The permanent magnet synchronous motor is the most commonly used motor in servo systems. Torque ripple caused by the variation of the airgap magnetic field limits the steady-state performance of the servo system. In this article, a novel torque ripple model is established based on the general airgap field modulation theory. A compound control algorithm based on the current feedforward algorithm is proposed to suppress the torque ripple caused by the field modulation behavior. Finite element analysis simulation is conducted to verify the effectiveness of the proposed torque ripple model. Experimental results on a prototype machine show that the proposed torque ripple model is valid and the proposed control algorithm can effectively reduce the torque ripple and improve the steady-state performance of the servo system at medium or high speed.

In this article, the surface-mounted permanent magnet machine is regarded as a salient pole reluctance machine to take into account the effect of stator teeth. The field modulation behavior of the magnetizing field is firstly introduced, and the field model is then derived using the general airgap field modulation theory (GAFMT). The properties of the modulated field harmonics are explored based on the proposed field model. Subsequently, a general cogging torque model based on the virtual work method and the GAFMT is proposed to describe the relationship between the field harmonics and the cogging torque. On this basis, the mechanism of the cogging torque is studied, its frequency, effective field harmonics, and the contribution of each harmonic are revealed. The proposed model is then validated by comparing its results with those obtained from the Maxwell Stress Tensor method and the finite-element analysis, and a good agreement is observed, demonstrating the effectiveness of the proposed model. Furthermore, the experimental results also confirm the effectiveness of the proposed model.

A hybrid model for the flux-switching permanent-magnet (FSPM) machine is proposed in this paper. In this hybrid model, the air-gap magnetic field in FSPM machine is investigated from the perspective of the stator modulation effect and rotor modulation effect. The stator modulation is discussed from the perspective of equivalent air-gap in the stator slots and permanent-magnets (PMs). The rotor modulation effect is divided to two aspects, namely the effect on the magnetomotive force (MMF) and the effect on stator modulation effect. Different from the conventional model where the stator modulation effect and the rotor modulation are independent of each other, stator modulation effect in the proposed model is coupled with the rotor modulation effect by the minimal reluctance principle. Therefore, MMF and the stator modulation effect in FSPM machine become susceptible to rotor positions with the influence of the rotor modulation effect. Air-gap flux density in FSPM machine is calculated by this hybrid model and compared with those by conventional model and finite element analysis (FEA). Finally, the effectiveness of the proposed hybrid model is validated by comparison of the electromotive force with FEA and experimental results.

The objective of this paper is to investigate the possibility to improve the torque characters of electric machines featuring rotor salient pole reluctance from the perspective of the general airgap field modulation theory. The torque production mechanisms of two typical field modulated machines, namely the magnetically–geared machine (MGM) and the flux–reversal permanent magnet (FRPM) machine, are discussed based on the Maxwell Stress Tensor (MST) method, where the mono–harmonic mechanism of rotor PM machine like the MGM is revealed. Several common theoretical salient rotor pole configurations, like the upright/inverted trapezoidal configuration etc. are introduced in detail, based on which general and modified rotor configuration advices for the two electric machines are proposed to provide initial design and future optimization guidance. It is proven that there is a possible opportunity to make the torque characters better via reasonable selection of rotor configuration and topological parameters. Electromagnetic performances validation based on 2–D finite element analysis, such as improved airgap magnetic field harmonic distributions, load flux linkage/electromotive force (EMF) and general torque performances of two field modulated machines are provided to demonstrate the effectiveness of theoretical analysis. It is also verified by experimental measurements on the FRPM machines with different pole pair combination.

This article proposes a negative sequence current compensation based coordinated control strategy for dual-cage rotor brushless doubly fed induction generator (DCR-BDFIG), where the machine side converter (MSC) and grid side converter (GSC) cooperates to mitigate the imbalance in the control winding (CW) current, total output power and total grid current. Based on the machine dynamic model withstanding unbalanced grid voltage, the negative sequence current references, including four targets for MSC and three targets for GSC, are calculated and sent to the inner-current-loop controllers, where the GSC current controller is designed based on super–twisting sliding mode control (ST–SMC) with the stability analyzed. This proposed control strategy omits the outer-loop controller in the negative sequence frame, which has a more simple control structure and becomes more easy-implemented. Finally, the whole proposed coordinated control system is designed and implemented in both simulation and experiments under unbalanced grid conditions, verifying the effectiveness of the proposed control strategy.

This paper proposes a novel torque ripple model of V-Shape interior permanent magnet (IPM) synchronous machine based on the general field modulation theory (GAFMT). Firstly, the magnetic field modulation behavior of a 12-stator-slot/8-rotor-pole (12/8) IPM machine is discussed, where the expressions of permanent-magnet-excited (PM-excited) and armature fields are derived. Secondly, the total torque ripple is divided into three components, namely, the PM-excited cogging torque, the armature cogging torque, and the modulation torque ripple. Additionally, the relationship between the field harmonics and the torque ripple is discussed based on the GAFMT. Then, a finite element analysis (FEA)-assisted dual fast Fourier transformation (FFT) method is proposed to obtain the accurate value of the field amplitude for torque ripple calculation. The field analysis results based on the GAFMT and the proposed torque ripple are then validated by comparing their results with those obtained from the FEA simulations, and a good agreement is observed, demonstrating the effectiveness of the field analysis and the proposed torque ripple model. Finally, experiments on a prototype 12/8 IPM machine demonstrate the validity of the torque ripple model, providing an effective method for torque ripple suppression of IPM machines.