Novel Doubly Salient Stator Slot Permanent Magnet Electrical Machines

It is well known that the torque density in electrical machines is limited by magnetic saturation and thermal constraints on the winding insulation and permanent magnets (PMs). In particular, doubly salient electrically-excited machines with the armature and DC windings on the stator, for example, the variable-flux machine (VFM), have (a) limited stator slot area for both windings, (b) severe magnetic saturation due to the DC excitation, and (c) negligible reluctance torque, and may exhibit high copper loss and high magnetic saturation. A novel method to alleviate magnetic saturation in the stator of VFMs is proposed. It is achieved by pre-magnetizing the stator core using PMs placed in the stator slots. The PM effects and performance improvements are analyzed by the finite element method based on the frozen permeability (FP) method. The developed novel VFM with PMs is a hybrid excited stator slot PM (HSSPM) machine. The basic operation principle and the electromagnetic performance with different stator and rotor pole combinations having double (all pole wound concentrated windings) and single layer (alternate pole wound concentrated windings) windings are investigated. HSSPM machines have improved electromagnetic performance and also retain the good flux regulation capability of VFMs. They can also be operated without the DC excitation, i.e. only with the armature and PM excitation. Thus, a new machine configuration – stator slot PM machine (SSPM) is further developed and investigated in terms of the influence of stator/rotor pole combinations and double and single layer windings. The newly developed SSPM machine also has the potential for fail-safe capability in the event of drive faults, and in addition, the requirements on the DC inverter and controller can be eliminated. The finite element predicted electromagnetic performances of HSSPM and SSPM machines are experimentally validated. Finally, the PM- and iron losses in HSSPM and SSPM machines having different stator/rotor pole combinations with single and double layer windings and their demagnetization ratio are analyzed. The influence of leading design parameters on their machine losses and efficiency is further investigated and their electromagnetic performance compared.