As a submersible permanent magnet synchronous motor (SPMSM) must function in downhole high temperature crude oil for long periods of time, the accurate prediction of its temperature rise is crucial to improve the stability of the motor. However, the analysis of its temperature field involves multiple physical fields, such as the electric field, the magnetic field, the fluid field and so on, and it is difficult to calculate accurately. Motor loss is usually loaded as a fixed value when calculating the temperature field, while in reality, the loss always changes with temperature. Therefore, the calculation of temperature is inaccurate using this one-way coupled method. In this paper, the relationship between loss and temperature is investigated and an electromagnetic-thermal fluid multi-physics two-way coupled analysis method suitable for SPMSM is proposed. The loss can be loaded as a variable by this new two-way coupled method, which significantly improves the temperature calculation accuracy. In order to prove the feasibility of the two-way coupled method, experiments based of a prototype of high torque and low speed SPMSM and cavity pump are conducted with the fiber Bragg grating (FBG) sensor measuring SPMSM temperature. Finally, the multi-physics two-way coupled method proposed in this paper is proven to be rational and feasible in the analysis of the SPMSM temperature rise.

With the development of global deepwater oil and gas and offshore wind power resources, there is an increasing demand for ultra-deep water pile hammers (UDPH). In this paper, a permanent magnet synchronous motor (PMSM) with oil fill is proposed for UDPH on the basis of underwater 2500 m depth and 450 kJ impact energy requirements. First, the rated parameters of the PMSM are calculated based on the power required by hydraulic pumps, and then, the method of combining empirical formulas and path algorithms is used to complete the electromagnetic scheme design. Second, finite element analysis of the electromagnetic field is carried out by Maxwell under both no-load and load conditions to verify the rationality of the PMSM. Furthermore, aiming at improving efficiency and reducing cogging, parameter optimization is carried out by a robust parameter optimization design method, and the optimal parameter scheme of the PMSM is obtained. In addition, loss analysis and temperature field coupling calculations of the optimized PMSM are conducted to verify that the temperature of this motor can meet the requirements under different working conditions. Finally, a comparative analysis is conducted between the proposed PMSM and the three-phase asynchronous motor used in the underwater 2,500 m-450 kJ UDPH. The results indicate that the new PMSM introduced in this paper demonstrates significant advantages in terms of weight, volume, and efficiency; moreover, the new PMSM is reasonable and more suitable for UDPH. Therefore, the PMSM proposed in this paper is reasonable and can provide a theoretical basis for improving the traditional UDPH.