Low-Order Response Modeling for Wind Farm-MTDC Participating in Primary Frequency Controls

A low-order and system-level response model for wind farms (WFs) and voltage source converter based high-voltage direct current (VSC-HVDC) participating in primary frequency regulation using virtual synchronous machine (VSM) control is developed and validated. The VSM control with virtual power system stabilizer (PSS) function is presented being applicable to all multi-terminal HVDC (MTDC) VSCs. In this context, a general low-order response model (LRM) for presenting the WF-MTDC participating in the frequency control of main AC system is readily established. This modeling method derives transfer function based block diagram offering an illustrative insight into dynamic interaction between AC frequencies and DC voltages. Such a model can also provide a convenient way performing control system designing and parameter tuning. As a paradigm, LRM-based linear quadratic regulation optimization is applied to obtain the droop and damping gains for feasible frequency regulation. The effectiveness of the LRM method is verified through comparisons of the simulation results obtained from different models, controller designs, and parameter tuning approaches, which are all performed on a five-terminal VSC-HVDC connecting WF-side and main AC systems.