A Dual Observer for Parameter-free Encoderless Control of Doubly-fed Reluctance Generators

A novel, cascaded model reference adaptive system (MRAS) observer design for speed and reactive power (Q) control of the emerging brushless doubly fed reluctance generator (BDFRG) without a shaft position sensor and no machine parameter knowledge is proposed. The main advantages of the underlying estimation technique over the existing ones reported in the open literature are therefore the intrinsic versatility, robustness and accuracy offering entirely decoupled torque (power) and Q responses. The reference model of the rotor angular velocity and position MRAS observer is purely based on the current measurements of the converter-fed (secondary) winding, and its adaptive counterpart on the measured grid voltages and currents at line frequency. The latter requires the inductance ratio for calculations, the on-line estimates of which being generated by the supplementary MRAS observer working in parallel. Doing so, a complete machine parameter independence and stability of the scheme have been achieved, and its viability fully experimentally validated under variable loading conditions of the small-scale BDFRG wind turbine emulated in a laboratory environment.