A new method for voltage and frequency control of stand-alone self-excited induction generator using pulse width modulation converter with variable DC-link voltage

Three-phase self-excited induction generators play an important role in renewable energy sources such as wind and hydraulic energy. Their main disadvantage is poor voltage and frequency regulation under varying load and speed. This article introduces a new and simple method for voltage and frequency control of three-phase unregulated speed induction generators in the islanding mode. The method uses a constant voltage constant frequency pulse width modulation converter without regulating the DC capacitor voltage. The capacitor voltage is left changing with the loading conditions, and the AC side voltage is regulated by controlling the modulation index or the normalized d-axis reference voltage for space vector modulation. This eliminates the need for an auxiliary switch in the DC side, reducing the cost and high-frequency current components flowing in the DC capacitor and increasing its lifetime. Simulation results are given for comparing between the conventional and the proposed techniques when applied to a 6-kW generator. The proposed technique is tested under step changes in load and prime mover speed, and it gives the same response as the old technique but without the use of DC side switch. Experimental implementation of the proposed technique is tested on a 1-hp generator, and both simulation and experimental results are given to validate the proposed technique.