Design and Implementation of a PV Converter for DC Microgrid with Fast and Accurate MPP

78 Pages·2017·3.16 MB·English

by  Yang Zhou

Design and Implementation of a PV Converter for DC
Microgrid with Fast and Accurate MPP Tracking Strategy
using Boundary Controller

by

Yang Zhou
A Thesis submitted to the Faculty of Graduate Studies of
The University of Manitoba
in partial fulfilment of the requirements of the degree of
MASTER OF SCIENCE

Department of Electrical and Computer Engineering
University of Manitoba
Winnipeg
Copyright © 2017 by Yang Zhou
Abstract
Photovoltaic (PV) is an important application of solar energy that widely used in microgrid
systems. This thesis proposes a fast and accurate Maximum Power Point Tracking (MPPT)
algorithm used for PV application where a dp/dv tracker and a second-order switching surface
control technique are applied to perform fast switching in a boost-type converter. A fast action of
tracking Maximum Power Point (MPP) and stable operation at the point are achieved as soon as
the environmental conditions are changed. The operating principles of the proposed control
technique and mathematical derivations of the control law and steady state characteristics are
presented. Simulation result shows that the proposed controller has a dramatic improvement in
terms of dynamic response comparing with conventional PI based MPPT controller. A 280 W
prototype for the proposed controller is built and tested with PV panels. Experiment results show
a good agreement with the derived theory.

ii
Publications from This Thesis
Conference Papers
[1] Y. Zhou, C. Ho, “A review on Microgrid architectures and control methods,” IEEE ECCE-
Asia, Hefei, China, 2016, pp. 3149 – 3156.
[2] Y. Zhou, C. Ho and K. M. Siu “A Fast and Accurate MPPT Control Technique using
Boundary Controller for PV Applications, IEEE Applied Power Elec. Conf. and Ex. (APEC)
Tampa, US, 2017.
Transaction Papers
[1] Y. Zhou, C. Ho and K. M. Siu “A Fast and Accurate MPPT Control Technique using
Boundary Controller for PV Applications, IEEE Transactions on Power Electronics.
(Submitted)

iii
Acknowledgments
Firstly, I would like to thank my supervisor Dr. Ngai Man (Carl) Ho for his valuable
guidance throughout my entire master program. It is him who brought me into the research field
of power electronics where I am able to work on the meaningful and exciting projects. I also
learned a lot from him both knowledge and professionalism, also his attitude towards research
inspire me to concur the difficulties with faith.
I would like to express my great gratitude to my RIGA lab mates who offered lots of help
during my two years’ study, especially Mr. Mandip Pokharel, Mr. King Man (Ken) Siu and Mr.
Dong Li who provided their valuable experiences on the simulation, hardware and controller
design. I also owe thank to Ms. Radwa Abdalaal and Mr. Isuru Jayawardana for sharing their
knowledge to help me to better understand the theory of power electronics that used in my project.
I also really appreciate the help of my other lab mates for their help suggestions and comments on
my thesis. I would also thank to all my fellows and friends in Department of Electrical Engineering
and Computer, especially Mr.Erwin Dirks for technical support.
Last but not the least, I would like to thank my family for their unconditional love and
support all the time, I would not have the opportunity to come to Canada and conduct further
research without their understanding and support.

iv
Dedications
To my beloved mother, father, my sister and her husband and the lovely child and my girlfriend
Zhuang Zhang.

