Modeling and testing of line start permanent magnet motors

Abstract: This licentiate thesis describes the modeling and measurements performed with the aim of developing design guidelines for Line Start Permanent Magnet Synchronous Motors, LSPMSMs. LSPMSMs can offer higher efficiency than standard induction motors used in the industry today, especially for small motor sizes. The increase in efficiency results in lower environmental impact and reduced electricity cost. The LSPMSM has, however, several drawbacks, among the most important is the reduced starting capability compared to induction motors. Furthermore, the rotor construction is complex and the added cost of magnet material makes the LSPMSM a comparably expensive motor type. The design of a LSPMSM is a trade-off between starting capability and steady state performance. The thesis discusses these trade-offs and the models that can be used as a basis for design and optimization. The models make use of different motor parameters, and a number of measurement methods for measuring these parameters are described and compared. Among these is a step response adapted measurement method that provides most of the parameters of interest. The development and setup of a brake bench for measuring both start-up and steady state performance is presented. Furthermore the start-up behavior and steady-state performance is calculated using measured parameters. The calculated performance is compared to measured performance and found to correlate well for nominal operating conditions. Thus, design guidelines can be based on the models proposed.