An Improved Control Method for Type-IV Wind Turbine Connected to Weak Grid Systems.

This paper presents an improved control strategy for a type-IV wind turbine using the machine-side converter to control the dc voltage and the grid-side converter operation in the grid-forming (GFM) control mode. When wind power becomes a considerable portion of the power system or even the only energy source, the wind power systems must operate as a voltage source to maintain the terminal voltage magnitude and frequency by adjusting the real and reactive power. The generator output power should track the power to the grid to maintain the DC voltage. This paper proposes the coordinated control of the generator’s output power with a DC-link voltage controller for the generator-side converter. A dynamic model of the grid-side converter operating in GFM control mode has been built, and the voltage and frequency regulation strategy is presented. Simulation results using PSCAD/EMTDC demonstrate the control performances under various grid conditions, i.e., a wide range of short circuit ratio (SCR) and islanding grid conditions.