Sensorless Control Strategies For Pmsm Low Speed Operation Based On Singel Dc-link Shunt

With the wide application of PMSM drive system in household appliances,the demand for its high reliability and low cost is increasing.The conventional vector control system requires three phase current sensors and a position sensor fixed on the shaft end of the motor rotor to obtain the rotor position and winding current information for closed loop vector control.Excess sensors increase the cost and volume of the system,and reduces the robustness of the drive system in harsh operating conditions.In order to improve the competitiveness of household appliances equipped with PMSM drive system,the single DC-link shunt based current reconstruction technology,which uses a single current sensor in series on the DC link to reconstruct the current information of three-phase motor by time-sharing sampling method,has been widely paid attention to in the field of cost-effective motor drive.At the same time,the rotor position is not obtained through the position sensor,but is extracted from the motor current through the design algorithm for sensorless vector control,which can further improve the system robustness under extreme conditions.The absence of the position sensor makes the cost of the system also decreases.In this dissertation,the low speed sensorless control technology of PMSM is studied based on single DC-link current shunt.Aiming at the reconstruction deadzone problem caused by phase current reconstruction scheme of single DC-link current sensor,an improved space vector modulation(SVPWM)method based on vector phase shift is studied.Firstly,the minimum sampling time limit caused by unideal sampling in the actual digital control system is analyzed.On this basis,different modulation strategies are proposed to solve the problem of low modulation ratio in the vector hexagon region and non-sampling region in the sector boundary region,so that the deadzone of traditional SVPWM can be completely eliminated.In order to reduce the influence of time-sharing sampling error caused by sequential sampling of single current sensor on the reconstruction accuracy,a current reconstruction compensation scheme was proposed.Firstly,the ripple characteristics of different sampling sectors of the three-phase current are analyzed,and the errors caused by time-sharing sampling are analyzed in detail and mathematically modeled.Finally,a method for calculating the current change rate of the motor based on the voltage equation and the sliding mode observer is proposed.The sampling current is compensated by estimating the current change rate of the motor during the action of the basic vector.After the completion of high-precision current reconstruction,the low-speed sensorless control strategy of PMSM based on high frequency auxiliary signal injection is studied.Firstly,the high frequency model of PMSM is modeled,and the relationship between the response of high frequency voltage signal and the actual rotor position is deduced.Then,on the basis of injecting high-frequency square wave voltage signal into the rotating observation shaft,the high-frequency current signal containing rotor error information is extracted from the defined 45° measurement shaft lagging behind the observed rotation shaft.Finally,the signal extraction algorithm is designed to extract the position information.After the theoretical analysis and simulation verification,the current reconstruction algorithm,current compensation algorithm and sensorless control algorithm are verified and implemented on the integrated motor drive controller respectively.The proposed methods are verified by experimental results.