Analysis on stability and characteristics of current mode controlled converter using new small signal modeling

Abstract

There have been a great deal of researches on the current-mode controlled converter. The current-mode control is reported as having good characteristics such as automatic overload protection, easy paralleling of multiple converters, and especially design flexibility in improving small signal dynamics. However, it also reveals the possibility of the current loop instability. In order to explain this phenomenon and to understand the characteristics of the current-mode control, many modeling methods have been presented until now. Previous studies concerning modeling, analysis and control of current mode controlled power converters can be classified into three fundamentally different approaches: 1) low-frequency modeling by using averaging approaches, 2) discrete time and sampled-data approach, 3) integration of both discrete and averaging techniques. The first approach gives simple and accurate models at low frequencies, but is inaccurate at high frequencies. The second approach gives accurate models even for high frequencies, but it requires heavy computations and does not provide the design insight of power converter. The third approach gives simple models and accurate enough behavior at frequencies lower than half the switching frequency. However, the applications of previous studies utilizing this methods is also limited on the peak current-mode control. In order to explain the dynamic characteristics and the stability conditions of the current-mode control, the new modeling method and new small signal model are proposed. The proposed method is applied to both the peak current-mode control and the average current-mode control. In the proposed method, two ideal samplers are introduced in order to consider the sampling effect presented in a current loop. By the proposed modeling methods, the discrete time model can also be obtained, which can be used to explain the stability problem and to evaluate the control performances. Using the proposed continuous time mo...