System level wind turbine controls with seamless transitions between standalone and grid connected mode

The aim of this work is the development of a system-level wind turbine control strategy that allows wind turbines to operate in grid-connected or off-grid mode and transition seamlessly between these modes of operation. Conventional wind turbines with a front-end inverter are designed to work as a grid tie system meaning that the inverter needs the grid voltage to synchronize and the inverter becomes a current source. As opposed to current practice, this paper proposes a wind turbine control strategy designed to work as a controlled voltage source emulating the behavior of large synchronous generators. This mode of operation will allow wind turbines to transition seamlessly from grid-connected to off-grid mode of operation. Furthermore, because of its power sharing features it will allow wind turbines to operate in remote areas without causing power quality or instability issues. The turbine will also be able to interface with microgrid systems or form a microgrid. This paper presents an overview of the proposed control strategies and simulation results demonstrating the feasibility of this approach.