltage: 415 V
Input AC current:
Output DC Voltage: 600 V
Supply frequency: 50 Hz
Switching frequency: 10 KHz
Determine L: The L for this converter is L= 6 mH

Figure 6.2: Inductor
Sensor Circuit Design
AC Sensors
Voltage Sensor
Using operational amplifiers ac voltage has been sensed. For hardware making LM358 (OPAmp),which contains 2 OPAmp in its IC is used. For taking a shifted output offset circuit has been used and getting a shifted output in the range of 2.5V to 7.5V. Schematic circuit of Sensing circuit is shown in Figure 6.3 and hardware results are shown in Figure 6.4and in Figure 6.5
Operation of Voltage sensing circuit:
The circuit diagram of voltage sensing circuit is shown in Figure 6.3. Input ac voltage is stepped down by voltage divider circuit and bring it between +5V to -5V. If input divided voltage is greater than its limit than antiparallel diode works and disconnects the circuit this voltage comes to OPAmp 1 and then this voltages are shifted by 5V. Then this circuit is followed by Voltage follower which provides an isolation to other circuit to which it be connected from noise and fluctuation from in input side.

Figure 6.3: Voltage sensing circuit

Figure 6.4: Hardware Result for AC Voltage Sensor (sensed AC voltage after shifting)

Figure 6.5: Hardware Result for AC Voltage (CH1: sensed AC voltage after shifting,
CH2: single phase AC voltage-230 V)
Current Sensor
Using operational amplifiers AC current has been sensed. For hardware making LM358 which contains 2 OPAmp in its IC is used is used. For taking shifted output offset circuit has been used and getting a shifted output in the range of 2.5V to 7.5V.Figure 6.6 shows the current sensing circuit. Hardware result is shown in Figure 6.7.

Figure 6.6: current sensing circuit
Operation of Current sensing circuit:
The circuit diagram of voltage sensing circuit is shown in figure 6.5. Input ac Current is measured as a voltage across burden. This voltage is stepped down by voltage divider circuit and bring it between +5V to -5V. If input divided voltage is greater than its limit than antiparallel diode works and disconnects the circuit this voltage comes to OPAmp 1 and then this voltages are shifted by 5V. Then the circuit is followed by Voltage follower which provides an isolation to other circuit to which it be connected from noise and fluctuation from in input side.

Figure 6.7: Hardware Result for AC current sensor
DC Sensor
DC voltage sensor circuit:
Using operational amplifiers DC voltage has been sensed. For hardware making LM358 (OPAmp),which contains 2 OPAmp in its IC is used. Schematic circuit of Sensing circuit is shown in Figure 6.8.

Figure 6.8: DC Voltage Sensing Circuit
Operation of Voltage sensing circuit:
The circuit diagram of DC voltage sensing circuit is shown in Figure 6.8. Input ac voltage is stepped down by voltage divider circuit and bring it between +5V to -5V. If input divided voltage is greater than its limit than antiparallel diode works and disconnects the circuit, this voltage comes to OPAmp 1. Then yhe circuit is followed by Voltage follower which provides an isolation to other circuit to which it be connected from noise and fluctuation from in input side.
By this circuit resulting waveforms are of pulsating DC voltage. Hardware result is shown in Figure 6.9

Figure 6.9: Hardware Results of DC Voltage Sensor
Hardware of Sensing Circuits
Figure 6.10Shows Hardware Implementation of sensing Circuits

Figure 6.10: Hardware of Sensing Circuit
DSP TMS320f2812
Figure 6.11 shows the hardware kit for DSP TMS320F2812

