Improving Grid Transmission Capacity and Voltage Quality in Low-Voltage Grids with a High Proportion of Distributed Power Plants

AbstractThe proportion of renewable energies in power generation is increasing according to the political aims in recent years. In low-voltage grids, these are mostly decentralized renewable energy systems such as photovoltaic power plants (PV) connected through inverters to the grid. The temporary reversal of the power flow causes overvoltage problems. Consequently, regenerative sources need to be turned off temporarily or on the long term the grid infrastructure has to be extended by the network operator. This paper describes two concepts to increase power capability and voltage quality of the grid. On the one hand reactive power generated by solar inverters is used to influence the grid voltage locally. On the other hand a controllable tap changer in a low-voltage transformer is able to influence the voltage in the whole low-voltage grid. Thus grid extension can be avoided in many cases or at least can be delayed. Voltage fluctuations due to varying power input, e.g. caused by passing clouds, can be reduced. Distributed data collection and central control is required to control a distributed system of multiple solar inverters installed in a grid segment. The concept can be applied not only to PV systems; it is rather a basic technology which can be used in future grids with distributed generation and storage