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