Research On Sensorless Control Strategies Of PMSM Drives For Wide Speed Operation

Permanent magnet synchronous motors(PMSMs)are widely used in the fields of industry because of their high efficiency and high power density.Position-sensorless drive techniques can estimate rotor position information at both low and high speeds,which reduces the system's costs and improve the reliability,and also these techniques have become a hot spot for current research.However,zero-and low-speed sensorless methods are limited in applications due to high-frequency noise pollution,negative effects of digital filters,and low estimation accuracy;medium-and high-speed position estimation schemes are vulnerable to inverter nonlinearity and spatial harmonics.Therefore,aimi ng at the problems existing in the traditional methods,this paper studies the corresponding solutions.First,the low-acoustic-noise position estimation strategy at zero-and low-speed based on low-frequency pulse voltage injection is studied.By separating the control period and the injection period,and lowering the frequency of the injected signal,the high-frequency acoustic noise pollution is reduced.To improve the accuracy of the position estimation,a vector observer based on the Space Fourier series is proposed,and the influence of the estimation error on the observer is analyzed.The harmonic elimination scheme using notch filter is used to further improve the accuracy of the rotor position estimation.Through the proposed method,while reducing the acoustic noise pollution,it can also ensure the accuracy of position estimation.Then,in order to improve system stability and position estimation accuracy at zero-and low-speed,a position estimation scheme based on orthogonal square-wave voltage injection into stationary reference frame is proposed.Orthogonal square-wave voltages are injected into the stationary reference frame so that the rotational reference frame does not need to be estimated,ensuring the validity of the positional convergence.The signal processing process is established in the form of discrete sequences.By simple addition and subtraction,the position signal can be extracted from the high-frequency currents without using low-pass filters.Simultaneously taking into account the negative effects of high-pass filters and system delays,the accuracy of the position estimation is further improved.Based on the researches of position estimation strategy at zero and low speed,a medium-and high-speed position estimation scheme based on cross-decoupling complex filter is proposed.The rotor position at medium to high speeds can be obtained from the back-EMF estimated by the sliding mode observer.At the same time,the effects of inverter nonlinearity and spatial harmonics on the accuracy of position estimation are analyzed.A position observation scheme based on cross-decoupling complex filter is applied,and a frequency adaptive link is constructed to achieve self-elimination of harmonics when the speed changes,improving the position estimation accuracy at medium-and high-speed range.In order to realize the full-speed position sensorless operation of PMSMs,a switching process is designed to combine the low-and high-speed sensorless control methods.By the proposed method,the smooth switching between the two schemes is achieved.Finally,based on the theoretical analysis,the Matlab/Simulink and a 2.2k W PMSM drive platform were used to simulate and verify the proposed method.The results showed that the position estimation strategies proposed in this paper can achieve the established goals well,so that improving the quality of the sensorless motor drives of PMSMs.