Design Optimization of the Snubber circuit for Three- level NPC Converter pole for Hard switching Application
Sanket Parashar, Nithin Kolli, Raj Kumar Kokkonda, Subhashish Bhattacharya, Ashish Kumar
Abstract
This paper describes the design and selection criteria of RC snubber circuit for the Three level Neutral Point Clamped (NPC) converter pole with series connected SiC MOSFETs and clamping diodes. The converter pole is used as a building block for implementing a three phase converter for hard switching applications. Passive RC snubbers have been used for voltage balancing among series connected MOSFETs and clamping diodes because they ensure reliable dynamic voltage sharing. Traditional snubber designs involve limiting resistor (R) of high power rating and large footprint. Moreover, the existing methodology is not optimized for three level converter poles involving MOSFETs and clamping diodes during switching process. This paper proposes a novel design methodology of RC snubbers for three level converter poles by modelling the switching dynamics. RC snubbers have been optimized for lower switching losses, considering voltage overshoot due to parasitic inductance and gate pulse mismatch. The proposed design reduces the switching loss in converter pole compared to conventional designs, thereby reducing power rating and footprint of snubber resistor. The design methodology has been validated with simulation results. Experiments have been conducted on three level converter pole at 2.5kV DC bus for analyzing the voltage balancing of MOSFETs and clamping diodes.