The conventional rotor flux estimation method has issues of dc offset and harmonics, which are caused by initial rotor flux, detection errors, etc. To eliminate these defects, one improved nonlinear flux observer is proposed for sensorless control of permanent magnet synchronous machine (PMSM). Firstly, the rotor position estimation method based on PMSM rotor flux observation is studied. Meanwhile, the limitations of the traditional rotor flux estimators, i.e., the saturation of pure integrator, phase shift and amplitude attenuation of low-pass filter are analyzed. Then, two novel flux observers, second-order generalized integral flux observer (SOIFO) and second-order SOIFO are designed for the rotor flux estimation of PMSM. Based on second-order generalized integrator (SOGI) structure, the SOIFO can limit the dc component to a certain value. Furthermore, the second-order SOIFO is developed from the SOGI, which is characterized with effective dc and harmonics attenuation capability. With the second-order SOIFO, even without magnitude and phase compensation, the dc offset and harmonics of estimated rotor flux could be well eliminated. Therefore, the speed and rotor position can be estimated accurately. All the performances of the four methods are analyzed by transfer functions and Bode diagrams. Lastly, the new sensorless control strategy is validated by comprehensive experimental results.

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In this paper, a frequency-sweep based load monitoring method is proposed for weakly-coupled series-series (SS) compensated wireless power transfer (WPT) systems. By only measuring the input voltage and current of the transmitter coil, the proposed monitoring method can estimate the load resistance without any feedback signals from the receiver even for mid-range applications with very small coupling coefficients. Compared to the existing monitoring methods for short-range applications, the proposed monitoring method uses a simpler estimation equation. Both simulation and experimental results are included to confirm that the proposed monitoring method can accurately estimate load resistances of weakly-coupled SS compensated WPT systems.

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