Vector control of a diesel-driven doubly fed induction machine for a stand-alone variable speed energy system

This paper describes a control structure for a vector controlled doubly-fed induction generator, used for a variable speed energy conversion system, driven by a diesel engine. The paper focuses on an energy system, feeding an isolated load, with two back-to-back PWM converters connected between the stator and the rotor for sub and super synchronous speed operation. A d-q reference frame aligned with the stator flux is used for rotor current control, with correct orientation assured by controlling the q-axis rotor current. Indirect control of the stator voltage is achieved by regulating the stator flux via the d-axis rotor current. Minimum fuel consumption of the diesel, for any given load, is obtained by regulating the speed to follow an optimum operating curve. Given the nonlinear characteristic of the diesel engine, a fuzzy logic structure is used to adapt the parameters of the speed controller. Results are presented for step load impacts and for the tracking of the optimum speed.