Soft start and synchronous switching of permanent magnet synchronous machines without damping windings

Abstract

This paper proposes the extending application of permanent magnet synchronous machines (PMSMs) without damping windings, or non-line-start PMSMs (NLSPMSMs) to achieve effective soft start and synchronous switching from inverter drive to grid drive. The system electromechanical model during switching is deduced, and numerical analysis is adopted to verify the stability under grid drive. For the control strategy, two phase lock loops (PLLs) are adopted to obtain the phases of gird and inverter voltages. Then speed and current regulation is exerted to minimize the difference between inverter output and grid. Experiment results show that the 37kW NLSPMSM prototype can be safely switched to grid drive and robust to large load variation. Tested waveforms are coincident with numerical analysis.