Table 9 FRT technologies of HVDC (four topologies)

LCC-HVDC

Voltage control

[54, 140]

•  Capacitor bank

•  Rectifier station

•  Controlled voltage source

•  Power balance achieved

•  Voltage obtained

•  System stability enhanced

****

**

**

DC-link current control

[145, 146]

•  PMSG

•  Grid-side converters

•  Rectifier firing angle

•  Power reduction without communication

•  Undesired tripping avoided

****

****

****

Frequency control

[54, 146]

•  Power flow

•  Grid frequency controllers

•  Capacitor

•  Frequency obtained

•  Power balance achieved

•  FRT realized

****

****

****

VSC-HVDC

Chopper resistor

[147]

•  Converter station

•  Wind farm excess energy

•  Power of unloading resistance

•  Dynamic reactive support provided

•  Power balanced

***

****

***

Voltage control

[148,149,150]

•  Controlled voltage drops

•  Coordinated control scheme

•  Onshore station

•  Fast power reduction achieved

•  Communication delay eliminated

•  Over-voltage control ability improved

System stability increased

****

***

***

Frequency control

[88, 150,151,152]

•  Capacitors

•  WTs

•  Onshore VSC stations

•  Frequency extremes and rate reduced

•  Frequency deviation eliminated

•  SFD alleviated

•  Frequency support provided

***

***

****

WT output control

[88, 150, 153,154,155]

•  Reactive power compensation

•  Receive end converters

•  Power reduction factor

•  Positive-sequence-voltage-dependent (PSVD)

•  DC voltage limited

•  AC grid stability improved

•  FRT compliance improved

***

***

****

DC protection

[142,143,144]

•  MMC

•  DC circuit breakers

•  Hybrid circuit breaker

•  Resiliency of DC faults enhanced

•  Continued operation ability improved

•  Switching time shortened

•  Transient response augmented

***

***

****

Hybrid-HVDC

AC fault protection

[156,157,158]

•  Overvoltage fixed firing angle

•  AC and DC components of voltage

•  Inverter-side overvoltage reduced

•  Safety and stability maintained

***

***

****

DC fault protection

[158,159,160]

•  DC chopper (DCC)

•  Voltage-dependent current order limiter (VDCOL)

•  Short-term overload capacity of MMC

•  HB-MMC

•  High rating series diode valve

•  Unbalanced power eliminated

•  Commutation failure suppressed

•  VSC DC overvoltage suppressed

•  Electric eliminated

•  DC overvoltage level reduced

•  Fault currents blocked

***

***

****

DR-HVDC

DC fault protection

[119, 161]

•  WT current

•  WT converters

•  FB-MMC

•  System fast recovery facilitated

•  Potential overcurrent risk reduced

•  Semiconductor losses decreased

***

***

****

AC fault protection

[162, 163]

•  Communication-free LVRT strategy

•  Voltage control

•  Current control

•  Voltage restoration enhanced

•  Rotor angle stability strengthened

•  Rated power delivery resumed

***

***

****