Controllability Analysis Of High Order DC-DC Converters Based On Switched Linear System Models

With the development of photovoltaic power generation, LED lighting, DC motor and other areas, high order DC-DC converters have been widely used for building high-performance DC-DC converter systems. Existing theoretical studies focus on the basic DC-DC converters(Buck, Boost, Buck-boost), but the research of high order DC-DC converters(Cuk, Zeta, SEPIC) is less. As an essential preprequisite for the feasibility of topology structure and control strategy design, controllability is one of the basic characteristics of high order DC-DC converter.The main achievements obtained in this paper are as followings:1) High order DC-DC converters are typical hybrid dynamic systems which are switched linear systems. Thus, the high order DC-DC converters are built as switched linear system models which can describe the dynamic characteristics of high order DC-DC converters. The controllability of high order DC-DC converters is researched based on the model.2) Directed graphs of high order DC-DC converters are obtained based on switched linear system in accordance with the principle of convex combination. Structural controllability of high order DC-DC converter is analyzed. The theoretical analysis is verified by experiments, in which the prototypes of three types of converter are produced.3) Structural controllability can not guarantee that high order DC-DC converters can be controlled in the case of any circuit parameters. Therefore, their state controllability need to be carried out when the paremeters of high order DC-DC converters already are given. The controllability condition are demonstrated rigorously based on the mathematical model. And the theory is verified by simulation. The relationship between controllability of subsystems and controllability of the entire system is explored, which enriches switched linear systems controllability theory.4) Output controllability of high order DC-DC converters is demonstrated rigorously based on output controllability theory of switched linear systems. The output controllability of high order DC-DC converters is validated by experiments, in which the loads of the converters step change. One cycle control(OCC) and multi-cycle control are proposed for the high order DC-DC converters. The analysis results indicate that the PWM high order DC-DC converters are output controllable both in one-cycle and multi-cycle. It can be seen that OCC can be applied to the high order DC-DC converters. Theoretical analysis result is consistent with MATLAB/Simulink simulation verification of Cuk converter. The analysis method can be applied to study OCC feasibility for others switched converters or systems.