Power-current coordinated control without sequence extraction under unbalanced voltage conditions

The increasing penetration of renewable power sources into power system is calling for an evolution of grid interconnection control strategy. In particular, during asymmetrical grid faults, power turbulence and current distortion of three-phase inverter cannot be balanced unless coordinated control is adopted. Several coordinated control strategies are usable for operating under unbalanced grid voltage nowadays. These control strategies usually require a real-time sequence detection block for reference generation. This study explores a coordinated control strategy without real-time sequence detection. It has three theoretical innovations: (i) the internal mathematical connection between power fluctuation and current quality is derived; (ii) a control strategy with a continuous adjustable factor is proposed. The power oscillations and the current quality can be controlled flexibly by adjustment factor without using the filter and sequence extraction calculation; (iii) the method for selecting the continuous adjustable factor is also presented. The experiment and simulation results prove that these innovations facilitate power-current coordinated control with simple reference selection criteria and excellent performance.