A novel concept for balancing of the phase modules of a three-phase unity power factor Y-rectifier

The isolated star point of a three-phase star-connection of single-phase unity power factor PWM rectifier systems (Y-rectifier) results in a mutual coupling of the individual phase module outputs, i.e. the individual DC link voltage control loops. Starting from the theoretical analysis of a series connection of two DC-DC boost converters a control-oriented equivalent circuit of the three-phase Y-rectifier system is derived in analytically closed form. Based on this a robust multivariable control is designed which ensures constant DC link voltage levels for unsymmetric disturbances, i.e. step load changes of the phase modules, All theoretical findings are verified via numerical simulations.