Fault-Tolerant Control of Regenerative Braking System on In-Wheel Motors Driven Electric Vehicles

A novel fault tolerant brake strategy for In-wheel motor driven electric vehicles based on integral sliding mode control and optimal online allocation is proposed in this paper. The braking force distribution and redistribution, which is achieved in online control allocation segment, aim at maximizing energy efficiency of the vehicle and isolating faulty actuators simultaneously. The In-wheel motor can generate both driving torque and braking torque according to different vehicle dynamic demands. In braking procedure, In-wheel motors generate electric braking torque to achieve energy regeneration. The strategy is designed to make sure that the stability of vehicle can be guaranteed which means vehicle can follow desired trajectory even if one of the driven motor has functional failure. Considering longitudinal velocity and yaw rate control, Electric vehicle with four independent In-wheel driven motor is a typical over-actuated control system whose control inputs outnumbers the state variables. Therefore, typical nonlinear controller design methods based on Lyapunov theory cannot be applied directly. In this paper, the problem is settled down by transferring the input matrix whose dimension is larger than the number of state variables into a square matrix whose dimension is the same as the number of states variables with virtual inputs. By doing this, typical nonlinear controller design method can be carried out. The occurrence of functional failure in In-wheel motor can be regarded as disturbance to the control system. Integral sliding mode control method (ISM) is designed to generate the desired virtual control inputs for its outstanding performances in dealing with disturbances and also its initial stability. Optimal online inputs allocation is proposed to avoid large-scale reconfiguration of the upper controller when failure occurs by which instability of the upper ISM controller can be also avoided. The optimal allocation is designed to guarantee the stability. Straight line braking and steering step input braking test scenarios, with an initial speed of 70 km/h, are conducted to verified the proposed control strategy and functional failure of In-wheel motor is injected during the test procedure. The results showed that the injected actuator faults are mitigated, the vehicle stability are ensured.