Download control of vsc based hvdc link

CONTROL OF VSC BASED HVDC LINK
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
1
CONTROL OF VSC BASED HVDC LINK
A VSC of hvdc link injects a controllable voltage at the AC terminals given by
Ȇ=m Ea< θ+ α
where
Eao=K Vdc
K= √6/ π
K=constant depending on the convertor configuration
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
2
CONTROL OF VSC BASED HVDC LINK
Line commuted thyristor based convertor can only draw
reactive power depending on the power flow through the convertor.
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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CONTROL OF VSC BASED HVDC LINK
They are two level controllers
1. m(normalized modulation index)
2. α(phase angle) are control variables used to control power
and reactive power
IP=Q/Vs
m&α(normalized modulation index, phase angle)
α =tan-1 e r/e p
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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Activity
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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DESIGN OF CUREENT CONTROLLERS
Active current is in phase with source voltage with
magnitude Vs and the positive reactive current drawn by the convertor lags
source voltage by 90 degree.
Gc(S)=Kc(1+STc/STc ) For PI controller
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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DESIGN OF CUREENT CONTROLLERS
PI controller time constant Tc ,can be chosen to cancel the poles
introduced by the current flow in the inductive circuit
I p=1/1+STi I p*
I r =1/1+STi I r*
Control hierarchy and system control
The control hierarchy in a VSC based HVDC link similar to
that in a LCC based HVDC link except for some major difference.
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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Three levels of control in a VSC
based HVDC links
The valve firing sequence is regulated by the type of PWM applied
selective harmonic Elimination(SHE) method of PWM results in the least number
of valve switching's per cycle to cancel a selected number of harmonics .
Control characteristics for terminal
Mode of switching from DC voltage control (or) vive versa may be
required if there are limits imposed on the power flow.
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
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Control characteristics for terminal
The convertor control sets the magnitude and phase angle of the
injected voltage of the convertor.
The operating is determined by the intersection of the two characteristics
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
9
Thank You
2/28/2017
UNIT3/HVDC/ CONVERTER AND HVDC
SYSTEM CONTROL/C.K.GOBU
10