High-Power Medium-Voltage Wind Turbine Driven by Converter Solution with Modular Multilevel Structure and Decentralized Battery Integration Operating in Both Grid-Following and Grid-Forming Modes

Abstract

Upscaling is a trend in the wind-power industry, which means to build wind turbines with increased power ratings and reduced structural costs. With the increased wind-turbine power levels, adopting a medium-voltage structure could be a solution to avoid problems related to high currents such as the intolerably high losses and the necessity of bulky, heavy, and expensive conductors. Moreover, a transformer-less wind turbine could be built due to the medium-voltage levels, which would contribute to the lightness and compactness of the entire solution. The high penetration of renewable-energy sources into the electrical grid leads to the necessity of energy-storage systems to assist in the preservation of the power-system stability. Wind power plants with energy-storage integration can operate in a dispatchable fashion, providing benefits to the operation of the power system such as the frequency-stability support, reduced voltage variations of the weak grid and the improvement of the economic dispatch. Furthermore, the wind-power-plant owner can improve his revenues by having an energy-storage system since it is possible to avoid penalties related to the mismatches between the forecasted power and the generated power, besides the possibility of providing ancillary services to the grid. Moreover, due to the presence of the energy-storage system, the wind power plant can keep active, generating power, if a fault occurs isolating the power plant from the main grid. In this paper, a new converter solution with modular multilevel structure and decentralized battery integration is used to drive a medium-voltage wind turbine. The integration of the batteries into the wind-turbine converter prevents the need of extra converters exclusively dedicated to the batteries. The wind turbine with energy storage can behave as a dispatchable generation when operating in the grid-following mode. In this mode, the wind turbine injects power into the grid according to a desired setpoint. When the wind power plant is isolated from the grid, the wind turbine driven by the new converter solution can operate in a grid-forming mode, absorbing the power generated by other wind turbines without an energy-storage system. In this paper, simulation results are shown illustrating the different operation modes of this new wind-turbine solution.