Research On Paralleled Inverters Fed Permanent Magnet Synchronous Motor And Related Modulation Strategy

In low-voltage high-current occasions like ship electric propulsion,paralleled inverters can effectively increase the capacity of the system and improve the reliability of the system.So it is an effective solution in low-voltage high-current occasions.In this paper,circulation problem and related modulation strstegy under the paralleled inverters with the load of permanent magnet synchronous motor are studied.Aiming at the problem of circulation,the mechanism of circulation is analyzed respectively under independent bus paralleled inverters and under common bus paralleled inverters.The excitation sources of circulation are classified,and the harmonic components of circulation are analyzed respectively with carrier synchronization and carrier phase shift.When operated in parallel with independent bus,circulation is caused by DC side capacitance in different phases between inverters under a special switching state.Aiming at the problem of circulation under carrier phase shift,a method for the time-averaged distribution of circulation by pulse phase shift is proposed,and its feasibility is analyzed.When operated in parallel with common bus,from the “micro” point of view,Zero Sequence Circulating Current(ZSCC)is caused by all of the same phase circulation,and a two-level simplified suppression algorithm under carrier phase shift is proposed.Furthermore,under carrier phase shift,a three-level simplified suppression algorithm which can simultaneously suppress ZSCC and Common Mode Voltage(CMV)is proposed.From the “macro” point of view,ZSCC is caused by the difference in zero sequence voltage between inverters,and its suppression measures are given.To the mechanism of ZSCC as an opportunity,the intrinsic equivalence relationship between Sinusoidal Pulse Width Modulation(SPWM)and Space Vector Pulse Width Modulation(SVPWM)is explored.Aiming at the problem of neutral-point potential unbalance under three-level common bus paralleled inverters,the modulation wave decomposition method is introduced,which can control neutral-point potential under the premise of suppressing ZSCC.Aiming at the problem of large CMV in motor system,a three-level CMV suppression method is proposed.Verified by simulations and related experiments,the intrinsic equivalence relationship between SPWM and SVPWM is obtained;ZSCC under common bus is effectively suppressed;neutral-point potential under three-level common bus paralleled inverters can be effectively controlled;three-level CMV is effectively suppressed.