HIGH PERFORMANCE OF DIRECT TORQUE CONTROL FOR FIVE-PHASE INDUCTION MACHINE

Transcription

1 HIGH PERFORMANCE OF DIRECT TORQUE CONTROL FOR FIVE-PHASE INDUCTION MACHINE LOGAN RAJ A/L LOURDES VICTOR RAJ MASTER OF SCIENCE IN ELECTRICAL ENGINEERING 2016

2 HIGH PERFORMANCE OF DIRECT TORQUE CONTROL FOR FIVE PHASE INDUCTION MACHINE LOGAN RAJ A/L LOURDES VICTOR RAJ A thesis submitted in fulfillment of the requirements for the degree of Master of Science in Electrical Engineering Faculty of Electrical Engineering UNIVERSITI TEKNIKAL MALAYSIA MELAKA 2016

3 APPROVAL I hereby declare that I have read this dissertation/report and in my opinion this dissertation/report is sufficient in terms of scope and quality as a partial fulfillment of Master of Science in Electrical Engineering (Power Electronics and Drives). Signature :... Name :... Date :...

4 DECLARATION I declare that this thesis entitled High Performance of Direct Torque Control for Five- Phase Induction Machine is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature :... Name :... Date :...

5 DEDICATION To my parents, supervisor Dr Auzani bin Jidin, and friend Sundram Rahmalingam for their support, care and patience.

6 ABSTRACT In recent years, research on multiphase AC drives has received great attention due to its several advantages over three-phase drives such as reducing the amplitude and increasing the frequency of torque pulsations, reducing the rotor harmonic currents, reducing the current per phase without increasing the voltage per phase, and lowering the DC-link current harmonics and higher reliability. Until now, however, neither a circular flux operation nor a decagonal flux operation in formulating an optimal switching strategy has been proposed to achieve high-torque control performance of Direct Torque Control (DTC) of five-phase induction machines. A few previous studies on DTC of five-phase induction machine are limited to analyze the effects of selecting different voltage vectors on torque and flux control performances, which do not facilitate the DTC to obtain fast torque dynamic control, reduced torque ripple and switching frequency. This thesis proposes an optimal switching strategy of DTC of five-phase induction machines for highperformance torque control. By employing a five-phase inverter in the proposed method, it provides a greater number of voltage vectors as compared to that offered in the three-phase inverter which gives more options to select the most optimal voltage vectors. The analysis of effects of selecting different voltage vectors on DTC performances are carried out to identify the most optimal vectors that can be chosen to improve torque control performances for every operating condition. The identification is made with the aid of vector diagrams and some equations which are, equations of torque rate, slip angular frequency and current dynamic. Once the identification is done, all optimal vectors are tabulated into a look up table, and the optimal switching of vectors is accomplished by providing appropriate error status and flux sector into the look up table. The appropriate error status are obtained from the hysteresis comparators which are reponsible to determine proper amplitude of vectors and flux control operations, either to form the flux trajectory into a circular or a decagonal locus. The improvements of the proposed method are verified via simulation and experimental results. The results have shown that the torque ripple and switching frequency in the proposed method are greatly reduced about 50 % and 40 %, respectively from that obtained in the DTC with non-optimal switching strategyof five phase inverter, particularly at low-speed operation. The results have also showed that the proposed DTC with decagonal flux control produces a faster torque dynamic response than the non-optimal switching strategy of five phase inverter DTC. These improvements offered are important features for the electrical drive applications that require highperformance torque control and reduced switching losses or high-efficiency.

