CURRENT MODE FUZZY BASED CONTROLLER FOR MULTILEVEL INVERTER
FAZAL REDZA BIN ABD RADZAK
A project report submitted in partial fulfilment of the requirements for the award of the degree of
Master of Engineering (Electrical Power)
School of Electrical Engineering Faculty of Engineering Universiti Teknologi Malaysia
iii DEDICATION
This project report is dedicated to my beloved parents, my lovely wife and sons as well as to my sibling for their never-ending encouragement and support, who
taught me not too easily surrender and feel defeated. Instead, keep up the challenge and feel the joy of the victory.
Not to forget to my mighty and respectful supervisor, lecturer and friend who give a valuable knowledge and help in this journey.
iv
ACKNOWLEDGEMENT
In the name of Allah, the Most Gracious and the Most Merciful.
First and foremost, I would like to thank Allah for giving me an opportunity to still learn, to work on my dissertation project, to complete this project report, and to complete my Master journey.
In preparing this project report, I have a special gratitude and my sincere appreciation to my main project report supervisor, Dr Shahrin Bin Md Ayob, for encouragement, guidance, support and friendship. The knowledge, advices and ideas given is so priceless and without a continued support and interest, this project report would not have been the same as presented here.
My appreciation also goes to my parents and family for continuous supports and motivations. Special thanks dedicated to my lovely wife, for being very understanding and supporting throughout this short yet challenging two years journey.
I am also indebted to Universiti Teknologi Malaysia (UTM) as my platform to complete my master journey which deserve special thanks for the assistance and facilities.
My fellow postgraduate student should also be recognised for their support. My sincere appreciation also extends to all my colleagues and others who have provided assistance at various occasions. Their views and tips are useful indeed. Unfortunately, it is not possible to list all of them in this limited space.
v ABSTRACT
Multilevel Inverter (MLI) has come to attention from industries for its practical and convenient solution especially in high power application. It produces staircase voltage waveform which gives more sinusoidal like waveform and as a result it has a lower THD percentage. Through the evolution in MLI topologies and advancement of power electronic devices, it become more viable technology and attracted wide interest for its number of advantages such as above. However, the selection of suitable switching technique to control the MLI has an effective and important role in generating an ideal output voltage that reduce the error as well as the harmonic content. A controller that been introduced into the system must has a characteristic of very fast and responsive, so that it will give more advantage to the MLI. This project will propose and design a current mode fuzzy based controller for five level cascaded multilevel inverter. It is a current mode-based control method offers good performance with faster response as compared to voltage mode control with an expense of additional current sensor. While, the employment of fuzzy control provides a better regulation performance with nonlinear load by manipulating the fuzzy logic structure through heuristic knowledge characteristic of the controller. Hence a system perform with tuneable controller is expected. To validate its performance, a simulation base on MATLAB/SIMULINK® will be conducted with a single phase five-level cascaded multilevel inverter where it been controlled by a proposed fuzzy controller in a current feedback loop. The results of the simulation were observed and analysed.
vi ABSTRAK
Penyonsang pelbagai aras (MLI) telah mendapat tumpuan oleh pihak industri kerana menyediakan penyelesaian yang lebih praktikal dan mudah terutamanya dalam aplikasi berkuasa tinggi. Ia menghasilkan gelombang berbentuk tangga yang memberi lebih banyak kesamaan kepada bentuk sinusoidal dan seterusnya menghasilkan peratusan THD yang lebih rendah. Melalui evolusi yang berlaku di dalam topologi MLI dan kemajuan peranti kuasa elektronik, ia telah menjadi MLI satu teknologi berdaya maju dan dapat menarik minat yang luas dari pihak industri kerana kelebihannya seperti di atas. Namun begitu, pemilihan teknik pensuisan yang bersesuian dalam mengawal keluaran MLI adalah berperanan penting dan berkesan dalam menghasilkan voltan keluaran yang ideal seterusnya dapat mengurangkan kesilapan dan kandungan harmonik. Pengawal yang diperkenalkan ke dalam sesuatu sistem haruslah mempunyai ciri yang sangat cepat dan responsif. Ini akan memberi banyak kelebihan kepada MLI. Projek ini mengusulkan dan merekabentuk kawalan berasaskan logik kabur arus untuk penyonsang pelbagai aras (MLI). Ia berdasarkan kaedah kawalan berasaskan mod arus yang mana menawarkan prestasi yang baik dengan tindak balas yang lebih cepat berbanding kawalan berasaskan mod voltan dengan tambahan kos sensor aliran. Sementara itu, penggunaan kawalan logic kabur menyediakan prestasi peraturan yang baik terhadap beban tidak linear dengan memanipulasi struktur logik kabur melalui pengetahuan heuristik pengawal. Oleh itu, prestasi pengawal yang lebih mudah diserasikan dengan penalaan adalah dijangka. Untuk mengesahkan prestasi pengawal tersebut, simulasi berasas kepada MATLAB / SIMULINK® akan dijalankan dengan dengan menggunakan aliran kuasa satu fasa terhadap lima peringkat penyonsang pelbagai aras yang dikawal oleh pengawal logik kabur menggunakan kaedah maklum balas aliran arus. Keputusan simulasi akan dikaji dan dianalisa.
