A Model Predictive Control With Grid-Forming Capability for Back-to-Back Converters in Wind Turbine Systems

With the increasing penetration of wind turbine (WT) systems with permanent magnet synchronous generators (PMSGs) into the power grids, the back-to-back converter (BTB) has become the key element interfacing wind sources and power grids. Compared to the grid-following voltage source converter (GFL-VSC), the grid-forming VSC (GFM-VSC) shows voltage and frequency support capabilities, which meets the requirement of grid codes for WT systems. Usually, the linear regulator is employed to realize the tracking of voltage and current of GFM-VSCs, but it has limitations of complex parameter design and dynamic performance. Recently, the model predictive control (MPC) is a promising alternative controller due to the easy adoption and fast control response. This paper proposes a novel MPC method for BTB to achieve grid-forming function. The model-based control concept of the MPC effectively overcomes the complex parameter-tuning process of the cascaded linear regulators. In addition, the overshoot in the step-response of the active power of GFM-VSCs during transient process is effectively improved by using a new multi-objective cost function. The reduced power overshoot is beneficial for fully utilizing the overload capacity of the converter, avoiding damage to semiconductor devices and causing system blocking. Finally, the simulation and experiments have confirmed the feasibility of the proposed MPC method.