7 ABSTRAK Sejak kebelakangan ini, kajian tentang pemacu AC berbilang fasa telah menerima perhatian yang tinggi disebabkan oleh banyak kelebihan yang dimilikinya berbanding dengan pemacu tiga fasa seperti pengurangan amplitud dan peningkatan frekuensi bagi denyutan dayakilas, pengurangan harmonik arus angker, pengurangan arus per fasa tanpa peningkatan voltan per fasa, dan pengurangan harmonik arus penghubung-dc dan keboleharapan yang lebih tinggi. Namun begitu, sehingga sekarang, tiada pengoperasian fluks membulat mahupun pengoperasian fluks dekagon dalam memformulasikan sebuah strategi pensuisan optimal dicadangkan untuk mencapai prestasi tinggi kawalan dayakilas bagi Kawalan Dayakilas Langsung (DTC) motor aruhan lima fasa. Segelintir kajian terdahulu tentang DTC motor aruhan lima fasa dihadkan untuk menganalisis kesan-kesan bagi pemilihan vektor voltan yang berlainan terhadap prestasi kawalan dayakilas dan fluks, yang mana tidak menyediakan DTC untuk mendapatkan kepantasan kawalan dayakilas dinamik, pengurangan riak dayakilas dan frekuensi pensuisan. Tesis ini mencadangkan sebuah strategi pensuisan yang optimal bagi pemacu DTC motor aruhan lima fasa untuk prestasi tinggi kawalan dayakilas. Dengan menggunakan sebuah penyongsang lima fasa dalam kaedah cadangan, ia menyediakan bilangan vektor voltan yang lebih banyak berbanding dengan yang ditawarkan dalam pemacu tiga fasa yang memberikan lebih banyak pilihan untuk memilih vektor voltan yang paling optimal. Analisa bagi kesan-kesan pemilihan voltan vektor yang berlainan terhadap prestasi DTC telah dilakukan untuk mengenalpasti voltan vector yang paling optimal yang boleh dipilih untuk menambahbaik prestasi kawalan dayakilas untuk setiap keadaan operasi. Pengenalpastian ini dilakukan dengan bantuan rajah vektor dan beberapa persamaan, iaitu persamaan kadar dayakilas, frekuensi sudut gelinciran dan arus dinamik. Apabila pengenalpastian ini telah dilakukan, kesemua vektor-vektor yang optimal telah dijadualkan ke dalam sebuah jadual carian, dan pensuisan vektor optimal disempurnakan dengan menyediakan status-status ralat yang bersesuaian dan sektor fluks ke dalam jadual carian tersebut. Status-status ralat yang besesuaian diperoleh daripada pembandingpembanding histeresis yang bertanggungjawab menentukan amplitud vektor yang sesuai dan operasi kawalan fluks, sama ada untuk membentuk trajektori fluks dengan lokus membulat atau dekagon. Penambahbaikan-penambahbaikan bagi kaedah cadangan telah disahkan menerusi keputusan simulasi dan eksperimen. Keputusan tersebut telah menunjukkan bahawa riak dayakilas dan frekuensi pensuisan dengan kaedah cadangan dikurangkan sehingga 50 % dan 40 % daripada yang diperoleh dalam DTC dengan strategi pensuisan yang tidak optimal pemacu lima fasa, terutamanya pada operasi kelajuan rendah. Keputusan juga menunjukkan bahawa DTC cadangan dengan kawalan fluks dekagon menghasilkan sambutan dayakilas dinamik yang lebih cepat berbanding dengan DTC dengan strategi pensuisan yang tidak optimal pemacu lima fasa. Penambahbaikan-penambahbaikan ini merupakan ciri-ciri penting bagi aplikasi pemacuan elektrik yang memerlukan prestasi tinggi kawalan dayakilas dan pengurangan kehilangan pensuisan atau kecekapan yang tinggi.

8 ACKNOWLEDGEMENTS I acknowledge, with gratitude, my debt of thanks to Dr. Auzani bin Jidin for his guidance, ancouragement and patience on assisting me throughout my research and towards the completion of this thesis. I would also like to thank everyone who have contributed to this thesis particularly my friend and co-researcher Sundram Rahmalingam for their undisputed support and encouragament. This research was fully supported by Universiti Teknikal Malaysia Melaka. I am grateful to this institution for providing me the platform and support through scholarship and sponsorship to complete this study. Finally, I would like to thank my parents and family members for their moral support encouragement and tollerence throughout my study. iii

9 DECLARATION APPROVAL DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF APPENDICES LIST OF SYMBOL LIST OF ABBREVIATIONS LIST OF ACHIVEMENTS TABLE OF CONTENTS PAGE i ii iii iv vii viii xvii xviii xx xxii CHAPTER 1. INTRODUCTION Research Background Motivation of Research Problem statement Large Torque Ripple High Switching Frequency/Losses Slow Torque Dynamic Control Objectives Methodology Contribution of Thesis Thesis organization LITERATURE REVIEW Introduction Principle of Direct Torque Control (DTC) of Three- Phase Induction Motors Mathematical Modelling of Three-phase Induction Machines Three-Phase Voltage Source Inverter Control Strategy of DTC Control of Flux Control of Torque Simultaneous Control of Torque and Flux Structure of Direct Torque Control Principle of Direct Torque Control with Hexagonal Flux Control for Three-Phase Induction Motors Hexagonal Flux Control based on the Hysteresis Controllers Hexagonal Flux Control based on the Modification of Torque Error Status Performance Analysis of Torque Dynamic Control 44 iv

