A Novel EV Inverter Drive System with Integrated Single Stage Buck-Boost and Sinusoidal Output Voltage

A battery electric vehicle (BEV) employs a traction inverter to control a traction motor. One popular configuration is to make a HV battery directly connected to the input of the motor inverter. As a result, the maximum motor voltage is limited by the state of charge (SOC) of the traction battery. When the battery voltage is low the maximum motor speed and power are limited. This voltage limitation can be solved by using a traditional boost converter-based inverter. However, this approach has several disadvantages. The motor winding terminals see a PWM voltage, which results in high frequency harmonics that lead to EMI, NVH and potential additional insulation stress. Also, there are PWM-induced common mode voltages that are known to produce bearing failures as well as EMI/EMC problems that are extremely difficult to eliminate. Finally, the topology is significantly more expensive due to the high number of active switching devices needed. To solve some of the limitations and issues described above, a buck-boost inverter topology-based motor drive system is proposed. The new system employs a single-stage voltage buck/boost integrated inverter. The main advantage of this topology is that it produces a sinusoidal output voltage instead of the traditional PWM output voltage, and a constant common mode voltage instead of a pulse voltage. These features provide benefits to the electric drive with a wide range of motor voltage regardless of battery SOC without additional active switches, no high-frequency harmonics to motor, less NVH and EMI/EMC concerns, potential lower motor losses, reduction of voltage stress in stator windings, and drastically reducing potential bearing current-related failures. The paper addresses technical details of the proposed electric drive system in terms of its traction inverter circuit topology, operating principle, control method, and verification to demo the above advantages.