Harmonic Compensation with Zero Sequence Load Voltage Control in a Speed Sensorless DFIG Based Stand-Alone VSCF Generating System

Doubly Fed Induction Generator (DFIG) based stand-alone VSCF systems reported so far cannot supply nonlinear unbalanced load current containing co-phasor components. This paper presents three topologies of a standalone DFIG which can handle this type of load. The harmonic/unbalance component of the load current in each case is supplied by the stator side converter. In the first option a Ä/Õ transformer with neutral connection supplies the load. However, the harmonic current circulating in the delta winding still distorts the load phase voltage beyond the acceptable limit. As a solution the zero sequence load voltage is actively controlled through the stator side converter with the load neutral connected to the midpoint of the dc link capacitor. But this configuration also fails when the load current contains dc component as in half wave rectifiers. Finally, a configuration with an additional inverter leg connected to the load neutral is proposed in conjunction with the zero sequence stator voltage controller. Simulation and experimental results from this last configuration demonstrate its excellent load voltage regulation property while supplying various nonlinear and unbalanced loads. The control algorithm is implemented without any speed/ position sensor.