P - RMANC a EVALUATION OF VSI CONTROLLED SEIG

Abstract

The increased emphasis on renewable energy sources has accelerated research and development of the Self-Excited Induction Generators (SEIG) for autonomous power generation. SEIG has emerged as a very good candidate for the autonomous power generation due to its simplicity, ruggedness in construction, lower unit cost, relatively easy in operation and maintenance as compared to conventional synchronous generators. Now a day SEIGs are preferred over synchronous generators in power generation upto 1MW. For the excitation of induction generators considerable information is present in the literature but there is not much attention about transient performance. The main drawback in the power generation by using SEIG is its inherent poor voltage regulation. This dissertation work carried out with the analysis and performance of SEIG with different values of excitation capacitors and with different loads. The observations are made with constant prime-mover torque. In the second part a Current-Controlled Voltage Source Inverter (CC-VSI) is simulated and its performances are observed in two conditions. In first condition the reference signals, which are given to the hysteresis current controller, are balanced in nature while in second case the reference signals are taken unbalanced in nature. In this dissertation to overcome the difficulty of poor voltage regulation in SEIG different techniques are used. In first technique shunt capacitors are used to overcome from the above-mentioned difficulty. In second and third techniques Current Controlled Voltage Source Inverters are used which may either fed or absorb the reactive power required to regulate the terminal voltage of SEIG. To get the reference signals for CC-VSI the DC value of terminal voltage is compared with a prespecified value and the error signal is passed through a PI controller. This gives the q-component for the reference signal. At the same time the voltage of capacitor, which is used as DC source in VSI is compared with another specified value and the error is passed through PI controller. This becomes the d- II component for the reference signal. These d-q components are then transformed into three phase abc-quantities for the reference signal of CC VSI. The CC-VSI generates the same current as given to the reference signals and finally the voltage of the SEIG is regulated. In the next technique the reference signals are generated by introducing a new concept of instantaneous reactive power. In this the three phase voltages and currents are transformed intoc( 0-quantities. These a(-axis and n-axis are mutually perpendicular to each other. The product of voltage along one axis with the current along another quadrature axis is defined as the instantaneous reactive power. This instantaneous reactive power is the basic for generating the reference signals for CC VSI. Finally the comparisons between the performances in different techniques are done. III