Proportional Resonant Control of Three-Phase Grid-Connected Inverter During Abnormal Grid

210 Pages·2017·7.01 MB·English

Proportional Resonant Control of
Three-Phase Grid-Connected Inverter
During Abnormal Grid Conditions

Ahmed Othman Althobaiti
Electrical Electronic Engineering
School of Engineering

Newcastle University

A thesis submitted for the degree of
Doctor of Philosophy
November, 2017

Proportional Resonance Control of Three-Phase Grid-Connected Inverter
Abstract
The development of using grid-connected three-phase inverter has augmented the standing of
realizing muted distortion along with high-quality current waveform. The standard three-phase
grid-connected inverter is the full-bridge voltage source inverter. This inverter is usually
controlled by proportional integral (PI) controller in order to ensure sinusoidal current injection
to the grid. Although the PI controller is well established and easy to use under normal grid
conditions, it leads to system instability under abnormal grid conditions. When abnormal grid
conditions are likely to occur, the control system with PI controller can be configured to include
two separate PI controllers for the positive and negative sequence components of the grid
current. However, this increases control complexity and total harmonic distortion (THD).
More recently, the proportional resonant (PR) controller started to replace PI controller in a
different application including grid-connected current control. In this thesis, a comprehensive
theoretical and experimental comparison between the PI and PR controllers is presented. The
comparison shows that the PR controller offers lower total harmonic distortion (THD) in the
current signal spectrum and is simpler to implement as it uses only the positive sequence
component of the grid current and consequently only one PR controller is needed. For these
reasons, the PR controller is adopted in this thesis.
Despite the PR controller offering enhanced functioning under abnormal grid conditions
compared to PI controller, a sudden change in the grid voltage could additionally raise the error
between the reference signal and the controlled signal which results in causing significant
divergence from its ostensible value. In this case, the performance of the conventional PR
controller will not keep up with the increase in the error which weakens controller performance.
To overcome this problem, a new design concept for controlling the current of the three-phase
grid connected inverter during normal and abnormal conditions is presented in this thesis. The
proposed technique replaces the static control parameters by adaptive control parameters based
on a look-up table. This adaptive PR, controller has been investigated and demonstrated with
different normal and abnormal grid conditions. The proposed control technique is capable of
providing low THD in the injected current even during the occurrence of abnormal grid
conditions compared with PI and PR controllers. It also achieves lower overshoot and settling
time as well as smaller steady-state error.

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Proportional Resonance Control of Three-Phase Grid-Connected Inverter
Additionally, despite the fact that both PI and PR controllers are relatively straightforward to
tune, and are sometimes capable of dealing with many time-varying grid conditions. This
research also presented an adaptive controller tuned using advanced optimization techniques
based on particle swarm optimisation (PSO). PSO is presented to optimize the control
parameters of both PI and PR controllers for the three-phase grid-connected inverter. There are
many advantages of using PSO, such as no additional hardware being required. Thus, it can be
extended to other applications and control methods. In addition, the proposed method is a self-
tuning method and can thus be suitable for industrial applications where manual tuning is not
recommended for time and cost reasons. Simulation and experimental test were carried out to
investigate the performance of the proposed techniques. In the simulation, the system was tested
under 100 kW model using Matlab/Simulink environment. In addition, the system was also
investigated through a practical implementation of the control system using a Digital Signal
Processor (DSP) and grid-connected three-phase inverter. This practical system was
demonstrated a 300 W scaled-down prototype. As a result, the comparisons between
experimental and simulation results show the behaviour and performance of the control to be
accurately evaluated.

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Proportional Resonance Control of Three-Phase Grid-Connected Inverter
Acknowledgements
I want to thank God (Allah), the most merciful and the most gracious, who gave me patience,
strength and help to achieve this scientific research.
First and foremost, I would like to thank Dr. Matthew Armstrong for his guidance and support,
throughout these years and for patiently reading and commenting on this thesis. I also appreciate
the input of Dr. Mohammed Elgendy throughout my time at Newcastle University for his trust,
guidance and support. Very sincere thanks are due to my friends in the UG lab, technicians and
staff.
I have not enough words to thank my ever first teachers in this life, my parents, who have been
inspiring me and pushing me forward all the way. Their prayers and blessings were no doubt
the true reason behind any success I have realized in my life.
Special thanks to my wife. Thank you for supporting me for everything, and especially I can't
thank you enough for encouraging me throughout this experience. To my beloved son Anas and
daughter Aleen, I would like to express my thanks for being such good children always cheering
me up.
I am grateful to all my family members for their kind support, endurance and encouragements,
which have given me the energy to carry on and to motivate myself towards crossing the finish
line.

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Proportional Resonance Control of Three-Phase Grid-Connected Inverter

To my dear father and mother

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Proportional Resonance Control of Three-Phase Grid-Connected Inverter

Acronyms
Acronyms Full Names
AIO Artificial intelligent optimization
ANN Artificial neural networks
BJT The bipolar junction transistor
BPSC Balance positive sequence control
DD-SRF-PLL Decoupled double synchronous reference frame phase
locked loop
DG Distribution generator
DSC Delayed signal cancellation
Digital signal processor
DSP
FFT Fast Fourier Transform
FL Fuzzy logic
GA Genetic algorithms
IARC Instantaneous active reactive control
IEEE Institute of Electrical and Electronic Engineering
IGBT Insulated-gate bipolar transistor
ISE The integral of squared error
ITAE The integral time absolute error
MATLAB Matrix laboratory
MOSFET The metal-oxide-semiconductor-field-effect-transistor
Maximum Power Point
MPP
Maximum Power Point tracking
MPPT
NSS Negative sequence signal
PCC Point of common coupling
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Proportional Resonance Control of Three-Phase Grid-Connected Inverter
Acronyms Full Names
PI Proportional integral controller
PLL Phase locked loop
PNSC Positive and negative sequence control
PR Proportional Resonance
PSO Particle Swarm Optimization
PSS Positive sequence signal
Pulse width modulation
PWM
SOGI Second order generalized integrator
Sinusoidal pulse width modulation
SPWM
Synchronous reference frame
SRF
STATCOM Static synchronous compensators
Space vector pulse width modulation
SVM
Total harmonic distortion
THD
Sampling time (sec)
Ts
UPFC Unity power factor control
UPQC Unified power quality conditioner
VOC Voltage oriental control
VSI Voltage Source Inverter

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Proportional Resonance Control of Three-Phase Grid-Connected Inverter

Symbol
Symbol Full Names
I Current in phase a
a
I Current in phase b
b
I Current in phase c
c
Current in reference frame direct current (d)
I
d
I Current in reference frame quadratic current (q)
q
I Current in the stationary reference frame (α alpha transform)
α
I Current in the stationary reference frame (β beta transform)
β
k Integral gain of the controller
i
k Proportional gain of the controller
p
V Voltage in phase a
a
V Voltage in phase b
b
V Voltage in phase c
c
D Diode
f Frequency
L Inverter side inductance
1
L Grid side inductance
2
P Active power
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Proportional Resonance Control of Three-Phase Grid-Connected Inverter
Symbol Full Names
p.u Per unit
Q Reactive power
t Time
θ Phase angle

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