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As a new type of flux modulation machine, line-start permanent magnet vernier machine (LSPMVM) has drawn more and more attention. Thanks to the rotor starting winding, the self-starting capability of which can be acquired without applying the inverters. As a result, the system reliability has been improved and cost can be decreased, which is promising for industrial applications, such as pumps and fans. In order to extend the family of LSPMVMs and select the preferable topologies meeting the different requirements, four LSPMVMs, including V-shaped LSPMVM, consequent-pole U-shaped LSPMVM, dual-stator spoke LSPMVM and consequent-pole surface-mounted permanent magnet (SPM) LSPMVM, have been proposed in this paper. And the steady state performance, starting and synchronization capability are comprehensively analyzed and compared, where the regular commercial line-start permanent magnet synchronous machine (LSPMSM) is used as a counterpart. It is found that all the proposed LSPMVMs can acquire the higher torque density. Especially, the V-shaped LSPMVM and consequent-pole U-shaped LSPMVM have the highest torque density, while the consequent-pole SPM LSPMVM can be a better candidate where the low cost is desirable. Finally, the prototype of V-shaped LSPMVM has been manufactured, where experimental results match well with finite element analysis (FEA).

Vernier permanent magnet (VPM) machine has become a good candidate to drive the pump and fan loads, since these loads always operate at low speed and require high output torque. In these applications, the machine operates near a fixed speed and requires no speed adjustment capability. Hence, the inverter can be replaced by a line-start unit, and the machine can be connected directly to the grid, which reduces the weight, volume, and cost of the whole system. However, the novel magnetic gearing effect in the VPM machine causes two issues. First, the abundant magnetic field harmonics interact with the line-start unit and produce strong braking torque even at steady-state operation; second, large harmonic leakage inductance reduces the starting capability. Therefore, the traditional method to build a line-start machine is not suitable for the VPM machine. In this article, a line-start VPM (LSVPM) machine topology is proposed. By analyzing two issues above, the structure and pole-pair of both stator armature and rotor wound windings are carefully selected, and finally pole-changing strategy is chosen to start the machine. The performances of the proposed machine are verified by finite element analysis (FEA), which shows it has 49% higher torque density than regular line-start permanent magnet machine, and has the capability to start with the rated pump load. A prototype also has been built and tested to demonstrate the analysis and simulation.

Line-start permanent magnet (LSPM) machines have significant advantages in efficiency and power factor compared with regular induction motors; however, the poor starting torque and synchronization capability prevent the widespread of LSPM machines. In this article, winding reconfiguration methods are proposed to improve the starting performance and steady-state performance of LSPM machines. The turns-changing method is to increase asynchronous torque by reducing coil turns in starting, and the pole-changing method is to reduce and even eliminate the permanent magnet (PM) braking torque by changing the pole pair number of stator windings in the early starting period. Both of them can be adopted for an LSPM machine simultaneously to improve average torque in the starting stage. The starting performance is also compared between the turns-pole-changing LSPM machine and pole-increasing LSPM machine. Finite-element analysis is carried out to show the performance differences of LSPM machines using different starting strategies. A turns-changing LSPM machine is also manufactured and tested to validate the starting improvement.

Combined with line-start permanent magnet (LSPM) machine and vernier permanent magnet (VPM) machine, the line-start vernier permanent magnet (LSVPM) machine has the advantage of self-starting capability and higher torque density, which can be the better candidate for pump and fan applications. However, same to the traditional LSPM machine, the LSVPM machine also suffered the poor transient performance, such as weaker starting and synchronization capability, which is difficult to simultaneously resolve considering the tradeoff between steady state and transient performances. In this paper, a novel double rotor winding LSVPM machine has been proposed, where the rotor is constructed by the starting winding and damping winding with carefully selected winding pole-pair, and the stator winding applies the centrifugal switch to operate pole-changing and turn-changing strategy, all of which can significantly improve the transient capability of LSVPM without the sacrifice of steady state performance. According to finite element analysis (FEA), the superior performance of the proposed LSVPM has been verified.

This paper presents a study about the integration of the line-start capability to a flux modulation machine, well known as Vernier motor (VPM). A line-start Vernier motor (LSVPM)could bring the VPM assets, such as a high torque density or direct-drive, to fixed-speed applications. But due to the various magnetic fields of the VPM, some currents still flow into the rotor cage at synchronous speed and change the performances. This analysis studies these rotor currents, especially the associated copper losses, at steady-state and transient, to understand first the LSVPM behavior, then what could be the best squirrel cage and VPM design for a line-start purpose.

