Study on Re-Energization Capability of a Hybrid Windfarm under a Microgrid-based Restoration Strategy

Under a microgrid based (bottom-up) restoration strategy, considering a disaster related outage, the local generation is required to energize and supply the unaffected part of the network. Considering 100% renewable generation, only hydro based generation systems, if well equipped, can be able to blackstart and re-energize the network. Wind Energy Conversion Systems (WECSs) have been restricted to the latter stages of restoration due to their source intermittency and non-dispatchability and in order for them to participate in the initial restoration stages, voltage and frequency support auxiliary devices are required. This paper investigates the capability of a hybrid windfarm to participate in the initial stages of restoration similar to a conventional blackstart unit: Re-energization of the various network components and pick up of load. The auxiliary equipment in this case is a dump load to absorb excess power produced by the windfarm and a synchronous condenser to provide a stable voltage reference required for normal operation of the WECS. Firstly, the nominal range of operation is determined with an additional pitch control mode linking the dump load power to individual WECSs introduced for frequency control. Flicker and harmonics are investigated in determination of the hosting capacity. Studies are undertaken to investigate energization of transformers, underground cables, overhead lines and other non-blackstart units (including other WECSs). Consideration is given to Type 1 and Type 3 WECSs to investigate the capability of a non-inverter and inverter based WECS. MATLAB/Simulink has been used as the simulation platform due to its modelling flexibility.