Research On EHPS And Phase Current Reconstruction Using A DC-link Sensor

The electro-hydraulic power steering system (EHPS) is a new generation of motor vehicle power steering system based on the traditional hydraulic power steering system as prototype. With the development of power electronics, permanent magnet technology and microelectronic technology, the permanent magnet brushless DC motor is becoming important part of motor products with its advantages of size, reliability, control performance, power density and operating efficiency. Electric hydraulic power system does not use the engine as a power source, but use a single permanent magnet brushless DC motor to provide the power for the system. The electronic control unit of EHPS controls the operation of the motor to provide optimal booster at different operating conditions. The EHPS system occupies an important position in the field of power steering system with the advantages of low energy consumption, high efficiency, good boost torque and excellent operating feel.The mathematical model and general characteristics formula of the permanent magnet brushless DC motor is analyzed. The structure, the basic operating principles, commutation and freewheeling process of the four-phase half-bridge permanent magnet brushless DC motor are discussed on the basis of structure and operating principle of three-phase brushless DC motors. The affection of the operating state of the motor caused by modified advanced angle and condition angle is also adopted. The design of controller’s hardware of EHPS system, including minimum MPC5602P system, the current sampling circuit and ignition signal detection circuit, is analyzed in order to build hardware platform. Based on that, the software of controller, including the main structure, the high-resolution rotor angle calculation program, speed calculation and speed PI closed-loop control program and communication program through CAN, is discussed to combine the hardware and software to complete the design of system control platform.This article verifies the motor controller performance of EHPS system through tests. The performance of BLDC of EHPS system is test on different condition of advanced angle condition angle and speed calculation method, to verify the effect of the optimization algorithm. The results show that optimization of program improves the control performance of the motor. At the end of this article, the three-phase current reconstruction for AC motor drives using a DC-link single current sensor is investigated. After the analysis of unobserved region of phase current of this method based on SVPWM and BCPWM, a method was presented to solve the problem of unobserved region by using asymmetric PWM output. The method of phase current reconstruction using DC bus current on whole region was tested based on PMSM. The results indicate that this method has feasibility on both SVPWM and BCPWM.