Research For Current Decoupling Of Induction Motor Used In EPS System

Compared to mechanical hydraulic power steering systems, the electric power steeringsystem (EPS) has effective vehicle handling performance, high efficiency, small space, easyinstallation, less environmental pollution and some other advantages. The motor is the keycomponent in the system, and its performance directly affects the driver’s driving experience.Because of its simple structure and high reliability, AC induction motor has got more andmore applications in the EPS system.In the condition of rotor field oriented vector control, the relationship between torqueand T-axis is expected to be linear, which requires high-precision motor control in fluxobservation position. Under the current-speed rotor flux observer, the rotor flux positiondetection accuracy is affected by the rotor resistance and rotor inductance precision, and theywill vary with the motor operating conditions.EPS assisted motor working environment is poor, and the working conditions havegreat impact on the motor parameter. By analyzing the experimental data, it is known thatthe motor rotor inductor changes little with the current, speed and temperature. Therefore therotor resistance is focused in this paper.Using the difference between the value of measured and calculated Reactive power asthe feedback, rotor resistance identification system is designed based on MRAS theory. Thestability of this system is proved by the Popov stability theory. Then the parametersensitivity analysis and feasibility of the method are done by simulation. However, when thereactive power deviation is zero, the rotor resistance cannot converge to the true value whenthe experiment is organized. By large number of experiments and analysis, we know that thepresence of un-modeled dynamics in the motor rotor and stator voltage equation leads to theerror between the estimated value of the reactive power and the true values. Therefore the look-up table of reactive power compensation is designed. The reactive power deviationchanges with the motor speed, motor current and operating temperature. The reactive powercompensation table is made at different temperatures. When using online identification, thecompensation value is added to the reactive power estimated value based on work conditions.In fact, the working temperature of the motor cannot be obtained. Therefore the reactivepower compensation with temperature cannot be achieved. Finally, based on the reactivepower error compensation, this paper proposes a rotor resistance online identificationmethod which combines the MRAS identification method and the off-line look-up table. Theidentification start from ambient temperature, the identification temperature increases acertain value when the next identification is executed. The error between the result of MARSsystem and look-up table is obtained in each temperature. The temperature value when theerror is minimum is the current temperature, and the present rotor resistance is obtained.Experiments show that this method for induction motor current decoupling has someimprovement.