Research On Position Sensorless Control Strategy For Permanent Magnet Synchronous Motor In Full Speed Range

Permanent magnet synchronous motors(PMSMs)have been extensively applied in the fields of household appliances,aerospace appliances and electric vehicles due to its simple structure,high power density and strong flux-weakening ability.The usage of mechanical position sensor decreases the robustness of PMSM drives and increases the cost and volume of PMSM drives,which limits the application of motor drives in some occasions.In order to overcome the above-mentioned shortcomings,sensorless control technologies have become one of the important research directions in related fields.However,the traditional sensorless control strategy cannot be applied to some high performance drive applications because of the limitation of observation accuracy.The conventional sliding mode observer has the inherent chattering phenomenon introduced by the signum function and the phase lag problem caused by low-pass filter.Hence,it is necessary to adopt the corresponding position compensation strategy,which increase the complexity of the system.In addition,the constant sliding-mode gains may lead to the observer's large chattering phenomenon in the low speed region and instability in the high speed region.In order to solve the above problems,an adaptive super-twisting sliding mode observer is proposed,which can eliminate the chattering phenomenon of the traditional sliding mode observer by introducing the super-twisting algorithm so that the use of low-pass filter can be avoided.Moreover,the sliding mode gains varying with rotor speed is introduced to expand the speed range of the observer.This strategy not only keeps the traditional sliding mode observer's advantages of simple structure and strong robustness,but also effectively suppress the chattering phenomenon and extend the speed range of the observer.When applied to sliding mode observer,the traditional quadrature phase-locked loop will produce a positional error of 180 degree when the motor reverses,thus losing its accuracy.The tangent-based quadrature phase-locked loop can solve the inversion problem of the traditional method,but it is vulnerable to the harmonic and noise interference.In order to solve above-mentioned problems,an improved quadrature phase-locked loop(PLL)is proposed based on a new method to obtain the equivalent position error,which can eliminate the influence of estimated EMFs' symbol variations on the equivalent position error's symbol,without involving the tangent function and excessive divisions.This strategy can solve the motor inversion problem of the conventional quadrature phase-locked loop and the harmonic interference problem of the tangent-based quadrature phase-locked loop.Inverter nonlinearities can lead to significant(6k±1)th harmonic ripples in ??-axis stator currents and back EMFs when the motor runs at low speed,which eventually lead to significant(6k)th harmonic components in speed and position estimations.To solve the above-mentioned problem,a second-order lead compensator-based quadrature phase-locked loop(SOLC-QPLL)is proposed to eliminate 6th position estimation errors only by introducing a second-order lead compensator,without influencing the bandwidth of quadrature phase-locked loop.Moreover,the SOLC-QPLL does not cause the phase delay for the phase-locked loop system and it is easy to implement digitally due to its simple structure.In the conventional high frequency square-wave injection method,low-pass and band-pass filters usually are used to separate high frequency response signals from fundamental frequency signals.This limits the bandwidth of the system,occupying more system resources,and reducing the current's and position observer's response speed.In addition,inverter nonlinearities can distort the injected high-frequency voltage,which affect the position observer's estimation accuracy.To solve the above problems,a novel high frequency square-wave injection method is proposed,which separates the field-oriented control period from the high frequency voltage injection period,so that the magnetic field orientation signal and the high frequency voltage signal are alternately carried out.Therefore,the separation of the fundamental frequency current signals and the high frequency current responses does not need digital filters,then the dynamic response of the system can be improved.At the same time,two voltage vectors with equal amplitude and opposite direction are injected into the estimated d-axis and a new demodulation method of position orthogonal signals is proposed to eliminate the influence of inverter nonlinearities and improve the accuracy of the position estimation.The sensorless control strategy for the full speed domain based on the novel high-frequency square-wave injection method and the adaptive super-twisting sliding mode observer is proposed.The smooth switching of two methods in transition speed domain is realized by the weighted switching algorithm so that the sensorless control of permanent magnet synchronous motor for the full speed domain can be realized.Finally,on the basis of theoretical analyses,the validity of the proposed method is verified by the Matlab/Simulink simulation results and experimental results of 60 k W permanent magnet synchronous motor platform,and the simulation and experimental results show that the proposed sensorless control strategy has excellent control performance.