Input voltage pumping control for a multi-level switching amplifier

The paper describes energy pumping among dc busses in a multilevel inverter with isolated power supplies driving a passive load, and an algorithm to eliminate it. In the current switching amplifier application, the output current waveforms are required to be of almost arbitrary shape. Modulation techniques are known to be well suited for conventional inverter operation, however when driving some output current waveforms, they can produce dc bus over voltages due to an undesired energy transfer between busses. The specific cases that cause the pumping are described and an algorithm is proposed that eliminates the effect without disturbing the correct operation of the inverter. The algorithms have been tested in a prototype to verify the expected performance.