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Phase staggering control of a series-resonant dc-dc converter with paralleled power modules

A method of decreasing the ripple on the output voltage of high power ac-dc or dc-dc series resonant converters without increasing the internal converter frequency or the capacity of the energy storage elements is discussed. This improvement is accomplished by subdividing the converter into two or more series resonant power modules. The power modules are operated with a constant relative phase shift (phase-staggering control). The method of eliminating the harmonic components in the input and output currents of the conversion system, without increasing the internal pulse frequency, is justified by Fourier analysis of the current waveforms. The frequency spectra of the source and output waveforms for the continuous and discontinuous resonant current mode are shifted to higher frequency ranges as computations show for both one single module and paralleled modules. Inadequacies in the phase-staggering control method applied to series-resonant converters are indicated in relation to the dominant harmonic component, in particular for two modules. The presentation is supported by experimentally acquired waveforms. The control method decreases the rms current through the input and output capacitors of the converter and the losses in the indicated components, which is especially advantageous for low-voltage, high-current applications. High-frequency current components to the source and to the load are reduced, resulting in smaller input and output filters. The resolution of the control of the flow of energy from the source to the load is improved, resulting in a faster system response.