Introduction

This model represents the power component and the control system of a Static Var Compensator (SVC). The power component consists of a thyristor controlled reactor (TCR inductive branch) and three Thyristor Switched Capacitors (TSC capacitive branches).

Note: The transformer is not modeled internally and must be added by the user. The transformer parameters considered internal to the block should be the same as the user would add external to the block

The control system includes measuring, synchronization, regulation, distribution and firing subsystems. Depending on the operation mode, the model allows users to study step responses either for a voltage reference or a susceptance reference. This can be used to optimize the regulator parameters. The thyristors can also be fired by signals generated from an external source.

Description

Diagram

Figure below shows the diagram of the model with the TCR and TSC branches

Power Component

The models of the four branches of a static compensator are as shown in the figure above. Resistances R and r respectively represent ohmic losses in the capacitor and the reactor. The two resistances, the capacitor and the reactor form a type of black box. Hence, it is not possible to measure the voltage across one of the resistances or the reactor. However, the voltage across the capacitor is calculated and available as a signal. This is also the case for the voltages across the thyristors.

Control system synchronization unit

The synchronization unit consists of a phase-lock loop (PLL) applied to each voltage phase on the transformer primary. The PLL calculates the frequency and phase angle required to fire the thyristors. Figure below shows a simplified diagram of this unit.
This type of synchronization has the advantage of being insensitive to harmonics and stable in frequency.

Measuring unit
Figure below shows the measuring unit. Voltage measuring must be accurate, fast and insensitive to harmonics. To do this, the output of the Park conversion block is integrated and the voltage is measured by subtracting two consecutive samples of the integrator output with a delay of one cycle between them.

Control Unit

The control unit consists of a proportional and integral (PI) controller. The latter compares the voltage measured and voltage reference to achieve.

The output of the controller is given by:

Bp is the required susceptance on the primary side for regulation. The current I is not measured but calculated using Bp and Umes. The response of the controller depends on the value of the gains. The integral gain determines the speed of the controller, while the proportional gain can be used to compensate for the delay in the firing system.

Distribution unit

The distribution unit receives the following input:

The leakage inductor of the transformer
The signal Bp from the PI
The states and values of each TSC capacitive and TCR inductive branch
And the value of the hysteresis to apply at transition points

From the primary susceptance Bp of the static compensator and the leakage inductance of the transformer, the susceptance Bs on the secondary side is calculated and then represented as a parallel combination of the TSC capacitive and TCR inductive branches.

The value of the capacitance Bcap produced by the parallel capacitive branches and the value of Bind is given by the non-linear function:

The calculation of the equivalent impedance of the parallel TSC capacitive branches take into account the availability of the branches. Therefore, it is possible to operate in downgraded or degradation mode.

In order to avoid oscillations when the capacitors are switched, hysteresis is used at transition points when the number of parallel TSC capacitive branches changes.

Firing Unit

The function of the firing unit is to send the firing orders to the thyristors of the different branches. To do this, it receives the following input:

Phase angle (omega) of the synchronization voltage
Firing angle alpha
Firing order of the TSC capacitive branches

Since the TCR inductive branch is controlled, the firing unit sends the omega t degree pulses after the last zero-crossing of the synchronization voltage. Since the TSC capacitive branches are only switched and not controlled, their firing is always executed at the same time on the waveform, that is 90 degrees before the zero-crossing of the voltage.

Table of Contents

Mask and Parameters

Mask

General Tab

Name	Description	Unit	Variable = {Possible Values}
Name of primary XFO Bus name	Name of the bus on the high voltage side of the static compensator transformer
Primary Transformer voltage	RMS Line-line rated voltage on the primary side of the transformer	kV	{(0,1e12]}
Secondary Transformer voltage	RMS Line-line rated voltage on the secondary side of the transformer	V	{(0,1e12]}
Leakage reactance	Leakage inductance of the primary winding of the transformer	pu/100MVA	{[0,1]}
Delta connection type	Specifies the connection of the transformer and the Delta windings lagging or preceding the Y winding
TCC mode	On = synchronized firing of the TSC capacitive branches, Off = continuous firing
Valve blocking and unblocking	Deblock = valve firing enabled, Block = valve firing disabled
Regulation - Kp	Proportional gain	puB/puV	{[0,1]}
Regulation - Ki	Integral gain	puB/puV/s	{(0,1e12]}
Regulation - Slope	Slope of voltage controller	pu/100MVA	{[0,1]}
Regulation - Hysteresis	Hysteresis	pu/100MVA	{[0,1]}
Protection - Strategy Vmax	Maximum value of primary voltage (pu). Above this value, the static compensator is disabled	pu	{[0,1]}
Protection - Strategy Vmin_on	Minimum value of primary voltage (pu). Below this value, the static compensator is disabled	pu	{[0,1]}
Protection - Strategy Vmin_off	Minimum value of primary voltage (pu) required to enable the static compensator	pu	{[0,1]}
AC Fault - Vac_min	Primary voltage threshold (pu) below which a fault is detected	pu	{[0,1]}
AC Fault - Fault duration	Fault duration	s	{(0,1e12]}
AC Fault - Fault delay	Delay in fault application	s	{(0,1e12]}
AC Fault - Under voltage delay	falling edge delay during a specified time interval is applied	s	{(0,1e12]}
Disturbance type	Vref or Bref
Disturbance - Delta_Vref	Value of step in the voltage reference	pu	{[0,1]}
Disturbance -Delta_Bref	Value of step in the value of the susceptance reference	pu/100MVA	{(0,1e12]}
Disturbance -dist_start	Time when the disturbance is applied	s	{(0,1e12]}
Disturbance -dist_end	Time when the disturbance is removed	s	{(0,1e12]}
Filter - Base frequency	Base frequency	Hz	{(0,100]}
Filter -Minimum frequency	Minimum frequency of PLL	Hz	{(0,100]}
Filter -Maximum frequency	Maximum frequency of PLL	Hz	{(0,100]}
Filter - Bandwidth	Band pass filter bandwidth	Hz	{(0,100]}

