Methods for Increasing the Quality and Reliability of Power System Using FACTS Devices

Author Biography

I am Dr. Hidaia Mahmoud Mohamed Alassouli. I completed my PhD degree in Electrical Engineering from Czech Technical University by February 2003, and my M. Sc. degree in n Electrical Engineering from Bahrain University by June 1995. I covered most subjects in Electrical Engineering, Computer Engineering and Telecommunications Engineering during my study. My nationality is Palestinian from gaza strip.

I was working also as a computer networking administrator in government computer center at Palestine Ministry of Telecommunication and Information Technology. I worked also as electrical engineer trainee in Bahrain Ministry of Power & Water, Bahrain. I worked  also as electrical and telecommunication engineer trainee  in Bahrain Telecommunication Company, Batelco.

I had considerable undergraduate teaching experience in several types of courses in many universities. I handled teaching the most important subjects in Electrical and Telecommunication and Computer Engineering.

I could publish 5 papers in a top-tier journals, and 25 papers in conference proceedings besides a lot of published books in Lulu.com book store.

I have website that I  publish on it all my articles concerning anticorruption: anticorruption.000space.com

My personal website: www.hidaia-alassouli.000space.com

Email: [email protected]

Acknowledgments

I would like to thank our God and the Czech goverment for their support and for the opportunity to study here in the Czech Republic.

I want to express my deepest gratitude and appreciation to my supervisor, Doc. Ing. Josef Tlustý, CSc., for his advice, support and encouragement during my studies here in Prague.       

I also want to thank all the members of the electroenergetic department, my teachers and colleagues at CVUT for their assesments.

Table of Contents

Perface

Chapter 1: Basic Power System Quality Problems

Chapter 2: FACTS Devices and Active Filters

Chapter 3: Control Strategies for Shunt and Series FACTS Devices

Chapter 4: Three Phase Shunt Active Power Filter Control Algorithms

Chapter 5: Other Three Phase Active Power Filter Topologies Control Algorithms

Chapter 6: Optimal Control

Chapter 7: Optimal Control of UPFC for Load Flow Control and Voltage Flicker and Current Harmonics Elimination

Chapter 8: Summery

References

Preface

FACTS are one aspect of power electronics revolution that is taking place in all areas of electrical energy. A variable of powerful semiconductor devices not only offer the advantage of high speed and reliability of switching but, more importantly, the opportunity offered by a variety of innovative circuit concepts based on these power devices enhance the value of electric energy.

In generation area, the potential application of power electronics is largely in renewable generation. Photovoltaic and fuel cells requires conversion of dc to ac. Generation with variable speed is necessary for economic viability of wind and small hydro generators. Variable-speed wind generators and small hydro generators requires conversion of variable frequency ac to power system frequency. These applications of power electronics in renewable generation area require converter sizes in the range of few kilowatts to few megawatts.

In coming decades, electrical energy storage is expected to be widely used in power systems as capacitor, battery and superconducting magnet technologies move forward. Batteries are widely used already for emergency power supplies. These require ac/dc/ac converters in the range of a few kilowatts to a few tens of megawatts. On the other hand, variable speed hydro storage requires converters of up to a few hundred megawatts.

In transmission area, application of power electronics consists of High Voltage Direct Current (HVDC) power transmission and FACTS. HVDC is often an economical way to interconnect certain power systems, which are suited in different regions separated by long distances or those have different frequencies or incompatible frequency control. HVDC involves conversion of ac to dc at one end and conversion of dc to ac at the other end.

What is most interesting for transmission planners is that FACTS opens up new opportunities for controlling power and enhancing the usable capacity of the lines. The possibility that current through a line can be controlled at reasonable cost enables a large potential of increasing the capacity of the existing lines with larger conductors, and use one of the FACTS controllers to enable corresponding power to flow through lines under normal and contingency conditions. These opportunities arise through the ability of FACTS controllers to control the interrelated parameters that govern the operation of transmission line including series impedance, shunt impedance, current, voltage, phase angle, and the damping of oscillations at various frequencies below the rated frequency.

In distribution area, an exciting opportunity called Custom Power. The custom power concept incorporates power electronics controllers and switching equipment, one or more of which can be used to provide a value-added service to the customers.  In general, these custom service applications represent power electronics in the range of few tens of kilowatts to few ten of megawatts of conversion or switching equipment between the utility supply and customer.

