Single shunt current sensing technique in three-level PWM inverter

This paper describes how to reconstruct the three phase current using the only single shunt in a three level Neutral-Point-Clamped (NPC) PWM inverter. The area where phase currents are measurable is analyzed and the reconstruction method is proposed in three-level PWM inverter. According to the characteristics of the immeasurable areas in voltage plane, the voltage injection method, which relocates the original voltage reference in the immeasurable area to that in a measurable area in the voltage plane, has been devised. For this relocation, the compensating voltage is added and subtracted to the voltage reference in a switching period. And a control algorithm to inject the compensating voltage is also proposed. The proposed reconstruction of the phase currents in the single shunt sensing inverter has been tested by the computer simulation at various reference voltages, being in or passing in the immeasurable area. The results show the satisfactory measurement of the phase currents in overall operating conditions.