Sequence impedance measurement of three-phase inverters using a parallel structure

This paper proposes a method of sequence impedance measurement of three-phase inverters by using a parallel structure with another inverter as the measurement unit, in order to apply the impedance-based stability analysis of power converter systems. The paralleled inverter not only injects small-signal perturbations but also creates the desired operating conditions for the inverter under test. The measurement setup is simple, since no additional AC source or load banks are needed. First, the sequence impedance model of three-phase inverters is described. Then the measurement setup and injection method are presented. Zero-sequence circulating current reduction and open-loop control with voltage compensation strategies guarantee the measurement accuracy. The agreement between the theoretical analysis and the measurement results in both simulation and experiments verifies the effectiveness of the proposed method.