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The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

This paper presents the design, development, control, and supervision of a hardware-based laboratory multiterminal-direct-current (MTDC) testbed. This work is a part of the TWENTIES (transmission system operation with large penetration of wind and other renewable electricity sources in networks by means of innovative tools and integrated energy solutions) DEMO 3 European project, which aims to demonstrate the feasibility of a dc grid through experimental tests. This is a hardware-in-the-loop dc system testbed with simulated ac systems in real-time simulation; the dc cables and some converters are actual, at laboratory scale. The laboratory-scale testbed is homothetic to a full-scale high-voltage direct-current (HVDC) system: electrical elements are the same in per unit. The testbed is supervised by a supervisory control and data acquisition system based on PcVue. A primary control-based droop control method to provide dc grid power balance and coordinated control methods to dispatch power as scheduled by a transmission system operator are implemented. Since primary control acts as converter level by using local measurements, a coordinated control is proposed to manage the dc grid power flow. The implemented system is innovative and achievable for real-time real-world MTDC-HVDC grid applications. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) is becoming a promising converter technology for HVDC transmission systems. Contrary to the conventional two- or three-level VSC-HVDC links, no capacitors are connected directly on the dc bus in an MMC-HVDC link. Therefore, in such an HVDC link, the dc bus voltage may be much more volatile than in a conventional VSC-HVDC link. In this paper, a connection between the dc bus voltage level and the stored energy inside the MMC is proposed in order to greatly improve the dynamic behavior in case of transients. EMT simulation results illustrate this interesting property on an HVDC link study case. [ABSTRACT FROM PUBLISHER]