This work presents an optimal reactive power management strategy for the operation of a transmission connected distribution grid with high share of wind power. Main control objective is minimizing reactive power exchange with the overlaying transmission grid. For this purpose, a mixed integer non-linear optimal power flow (MINLP-OPF) problem is formulated utilizing reactive power capabilities of wind farms and transformer tap-changer positions whilst respecting voltage limitations. Loss minimization and flat voltage profile are possible secondary sequential optimization objectives. The proposed control is evaluated for a real German 110-kV distribution grid with 1.6 GW installed wind power and yearly time series. Throughout a year, reactive power exchange with the transmission grid can be reduced by 96.8% while minimizing the increase in active power losses to 11.1%. Choosing voltage profile as secondary objective, reactive power exchange is reduced by 96.5% while quadratic deviation from nominal voltage is reduced by 30.8%
In this paper a novel co-simulation is developed, to study the dynamic exchange of reactive power from a distribution grid to the transmission grid. This exchange is performed under a regulatory scheme. In particular, a distribution grid optimizer signals to the transmission grid the available reactive power interval at the distribution/transmission nodes every 15 minutes. A transmission grid optimizer uses this information to compute a reactive power set point, to stabilize the voltage in the transmission grid. The distribution grid optimizer receives this set point and translates it into settings for transformers and renewable generators. This strategy is tested on a running grid simulation, with the tools working in parallel. It is shown that the voltage in the transmission grid can be improved, but at the cost of power losses in the distribution grid and renewable generators
This paper focuses on a scenario with a high amount ofrenewable generators (DGs) in the distribution grid; a local gridoperator (DSO) utilizes reactive power provision by the DGs, toimprove the reactive power balance at the connection points tothe transmission grid. At the same time, the transmission gridoperator (TSO) aims to optimize his voltage, by computingreactive power setpoints for the DSO. This is a decentralizedoptimization problem, where two optimizers (“DSO” and “TSO”)balance the reactive power flow between their grid areas. Nooptimizer has detailed information about the neighbouring gridarea and uses a very simple equivalent model for it. In case these equivalents are updated iteratively, we find that both optimizersmostly converge within only afew iterations for a realistic Danishgrid topology. However, it is also found that the accuracy of theresult highly depends on the built-in component models that eachoptimizer uses, within its own grid area
This paper presents a co-simulation environment fortesting different operation, control and aggregation strategies ona power network model with multiple voltage levels. Inparticular this environment, called "OpSim", is used toinvestigate the question of how multiple grid operators -controlling different voltage levels and I or grid areas - couldinteract in a future grid scenario with a high amount ofrenewable energy resources. First the architecture of "OpSim"is presented, which uses a message bus to connect andsynchronize multiple simulators, representing the grid, as wellas grid operators strategies. Second, a proof-of-concept isdemonstrated in which an interaction between multiple gridoperators is investigated. The message rate between simulationcomponents is evaluated and results indicate that a stablesimulation operation is possible. Finally, the furtherdevelopment stages of "OpSim" are explained, as well as a firstapplication with industrial partners
In this publication, the authors present methodology and example results for the analysis of ancillary services of an offshore wind farm cluster and its electrical power system. Thereby the operation tool Wind Cluster Management System (WCMS) is used as simulation tool to evaluate certain planning scenarios. Emphasis is made on two topics: 1) the integration of high voltage direct current (HVDC) technology to the WCMS, 2) the ancillary service analysis. As examples, voltage source converter based HVDC (VSC-HVDC) and the provision of reserve respectively balancing power are discussed in detail. The analyzed study case considers the Kriegers Flak area while the associated power system connects wind farms to Sweden, Denmark and Germany.
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