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In this paper the basic concept of static characteristics is reviewed along with the major advantages and disadvantages of LCC and VSC in a multi-terminal configuration. The main objective of the paper is to describe the use of Static Characteristics to look at alternative control mode arrangements that could be utilised for multi-terminal operation and to assess the advantages and disadvantages of...
This paper investigates the use of MMC HVDC for low frequency active Power Oscillations Damping (POD). The advantage of the MMC topology is that it the converter has an inherent energy storage capability and some of this capability can be used to store or release energy corresponding to active power oscillations without affecting the HVDC voltage level. The proposed MMC POD controller has been validated...
The paper presents a protection coordination strategy for DC fault clearance for the multi-terminal HVDC networks which relies on an inverse Idc vs dIdc/dt protection characteristic. Separate characteristics are provided to the converters and HVDC breakers to prioritize the opening of HVDC breaker over the converter block, that is, a grading margin is applied. The strategy ensures the minimum number...
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...
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...
Much research has been done regarding the control and coordination of VSC converters in a Multiterminal HVDC network or grid. Amongst those, one underlying concept is the most common- the DC voltage droop control.
A multi-converter network, either radial or meshed, requires not only a means of clearing faults on the DC network but also means of detecting and locating these faults. The characteristics of these DC side faults are fundamentally different to those in AC systems and therefore a DC network protection system requires special consideration. This paper explores the types of fault currents and fault...
Early proposals for multi-terminal HVDC interconnections have been predominantly radial type connections, that is, between any two nodes there is only one branch. However, plans for ‘HVDC Grids’ in the not too distant future are, or include, meshed sections where there are parallel branches between nodes in the HVDC Grid. In such meshed HVDC Grid the DC current will inherently flow from one node to...
There has been much discussion over how HVDC grids incorporating many converters should be controlled and several methodologies have been proposed. An underlying principle of a proposed method, Voltage Droop control, was the minimisation of the inter-dependency of the control of the individual converters, inferring little, or no, reliance on a communication system. Since then further work has shown...
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...
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 multi-level (MMC) HVDC VSC converter topology is becoming widely accepted as the de facto standard topology. Whilst it is normal to consider primarily the real power capability of such a converter it is worth bearing in mind that the origins of the circuit application to AC power systems was in STATCOM applications. This paper will look at the basic main circuit components of a modular...
This paper considers the challenges faced by power system planners and operators with regards to heavily loaded transmission corridors which constrain power flows within the AC system, that is, they are ‘bottlenecks’ within the AC system. Particular reference is made to long distance inter-area AC transmission lines. The addition of back-to-back HVDC schemes within these AC transmission circuits is...
The use of HVDC as an effective means of transmitting electrical energy now has a 50 year history since the first modern schemes were developed. Technological advances have resulted in HVDC becoming a reliable and efficient means of power transmission, both in competition with, and complementary to, AC transmission schemes. This paper will consider the opportunities and also some of the challenges...
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