Electronic differential with sliding mode controller for a direct wheel drive electric vehicle

Traction drives used in electric vehicles can be divided into two categories, (i) single drive systems, and (ii) multi-drive systems. With multi-drive systems the motor controllers must additionally be configured to provide an electronic differential effect i.e. they must also perform a similar function as their mechanical differential counterpart. Thus the electronic differential must take account of the speed difference between the two wheels when cornering. This paper presents a design for an electronic differential utilising a sliding mode controller employing a 4-switch 3-phase inverter. This type of inverter is particularly suitable for this application as the supply batteries can be easily split into two separate battery strings. The system is evaluated on a test vehicle in which the rear wheels are directly driven by permanent magnet brushless motors. Results indicate that this arrangement can be successfully implemented into an electric vehicle drive train.