Small-signal impedance identification of three-phase diode rectifier with multi-tone injection

AC and DC impedances of power converters are used for stability analysis of modern power systems at AC and DC interfaces. The basic idea for impedance extraction is AC sweep approach with sinusoidal signal injection, here denoted as single-tone. However, the approach is time consuming because the time-domain measurement will run many times. Therefore the approach of multi-tone signal injection is implemented in which multiple frequency responses could be measured in only one time-domain measurement. In linear loads, the multi-tone approach could give the same results with single-tone approach because superposition holds for linear system. For three-phase nonlinear loads, different results are observed from multi-tone and single-tone approach. In this paper, 6-pulse Diode Bridge Rectifier is studied to analyze the reason of result difference. An algorithm is proposed to improve the multi-tone approach and avoid result differences.