RHP zero elimination with near optimum regulation in a current controlled tri-state boost converter through inductor current filtering

This paper demonstrates how load regulation can be improved in a current controlled tri-state boost converter along with the elimination of the right-half-plane (RHP) zero. Although use of a PI controller improves regulation, it degrades the dynamic performance, and a higher integral gain results in a considerably reduced phase margin. The objective of this paper is to investigate an alternative method to improve load regulation and to eliminate the effect due to the RHP zero as well in a tri-state boost converter. A tri-state boost converter is similar to a conventional boost converter, additionally incorporating a freewheeling switch across the inductor. The main switch is controlled through a filtered current control loop, and the freewheeling switch is controlled through the feed-forward of the input voltage and an adjustable voltage. Considering the filter to be a high pass one, it is shown that the closed loop DC gain can be made independent of the load resistance, resulting in load invariant regulation. The closed loop bandwidth is also shown to be improved. The significant improvement in the performance is, however, achieved with the price of 2-3% reduction in efficiency, because of the additional freewheeling switch.