Analytical Validation of Dual-Pole Permanent Magnet Machine Theory

Dual-pole line start permanent magnet (PM) synchronous machine is an emerging technology for replacing induction machines in two-speed applications, such as air coolers, compressors, and pumps. The machine structure includes two magnetic pole numbers on a single rotor layout and two separate sets of stator windings. Due to the unconventional and complex rotor structure, to this date, the design and analysis have solely been based on finite element (FE) method. This article aims to analytically validate the theory and the overall functionality of dual-pole PM machines in both steady state and transient regime. For this propose, a detailed magnetic circuit model is developed for calculating the PM flux distribution and the back electromotive force waveform. However, a single magnetic circuit cannot adequately represent the flux flow of the armature reaction, since the path of the armature flux is a function of rotor position. This is even more challenging in dual-pole machines, where the armature flux is originated from two different sets of stator winding. To avoid the necessity of having multiple magnetic circuits, the concept of magnetic islands is employed to capture the motor response at the loaded condition. For verification, analytical results are all supported via FE, and partially with experimental tests.