Cheng Luo

The embedded discrete-time repetitive active disturbance rejection control (EDTR-ADRC) is a promising solution for suppressing periodic disturbances in permanent magnet synchronous motor (PMSM) drives. However, conventional discrete-time implementations suffer from two inherent discretization challenges: the frequency mismatch caused by rounding fractional delay period, and the phase compensation error due to integer-order phase lead step. These discretization errors inevitably degrade the disturbance rejection capability and stability margin. To address these challenges, this article proposes a double fractional-order-based embedded discrete-time repetitive ADRC (DFER-ADRC) strategy. With Lagrange interpolation, a double fractional-order structure is designed to precisely reconstruct both the fractional delay period and the phase lead step. It approximates the ideal non-integer characteristics via polynomial fitting, effectively eliminating the quantization errors. This design guarantees precise alignment between the controller's resonant frequency and the actual harmonic frequency while achieving zero phase shift at arbitrary speeds. On this basis, the proposed strategy maximizes the equivalent open-loop gain at multiple targeted harmonic frequencies. As a result, the total harmonic distortion of the currents is significantly minimized, and the waveform quality is enhanced as well. Furthermore, a comprehensive stability analysis and parameter selection criteria are derived in the discrete-time domain. Finally, the proposed method is validated on a 1.0-kW PMSM platform.

Permanent magnet synchronous motors (PMSMs) find extensive application across diverse domains thanks to their merits of high torque density and efficiency. An eccentric magnet-shaped design for a permanent magnet (PM) can effectively reduce the harmonic components in the air-gap magnetic field and suppress the torque ripple of the motor. The electromagnetic performance of the PMSMs is mostly analyzed by the finite element method (FEM), which requires a lot of time and computational resources. Therefore, a rapid optimization method for eccentric magnet-shaped PMSMs is proposed based on an accurate magnetic network model (MNM). The magnetic field characteristics of a six-phase eccentric magnet-shaped PMSM are analyzed based on the proposed model. Firstly, through an analysis of the motor’s magnetic circuit, an accurate MNM is established. Then, the established model is employed to achieve rapid and accurate calculation of the air-gap flux density (AGFD). Finally, the PM’s structure parameters are optimized. After the optimization by MNM, cogging torque (peak-to-peak) reduced from 2.2 N·m to 0.74 N·m; torque ripple (rated condition) from 0.14% to 0.05%; MNM time 20–30 s vs. FEM time 820 s. Compared with the experimental results, the MNM exhibits an error of 5.04% in EMF, 1.16% in output torque, and 0.67% in torque ripple. The effectiveness and accuracy of the MNM have been verified. The MNM can significantly shorten the design period while ensuring the calculation accuracy.

For speed-sensorless induction motor (IM) drives (SSIMD), the adaptive magnetizing current control has already been presented to enhance the speed observability at low synchronous speeds. However, the rapid variations of magnetizing current reference would introduce inherent ripples during zero frequency crossing (ZFC). To solve this problem, this article proposes a variable-slope-based ripple reduction method (VSRRM) for SSIMD to relieve the ripples of speeds and currents during ZFC. First, the qualitative analyses are carried out to elaborate the origin of the ripples during ZFC. On this basis, the slope angle of VSRRM is derived to rearrange the operating point trajectory, reducing the ripples with rapid magnetizing current changes. Considering the introduced slope angle, the boundary points of ZFC are optimized by average current to reduce the ripples. Furthermore, the IM operating trajectory and output torque capability are analyzed with respect to magnetizing current limit. Finally, the effectiveness of the proposed method is verified on a 2.2 kW IM experimental setup.

The active disturbance rejection controller (ADRC) can be integrated with advanced controllers to further improve its current disturbances suppression capability. However, the performance of existing methods would be deteriorated under the multiple specific periodic disturbances of current loop and the improper parameters of ADRC. To fill this gap, an embedded discrete-time repetitive ADRC (EDTR-ADRC) is proposed to suppress multiple frequency current disturbances in this article. First, the dc and low-frequency disturbances can be eliminated by extended state observer (ESO) of ADRC. Then, the discrete-time repetitive controller is embedded into the control law and adopted to extract multiple specific periodic frequencies signals without phase shift. On this basis, the disturbances rejection capability can be improved by EDTR-ADRC. Meanwhile, the parameter selection can be further optimized by combining the amplitude and phase characteristics of ESO to various disturbances. Then, the stability analysis and antidisturbance ability of the proposed method are elaborated in discrete-time domain. Finally, the effectiveness of the proposed method is verified on a 1.0 kW IPMSM setup.

The adaptive magnetizing current control (AMCC) has been presented for speed-sensorless induction motor (IM) drives to enhance speed observability around zero stator frequency. However, adaptive variations of magnetizing current result in inevitable harmonics of speeds and torque. Addressing this problem, this article proposes a predictive compensation-based AMCC (PC-AMCC) method to compensate the reference of torque current, and relieve the harmonics of speeds and torque. With the equivalent model of synchronous speed control loop, the analysis is carried out to clarify the origin of harmonics. Then, the torque current variations are predicted by tangent of electromagnetic torque in sampling periods according to the variations of stator current and torque current error. On this basis, the reference of torque current of current loop can be compensated to relieve the hysteresis effect and suppress speeds and torque harmonics. Furthermore, the selections of feedback gains are elaborated with respect to flux error in low-speed motoring region. Finally, the effectiveness of proposed method is verified on a 2.2 kW IM experimental setup.

To increase torque density, a combined-Halbach array for the axial flux permanent magnet machine (AFPMM) with a yokeless and segmented armature (YASA) is presented in this article. First, the YASA machine models with conventional axial magnets and combined-Halbach array magnets are established by using 3-D finite-element method (FEM). Then, the torque, torque per magnet-volume, and no-load back electromotive force (back EMF) are calculated, and the performance of the two machines is analyzed and compared. It is demonstrated that the combined-Halbach array can improve the torque density of the machine and the utilization rate of the magnets. Finally, the combined-Halbach array rotor is optimized, where the rotor with unequal-thickness magnets is established, and its torque density is calculated under different thickness. The results show that the combined-Halbach array with unequal-thickness magnets can decrease the amount of permanent magnet (PM) materials, thus improving the utilization of magnets and reducing the costs.

This article deals with speed observation methods for sensorless induction motor drives (SIMD). The speed observability of SIMD near zero stator frequency is a well-known concern. Using adaptive magnetizing current, existing methods are capable of crossing the zero-stator-frequency line, but still limited to constant load conditions. To solve these problems, this paper presents a phase compensation factor-based low frequency crossing method with changing loads (PCF-LFCCL) to realize low frequency crossing process with decreased overcurrent and speed spikes. Firstly, the influence of load variations is studied finely, the LFCCL method is proposed with adaptive magnetizing current. Secondly, the torque output capacity analysis is given and illustrated. On this basis, the synchronous speed limit can be adopted properly. Thirdly, a generalized current model is developed for SIMD. The model reveals the phase delay phenomenon between magnetizing current reference and actual torque current, which can lead to speed spikes and overcurrent. To address this issue, a phase compensation factor (PCF) based method is developed by reconstructing compensation values to correct the torque current. Finally, comparative experiments are presented to validate the PCF-LFCCL method, including stator resistance error test for parameter robustness.