Distribution Congestion Management Using CVSR Devices

Power demand and supply must be in balance to maintain frequency and stable power flow in distribution and transmission networks. Power flow control is an important problem where flows must be held within equipment limits. Distribution systems may experience congestion during peak consumption hours. Such congestion can overload distribution lines and transformers, particularly, in dense urban areas. Similar to the power electronic devices in the transmission network, power flow control devices are available for the distribution systems. However, there are very few control units in the distribution systems. D-STATCOM, energy storage, phase-shifting transformers, distributed generation (DG) and switches can be used to control power flow in the distribution systems.

The continuously variable series reactor (CVSR) is a newly proposed device and is used in this study for its ability to control distribution power flow. Compared to other power flow control equipment, the CVSR device is a reliable, fast-acting unit, and most importantly, economically low cost. The CVSR can be used to regulate the reactance on the primary side of a transformer to control power distribution among transformers in order to relieve overloading in a meshed distribution grid. This approach can allow a distribution system to avoid or defer transformer upgrades. An optimization problem is formulated to identify location and settings to relieve overloads. To integrate and model the CVSR device in the distribution network, a method is developed and simulation is performed using MATLAB and OpenDSS. The results are verified with the benchmark results on OpenDSS software. As a result, a few ohm reactance CVSR is shown to be adequate to relieve loading on the transformers in a practical system. In addition, it was found that a piecewise approximation works well for mitigating the overloads and optimal CVSR locations on realistic meshed networks. The IEEE 342-node low voltage networked test system (LVNTS) and a portion of the Consolidated Edison's partial meshed distribution system are used to evaluate performance. Future work includes optimal location of CVSR devices with consideration of dynamic conditions, integration of advanced optimization techniques, expansion to other test systems and identification of open-mains in the meshed grids.