Novel LVRT Testing Method for Wind Turbines Using Flexible VSC Technology

Wind energy is one of the fastest growing renewable energy sources. For this reason, several countries have included requirements in their grid codes to guarantee proper operation of wind turbines under stable operations of the power systems as well as under grid disturbances. This paper presents a novel methodology for grid code testing of wind turbines based on voltage source converter (VSC) technology. In particular, this paper focuses on a low voltage ride through (LVRT) test of a full size converter-based wind turbine. The investigated testing setup consists of a 4-MW wind turbine and an 8-MW back-to-back VSC system, operated as test equipment. The control algorithm of the testing device is derived in detail and validated through time-domain simulations. The risk of poorly damped resonances and possible interaction between the testing equipment and the tested object is investigated through small signal analysis. The obtained results demonstrate the flexibility of the proposed approach in controlling the voltage at the wind turbine terminals, including the ability in emulating the short-circuit impedance of the grid at the connection point.