v
Table of Contents
Publications from This Thesis ....................................................................................................... iii
Acknowledgments.......................................................................................................................... iv
Dedications ......................................................................................................................................v
Table of Contents ........................................................................................................................... vi
List of Tables ............................................................................................................................... viii
List of Figures ................................................................................................................................ ix
List of Abbreviations ..................................................................................................................... xi
Chapter 1 Introduction ..............................................................................................................1
1.1 Microgrid Overview.............................................................................................................1
1.1.1 Structure of DC Microgrid .......................................................................................3
1.1.2 Power Converters Used in Microgrid ......................................................................5
1.1.3 Review of Converter Control Techniques .............................................................10
1.2 MPPT Control Technique Used in DC Microgrid .............................................................12
1.3 Motivation of the Thesis ....................................................................................................16
1.4 Organization of the Thesis .................................................................................................17
1.5 Contributions of the Research ............................................................................................19
Chapter 2 Operation Principles of the Proposed MPPT Controller........................................21
2.1 dp/dv tracker algorithm ......................................................................................................22
2.2 Control Laws of Boundary Controller ...............................................................................28
2.3 Overall Controller ..............................................................................................................32
Chapter 3 Steady State Characteristics and Analysis of the Proposed MPPT Controller ......33
3.1 PV Array Characteristics – V-I curve ................................................................................33
3.2 PV Array Characteristics – V-P curve ...............................................................................35
3.3 Voltage of PV Array at MPP .............................................................................................35
vi
3.4 Capacitor Voltage Ripple ...................................................................................................36
3.5 PV Output Current Ripple .................................................................................................36
3.6 Duty Ratio ..........................................................................................................................36
3.7 Inductor Current Ripple .....................................................................................................36
3.8 Switching Frequency .........................................................................................................37
Chapter 4 Simulation Results of the Proposed MPPT ............................................................38
4.1 Steady-State Operation ......................................................................................................38
4.2 Transient Performance .......................................................................................................42
Chapter 5 Experimental Verifications ....................................................................................45
5.1 Experimental Setup ............................................................................................................45
5.2 Experimental Results – Steady State .................................................................................48
5.3 Experimental Results – Transient Performance .................................................................50
5.4 Experimental Results – Quantifying of PV Converter Efficiency .....................................53
Chapter 6 Conclusion and Suggestion for Future Research ...................................................55
6.1 Conclusion .........................................................................................................................55
6.2 Suggestion for Future Research .........................................................................................56
References ......................................................................................................................................57
Appendix ........................................................................................................................................63
A. Derivation of (4) and (6) ......................................................................................................63
B. Derivation of (10) and (11) ..................................................................................................64
C. Derivation of (13) .................................................................................................................65
D. Derivation of (17) .................................................................................................................65
E. Derivation of (18) .................................................................................................................66
F. Derivation of (19) .................................................................................................................66

vii
List of Tables
Table 1-1 Commonly Used Converters Technique in Microgrid ................................................... 6
Table 4-1 Parameters of Calculating Theoretical Values ............................................................. 40
Table 4-2 Steady State Simulation and Theoretical Values.......................................................... 41
Table 4-3 Comparison of Simulation Parameters and Results ..................................................... 42
Table 5-1 Specification of the PV Converter Prototype ............................................................... 47

viii
List of Figures
Fig. 1-1 Illustration of Topology for Future Smart Grid. [3] ............................................... 2
Fig. 1-2 Structure of A DC Microgrid .................................................................................. 4
Fig. 1-3 A Typical PV Converter in an AC Microgrid. ........................................................ 7
Fig. 1-4 PV System with Energy Storage in A DC Microgrid. ............................................ 9
Fig. 1-5 Current/Voltage and Power/Voltage Characteristic of PV array. ......................... 13
Fig. 1-6 Fast Moving Vehicle with PV Panel On-top Under Rapidly Changing Irradiance.
16
Fig. 2-1 Structure of the Proposed Control Scheme with a Boost-type PV Converter. ..... 21
Fig. 2-2 PV V-P Characteristic and Pinciple of Maximum Power Point Tracker. ............. 25
Fig. 2-3 Flow Chart of dp/dv Tracker. ................................................................................ 26
Fig. 2-4 Slope of P-V curve of PV when (a) 𝑑𝑝/𝑑𝑣𝑐 > 0 (b) 𝑑𝑝/𝑑𝑣𝑐 ≅ 0 (c) 𝑑𝑝/𝑑𝑣𝑐 <
0. 27
Fig. 2-5 State of PV Converter When Switch (a) ON and (b) OFF. .................................. 28
Fig. 2-6 Capacitor Voltage and Current Waveforms in Steady State. ................................ 29
Fig. 2-7 Flow Chart of Boundary Controller. ..................................................................... 31
Fig. 3-1 The Single-diode Model Equivalent Circuit of a PV Cell [51]. ........................... 33
Fig. 3-2 An Ideal PV V-I Curve. ........................................................................................ 34
Fig. 4-1 Simulation Waveforms in Steady State. ............................................................... 39
Fig. 4-2 Dynamic Response of PI and Proposed MPPT Controllers.................................. 44
Fig. 5-1 Test Bed Setup (a) Schematic of Test Bed, and (b) Laboratory Setup. ................ 46
ix
Fig. 5-2 Experimental Steady State Waveforms ................................................................ 49
Fig. 5-3 Experimental Results in (a) V-I Curve, and (b) V-P Curve in Steady State. ........ 49
Fig. 5-4 Experiment Results of Step Change of (a) Switched from 2 to 4 Panels, and (b)
Vice Versa. 51
Fig. 5-5 Power and Inductor Current Trajectory for Fig. 5-4 (a). ...................................... 52
Fig. 5-6 Topology of Converter for Quantifying Efficiency .............................................. 53
Fig. 5-7 Converter Efficiency In Regard to Input Power and Voltage When Switching
Frequency is 5 kHz ....................................................................................................................... 54

x