10 2.4 Direct Torque Control of Five-Phase Induction Motors Comparison of DTC and FOC Conceptual of DTC of Five-Phase Induction Machines Conclusion RESEARCH METHODOLOGY Introduction Mapping of Voltage Vectors for Five-Phase Inverter Five-Phase Voltage Source Inverter Space Voltage Vector of Five-phase Voltage d- and q- Components of Stator Voltage Voltage Vectors of Five-phase Inverter on the Voltage Vector Plane An Improved Switching Strategy Investigation on Effects of Selecting Different Switching Voltage Vector Options on Torque Control Behaviour Analysis on Torque Dynamic Control using Torque Rate Equation Analysis on Torque Control Capability based on the Maximum Slip Angular Frequency Analysis on Torque Slopes for Various Motor Operating Conditions Identification of Optimal Voltage Vectors Improvement 1: Reduction of Switching Frequency Improvement 2: Reduction of Torque Ripple Improvement 3: Fast Torque Dynamic Control Definition of Flux Sectors for Selecting Optimal Vectors Look-up Table for Selecting Optimal Voltage Vectors Proposed Control Structure Simulation Model of DTC of Five-Phase Induction Machine Five-Phase induction machine Simulation Model of Five-Phase inverter Simulation Model of d- and q-components of Stator Voltage Simulation Model of d- and q-components of Stator Current Simulation Model of Flux and Torque Estimation for Five-Phase Induction Machine Simulation Model of Five-Phase Sector Definition Description on Experimental Setup DS1104 R&D Controller Board FPGA Altera DE0 Board Hall Effect Current Sensor Gate Drivers Five Phase Voltage Source Inverter Five Phase Induction Machine Conclusion RESULT AND DISCUSSION Introduction 138 v

11 4.2 Performance Analysis of Torque Ripple, Switching Frequency and Torque Dynamic Control via Simulations Improvement 1: Reduction of Torque Ripple Improvement 2: Minimization of Switching Frequency Improvement 3: Fast Torque Dynamic Control Verification Improvements via Experimental Results Reduction of Torque Ripple and Switching Frequency Improved Torque Dynamic Control Conclusion CONCLUSION AND RECOMMENDATIONS Conclusions Constrains and Limitations of Research Future Works 178 REFERENCES 181 APPENDICES 193 vi

12 LIST OF TABLES TABLE TITLE PAGES 2.1 Selection of Voltage Vectors as Proposed in (Takahashi and Noguchi, 1986) Table 2.2 : The look up table proposed in (Toliyat and Huangsheng, 2000) (a) Longgest Voltage Vector (b) Medium Voltage Vector (c) Shortest Voltage Vector Stator Flux and Torque Variation for Different Voltage Vectors for Sector I, as Reported in (Mythili and Thyagarajah, 2005) Classification of Voltage Vectors of Five-Phase Inverter Look-up table of DTC with Circular Flux Control (Optimal Vector Selection) Look-up table of DTC with Decagonal Flux Control and with Optimal Vector Switching Parameters of 5-Phase Induction Machine Parameters of Five-Phase Induction Motor 139 vii

13 LIST OF FIGURES FIGURE TITLE PAGE 1.1 DTC Structure Proposed in (Takahashi and Noguchi, 1986) Control Structure of DTC of Five-Phase Induction Motor Flow chart of Research Methodology Block Diagram of the Mathematical Modelling of an Induction Machine A Three-Phase Voltage Source Inverter Voltage Vectors (including Switching States Information) on the Voltage Vector Plane Trajectory of Stator Flux Vector in DTC A Decoupled Control Structure with a Look-up Table for Establishing Simultaneous Control of Stator Flux and Torque Production of Flux Error Status σ_φ and Torque Error Status σ_t using (a) 2-Level Hysteresis Comparator and (b) 3-level Hysteresis Comparator, Respectively 27 viii

14 2.7 Typical Waveforms of the Torque, the Torque Error, the Stator Flux, the Flux Error, the Torque Error Status and the Flux Error Status including Voltage Vectors Selection for Controlling the Stator Flux and Torque in Sector III Structure of Direct Torque Control (DTC) based Induction Machine, as Proposed in (Takahashi and Noguchi, 1986) Structure of Direct Self Control (DSC) based Induction Machine, as Proposed in (Depenbrock, 1988) Simulation Result of the Typical Waveforms in Direct Self Control A Hexagonal Flux Shape obtained in DSC Scheme Structure of DTC with Inclusion of Modification of Torque Error Status, as Proposed in (Jidin et al., 2011a) The Modification Block for Hexagonal Flux Operation Modified Flux Error Status σσ φφ nnnnnn for Every Sub Sector (in Each Sector) for Hexagonal Flux Control The Shrinking of Hexagonal Flux Locus Flux Keeps the Increase as it Enters to Sub sector ii Until it Reaches to the Point c. (i.e. path b-c) with the σσ φφ nnnnnn = 0 43 ix

