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This paper presents the continuous model for the Modular Multilevel Converter (M2C). The model operates in two modes, either operating as a voltage source in deblocked mode or as a rectifying diode bridge in blocked mode. The model is validated by comparison with a detailed M2C model having 36 submodules per arm, using different control strategies. The comparison is based on time-domain simulations...
The growing demand on non-fossil fuel energy has escalated the desire for mega-scale renewable energy power generation. This demand can no longer be satisfied by solely relying on onshore renewable energy power plants (i.e. onshore wind farms, PV farms, etc.). Outcomes from a recent project funded by the Sixth European Union Framework Programme (FP6), “Project Upwind” concluded that larger offshore...
The prevalence of cabled infrastructure associated with wind farms, combined with the surge in power-electronic interfaces in wind turbines and reactive power plant, has highlighted the pervasive nature of harmonics on electricity networks. Insufficient consideration is given to the effects of harmonics through the low prioritisation of power quality in the Front-End Engineering and Design (FEED)...
In future HVDC grids, or ‘Supergrids’, high voltage DC circuit breakers will almost certainly be used in order to remove a faulted element of the HVDC Grid whilst allowing power flow to continue on the remaining grid. However, associated with these HVDC circuit breakers will be the need for a means of fast fault detection, location and isolation. This paper presents a none-conventional approach to...
The use of Voltage Source Converter (VSC) based HVDC transmission has been strongly suggested for the interconnection of various power networks. However, VSCs susceptibility to DC faults, particularly the potential damage caused to the converter IGBTs due to overcurrent, is an issue that must be addressed. This paper analyses the behaviour of a VSC-based HVDC system under varying DC fault conditions...
A Modular Multi-level Converter (MMC) is an attractive topology for HVDC Transmission applications due to its modular structure. Since MMCs are essentially Voltage Sourced Converters, their performance under ac side faults is of particular interest. The possible unbalanced over-currents and capacitor voltage fluctuations are of particular concern as they may cause the converter to trip. In this paper,...
This paper proposes a recovery strategy for wind energy-fed voltage source converter high voltage DC transmission systems, capable of maintaining power balance between the AC and DC sides during different AC faults. This prevents the DC link voltage rise as a result of trapped energy. This reduces the voltage and current stresses on the switching devices. Also, the strategy ensures the converters...
The growth in electricity demand, the low-carbon targets and the rising penetration of renewable energy sources are causing the electricity systems to work closer to their operational limits, therefore their reinforcement is becoming urgent. The construction of a European Super Grid, where existing AC systems are connected through High Voltage Direct Current (HVDC) corridors, is a valuable solution;...
DC power flow can be controlled though N-1 different DC lines/cables in a DC grid having N individual AC/DC converters. A large meshed DC grid can have more DC lines, and since we can not control power in all lines/cables, an overload may result. In this paper, two methods are proposed for DC power flow control through DC lines/cables. The first method involves using extra resistors embedded in series...
Manitoba Hydro is currently making plans for the development of Bipole III (BPIII), a 2300MW, +/-500kV HVdc Bipole that will run from Northern Manitoba to the Load centre in the south over a length of approximately 1300km. Both LCC and VSC options are considered for the new BPIII HVdc scheme [1]-[2]. One of the features being investigated is the option to parallel the new Bipole III converters with...
This paper presents the detailed system design of Shanghai Nanhui project — the first VSC-HVDC demonstration project in China. Two 18MW VSC converters based on Modular Multi-level topology are connected to transfer the energy generated by 11 wind turbines into Nanhui AC network. It has been verified that an improvement on voltage quality and fault ride through performance of Nanhui windfarm have been...
This paper focuses on generic Type 4 wind turbine generators models, their applicability in modern HVDC connections and their capability to provide advanced ancillary services therefrom. A point-to-point HVDC offshore connection is considered. Issues concerning coordinated HVDC and wind farm control as well as the need of a communication link are discussed. Two possible control configurations are...
This paper presents a review of modulation strategies that can be applied on a novel large power voltage source converter arrangement. This arrangement employs four three-level, three-phase neutral-point-clamped inverters, combined by means of low volt-ampere rating intermediate magnetic elements. The 12 resulting inverter poles are paralleled up in pairs by using six interphase transformers (IPTs),...
Z-Source inverters have been proposed as an alternative power conversion concept as they have both voltage buck and boost capabilities. These inverters use a unique impedance network to couple the converter main circuit to the power source, to provide both the voltage buck and boost properties which cannot be achieved with conventional voltage-source and current-source inverters. To understand the...
Up to date numerous HVDC projects have been realized all over the world. But all of them are point to point transmission lines or non meshed multi terminal HVDC systems. To guarantee redundancy and hence security of supply and system stability, a meshed HVDC grid (MTDC) is necessary and also intended i.e. for Europe. Since there is no realized MTDC project the network calculation and operation also...
This paper introduces two new simulation developments called Electro-Magnetic Transient (EMT) Parallel Processing and Hybrid Simulation. Parallel Processing allows the EMT simulation to be broken up into several processes on local or remote computers and run them in parallel while communicating each other. Hybrid Simulation creates a dynamic interface between industry leading EMT and Transient Stability...
This paper identifies potential problems in integrating a point to point voltage source converter based HVDC system to an AC network. The AC network utilizes the classical two-area system where all generators are equipped with voltage and damping controls. A detailed model of the VSC transmission system and its control are provided. For simplicity, the windfarm is modelled as a negative load with...
This paper examines methods of control schemes of multiterminal VSC-HVDC systems for offshore wind farm integration. Modelling strategies of droop DC voltage characteristics for grid side converters are analysed in detail. Differences between voltage-current and voltage-power characteristics are briefly described. A four-terminal VSC-HVDC model with three onshore terminals is established in simulation...
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