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Grid-forming converters are attracting attention for their significant advantages in terms of stability in a weak grid and simulated inertia. However, while they offer great flexibility due to the use of power semiconductors, they are also affected by their low current-carrying capacity. This means that during a fault, instead of the usual voltage control, a current limiting control is active, which changes the dynamic performance of the converter and influences transient stability. This manuscript focuses on the dynamic performance of grid-forming converters during the restart phase at the post-fault period, and proposes an initial phase threshold to prevent the converter from going into current saturation. Based on this, the manuscript proposes several restart strategies during the post-fault period, by using some fast resynchronization methods in order to meet the requirements of the converter’s stable operation and fast active power restoration. Finally, the above findings and the proposed strategies are validated by a joint control hardware-in-the-loop system.

The precise control of output power by grid-connected converters relies on the correct identification and tracking of a grid voltage’s phase at the converter terminal. During severe grid faults, large disturbances cause the converter’s operating point to move away from the stable equilibrium point during normal operation. This leads to oscillations of both the active and reactive power fed into the grid. Using large-signal modelling, this study investigated the converter’s dynamic processes during and after such fault situations. The investigation considered the influence of the converter’s phase-locked loop (PLL), responsible for phase tracking, as well as that of the DC link on the converter-grid system, which has a major influence on the active power exchange with the grid. On this basis, this study also focused on the reactive current reference’s influence during and after fault clearing. Furthermore, an easily implementable strategy for reactive current injection, leading to minimum power oscillations, was presented. The results and the optimized strategies were validated via controller hardware-in-the-loop tests.

Due to the rising number of electric vehicles in operation the handling of charging stations concerning testing and personal safety has been becoming more and more a focus of interest in practice. Currently there are still open questions concerning safe installation, inspection and operation of such charging stations. This paper focuses on protective measures for safety and initial as well as periodic testing of DC charging stations. At the beginning of the work an overview of legal regulations and technical standards for charging stations is compiled. Further on different DC charging processes (of charging stations from different manufacturers in normal operation and in cases of faults) are measured as well as analysed. It shows that DC charging stations of different manufacturers react differently with regard to switch-off behaviour or switch-off times to various fault scenarios.