Analytical investigation of influence of grid following IBR control on distance protection

The number of inverter-based resources (IBR) in the electrical grid is increasing rapidly up to converter only grids. Therefore, their influence of on the grid behavior, in particular on the fault behavior, is increasing. To maintain security and reliability of the electrical grid, protection systems must remain functional. In order to ensure this, the expert knowledge of IBRs and protection relays must be brought together and the influencing effects have to be examined and understood deeply. Only relay lab tests and the detection of malfunction do not solve the problem. This paper provides a comprehensive investigation into the impact of IBRs on distance protection, a widely spread protection function. The focus of the paper is on the analytical understanding of the IBR and the protection relay behavior. The adverse mutual effects are quantitatively assessed and analytically derived. It is shown that the amount and the relation between the fed-in active and reactive power as well as their resulting currents lead to unexpected complex-valued impedance measurement errors of the distance protection, because the fault currents of grid-following IBRs behave different as with classical synchronous machines. The analytical results were validated using real protection relays and real-time simulations in the grid lab.