Improving load regulation in current mode control through inductor current filtering

TLDR: In this article, a high pass filter in series with the current sensor in current mode control (CMC) is proposed to achieve improved output impedance without using an integral controller, and the closed loop DC gain of a CCM buck converter is shown to be almost independent of the load resistance.

Abstract: Current mode control (CMC) though offers improved line regulation, phase margin and high bandwidth suffers from high output impedance. Although load regulation can be improved by incorporating an integral gain, it reduces the phase margin and increases the overshoot. The objective of this paper is to achieve improved output impedance without using an integral controller. Incorporating a high pass filter in series with the current sensor in CMC, the closed loop DC gain of a CCM buck converter is shown to be almost independent of the load resistance, thus improving load regulation using a proportional controller only. Improved features of CMC are also retained. Following VMC modeling approach, we develop a method to obtain the small signal model of the proposed scheme, and extended to CMC with an accurate low frequency characterisation. The proposed scheme is implemented on a buck converter, and the theoretical results are validated by experiments.