Self-excited Induction Generator With A Carrying Capacity Study

In the exploitation of renewable energy and applications of military equipments such as aeroplanes and warships, self-excited induction generators have obvious advantages when used as generating equipments in the isolated power systems. Thus the study on the self-excited induction generator has important effects on taking full use of the renewable energy and enhancing fighting strength of the military equipments. In spite of the inherent advantages, the self-excited induction generator has poor capacity for carrying loads, on which corresponding studies are carried out and proper schemes for reactive power compensation are proposed in the paper.The steady-state model is derived from the steady-state equivalent circuit of the self-excited induction generator under the base frequency. The external characteristics and output power under various loading conditions are studied, and the critical impedances are determined for loads with different power factors. The state equations are deduced based on the transient equivalent circuit of the self-excited induction generator under stationary reference frame. The influences of load fluctuation on the transient voltage are analyzed, and dominant eigenvalues of the state matrix are used to determine the critical condition for the induction generator to maintain self excitation.Short-shunt connection of capacitors and long-shunt connection of capacitors are proposed to compensate reactive power for the self-excited induction generator, and the short-shunt connection of capacitors is found to be the perfect scheme for reactive power compensation after comparative analysis. The absolute value of the voltage regulation is defined to identify the voltage stability of the induction generator, and the optimal short-shunt capacitance is determined for loads with given power factors, by using one-dimensional optimization method twice. The analysis results indicate that required voltage stability is obtained by reactive power compensation of the optimal short-shunt capacitor.According to the state equations of the short-shunt connected induction generator under inductive loading condition, the magnetizing inductance is used to estimate the feasibility of the generator for maintaining self-excited when given loads are switched in. The critical short-shunt capacitance for the induction generator to maintain self-excited is determined. Meanwhile, the transient model is utilized to analyze the effects of various short-shunt capacitors on the terminal voltage and output voltage of the induction generator in the transient process.The theoretical calculations are validated by corresponding experiments in the paper. The good agreements between the calculated results and experimental results confirm the correctness of the analytical method and the high accuracy of the mathematic model.