Low Voltage Soft Open Point with Energy Storage: System Simulation and Prototype Preliminary Test Results

Operation of a distribution grid under normal conditions and during a grid fault have contradictory requirements. In the first case, a meshed grid is preferable since it permits load balancing between adjacent lines and leads to better voltage profiles. However, a radial structure is preferable in case of a grid fault such as short-circuit, since it requires simpler protection schemes for fast and effective fault isolation. These issues become more vital with the increasing penetration of distributed energy generation. A soft open point is a power electronic device, generally consisting of two back-to-back mounted voltage source inverters that allows combining the advantages of both grid topologies described above. The soft open point can control both active and reactive power flow between two feeders permitting load balancing and reactive power compensation. In case of a grid fault, the soft open point limits fault current contribution of neighboring feeders. The soft open point is extendable to a soft open point with energy storage, permitting to mitigate transients of nearby distributed energy generation. A soft open point with energy storage is a powerful tool for the distribution system operator. This paper describes the design and simulation of a global control strategy of a low voltage soft open point with energy storage prototype. The simulation was set up to realize the prototype in a second step. The simulation and the prototype will allow to gather practical experience with this innovative device and to develop upper system level control strategies. In this paper the design, simulation and preliminary test results of the small-scale prototype of soft open point with energy storage system will be presented.