Adaptive Sliding Mode Variable Structure Control For Electric Power Steering System

Electric power steering system (EPS) is a system with high efficiency, energy-saving, environmental protection, convenient adjustment and compact structure, which is the development trend of power steering technology. And it will have a broad market. The control theory, the hardware device and the software system of EPS were particularly studied in this paper.At first, the dynamic model and the simulation model of the column electric power steering system were established. After the steering portability, the handing stability and the road feel of an automobile were considered, an assist map of EPS was designed in this paper.Second, the control strategy of EPS was divided into two layers that were the top layer strategy and the bottom layer strategy. Two kinds of work mode were designed, which were the assist mode and the damp mode. To overcome disadvantages of PID controller for the bottom layer strategy, an adaptive sliding mode variable structure controller was developed to follow the target current. Simulation showed that it can be used to robust control for EPS and the adaptive design for exponential approach law can weaken the chattering.Third, the electric control unit of EPS was developed based on TI DSP TMS320F2812, which consists of the motor driving circuit, the signal processing circuit and the self-diagnosis circuit. And control software was developed with assist control, damper control and self-diagnosis in CCS. A low pass FIR filter was designed with the assemble language. The experimental result showed that the FIR filter accuracy is high, and its stability is good.At last, the steering portability experiment was done on the test bench of EPS, and the results showed the electric power steering system is good at the assistance; the adaptive sliding mode controller is effective, the hardware and soft system work well.