15 2.17 State Diagram of Finite State Machine that Establishes the Modified Flux Error Status for Proper Hexagonal Flux Locus Operation (as Proposed in (Jidin et al., 2011a)) Effects of Selecting Different Switching under Dynamic Condition. (a) Stator Voltage Vector in Stator Flux (b) Comparison of the Load Angle, δ sr generated by the Same Magnitude of Appropriate Voltage Vectors Structure of Field Oriented Control of Five-Phase Induction Machine Structure of Direct Torque Control of Five-Phase Induction Machine A Five-Phase Voltage Source Inverter Connected to a Five-Phase Induction Machine Voltage Vectors (on the voltage vector plane) offered in a Five-Phase Inverter Control of Torque is Directly Influenced by the Variation of Angle δ sr due to the Irregular Motion of Stator Flux Vector (e.g. in Sector I) Hysteresis Comparators for (a) Torque Controller with 7- Level Hysteresis Band (b) Flux Controller with 2-Level Hysteresis Band 61 x

16 2.25 Simulation Results of Torque, Torque Error, Torque Error Status, Stator Currents and Phase Voltage obtained in Five-Phase DTC (Raj et al., 2013) Zoomed Images for Simulation Results of Torque and Torque Error as obtained in Fig. 2.24, for (a) Region 1, (b) Region 2 and (c) Region Simulation Results of Torque, Torque Error, Torque Error Status, Stator Currents and Phase Voltage obtained in Five- Phase DTC (Raj et al., 2013), at a Sampling Time 50 μμs Zoomed Images for Simulation Results of Torque and Torque Error as obtained in Fig. 2.26, for (a) Region 1, (b) Region 2 and (c) Region Torque Dynamic Control with Selection of Non-Optimal Voltage Vectors Simplified Five-Phase Inverter Connected to a Five-Phase Induction Machine Simplified Five-Phase Inverter with Consideration only for any Phase (or xx-phase) Definition of Phase Vectors in (3.4) Vector Units for Each Phase on the Rectangular Coordinates 77 xi

17 Voltage Vectors (on the Voltage Vector Plane) offered in a Five- Phase Inverter, as shown in Fig Space Vectors of the Applied Voltage, the Stator Flux and the Rotor Flux Phasor Diagrams of Vectors of Stator Voltage, Ohmic Voltage Drop and Back-Emf for (a) Low Speed Operation and (b) Base Speed Operation Analysis of Torque Dynamic or Slope based on Current Changes for Different Switching of Voltage Vectors in Sector III Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (Solid Line) at Low Speed Operations. (a) the Selection of Voltage Vectors and (b) the Variation of Torque inthe Hysteresis Band Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (Solid Line) at Medium Speed Operations. (a) the Selection of Voltage Vectors and (b) the Variation of Torque in the Hysteresis Band Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (Solid Line) at High Speed Operations. (a) the Selection of Voltage Vectors and (b) the Variation of Torque in the Hysteresis Band 98 xii

18 3.12 Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (solid line) at Low Speed Operations. (a) the Torque Waveforms (b) the Torque Error Waveforms, and (c) the Torque Error Status Waveforms Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (solid line) at Medium Speed Operations. (a) the Torque Waveforms (b) the Torque Error Waveforms, and (c) the Torque Error Status Waveforms Control of Torque using the Proposed Method (Dotted Line) and the Conventional DTC (solid line) at High Speed Operations. (a) the Torque Waveforms (b) the Torque Error Waveforms, and (c) the Torque Error Status Waveforms Performance Comparison of Torque Dynamic Control for (a) Conventional DTC with a Circular Flux Operation (b) Proposed DTC with a Decagonal Flux operation Flux Sector Definition and Optimal Voltage Vector Selection for Circular Flux Locus Flux Sector Definition and Optimal Voltage Vector Selection for Decagonal Flux Locus Control structure of the proposed circular flux DTC Control structure of the proposed decagonal flux DTC Complete simulation model of proposed circular flux DTC 115 xiii

