Multiple Decoupling Current Control Strategies for LCL Type Grid-Connected Converters Based on Complex Vectors under Low Switching Frequencies

In medium-voltage and high-voltage high-power converters, the switching devices need to operate at a low switching frequency to reduce power loss and increase the power capacity. This increases the delay of the signal sampling and PWM. It also makes the cross-couplings of the d-q current components more severe. In addition, the LCL filter has three cross-coupling loops and is prone to resonance. In order to solve these problems, this paper establishes a complex vector model of an LCL type grid-connected converter. Based on this model, two multiple decoupling current control strategies with passive damping / notch damping are proposed for the LCL type grid-connected converter. The proposed strategies can effectively eliminate the cross-couplings of the converter, achieve independent control of the d-q current components, expand the stable region and suppress the resonance of the LCL filter. Simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed strategies.