Hybrid, open-loop excitation system for a wind turbine-driven stand-alone induction generator

This study proposes a hybrid, open-loop exciter for the wind turbine-driven induction generator for low power applications. The hybrid exciter comprises one set of fixed capacitor bank and a parallel connected three-phase fixed frequency pulse width modulation (PWM) inverter fed from a battery. This hybrid exciter inherently adapts to the changes in the rotor speed or load on the generator while maintaining a near constant voltage and frequency at the load terminals. The whole system including the PWM inverter is operated in an open loop, without the need for any sensors other than the low-speed cut-in and high-speed cut-out mechanisms on the wind turbine. Results from simulations and laboratory tests show that the dynamic reactive power compensation of the generator is inherent in the proposed open-loop system. The volt ampere (VA) rating of the inverter and the battery capacity can be minimal, depending only upon the speed and load ranges of the generator and the choice of fixed capacitor var.