Multivariable-Feedback Sliding-Mode Control of Bidirectional DC/DC Converter in DC Microgrid for Improved Stability with Dynamic Constant Power Load

Abstract

In order to mitigate the influence of negative impedance characteristics on the stability of a DC microgrid with a constant power load, and the influence of nonlinear characteristics of a bidirectional converter on DC bus voltage, a control method of a bidirectional converter based on a multivariable-feedback sliding-mode control is proposed. The traditional control method usually uses the DC bus voltage error as a single controlled variable to optimize the design of the control law, which will lead to the lack of global coordination of each state variable. In this paper, the multi-state process variables-feedback sliding-mode control of a bidirectional DC/DC converter is designed, which can effectively improve the stability of the DC bus voltage, despite dynamic power disturbances. Firstly, the model of a bidirectional DC/DC converter, as well as the state equations of a converter with constant power load and resistive load, are analyzed. Secondly, to express various dynamic characteristics of the DC bus voltage fluctuation process, the output voltage error, the inductor current error and its integral are defined as the controlled state variables. Then, the multivariable weight combination-based sliding-mode surface is defined, and the sliding-mode controller is derived from a fast exponential power reaching law. Thirdly, the existence and stability of the multivariable-feedback sliding-mode control and the choice of control law parameters are discussed. Finally, MATLAB / Simulink software is used to simulate the proposed controller. Compared with PI and intelligent PID controllers, the proposed controller has the fastest response speed, the smallest steady-state voltage deviation and the best adjustment performance.