A simplified algorithm to solve optimal power flows in hybrid VSC-based AC/DC systems

Abstract

2019) 'A simplied algorithm to solve optimal power ows in hybrid VSC-based AC/DC systems.', International journal of electrical power and energy systems, 110 . pp. 781-794.The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractHigh Voltage Direct Current systems based on Voltage Source Converters (VSC-HVDC) are increasingly being considered as a viable technology with advantages, above all when using underground or submarine cables for bulk power transmission. In order to fully understand how VSC-HVDC systems can be best used within existing power systems, it is necessary to adapt conventional tools to carry out system-wide studies including this technology. Along this line, this paper proposes a simplified algorithm to solve optimal power flows (OPFs) in hybrid VSCbased Alternating Current / Direct Current (AC/DC) grids with multi-terminal VSC-HVDC systems. The proposed algorithm makes it possible to seamlessly extend a previous large-scale AC case to which several multi-terminal VSC-HVDC systems must be added. The proposed approach combines two ideas used previously in two different modelling approaches: each VSC is modelled as two generators with a coupling constraint; and DC grids are modelled as notional AC grids, since, in per unit, the equations for the former are a particular case of the latter with resistive lines and no reactive-power injections. In the proposed approach, the hybrid VSC-based AC/DC system is transformed into an equivalent only-AC system. Therefore, the OPF solution of the AC/DC system can be found with the same tool used for the previous AC problem and a simple extension of the original case.Index Terms VSC HVDC, HVDC transmission, multi-terminal, optimal power flow, power systems. NOMENCLATUREA G , A bus , A branch , A slacks : Sets of the generators, buses, branches and slack buses of the AC grids, respectively. A vsc , A dcbus , A dcbranch : Sets of the VSC stations, buses and branches of the multi-terminal VSC-HVDC systems. V i = V i ∠θ i : Voltage at AC bus ī S G,i = P G,i + jQ G,i : Active-(P) and reactive-power (Q) generation (bus i) S D,i = P D,i + jQ D,i : P/Q consumed by the loads (bus i) S i = P i + jQ i : P/Q injections into the AC grid at bus ī Y bus,ik = G ik + jB ik : Admittance matrix of AC line (i, k) I ik : Current through AC branch (i, k) (leaving bus i) (magnitude) S ik = P ac,ik + jQ ac,ik : P and Q flows through AC branch (i, k) (leaving AC bus i) Z ac,ik = R ac,ik + jX ac,ik : Series impedance of AC branch (i, k) B ac,sh,ik : Shunt susceptance of AC branch (i, k) V s,i = V s,i ∠δ s,i ...

Optimal Power Flow With Emerged Technologies of Voltage Source Converter Stations in Meshed Power Systems

“…The IEEE 30-bus is modified with emerged VSC stations, as a hybrid ac/mdc meshed power system. The modified system has two MDC grids [30] as depicted in Fig. 9 [55]; dragonfly algorithm (DA) [56]; crow search optimization algorithm (CSO) [57,58]; Bat algorithm (BAT) [59,60]; Marine predator optimizer (MPO) [61] are employed to solve the considered problem.…”

“…The assessment of VSC-HVDC systems in a lot of these papers were limited to two-terminal configuration. While, the embedded of meshed DC grids into an AC grid increases the complexity of operation and control analysis of such systems [25,30]. A few researchers ignore the modelling of some elements of AC/MDC to simplify the problem such as neglecting the DC power-flow equations [31].…”

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Security-Constrained Day-Ahead Operational Planning for Flexible Hybrid AC/DC Distribution Networks

“…Core to the MVDC interface model is the unified fundamental frequency model for the VSC which has already been introduced by us in [9,27,28]. The AC and DC sides of the VSC are coupled together through the following simple voltage relationship V cr = km a E dc , essentially modelling the VSC in a fundamental frequency as an ideal transformer with a continuous complex tap ratio (m a ) signifying the pulse width modulation (PWM) control of a real VSC.…”

“…Specifically, the DC parts of the network are represented as notional only-AC parts, with resistive AC lines (zero reactance). This is possible due the equivalence of the power-flow equations of resistive AC lines in AC systems and the power-flow equations, as discussed in [28]. With this modelling approach, bus voltages and currents of the DC systems will be complex numbers, as those in AC systems, but with a zero imaginary part.…”