Hardware in the loop, all-electronic wind turbine emulator for grid compliance testing

During the last years the distribution of renewable energy sources is continuously increasing and their influence on the distribution grid is becoming every year more relevant. As the increasing integration of renewable resources is radically changing the grid scenario, grid code technical requirements as are needed to ensure the grid correct behavior. To be standard compliant wind turbines need to be submitted to certification tests which usually must be performed on the field. One of the most difficult tests to be performed on the field is the low voltage ride through (LVRT) certitication due to the following resons: • The standards specify it must be performed ad different power levels. For this reasons it is necessary to wait for the right atmospheric conditions. • It requires a voltage sag generator which is usually expensive and bulky. • The voltage sag generator needs to be cabled between the grid and the wind turbine. • The voltage sag generator causes disturbances and perturbation on the power grid, for this reasons agreements with the distributor operator are needed. For all these reasons a laboratory test bench to perform the LVRT certification tests on wind turbines would be a more controlled and inexpensive alternative to the classic testing methodology. The research presented in this thesis is focused on the design and the realization of a test bench to perform certification tests on energy converters for wind turbines in laboratory. More specifically, the possibility of performing LVRT certification tests directly in laboratory over controlled conditions would allow faster testing procedures and less certification overall costs. The solution presented in this thesis is based on a power hardware in the loop implementing a digitally-controlled, power electronics-based emulation of a wind turbine. This emulator is used to drive the electronic wind energy converter (WEC) under test. A grid emulator is used to apply voltage sags to the wind turbine converter and perform LVRT certification tests. In this solution AC power supplies are used to emulate both the wind turbine and the grid emulator. For this reason the test bench power rating is limited to the AC supplies one. Two working versions of the test bench has been realized and successfully tested. The work here presented has evolved through the following phases: • Study of the grid code requirements and the state of the art. • Modeling of the parts of a wind turbine and complete system simulations.