Renewable power generation has increased in recent years, which has led to a decrease in the use of synchronous generators (SGs). These power plants are mainly connected to the power system through electronic converters. One of the main differences between electronic converters connected to power systems and SGs connected to the grid is the current contribution during faults, which can have an impact on protection systems. New grid codes set requirements for fast current injection, but the converters’ maximum current limitation during faults make it challenging to develop control strategies for such current contribution. This paper presents a positive and negative sequence current injection strategy according to the new Spanish grid code requirements for the novel grid-forming converter control algorithm based on virtual-flux orientation. The behavior of the proposed strategy is tested in a hardware in the loop (HiL) experimental set-up under balanced faults, meaning that the fault is symmetrically distributed among the three phases, and unbalanced faults, where the fault current is distributed asymmetrically between the phases.

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In recent years, the use of synchronous generators (SGs) has been displaced due to the increased use of renewable energy sources. These types of plants mostly use power electronic converters to connect to power grids, which, due to their mode of operation, cannot provide the same services. This paper analyzes the synchronization of Grid-Forming converters (GFM) without phase-locked loop (PLL) through the active power control loop. Stability analysis shows that when increasing the emulated moment of inertia in a voltage source converter (VSC) using grid-forming control, the system becomes oscillatory. The paper proposes a novel compensation mechanism in order to damp the system oscillation, allowing the implementation of inertia emulation. Finally, the real-time implementation is executed using a Hardware in the Loop experimental set-up. The response of VSC under grid disturbances is simulated in a real time simulator, while the proposed control system is implemented in a real-time controller platform.