Fault ride-through capability of multi-pole permanent magnet synchronous generator for wind energy conversion system

Abstract

Wind has become one of the renewable energy technologies with the fastest rate of growth. Consequently, global wind power generating capacity is also experiencing a tremendous increase. This tendency is expected to carry on as time goes by, with the continuously growing energy demand, the rise of fossil fuels costs combined to their scarcity, and most importantly pollution and climate change concerns. However, as the penetration level increases, instabilities in the power system are also more likely to occur, especially in the event of grid faults. It is therefore necessary that wind farms comply with grid code requirements in order to prevent power system from collapsing. One of these requirements is that wind generators should have fault ride-through (FRT) capability, that is the ability to not disconnect from the grid during a voltage dip. In other words, wind turbines must withstand grid faults up to certain levels and durations without completely cutting off their production. Moreover, a controlled amount of reactive power should be supplied to the grid in order to support voltage recovery at the connection point. Variable speed wind turbines are more prone to achieve the FRT requirement because of the type of generators they use and their advanced power electronics controllers. In this category, the permanent magnet synchronous generator (PMSG) concept seems to be standing out because of its numerous advantages amongst which its capability to meet FRT requirements compared to other topologies. In this thesis, a 9 MW grid connected wind farm model is developed with the aim to achieve FRT according to the South African grid code specifications. The wind farm consists of six 1.5 MW direct-driven multi-pole PMSGs wind turbines connected to the grid through a fully rated, two-level back-to-back voltage source converter. The model is developed using the Simpowersystem component of MATLAB/Simulink. To reach the FRT objectives, the grid side controller is designed in such a way that the system can inject reactive current to the grid to support voltage recovery in the event of a grid low voltage. Additionally, a braking resistor circuit is designed as a protection measure for the power converter, ensuring by the way a safe continuous operation during grid disturbance.