Design of a Bias Power Supply for GaN Switch Based Multilevel Traction Inverter

MSc defense of Naman Agarwal

There has been significant research into the use of multilevel inverter topologies using Wide Band Gap (WBG) semiconductors in Electric Vehicle (EV) powertrains. This combination promises an increased power density and efficiency which should boost the viability and adoption of EVs. However, a reliable power supply is required for the inverter switches, which counters some of the challenges presented by these topologies. These challenges include the issue of high side power supply and Electromagnetic Interference (EMI) mitigation.

To begin with, certain requirements for a high side power supply are drawn up and various architectures are compared based on their merits and demerits. Based on this comparison, the LLC resonant converter is chosen as the most suitable topology due to its high efficiency, power density and potential for EMI mitigation. The operating principles of this topology are examined and used to optimally design a one output LLC converter. These principles are then further extrapolated to the design of a LLC converter with six isolated outputs which are required for a multilevel converter. Both these designs are then prototyped and tested to verify their performance. It is found that the multi output converter performs at par or better than the commercially available solutions, while fulfilling the design requirements.