Fault Ride-through Strategy of Microgrid Under Harmonic and Unbalanced Grid Faults Conditions

In order to eliminate the impact of harmonic and unbalanced faults on the point of common coupling (PCC) and improve the fault ride-through (FRT) capability of microgrid. In this paper, the cascaded H-bridge flexible fault current limiter (CHB-FFCL) is used to compensate the PCC voltage and realize the functions of voltage regulation, current limiting and active power filtering (APF). Under the multi synchronous reference coordinate system, the dq-axis DC components of electrical quantities can be extracted without phase-locked loop (PLL) by giving the rotation angular frequency of the coordinate system, which overcomes the frequency oscillation problem of the traditional PLL. An improved harmonic voltage frequency dividing control strategy of CHB-FFCL based on amplitude feedback is proposed, which reduces the number of control loops of the traditional double loop control strategy and is beneficial to the parameter tuning and design of the controller. The simulation on MATLAB/Simulink verifies the effectiveness of the proposed scheme and its ability to improve FRT of microgrid under complex grid conditions.