A high voltage multi level arbitrary waveform generator for insulation testing

Due to the extensive applications of power electronic devices in power grids, many insulation components will be stressed by high voltage PWM, multilevel or even more complex waveforms. In this paper, a high voltage generator able to produce various waveforms is developed. The generator is based on cascade connected multilevel modular converter (MMC) topology, including 20 half bridge MMC cells with the capability of 21 output voltage levels. Half of the series-connected MMC cells are charged positively, while the other half are charged negatively. Each positive and negative half bridge MMC cell is connected alternately to optimize the insulation design. The power supply of the driving circuit for each MMC cell is provided by an individual fly-back converter fed by the cell capacitor to realize a compact design. On the basis of simulations, a multilevel arbitrary waveform generator prototype was constructed, with the maximum peak-to-peak voltage of ~ 28 kV. A capacitor switching strategy is utilized to solve the voltage-imbalance problem resulted from the difference of the element parameters and other reasons. Finally, it was tested on a typical insulation with a simulated defect.