Real-time Validation of a DC-link Tuning Method for an AC-AC Wind Converter in Fractional Frequency Transmission System

Wind power converters with modularity and scalability features paly pivotal role in interfacing of wind farms with the medium/high-power systems. These offshore or onshore grids are vulnerable to instabilities during certain working conditions that adaptive control solutions could overcome some of those stability issues. Additionally, computational burden of existing control strategies, such as model predictive control (MPC) has caused implementation barriers. In this work, the operational performance of the Modular Multilevel Matrix Converter (M3C) is assessed to transmit power produced from offshore wind farm to interconnect with onshore AC grid. Small-signal impedance measurement-based stability analysis are not efficient to predict large-signal stability characteristics. The two-layer control design architecture is proposed to regulate the converter branch voltages and currents. The second-layer iterative controller is embedded into an integrated perturbation analysis and sequential quadratic programming (IP A-SQP) method for handling uncertainty and overcome instability issues arise from capacitor voltage fluctuations. The complete control scheme objectives are lowering sampling time, optimization of variable constraints, and offering adaptive damping to enhance stability margin. The outcomes are verified via Real-Time simulation study using OP AL-RT platform for a designed 9-level M3C conversion system functions with an equal or low operating frequency at the input or output AC grids.