Abstract：Electrical resonance with the grid is an increasingly common problem for wind farms involving cascaded H-bridge static var generator (SVG) in a regional large-scale renewable energy system. To analyze and solve such resonance problems, it is necessary to fully understand the frequency-domain behavior of cascaded H-bridge SVG. Because the existing harmonic linearization method has complicated linearization process and ignores the harmonic influence when establishing the module multilevel converter (MMC) model, a double-harmonic linearization method, which only considers the effects of the fundamental and second harmonics, was proposed to develop the sequence impedance model of cascaded H-bridge SVG. This method considers the harmonic effects of each variables in power and control circuits, and introduces a matrix formulation to simplify the linearization process and sequence impedance models. In addition, to improve the accuracy of models, the effects of overall module capacitor voltage control were considered in small-signal modeling. The developed sequence impedance models were verified by the specific converter circuit simulation and the experiment based on a scaled-down prototype. The influencing factors of frequency coupling and the design of sub-module capacitor were analyzed and discussed.
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2019, Vol. 34 