vii TABLE OF CONTENTS TITLE PAGE DECLARATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT v ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES ix
LIST OF FIGURES x
LIST OF ABBREVIATIONS xiii
LIST OF SYMBOLS xiv
LIST APPENDICES xv CHAPTER 1 INTRODUCTION 1 1.1 Research Background 1 1.2 Problem statement 3 1.3 Objectives 3 1.4 Scope of study 3
CHAPTER 2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Multilevel Inverter Technology 5
2.3 Multilevel Inverter Concept 7
2.4 Multilevel Inverter Topologies 10
CHAPTER 3 METHODOLOGY 13
3.1 Introduction 13
viii
3.3 PWM Techniques 15
3.4 Relationship of PI controller with Fuzzy Logic
Controller 18
3.5 Fuzzy Logic controller design 23
3.6 Project scheduling 26
CHAPTER 4 SIMULATION RESULT AND DISCUSSION 28
4.1 Introduction 28
4.2 Simulation of open loop five-level cascaded multilevel
inverter 28
4.3 Fuzzy Logic Control Scheme of the closed loop MLI
and simulation 37
CHAPTER 5 CONCLUSION 45
5.1 Summary 45
5.2 Recommendation/ Future Work 45
REFERENCES 46
ix
LIST OF TABLES
TABLE NO. TITLE PAGE
Table 2.1 Comparison of different type of MLI 14
Table 3.1 Gain response of FLC 23
Table 3.2 The rule table of FLC 24
Table 4.1 Switching state for 5-level Multi Level inverter 32
Table 4.2 Simulation result of open loop MLI with no load and rated load
37
x
LIST OF FIGURES
FIGURE NO. TITLE PAGE
Figure 1.1 Block diagram of FLC 2
Figure 2.1 (a) Voltage source inverter. (b) Current source inverter.
6
Figure 2.2 An MLI with two dc sources, each with H-bridges implemented with power electronic switches.
7
Figure 2.3 Voltage output waveform of each H bridges and the resultant output waveform for the MLI of Figure 2.2
8
Figure 2.4 MLI concept 8
Figure 2.5 Single phase 5-level diode clamped MLI 10
Figure 2.6 Flying capacitor clamped MLI 11
Figure 3.1 Project process flow 14
Figure 3.2 (a) Sinusoidal reference and triangular carrier; (b) Output pulse voltage that alternate between +𝑉𝑑𝑐
and −𝑉𝑑𝑐 depending on comparison result between reference and carrier
xi
Figure 3.3 (a) H-Bridge for unipolar PWM; (b) Reference and carrier wave; (c) Bridge voltage; (d) Output voltage
17
Figure 3.4 PI controller configuration 18
Figure 3.5 Block diagram representation of equation (3.6) 20
Figure 3.6 Block diagram representation for digital implementation of FLC
21
Figure 3.7 FLC based control system 22
Figure 3.8 Input membership function of FLC 24
Figure 3.10 MATLAB’s FLC tool with two input and single output, (b) the membership function of the input
26
Figure 3.11 Project schedule 27
Figure 4.1 Simulation block diagram of 5-level MLI 29
Figure 4.2 Superimpose of reference and carrier signals in SPWM
30
Figure 4.3 (a) 100ms timeframe for pulses in PWM for each switch, (b) close up view by 20ms
31
Figure 4.4 (a) The output voltage of MLI in 100ms timeframe (b) a close up view of the output voltage.