This paper presents a novel dual stator line-start permanent magnet synchronous motor (LSPMSM), which can remove the contradiction between the starting torque and the synchronization capability existing in the conventional LSPMSM by fundamentally eliminating the braking torque at the starting stage. The structure and principle of the proposed machine are given, which can be considered as the combination of the outer rotor induction machine and the inner rotor surface-mounted permanent magnet (SPM)machine. The braking torque can be removed by locating the PM far away from the inner stator windings. Then, the detailed performance of the proposed LSPMSM, the pole-changing LSPMSM and the traditional LSPMSM is compared and analyzed by finite element analysis (FEA). The analysis results show that the proposed LSPMSM has the superior performance in terms of the starting capability, the synchronization capability and the on load capability.

Vernier permanent magnet (VPM)machines have attracted more and more attentions due to their desirable features of high torque density. However, nearly all the proposed VPM machines are driven by converters. In this paper, two methods to acquire self-starting ability for VPM machine are proposed. The inverter is omitted due to the self-starting capability of the proposed topology. Firstly, a consequent-pole line-start vernier permanent magnet (LSVPM)machine is analyzed to clarify traditional method by embedding squirrel cage in the rotor is not suitable for VPM machine. Then the structure and circuit of the dual-stator line-start VPM (DSLSVPM)machine is proposed. The decoupling of starting performance and steady performance is analyzed. The PM braking torque is eliminated during the whole starting process. Finally, the starting and steady performance is validated by finite element analyzes (FEA). The torque density is increased 80% compared with conventional line-start PM machine.

Permanent magnet vernier (PMV) machines have attracted more and more attentions due to their desirable features of high torque density. However, nearly all the proposed PMV machines are driven by converters. In this article, two methods including stator winding pole-changing and cascading method to acquire self-starting capability for PMV machine are analyzed and compared. The inverters can be omitted due to the self-starting capability of the novel topologies. First, the structure and circuit of pole-changing line-start permanent magnet vernier (PCLSPMV) machine are given and analyzed. Then, a dual-stator LSPMV machine, which cascades an induction machine and a PMV machine is also analyzed. Additionally, the starting and steady-state performance between pole-changing and cascading LSPMV machine. Finally, a prototype of a PCLSPMV machine has been built and tested to demonstrate the analysis and simulation.

Line-start permanent magnet motors (LSPM) have significant advantages in efficiency and power factor compared to regular induction motors. However, the poor starting torque and synchronization capability are the key issues, and this influences LSPM motors used in many applications. In this paper, coil turns-changing method is proposed to relieve the contradiction between starting and steady-state performance, and improves starting torque and synchronization capability. In order to further remove the magnet braking torque, a novel coil turns-pole-changing method is also proposed to remove the contradiction. The permanent magnet braking torque can be eliminated, in additions, the starting-state and steady-state performance can be nearly decoupled totally. Furthermore, these two turns-changing methods can also start successfully even when network voltage is low. Finite element analysis is carried out to validate the big starting torque and strong synchronization capability.

Pole-changing line-start permanent magnet (LSPM) motors eliminate the braking torque during starting process. The pole-changing LSPM motors often starts with pole-decreasing way in order to synchronize successfully, however, the asynchronous torque in starting stage is reduced and winding factor in steady stage is also decreased. In this paper, a pole-increasing-start LSPM motor is studied. The asynchronous torque increases effectively by increasing pole pairs number during starting process but the speed cannot accumulate up to synchronous speed directly in starting stage. So the starting process should be divided into pole-increasing starting stage and steady pole pairs starting stage. The starting torque becomes larger effectively in early process and the synchronization capability even better compared with conventional LSPM motors. Furthermore, the starting performance and steady-state winding factor are compared between pole-increasing and pole-decreasing LSPM motors. Finite element analysis is carried out to show the performance differences of those two kinds of motors.

Stator DC winding Excited Vernier Reluctance Machines (DC-VRMs) are a kind of novel machines, which are investigated more and more owing to absence of expensive permanent magnet material. However, DC-VRMs are found to have large torque ripple if they are not carefully designed. There are a lot of existing methods to reduce the cogging torque in permanent magnet (PM) machines, but the design techniques for DC-VRMs have only been mentioned recently in few papers. In this paper, some new methods are proposed including shifted rotor tooth, stepped rotor skewing with multiple modules, T-shape rotor tooth, various rotor tooth arc, rotor tooth-chamfering, different length of air gap, and these methods are based on the techniques for PM machines to reduce torque ripple. The influence of the proposed methods on torque ripple is examined by using Finite Element Analysis (FEA) and it is found that the torque ripple can be reduced significantly.