Ancillary services and dynamic behavior of inverters connected to the low voltage grid

Small generators connected to the low voltage grid must be able to provide ancillary services in order to support system stability nowadays and in the future. Grid codes have been implemented that demand for load-frequency control and reactive power control. Together with anti-islanding-detection, these control algorithms mainly affect the dynamic behavior of the inverters in case of loss of mains. In this paper, an inverter model is presented that complies with the major grid codes. Islanding tests show new effects that arise because of the interaction between different control algorithms. Oscillating operating points may occur under special circumstances. This leads to further investigations on frequency dynamics. The additional benefit of rate-of-change-of-frequency (ROCOF) monitoring is numbered in a quantitative analysis and simulation. Not only steady state, but dynamic behavior is investigated with respect to the Non-Detection-Zone (NDZ). It is shown, that using frequency dynamics, scales down NDZs of passive anti-islanding methods significantly.