Modeling and Simulation of an Asynchronous Generator with AC/DC/AC Converter Fed RLC Series Circuit in an Isolated Power Generation System Subramanian K. School of Electrical Engineering Vellore Institute of Technology University Vellore, Tamilnadu, India Email id: ksubramanian@vit.ac.in Ray K.K. School of Electrical Engineering Vellore Institute of Technology University Vellore, Tamilnadu, India Email id: kkray@vit.ac.in Abstract—This paper expounds a simulation model of a self-excited asynchronous generator (SEASG) feeding R L load in conjunction with an AC/DC/AC converter fed RLC series circuit connected at the point of common coupling (PCC). Simulation model of the proposed system have been developed by using Matlab/Simulink. The result shows that the effect of RLC series circuit when operated at variable frequency affects the generation voltage profile. This reflects that an additional capacitance or inductance effect is possible to inject when the RLC is operated at frequency lower than the resonance frequency or the higher than the resonance frequency. This simulation model validates the injections of capacitance in a SEASG is possible to match the lagging reactive power of the RL load to maintain a constant voltage at the load bus. Keywords-asynchronousgenerator;rectifier-inverter; simulation model I. INTRODUCTION The use of non-conventional energy sources has become eminent due to fast depletion of conventional energy sources. The recent trend to tap solar, wind and tidal energy are becoming popular amongst the renewable energy sources. At present, to decentralize the power generation system, attempts have been in the direction of generating small power and distributing it locally. This prompted the use of wind and solar energy to cope with the present day energy crises. Self-excited asynchronous generator has emerged as a possible alternative for isolated power generation from renewable energy sources because of its low cost, less maintenance and rugged construction [1]-[3]. However, it requires a suitable controller to regulate the voltage due to variation of consumer loads. From the characteristics of voltage generation in a SEASG, it is essential to have a variable capacitance at the machine terminals to maintain constant voltage with variable load. J. K. Chatterjee et al [4] has developed a variable lagging reactive volt-ampere (VAr) source/sink to maintain the generation voltage of SEASG constant. K. K. Ray [5] applied the above concept in a stand-alone system and verified it experimentally. S.S. Murthy et al [6]–[7] explain the steady state analysis of self-excited induction generators. R. Bonert et al [8]–[9] discussed the impedance controller of SEASG for voltage regulation. S.S. Murthy et al discussed the practical implementation of electronic load controller in his works [10]–[11]. Since voltage and frequency of an ASG is dependent on load and the speed of the prime mover, the authors made an attempt to investigate the effect of series resonance circuit on input side of uncontrolled rectifier experimentally by keeping the prime mover speed constant [12] - [13]. The subsequent section describes the system configuration. In Section–III Modeling of the proposed scheme has been explained in details. Control strategies have been discussed in section IV. Section V and VI discuss the interpretation of the result and conclusion respectively. II. SYSTEM CONFIGURATION The schematic arrangement of the proposed system is shown in Fig.1. It consists of an SEASG, rectifier – inverter fed RLC series circuit with RL load. SEASG is driven at a constant speed along with static capacitor at the stator terminals of the SEASG. The effect of changing load on the generated voltage was found to be drooping with an increase of load. To compensate this drooping voltage, an R L C series resonance circuit fed from an AC/DC/AC converter is connected at PCC. The AC/DC/AC converter is operated at a frequency lower than the resonance frequency to inject the capacitance effect on the system such that the voltage drop due to inductive load is compensated. The resonance circuit thus could operate to inject lagging or leading VAr effect on the input current by operating the AC/DC/AC converter at various frequencies. The instantaneous reactive power compensator (i.e. AC/DC/AC along with RLC series circuit) proposed in this paper to balance the instantaneous reactive power required by the load. III. MATHEMATICAL MODELING The mathematical model of the system refers the equations (1) - (13) is developed through using Matlab / Simulink software [14]. It is well known that when a squirrel cage induction motor is driven at a speed higher than the synchronous speed a voltage will be induced in the stator terminals when external capacitance is connected across the stator terminals. The magnitude of the voltage builds up depends on the capacitance value to neutralize the magnetizing reactance of the machines. This technique is known as self-excitation [1]. 2010 International Conference on Recent Trends in Information, Telecommunication and Computing 978-0-7695-3975-1/10 $25.00 © 2010 IEEE DOI 10.1109/ITC.2010.60 80 Authorized licensed use limited to: VELLORE INSTITUTE OF TECHNOLOGY. Downloaded on August 04,2010 at 10:16:59 UTC from IEEE Xplore. Restrictions apply.