IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, VOL. 4, NO. 3, JULY 2013 725 Offshore Power System Operation Planning Considering Energy Market Schedules Krzysztof Rudion, Member, IEEE, Antje G. Orths, Member, IEEE, and Peter Børre Eriksen, Member, IEEE Abstract—This paper analyzes selected issues concerning op- erational strategies for multiterminal dc offshore power systems (OPSs). In the first section, the main challenges regarding the operation of such an OPS are discussed, and a proposal is given for a new observer-based management system (OBMS) used for operation coordination using references from the energy market. In the second section, different operational scenarios for the OPS are investigated in order to present the OBMS application. For this purpose, a test system that considers the expected Euro- pean future wind power development is introduced. Then, using reference power flows from the hourly market, the influence of the OBMS optimization process on the power flows aiming at minimum deviations from the reference energy market signals will be presented. Some exemplary test simulations are performed and recommendations are given. Index Terms—Multiterminal voltage source converter (VSC) HVDC, network planning, operation planning, offshore power system (OPS), wind energy. NOMENCLATURE Assumed tolerance band required to finish the iteration process. Angular frequency of the grid voltage. Voltage increment used for optimization of the dc slack voltage. ci Converter index of all considered converters so that . Iteration index. li Transmission line index within the dc part of the offshore power system (OPS). nb Number of busses. Time point index for period . Shunt capacity at node — . DF Division factor used to adapt the size of the resulting voltage step. AC brunch current between nodes and — . Manuscript received August 20, 2011; revised November 30, 2012; accepted January 01, 2013. Date of publication March 07, 2013; date of current version June 17, 2013. K. Rudion is with Otto-von-Guericke University Magdeburg, D-39106 Magdeburg, Germany (e-mail: rudion@ieee.org). A. G. Orths and P. B. Eriksen are with the Danish Transmission System Op- erator Energinet.dk, DK-7000 Fredericia, Denmark (e-mail: ano@energinet.dk; pbe@energinet.dk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TSTE.2013.2245350 DC brunch current between nodes and — . Current of the converter ci resulting from the physical power flow. The upper limit for the current of converter ci. Brunch inductance between nodes and — . NC Number of the last converter within the OPS. NL Number of considered lines. Nodal active and reactive power at node , respectively. Value of power losses at transmission line li. Reference active power from market model at converter ci. Active power at converter ci from physical power flow at time . Brunch resistance between nodes and — . Index providing a positive or negative algebraic sign, which causes an increase or decrease of initial value of the slack voltage. SPI Slack position index defining converter operating as dc slack. DC voltage level at converter ci from physical power flow. Voltage at node or . Maximal value of the dc voltage among all nodes. Upper limit for the voltage at converter ci. Lower limit for the voltage at converter ci. Maximum allowable voltage value for the dc grid according to (3). DC slack voltage. Weighting factor for power deviation and losses term, respectively. Diagonal and off-diagonal elements of admittance matrix. I. INTRODUCTION T HE European Commission (EC) is expecting a significant, European-wide increase in the installed wind power ca- pacity, not only onshore but offshore as well, up to the level of 150 GW by the year 2030 primarily located in the North Sea [1], [2]. Additionally, ENTSO-E—the European Network Transmission System Operators for Electricity—expects about 1949-3029/$31.00 © 2013 IEEE