Black Start and Islanding Operation of Wind Turbines with Auxiliary Power Converters and Energy Storage Systems

The ability to black start a grid and operate it in islanded operation is an important feature in power generation units. For renewable energy sources, especially wind turbines, a unified black start strategy does not yet exist and different methods are possible. In general, this is done with a grid-forming control, which can be implemented in the wind turbine controller but also requires major modifications. This paper proposes a novel black start strategy which uses an auxiliary converter to black start the wind turbine and control a microgrid. The advantage of this method is that there is no need to change the overall wind turbine control and it can operate in the conventional grid-feeding or grid-supporting mode. The only changes needed can be done through the active and reactive power set-points and reference values. A grid-forming control with an auxiliary converter as well as three different ways of calculating suitable power set-points for the wind turbine are presented which allow for a stable microgrid control and accurate load-sharing of the two converters. In the end simulations are carried out and the developed methods are compared. The results show that this system setup offers multiple successful control strategies for the black start and grid control which can be used in future microgrids.