Networked Control and Power Management of AC/DC Hybrid Microgrids

Abstract

This paper addresses power management and control strategies of a hybrid microgrid system that comprises ac and dc subgrids. Each subgrid consists of multiple distributed generation (DG) units and local loads. Both entities are interconnected by voltage source converters (VSCs) to facilitate a bidirectional power flow and increase the system reliability. The control of the interconnecting VSC can be achieved autonomously. However, it is shown that the autonomously controlled hybrid microgrid fails to operate following variations in the power generation characteristics of local DG units (such as droop coefficients, set points, or loss/connection of DG units, etc.) A centralized controller is therefore proposed and compared to the autonomous scheme. The centralized control strategy provides an accurate and optimized power exchange between both subgrids. Parallel operation of multiple interconnecting VSCs is considered so that the transmitted power is shared according to their power ratings. Small-signal stability analysis is conducted to investigate the influence of the communication delays on the system stability. A hierarchical control strategy has been proposed by setting the autonomous controller in a primary layer whereas the centralized controller is set into a secondary layer to generate a compensation signal. Time-domain simulations results are presented to show the effectiveness of the proposed techniques and the drawbacks of the conventional scheme.