Charge controlled modulation of a current source inverter

The two major three-phase power converter topologies are the voltage source inverter (VSI) and the current source inverter (CSI). Of these, the VSI has attracted much more research interest, and is consequently far more dominant in industrial applications. Nevertheless, the CSI has some attractive intrinsic features which make it worthy of further consideration, including direct output load current control, easier regeneration capability back into the DC supply and implicit output short circuit protection, to name but a few. However, one of the limitations for the wider usage of a CSI is the lack of sophisticated modulation strategies which achieve a performance equal to VSI modulation schemes. In this paper, a new modulation strategy for a CSI is proposed, which controls the switched current integral (charge) to follow a circular locus in the steady-state. This charge controlled modulation achieves precise current regulation and provides a rapid transient response capability, which improves the performance of the CSI substantially compared to existing modulation techniques. Charge controlled modulation is a carrierless scheme switching at a variable frequency, and achieves spectral performance similar to hysteresis control for a VSI. Full simulation and experimental results are also shown.