Phase current reconstruction with single DC-link current sensor for six-step operation in three phase inverter

This paper proposes the current reconstruction method in the single current-shunt inverter (SCSI) during the six-step modulation. Since the voltage vectors of the six-step operation are placed in the immeasurable areas of SCSI, the phase current cannot be reconstructed in the conventional researches. However, by changing the position of the sampling period, the current signal can be reconstructed even in the six-step operation. Here, the variable time step control is implemented. To reconstruct the phase currents, the shunt currents are sampled at 12 times for one fundamental period. But with this method, the two types of the sampling errors are incurred. One is caused by harmonic components of d- and q-axis currents in six-step operation and the other is caused by not measuring the two phase currents at the same time. The compensation methods for the error are developed; model based error estimator. The feasibility of the proposed method has been verified by experiments.