Enhanced Frequency Support of MMC-MTDC Systems with Offshore Wind Plants Integration

With the increasing penetration of renewable energy generation in the power grid, there have been several actual cases of high-voltage direct-current (HVDC) systems replacing conventional high-voltage AC power transmission systems for long-distance power transmission. The widely used full-scale converter (FSC) wind turbines (type 4), unlike the traditional synchronous generators, cannot provide inertial constant support for system frequency stability owing to their special structural problem. Therefore, a control strategy that provides virtual inertia for a system using an HVDC inverter is proposed. Currently, this method is mostly used in a single HVDC transmission line. This study investigates the frequency stability of a modular multilevel converter-based multi-terminal HVDC combined with offshore wind power plants. An enhanced virtual inertia compensation strategy is proposed to improve the frequency stability of onshore AC systems. This study uses the multi-terminal HVDC network of the CIGRE benchmark to build a power grid model and simulate AC systems with different levels of robustness. The simulation results prove the effectiveness of the reinforcement method.