Voltage Balancing of Series Connected Clamping Diodes in Medium Voltage NPC Converter enabled by Gen-3 10 kV SiC MOSFETs for Asynchronous Micro-Grid Power Conditioning System (AMPCS)

Abstract

Asynchronous micro-grid power conditioning system (AMPCS) had been proposed for integrating two medium voltage nonsynchronous grids. Neutral point clamped (NPC) converter based active front-end converters (AFECs) and three-phase dual active bridge (DAB) are used as basic building blocks for the AMPCS. Switching and voltage clamping operations of these NPCs are achieved using series connected 10 kV SiC MOSFETs and 10 kV SiC JBS diodes, respectively. In the earlier reported work on AMPCS, voltage balancing across the series connected MOSFETs is reported. It is observed that in a few cases voltage unbalance also appears across the series connected clamping diodes due to dissimilar nature of their characteristics. This voltage imbalance across the clamping diodes can affect the operation of AMPCS. In this digest, a balancing scheme for series connected clamping diodes of the AMPCS system using passive snubber circuit is presented. A systematic set of experiments have been reported which can be conducted to ensure the voltage balancing across the series connected clamping diodes before applying them in actual medium voltage AMPCS. The balancing scheme is validated using the experimental results.