Minimising in-rush current at resonant converter start-up

This paper proposes a solution to the large start-up input current-inrush problem in a DC-DC converter without the use of a current-limiting resistor. The converter topology is H-bridge and designed to step up the input dc voltage. Resonance is achieved by resonating the transformer's leakage inductance with a suitable capacitor. The output from the transformer is rectified and filtered to provide a stiff DC voltage at the input to an inverter linking a utility grid. It is the inrush current to the filter capacitor that is under consideration. Evidence for the magnitude of the inrush confirms the problem. From an analysis of the problem it is deduced that traditional single-chip soft-start circuits are of limited use for this application. An extension of this analysis provides the basis of an algorithm to reduce the inrush current magnitude. From this it is shown that a DSP has the means of assisting this problem. Experimental results of a DSP-controlled resonant converter are presented in support of the technique. These confirm the basis of the analysis and proposed solution