Study and Implementation of a Single-Phase Diode- Clamped Five-Level Inverter with Auto Equalization

In this paper, a stand-alone single-phase diode-clamped five-level inverter is studied and implemented. This prototype circuit makes the input voltage shared by series-connected switching devices. Besides, this topology needs clamped diodes to clamp the voltage on the MOSFETs. On the other hand, the control signals of the power devices are generated by sinusoidal pulse-width-modulation (SPWM). The desired output voltage can be modulated by the amplitude modulation index. The circuit operation naturally causes the input capacitor voltages unbalance. Accordingly, a switched-capacitor charge equalization technique is implemented to solve the imbalance problem.A prototype circuit with the switched-capacitor equalizer has been built and tested successfully in this paper. The circuit is with rated power of 630 W, 800 V input voltage, and 230 V output voltage. A digital-signal processor chip is used to realize the controller of this inverter. The measured efficiency is always higher than 90% within the overall range of load conditions.