The Occurrence of DC Magnetic-Flux Deviation, and its Suppression, in a Doubly-Fed Flywheel Generator System.

This paper points out that dc magnetic-flux deviation may occur in a doubly-fed flywheel genarator with primary-current feedback control. The flux deviation discussed in this paper, which is different from the common flux deviation caused by a dc output voltage of a PWM converter, is induced by an ac output voltage of the PWM inverter operated at the angular frequency of the rotor. It may be impossible to detect such a dc flux from the primary current and/or voltage, because the dc flux induces no voltage on the primary windings. This paper reveals that the primary-current control induces a dc flux in the primary windingsand prevents the dc flux from decaying. A new control method for suppressing the dc flux deviation, which is based on calculating the exciting current from the primary and secondary currents, is proposed. Experimental results verify the viability of the control method proposed in this paper.