Digital peak current mode control of isolated current‐fed push‐pull DC‐DC converter with slope compensation

Abstract

AbstractThe isolated current‐fed push‐pull dc‐dc converter has some practical advantages such as improved cross regulation characteristics, reduced output noise, and good overall efficiency. Although detailed insight on this converter is available in the literature, the use of digital peak current mode with slope compensation control methodology has not been explicitly presented. This paper discusses digital peak current mode control of a current‐fed push‐pull converter with a novel double digital pulse‐by‐pulse current limiting scheme. Push‐pull topology is implemented on the primary side of an isolation transformer in a dc‐dc bidirectional converter. Achieving this control solution of isolated push‐pull converter is attractive especially in controlling battery power flow in smart micro‐grids. By using a digitally controlled push‐pull converter, the ability to change controller parameters and the use of droop control methods for storage are easier. Furthermore, current mode control provides capability of equal current sharing between parallel converters and eliminates the transformer saturation problem that is common in push‐pull topology. Using continuous time model of the converter, a Type II compensator is designed and implemented in discrete time domain. Digital slope compensation is applied to eliminate the high frequency oscillations caused by current feedback loop. The control method and slope compensation are implemented on STM32F303 mixed‐signal microcontroller. On‐chip analog comparator disabled the PWM output if the sensed current exceeds the reference current until next PWM cycle. The digital controller performance is confirmed by 13 W hardware implementation including fast transient response and stable operation.