Nonlinear performance characteristics of 3-phase flux-switching permanent magnet motors (FSPM) are overviewed. These machines show advantages of a robust rotor structure and a high energy density. Research on the FSPM is predominated by topics such as modeling and machine comparison, with little emphasis given on its performance and limits. Performance characteristics include phase flux linkage, phase torque, and phase inductance. In the paper, this analysis is done by a cross-correlation of rotor position and armature current. Due to the high amount of processed data, which cannot be handled analytically within an acceptable time period, a multistatic 2D finite element model (FEM) is used. For generalization, the most commonly discussed FSPM topology, 12/10 FSPM, is chosen. Limitations on the motor performance due to the saturation are discussed on each characteristic. Additionally, a focused overview is given on energy conversion loops and

Nonlinear magnetic behaviour is a common phenomenon in electromechanical systems, that are pushing the boundaries. An example of such a system is flux-switching permanent magnet (FSPM) motor. This motor provides significant advantages such as a robust rotor structure, high speed capability, and high energy density. In the FSPM, the dominant nonlinear behaviour is a result of rotor position and armature current variations [

Common practice shows that to account for the nonlinear magnetic behaviour, analytical models make use of external data obtained either by numerical models or by measurements [

In the limited amount of publications regarding the performance analysis of the FSPM, the general focus is set on the comparison with machines such as brushless AC/DC and double salient machines [

A 3D illustration of the FSPM with 12 stator poles and 10 rotor teeth.

The finite element model (FEM) of the 12/10 FSPM is created by the Flux software. The geometrical model with the mesh elements are given in Figure

FEM model of the 12/10 FSPM used in the calculations.

2D FEM calculations of the FSPM are based on the vector magnetic potential,

Definitions of the

(a) Phase flux linkage with increasing current, (b) nonlinear energy conversion loops of the FSPM.

Up to four times the rated value

By applying the Maxwell Stress Tensor (MST) in the middle of the airgap, the maximum torque capability of the machine is calculated as a function of the phase current. In Figure

(a) Static torque calculations with increasing current, (b) nominal output torque varying with armature current.

As the armature current increases, torque versus position in Figure

The stator back iron is decomposed into

Effective

Element no. | Relative permeability |
Flux density |
||||
---|---|---|---|---|---|---|

0 A | 10 A | 100 A | 0 A | 10 A | 100 A | |

1 | 5016 | 4392 | 14 | 0.53 | 0.4 | 2.25 |

2 | 4388 | 4536 | 553 | 0.2 | 0.32 | 1.66 |

3 | 5093 | 4610 | 213 | 0.5 | 0.37 | 1.8 |

4 | 4937 | 4945 | 415 | 0.78 | 0.53 | 1.7 |

5 | 3537 | 4564 | 2156 | 1.16 | 0.88 | 1.42 |

6 | 2128 | 2966 | 4804 | 1.5 | 1.27 | 0.88 |

7 | 5256 | 4379 | 24 | 0.64 | 0.45 | 2.18 |

8 | 5143 | 4738 | 2329 | 0.51 | 0.36 | 1.1 |

9 | 4987 | 4636 | 529 | 0.43 | 0.39 | 1.67 |

10 | 4344 | 4879 | 73 | 0.34 | 0.53 | 2 |

11 | 4909 | 5121 | 27 | 0.53 | 0.8 | 2.1 |

12 | 5016 | 4561 | 81 | 0.79 | 1 | 2 |

Considering the simulation time, cogging torque

(a) Cogging torque calculations on one stator period and (b) on the full machine.

For the study of cogging torque investigation, two different soft magnetic materials are used with the magnetic characteristics given in Figures

(a)

The second material M400–50 A in Figures

In a saturated grid element (ele. 1) and a nonsaturated one (ele. 6), both materials are used to calculate the effective flux density levels in the stator back iron. Results in Figure

For field weakening, it is important to know the torque-commutation angle characteristic. To get this characteristic, the rotor is fixed at the

Torque versus commutation angle with rotor fixed at

In literature, there are several mathematical definitions for inductances [

Static inductance of a phase coil gives the linear relationship between the total flux

To obtain the incremental inductance

For linear magnetic materials, both methods yield identical results. However in the nonlinear region, the cross-coupling (cross-saturation) greatly affects

(a) Incremental inductance, (b)

Flux switching machines have similar phase flux linkage as the switched reluctance machines (SRM), however with the advantage of being bipolar. The incremental inductance at

Based on the

With their high torque density and robust and simple rotor structures, FSPMs have a significant application potential among PM machines. This paper investigated FSPM’s nonlinear magnetic behaviour in a general overview of the performance characteristics. Cross-correlating the armature current and rotor position gave information on the capabilities of the FSPM, with special emphasis on energy conversion loops, cogging torque, and

Findings showed a linear overloading capability of four times the rated current, however with specific impact on phase inductances. New

See Table

FSPM size and parameters.

Number of phases | 3 |

Rotor pole number | 10 |

Stator pole number | 12 |

Frame size | 90 mm |

Stator inner diameter | 55 mm |

Shaft diameter | 20 mm |

Active stack length | 25 mm |

Airgap | 0.5 mm |

Number of turns per phase | 72 |

Remanent flux density of permanent magnet | 1.2 T |

Relative permeability of permanent magnet | 1.05 |

Phase current (rms) | 10 A |

Rated torque | 2.2 Nm |

Rated speed | 4400 rpm |

Power | ~1 kW |

Rated phase current

Phase flux linkage

Incremental phase inductance

Mechanical rotor position

Armature current

Commutation angle

Torque

Cogging torque

Relative permeability;

Subscripts for direct-quadrature-axes quantities;

Subscript for stator back-iron period.