A Passivity-Based Stability Analysis of the Active Damping Technique in the Offshore Wind Farm Applications

The LCL-based filter has been widely applied to mitigate the size of the inductor in the high-power converter, but it usually leads to resonance in the system. Therefore, an active damping technique based on the virtual resistor is provided in this paper for the LCL-filter system. The literature papers only suppressed the resonance of the LCL-filter and focused on the stability of the internal current control loop with an inductive grid impedance. Therefore, these previous stability analysis methods cannot be suitable for offshore wind farm applications due to the multiple resonance frequency characteristic of the transmission cable and multiparalleled converters. Therefore, this paper analyzes the control stability with both of the internal resonance (LCL-filter) and external resonance (between the grid impedance and current controller). Besides, the behavior of multiparalleled converter and the multiple resonance frequency of long transmission cable are discussed and analyzed for the offshore wind farm applications. Finally, the laboratory and simulation results are for the proposed met hod verification.