Stabilizing Controller Design for Multibus MVdc Distribution Systems Using a Passivity-Based Stability Criterion and Positive Feedforward Control

A power-electronics-based dc distribution system is a complex and extensively interconnected system consisting of multiple power converters. As a result, a number of system-level challenges related to stability arise due to interactions among multiple converter subsystems. The design of this type of system is difficult due to limited understanding of the problem and general lack of proper analysis tools for multibus systems. Conventional stability criteria, such as the Middlebrook criterion and its extensions, apply only to single-bus systems. This paper proposes a stability analysis and stabilizing controller design technique for multibus MVdc converter systems. First of all, an unterminated two-port modeling technique is used to construct the impedances of all system buses. Then, overall system stability is evaluated utilizing the recently proposed passivity-based stability criterion. In order to ensure good stability margin and dynamic performance, the new concept of an allowable impedance region is introduced based on the Nyquist contour of the bus impedance. Finally, a stabilizing controller is designed using a positive feedforward control technique to ensure passivity of the system buses, providing stability and good performance. Validation of the proposed techniques is provided through the simulation and experimental results.