Design Methodology of a Line-Frequency Zig-Zag Transformer to Utilize its Winding Leakage Inductances as Integrated Boost-Inductances in a Unified AC-DC System

A zig-zag transformer with interleaved secondary windings helps integrate grid (ac) and photovoltaic (dc) power sources in a unified ac-dc power conversion system. Winding leakage inductances of a zig-zag transformer can be utilized as integrated boost-inductances for the PWM rectifier stage, thereby reducing component count and improving overall power density. This paper presents a design methodology of such a zig-zag transformer, suitable for unified ac-dc power conversion system. Using classical approach, appropriate expressions of leakage inductance for windings with rectangular geometry are derived. It is verified using finite element method (FEM) in MagNet. Aiding effect of interleaved winding is examined, which enhances integrated-boost inductance for photovoltaic (PV). An experimental prototype of a 1.0 kW, 415/130 V, 50 Hz delta/zig-zag transformer is built and tested. Thus, analytical calculations are corroborated with the help of 2-D FEM simulation and experimental results. It confirms the modeling accuracy of the proposed analytical method to calculate leakage inductances of rectangular winding and validates the design methodology of an interleaved zig-zag transformer for a unified ac-dc system.