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.