A Flexible Full-Scale Converter with Reconfiguration Functionality for Wind Turbine

High penetration of the inverter-based renewable energy generation is diminishing the grid strength due to its limited overload capacity. Under certain operation conditions, particularly during short-circuit ground faults, substantial reactive power currents are required from generating units. Increasing the current rating of the power electronic devices can meet this demand, however the cost is also increased due to low utilization rate. To address this issue, this paper proposed a flexible full-scale converter topology for wind turbine. Typically, these turbines have high generator ratings, leading to the construction of converters with more than one back-to-back converters operating in parallel. To accommodate the varying requirements of the power gird under both normal and fault conditions, the generator-side inverter units included in the whole converter are designed with flexible functionality. Specifically, they can be assigned, as conventionally done, to the generator side under normal grid condition, however, one or more of these units can be switched to operate in parallel with the grid-side inverters during grid fault conditions, thereby enhancing the full-scale converter’s current capacity to support reactive current to the grid. Consequently, grid strength is increased without increasing extra current capacity of the converter, simply by introducing flexibility to the generator-side inverters. This approach also enhances the hardware utilization rate. The proposed concept is validated through MATLAB simulations, and the feasibility of switching the generator-side inverter to the grid side is further confirmed through experiments made on a small-scale laboratory platform.