Trends in SmartGrids: Unbalanced Control in Distribution Systems
DIgSILENT Ibérica SmartGrids' WIP is mainly focusing on the use and exploitation of data from Smart Meters. In this application example, distributed generation is used to balance a feeder and improve voltage quality for all end-users.
Distribution networks are naturally unbalanced due to single phase, two phase loads or even unbalanced sections of the network. More and more dispersed or distributed generation is being connected to the distribution network, mainly based on full rated inverters, a very flexible technology with plenty of system services potential. The inverter-based generation can be equipped with an unbalanced control, to be able to control not only voltage magnitude but also the imbalance of the system.
DIgSILENT Ibérica has implemented a controller installed at the top of a LV feeder. The controller takes measurements of voltages of phase A, B and C from the Smart Meter. The algorithm computes active and reactive power set-points for each phase in order to compensate voltage deviation between phases:
- Single-phase inverters receive the set-points via PLC protocol for instance: lower P, generate or consume Q.
- Three-phase inverters incorporate a fully unbalanced control in positive, negative and zero-sequences.
Colouring options in DIgSILENT PowerFactory are the best way of verifying the results of any algorithm or control system. A feeder with single-phase loads and distributed generation with voltage quality problems is coloured in orange (top figure). The result of the controller action is that each customer sees a “better” voltage quality: imbalance is reduced significantly and voltage magnitude is close to 1 p.u. (middle and bottom figure).