A Fault-Tolerant, Passivity-Based Controller Enhanced by the Equilibrium-to-Equilibrium Maneuver Capability for the DC-Voltage Power Port VSC in Multi-Infeed AC/DC Modernized Grids

Due to the simplicity, practicality, and absence of communication needs, stabilizing the dc voltage via a dc-voltage power port voltage-sourced converter (VSC) connected to an ac grid (also known as the master VSC in some works of literature) is a favorable option in multi-infeed ac/dc modernized grids (MI-AC/DC-MGs). However, in MI-AC/DC-MGs, several devices may be connected/disconnected to/from the dc link. This affects the effective inductance and capacitance seen from the dc side of the dc-voltage power port VSC. Moreover, the use of a dc-side LC-filter to improve the power quality aspects associated with the power feeding to the dc loads and with the power generated by dc generators is increasing. Such factors complicate the dynamics of the dc-voltage power port VSC and threaten its stability, as well as its transient performance. This paper proposes an enhanced nonlinear control approach (compared with existing methodologies) for the dc-voltage power port VSC in MI-AC/DC-MGs considering the following very influential factors. First, it considers a nonlinear control approach considering the presence of the dc-side energy-storing components with uncertain parameters. The proposed controller accounts for complete nonlinear dynamics of the dc-voltage power port VSC with a dc-side inductance without any cascaded control structure. Thus, it 'globally' stabilizes nonlinear dynamics by means of a passivity-based design approach with equilibrium-to-equilibrium maneuver capability. Second, it considers fault-tolerant control of the primary control of such systems in order to enhance the MI-AC/DC-MGs' resiliency, which is highly required to improve the reliability of MI-AC/DC-MGs of the future. Making the primary control of the dc link 'fault-tolerant' is a vital factor in order to have better-guaranteed power quality in the MI-AC/DC-MGs undergoing many types of events. This will cause MI-AC/DC-MGs to have fault ride-through (FRT) feature. Also, this feature, which is proposed and enhanced in this paper, generally strengthens the flexibility of MI-AC/DC-MGs by removing additional requirements for the controllers of other currently connected VCSs (e.g., those are working as constant P/Q active loads, and so on, which are forming other entities of the multi-infeed ac/dc grid) in order to effectively benefit from them. Theoretical analyses, simulation results, and experimental tests are presented in order to show the effectiveness of the proposed controller in this paper.