Development of an unbalanced switching scheme for a current source inverter

The development of an unbalanced switching scheme for the power conditioning system of a superconducting magnetic energy storage (SMES) device is described. The pulse-width modulation switching scheme for a current-source inverter, based on the unified switching algorithm, is presented. A device sequencing scheme and pulse merging arrangement is developed which minimises low-order harmonics. The balanced switching scheme is extended to an unbalanced scheme where the positive and negative sequence components of the output AC currents are controlled directly by their respective modulation indices and delay angles. The switching scheme is implemented on an experimental SMES device and its performance is assessed with respect to modulation linearity, harmonic generation, independent control of active and reactive power, and independent control of sequence currents