Three-Level Hysteresis Power Control for Pulse-Density-Modulated Series Resonant Converters

Modern power conversion electronic devices must not pollute the power distribution system and keep a unit power factor. Furthermore, their design must be size and cost effective. It is also expected that all new designs should have an entirely digital control by 2008. We present a series resonant power converter that is driven by a pulse density modulation (PDM) strategy combined with a three level hysteresis controller to adjust output power. This approach is suitable for a fully digital control design. A single digital signal controller is used to monitor and control the whole system. By the means of simulations and experimental results, it has been shown that a traditional sixteen-level PDM approach helps to maintain a near unity power factor and a low total harmonic distortion. However, such converter can only deliver sixteen output power levels. Design parameters are such that a 25 kHz signal is delivered to the load. Research presented here shows that using the proposed hysteresis control the PDM series resonant converter is able to deliver a wide output power range with 1 W resolution (range from 5 to 360 W). The mean output power error is less than 0.3 %. This strategy can be combined to other PDM approaches to obtain a better power factor and an improved THD within desired power range