Advanced modeling and control of voltage source converters with LCL filters

In this chapter, various mathematical models of the voltage source converters with LCL filters are developed in the balanced/unbalanced three-phase power systems, including the commonly used moving averaged model and coordinate transformation technique, the generalized averaging model, and the harmonic state space model for unbalanced grid analysis. Afterward, the decoupling technique using complex variables is introduced to control the alternative grid current. Especially, focusing on the resonance phenomenon of LCL filter, different damping control methods are applied to suppress the peaky magnitude response and to soften the stepped phase transition. Next, a brief introduction of the positive-and negative-sequence current control under unbalanced grid voltages is presented. Finally, an impedance-based stability analysis method is explained. In each part, simulation results are shown to validate the theoretical analysis.