Dynamic DC-link Voltage Adjustment for Electric Vehicles Considering the Cross Saturation Effects

Abstract

The demands of remarkable reliability and high power density of traction systems are becoming more and more rigorous. The conflicting requirements imposed on the control strategy are higher accuracy and higher efficiency over the whole speed range. However, parameter variations caused by the cross coupling and magnetic saturation effect (omitted from the cross saturation effects in the following) are usually neglected in conventional control strategies, which could reduce the control precision. In order to fully consider the influence of parameter changes on the motor control and derive an approach that could realize the maximum efficiency during the whole speed range, this paper proposes a dynamic DC-link voltage adjustment strategy considering the cross coupling and magnetic saturation effects. The strategy can be categorized into three parts. Firstly, the torque request is transformed to the optimal current reference signal. Secondly, the differences between the setpoint and the real-time feedback signals of torque and voltage can be applied in the linearized function in the did,q coordinate. The solution guides the current vector into the optimal direction under the current and voltage limits to ensure the safety and reliability of the motor. Finally, last, the bus voltage can be modified according to the asked terminal voltage. A 10 kW prototype which instrumented a bidirectional DC-DC converter to regulating the bus voltage has been studied. The simulation and experiment results verify that the proposed control strategy can reduce the inverter losses in low speed region by offering the low bus voltage and track the actual maximum torque control trace more accurately, meanwhile, the flux weakening region can be delayed in high speed region by applying a high bus voltage. It helps the motor realize the high utilization rate of the DC-link voltage and guarantees the system reliability and robustness.