Voltage limitation by autonomous reactive power control of grid connected photovoltaic inverters

Abstract

The increasing decentralized power generation in the public low voltage grid may lead to a reversed load flow. The common assumption that the highest voltage in a low voltage grid is on the transformer busbar is then no longer appropriate. Therefore the risk of overvoltages rises significantly. A highly effective way to keep the voltage within the allowed bandwidth is to utilize the ability of modern voltage source converters (VSC) to provide or absorb reactive power while feeding active power into the network (4-quadrant operation). With a reactive power consumption while active power is fed in the voltage rise can be limited. For practical use a grid adaptive reactive power control system which works without manual set up or communication requirements is desirable. Therefore an exemplary adaptive control system was designed, modeled in a load flow simulation program and tested on different low voltage (LV) grid models for network classes prone to voltage problems. The results show that simple parameter sets can be found which will work on most grid infrastructures without further adjustment. But they also show the problems to keep the voltage within the limits without decreasing the maximum grid transport capacity by consuming innecessary reactive power.