Research On Sensorless Field Weakening Control And Dual-mode Overmodulation Strategy For High Speed Pmsm

High-speed permanent magnet synchronous motors have the advantages of high efficiency,high power density and high control accuracy,which have been widely used in household appliances,rail transit,textiles,and aerospace fields.High-precision control systems need to accurately obtain motor rotor position information to decouple current and voltage information.In order to deal with environmental factors such as temperature and humidity that cause mechanical encoder aging and decreased observation accuracy,position sensorless control systems are gradually being favored by enterprises due to their lower cost and stronger robustness.At the same time,in order to broaden the motor speed,improve the utilization of the bus voltage,field weakening control strategies and overmodulation strategies have gradually become the research focus of scholars at home and abroad.This paper focuses on the sensorless field weakening control and dual-mode overmodulation strategy of high-speed permanent magnet motors.First,the research is based on the rotor position observation method of the rotating shaft system.The traditional rotor position observation method estimates the back EMF based on the voltage and current information of the stationary shaft system,and extracts the position error information by decoupling the back EMF through a phase-locked loop.However,due to non-ideal factors such as calculation delay in the control system,the position information observed by this method has a large delay,which is not conducive to the position observation of high-speed motors.Therefore,the method studied in this paper is based on the rotor position observation method of the rotating shaft system and the observer bandwidth and damping ratio are designed according to the complex vector model.This method avoids the decoupling of the phase-locked loop and reduces the delay of the observer,which has a faster response and higher observation accuracy.The observation position error is within 12°.In order to broaden the motor speed and make full use of the bus voltage,a field weakening control strategy based on voltage phase angle regulation is studied.The performance of the traditional dual current regulation control system is inevitably affected by the cross-coupling voltage,and there are current ripples that are integer multiples of the operating frequency in the direct-axis current.Therefore,this paper studies a magnetic weakening method based on voltage phase angle regulation,which calculates the voltage phase angle through quadrature axis current error.The degree of freedom of the control system is reduced to 1,and the problem of coupling voltage disturbance on the control side is solved.On this basis,the direct-axis high-frequency current compensation is added,and the controller parameters are selected according to the transfer function after the linearization of the current loop.The rapid start at the twice rated speed is within 1.5s,and the suppression of direct-axis current ripple can reach more than 60%,so that the steady-state performance of the motor in the high-speed field weakening area is improved.Since the maximum operating frequency that can be achieved by the field weakening control is proportional to the field weakening limit voltage,researching the dual-mode over-modulation strategy can further improve the utilization of the bus voltage.The traditional dual-mode overmodulation strategy meets the problem that the number of effective sampling points in the high-speed overmodulation state is reduced.After correction,the amplitude and phase jump of the output voltage increase,and the THD index of the output phase current increases.Therefore,the optimized dual-mode overmodulation strategy proposed in this paper adopts the minimum component correction method in the over-modulation area I to make the effective sampling point distribution more uniform.This solution increases the modulation depth of the output voltage under the same reference voltage and breaks through the traditional weakening voltage limit.The voltage utilization rate is up to 65%,which is 12.6% higher than the traditional space vector pulse width modulation method.When the voltage utilization rate is 60% and 65 %the phase current THD suppression effect in the operating state can reach 65.9% and55.9%.On the basis of theoretical research and simulation analysis,an 11 k W controller platform is used to achieve sensorless field weakening control and dual-mode overmodulation strategies for a 6k W high-speed permanent magnet motor.The feasibility of the proposed algorithm is verified by the statistics of motor operating indicators under different working conditions.