DESIGN ANALYSIS AND DEVELOPMENT OF STAND ALONE POWER UNIT

Abstract

The fast depletion of fossil fuels has drawn attention towards the use of non conventional energy sources wind, tidal, biomass and small hydro energy. In remote areas which are rich in non conventional energy sources, stand alone systems are considered as promising option due to difficulty and costly to install grid systems for electrification. The squirrel cage induction generator is most suitable to convert the mechanical energy into electrical energy due to its inherent advantages. It is well known that an externally driven induction machine can be successfully operated as an induction generator with sustained self excitation when an appropriate value of a capacitor bank is appropriately connected across the terminals of the induction machine. Such an induction machine is called a self.- excited induction generator (SEIG). Self-Excitation process in induction generators is a complex physical phenomenon, which has been studied extensively in the past. The interest in this topic is sustained primarily due to its application in isolated power systems for power generation. The terminal reactive power support in case of isolated generator is required to be adjustable so that the proper amount of reactive power can be supplied under different operating conditions. Consequently, a controllable terminal voltage for the self-excited generator can be obtained through an appropriate control scheme. To fulfill the objective of varying the equivalent capacitance connected to the generator terminal continuously; some power electronic circuits need to be introduced into such a system. The self-excited induction generator is analyzed using the generalized-machine theory transient representation of the machine. Such an analysis produces instantaneous currents, which can be used to investigate the process of current and voltage build up during self-excitation and similarly perturbations due to load changes. iii In this dissertation work the transient analysis of self-excited induction generator is carried out. The Dynamic model of three phase squirrel cage induction generator is developed on stationary d-q axes reference frame and the instantaneous values of direct and quadrature axis stator and rotor currents and voltages for different load currents are found by solving these differential equations representing the dynamic behavior of the machine. This includes the building up of voltage during the initiation stage of self-excitation and the perturbations of the terminal voltage and the stator current, which result from load changes. The work is extended to chopper based ELC which tries to control the duty cycle of chopper so that generated power is divided between the dump load and consumer load and hence maintaining the generator output power constant. The fourth chapter includes the design of ELC and development of hard ware chopper control circuit. In the fifth chapter the design of full rating and reduced rating STATCOM for UPF loads and the Mathematical modeling of STATCOM for improvement of voltage regulation are discussed. Finally, the last chapter 6 includes the simulation results of transient behavior of SEIG and SEIG-STATCOM. This also includes the introduction to DSP for future work. Iv