Optimal Control Of Six Phase Permanent Magnet Synchronous Motor In Electric Vehicle

As the world’s largest new energy vehicle market,China has seen rapid development in both electric vehicles and gasoline-electric hybrid vehicles in recent years.Compared with traditional vehicles,new energy vehicles have better driving experience and dynamic performance,and emit less carbon dioxide and toxic gases during driving.In particular,pure electric vehicles have achieved zero emissions during driving,so the country is also vigorously promoting the development of new energy vehicles.In the research and development process of electric vehicles,the three-electric system cannot be bypassed,that is,the battery,motor and electronic control system of the electric vehicle.Permanent magnet synchronous motors are widely used in electric vehicles because of their large torque output capability,high energy density and work efficiency.Compared with the traditional three-phase permanent magnet motor,the multi-phase motor has the advantages of high torque output capacity,small torque ripple,high efficiency and high reliability.This paper mainly studies the optimization of control strategy of six phase permanent magnet synchronous motor for electric vehicle.Establishing the mathematical model of the permanent magnet synchronous motor is a necessary condition for designing a robust and fast response control system.Therefore,this paper first studies the mathematical model of the six-phase permanent magnet synchronous motor,and establishes a solution based on double d-q axes and space vector in Simulink.Two mathematical models of the six-phase permanent magnet synchronous motor under the coupled VSD theory.The modelling method of the double d-q axis is to regard the six-phase permanent magnet synchronous motor as the parallel connection of two three-phase permanent magnet synchronous motors,but the coupling characteristics between the two motors must be considered.In the VSD model,the six-phase PMSM is regarded as a whole,the current harmonics of the six-phase permanent magnet synchronous motor are analysed,and different current harmonics are mapped into mutually orthogonal subspaces to realize the complete decoupling of the motor control.Based on the space vector decoupling model,the control strategy of the six-phase permanent magnet synchronous motor under different working conditions is mainly studied.In the low speed region of the motor,according to the motor control loop in Simulink,the differences and advantages and disadvantages of the two control strategies4)_{（9）=0 and maximum torque to current ratio（MTPA）are compared.Although the control method of4（9）=0is simple and easy to implement,the heat loss during the operation of the motor is large,and the reluctance torque cannot be fully utilized,and the motor efficiency is low.It is only suitable for surface-mounted hidden pole motors.Compared with the control strategy of4(}（9）=0,the motor under MTPA control can make full use of the reluctance torque part and has higher torque output characteristics.Moreover,the motor under MTPA control requires less current to achieve the same torque,and the heat loss is relatively small.These characteristics make MTPA control the preferred method for controlling salient pole motors.Under the condition of high motor speed,the motor needs to perform field weakening control.This paper innovatively proposes to solve the problem of d-q axis current distribution by Newton’s iterative method.In the high-speed region,since the permanent magnet flux of the permanent magnet synchronous motor cannot be changed,the field weakening control of the motor can only be performed by increasing the current i_d and decreasing the current i_d in the negative direction of the permanent magnet.This paper firstly deduces the mathematical formula of the complete current distribution under all operating conditions,and proposes to use the Newton iteration method to obtain the constant torque field weakening control based on the maximum current and voltage limits.The field weakening control methods are compared,and the correctness of the Newton iteration method in motor control is verified.The Newton iteration method can use the formula to give the current distribution strategy under various working conditions very accurately,and the motor response time is shorter.The Newton iteration method plays an important auxiliary role in the design,testing and calibration of motor control system.At the same time,it is of great significance for the promotion and application of six phase permanent magnet synchronous motor in the field of electric vehicles.