Control of a series resonant converter by pulse density modulation

This paper presents the pulse density modulation (PDM) technique to control the half-bridge series resonant DC/DC converter. The switching devices of the converter when operates, work alternately only at a constant frequency or they are kept off. The control is exercised by modulating the train of pulses applied to the resonating network. The converter is operated at the constant frequency for a definite time decided by the controller and then the gate pulses are withdrawn during the rest of the time period. The time period is set by the frequency of a saw-tooth signal generator. The converter may be smoothly controlled from no-load to full-load range that is not possible by controlling the operating frequency or by pulse width modulation (PWM) or the half-bridge series resonant converter (SRC). The closed-loop controller is simulated in PSPICE. A laboratory prototype is also fabricated. The simulated and the experimental results match well confirming the validity and usefulness of the proposed technique.