A two-step analytic design and optimization of small variable speed PMSMs for home appliances

This paper presents the design of an inner rotor Permanent Magnet (PM) motor using a two-step approach. The first step consists of retrieving the basic geometric and electric constants using a combination of both an analytic and a multi-objective Genetic Algorithm (GA). This technique allows the most efficient and cheapest motor for a certain type of home appliances application to be found when harmonics are neglected during the optimization design. This assumption implies that iron losses are only relevant in the stator domains. The peculiarity of the optimization of the motor is the fact that the most efficient operating point is located at one tenth of the maximum load of the electric motor. The second step consists of comparing the resulting optimized motor using Finite Element Analysis. This step is crucial to accurately compare the efficiency of the resulting drive with the analytic results. The advantage of using this tool is that we can also include the effect of the different space harmonics in the efficiency computation. These harmonics rotate at a different speed than the rotor and can produce additional losses in the rotor's iron parts. The agreement between the results of the two-step analysis infers that the effect of the space harmonics is not relevant for this drive. The decay of efficiency due to these space harmonics is in the order of 0.05%.