On the end-user side, power electronics conversion and switching technology has been fast growing area. Complementing the Custom Power technology is the whole area of power conditioning technology used by customers, under the term Power Quality. Uninterruptible power supplies (UPS) and voltage regulators represent the major growth area in power electronics. In end use, the converter sizes range from a few watts to ten of megawatts.

The term active filter is a general one and is applied to a group of power electronic circuits incorporating power switching devices and passive energy storage circuit elements such as inductors and capacitors. The functions of these circuits vary depending on the applications. They are generally used for controlling current harmonics in supply networks at the low and medium voltage distribution level or for reactive power and/or voltage control at high voltage distribution level. These functions may be combined in a single circuit or in separate active filters.

Thesis Objective

The thesis will try to summarise the major power system problems and the important role of the FACTS devices to enhance the power system quality. Then, it will give a brief description for various FACTS and Active Filters controllers as mentioned on the existing publications.

Most of the control schemes introduced in the existing papers were designed either for eliminating current harmonics or eliminating voltage flickers or for load flow control. So, this work is devoted to find a proper optimal control schemes for a system with series or shunt or series and shunt converters that can provide all functions together.

Various optimal control schemes will be designed for systems with series, shunt and series-shunt converters with the objective to control the load flow through a lines and to eliminate current harmonics and voltage flickers with different strategies for tracking. 

Chapter 1: Gives ageneral description of most power system problems and the basic techniques used to improve the power system quality. It also gives idea about basic objectives from the FACTS devices.

Chapter 2: Offers detailed description for the basic types of FACTS devices and active filters existing in power industry.

Chapter 3: Describes various shunt controllers for control of the Static Compensator (STATCOM) and various series controllers for the control of the Static Synchronous Series Compensator (SSSC) and various Unified Power Flow Controllers (UPFC) as covered in most existing papers.

Chapter 4: Describes the major control schemes for the shunt active filter as covered by most existing papers.

Chapter 5: Describes the major control schemes for the other types of active filters as covered by most existing papers.

Chapter 6: Gives description for optimal control design.

Chapter 7: Case studies to design different optimal control schemes for system with UPFC unit to control the power flow, eliminate voltage flicker and eliminate current harmonics. The case studies were repeated for system with only series or shunt converters.

Chapter 1: Basic Power System Quality Problems

The information given in this chapter are based on Ref. [1], Ref. [2] and Ref. [3].

1 Basic Power System Problems

1.1 Transient

An undesirable event that is undesirable and momentary in mature.

1.1.1 Impulsive Transient

Sudden non power frequency change in steady state conditions of voltage or current (i.e. lightening is impulsive transient).

1.1.2 Oscillatory Transient

Consists of voltage and currents whose instantaneous value changes polarity rapidly. It is defined by its spectral content, duration and magnitude. The spectral contents subclasses are high, medium and low frequency. The oscillatory transients with frequency greater than 500 kHz and duration measured in microseconds are high frequency oscillatory transients. The oscillatory transient with frequency 5-500 kHz and duration 10 microseconds are medium frequency oscillatory transients. Back to back eneregization of capacitor results in oscillatory transient currents in 10 kHz. Transient with frequency components less than 5 kHz and (0.3 to 0.5 ms) is low frequency transient. Oscillatory transients with principal frequencies less than 300 Hz can also be found in distribution system. These are generally associated with ferroresonance and transformer energization.

1.1.3 Principe of Overvoltage Protection

The main sources of the transient over voltage protection are capacitor switching, magnification of capacitor switching transients and lightening.

The fundamental principles of overvoltage protection of load equipment are:

Limit the voltage across sensitive insulation.

Divert the surge current a way from the load.

Block the surge current from entering the load.

Bond ground references together at the equipment.

Reduce or prevent surge current from flowing between grounds.

Create a low pass filter using blocking or limiting principles.

The surge arresters and transient voltage surge supressors are widely used. Their main function is to limit the voltage that can appear between two points in the circuit.

1.2 Long Duration Voltage Variation

1.2.1 Overvoltages

Increase in rms. ac voltage greater than 110% at the power frequency for longer than 1 min. It results from load