A Design Method of DC-link Capacitor for Three-Phase SPWM Rectifier Under Asymmetric Grid Faults

The instantaneous active power and DC-link voltage of three-phase SPWM rectifiers can have the components of double fundamental frequency under asymmetric grid faults, affecting the system reliability and power quality. Firstly, the instantaneous active power characteristics of three-phase SPWM rectifiers both on the AC and DC sides are analyzed quantitatively, and the expression of double fundamental frequency component of the DC-link voltage is derived. Next, the most common asymmetric grid fault, single phase-to-ground fault, is considered through introducing a voltage drop coefficient. Then, the influence of single-phase voltage drop coefficient on the DC-link capacitor is analyzed. And the limit value of the DC-link capacitance is obtained, meanwhile considering the third harmonic constraint of the grid current. Finally, the simulation verifications are carried out, and the results have proven the correctness of the theoretical analysis in the paper.