Impedance modeling and control of STATCOM for damping renewable energy system resonance

Electrical resonance with the grid is an increasingly common problem for wind turbines and PV inverters, especially those connected to a weak grid. Such resonance problems can usually be solved by modifying turbine or PV inverter control to reshape its output impedance. There are, however, situations where this may not be effective or not feasible at all due to e.g. limitations in turbine design or complexity of the system. This paper proposes the use of STATCOM to damp system resonance. The idea is to shape STATCOM output impedance through active control in such a way that adds damping in the frequency range of system resonance. Modeling of STATCOM impedance will be presented first to support this method. The effects of STATCOM on system resonance will be analyzed to guide the design of its control to achieve the required damping effects. The method extends the existing application of STATCOM in damping low-frequency oscillation in conventional power systems, and is different from harmonic filtering functions of STATCOM proposed recently in the literature by focusing on impedances and resonances that are the root cause of harmonics. Detailed simulation of a representative wind power plant will be presented to demonstrate the proposed concept.