Due to the changes occurring in the world’s power systems, as more and more converter interfaced generation, and power electronic devices (PED) are being connected to the grid, new methods have been proposed in literature on how tools such as the multi-infeed interaction factor (MIIF) should be utilized. The MIIF, originally used for predicting risks for interactions between line commutated converter (LCC) high voltage direct current (HVDC) inverters, has been extended to cover many more types of PEDs connected to the power system. Conflicting descriptions on how the MIIF tool should be used exists in the literature though, which makes it difficult to determine how to implement the extended definitions of the MIIF together with the expanded set of PEDs. Also, since the MIIF tool is an integral part in calculating the multi-infeed interactive effective short circuit ratio (MIESCR), a tool used to measure the alternating current (AC) network strength in multi-infeed systems when connecting new HVDC links, how the MIESCR should be calculated is unclear as well. There are doubts as to whether the original MIIF risk for interaction limits defined for LCC HVDC systems can be carried over to voltage source converter (VSC) HVDC systems, which is what has been assumed in literature without evidence showing that this is the case. There is also the question of if the limit values of the MIESCR originally defined for LCC HVDC systems, can be transferred to VSC HVDC systems. To answer these questions, simulations were performed in the software PSCAD/EMTDC with a model of a multi-infeed system, comprised of two VSCHVDC systems injecting power into a common AC network. Unstable conditions were created artificially by lowering the network strength, to make it possible to determine the MIIF values corresponding to instability between VSC HVDC systems, in order to define the MIIF limits for VSC HVDC systems, to determine how the MIESCR should be calculated for VSC HVDC systems, and to define the critical MIESCR value for VSC HVDC systems. The results of the study demonstrated that the MIIF limits defined for LCCHVDC systems do not apply to VSC HVDC systems. The study did however determine how the MIESCR should be calculated for VSC HVDC systems and other PEDs connected to the power system. It was also concluded that the same MIESCR limits in the LCC case could in some cases be used for VSC HVDC systems, depending on the control mode of the system.