| With the rapid development of motor design technology,processing and manufacturing technology,power electronics technology and the permanent magnet material technology,the high-speed permanent magnet synchronous motors have been widely used in aerospace,mold processing,new energy vehicles and other fields.Limited by the switching frequency of ordinary IGBT(no more than 15k Hz under normal operating conditions),the ratio of the switching frequency to the motor frequency(carrier ratio)is quite low when the high-speed permanent magnet synchronous motor is running at the rated speed,which leads to the delay of sampling and PWM update of a digital processor largely,causing the output voltage of the inverter under closed-loop vector control to lag seriously,the rotor position estimation is inaccurate,and the current loop oscillates,ultimately makes the high-speed permanent magnet synchronous motor out of control.It is of great significance to study the control strategies of the high-speed permanent magnet synchronous motors.Herein,two control strategies for high-speed PMSM operating on the low carrier are proposed in this paper.The first control strategy proposed in this paper is to optimize the V/F control method of high-speed permanent magnet synchronous motor with damping ring.The traditional V/F method is a scalar control method,which only needs to control the size and frequency of the output voltage,so it can effectively avoid a series of effects caused by low carrier ratio,including position estimation errors,inverter voltage output lag,etc.,and it’s very suitable for high-speed pumps,fans and other occasions that require low accuracy.Due to the low damping of the high-speed permanent magnet synchronous motor,the loading capacity is poor when using traditional V/F control,and it is easy to get out of step.Although some articles and methods have been optimized,most of them need to use the high-pass filters,whose parameter calculation is complicated and the effect is poor,it’s not applicable for engineering practice.This paper analyzes the transfer function of the small-signal model of the high-speed permanent magnet motor in detail,and proves that the compensation of the motor speed fluctuation to the V/F given speed can increase the system damping effectively.The specific implementation is to use the motor model under V/F control as a reference,and estimate the speed fluctuations,then compensate to the given speed of V/F method.After testing,this method has extremely strong stability and load capacity,and it is less affected by the motor parameters.In addition,this article also predicts i_d to establish the voltage compensation link to realize the automatic adjustment of the voltage curve so that the surface-mounted permanent magnet synchronous motor maintains i_d=0 control,avoiding the defect that the size of the current cannot be controlled under the V/F method.In order to meet the demand of vector control of the high-speed permanent magnet synchronous motors,a dynamic compensation strategy is proposed for voltage lagging one cycle of high-speed permanent magnet synchronous motors in this paper.When the permanent magnet synchronous motor is running at high speed and low carrier ratio,the interval of PWM lagging by one beat is very long,resulting in a large phase lag in the output voltage of the inverter.In severe cases,the current loop oscillates and the high speed permanent magnet synchronous motor loses control.In order to better reduce the impact of the output voltage one-shot lagging on high-speed permanent magnet synchronous motors,this paper analyzes the mechanism of the voltage one-shot lag,and deduces the relationship between the specific error value of the voltage phase lag and the carrier ratio in detail,and uses this fixed value to compensate the phase of the output voltage.In addition,in order to obtain better dynamic performance,on the basis of fixed compensation,this article uses the difference between the d-axis voltage of the lag state and the ideal state to form a PI regulator to dynamically compensate the phase of the output voltage.The combined use of the two compensation methods can effectively and quickly reduce the phase lag of the output voltage of the inverter to ensure the closed-loop vector control system of the high-speed permanent magnet synchronous motor stably operate. |
