Implementing adaptive digital control on an existing LLC DC-DC resonant converter

In this paper, the implementation and design process of integrating an adaptive digital PID control scheme on an existing 650W LLC DC-DC resonant converter is presented. The objective is to improve the converter´s dynamic response while maintaining adequate gain and phase margins over several different operating ranges and to improve the converter´s ability to reject the 120Hz disturbance produced from the AC line source. The small signal models of the converter are obtained using MATLAB´s System Identification Toolbox, which estimates a mathematical model based on the empirical uncompensated loop-gain frequency response data collected either from PSIM simulation or from the physical converter using a Venable frequency response analyzer. Compensator designs are based on the estimated models and digital control is performed using a TMS320F28035 digital signal microcontroller. Simulation and experimental results are presented which validates the estimated model and the compensator design process. The adaptive compensation control performance is compared to a typical single compensation controller to show the performance advantages.