Hybrid inverter concept for extreme bandwidth high-power AC source

A hybrid inverter concept for switch-mode power amplifiers as used, e.g. in power-hardware-in-the-loop testing is proposed. A main converter operating from the supplying DC voltage generates a multilevel output voltage by means of parallel-interleaved operation of several bridge legs and combination of the bridge leg output voltages with coupled inductors into a multilevel waveform. A second, series-connected inverter features a floating DC bus with only a fraction of the main converter's DC voltage, which enables a significantly higher switching frequency. The series inverter compensates the deviation of the main inverter's multilevel output voltage from the reference voltage, whereby pulse-width modulation with sawtooth carriers is employed, and hence defines the effective switching frequency of the hybrid inverter's overall output voltage. This allows for a higher output filter cutoff frequency and ultimately features a significant increase of the full-range system bandwidth, which improves by more than an order of magnitude for the considered 100 kVA example system compared with a conventional approach. Finally, closed-loop circuit simulations verify the high performance of the proposed system.