A Passivity-Based Globally Stabilizing Pi Controller For Primary Control Of Radial Power Distribution Systems

Proportional-Integral (PI) control is a commonly used control mechanism for regulation of power flows in distribution-level power systems. Such controls, however, come at the cost of guaranteeing only local stability, meaning that as the system load changes the controller gains need to be tuned as well in order to maintain stability of the primary control loop, thereby necessitating a large schedule of controller switching to cover the load space. This paper resolves this problem by designing an alternate PI controller that can stabilize a radial distribution network for any choice of load. The fundamental property behind this stabilization is passivity. It is shown that by choosing the right set of passive input-output pair for the models of the power converters it is possible to globally regulate the power flowing between the distribution feeder and the loads by a fixed set of control gains that are independent of the magnitude of the load as long as the power flow solution exists. Results are validated using a networked microgrid model with three power converters. Comparison is drawn between fully decentralized, sparsely distributed, and all-to-all connected communication topologies for implementing the controller.