Rotor eccentricity commonly exists in permanent magnet synchronous machines (PMSMs) due to improper assembly, excessive vibration, and continuous operation. Consequently, the unbalanced magnetic pull, introduced by rotor eccentricity, may lead to unfavorable noise, vibration, and even bear damage, which makes the detection of eccentricity meaningful. Although motor current signal analysis is the most popular method to diagnose eccentricity based on the amplitudes of sideband component, it is a big challenge to classify different types of eccentricities and quantify the eccentric ratio due to the spatiotemporal coupling effect. In this article, by installing a set of Hall sensors at stator slots of PMSMs to measure the magnetic flux density in time domain, the static eccentricity and dynamic eccentricity can be easily separated. This article provides a novel complex-analytical model to reveal the single side band modulation effect in air-gap filed due to dynamic eccentricity. Moreover, a diagnosis algorithm based on frequency-adaptive notch filter is designed to identify the eccentricity type and the corresponding degree. The effectiveness of the novel diagnosis method is validated by both simulations and experiments.

The Type-II synchronous-reference-frame (SRF) phase locked loop (PLL) fails to precisely keep tracking on phase of input signals when the frequency of input signals is under ramp state, whereas the type-III SRF-PLL addresses the above issue but stability problem arises. In this letter, a forward compensation (FC) module is introduced to the Type-II SRF-PLL to minimize the dc phase error due to the ramp frequency of input signals, named as FCSRF-PLL, which features low computational burden, simple structure, noise immunity, and high robustness. More importantly, the parameter tuning in the proposed method will not cause stability problem. The effectiveness of the proposed FCSRF-PLL is verified through experiments based on dSPACE.

The sensorless control for dual three-phase motors (DTMs) under faulty conditions are insufficiently studied in previous research. This research aims to investigate the effects of single open-phase faults (SOFs) on the high-frequency (HF) injection (HFI)-based sensorless control for a DTM and present a new sensorless control method robust to the SOFs. Firstly, the HFI-based sensorless control is introduced into the αβ -subspace, where responded HF currents can reflect changes of two sets of three-phase windings simultaneously. Next, an HF fault analysis method is given to simplify the analysis process by making the inductance matrixes in the HF models unchanged under healthy and faulty conditions. Besides, an equivalent coordination method is proposed to extend the result under the phase-A SOF to an arbitrary SOF, avoiding repetitive derivation and obtaining a generalized conclusion directly. The SOFs cause the negative sequence components and varying amplitudes in the HF currents, resulting in large rotor position estimation errors. Then, a new rotor position estimation method based on a modified adaptive filter is presented to suppress these effects, which is robust to the SOFs without any fault diagnosis. The validity of the proposed analysis methods and sensorless control methods are all verified on a prototyped DTM.

Conventional sensorless control methods fail to estimate the accurate rotor position in case of open-circuit faults (OCFs) in dual three-phase interior permanent magnet machine (DT-IPM) drives, resulting in poor stability of the system. OCFs regularly contain open-phase faults (OPFs) and open-switch faults (OSFs). However, the current under OSFs can be considered as a combination of a one-half period of health status with a normal current and the other half period of OPF with zero current. Consequently, OSF is regarded as a generalized OPF. Based on the general solution to OCFs, a novel high-frequency (HF) square-wave voltage injection (HFSVI) sensorless control method is proposed for DT-IPMs at low speed to improve the fault-tolerance ability, which is robust to both OPFs and OSFs. With the help of vector space decomposition, the HFSVI is implemented in the decoupling space, where the effects of OCFs, e.g., varying amplitude and extra negative-sequence component of responded HF currents, can be compensated by HF currents in both αβ - and xy -subspaces in the rotor position estimation module. Compared with the noncompensation method, the proposed one is robust to parameter mismatches and only increases the computation burden slightly. Finally, experiments on a prototyped DT-IPM verify the proposed method.

Stator axial pairing of tooth tips is proposed in this article to suppress the open-circuit dc winding induced voltage and torque pulsation in the wound field switched flux machine. In the proposed method, the stator is divided into two segments axially and these two segments have different arcs of tooth tip. The finite element analysis results show that the proposed technique can reduce the on-load torque ripple from 17.91% to 6.99%, reduce the peak-to-peak value of cogging torque by 90.66% from 5.14 N·m to 0.48 N·m, and reduce the peak-to-peak value of open-circuit dc winding induced voltage at 1500 r/min by 84.39% from 79.58 to 12.42 V. Although the efficiency of the paired machine is slightly reduced from 84.93% to 84.11%, the average electromagnetic torque does not deteriorate by more than 5%. The paired machine is prototyped and tested, and the experimental results validate the effectiveness of the proposed method.

In a sliding mode observer-based sensorless drive system, the estimated back electromotive force (BEMF) always contains abundant low-order harmonics caused by nonideal factors, e.g., flux spatial harmonics, inverter nonlinearity, and current measurement error, resulting in large estimated position errors. In previous studies, adaptive notch filters are usually adopted to suppress the BEMF harmonics. However, these filters suffer from enormous computation and increase system complexity, especially facing numerous low-order harmonics. In this article, a new frequency-adaptive notch filter employing delay signal cancelation (DSC) is proposed, which can be tailored to eliminate multiple harmonics with a simple structure. First, Lagrange interpolation is applied to realize fractional-order delay in the frequency-adaptive DSC (FADSC). Then, a frequency-dividing record method is designed to shorten the recording array length for the FADSC at low speed. Next, a switching procedure is introduced to change the frequency-dividing factor smoothly at different speeds. Finally, the transformation matrix in the DSC is changed in the FADSC by adding the rotation direction to make it suitable to forward and reverse rotations of an interior permanent magnet synchronous machine (IPMSM). The accuracy of the estimated rotor position can be improved by FADSC, which is verified by experiments on a prototype IPMSM.