Geometric control breaks tracking performance limits using linear control in a buck converter

This paper highlights performance and efficiency benefits using time optimal control (TOC) in a synchronous buck converter, over an optimally tuned current mode control (CMC) for a step reference transient. An approximate second order closed loop model is obtained for CMC using type-II compensation, and critical performance limits are derived using a normalized framework. Under frequent step change in reference voltage, an analytical study comparing transient performance and efficiency is carried out for CMC and TOC. This study shows that both performance and efficiency can be improved significantly using TOC, however at the cost of larger peak inductor current during the transient. Possible alternate solutions using performance-efficiency trade-off are discussed under peak (inductor) current limits. A buck converter prototype is fabricated, and the test results are obtained using a FPGA device.