Cascaded High-Voltage Direct-Hanging Energy Storage and Energy Dissipation Device Integrated Collaborative Fault Ride-Through and Control Method

With the escalating proportion of renewable energy sources such as offshore wind and solar PV in global energy portfolios, their inherent intermittency and variability pose significant challenges to the stability and power balance of flexible DC transmission systems. By deploying energy storage systems such as pumped hydro storage and electrochemical energy storage, the objectives of power quality management and system stability can be achieved. To address these issues, this paper proposes a cascaded high-voltage direct-connected energy storage and dissipation integrated device, featuring a modular multilevel topology that enables collaborative fault ride-through control and its engineering solutions, systems and control strategies in the application field are explored. The DC energy storage device proposed in this work exhibits favorable battery operating conditions, requires fewer batteries, and has a low cost. The proposed system effectively reduces battery capacity requirements by approximately 50% compared to standalone energy storage systems, and decreases dissipation device capacity by 50% relative to traditional centralized DC dissipation schemes. The topological structure and working principle of the DC direct-connected energy storage and consumption device are analyzed. The number and parameters of the cascaded sub-modules are designed. Based on the carrier phase-shifted modulation strategy, a control model is built for power transmission and allocation. The coordinated control strategy dynamically allocates surplus power between storage and dissipation modules based on DC voltage levels and battery SOC, achieving response times below 15 ms. Simulation results on MATLAB/SIMULINK and hardware-in-the-loop platforms validate the feasibility and effectiveness of the proposed design under various fault conditions, including DC pole-to-pole faults, monopole grounding, and AC side short circuits. The system maintains DC voltage stability, ensures battery SOC balance, and enhances the economic efficiency and reliability of flexible HVDC systems.