Wind Energy Converter Generator Side Voltage Control with Mechanical Damping including Load Step Investigations and DC-link Capacity Design

The grid side control of renewable energy power converter have to fulfil requirements in frequency, voltage and synchronisation support to ensure a stable grid in case of power converter dominated grids. To be able to handle these requirements, a free choice of the control structure without taking into account DC-link voltage stabilization from the grid side is to be preferred. In case of a wind turbine without additional storage, stabilizing the DC-link voltage from the generator side is coupled to the need of damping the eigenfrequencies of the drivetrain. The need for damping is especially essential in the event of faults in the grid, since by the use of grid forming control an abrupt change in grid power supply is possible. In this paper a control structure with state feedback control for the grid side control of wind turbines is investigated. The aim is to address rules for the placement of the poles to reach an optimal compromise between reducing the voltage drop, ensuring damping of the first eigenfrequency and minimising the current overshoot. In addition, possibilities for further reducing the voltage drop are given and a design criterion for the DC-link capacity is presented.