New grid-connected systems have imposed additional requirements regarding reliability, power quality, high levels of power processing capacity, and fault support, where power converters have a crucial role in fulfilling these requirements. Overcoming one of these challenges, this paper proposes a new alternative application to improve the low-voltage ride-through (LVRT) support based on the arm impedance employment of the modular multilevel converter (MMC) by attenuating the fault impacts, avoiding overcurrents and overvoltages. This proposal does not require additional hardware or control loops for LVRT support, only using PI controllers. This paper evaluates symmetrical and asymmetrical grid fault impacts on the converter DC side of four converter topologies: two-level voltage source converter topology (2L-VSC), neutral point clamped (NPC), MMC, and 2L-VSC equipped with a DC-chopper, employing the same control structure for the four topologies, highlighting that the MMC contributed better to LVRT improvement under severe grid conditions.

Real-Time Digital Simulation (RTDS) is a powerful tool in modeling and analyzing electrical and drive systems because it provides an efficient and accurate process. There are several hardware devices for this type of simulation; however, their high costs have led to the increasing use of more affordable and reconfigurable technologies. In this context, many logic blocks and storage elements make the Field Programmable Gate Array (FPGA) an ideal device to perform RTDS. This work proposes a technique to embed a real-time digital simulator in an FPGA through Hardware Description Language (HDL) since it provides liberty in the architecture choice and no dependency on commercial ready-made hardware–software packages. The approach proposed focuses on system design developing with expression tree graph, synthesizing and verifying, prioritizing the performance and design accuracy concerning area and power consumption. Thus, the result acquisition occurs at a time step considered in real-time. A simulation of a direct current (DC) motor speed control has been incorporated into this work as an example of application, which includes the embedding and simulation of the electric machine and its drive system. Performance tests have shown that the developed simulator is real-time and makes possible realistic analysis of the interaction between the plant and its control. In addition, an idea of the hardware requirement for real-time simulation is proposed based on the number of mathematical operations.

The high integration of Distributed Generation (DG) into the conventional electric system brings many challenges to the operating sector, in view of the growing concern associated with the reliability of the system and the quality of the energy generated, due to main sources of DG do not have control over the production of active power, and besides being dependent on the of MPPT (Maximum Power Point Tracking) algorithm. On the other hand, DG are normally coupled to the power grid through fast-response power converters, which do not possess any inertia, affecting stability of electric systems. This paper presents a control method for the grid-side voltage source inverter (VSI) of DG units based on virtual synchronous generator (VSG). The technique to be used is the Synchronverter, enabling control over the active and reactive powers generated, by acting in grid support as ancillary services. Simulation results suggest the effectivity of the Synchronverter.