TCR Tab

TCR

Name	Description	Unit	Variable = {Possible Values}
Connections	Y ground; Y floating; Delta
r	Resistance in parallel with branch reactor	Ohm	{(0,1e12]}
L	Series inductance	H	{(0,1e12]}
R	Branch resistance	Ohm	{(0,1e12]}
Rsnubber	Snubber resistance	Ohm	{(0,1e12]}
Csnubber	Snubber capacitance	F	{(0,1e12]}
Ropen	Valve resistance when open	Ohm	{(0,1e12]}
Rclose	Valve resistance when closed	Ohm	{(0,1e12]}
Imin	Chopping current	A	{(0,1e12]}
Fbov	Forward break overvoltage	V	{(0,1e12]}
Rbov	Reverse break overvoltage	V	{(0,1e12]}
Tq	Time for the valve to stop conducting	s	{(0,1e12]}
Vmin	Minimum forward voltage across valve to conduct	V	{(0,1e12]}

TSC Tab

TSC

Name	Description	Unit	Variable = {Possible Values}
Connections	Y ground; Y floating; Delta
r	Resistance in parallel with branch reactor	Ohm	{(0,1e12]}
L	Series inductance	H	{(0,1e12]}
R	Branch resistance	Ohm	{(0,1e12]}
C	Branch capacitance	F	{(0,1e12]}
Rsnubber	Snubber resistance	Ohm	{(0,1e12]}
Csnubber	Snubber capacitance	F	{(0,1e12]}
Ropen	Valve resistance when open	Ohm	{(0,1e12]}
Rclose	Valve resistance when closed	Ohm	{(0,1e12]}
Imin	Chopping current	A	{(0,1e12]}
Fbov	Forward break overvoltage	V	{(0,1e12]}
Rbov	Reverse break overvoltage	V	{(0,1e12]}
Tq	Time for the valve to stop conducting	s	{(0,1e12]}
Vmin	Minimum forward voltage across valve to conduct	V	{(0,1e12]}

TCR

Ports

Name	Description
Port	ABC power signal for connection to other network elements

Sensors

Name	Description	Unit
CMD12phase_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	Firing pulse of the positive valve in the x branch
CMD21phase_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	Firing pulse of the negative valve in the x branch
Iphase_ x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	Current through the branch	A
STATE12phase_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	State of the positive valve in the x branch
STATE21phase_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	State of the positive valve in the x branch
VphaseTh_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	Voltage across the valves in the x branch	V
VCAPphase_x_y where (x= TCR1, TSC1, TSC2, TSC3; y = 1,2,3)	Voltage across the capacitor in the x branch	V
pulsePat_int	Signal containing the binary code representing the firing orders of the valves
VSYNCphase	Voltage signal used by synchronization unit	V
DelayImpInt	Firing delay (as a fraction of calculation step) calculated by the internal command of the static compensator
DelayImpExt	Firing delay (as a fraction of calculation step) calculated by an external command of the static compensator
DelayImp	Firing delay (as a fraction of calculation step) sent to the static compensator
DelayImpUsed	Firing delay (as a fraction of calculation step) used by the static compensator
V_Ref	Voltage reference for the controller	pu
B_Ref	Susceptance reference for the controller	pu
Slope	Slope of the controller
Deblocked	Signal specifying that the firing pulses are blocked or not
TCC_Mode	Signal specifying that the TCC mode is enabled or disabled
ManualMode	Signal specifying that the manual mode is enabled or disabled
Period	Period of the network (inverse of the frequency)
Frequency	Network frequency	Hz
Alpha_TCR1	Firing angle of the TCR inductive branch	Degree
wtphase	Phase angle of synchronization voltages	Degree
V_Prim	Voltage measured by the system	V
V_Error	Input of PI regulator of regulation unit	V
B_SVC	Susceptance seen from primary side of transformer
B_TSC	Capacitive susceptance required
B_TCR	Inductive susceptance required

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