HVDC: line-commutated links#
The two-terminal line-commutated converter model enforces its scheduled quantities, converter angles, and tap limits.
Converter model#
Each terminal is a line-commutated converter of NBR (rectifier) or NBI
(inverter) bridges fed through a converter transformer with ratio \(t\). With
\(V_{ac}\) the per-unit AC terminal voltage, \(\theta\) the firing angle
\(\alpha\) at the rectifier or the extinction angle \(\gamma\) at the inverter,
\(X_c\) the commutating reactance, and \(I_d\) the direct current, the DC-side
voltage of a converter follows the bridge relation
and the two terminals are joined by the line resistance: \(V_{d,r} - V_{d,i} = R_{dc} I_d\).
Scheduled quantity#
MDC selects the scheduled quantity. Mode 1 holds the scheduled DC power
SETVL in MW: a non-negative SETVL schedules the power at the rectifier,
and a negative value schedules its magnitude at the inverter. Mode 2 holds
the scheduled direct current SETVL in amperes. VSCHD is the scheduled
DC voltage in kV, held by the voltage-controlling terminal. A nonzero
compounding resistance RCOMP displaces the voltage-control point along
the line by RCOMP times the direct current.
Angle and tap limits#
The rectifier holds the schedule with the firing angle inside
[ANMNR, ANMXR]; the inverter holds the voltage with the extinction angle
inside [ANMNI, ANMXI], all in degrees. The converter transformer taps
move within [TMNR, TMXR] and [TMNI, TMXI] in steps of STPR and STPI
to keep the angles inside their ranges. When an angle reaches a limit it is
held there, and the operating point follows from the remaining relations.