Flow Batteries for Enhancing Wind Power Integration

Providing frequency response capability from wind farms is technically feasible, but relies on spilling the wind. Wind intermittency and the planned expansion in offshore wind power in the U. K. are expected to lead to increased requirements for frequency response capability. This may necessitate times where wind farms operate in a frequency sensitive manner and output only a proportion of the available power. Compensating for spilt wind energy would likely lead to increased costs of balancing the power system. This paper highlights the alternative to spilling wind to provide frequency response capability: using wind farm level energy storage. The Vanadium Redox Flow Battery is shown to be capable of providing this and other benefits to the wind farm. The work further demonstrates that flow batteries could often be incorporated with reactive power compensation equipment such as a wind farm level IGBT SVC. The control of the power electronic interface of the battery is introduced and a control method for supporting the dc link under grid faults is developed and simulated. This control is shown to give the added benefit of supporting the fault current contribution through an extended and severe fault. The capability of the Vanadium Redox Flow Battery to enhance power and energy applications is then explored by considering integrated control with a wind farm to energy time shift and provide frequency response. A novel controller is introduced, which manages the state of charge of the flow battery while providing some output smoothing to the wind farm and a variable level of reserve for the power system. The simulations of this controller also demonstrate that the energy store can be used to time-shift some of the wind farm's energy to times of higher prices.