Per phase power balancing in grid connected cascaded H-bridge multilevel converter for solar PV application

Abstract

Three phase power in solar PhotoVoltaic (PV) application is often unbalanced due to non-uniform radiation and temperature level on each cluster solar PV array. This is also true for PV fed cascaded H-bridge (CHB) multilevel converter. Thus the grid current supplied by the converter is unbalanced which is not desirable in balanced grid system. For supplying balanced three phase current, a common mode voltage is added with the pole voltages of CHB converter. It circulates active and reactive power in the phase clusters and allows balanced three phase power to be supplied to the grid. This paper presents a geometrical approach to calculate common mode voltage during unequal power level on three phase cluster. The capacitor voltage balancing of individual cluster and cell are also presented during different power level in the cell. Mathematical derivation of common mode voltage based on unequal phase cluster power are also included in the paper. Phase shifted Sinusoidal Pulse width modulation (SPWM) technique is used to operate the CHB multilevel converter. Simulation results of three phase current balancing during non-uniform radiation are verified using Matlab/Simulink.