Description
ABSTRACT
The increasing penetration of distributed power generation into the power system leads to a continuous evolution of grid interconnection requirements. In particular, active power control will play an important role both during grid faults (low- voltage ride-through capability and controlled current injection) and in normal conditions (reserve function and frequency regulation). The aim of this paper is to propose a flexible active power control based on a fast current controller and a reconfigurable reference current selector. Several strategies to select the current reference are studied and compared using experimental results that are obtained during an unsymmetrical voltage fault. The results of the analysis allow selection of the best reference current in every condition. The proposed methods facilitate multiple choices for fault ride through by simply changing the reference selection criteria.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE PROJECT
- AIM AND OBJECTIVE OF THE PROJECT
- SCOPE OF THE PROJECT
- SIGNIFICANCE OF THE STUDY
CHAPTER TWO
LITERATURE REVIEW
- FAULT DEFINITIONS AND TAXONOMY
- OVERVIEW OF DISTRIBUTED GENERATION
- DISTRIBUTED POWER GENERATION TECHNOLOGIES
CHAPTER THREE
METHODOLOGY
- GRID FAULT CONSIDERATIONS
- FAULT CONTROL IN GRID AND MICRO-GRID
- CURRENT CONTROL STRATEGIES WHEN RUNNING ON GRID FAULTS
- FAULT CONDITIONS
CHAPTER FOUR
4.0 RESULTS
4.1 RESULT
CHAPTER FIVE
- CONCLUSION
- RECOMMENDATION
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
In the last decade, distributed power generation systems (DPGSs) based on renewable energies contribute more and more to the total amount of energy production on the globe. Wind turbines (WT) as well as photovoltaic (PV) systems are seen as reliable energy sources that should be further exploited in order to achieve maximum efficiency and overcome the increasing power demand in the world. These systems are no longer regarded as engineering issues, but they are widely recognized as reliable systems, which can have a large share in energy production in the future.
The possibility of energy production using a clean technology makes both Wind turbines (WT) and photovoltaic (PV) systems very attractive, but the control of these systems is a challenge due to the uncertainty in the availability of the input power [1]. Moreover, the increased amount of distributed systems that are connected to the utility network can create instability in the power systems, even leading to outages.
In order to maintain a stable power system in countries with a large penetration of distributed power, transmission system operators issue more stringent demands regarding the interconnection of the DPGS to the utility grid [2]–[4]. Among the new demands, power generation systems are requested to ride through grid disturbances and to provide ancillary services in order to behave as a conventional power plant, and hence to have the capability of sustaining the utility network in the situation of a fault. Therefore, the grid fault influence on the control of DPGS needs to be investigated.
This paper discusses some possible control strategies that a DPGS can adopt when running on faulty grid conditions. First, a classification of the grid faults is presented, followed by some consideration of the control strategy when an unbalanced fault takes place in the grid. Finally, experimental results are presented in order to verify the theory of each control strategy.
1.2 AIM AND OBJECTIVES OF THE STUDY
The main aim of this work is to propose a flexible active power control based on a fast current controller and a reconfigurable reference current selector. The objectives of the study are:
- To discuss different types of gird faults
- To study different strategies that distributed power generation systems (DPGSs) can adopt when running on faulty grid
- To generate an algorithm that is used for detecting the positive and negative sequences of the grid voltage
1.3 SCOPE OF THE STUDY
The scope of this work is on flexible action power control of distributed power generation systems during grid faults. This work investigates the control possibilities of a distributed power generation systems when running on unbalanced grid faults. For simplicity, only the grid-side converter is considered here. The input power source and its control are disregarded. Hence, the investigated control strategies can be applied to a variety of distributed power generation systems. Additionally, the dc-link voltage controller is not included in the control strategy.
1.4 SIGNIFICANCE OF THE STUDY
This study will be of great benefit to all electrical engineers and studies in that it will expose them to different ways distributed power can be generated and how it can be controlled during grid fault.
CHAPTER FIVE
4.1 CONCLUSION
The aim of this paper was to investigate several methods that deal with the control of DPGS in the case of unbalance conditions that are caused by faults in the utility grid. The results of the analysis allow for the design of a flexible active power controller that is capable of adapting itself to the fault situation and is reconfigurable in case the grid requirements change. In particular, it has been proven that, during unbalance conditions, it is possible to obtain zero active and reactive power oscillations only by accepting highly distorted currents. However, an intermediate solution allows having sinusoidal grid currents compensating for the oscillation in the active power only, while oscillations are present in the reactive one. It has been proven that the DPGS can be a very flexible power producer that is able to work in constant current, constant active power, or constant reactive power modes depending on the grid fault type and the utility network necessity.
