Synchronous switching of non-line-start permanent magnet synchronous machines between inverter and grid drives

Non-Line-Start Permanent Magnet Synchronous Machines (NLSPMSMs) have no damping windings in the rotor and hence cannot start themselves directly to the grid. For ap-plications where a constant speed drive is preferred, NLSPMSMs are required to be driven by the grid. Therefore, inverter aided soft startup and soft stop of such kind of motors are necessary. In this paper, a modified method of switching NLSPMSMs from inverter to grid mode drives, which is named as “forward switching” is proposed by introducing an additional V/f control after phase tracking in order to achieve voltage magnitude tracking. Furthermore, the method of switching the NLSPMSMs from grid to inverter drives, which is named as backward switching is also proposed. No position sensors are used, and the extended ElectroMotive Force (EMF) based position sensorless control algorithm is adopted during inverter drive. Experiments on an 18.5 kW NLSPMSM prototype are carried out to verify the effectiveness of the proposed methods.