Study of Multisampled Multilevel Inverters to Improve Control Performance

A classic digitally controlled power converter usually uses the same sampling and switching frequency. The technique is known as uniform sampling. As the performance of digital signal processors is increasing dramatically and the price is decreasing, applying high sampling frequency becomes increasingly feasible. The multisampling technique is developed to reduce switching delay. However, the control gains are still limited by the switching frequency. To demonstrate an alternative way of improving the control performance without increasing the switching frequency, this paper discusses multisampled multilevel inverters. The example of a voltage controlled multilevel inverter with cascaded control loops is provided. The filter current ripple frequency is increased by the phase-shifted pulsewidth modulation. The multisampling is synchronized to the peaks of the phase-shifted carriers. The small-signal z-domain model is derived to analyze the multisampled multilevel inverter. Compared to the bipolar switched inverter, the multisampled multilevel inverter is characterized by the capability of achieving higher feedback control gains, which improves the control performance. An experimental prototype based on a 10-kHz switching frequency, 80-kHz sampling frequency five-level single-phase H-bridge inverter is tested to demonstrate the validity of the analysis.