Optimal power flow in multi-terminal HVDC grids with offshore wind farms and storage devices

Abstract

a b s t r a c tThis work presents a power flow strategy for multi-terminal HVDC grids. Energy is mainly generated via renewable energy sources and there are nodes in the network with the possibility to store energy. This energy is generated taking into account real weather conditions in order to make the best scheduling of the system in a realistic approach. An optimization scheme is proposed in which all these elements are included as well as real operation constraints. Distribution losses are minimized for the whole network. This gives as a result a control strategy being able to deal with the whole system and its inherent constraints giving the framework for a multi-objective optimization control.Ó 2014 Published by Elsevier Ltd. IntroductionThe difficulty of satisfying the constant growth in worldwide energy demand is exacerbated by a number of well-known factors regarding the supply and use of conventional energy resources (oil, gas, etc.): the inconvenient geographical location of many conventional energy production sites vis-à-vis their centers of use, the continuous price inflation accompanying these resources and, of course, the fact that their use releases undesirable emissions into the atmosphere. These disadvantages are turning the world's attention towards a number of renewable energy solutions, among which offshore wind farms present a particular interest. There are several advantages to developing offshore wind energy, notably: wind conditions are more favorable out to sea than on land; the average wind speed is higher therefore providing more energy, and the wind direction tends to remain more constant in the absence of obstacles [1]. Furthermore, the wind is less turbulent because variations in temperature between the different layers of air are smaller over the sea than over land. For these reasons, offshore wind turbines have a larger up-time than onshore turbines. These are some of the reasons why wind farm investment is chiefly being channeled to offshore facilities rather than to their landbased equivalent despite their higher initial installation costs.Energy transmission has historically been carried out in alternative current (AC). However high voltage direct current (HVDC) transmission is investigated in this study due to several advantages it possesses over AC lines. First of all the reactive power makes AC transmission losses greater than HVDC applications. Additionally, transmission capacity is also greater in HVDC lines due to the non-existence of the skin effect, and also the efficiency and controllability of DC converters are higher [2][3][4][5]. Another advantage of using HVDC is that the use of fewer cables in DC lines also implies lower costs and weight enabling therefore the possibility of operating in remote marine regions where wind conditions are even more favorable [6,7].Although multi-terminal HVDC systems are technically feasible, they have not been widely accepted as a cost-effective transmission solution. There are only two HVDC installations which have operated as mult...

Adaptive sliding mode with time delay control based on convolutions for power flow reference tracking using a VSC-HVDC system

“…(11), the term ∆P = P s − P r represents the DC link control and P loss is considered as a disturbance that is assumed to be unknown. Since the dynamics of the DC link is linear and relatively slow, a conventional PI controller can be used to regulate DC voltage U C2 to its rated value U C2ref and reject external disturbances P loss [6][7][8][9][10][11][12][13][14][15][16], as shown in Figure 5. …”

“…We intend to develop a state feedback control that forces the system to track a nonconstant reference current 2154 X ref (t) in the presence of plant uncertainties and external disturbances that unavoidably affect the state space model Eq. (5) [6][7][8][9][10][11][12][13][14][15][16].…”

Inertia Emulation in AC/DC Interconnected Power Systems Using Derivative Technique Considering Frequency Measurement Effects

“…Content may change prior to final publication. Citation information: DOI 10.1109/TPWRS.2016.2644698, IEEE Transactions on Power Systems 2 HVDC and converter based systems [15]- [16]. Grid-scale energy storage is widely believed to have the potential to provide more flexibility [17] which led to research investigation on both the technical and economic issues surrounding ESS applications.…”

Multi-Objective Scheduling Optimization Based on a Modified Non-Dominated Sorting Genetic Algorithm-II in Voltage Source Converter−Multi-Terminal High Voltage DC Grid-Connected Offshore Wind Farms with Battery Energy Storage Systems

“…Compared to other technologies, the battery energy storage system (BESS) is the most cost-effective option coupled with power-electronic devices for an optimal operation of power systems. In recent times, various studies have been conducted on integrated systems for optimal operation [16][17][18]. A control strategy including a hierarchical scheme has been developed for a multi-terminal HVDC network [16].…”