Centralized and Decentralized Volt/Var Control Schemes for the FREEDM System

This study first investigates the impact of high-penetration residential photovoltaics (PV) on power distribution systems, both Green Hub-type and Future Renewable Electric Energy Delivery and Management (FREEDM)-type power distribution systems. Voltage varies during daily operation as the load and PV profile changes. In order to meet the requirement of system normal operation, Volt/Var Control (VVC) schemes are proposed in both centralized and decentralized fashion. The objective of VVC is formulated as minimizing system power loss while regulating voltage profile within acceptable limits. The centralized VVC scheme is a two-phase control scheme where gradient based Phase I control targets at regulating voltages and linear programming (LP)-based Phase II optimization aims at minimizing power loss. Compared with the heavy computational burden and dependence on communications infrastructure, decentralized control can achieve a system-wide optimization goal as well as parallel computation and a weaker requirement for communications. The proposed Dantzig Wolfe (DW)-based decentralized VVC partitions the original large-scale optimization problem into smaller subproblems. The proposed centralized and decentralized VVC schemes are tested on the FREEDM IEEE 34 node test feeder and the FREEDM Notional System, respectively. Improvements have been made for each control scheme. Based on the simulation result, it is clear that both proposed schemes can achieve the optimization goal of minimizing power loss while maintaining voltages within the feasible region. When comparing the control effect between centralized and decentralized VVC schemes, although the control effect of DW-based decentralized VVC is not as good as centralized VVC, it can still provide acceptable results.