The sensorless drive method of the permanent magnet synchronous motor (PMSM) has attracted wide attention for its low cost and high reliability. As a critical technology, a fast and high-precision rotor position estimation is essential. This work addresses the position estimation deviation issue of the sensorless drive method based on the sliding mode observer (SMO) and phase-locked loop (PLL). A non-linear equivalent model of the SMO is established to analyze and compensate for the position estimation deviation caused by the SMO, and a feed-forward PLL is employed to suppress the steady-state position tracking error under variable speed operation. Firstly, the phase-frequency characteristic of the SMO is obtained by studying the SMO and the switching functions in detail. Then, the analysis of the conventional PLL is carried out in terms of the error transfer function. Besides, the position estimation performance of the feed-forward PLL is discussed with the dynamic error coefficient method. Theoretical analysis and experimental evaluation validated the effectiveness of the proposed position estimation deviation suppression technology of the PMSM combining the phase self-compensation SMO and the feed-forward PLL.

Sensorless control is an effective measure to improve reliability and reduce cost for the brushless dc motor (BLDCM). However, the performance is generally related to the cost and complexity of the system, making it difficult for engineering applications. Therefore, this article proposes a high-dynamic and low-cost sensorless control method for high-speed BLDCMs using the rich built-in resources of the digital signal processor. First, a variable relating to the commutation moment is constructed and detected, which is not affected by modulation noise. Then, a detailed commutation process is presented based on the relationship between the back electromotive force (back-EMF) integral and the commutation point. Moreover, an integral prediction method is proposed by linearizing the back-EMF to cope with the effect of discrete sampling on commutation accuracy. Finally, experimental tests are performed on a magnetically suspended control moment gyroscope, which verifies the effectiveness of the proposed high-dynamic and low-cost sensorless control method.

As aerospace applications, high reliability and low power consumption operation of the brushless direct current (BLDC) motor for the magnetically suspended control moment gyro (MSCMG) is the primary consideration. To guarantee reliability, the sensorless control method without physical position sensors is adopted. Due to the phase lag caused by hardware and software, the commutation error is inevitable. In order to improve commutation accuracy for reducing losses, this paper proposes a fast commutation error compensation method. First, the control topology of the BLDC motor with a Buck converter and the commutation points detection circuit are presented. Then, the conducting back electromotive force (EMF) in a novel derived DC-link voltage expression is estimated through an extended state observer (ESO). Finally, the commutation error is extracted through the conducting back-EMF for compensation. Different from the conventional closed-loop correction method based on the back-EMF symmetry, the proposed commutation error compensation method can obtain the commutation error within only one commutation cycle by a continuous estimation with the ESO. The effectiveness of the proposed fast commutation error compensation method was evaluated with an MSCMG system.

Due to the asymmetry of the actual back electromotive force (back EMF), the performance of the conventional commutation deviation correction method degrades in sensorless control of the brushless direct current (BLDC) motor. This article proposes a high-precision sensorless optimal commutation deviation correction strategy, which considers the asymmetry problems of the back EMF. First, this article discusses the optimal commutation issues and the internal power factor angle based commutation deviation correction method. Then, given the issue of the nonsinusoidal phase current integration and the asymmetric back EMF, a dual improved second-order generalized integrator with a positive sequence component extractor (DISOGI-PSCE) is proposed. The DISOGI-PSCE can effectively deal with the dc component and harmonics in flux-linkage and current integration, as well as the asymmetry of the back EMF. Finally, experimental tests are performed on a magnetically suspended control moment gyroscope BLDC motor, which verified the effectiveness of the proposed high-precision sensorless optimal commutation deviation correction method.

Imaging the heart magnetic field to diagnose is a cutting-edge development direction to overcome cardiovascular diseases. Since the heart's magnetic field is extremely weak, the magnetic field must be detected in a magnetic shielding device when imaging the heart magnetic field. To improve the antidisturbance ability of the magnetic shielding device, this article proposes a disturbance suppression based high-precision magnetic field compensation (MFC) method for a magnetic shielding cylinder (MSC). A set of experimental system based on a MSC is built up and experiments verify the effectiveness of the proposed method in suppressing the external disturbance magnetic field.

Accurate commutation point is essential to ensure the ideal torque performance and low power consumption for brushless DC (BLDC) motor. In order to achieve the precise sensorless commutation at a constant or the rapidly varying speed, a fast commutation error correction method is proposed in this article. First, it is pointed out that the controlled variable variation, the high rate of commutation error relative to the low speed and the nonlinearity of the correction loop are the main origins of commutation error when the speed varies rapidly. Then, a novel commutation error correction method is proposed through the following three aspects: first, constructing a controlled variable first utilized for commutation correction, which keeps constant at the rapidly varying speed; second, incorporating feedforward compensation for the phase shift caused by low-pass filter; third, using feedback linearization to reduce the nonlinearity of the correction loop. The proposed commutation error correction method not only corrects the commutation error fast at a constant speed, but also achieves precise commutation when the rotor speed changes rapidly. Moreover, the proposed method is based on the principle of closed-loop control, thus, it also has the advantage of anti-interference. At last, the experimental results are shown to validate the effectiveness of the proposed method.