Performance of line-start single phase permanent magnet motors for domestic applications

Many domestic appliances require low-power motors operating at essentially constant speed to drive pumps and fans. Line-start permanent-magnet motors can provide an alternative to the conventional single-phase induction motor in the fractional kW range. These motors employ a 2-pole magnet rotor and a simple skeleton stator construction with a bobbin coil for ease of manufacture. The motor can run synchronously in either direction and relies upon an impulse torque to start. The paper describes a combined circuit/finite-element approach that employs the power of the FE approach to accommodate the complex geometry and magnetic saturation and the simplicity of the circuit method for time-stepping transient solutions. This approach can be formulated in a manner that keeps computational solution times to a reasonable level, The analytical model is used to illustrate the run-up and steady-state performance of a commercial domestic pump motor with experimental measurements included to provide verification of the approach. The paper investigates the influence of certain key design features on the performance of the motor and in particular the direction of rotation.