Modeling and analysis of a 5-leg inverter for an electric vehicle in-wheel motor drive

In most conventional electric vehicle (EV) applications, a central high speed electric motor is mechanically coupled to the wheels by a single speed reduction gearbox and a mechanical differential. An innovative alternative utilizes low speed, high torque, gearless, electric motors, mounted inside the rim of the wheels, to provide instantaneous torque. These wheel motors depict numerous advantages, including absence of mechanical linkages and independent and precise torque control of each wheel. Overall control of vehicle and drive cost are the main disadvantages of such a drive. A 5-leg single inverter for controlling two 3-phase PMSM motors independently provides an innovative solution to reduce the switch count, and hence, decrease the overall cost of the drive. In addition, such an arrangement also reduces the controller and sensor cost. In a 5-leg single inverter, two phases of each of the in-wheel motors are connected to each leg separately, whereas one of the phases of each motor is connected to a common leg. The goal of this paper is to study the applicability and analysis of a 5-leg single inverter, for controlling in-wheel motor based direct drive systems, for electric vehicle propulsion applications. Furthermore, the paper will present the detailed modeling and simulation analyses of the proposed in-wheel drive strategy. Finally, the proposed in-wheel traction motor drive methodology will be analyzed in terms of converter efficiency, torque ripple, converter rating, vehicle performance, and cost.