An analytical method is proposed to predict and optimize cogging torque accurately. It is derived by the exact subdomain model, equivalent current sheet of magnet, and modified particle swarm optimization (PSO), in surface-mounted permanent magnet machines (SPMs) accounting for the effect of stator slotting and tooth-tips. The analysis works for internal/external rotor motor topologies, radial/parallel magnetization, as well as for any combinations of pole and slot numbers. Then, four important design parameters, viz. magnet thickness, air-gap length, slot-opening to slot pitch ratio, and pole-arc to pole-pitch ratio, are adopted as optimal variables, and the peak of fundamental order of the radial component of the air-gap flux density is constrained to optimize cogging torque by modified PSO based on forgoing model. Finally, the cogging torque of two prototype machines with both radial and parallel magnetizations is optimized notably. The paper validates the results of analytical prediction by finite-element analysis.

The multi-disc axial flux permanent magnet synchronous machine (AFPMSM) can provide high fault tolerance capability in applications requiring high reliability. Firstly, a topological structure of coreless AFPMSM is proposed, the magnetic circuit and the air-gap flux intensity are discussed in detail to improve stable operation of machine in this paper. The relationship between air-gap flux density and the parameters of rotor are clarified respectively based on finite element algorithm (FEA). Furthermore, the winding structure and power driver topology with fault tolerance are presented. And the 3D FEA analyzes the operation characteristics and stress of the machine. Finally, the prototype is manufactured. The results are demonstrated that the torque output and fault tolerance performance is better.

This paper proposes an analytical method to calculate the magnetic field, back electromotive force (BEMF), inductance and torque of spoke-type permanent-magnet machine (PMM) accounting for eccentric magnetic pole. The magnetic field in the slotted spoke-type PMM is predicted according to conformal mapping, flux continuity theorem, double reaction theory, superposing principle and complex relative air-gap permeance. Then BEMF, inductance and torque are obtained according to the results of magnetic field. A spoke-type PMM with eccentric magnetic pole is used to verify the analytical model. The harmonics of BEMF and torque ripple of spoke-type PMM with eccentric magnetic pole are very slight. Results of magnetic field, BEMF, inductance and torque by the analytical model are verified by finite element. The validation to calculate BEMF and electromagnetic torque with analytical model is confirmed by experimental result. The analytical method proposed in the paper can be applied to the spoke-type PMM with all kinds of magnetic-pole shape.

To fully suppress the current harmonics of torque plane and zero-sequence dimension in open-end winding (OW) permanent-magnet synchronous motor (PMSM), a novel 3-D space vector pulsewidth modulation (SVPWM) strategy is proposed in this article. First, the distribution of 3-D space vectors is analyzed. Then, a subspace-based vector selection method is developed to utilize the adjacent vectors in space to synthesize the reference vector. On this basis, a repetitive controller is equipped for zero-sequence current to guarantee precise current tracking. By using the proposed 3D-SVPWM strategy, the current controls in 3D can be well balanced. Besides, the fault-tolerant control of open-phase fault in OW PMSM drive is realized with the proposed 3D-SVPWM strategy by simply changing zero-sequence current reference. The experiments are carried out to prove the effectiveness of the proposed strategy.

Model-free predictive current control (MFPCC) completely separates from the motor model, and only needs to read the current variations in the lookup tables to predict future currents, thus having strong parameter robustness. However, the stagnation of current variations is a core issue that needs to be addressed in existing MFPCCs. Therefore, this article proposes a more effective MFPCC strategy of permanent magnet synchronous motor. First, an advanced strategy is proposed to estimate current variations using a variant of the ultralocal model, where the local variables in the model are provided in real-time by sliding mode observer. This method can easily extract the current variations corresponding to all voltage vectors from the measured current variations caused by the voltage vectors applied in the previous period. Secondly, an anti-stagnation mechanism with higher reliability and better performance was designed. This mechanism effectively improves prediction accuracy by utilizing a pair of antiphase vectors and corresponding current variations, avoiding update stagnation. Since non-optimal vectors are not forced to be applied, this anti-stagnation mechanism has no impact on control performance. Finally, through comparative experiments on multiple predictive current control schemes, it is demonstrated that the proposed MFPCC has improved both steady-state and dynamic performance.

This paper presents an analytical method for calculating and optimizing magnetic field in spoke-type permanent-magnet machines accounting for eccentric pole-arc shape. Normalized flux density is derived from conformal transformation taking into account eccentric pole-arc shape, and final field solution is predicted according to the flux continuity theorem. The optimal results show the harmonic content of flux density can be reduced a lot by optimizing eccentric distance of eccentric pole arc while fundamental content will reduce a little. The proposed analytical solution on prototype machines is implemented. The finite element (FE) and experimental results confirm that the developed analytical method has high accuracy for predicting and optimizing magnetic field.