Digital voltage feed-forward control for isolated DC/DC converters

For an isolated DC/DC converter with a controller located on secondary side, fast primary input voltage sensing and feed-forward control are desirable features to minimize output voltage disturbance at large input voltage step change. This paper presents a new method by using digital control loop´s error ADC (EADC) and Control Law Accelerator (CLA) to implement these features. The EADC measures primary voltage each switching cycle and compares it with a reference value programmed to the DAC. The difference is digitized and fed to the downstream CLA, which is configured as a nonlinear amplifier. The CLA´s output is used to scale DPWM duty cycle, to maintain the same voltage*second (V·S) at transformer output and to minimize output voltage disturbance. A 240W 48V/12V 1/8^th brick module was built for the control validation. Large input voltage surge and primary voltage sensing accuracy test data are provided.