Low frequency ripple propagation analysis in LLC resonant converter based on signal modulation-demodulation theory and reduction based on PIR control strategy

Two-stage AC-DC-DC converters are widely used in battery charge systems. While in a single-phase two-stage AC-DC-DC converter system, the pulsating power which is twice of the grid´s fundamental frequency will affect the DC bus voltage, which will eventually deteriorate the quality of output voltage. This paper analyzed the propagation of low frequency voltage ripple in LLC DC-DC resonant converter based on signal modulation-demodulation theory and quantitative relationship between the amplitude of input and output low frequency ripple voltage was obtained. A PIR controller was designed to reduce the output low frequency voltage ripple. Experimental results with a 1kW prototype verified the accuracy of the obtained quantitative expression and the designed PIR controller can reduce 76.7% 100Hz ripple voltage at output side of LLC resonant converter^.