A Digital Phase-Locked Loop (DPLL) Controller For Resonant Converters With LLC Topology

In order to transfer maximum power to a DC load, employment of a suitable compact converter that not only could operate at high frequencies but also exhibit minimum switching losses is necessary. Resonant convertors are proposed for this purpose. To maintain system operation at maximum efficiency at variable loads a simple and reliable control method is required which continuously tracks the circuit variable resonant frequency. In this paper a Digital Phase-Locked Loop (DPLL) circuit is designed and deployed in order to adjust a12 V DC output and 300 watts, LLC Resonant Converter operation frequency. The complete system performance is evaluated based on simulation. Simulation result shows that by using DPLL control method, the phase difference between resonant tank current signal and class D inverter output voltage signal becomes constant and switching frequency always follows resonant frequency which will guarantee minimum power loss.