Control and Limit Enforcements for VSC Multi-Terminal HVDC in Newton Power Flow

This paper proposes a novel method to automatically enforce controls and limits for Voltage Source Converter (VSC) based multi-terminal HVDC in the Newton power flow iteration process. A general VSC MT-HVDC model with primary PQ or PV control and secondary voltage control is formulated. Both the dependent and independent variables are included in the propose formulation so that the algebraic variables of the VSC MT-HVDC are adjusted simultaneously. The proposed method also maintains the number of equations and the dimension of the Jacobian matrix unchanged so that, when a limit is reached and a control is released, the Jacobian needs no re-factorization. Simulations on the IEEE 14-bus and Polish 9241-bus systems are performed to demonstrate the effectiveness of the method.Comment: IEEE PES General Meeting 201

Analysis of harmonics in subsea power transmission cables used in VSC-HVDC transmission systems operating under steady-state conditions

Subsea power cables are a critical component of a voltage-source converter-high-voltage direct current (VSC-HVDC) transmission system in any offshore electrical power scheme. Subsea cables have complicated structures consisting of many different layers: conductor, insulation, sheath, and armor. Harmonic performance of the system depends upon the interactions between the subsea cable, the power converters, and other system components, such as smoothing capacitors. In this paper, a mathematical model of an HVDC-VSC transmission system is developed and its harmonic performance is investigated for steady-state operating conditions. The results suggest that the design of the subsea transmission cable has important effects on harmonic levels in the voltage and current waveforms in the cable and upon power loss within the transmission system. This paper demonstrates that it is always important to consider interactions between all of the system components when predicting harmonic performance in a VSC-HVDC transmission system

Impedance-compensated grid synchronisation for extending the stability range of weak grids with voltage source converters

This paper demonstrates how the range of stable power transfer in weak grids with voltage source converters (VSCs) can be extended by modifying the grid synchronisation mechanism of a conventional synchronous reference frame phase locked loop (PLL). By introducing an impedance-conditioning term in the PLL, the VSC control system can be virtually synchronised to a stronger point in the grid to counteract the instability effects caused by high grid impedance. To verify the effectiveness of the proposed approach, the maximum static power transfer capability and the small-signal stability range of a system with a VSC HVDC terminal connected to a weak grid are calculated from an analytical model with different levels of impedance-conditioning in the PLL. Such calculations are presented for two different configurations of the VSC control system, showing how both the static power transfer capability and the small-signal stability range can be significantly improved. The validity of the stability assessment is verified by time-domain simulations in the Matlab/Simulink environment.Peer ReviewedPostprint (published version

Formality of a higher-codimensional Swiss-Cheese operad

We study configurations of points in the complement of a linear subspace inside a Euclidean space, $\mathbb{R}^{n} \setminus \mathbb{R}^{m}$ with $n - m \ge 2$. We define a higher-codimensional Swiss-Cheese operad $\mathsf{VSC}_{mn}$ associated to such configurations, a variant of the classical Swiss-Cheese operad. The operad $\mathsf{VSC}_{mn}$ is weakly equivalent to the operad of locally constant factorization algebras on the stratified space $\{\mathbb{R}^{m} \subset \mathbb{R}^{n}\}$. We prove that this operad is formal over $\mathbb{R}$.Comment: 50 pages, comments welcome. v2: Added two appendices and corrected Section 5.

Twelve Hour Longevity of the Oral Malodor-Neutralizing Capacity of an Oral Rinse Product Containing the Chlorine Dioxide Precursor Sodium Chlorite

open access articleObjectives: The objectives of this investigation were to investigate the effectiveness and longevity of an oral rinse product containing 0.10% (w/v) of the chlorine dioxide precursor sodium chlorite (1) on oral malodor in participants throughout a 12 h daylight diurnal cycle. Materials and methods: Thirty healthy participants (17 male, 13 female) were recruited to the study. Volatile sulfur compound levels (VSCs: H2S, CH3SH and (CH3)2S) were simultaneously monitored in their oral cavity air samples both before (0 h) and at 0.33, 4, 8 and 12 h after using the above oral rinse, or water as a negative control (participants refrained from oral hygiene measures during this 12 h period). The experimental design for this cross-over investigation was a mixed model ANOVA-based system incorporating treatments, sampling time-points and participants, together with their first-order interactions, as components of variance. Results: Results acquired demonstrated that the oral rinse formulation effectively suppressed VSC production in the oral environment for 12 h periods (p<0.0001, 0.0001 and 0.002 for H2S, CH3SH and (CH3)2S respectively). Mean 0 vs 12 h reductions in oral cavity H2S and CH3SH concentrations were much greater than those observed for the H2O negative control (p<10-8), but not so for (CH3)2S. Principal component analysis (PCA) a H2S/CH3SH linear combination and (CH3)2S alone significantly loaded on the first and second separate orthogonal components respectively, an observation confirming differing sources for these variable sets. Conclusions: The oral rinse explored effectively blocked VSC production in the oral cavity for a period of 12 h. This extended efficacy duration is likely to be ascribable to the ability of its active ClO2- ingredient to exert a combination of biochemical (direct VSC- and amino acid VSC precursor-consuming) and microbicidal actions in vivo. Clinical relevance: The 12 h longevity of product’s# oral malodor-neutralizing actions is of much clinical significance in view of the involvements of VSCs, particularly CH3SH, in the pathogenesis of gingivitis and periodontiti

Multiuser Communication through Power Talk in DC MicroGrids

Power talk is a novel concept for communication among control units in MicroGrids (MGs), carried out without a dedicated modem, but by using power electronics that interface the common bus. The information is transmitted by modulating the parameters of the primary control, incurring subtle power deviations that can be detected by other units. In this paper, we develop power talk communication strategies for DC MG systems with arbitrary number of control units that carry out all-to-all communication. We investigate two multiple access strategies: 1) TDMA, where only one unit transmits at a time, and 2) full duplex, where all units transmit and receive simultaneously. We introduce the notions of signaling space, where the power talk symbol constellations are constructed, and detection space, where the demodulation of the symbols is performed. The proposed communication technique is challenged by the random changes of the bus parameters due to load variations in the system. To this end, we employ a solution based on training sequences, which re-establishes the signaling and detection spaces and thus enables reliable information exchange. The presented results show that power talk is an effective solution for reliable communication among units in DC MG systems.Comment: Multiuser extension of the power talk concept. Submitted to IEEE JSA

Unified reference controller for flexible primary control and inertia sharing in multi-terminal voltage source converter-HVDC grids

Multi-terminal dc (MTDC) grids are expected to be built and experience rapid expansion in the near future as they have emerged as a competitive solution for transmitting offshore wind generation and overlaying their ac counterpart. The concept of inertia sharing for the control and operation of MTDC grids, which can be achieved by the proposed unified reference controller. The control objectives of the MTDC grids voltage source converter (VSC) stations are no longer limited to the stabilisation of MTDC grid, instead, the requirements of ac side are also met. The interaction dynamics between the ac and dc grid is analysed to illustrate the proposed concept. In addition, the voltage source converter stations can work in different operation modes based on the proposed unified control structure, and can switch among the operation modes smoothly following the secondary control commands. Simulation results exhibit the merits and satisfactory performance of the proposed control strategy for stable MTDC grid operation.Peer ReviewedPostprint (author's final draft