Research On Rotor Position Estimation Method Of PMSM At Low Speed

Permanent magnet synchronous motor(PMSM)is widely used in electric vehicles,compressors,wind power and other fields because of its high power density,high efficiency,wide speed range and low noise.The position and speed information of motor rotor are usually obtained by mechanical sensor for high performance vector control of motor,but the mechanical sensor needs to occupy a certain amount of space,which increases the cost and complexity of the system and reduces the reliability.Therefore,sensorless control technology is of great significance.At low speed of PMSM,the back EMF is very small,so sliding mode observer algorithm is not suitable for rotor position estimation.Therefore,rotor position estimation is usually carried out by injecting high frequency signal at low speed.The main research contents of this article are as follows:(1)In three-phase PMSM,considering the influence of inverter nonlinear on the injection accuracy of high frequency injection signal,a new signal demodulation method is proposed.Also,in the process of speed loop signal demodulation,LPF is not needed,which improves the bandwidth of the speed loop.Simulation results prove the feasibility of the proposed method.(2)In three-phase PMSM,using band pass filter(BPF)to extract high frequency current will cause certain phase lag.In this paper,high frequency and fundamental frequency separation injection method was used instead of high frequency and fundamental frequency superimposed injection method,which can avoid the use of BPF and improve the accuracy of rotor position estimation.The simulation comparison results prove the superiority of the proposed method.(3)In order to solve the high-order harmonic problem in the zero-sequence carrier voltage of three-phase PMSM,the high-frequency signal injection mode and the signal demodulation method are designed.High-frequency square wave signals are alternately injected at the d and q axes,the zero sequence carrier voltage signals in the sinusoidal form and cosine form are respectively extracted,and the rotation speed and the rotor position can be estimated by the phase-locked loop after demodulation.Simulation results prove that the proposed method can effectively decreases the influence of high order harmonic for estimated rotor position.(4)In order to solve the high-order harmonic problem in the zero-sequence carri-er voltage of the dual three-phase PMSM,two sets of high frequency square wave signals are injected into the d axis of estimated synchronous rotating coordinate.Utilizing the phase difference between two sets of winding,two sets of zero sequence carrier voltages in the form of sine and cosine are extracted,which can estimate the rotor position information well.The proposed algorithms are verified by simulation,which solved the problem of high order harmonic for estimated rotor position.Finally,the hardware system is built.The vector control system of three-phase PMSM is programmed,and the experimental results verify the reliability of the program design.