Research On Sensorless Control Of Permanent Magnet Synchronous Machines In Medium-low Speed

Sensorless techniques for PMSMs control have attracted considerable research because they can effectively avoid several disadvantages of adding to the machine size,install difficulty and limited practical applications.Nowadys,those methods for the acquisition of the rotor position based on the electromotive force of PMSMs are mature and have good experimental results in the practical applications.However,when the machine runs in the low-speed region,the precision of the rotor position estimation is severely degraded,and even cannot be used because of some negative factors,such as parameter uncertainties induced by inherent characteristics of PMSMs,the cross-coupling effect,nonlinear characteristics of the inverter and the delay of the hardware processing circuit,which will lead to some defects of the poor startup with heavy load in the low speed,the low dynamic response and the poor stability.Thus,in this thesis,the focus is to improve the control performance of PMSMs in the medium-low speed range and expand its suitable speed range.According to the analysis of conventional pulsating high frequency signal injection(HFI)method,two new multiple-HFI methods are proposed in this thesis by changing types and injection directions of the pulsating high frequency voltages: pulsating multiple-HFI method and pulsating-rotating multiple-HFI method.With the proposed methods,the rotor position can be obtained directly by utilizing both d-and q-axis carrier current,which can not only cancel the essential position tracking observer with potential convergence failure in the conventional scheme and enhance the system stability,but also largely reduce the estimated angle errors induced by the system delay and the cross-couple effect of the motor and greatly improve the estimation accuracy of the rotor position.After that,according to the inherent saturation effect of the PMSM,the mean current judgment method based on single high frequency sinusoidal voltage signals and the method based on the second harmonic current detection is presented to identify the magnetic polarity quickly and simply.In order to further improve the estimation accuracy of the rotor position and improve the control performance,considering the effects induced by the system delay,the stator resistance,the cross-coupling effect and the nonlinear characteristics of the inverter and so on,a rotating multiple-HFI method is presented in this thesis.Four independent equations are constructed and obtained by demodulating every frequency components in the response currents.The accurate rotor position can be calculated directly by solving these four equations.In order to avoid HF noise interference in HF signal injection method,a combining the fundamental pulse width modulation excitations(FPE)and additional test vectors hybrid strategy for PMSM sensorless control is proposed in this thesis.With the proposed methods,voltage space vectors applied in different directions for the rotor position estimation can be obtained from both the active vectors of FPE and additional test vectors.Meanwhile,a new pulse width modulation scheme for four-space-vector pulse width modulation(FSVPWM)is presented to estimate the rotor position in one PWM cycle by means of PWM counter double update mechanism of microcontroller(DSP),which expand the suitable spped range of based-PWM transient current detection method.Finally,the experimental results demonstrate the validity and feasibility of the proposed sensorless control solutions.The effectiveness and feasibility of those proposed methods is successfully verified in the physical system,such as air conditioning compressor,hydraulic press and textile machine,which shows the control solutions have a certain general practicality.