The Precise Torque Control Of Permanent Magnet Synchronous Motor Drive System For Electrical Vehicle

With the background of the development of automobile industry and the appeal " to reduce emission and to improve air quality", the world-wide automobile manufactures have invested in the development of new energy vehicles. With the superior performance, the interior permanent magnet synchronous motor (IPMSM) has become the main drive motor of electric vehicle drive system, and study on the high performance control method of PMSM is one of the hot research direction. The IPMSM drive system for new energy vehicles requires not only the wide speed range, but also the precise torque output. However, the motor is faced with unavoidable uncertainties and parameter variations because of the complicated operating conditions, which makes the traditional IPMSM drive system based on proportional plus integral (PI) controller difficult to achieve the precise torque control. Under this premise, the paper has focused on the research of the precise torque control strategy of PMSM drive system.Firstly, the paper analyzes and establishes the model of IPMSM considering the influence of magnetic saturation and cross coupling effect on the motor parameters and the model of inverter considering the nonlinear characteristics. Then, the simulation model of the whole IPMSM drive system is established and verified by simulation results. All of the above lay the foundation for the research on the core control strategies of IPMSM drive system.In the structure of IPMSM vector control based on rotor field oriented, to control the torque output of IPMSM is essentially to control the stator current vector. The paper analyzes the differences in finding the optimal current command between the maximum torque per ampere (MTPA) control and the flux-weakening control methods, and the reason why the traditional field weakening control strategy based on the gradient descent method fails to track the reference torque. Then a new current command generation strategy and the whole precise torque control method of IPMSM drive system based on the double gradient descent method are presented to achieve the precise torque output no matter in the MTPA or in the flux-weakening operating condition.In the traditional vector control structure, the current loop employs synchronous frame PI current controllers with an active state-decoupling scheme, but this scheme requires the full knowledge of machine parameters. However, the unavoidable uncertainties and parameter variations of IPMSM makes the active state-decoupling fail and degrades the dynamic performance of current loop. To this end, the IPMSM model considering parameter uncertainty is first set up, which is equal to the combination of a reference model and an error model. Then, a model-free adaptive control (MFAC) method is proposed to estimate the error model caused by parameter uncertainty and stabilize the IPMSM system with parameter uncertainly to the system based on reference model. Moreover, the output torque of IPMSM is real-time estimated using the outputs of MFA controller to improve the dynamic performance of current inner loop and achieve the precise torque control of IPMSM system.