A Flexible Energy Gateway for Hybrid Nanogrids

Abstract

This article presents the topology and control of a three-port energy gateway (EG) for hybrid ac/dc nanogrids. The simple hardware architecture allows connecting renewable energy generators, energy storage (ES) devices, such as ultracapacitors, and the utility grid through three different interface converters, which, altogether, define the three-port EG of the nanogrid. The proposed EG represents a tradeoff between circuit complexity and controls flexibility, allowing: 1) operation of the ES port over a wide voltage range; 2) control of the local dc-bus voltage at a predefined set-point; 3) multidirectional power flow; and 4) support of the local ac-bus voltage with the possibility to transition into islanded operation. A hierarchical control strategy is presented that enables flexible power exchange between the ac and dc buses. At the top of the control hierarchy, a human–machine interface is dedicated to operation mode selection and parameter preset; then, a supervisory control layer is present for system-level monitoring and control functions; the lower layer of the hierarchy is constituted by converter control functions for power flow regulation, achieved leveraging on voltage and current controllers. The flexibility and effectiveness of the proposed EG architecture, control, and implementation are demonstrated in this article in a variety of operation modes by means of experimental results.