Figure 6.11: Hardware Kit for DSP320F2812
Description of DSP 320F2812
The TMS320F2812 device is a member of the TMS320C28X. DSP generation, is highly Integrated, high-performance solution for demanding control applications and is the first 32 bit 150 MIPS (Millions of Instructions per second) DSP with on-chip ‘ash memory and on-chip high-precision analog peripherals. In addition, its architecture is specially optimized for C/C++. Further, this device enables users to develop their code in virtual floating point via the IQ math capability. In this chapter, TMS320F2812 is abbreviated as F2812.
The embedded control DSP, F2812, is based on a 32 bit DSP core delivering 150 MIPS of performance on a flash process and impressive 32 32bit MAC in a single 6.67ns cycle. This DSP also feature a large amount of fast-access on-chip flash memory so that code can be executed internally without adding costly external flash memories. In addition, it incorporates a high-precision ultra-fast analog to digital converter (ADC) together with many control and communication peripherals for truly single-chip designs.
The huge majority of embedded applications are not requiring greater than 150 MIPS of performance, greater than 12 bits of analog precision, or an external 16 Mbyte commodity flash memory. As a matter of fact, solutions featuring up to 150 MIPS of DSP performance, a solid 10 bit or 12 bit analog to digital converter and several kilo-words of flash memory on the same chip, are not only "good enough to do the job" but also provide a much lower cost solution.
The C28x DSP core is designed to have general purpose processor (GPP) features like a unified memory space and addressable registers for faster interrupts and a very efficient C/C++ compiler. Some of the key core features are:
Architecture designed and optimized for GPP
Efficient atomic operations those are common in GPP
Most common instruction that are coded in 16 bits
C/C++ compiler tuned for GPP
The F2812 feature a very fast integrated 12 bit ADC. This 16 channel high-speed ADC has a single conversion time of 200 ns. However to further increase performance this pipeline ADC is capable of achieving up to 16 conversions at 60 ns each with- out any CPU intervention. The ADC also has the ability to auto-sequence a series of conversions. The versatile sequencer can be operated as 2 independent 8-states sequencer or as a large 16 states sequencer.
The F2812 has 2 Event Manager peripherals on-chip to provide a broad range of functions and features that are particularly useful in control applications the event manager modules include general-purpose (GP) timer. Full-compare/PWM units, capture units, and quadrature-encoder pulse (QEP) circuits. The 2 Event manager modules are identical peripherals intended for multi-axis/ digital control applications. [16]

CHAPTER 7
CONCLUSION AND FUTURE SCOPE

Conclusion And Future Scope
Conclusion
SVPWM based PWM rectifier model is presented which gives the boost constant DC output voltage from three phase. The voltage oriented control (VOC) strategy is used, which includes two PI controllers which are used to regulate the AC current and an outer DC voltage loop. Simulation model is built in MATLAB/SIMULINK. In a simulation model, SVPWM generation block generates switching pulses; these pulses are exactly matches with its ideal pattern Simulations results show that the dual closed loop strategy has good control effect providing a good regulation of dc voltage. This model can generate desired voltage with R load as well as RL load. Both the goals are achieved as input power factor is unity and the line current wave-shape is pure sinusoidal. By FFT analysis the THD obtained of input current with R load is 1.09% and with RL load is 1.13% which is according to IEEE 519 Standards. At hardware side we have made Power card which contains sensing circuit, IGBT bridge and generated code for DSP by code generation feature of MATLAB. By using DSP TMS320F2812 which has the maximum clock speed of 150MHz which is faster and capable enough to sense and convert the voltage and current signals and also to generate the suitable PWM signals at 10 KHz for our control strategy of the three phase active front end convertor.
Future Scope
The whole hardware setup for Active Front End Rectifier with closed loop control using DSP and code implementation to DSP are yet to be made. The Three Phase Active Front End convertor can also work as a bidirectional AC to DC as well as DC to AC convertor. The regenerative energy can also fed back to the AC mains. This project can be further extended as a Bidirectional PWM convertor as a new research topic.

APPENDIX A
Hardware Setup

Figure A: Hardware Setup For Three Phase Active Front- End Rectifier

APPENDIX B
List of Paper Published
Dhairya S. Purohit, Ruchita H. Koshti, and Pof. Nirav D. Mehta, ‘Simulation Of Active Front End Rectifier Based on Space Vector PWM’, National Conference on Emerging Trends in Engineering and Technology (NCETET), shri U.S.B College of Engineering and Management, Abu, Rajasthan, 30th March, 2014.
Ruchita H. Koshti, Dhairya S. Purohit, Prof. Nirav D. Mehta,’ Design and Simulation of Three-Phase Voltage Source Space Vector Based PWM Rectifier’, International Journal of Latest Technology in Engineering Managmnent & Applied Science (IJLTEMAS).
APPENDIX C
List of Poster Presentation
Dhairya S. Purohit, Ruchita H. Koshti, Mr. Chirag V. Chuhan, and Prof. Nirav D. Mehta, ‘Three-Phase Active Front End Rectifier Based on Space Vector PWM’, Open House, Power Electronics Department, Vishwakarma Government Engineering College, Chandkheda, Ahmedabad.

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