Study on the influence of the number of pole pairs on torque of synchronous reluctance machines

At present, permanent magnet synchronous machines(PMSMs) are widely used. Although PMSMs have the advantages of high torque density, high power density and high efficiency, the use of permanent magnets increases the cost and processing difficulty of PMSMs. Synchronous reluctance machines(SynRMs) are a competitive alternative to PMSMs with their low cost and high reliability. However, due to the lack of permanent magnets,the torque density of SynRMs is less than that of PMSMs under the same conditions. This is a major disadvantage of SynRMs and needs to be further explored. Many factors affect the torque of the SynRMs, and the number of pole pairs is the first consideration when designing machines. This paper proposes a equation for calculating the inductance of d-axis , q-axis and torque based on the simplified magnetic circuit model and analyzes the influence of the number of pole pairs on the inductance and torque theoretically. It is found that with the increase of the number of pole pairs, the inductance of d-axis, the inductance of q-axis and the torque of SynRMs decrease. Finally, the relationship between the number of pole pairs and torque is verified by Finite Element Method (FEM), and also explains why the number of pole pairs of most SynRMs is 2.