Research On Sensorless Control Of Permanent Magnet Synchronous Motor For Air Compressor

Air compressors widely use Permanent Magnet Synchronous Motor(PMSM)as the drive motor,but considering the equipment is in some harsh environments such as high temperature and high pressure,the cost of position sensors is higher and the installation space is smaller,PMSM drives The air compressor is more suitable for adopting the sensorless control scheme.Based on the above problems,this paper takes PMSM for air compressor as the research object,analyzes and improves its position-free control algorithm in low-speed section,medium-high speed section and composite control area to obtain better sensorless control effect.First of all,this paper describes in principle the rotation in the low-speed region,the pulse high-frequency voltage injection method and the factors that affect the rotor position observation of the two methods.For the rotating high-frequency voltage injection method,it is pointed out that its signal demodulation uses multiple filters,which causes the attenuation of the high-frequency current response signal amplitude and the phase lag,so the subsequent rotor position observation produces errors.For this reason,in signal demodulation,this paper uses an improved second-order generalized integrator(Second Order Generalized Integrator,SOGI)to replace the multiple fixed cut-off frequency filters of the traditional scheme,on the one hand,obtain high-frequency negative sequence containing rotor position information The current component,on the other hand,can realize the frequency selection function according to the speed;for the pulse vibration high-frequency voltage injection method,the rotor position observation error caused by the asymmetric phase resistance and inductance of the motor is analyzed.For this reason,this paper uses SOGI and a The new All Pass Filter(APF)extracts high-frequency current components and eliminates the second harmonic component in the rotor position error angle,respectively.Compared with the traditional rotating and pulse high frequency voltage injection method,the improved rotating and pulse high frequency voltage injection method has a greater improvement in rotor position observation accuracy;second,the traditional sliding mode observer in the middle and high speed area(Sliding Mode Observer,SMO)is introduced by the principle of sliding mode variable structure,and then the three factors that affect the observation effect of traditional SMO are analyzed.Except for the high-order harmonics caused by the nonlinearity of the inverter,a large error occurs when the back EMF crosses the zero point due to the use of the arc tangent function.In response to the above problems,this paper designs a new SMO,using the sigmoid function to replace the signum function in the traditional SMO method to solve the chattering problem caused by high-frequency signal switching.The nonlinearity of the inverter causes a large number of harmonics in the back-EMF,resulting in errors in rotor position and speed observation.A new type of filter is used to suppress the harmonics.At the same time,the phase-locked loop(Phase Locked Loop,PLL)extracts the filtered back-EMF toobtain the rotor position and speed information;again,for the PMSM switching from the zero low speed zone to the medium and high speed zone,that is,the composite control problem,The switching strategy based on hysteresis switching is introduced.Then,through theoretical analysis,it is found that both the pulsed high-frequency voltage injection method and the traditional SMO method obtain rotor position and speed information from the rotor position error angle.Therefore,this paper focuses on the two methods The rotor position error angle is normalized and weighted.The angle error after the weighting of the two can obtain the position angle through the same PLL.At the same time,a certain theoretical and simulation study on the switching interval based on the angle error weighted composite control scheme is made.Finally,in order to verify the correctness and effectiveness of the PMSM improved algorithm theory in the above-mentioned low-speed zone,medium-high speed zone and composite control zone.Build Simulink models of traditional and improved schemes,repeatedly debug and analyze the parameters.At the same time,the software program algorithm is written by the traditional and improved rotating high frequency voltage injection method rotor position observation principle.In the fifth chapter,a physics experiment platform was built,on which a comparative experiment of traditional and improved rotating high-frequency voltage injection method was carried out.Experiments show that(1)the improved rotating and pulsed high-frequency voltage injection methods can effectively reduce the observation error caused by the introduction of filters and asymmetry of motor parameters;(2)the improved SMO method compared with the traditional SMO The method has a higher effect of rotor position and speed observation;(3)Compared with hysteresis switching,the proposed composite control scheme based on the weighting of angle errors in the full speed range can more accurately observe the rotor position and rotor speed,and achieve more Smooth full speed range without position control.