Distributed power balance and damping control for high power multiport LCL DC hub

DC hubs are centrally located in DC grids and they are expected to operate autonomously under wide range of operating conditions. To achieve secure operation without intervention from dispatcher and to damp the internal oscillatory modes, a distributed power balance and damping controller for high power multiport LCL (Inductor-Capacitor-Inductor) DC hub is proposed in this paper. Natural power balance mechanism of the hub is analyzed. To avoid over-voltage and over-power during un-balanced power orders, an actively controlled distributed power balance control for each port of the hub is proposed. As LCL circuit is used in the hub, there might exist prolonged oscillations in the hub. Small signal modelling and eigenvalue studies are used to identify the dominant oscillation mode of the hub. The participation factors are calculated to identify the state variables that best represent the dominant oscillation modes. The residue analysis is used to pair the feedback signals and design the structure of the damping controller. Robustness of the damping loop against topology changes is analyzed. Effectiveness of the designed controller in terms of secure operation and transient responses is verified by extensive PSCAD/EMTDC simulations on a 4-port test LCL DC hub.