Digital Hysteretic Average Current Control for Fast Recovery in a Non-Inverting Buck-Boost Converter

This paper proposes a mixed-signal hysteretic average current control (MSHACC) technique in a non-inverting buck-boost converter (NIBBC) for improving reference transient performance and to achieve smooth mode transitions. The sensed inductor current is compared with the reference commands i high and i low in the analog domain. A digital-to-analog converter (DAC) is used to generate i high and i low using the output of a two-degree-of-freedom digital controller and the hysteresis band ∆i H with the objectives to achieve smooth mode transitions, online (switching) frequency programming, and superior reference transient recovery. The output voltage is sampled using an analog-to-digital converter (ADC) with an event-based approach, and the voltage controller is designed using internal model control (IMC) to achieve stable behavior and reduced error RMS voltage. Discrete-time models are derived for the proposed MSHACC scheme and are verified using SIMPLIS simulation. A NIBB converter prototype is made, and the digital controllers are realized using a field-programmable-gate-array (FPGA) device. Test results show the benefits of the MSHACC scheme over fixed-frequency mixed-signal current-mode control (MCMC).