Accurate rotor position information is important for the high-performance operation of position sensorless permanent magnet synchronous motor drives. However, during steady-state operation and variable speed conditions, traditional sliding mode observer with phase-locked loop (PLL) causes position estimation error. In this paper, an observer designed in rotary reference frame is proposed to reduce position estimation error during steady-state operation. Besides, a PLL with speed compensation is proposed to suppress the position estimation error caused in variable speed conditions. Experiments and simulation results verify the effectiveness of these two methods for position estimation error suppression.

Electrolytic capacitors are usually most seriously affected by aging in power electronic systems and it is necessary to timely indicate the degradation status of the electrolytic capacitor for ensuring the safe operation of the system. An online estimation method of the DC-link capacitance based on impedance analysis for permanent magnet synchro-nous motor (PMSM) drives with the boost power factor correction (PFC) converter is proposed, which does not need any additional signal injection or DC-link capacitor current sensor. Based on the principle of area equivalence, the capacitor current can be reconstructed by the inductor current and the duty ratio in the boost PFC converter. The bandpass filter (BPF) is applied to extract the 100Hz ripples from DC-link voltage and capacitor current. Through analyzing the capacitor impedance characteristics, the DC-link capacitance can be estimated by the 100Hz ripple voltage and the 100Hz ripple current. The experimental results verified the effectiveness of the estimation method.

In the high frequency boost power factor correction (PFC) converter, it is necessary to obtain the phase of the grid side voltage. However, in some cost-sensitive applications, there is only a sensor to detect the rectified voltage. This paper proposes a digital phase locked loop (PLL) scheme with a frequency predistortion digital bandpass filter to obtain the rectified voltage phase. Based on analyzing the frequency domain response characteristics of the digital bandpass filter, the continuous bandpass filter is digitized by bilinear transformation with frequency predistortion. On this basis, the rectified voltage is filtered to obtain its fundamental component as the PLL input. Then the grid side voltage phase is obtained at the output side, so the in-phase PFC reference current signal can be generated. Experiments have been carried out on the platform of the 70kHz PFC converter to verify the effectiveness of the strategy.

High frequency (HF) signal injection is commonly used in sensorless permanent magnet synchronous motor (PMSM) drives at low speeds and standstill. However, the extra acoustic noises caused by additional signal injection impose restrictions on its further applications. To address this issue, a pseudo-random frequency pulse voltage injection scheme is proposed for sensorless PMSM drives at low speeds. Compared with the pseudo-random signal injection, the proposed pseudo-random frequency pulse voltage injection scheme with pulse width adjustment can make all the discrete harmonics in the noise spectrum disappear, thus achieving effective noise attenuation. The signal injection design is performed via current power spectral density (PSD) analysis. According to the form of the injected signals, the signal demodulation procedure is designed to obtain estimated rotor position. The validity of the proposed scheme is verified on 2.2-kW IPMSM platform.