Direct grid connection of permanent magnet synchronus motor using auxiliary inverter and matrix converter with transition control

This paper discusses a direct grid connection system for the permanent magnet synchronous motor (PMSM). It is difficult to connect PMSM to the power grid directly due to the resonance between a synchronous reactance and the inertia moment. In order to solve this problem, the direct grid connection system which consists of an auxiliary inverter of small capacity and a matrix converter is proposed for PMSM. In the proposed system, a torque vibration caused by the resonance is suppressed by the auxiliary inverter and auxiliary windings in PMSM. Moreover, the matrix converter is used as a starter which accelerates PMSM up to synchronous speed of a power grid. In the direct grid connection mode, the matrix converter is matches voltage for PMSM with the grid voltage. Besides, the rush current is suppressed by the transition control which consists of an output voltage phase control mode and an output voltage amplitude control mode. In the direct grid connection mode, the matrix converter has no switching operation. Thus, the converter loss is remarkably low in a standby mode due to no switching loss. Additionally, the validity of the proposed system is demonstrated in the simulation and experimental results. From the results, the rush currents is suppressed to 2 A (18% of the rated current) by the transition control and the damping control when the PMSM is connected to the power grid.