This article proposes an optimal active disturbance rejection control (ADRC) strategy for permanent-magnet synchronous motors (PMSMs), to improve the speed performance under periodic and aperiodic disturbances. First, the speed harmonics and the weakness of conventional linear ADRC are analyzed, and the disturbance rejection ability is found to be degraded due to the limited bandwidth of the extended state observer (ESO). To enhance the disturbance rejection ability, a novel double-stage-ESO (2S-ESO) is proposed, which integrates the advantages of both cascaded-ESO and the quasi-resonant controller. In the proposed control scheme, 2S-ESO works through two stages where the cascaded structure is adopted to realize an increase in the numerator order of disturbance estimation error transfer function, and the estimation accuracy is improved. Meanwhile, a composite ESO embedded with the quasi-resonant controller is designed in the second stage, where accurate estimation and attenuation of the periodic disturbance can be achieved. Compared with the existing ADRC technique, both the dynamic response and steady-state accuracy with the proposed method are greatly improved, and strong robustness is also maintained. Experiments are carried out to validate the effectiveness of the proposed scheme.

In a hybrid-inverter open-winding permanent magnet synchronous motor (OW-PMSM) drive, the motor and the floating capacitor are controlled simultaneously. Besides, since the compensatory inverter barely provides active power under steady-state operation, the unity power factor control (UPFC) of the main inverter (MI) is also required. However, the conventional model-based predictive control of the hybrid-inverter OW-PMSM is highly sensitive to the accuracy of parameters, including the floating capacitance and stator inductance. Serious current distortions and system oscillations appear when the model parameters are mismatched with the actual ones. In addition, unmodeled parts such as power switch voltage drops and disturbances also degrade the system performance. Hence, a linear disturbance observer (LDO) based model-free predictive control (MFPC) is put forward. By using ultralocal models to substitute the mathematical models of the floating capacitor and OW-PMSM, the proposed scheme maintains satisfactory performance when system parameters are mismatched. Moreover, because system disturbances are obtained by LDO, the tracking errors can be eliminated even when parameters of ultralocal model are less appropriate. Thus, high precision of UPFC for the MI is guaranteed. Finally, experiments are carried out on a 500 W hybrid-inverter OW-PMSM drive, proving the superiority and effectiveness of the proposed MFPC strategy.

For conventional HTS synchronous generator, the superconducting (SC) field windings or armature windings are rotating, which could complicate their industrial feasibility for the offshore wind generation. In order to overcome this drawback, a kind of HTS double-stator flux modulation generator (HTSDSFMG) without rotating windings is proposed. This paper compares the electromagnetic performance of 10-MW HTS doublestator flux modulation generators with two different topologies, i.e., iron-cored stators with both field and armature coils, air-cored stator with field windings and iron-cored stator with armature windings. In addition, the system comparison of HTS-DSFMG with conventional HTS synchronous machine is conducted under the no-load, rated load and short-circuit fault conditions. It is found that the proposed machine can dramatically reduce the peak current and peak torque during a symmetrical three-phase shortcircuit fault, and its active material mass and cost are comparable with the synchronous one under rated load condition.

In this article, a computationally efficient cascaded model predictive control (CMPC) is put forward for the hybrid-inverter fed open-winding permanent magnet synchronous motor (OW-PMSM) drive, which significantly reduces the computational burden and eliminates the weighting factors. The hybrid-inverter consists of a main inverter (MI) and a compensatory inverter (CI), which are respectively powered by a voltage source and a floating capacitor. Hence, an additional weighting factor is required to tradeoff the control of OW-PMSM and the floating capacitor. To avoid the tedious tuning work, a cascaded two-stage structure is designed to coordinate the multiobjective control. However, the weighting factor is eliminated at the cost of the increased number of evaluations. To this end, a fast partial preselection strategy is proposed, which evaluates only the voltage vectors (VVs) of CI in the first stage and then evaluates the VV combinations of both MI and CI in the second stage. With the proposed scheme, the number of VV combinations to be evaluated is decreased from 64 to 32, where the total computational burden is lowered by 48%. Finally, experiments are carried out on a 500 W OW-PMSM drive to prove the effectiveness of the proposed CMPC.

Owing to the significant torque ripple and vibration reduction ability, flux-modulated doubly-salient reluctance motor (FMDRM) drives have been widely investigated. However, the parallel dual-inverter is commonly utilized in conventional FMDRM drives, where the power switch number is doubled compared to conventional ac motor drives. In this paper, to reduce the utilization of power switches, an optimized nine-switch converter-fed FMDRM drive is proposed to achieve integrated zero-sequence current regulation ability. Firstly, the winding connection is developed, and the equivalent vectors of the nine-switch converter are analyzed for the dc-biased sinusoidal current excitation. Then, a carrier-based space vector modulation strategy is put forward, where the regulations of the rotating and zero-sequence voltage components are achieved, ensuring the dc-biased sinusoidal current excitation. Moreover, to further improve the converter efficiency and release the power stress of the middle switches, the modulation index clamping method is developed, where the switching actions of middle switches can be effectively reduced without sacrificing current regulation accuracy. With the proposed drive, the number of power switches is reduced by one-fourth, and a similar linear modulation region is achieved. Finally, the feasibility of the proposed FMDRM drive is proved by the corresponding experiments based on a three-phase FMDRM prototype.