33
xii
Figure 4.6 Simulation block of 5-level MLI with low band pass filter
35
Figure 4.7 (a) Filtered Output Voltage waveform of MLI, with (b) FFT analysis result
36
Figure 4.8 FFT result for no load simulation of open loop MLI 37
Figure 4.9 Proposed five level multilevel inverter with fuzzy logic feedback
38
Figure 4.10 Performance of FLC MLI when subjected to disturbance
39
Figure 4.11 FFT analysis of large disturbance 40
Figure 4.12 FLC controlled MLI performance at large disturbance at (a) 7ms and (b) 25ms as shown in purple circle
41
Figure 4.13 Small-signal performance 42
Figure 4.13 Simulation result of capacitive load 43
xiii
LIST OF ABBREVIATIONS
MLI - multilevel inverter
THD - total harmonic distortion
PI - proportional integral
FLC - fuzzy logic controller
DC - direct current
VSI - voltage source inverter
CSI - current source inverter
NPC - neutral point clamped
xiv
LIST OF SYMBOLS
𝑉𝑑𝑐 - Direct current voltage
𝑆 - Switching
𝑉𝑜, 𝑣𝑜 - Output voltage
𝑣𝑡𝑟𝑖 - Triangular voltage, carrier voltage 𝑣𝑠𝑖𝑛𝑒 - Reference voltage, sine waveform 𝐾𝑝 - PI proportional gain
𝐾𝑖 - PI integral gain
𝑒 - Error
xv
LIST OF APPENDICES
APPENDIX TITLE PAGE
1 CHAPTER 1
INTRODUCTION
1.1 Research Background
Fuzzy Logic is one of logic form which has more than two (2) logics value as contras to Boolean Logic. Boolean Logic depends on two specific value of completely true (1) and completely false (0). As oppose to that, the logic value of Fuzzy logic can be fall on partially truth where the value may be in the range between of both one (1) and zero (0). This can be achieved by introduction of linguistic variable for a certain range, impose in a certain membership group or function. This function is made through the knowledge that been gathered and verified and uses the degree of truth in a mathematical model. Thus, process of fuzzification and defuzzification involved in a process that link between the input and the output of a system will be made according to the rule which been defined. The concept that been introduced by Prof Lofti Zadeh in 1965 is designed to mimic the way of human thinking in solving problem. This process can be simplified as in Figure 1.1.
For its flexible variables mapping based on the knowledge given, the Fuzzy logic has been used in many fields and mostly in a wide variety of controllers as well as in feedback systems. It allows engineer to exploit their empirical knowledge and fuzzy heuristic capability which can be represented in the IF-THEN rules and then transfer it to a functional block [12].
2
Figure 1.1: Block diagram of FLC
While multilevel inverter (MLI) is an inverter that convert dc sources to a desired sinusoidal ac output voltage through certain topologies or method where the number of the dc sources determine the step level of output staircase waveform. The dc sources may be obtained from batteries, fuel cell, or even a renewable energy system. Its application suitable in high voltage and high power industries such as photovoltaic solar system as well as wind turbine generation system. It has widely acceptable and becoming popular due to its advantages [13]. The minimum required switching frequency of the MLI has increased its efficiency and since the THD percentage is very low as result of low harmonic distortion, it contributes to the improvement in power quality and dynamic stability in power system. This is highly been regarded in power utility system.
Since, the quality of the output voltage produced by an inverter is paramount in determined the stability of the power system and the harmonic distortion that may result in serious effect to sensitive equipment. [11], several controllers have been proposed in order to improved efficiency and eliminating harmonic content in MLI topologies. Therefore, in this paper, for a Multilevel Inverter application, current base Fuzzy logic controller will be implemented as an alternative method. It will be verified through comparison of its robustness and response time against a PI controller.
