Analysis of Three Phase Self Excited Induction

Generator Using MATLAB/SIMULINK

Prerna Gaur, Avinash KishoreN.S.I.T., India

SELF excited induction generator (SEIGs) are slowly replacing conventional synchronousalternator in isolated power generation because of the former ruggedness lower unit cost, relativeease of operation and maintenance easily availability in lower rating even under low speedoperation. Since a majority of loads even in isolated system are dynamic in nature, widerapplicability of the SEIGs would depend on its capacity to handle such loads satisfactorily.Another bottleneck in the applicability of the SEIG is its inherent poor voltage regulation,and the conquest requirement of a well designed voltage regulator. The cost complexity andoperational problems associated with the regulator often vitiate the advantage gained in usingan induction machine for isolated application.

In an externally driven three phase induction motor, if a three phase capacitor bank isconnected across it’s stator terminals, an e.m.f. is induced in the machine windings due to selfexcitation provided by the capacitor. The magnetizing requirement of the machine is suppliedby the capacitors.

For self excitation to occur, the following two conditions must be satisfied:1. The rotor should have sufficient residual magnetism.2. The three phase capacitor bank should be sufficient value.

If the rotor has sufficient residual magnetism, a small e.m.f. is developed in the stator winding.The e.m.f. if sufficient in magnitude would circulate leading current in the capacitors. The fluxproduced due to these currents would assist the residual magnetism. This would increase themachine’s flux .This process is thus cumulative and the induced voltage keeps on rising untilsaturation is reached. As saturation occurs, the flux becomes constant and final steady statevalue of the voltage is obtained. This voltage continues to exist till value of capacitance andspeed dare maintained favorably. Also, the value of the three capacitance bank should be ofsufficient magnitude in order to initiate self excitation and generate e.m.f of suitable value.

To start with steady state analysis of the SEIG with the static load is critically analyzed. Theanalytical technique used for the static load is found not directly applicable to dynamic load.Consequently, a program is developed to predict the steady state performance of the SEIG.Effect of capacitance on the performance of the SEIG is studied to enable selection of suitablecapacitor for a given operating condition. To start steady state analysis a equivalent circuitis presented which represent the steady state model of SEIG. Using that circuit a equationsis developed to obtain the steady state behavior of the SEIG. In the steady state analysisthe magnetizing property of the machine is assumed to be linear. Following the circuit theparameters are obtained.

Following the steady state investigation response of the SEIGs for the different transientconditions is studied to know it’s suitability to sudden switching of loads. The d-q axes modelwhich is widely used for the analysis of an induction motor is developed for the SEIGs system.The condition which are considered for the studied include onset of self excitation, load per-turbation, loss of excitation and short circuit. Starting of the induction motor by the SEIGs isstudied and methods for reliable starting of the motor are suggested. Based on the inferencesdrawn from the steady state and transient performance of the system, guidelines are suggestedfor the design and operation of a dedicated SEIG system for applications such as irrigationpump sets.