Fault ride-through capability enhancement based on flywheel energy storage system for wind farms connected via VSC high voltage DC transmission

This paper proposes a recovery strategy for wind energy-fed voltage source converter high voltage DC transmission systems, capable of maintaining power balance between the AC and DC sides during different AC faults. This prevents the DC link voltage rise as a result of trapped energy. This reduces the voltage and current stresses on the switching devices. Also, the strategy ensures the converters remain connected to the AC network to provide the necessary voltage support, within the converter reactive power capability. The recovery strategy is implemented by introducing a flywheel energy storage system based on induction machine in parallel with the grid side inverter. Due to the parallel combination of the grid side inverter and flywheel induction machine (FW-IM), the trapped energy in the DC link during AC faults can be eliminated; as a result of finding another path for the power of the wind turbines during AC faults. To illustrate the feasibility of the proposed HVDC system, this paper assesses its dynamic performance during steady-state and network alterations, including its response to AC side faults.