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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...
This study investigates the possibility of using new transmission technologies such as Thyristor Controlled Series Capacitor (TCSC) and embedded High Voltage DC (HVDC) links to increase power transfer capabilities by means of improving the transient stability as well as oscillation damping in a power system. Initially, this paper discusses the need for stability control systems to ensure co-ordinated...
This paper considers the analysis and setting of harmonic distortion emission limits for the connection of an offshore wind farm considering the complexity introduced by other connections to the same electrical node. It goes on to present overall results following the design and inclusion of a harmonic filter in order to comply with the given emission limits. The paper demonstrates the importance...
In this paper, we present further applications of the timedomain simulation based frequency scanning technique which has been proposed in the earlier literature. The behavior of the complete HVDC system is modelled as the closed loop action of two independent systems (AC system and DC system). The separately obtained frequency scan results of these independent systems are used to get the frequency...
With increasing offshore wind generation, there is a strong argument for implementing a multi-terminal DC grid offshore by the interconnection of individual HVDC links. The point of intersection of three or more lines can be used to interconnect projects with different voltage levels and to control power distribution. It is being proposed that these points, or nodes, be implemented using DC devices...
Modular multilevel converters, based on cascading of halfbridge converter cells, can combine low switching frequency with low harmonic interference. They can be designed for high operating voltages without direct series connection of semiconductor elements. This has led to a rapid adoption within high-power applications such as high voltage direct current transmission. However, the overall hardware...
In this paper, PSPICE analysis and design of grid connected multilevel converter will be presented. This converter has all the features of H-bridge structure, while it has six semiconductor switches and drivers to produce five-level output voltage. Reduction of IGBTs and drivers decreases the converter losses and system cost. The PSPICE analysis is used to predict the spikes on the collector emitter...
The Authors have applied their combined experience of more than 50 years involvement in subsea cable projects, to present key issues and areas where effort must be applied to minimise the risk over the project life cycle. Pre-sanction engineering, manufacturing, installation and failure during operation are discussed. Specific issues are mentioned that have resulted in delay, cost escalation, reliability...
Given the pressing need for additional transmission capacity to accommodate renewable generation, a range of advanced, technically effective and economically efficient corrective (or post-fault) actions that can release latent network capacity of the existing system, has been proposed. However, the increased use of corrective control to manage post-fault transmission overloads, for instance, in the...
This paper considers two reactive power compensation devices for HVDC converter stations, the synchronous condenser (SC) and the Static Synchronous Compensator (STATCOM). The contribution of these devices to the networks inertia is very different. The paper discusses the impact of this inertia on frequency stability in the ac network. The impact is analyzed using analytical studies as well as numerical...
Models of a DC cluster based wind farm collection network with permanent magnet generators (PMG) and passive rectification are described and implemented to investigate the operability of groups of up to 5 paralleled wind turbines. The presence of a degree of slip between the rotating speeds of the machines and its relationship with the PMG stator inductances is discussed. The results of modelling...
This paper compares the site aspects of a Voltage-Sourced Converter (VSC-HVDC) project and a Line-Commutated Converter (LCC-HVDC) project of similar rating. Initially a brief description of the two technologies is presented. Then the project information for the EWIC (Shotton) and Grita (Galatina) sites is provided. Next, a comparison of the overall sites and converter buildings is given. This considers...
In this paper, a 3-phase, Y-connected, 5-level Static Synchronous Compensator (STATCOM) is proposed with reduced number of switches for single phase and unbalanced three-phase loads. The system is implemented and tested under different loading conditions. The level shifted carrier based SPWM method, instantaneous single phase active (P) and reactive (Q) powers are used to control the system. The simulation...
Fault Current Limiters (FCL) limit fault current levels to a more manageable level, this way it becomes possible to increase the transmission ratings of an electrical system, without changing the equipment. Thus, the existing equipment is able to handle the new currents and protect properly the system. In the paper, different types of FCLs are deeply identified, covering their characteristics, advantages...
The distributed generation (DG) has the characteristic of randomness which often results in the difference between the distributed generation actual output power and its planned value [1,2]. It is a popular method to introduce energy storage devices to compensate the difference so that to keep the power system in safe operation and qualified power quality. It is critical to determine the capacity...
Offshore wind power is attracting increasing levels of research and investment. The use of HVDC transmission and development of DC grids are topics with similar levels of interest that go hand in hand with the development of large scale, far from shore wind farms. In this paper, technical challenges resulting from the interaction between power electronic DC-DC converters and the cables in a DC transmission...
Interconnection of High Voltage Direct Current (HVDC) links into networks is key to a future HVDC grid spanning large regions. Various factors including the evolution of cable technology will lead to a variety of DC voltages and a need to provide a DC/DC step up/down at high power ratings (beyond 500 MW). This paper analyses a High Voltage (HV) DC/DC converter utilising an intermediate AC link between...
The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage direct current (HVDC) transmission applications. This paper mainly focuses on the hierarchical structure, functional components and hardware configuration of the control and the protection (C&P) system for MMC VSC-HVDC. The overall structure of (C&P) system based...
The introduction of HVDC light technology has been a significant step towards developing DC transmission grids. However, all voltage source converters (VSC) employed with HVDC are completely defenceless against DC faults, and significant further technical advances are required to achieve security and reliability levels that exist with AC grids. This paper proposes building DC grids using VSC converters...
This paper focuses on the control schemes required on offshore VSC-HVDC networks to transmit the power to the onshore grid and provide fast frequency response for the AC grid. The simulation results show the benefits of such control scheme to restore the frequency in the grid after a loss of generation. The results further investigated the consequence of frequency disturbance in the islanded offshore...
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