The field winding based flux adjustable permanent magnet (FWFAPM) machines, including the hybrid excitation topology and the memory topology, can offer excellent capabilities in terms of flux regulation, wide constant power operation as well as de-excitation (flux-weakening) under fault, thus, they are capable for using in More Electric Aircraft (MEA) generator systems. First, this paper probes four basic hybrid excitation modes, and based on that, a general method deriving PM machines to hybrid excitation machines is established. The basic characteristics of each hybrid excitation mode considering the relationship between S-pole and N-pole are obtained for the first time. The performance differences of each hybrid excitation mode combined with different PM machines are summarized. Then, this general topology derivation method are extended for the memory topology, The unified derivation method of the single-PM topologies, the double-PM topologies and the triple-PM topologies for memory machines is systematically established.The general laws of the electromagnetic performance of each double-PM mode and triple-PM mode considering different relationships between NdFeB and AlNiCo are summarized for the first time. Finally, the control strategies for voltage regulation of aircraft generator systems are discussed based on the different critical control variables and controller types, a torque impulse balance control method which shows excellent dynamic performance for both target control variable and critical control variable has been achieved experimentally.

The direct torque control system has excellent dynamic performance of electromagnetic torque, however, the dynamic performance of the speed is affected by the PI parameters of the speed closed loop. Hence, a control method which can realize the optimal dynamic performance of the speed is investigated in this paper. In this method, the integration balance of sine value for the torque angle is introduced, based on this, the speed and the electromagnetic torque can be controlled to converge simultaneously after the speed adjusting only once. Thus, the best possible dynamic response for the speed can be achieved. The proposed method is verified by both simulation and experimental results.

Permanent magnet (PM) machines inevitably suffer from cogging force, which does not contribute to the average output torque (force) but contributes as a type of torque (force) ripple. This paper provides an overview of the cogging force reduction methods for different types of PM machines. First, a systematic and comprehensive categorization of different kinds of cogging force reduction methods is given according to the reduction principle. Then, the cogging force reduction methods for different types of PM machines are analyzed and discussed based on the categorization. Finally, according to the versatility and feasibility of the cogging force reduction methods, practical methods are recommended for different types of PM machines. The categorization, analyses, and recommendations presented in the paper are useful for the design of different types of PM machines with the requirement of cogging force reduction or output torque (force) ripple suppression.

Linear flux‐switching permanent‐magnet (LFSPM) machines exhibit significant potential in many applications. A double‐sided sandwiched LFSPM (DSSLFSPM) machine with high thrust force capability is investigated in this study. After being optimised for optimal thrust force using Maxwell 2D, this machine is found to deliver higher thrust force when compared with an optimised conventional 12/14 LFSPM machine. However, low thrust force ripple is also required in many applications. Thus, in order to reduce the thrust force ripple, the DSSLFSPM machine is improved by a staggered stator teeth structure and an end permanent‐magnets method, then, two improved machines are obtained. The improved machines can reduce the thrust ripple to a very low level without thrust force density decrease. Further, the stator yoke thickness of the improved machines is optimised to reach optimal thrust force density. Finally, the performance of the DSSLFSPM‐ST machines is analysed including the normal force, the efficiency and the power factor. It shows that the improved DSSLFSPM machines exhibit relatively low normal force and high thrust force density as well as low thrust ripples, indicating that they are suitable for long‐stroke applications.

Fault-tolerant flux-switching permanent-magnet (FTFSPM) machines are suitable for high-reliability applications owing to their good fault-tolerant capability and relatively high torque density. Under a short-circuit fault, the torque ripple caused by the short-circuit current of the FTFSPM machine affects the steady-state performance of the system; in addition, the traditional proportional-integral (PI) controller of the speed loop can hardly guarantee the optimal dynamic performance of the speed. In this study, to solve these two problems, an improved control strategy that can offer two improvements for the FTFSPM machine under the short-circuit condition is investigated. As the first improvement, on the basis of analysis of the torque ripple caused by the short-circuit current, the feed-forward control is employed to reduce both the torque ripple. As the second improvement, on the basis of analysis of the influence of the speed loop PI parameters on the system dynamic performance, a torque integral balance-control method is proposed. This algorithm can make the speed and the electromagnetic torque converge simultaneously after only one adjustment of the speed. Thus, the best possible dynamic response for the speed can be achieved. Experimental results verify the correctness and effectiveness of the improved control strategy.

Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance is always affected by big thrust force ripple. In this paper, for two C-core LFSPM machines of high thrust force capability, including a 6/13 C-core LFSPM (6/13LFSPM-C) machine and a sandwiched C-core LFSPM (SLFSPM-C) machine, and a thrust force ripple reduction method is proposed. The proposed method is developed by reducing the slot effect component of the cogging force based on staggered stator tooth, and suppressing the thrust force ripple caused by unbalanced three phase back-electromagnetic forces (EMFs) based on two end PMs. Based on finite element analysis (FEA) results, both C-core LFSPM machines can achieve small thrust force ripples as well as high sinusoidal back-EMFs, and at the same time, maintain high thrust force capability with the proposed method. It was also found that, the improved SLFSPM-C machine exhibited the same thrust force capability as the improved 6/13LFSPM-C machine, but with a much smaller thrust force ripple.