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This paper proposes a new control scheme for the Voltage Source Converters (VSCs) of a High Voltage Direct Current (HVDC) grid connecting asynchronous AC systems, so that the latter can mutually support their frequencies after a disturbance. The scheme involves no communication between VSCs. It is activated upon detection of a significant frequency deviation, with the possibility to limit the support...
This paper considers the use of HVDC stability control with Wide Area Measurements in order to extend the transmission boundary capability limits. Both event- and response-based controls are considered. The event-based action is triggered faster, whilst the response-based action is slower but is more sensitive to the actual system response. The response-based action has the additional benefit of forming...
One of the major challenges of realising a Multi-Terminal DC grid has been the lack of a suitable HVDC Breaker. Previous designs of HVDC breaker were either too slow to be suitable for interrupting fast-rising fault currents or had conduction losses too high for economically viable operation on a grid. However, the new class of "hybrid" DC circuit breakers has fundamentally changed this...
HVDC technology is a key driver for the integration of renewable energy sources (RES) in large transmission systems. However, the displacement of conventional thermoelectric power plants due to RES development can hinder safe operation of LCC-HVDC converters, especially during inverter operation, mainly due to the reduction of short circuit power on the ac network. These issues are exacerbated in...
Traditional approaches to transmission system security assessment use deterministic criteria e.g. the application of `N-1' or `N-2' circuit depletion under prescribed heavy system loading conditions. However, such worst-case deterministic approach does not provide explicitly an assessment of the probability of overloading the system, and the likelihood of the outages is treated equally. Recent research...
Flexible AC Transmission System (FACTS) devices and Voltage Source Converter (VSC) High Voltage Direct Current (HVDC) systems have fast reactive power control capabilities which can be used to increase power system voltage stability. When located near a Line Commutated Converter (LCC) HVDC converter they can be used to support the performance of the LCC HVDC. This paper shows how well VSC HVDC, Static...
This paper presents a transient analysis modelling of a multiterminal HVDC network using PSCAD EMTDC on a parallel computing grid platform. The different dynamic cases, such as re-dispatch of power flow in DC network, DC network fault clearing with the application of HVDC circuit breakers and the redistribution of power after fault clearing, are simulated. The key considerations are discussed for...
Successful integration of offshore wind power via VSC based HVDC transmission systems into the existing power grid requires a full understanding of the inherent potential and possibilities to keep this complex system stable under worst case conditions. These conditions include in particular large onshore system disturbances decreasing the power transfer capacity of the grid suddenly to below the power...
As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. The modelling in a rotating dq frame is able to transform the quantities from ac variables to dc variables resulting in a significantly improved simulation speed. dq modelling is normally used for VSC converter in dynamic studies, while dc fault study is typically studied...
The paper focuses on developing the control for directly connected battery energy storage system (BESS) in low voltage direct current (LVDC) distribution systems. The main purpose of the control is to provide essential connection/disconnection and charge/discharge functions. Additionally, due to direct connection, it is necessary to implement control functions for management of the power flows in...
Modular Multilevel Converter (MMC) is becoming increasingly popular with the development of HVDC connections and, in the future, with the integration of Multi Terminal DC grids. A lot of publications have been published about this topology these last years since it was first proposed. Few of them are addressing explicitly the two different roles that are held by this converter in an HVDC link: power...
Next-generation medium and high voltage DC grids are expected to comprise multiple terminals that include generation, loads and interconnections to other networks. DC faults pose a significant challenge to the implementation of multi-terminal DC networks as high voltage DC breakers are complicated in design and will add a large cost and volume to the DC converter station. In this paper, a medium and/or...
The focus of this paper is transient phenomena in VSC-HVDC connected offshore wind power plants (WPPs). With the help of a case study modelled in PSCAD simulation software, energisation events are analysed in the time domain. A comparison with more well-known results obtained at energisation of AC connected WPPs indicates that significant differences arise as the energy involved in the switching event...
Low frequency AC (LFAC) provides an alternative to HVDC and HVAC connections for offshore wind farms. Charging current is reduced as compared to standard 50Hz or 60Hz transmission and cable length thus may be extended. LFAC links to wind farms may be interconnected to form an offshore network - a significant advantage over HVDC technology which currently lacks a matured circuit breaker technology...
This study focuses on the the reliability of HVDC grids, analysing the secure and optimal operation of transmission systems consisting of both HVDC (High Voltage Direct Current) and HVAC (High Voltage Alternating Current) interconnections, with high penetration of offshore wind, taking into account the system spinning reserves. While AC systems are usually operated N-1, it is not clear which should...
Beside the future need for offshore HVDC grids also the need for future onshore HVDC grids are currently extensively discussed. The requirements for HVDC substations as well as for HVDC connections for onshore and offshore applications differ a lot. This paper highlights the requirements for onshore HVDC substations and describes a solution for a multiterminal switchyard topology. This also includes...
This paper introduces the new concept of DC Independent System Operator, DC-ISO. The DC-ISO will be responsible for ensuring the reliability and security of the MTDC system in real-time and co-ordinate the supply of and demand for electricity, in a manner that avoids violations of technical and economic standards. A methodology for an optimal steady-state operation of a MTDC system based on DC-ISO...
HVDC grids have been made practical with the introduction of Voltage Source Converters (VSC). The development of VSC technology has, and continues to be rapid, with new converter topologies and new manufacturers entering the market. For the power transmission industry to fully exploit the benefits of this rapidly developing field of engineering a "multi-vendor" supply chain is considered...
This paper summarises some of the important challenges power transmission networks will be facing in the near future. Special focus has been laid on the operation of High Voltage Direct Current (HVDC) overhead transmission lines, which are expected to be used for extended parts of newly built HVDC transmission systems. As one of the most promising and emerging DC technologies, a Modular Multilevel...
The Alternate Arm Converter (AAC) is a voltage source converter being developed as an alternative to the Modular Multilevel Converter (MMC) for HVDC power transmission and reactive power compensation. Each Arm of the converter contains high voltage series IGBT Director Switches and full-bridge cells, which enables the VSC to ride through AC and DC network faults. This paper describes how the AAC can...
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