Inverse decoupling internal model control for multilevel buck converter with constant power load

Abstract

Multilevel buck converter has attracted much attention in power electronic systems for their advantages of low switching voltage stress, small filter size and easy capacity expansion. However, this kind of converter has the characteristics of multivariable, strong coupling and nonlinearity, which challenges the voltage balance of flying capacitor and the stability of output voltage. Meanwhile, a large number of electronic loads are connected to the multilevel buck converter. These loads are usually regarded as constant power loads (CPLs) with negative impedance characteristics, which seriously degrades the stability of the power system. This paper proposes an inverse decoupling internal model control strategy for a multilevel buck converter with CPL. A nonlinear mathematical model of the multilevel buck converter with CPL is built, and the reversibility of the model is analyzed based on the inverse system theory. The inverse system expression is derived, and the model is linearized and decoupled into multiple pseudo-linear subsystems, which offsets the effect of the negative impedance characteristics. By selecting filters, internal model controllers are designed for the pseudo-linear subsystems. Furthermore, the stability and robustness of the control system are explored. Compared with other control methods, experimental results show that the proposed control strategy has better dynamic regulation performance and stronger robustness against disturbances.