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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.

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.