Novel approach of integrated motor-inverter power module for 48v mild hybrid starter and generator (Mhsg)

Abstract

This paper presents a new design of a six-leg inverter power module, which is specialized for the 48V starter generator used in 48V mild hybrid vehicles. The inverter module, herein named mild hybrid starter generator (MHSG), is integrated with its motor to decrease system size and volume. This motor-inverter integration fosters supplementary challenges (e.g., limited cooling capability, required reduction in power loss, etc.), in addition to the challenges already demanded in 48V mild hybrid systems (e.g., increased power level, better switching performance, compatibility with 12V systems, etc.). Our MHSG power module addresses all of these challenges. MOSFET dies are solder-bonded on a direct bonded copper (DBC) substrate (instead of PCBs), and three DBCs (each DBC providing two legs) are assembled on a custom housing mounted on a forced air-cooler. Shunt resistors and SMD resistors are also soldered in DBCs. For better stability and balance, ribbon bonding is used instead of wire bonding, the dies and ribbons are re-positioned, and DBC patterns are modified. Approaches minimize the stray inductance, parasitic resistance, unbalanced/concentrated current density, and maximum MOSFET temperature of the 48V MHSG inverter module. These achievements are validated by finite element method (FEM) simulations as well as experimental results revealing electrical/thermal characteristics of the designed inverter module.