19 3.21 Complete simulation model of proposed decagonal flux DTC Simulation model of 5-Phase induction machine Detailed simulation model of 5-Phase induction machine Definition of Phase Voltage and Pole Inverter Voltage (e.g. in Phase aa) based on Simplified Five-Phase Inverter Simulation Model of Five-Phase Inverter Simulation Model of dd- and qq-component of Voltage Simulation Model of dd- and qq-component of Current Simulation model of flux and torque estimation Simulation block of sector definition Flow chart of sector definition for circular flux Flow chart of sector definition for decagonal flux Block diagram of Experimental Setup Photography of Experimental setup of DTC for 5-Phase Induction Machine FPGA Altera DE0 board Waveform with time delay applied Current sensor Schematic diagram of current sensor Schematic diagram of gate driver Five-Phase Voltage Source Inverter 135 xiv

20 3.40 Five Phase Induction Machine Waveforms of Torque, Stator flux, Phase Stator Currents and Stator Voltage at Low-Speed for (a) the DTC2, and (b) the DTC Waveforms of Torque, Stator flux, Phase Stator Currents and Stator Voltage at Medium-Speed for (a) the DTC2, and (b) the DTC Waveforms of Torque, Stator flux, Phase Stator Currents and Stator Voltage at High-Speed for (a) the DTC2, and (b) the DTC Mapping of Switching Vectors on the d- and q-axis Coordinate for (a) the DTC1 at Every Different of Speed Operations, (b) the DTC2at High-Speed, (c) the DTC2 at Medium-Speed, and (d) the DTC2 at Low-Speed Comparison of Switching Frequency Performance Resulted in Torque and Currents Waveforms for (a) Low-Speed, (b) Medium- Speed and (c) High-Speed Waveforms of Torque, Stator flux and d- and q-components of Stator Currents when a Step Change of Reference Torque is Applied, at Low-Speed for (a) DTC1, (b) DTC3, (c) DTC Comparison of Torque Dynamic Control Performance, when a Step Change of Reference Torque is Applied, at Low-Speed for (a) DTC1, (b) DTC3, and (c) DTC4 156 xv

21 4.8 Waveforms of Torque, Stator flux and d- and q-components of Stator Currents when a Step Change of Reference Torque is Applied, at High-Speed for (a) DTC1 and (b) DTC Comparison of Torque Dynamic Control Performance, when a Step Change of Reference Torque is Applied, at High-Speed for (a) DTC1, and (b) DTC Profiles of Current Components when a Step Change of Reference Torque is Applied, at High-Speed for (a) DTC1, and (b) DTC Experimental result of Torque, Stator flux, and Stator Voltage at Low-Speed for DTC1 and DTC2 (a) Overall, and (b) Zoomed Experimental Results of Torque, Stator Flux and Stator Voltage at Low-Speed for DTC1 and DTC3 (a) Overall and (b) Zoomed Simulation Results of Torque, Stator Flux and Stator Voltage at Low-Speed for DTC1 and DTC2 (a) Overall and (b) Zoomed Simulation Results of Torque, Stator Flux and Stator Voltage at Low-Speed for DTC1 and DTC3 (a) Overall and (b) Zoomed Experimental Results of Torque, Stator Flux and Stator Voltage at High-Speed for DTC1 and DTC2 (a) Overall and (b) Zoomed Experimental Results of Torque, Stator Flux and Stator Voltage at High-Speed for DTC1 and DTC3 (a) Overall and (b) Zoomed Simulation Results of Torque, Stator Flux and Stator Voltage at High-Speed for DTC1 and DTC2 (a) Overall and (b) Zoomed 169 xvi

22 4.18 Simulation Results of Torque, Stator Flux and Stator Voltage at High -Speed for DTC1 and DTC3 (a) Overall and (b) Zoomed Experimental Results of Torque, Stator Flux and Phase Voltage 172 in DTC Experimental Results of Torque, Stator Flux and Phase Voltage 172 in DTC Comparison of Torque Dynamic Control Performance Between DTC1and DTC Trajectory of Stator Flux (a) Circular Locus in DTC1 and (b) Decagonal Locus in DTC3 174 xvii

23 LIST OF APPENDICES APPENDIX TITLE PAGE A Matlab source code listing 192 B VHDL source code listing 202 xvii

24 LIST OF ABBREVIATIONS AC - Alternating Current ADC - Analog Digital Converter DAC Digital Analog Converter DC - Direct current DSC - Direct Self Control DSP - Digital Signal Processor DT - Sampling period DTC - Direct Torque Control DTC1 - Conventional DTC of Five Phase Inverter DTC2 - DTC with Optimal Voltage Vector Selection DTC3 - DTC with Decagonal Flux and Optimal Voltage Vector Selection FPGA - Field Programmer Gate Array FOC - Field Oriented Control IGBT - Insulated gate bipolar transistor IM - Induction Motor LB - Lower band SVM - Space vector modulated UB - Upper band xx