Torque distribution of a four in-wheel motors electric vehicle based on a PMSM system model

Abstract

This study investigates a method for determining the torque distribution between front and rear in-wheel motors in an electric vehicle to improve energy efficiency. The method is based on an analytical model of the permanent magnet synchronous motor (PMSM) losses, which consist of the losses from electric motors and inverters. The loss model is used to analyze the optimal torque distribution ratio for minimum system losses. The analysis is conducted for two cases: the first is for identical motor parameter values of the front and rear wheels; the second is for different motor parameter values. For the first case, the results show that the even torque distribution between the front and rear wheels results in minimum system losses if the motor loss is a convex function of electromagnetic torque. When the motor parameters for the front and rear wheels are different, the optimal torque distribution coefficient depends on the motor parameters. To validate the analysis results, simulations of the four-motor drive system were conducted. Furthermore, the idle loss is added to the system efficiency data and a numerical optimization method is used to resolve the optimal distribution ratio. It is shown that the optimal solutions are consistent with the analytical results. Finally, the proposed method is validated through bench tests and vehicle dynamometer tests.