Phase current reconstruction of three-level Neutral-Point-Clamped(NPC) inverter with a neutral shunt resistor

Abstract

This paper presents the reconstruction method of three phase current for AC motor by inserting a shunt resistor at the neutral point of a 3-level Neutral Point Clamped(NPC) inverter. To precisely acquire the phase currents from the shunt resistor, the switching time of the effective voltage vectors needs to secure the minimum time. For this reason, the direct measurement of the accurate phase current from the shunt resistor is impossible without using a special measurement algorithm. In the conventional methods, the phase currents are reconstructed by shifting the switching pattern of the space vector pulse width modulation (SVPWM) or injecting voltage. However, these methods cause a high Total Harmonic Distortion (THD) in the reconstructed phase current. To reduce the THD, this paper proposes the current reconstruction method using the estimated phase current and partitioning the current-unmeasurable area for the minimum voltage injection. The effectiveness of the proposed methods is verified through the simulation. The simulation is performed on a SPMSM (Surface mounted Permanent Magnet Synchronous Motor) of the washing machine.