Fast Frequency Support Strategy for a Novel DC Transmission System of Renewable Energy Based on Grid‐Forming Energy Storage

ABSTRACT

The DC collection and transmission scheme based on diode rectifier units (DRUs) has strong potential for large‐scale and low‐cost renewable energy delivery. However, its uncontrollable nature may introduce frequency stability risks to 100% renewable power plants. This paper focuses on a 100% renewable power plant equipped with a virtual synchronous generator (VSG)‐based grid‐forming energy storage (ES) and connected to a DRU converter station. The objective is to mitigate frequency instability by improving the control strategy of the ES system. To address the rapid frequency drop under severe disturbances, a novel fast frequency support strategy is proposed. The main contributions are as follows: (1) a dual‐layer model predictive control (MPC) framework that rapidly adjusts the total output power of the ES system for frequency support and (2) a state‐of‐charge (SoC) balancing mechanism that coordinates multiple internal ES units. Simulation results show that the proposed strategy improves the frequency response speed, reduces the frequency deviation and extends the effective support time of the ES system, thereby enhancing the frequency stability of the 100% renewable power plant.