Non-Isolated Single-Inductor DC/DC Converter with Fully Reconfigurable Structure for Renewable Energ

Abstract

A novel non-isolated three-port converter (NITPC) is introduced in this brief. The purpose of this topology is to integrate a regenerative load such as DC bus and motor with dynamic braking, instead of the widely reported consuming load, with a photovoltaic (PV)-battery system. Conventional methods require either a separate dc-dc converter to process the reversible power flow or employing an isolated three-port converter (TPC) which allows bi-directional power flow between any two ports. However, these methods require many switches which increases the converter size and control complexity. This brief hence presents a compact but fully functional design by combining and integrating basic converters to form a simplified single inductor converter structure while keeping minimum amount of switches. The resultant converter is fully reconfigurable that all possible power flow combinations among the sources and load are achieved through different switching patterns, while preserving the single power processing feature of TPC. This brief presents a design example of the proposed NITPC for a PV-battery powered DC microgrid.

Existing System

Current Control Technique.

Proposed System

A novel single-inductor NITPC is proposed for a PV battery-DC microgrid. A more flexible power flow can be achieved as two of the three ports are capable of handling reversible currents as compared to one bi-directional port in existing NITPCs. Moreover, a more compact design is realized without using the transformers and full-bridge converters in isolated TPCs which are the common solutions to integrate a bi-directional load. The proposed NITPC can work and transit smoothly between DC grid-connected mode and islanded mode. To maintain a single-stage power conversion of the TPC while providing a simple and compact structure for interfacing with a bi-directional load, particularly for low power applications, a NITPC is proposed with the following features: 1) It integrates and controls a current reversible load, hence, it can be applied in wider practical applications. 2) Only one inductor is used, the converter size and cost are reduced while the power density is further improved. 3) Single-stage power conversion between any two ports, which is a key feature in TPCs, is preserved. 4) Since in each mode the TPC reconfigures to basic buck converter and boost converter operations, the control strategies are simple and straightforward. 5) It can be flexibly reconfigured into single-input single output (SISO), dual-input single-output (DISO) and single-input dual-output (SIDO) modes, to fulfil all possible power flow combinations among the three ports.

Architecture

Proposed Converter Topology