UBC Theses and Dissertations
Dual-loop linear controller for LLC resonant converters Degioanni, Franco
For the last years, LLC resonant converters have gained wide popularity in a large number of domestic and industrial applications due to their high-efficiency and power density. Common applications of this converter are battery chargers and high efficiency power supplies, which require tight output voltage regulation. In traditional PWM converters, closed-loop controllers based on small-signal models are typically implemented to achieve zero steady-state error and minimize the effects of disturbances at the output. However, traditional averaging techniques employed in PWM converters cannot be applied to LLC's and highly complex mathematical models are required. As a consequence, designing linear controllers for this type of converter is usually based on empirical methods, which require high-cost equipment and do not provide any physical insight into the system. The implementation of current-mode controllers has been vastly developed for PWM converters. Employing an inner current loop and outer voltage loop has shown numerous advantages, such as, tight current regulation, over-current protection, and ample bandwidth. However, this control architecture is not commonly implemented in LLC resonant converters, and conventional single voltage loop controllers are employed. This work proposes a simple and straightforward methodology for designing linear controllers for LLC resonant converters. A simplified second order equivalent circuit is developed and employed to derive all the relevant equations for designing proper compensators. A dual-loop control scheme including an inner current loop and outer voltage loop is proposed. The implementation of the dual-loop configuration provides improved closed-loop performance for the entire operational range. The theoretical findings are supported by detailed mathematical procedures and validated by simulation and experimental results.
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