Submersible permanent-magnet synchronous machine with a stainless core and unequal teeth widths = Maquina síncrona de imán permanente sumergible con núcleo de acero inoxidable y anchos de dientes desiguales.

Abstract

In recent years, permanent magnet synchronous machines (PMSM) have gained popularity owing to their excellent performance compared with other kinds of electrical machines in numerous applications. Furthermore, advances in power electronics, digital signal processing, control schemes, and the development of electrical materials have contributed to the rapid development of PMSMs. Nowadays, designers of electrical machines investigate the PMSM to improve its performance and reliability by reducing the amount of materials while minimizing its cost. In this doctoral dissertation, a study is presented to improve the performance of a PMSM using asymmetric characteristics. The study aims to employ unequal teeth widths without changing the size of the machine to increase the winding factor and thus be able to increase the value of the induced voltage and the electromagnetic torque. The exploitation of this asymmetry is possible because of the tooth-coil winding (TCW), which has multiple advantages from both the electromagnetic and the manufacturing point of view. A submersible application consists of a scenario where the devices are operated in underwater environments, such as harvesting marine energy or a water pumping system. These applications require an electrical machine to be corrosion resistant, which makes its design and manufacture challenging. Currently, there are various submersible machines. The best known is the canned PMSM, whose stator and rotor are protected with cans, and whose active parts are made of traditional electrical materials, enabling water to flow through the air gap. However, a completely encapsulated traditional stator is a complex structure and has low heat transfer characteristics. In this doctoral dissertation, a stainless core submersible PMSM is presented as an alternative to the conventional submersible machine. The machine under study consists of a fully stainless stator, and a rotor-surface permanent magnet rotor, protected by a fiberglass cover. Ferritic stainless steel is used as stator core material, and the winding is made of polyvinyl chloride (PVC) insulated solid-conductor wire. To test the asymmetric characteristic of the stator and verify the functionality of the proposed submersible machine, a 1.7 kW, 80 r/min, 24-slot 20-pole fully submersible PMSM was simulated, constructed, and verified in a water tank and in a lake with fresh water. The analytical and the finite element method (FEM) results showed that it was possible to improve the machine performance by employing unequal teeth. This improvement was reflected in an 8% increase in the value of the induced voltage compared with the symmetric machine. However, the use of ferritic stainless steel showed that the stator core losses correspond to 40% of the total losses of the machine, indicating that the efficiency was 74% at the rated load. Despite this, the machine turned out to be functional.