A High Current High Power Density Motor Drive for a 48-Volt Belt-Driven Starter Generator (BSG) System

A 48 V Belt-Driven Starter Generator (BSG) System is featured with high output current, high starting torque, and highly efficient thermal management. This paper firstly elaborates hardware design considerations of a high power density three-phase BSG inverter to address the challenges of even current distribution among paralleled MOSFETs, small drain-source voltage spike and good thermal dissipation. In order to satisfy the high-current requirement, a careful selection of MOSFET device with high-current rating and low on-resistance has been presented. In order to suppress circulating current among paralleled devices, individual gate resistors have been placed in the gate loop of each MOSFET. In order to provide good thermal dissipation, an Insulated Metal Substrate (IMS) board and single-layer layout technique have been implemented. Multiple low-profile electrolytic capacitors are used to increase the power density of the prototype. Moreover, the use of automotive gate driver IC TLE9180 and microcontroller TC1782 makes the prototype more readily accepted by industry. An improved Interior Permanent Magnet (IPM) motor control strategy and a pump-back system based on a virtual machine concept have been implemented to facilitate the validation of the prototype under rated condition without using a real motor. The control algorithm automatically adjusts the onset of field-weakening by using an additional inverter voltage loop and takes into account the nonlinearity of the stator flux linkage by using curve fitting technique, which makes the motor drive adaptive to machine parameter changes as well as DC bus voltage fluctuation. A three-phase BSG inverter prototype with a peak power of 12 kW has been built and tested. The prototype power density has reached 20.3 kW/L. Both PLECS simulations and hardware experiments show a continuous and stable operation with up to 200 A phase current and up to 600 Hz output frequency.