Medium power distributed energy resources (DERs) are commonly connected to medium voltage distribution systems via voltage source converters (VSCs). Several guidelines and standards have been developed to establish the needed criteria and requirements for DERs interconnections. In this respect, it is preferred to reinforce the VSC fault ride through (FRT) capability, which considerably minimizes the DG outage period and reconnection time and results in a resilient system against short circuits. Considering the significant number of asymmetrical faults in distribution systems, the VSC response in such conditions must be investigated, and consequently, its FRT capability must be reinforced. In this paper firstly a comprehensive review on existing FRT methods has been presented and discussed. Accordingly, an adaptive virtual impedance-based voltage reference generation method is proposed, which enhances the VSC behavior under short circuits and increases the VSC FRT capability. Also, a fast sinusoidal current reference limiter is proposed to improve the performance. To evaluate the performance of the proposed scheme, state space analysis is presented, and a complete set of simulations is performed in PSCAD/EMTDC environment. Also, a comparison with the conventional method is presented.

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This paper proposes a new control scheme to eliminate the 3 rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3 rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a 3 rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup.

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