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Abstract-This work analyzes the behavior of an MMC-HVDC-connected off-shore wind power plant (WPP) during dc faults. For that purpose, detailed models of the dc cable, MMC stations and transformers have been used in order to obtain reliable results. The influence of the WPP control method in the short-circuit behavior of the HVDC link has also been studied. Results show that the dynamics of the WPP contribution to pole-to-ground faults are slightly slower than those of the wind turbines current control loops. Therefore, the wind turbine front end converters can be used to reduce the peak and average value of the fault current in such a system. Moreover, it has been found that ferro-resonant oscillations can appear in the off-shore ac-grid when the WPP delivers constant power during faults.
This paper analyzes the integration of lithium ion (Li-ion) batteries into large scale grid-connected PV plants. It performs a systematic analysis on both the operation improvement obtained by a PV+ES power plant and the ageing experienced by the Li-ion batteries used as Energy Storage (ES) system when operating under different energy management strategies (EMS). In this paper, the PV+ES power plant structure is presented and the selection of Li-on batteries as ES system (ESS) is justified. Moreover, the simulation model used for studying the Li-ion battery ageing is explained and tested for the different EMS. All the analyses conducted in this paper are based on actual data recorded from an operative PV power plant and using verified real models.Postprint (published version
Detailed models of modular multi-level converters (MMCs) are cumbersome for electromagnetic transient simulation programs because of their high number of components which involve large simulation times. In this work, the modeling of an MMC is addressed with the objective of reducing the simulation time. First, the MMC structure is presented, including the modulation technique, the voltage balancing algorithm and the circulating current control used to validate the model. Next, an efficient simplified model is proposed. This is formed by just one variable voltage source, one variable capacitor and one variable resistor per arm, regardless of the number of submodules. This simplified model allows the simulation time to be reduced while keeping the dynamics of the MMC. The comparison through several PSCAD simulations with a detailed 5-level MMC model proves its validity during both steady-state and transient conditions (ac and dc short-circuits).
Abstract.A new control scheme for the operation of offshore wind farms connected through a VSC-HVDC link to the main onshore grid is presented in the paper. The control strategy has been developed to allow the islanded operation and blackstart of the wind farm as these requirements will probably be of great interest in the future due to the progressive increase of distributed generation. A complete model of the offshore wind farm with a VSC-HVDC link and its control scheme has been developed and analyzed through PSCAD simulations. Results show that the proposed control scheme is able to operate the plant under different steady-state and transient conditions.
Key wordsOffshore wind power, VSC-HVDC transmission systems, islanded operation of wind farms, VSC control.
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