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A Microprocessor Controlled Static VAR Compensator for the Excitation of an Isolated Induction Generator

ABSTRACT

A self-excited induction generator offers certain advantages over a conventional synchronous generator as a source of isolated power supply in underdeveloped nations with limited energy resources. However, its practical applications have been restricted because of its inability to control the terminal voltage and the frequency under varying load conditions. In this paper a microprocessor controlled static VAR compensator is proposed and constructed. The self excitation of the generator and the control of the terminal voltage can be obtained using this type of static exciter that can be utilized globally in remote areas.

INTRODUCTION

Induction machines as motors are very common among electrical energy users. The ability of induction machines to operate as generators has been known for a long time. They have been used since the early twentieth century, but they were largely disappeared by the 1960s and 1970s. However, the induction generators had made a comeback since the price of oil began to increase in 1973. With high energy cost, energy recovery has become an important part of the economics of most industrial processes. Induction generators are being utilized in a variety of industrial applications. Due to emphasis on energy conversation, development of suitable isolated power generators driven by unconventional energy sources such as wind has recently assumed greater importance. Brushless rotor (squirrel cage), absence of a separate DC source and ease of operation and maintenance of these type of generators have advantages over the conventional synchronous generators. Difference studies have shown the cost-effectiveness of these machines. Furthermore, they are capable of operating over a wide range of rotor speed well above the synchronous speed, therefore, they have been considered as generators for aircraft, remote hydrostation and wind turbines. They can also be used in a large scale where stable power systems exist or in a smaller scale for cogeneration in remote areas. For instance, such a system does not exist in a wind power supply to isolate communities. However, for an isolated power supply a self-excited induction generator can be a good candidate.

The principle of self excitation is well know1. If an appropriate three phase capacitor bank is connected across the terminal of externally driven induction machines, an emf tends to be generated. This phenomenon is known as “capacitor self-excitation”. The induced emf and current in the stator winding will continue to increase until the equilibrium is attained because of the magnetic saturation in the machine. The capacitors provide the magnetizing VAR’s as well as reactive load requirement in case of lagging power factor. In order to reach a steady state generating mode, some permanent magnetism must initially be present in the machine core. The acceptability of these generators depend on their capability to provide desired voltage and frequency at all loads and speeds. However, their practical applications have been restricted

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Rahrooh, A., & Mossayebi, F., & Buchanan, W. (2010, June), A Microprocessor Controlled Static Compensator For The Excitation Of An Isolated Induction Generator Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--16196