Dual-Terminal Voltage Feedforward Based Direct Power Control Scheme and Stability Analysis of Dual Active Bridge Converter in DC Microgrid Systems

Abstract

The dual active bridge (DAB) dc-dc converter plays an important role in energy exchange between DC microgrids integrated with energy storage systems. To directly control the power flow between the adjacent DC microgrids rapidly and accurately, a dual-terminal voltage feedforward based direct power control scheme (DVF-DPC) with single-phase-shift control is proposed for the DAB dc-dc converter. The strategy makes the converter realize rapid and precise output power regulation under the following conditions, including the start-up process, load step-change, the desired output power step-change, and voltage fluctuations. An accurate discrete-time model is applied to analyze the system's dynamic characteristics, and a discrete-time small-signal model of the system is established to design the controller's parameters. In addition, a comprehensive and systematic analysis of all the possible unstable phenomena for adjacent DC microgrids is conducted based on the discrete-time model. Accordingly, the underlying mechanisms are revealed by analyzing the relationships among the state variables, the Floquet multipliers, and system parameters. Hence, the stability-oriented parameter design method is given which can provide guidance in practice. The theoretical analysis is verified in both the time domain and frequency domain. Finally, by comparing the DVF-DPC method with the traditional PI feedback control, the superiority of the proposed strategy is verified through theoretical analysis and experimental results, which demonstrates its application prospect in the field of electric energy dispatch control of the DC power supply network.