Table-based DPC for grid connected VSC under unbalanced and distorted grid voltages: Review and optimal method

The grid connected renewable sources with their inherent intermittent behavior are inevitably imposing significant challenge to the controller design of the voltage source converters. Majority of the control approaches have ambiguous statements in relation to their performances under non ideal grid voltage conditions which is prevalent in renewable energy integrated weak micro-grid system. On that account, this paper provides a comprehensive overview of the existing table-based direct power control (DPC) schemes and review of their performance on the basis of power tracking and total harmonic distortion (THD) of the grid current under various grid conditions. In order to mitigate the drawback of the existing table-based DPC which result in high current THD under unbalanced or distorted voltage supply, this paper also proposed a novel concept of table based DPC which adapted the extension pq theory into the virtual flux-based DPC. The feasibility of the proposed resilient virtual flux-based DPC (RVF-DPC) is verified by using MATLAB/Simulink and a comparative study is conducted to evaluate the superiority of the proposed controller with another three representative table based DPC schemes. Simulation results have shown that, for an increased degree of unbalance and distortion of grid voltages, the proposed RVF-DPC is able to maintain the total harmonic distortions of the grid currents to a certain extent while keeping the constant power tracking performance.