Decision Making Mechanis Defuzzification Fuzzification Input Output Rul e B as e Output Membership Input membership
3 1.2 Problem statement
Several PI controllers have been successfully integrated into multilevel inverter system as a mean to regulate the required output. Despite that, PI requires complicated and complex mathematical modelling to represent the actual system and seldom successfully control for large signal model.
This paper will look into the possibility of using a Fuzzy Logic Controller (FLC) as an alternative controller to the existing PI controller of MLI. And thus, to study its advantages in small and large signal model
1.3 Objectives
In order to achieve the aim of the study, the research proposal has the following objectives: -
1) To design a closed-loop control employing current mode fuzzy base controller for multilevel converter system
2) To analyse the performance of the purposed system
1.4 Scope of study
The scopes of the project give limitations and boundaries to the project in order to achieve its target. It to ensure the development of the project is within its boundaries while heading to the direction in fulfilling the objectives. There are several scopes indicated as follow: -
1) The project will focus on the proposing of closed-loop feedback by using proposed Fuzzy controller in a current feedback loop
4
3) To measure and to test its workability and functionality by using MATLAB/SIMULINK®.
REFERENCES
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[2] a. G. Perry, G. F. G. Feng, Y.-F. L. Y.-F. Liu, and P. C. Sen, “A Design Method for PI-like Fuzzy Logic Controllers for DC-DC Converter,” IEEE Trans. Ind. Electron., vol. 54, no. 5, pp. 2688–2696, 2007.
[3] N. a. Azli and W. S. Ning, “Application of fuzzy logic in an optimal PWM based control scheme for a multilevel inverter,” Fifth Int. Conf. Power Electron. Drive Syst. 2003. PEDS 2003., vol. 2, pp. 1280–1285.
[4] B.-J. Choi, S.-W. Kwak, and B. K. Kim, “Design and stability analysis of single-input fuzzy logic controller,” IEEE Trans. Syst. Man. Cybern., vol. 30, no. 2, pp. 303–309, 2000.
[5] K. K. Gupta, A. Ranjan, P. Bhatnagar, L. K. Sahu, and S. Jain, “Multilevel inverter topologies with reduced device count: A review,” IEEE Trans. Power Electron., vol. 31, no. 1, pp. 135–151, 2016.
[6] Daniel W.Hart, Power Electronics. 2011.
[7] E. R. C. da Silva and M. E. Elbuluk, “Fundamentals of Power Electronics,” Green Energy Technol., vol. 59, pp. 7–59, 2013.
[8] Y. Bai and D. Wang, “Fundamentals of Fuzzy Logic Control – Fuzzy Sets , Fuzzy Rules and Defuzzifications,” Adv. Fuzzy Log. Technol. Ind. Appl., pp. 334–351, 2006.
[9] A. Perry, G. Feng, and Y. Liu, “A design method for PI-like fuzzy logic controllers for DC–DC converter,” IEEE Transactions on. 2007.
[10] S. Eliezer, Fundamentals of. 2015.
[11] Z. S. M. S. Arif, S.M. Ayob, “Decomposed Fuzzy PID Controller for Power Inverter Regulation: An Overview.”
[12] R. Malhotra, N. Singh, and Y. Singh, “Fuzzy Logic Modelling , Simulation and Control : A Review,” Rev. Lit. Arts Am., vol. 4333, pp. 183–188, 2010.
[13] W. A. Halim, S. Ganeson, M. Azri, and T. N. A. T. Azam, “Review of Multilevel Inverter Topologies and Its Applications,” vol. 8, no. 7, pp. 51–56,
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[14] P. Ratnani, S. S. Shaha, and A. G. Thosar, “Simulation of Five-Level Inverter with Sinusoidal PWM Carrier Technique Using MATLAB / Simulink,” vol. 7, no. 3, pp. 367–376, 2014.
[15] J. Lakwal et al., “MATLAB Simulation of Single Phase Cascaded Multilevel Inverter for PV Systems,” no. June 2015, 2013.
[16] Z. Salam and J. Aziz, “Derivation of Switching Angles of the Cascaded Multilevel Voltage Source Inverter Subjected to a New Pulse Width Modulation Scheme,” vol. 72, no. 3, 2009.
