Fault Tolerant Control of a Grid Interfacing Converter for Bipolar DC Distribution

Abstract

Recent research on electric power conversion has focused on multiport power electronic converter topologies, in which a single converter can transfer power between more than two ports. These ports interface with alternating current (AC) and/or direct current (DC) systems, and exchange power between them for various applications, such as grid integration of wind and solar power and the fast charging of electric vehicles. In general, by multitasking certain components, these multiport converters have the advantage of fewer switching devices, smaller footprints, and reduced cost. However, many existing multiport converter designs have diminished reliability since internal components are typically shared between different power conversion stages. Consequently, a single switch failure in a multiport converter can end up rendering an entire system inoperative. This complete loss of power transfer on all ports presents an unacceptable level of risk to system reliability and operational resiliency. In comparison, conventional multi-converter systems do not suffer to the same degree from single points of failure. To address this gap, this work pursues new control strategies to allow a multiport converter topology to re-task healthy phase legs such that power transfer to all ports may continue during internal component failures. Focusing on a grid interfacing converter for bipolar DC distribution with the ability to handle unbalanced DC side power flows, a converter model and constraints are developed that allow for continued operation during single and dual phase leg faults. Controls are then developed to meet these constraints while realizing appropriate transient responses to faults and load changes. The system is tested using a new controller hardware-in-the-loop environment built using a NovaCor Real-Time Digital Simulator and Imperix Boombox controller, with communication achieved using the Aurora protocol over fibre.