STATCOM Based Solid State Voltage Regulation for Isolated Self-Excited Induction Generator

STATCOM Based Solid State Voltage Regulation for Isolated Self-Excited Induction Generator

Pallavi Thakkur (Sagar Institute of Research, Technology & Science, India) and Smita Shandilya (Sagar Institute of Research, Technology & Science, India)
DOI: 10.4018/978-1-4666-9911-3.ch009
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Self-Excited Induction Generator (SEIG) offers many advantages such as low cost, simplicity, robust construction, self-protection against faults and maintenance free in today's renewable energy industry. However, the SEIG demands an external supply of reactive power to maintain the constant terminal voltage under the varying loading conditions, which limits the application of SEIG as a standalone power generator. The regulation of speed and voltage does not result in a satisfactory improvement although several studies have been emphasized on this topic in the past. To improve the performance of the SEIG system in isolated areas and to regulate the terminal voltage STATic COMpensator (STATCOM) has been modelled and developed in this dissertation. The STATCOM consists of AC inductors, a DC bus capacitor and solid-state self-commutating devices. The ratings of these components are quite important for designing and controlling of STATCOM to maintain the constant terminal voltage. The proposed generating system is modelled and simulated in MATLAB along with Simulink and sim power system block set toolboxes. The simulated results are presented to demonstrate the capability of an isolated power generating system for feeding three-phase resistive loads.
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1. Introduction

The power system today is complicated network with many generating stations and load centers being interconnected through power transmission lines. An electric power system can be divided into three stages: i) generation, ii) transmission and iii) distribution. The basic structure of a power system is as shown in Figure 1. It is composed of generating plants, a transmission system and distribution system. These subsystems are interconnected through transformers T1, T2 and T3.

Figure 1.

Typical power systems

The power system is a highly nonlinear system that operates in changing conditions such as loads, generator outputs etc. When subjected to a disturbance, the stability of the system depends on the nature of the disturbance as well as the initial operating condition. The system must be capable to operate satisfactorily under these disturbing conditions and successfully meet the load demand. Also with increasing demand it becomes very important to utilize the existing transmission system assets. Flexible AC Transmission System (FACTS) controllers, based on the hasty development of power electronics technology, have been projected in recent years for better utilization of existing transmission facilities.

Now-a-days it is becoming very difficult to use it fully due to various reasons, such as environmental legislation, capital investment, rights of ways issues, construction cost of new lines, deregulation policies, etc. Electric utilities are now forced to operate their system in such a way that makes better utilization of existing transmission facilities. During the last decade, a number of control devices under the term FACTS technology have been anticipated and implemented. Application of FACTS devices in power systems, leads to better performance of system in many aspects. Voltage stability, voltage regulation and power system stability, damping can be improved by using these devices and their proper control (Haque, 2006). There are various forms of FACTS devices, some of which are connected in series with a line and the others are connected in shunt or a combination of series and shunt. The FACTS technology is not a single high power controller but rather a collection of controllers which can be applied individually or in coordination with other to control one or more of the inter related system parameters like voltage, current, impedance, phase angle and damping of oscillations at various frequencies below the rated frequency. Among all FACTS devices, static synchronous compensators (STATCOM) plays much more important role in reactive power compensation and voltage support because of its attractive steady state performance and operating characteristics. The fundamental principle of a STATCOM installed in a power system is the generation of ac voltage source by a voltage source inverter (VSI) connected to a dc capacitor. The active and reactive power transfer between the power system and the STATCOM is caused by the voltage difference across the reactance. The STATCOM can also increase transmission capacity, damping low frequency oscillation, and improving transient stability. The STATCOM is represented by a voltage source, which is connected to the system through a coupling transformer. The voltage of the source is in phase with the ac system voltage at the point of connection, and the magnitude of the voltage is controllable. The current from the source is limited to a maximum value by adjusting the voltage. Mathematical modeling and analysis of static compensator (STATCOM) is presented in (Padiyar & Devi, 1994) & (Rao, Crow, & Yang, 2000). It explains the use of STATCOM for improvement of transient stability and power transfer.


2. Facts Controllers

The IEEE Power Engineering Society (PES) Task Force of the FACTS Working Group has defined FACTS and FACTS Controller as given below (Hingorani & Gyugyi, 1999).

Flexible AC Transmission System (FACTS): Alternating current transmission systems incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability.

FACTS Controller: A power electronic-based system and other static equipment that provide control of one or more AC transmission system parameters.

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