Opportunities for Embedded High-Voltage Direct Current: Evaluating the Benefits for the Legacy ac Grid

High voltage direct current transmission cables to help decarbonisation in Europe: Recent achievements and issues

“…Of course, the development of a VSC MTDC grid poses several technical problems being extensively studied in the literature (see e.g. [1, 72–78]), since such grid can be considered as the first truly active transmission network where power flows can be fully controlled in principle and an ‘intelligent’ control scheme is required to: be able to realise the cleared market bids as actual power injections to the AC grid terminals; remain secure under contingencies; allocate in an optimum way the power mismatches caused by the limited predictability of RES and the needed reserves [74]. …”

“…Of course, the development of a VSC MTDC grid poses several technical problems being extensively studied in the literature (see e.g. [1,[72][73][74][75][76][77][78]), since such grid can be considered as the first truly active transmission network where power flows can be fully controlled in principle and an 'intelligent' control scheme is required to:…”

Impact of Grid Forming Power Converters on the Provision of Grid Services through VSC-HVdc Systems

“…Some of the key driving factors for increased adoption of HVdc systems include large scale integration of RES which are usually located away from load centers demanding long distance bulk power transfer, crossregional energy trading (e.g realization of integrated European energy market) and the flexibility offered by HVdc systems to provide additional services to the power system in the view of meeting the rising demand for a reliable power grid [4], [7]. Recently, embedded HVdc systems based on VSC-HVdc technology which connect two nodes within the same synchronous ac network have gained popularity, mainly because of their capabilities to provide additional services to the power grid [8]. A detailed comparison between LCC and VSC HVdc technologies can be found in [9].…”

“…Control action to maintain the bus voltage levels of the power system within allowable limits is termed as voltage regulation. Other than fulfilling expectations specified in grid codes, voltage regulation helps to minimize losses, improve power transfer capability and increase network stability [7], [8]. Flexibility of controlling reactive power references in VSC-HVdc converter stations independent of their active power flows (adhering to converter ratings) makes VSC-HVdc systems a promising candidate in providing grid voltage support services.…”

“…Specially, in the view of retirement of coal and nuclear power plants based on synchronous generators that conventionally provided reactive power support to the power system, it is important that capabilities of VSC-HVdc converters are utilized to make up for this deficiency. Embedded VSC-HVdc links integrated to highly meshed ac grids with parallel lines within relatively shorter distances exhibit promising potential in providing reactive power/ voltage regulation services to the power system [8].…”