The Role of the Internal Energy in MMCs Operating in Grid-Forming Mode

Abstract

With an increasing number of renewable energy resources being integrated into the power system through power electronics, conventional power plants based on large synchronous machines tend to be reduced in the upcoming future. With the Modular Multilevel Converter as the state-of-the-art power electronics solution for power systems, it will be necessary to operate some of these converters in grid-forming mode, in order to either preserve the stability and robustness of the ac grid or as the only solution to generate the ac grid in cases with no available synchronous generation. This paper aims to understand how the internal energy control of the MMC can be used to effectively mitigate the propagation of ac power disturbances to the dc side, thanks to its buffering capability. Different energy control structures are explored, and a comprehensive discussion and comparison among them is provided, including stability analysis, transient performance and tuning guidelines. Simplified and linear models are used to address the analysis, whereas detailed non-linear models implemented in MATLAB Simulink are used to verify the results via time-domain simulations.

Blackstart Capability of Modular Multilevel Converters From Partially-Rated Integrated Energy Storage

“…Assuming that the transformer has no residual flux in the core, the converter can soft-start the ac grid by ramping up the ac voltage in order to eliminate inrush current in the transformer. Assuming a passive R-L grid, grid forming control such as the one detailed in [34], [35] is adopted, with the modification that the converter is not connected on the dc side, therefore the energy balance has to be maintained by circulating currents replenishing the C-stack energy from ES-stacks, as shown in Fig. 14.…”

Testing Requirements and Control Strategies of Next-Generation Grid Emulator: A Review

“…The combination of energy-based internal control and grid-forming based external control of MMC is discussed in [45], [46]. It has been demonstrated that by controlling MMC internal energy, the grid-forming based MMC is identical to an equivalent 2-level VSI.…”

An Overview on the Recent Advances of the Voltage Source Converter Control Modes in Terms of their Roles in Transmission Grid Ancillary Services

“…The voltage at the PCC, denoted by 𝑣 , is also the voltage of the capacitance 𝑐 . This capacitance can be the physical capacitance of an LC filter [49] or the capacitance of an AC component such as an overhead line [50] if there is no filter. The control scheme is composed of the following blocks:…”