Simple method for measuring output impedance of a three-phase inverter in dq-domain

This paper introduces a simple method to measure the output impedance of a three-phase grid-connected inverter in dq-domain. The impedance measurements are most often used for model verification purposes but they can be also utilized to study impedance-based interactions between three-phase converters and the utility grid. Therefore, the methods to model and measure three-phase impedances can provide to the inverter manufacturers valuable information about their products. Implementation of the proposed method requires a three-phase voltage source, a digital signal processor, and a frequency response analyzer which are equipment typically available in most power electronic laboratories. The algorithms used in the method are explained, and the performance of the method is verified by means of frequency response measurements from a small-scale laboratory prototype.