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A novel online grid impedance measurement method based on injecting pulses designed in frequency-domain

Grid-connected converter systems could be unstable due to the interactions among power converters and/or sources/loads. Impedance-based stability analysis is an effective approach to predict system stability and provide specifications for power converter design. Therefore online grid impedance measurement is significant. This paper proposes a novel online grid impedance measurement method for grid-connected converter systems. The novel method is based on injecting an adequate pulse through the converter to the grid, and does not require any external injecting sources. While traditional methods are based on injecting pulses designed in time-domain, this method is based on injecting pulses designed in frequency-domain. Compared with traditional methods, the novel method reduces distortion on operating waveforms and ensures accuracy at each frequency point. Simulation and experiment demonstrate the effectiveness of the novel method.