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B4 TF-77 AC Fault response options for VSC HVDC Converters

Background:
The reduction in synchronous generation is leading some TSO’s (Transmission System Operator’s) to look at alternative sources of power infeed to provide a large reactive power during AC system faults to maintain some minimum AC system voltage remote from the fault.
One concept being proposed for future HVDC schemes is to utilise a type of converter control system and converter design which rapidly responds to changes in terminal voltage in a similar way to a synchronous machine, hence the term Virtual Synchronous Machine (VSM) is used. With a VSM the magnitude of reactive current during an AC fault is not constrained to be within the active power rating of the converter but rather it can be significantly higher in order to provide maximum AC system support.

Some alternative options have also been proposed, where the converter essentially remains as a current controlling device; but, even in some of these options, the fault current requirement may become the rating case for the converter hardware. Part of the perceived need of the TSO is not only to have a large reactive fault current but also, to be able to deliver this rapidly in response to an AC system fault. This is referred to as FFCI (Fast Fault Current Injection). The perception is that present day VSC controllers, which act to control the current seen by the power electronic converters, are not sufficiently fast enough to meet the future AC grid needs. A second perceived problem with FFCI requirement is that it can create temporary overvoltages following ac fault clearing in low short circuit level grid conditions.

Changing the fault response of a HVDC converter, considering FFCI, specifying fault currents greater than the converters active power rating, or even adopting a VSM type control concept will have an impact on both the converter hardware design, its rating, its losses and the effective utilisation of the capital investment by the owner.

Scope:

The objectives for the Task Force will be to set out the AC system needs as defined by several TSO's, the options achievable with a VSC HVDC converter and the implications on capacity, cost and losses that any changes to the VSC HVDC equipment would incur.

The Task Force would be complimentary to JWG C2/B4.38 as it will focus more on converter equipment aspects where JWG C2/B4.38 has more an overall system design and operation focus.

Terms of Reference (pdf, 25kB)

WG members:

NAMEGIVEN NAMESTATUSCOUNTRY CODE
GleadowJohnConvenerAU
BarnesMikeMemberUK
Canelhas AndreMemberUK
Carl Barker (GE)CarlMemberUK
AndersenBjarneMemberUK
RauhalaTuoumasMemberFI
SaadHaniMemberFR
DenisGuillaumeMemberFR
KoremanKeesMemberNE
SakmuriJayachandraMemberSW
BartzcshCarstenMemberGR
RittingerJuergenMemberGR
IfkerharalS MMemberGR
PathiranaVajiraMemberCA
ChenXiujuMemberCA
PaquinJean-NicholasMemberCA
Prieto Araujo EduardoMemberES
SchönleberKevinMemberES
BartlettSimonMemberAU
LiHaiyingMemberCN
YiRongMemberCN
Zhong Qing-ChangMemberUS
Love GeoffMemberIR