Table 4 Technologies of VSC-MTDC

Stability of system

Converter station

[86, 88]

•  Droop control

•  Active-power control

•  Reactive-power control

•  Double closed-loop space vector control (DCSVC)

•  Requirement of communication alleviated

•  Second frequency drop (SFD) reduced

•  Power flow change restrained

•  Automatic coordinated control

•  Unbalanced voltage

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DC voltage

[89, 95,96,97,98,99,100]

•  Single-point DC voltage control

•  Multi-point DC voltage control

•  Cooperative control

•  DC voltage margin control

•  Master–slave control

•  Droop control

•  Direct current matching control (DCMC)

•  Small signal stability analysis

•  DC link voltage maintained

•  Dispatching DC currents flexibility improved

•  Design of grid connection points

•  Communications

•  Dynamic responses

•  Expandability

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Stagey of network control

AC grid

[101, 102]

•  Perturbation observer-based nonlinear control (PONC)

•  Sliding-mode control nonlinear

•  Model predictive control

•  Power redistribution

•  Voltage stability of OWFs improved

•  Lumped perturbations alleviated

•  Frequency performance enhanced

•  Accurate model

•  Power balance

•  Power impulses

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Wind farm

[88, 103, 104]

•  Cluster control

•  Wind farm pitch control

•  Adaptive inertial droop control

•  Economic feasibility enhanced

•  Dynamic disturbances suppressed

•  Frequency deviation reduced

•  Compute of cluster's power

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DC power flow

[105,106,107]

•  Optimization algorithm

•  Droop control

•  Variable droop control

•  Transient performance improved

•  System losses reduced

•  Voltage deviations abated

•  Optimization of power flows

•  Load predictions

•  Power distribution

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