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SM ST5C

Discrete-time or continuous-time synchronous machine ST5C static excitation system with automatic voltage regulator

Since R2023a

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Libraries:
Simscape / Electrical / Control / SM Control

Description

The SM ST5C block implements a synchronous-machine-type ST5C static excitation system model in conformance with IEEE Std 421.5-2016 [1].

Use this block to model the control and regulation of the field voltage of a synchronous machine.

Switch between continuous and discrete implementations of the block by using the Sample time (-1 for inherited) parameter. To configure the integrator for continuous time, set the Sample time (-1 for inherited) parameter to 0. To configure the integrator for discrete time, set the Sample time (-1 for inherited) parameter to a positive scalar. To inherit the sample time from an upstream block, set the Sample time (-1 for inherited) parameter to -1.

The SM ST5C block comprises three major components:

  • The Current Compensator component modifies the measured terminal voltage as a function of the terminal current.

  • The Voltage Measurement Transducer component simulates the dynamics of a terminal voltage transducer using a low-pass filter.

  • The Excitation Control Elements component compares the voltage transducer output with a terminal voltage reference to produce a voltage error value. The component then passes this value through a voltage regulator to produce the field voltage.

This diagram shows the structure of the ST5C excitation system model:

In the diagram:

  • VT and IT are the measured terminal voltage and current of the synchronous machine, respectively.

  • VC1 is the current-compensated terminal voltage.

  • VC is the filtered, current-compensated terminal voltage.

  • VREF is the reference terminal voltage.

  • VS is the power system stabilizer voltage.

  • EFD and IFD are the field voltage and current, respectively.

Current Compensator and Voltage Measurement Transducer

The block models the current compensator by using this equation:

VC1=VT+ITRC2+XC2,

where:

  • RC is the load compensation resistance.

  • XC is the load compensation reactance.

The block implements the voltage measurement transducer as a Low-Pass Filter block with the time constant TR. Refer to the documentation for the Low-Pass Filter block for information about the exact discrete and continuous implementations.

Excitation Control Elements

This diagram shows the structure of the excitation control elements:

In the diagram:

  • The Summation Point Logic subsystem models the summation point input location for the overexcitation limiter (OEL), underexcitation limiter (UEL), stator current limiter (SCL), and power switch selector (V_S) voltages. For more information about using limiters with this block, see Field Current Limiters.

  • The Take-over Logic subsystem models the take-over point input location for the OEL, UEL, SCL and PSS voltages. For more information about using limiters with this block, see Field Current Limiters.

  • A parallel configuration of Lead-Lag (Discrete or Continuous) blocks offer independent control settings when a limiter is active. The model offers a common gain factor KR and two Lead-Lag (Discrete or Continuous) blocks for the AVR and for the underexcitation and overexcitation limiters. The SW_UEL and SW_OEL Switch blocks activate the appropriate control path when the VUEL and/or VOEL signals are connected to their respective alternate positions. The SW_UEL and SW_OEL Switch blocks are on position B when you set the Alternate UEL input locations (V_UEL) and Alternate OEL input locations (V_OEL) parameters to Take-over at voltage error.

  • The two Lead-Lag blocks in each control path model additional dynamics associated with the voltage regulator and with the underexcitation and overexcitation limiters. The first Lead-Lag block in each respective path represents a transient gain reduction, where TC (or TC2 and TUC2) is the lead time constant and TB (or TB2 and TUB2) is the lag time constant. The second Lead-Lag block allows the possibility of representing a transient gain increase, where TC1 is the lead time constant and TB1 is the lag time constant. See the documentation for the Lead-Lag block for information about the discrete and continuous implementations.

Field Current Limiters

You can use different types of field current limiter to modify the output of the voltage regulator under unsafe operating conditions:

  • Use an overexcitation limiter to prevent overheating of the field winding due to excessive field current demand.

  • Use an underexcitation limiter to boost field excitation when it is too low, which risks desynchronization.

  • Use a stator current limiter to prevent overheating of the stator windings due to excessive current.

Attach the output of any of these limiters at one of these points:

  • Summation point — Use the limiter as part of the automatic voltage regulator (AVR) feedback loop.

  • Take-over point — Override the usual behavior of the AVR.

If you are using the stator current limiter at the summation point, use the input VSCLsum. If you are using the stator current limiter at the take-over point, use the overexcitation input VSCLoel, and the underexcitation input VSCLuel.

Ports

Input

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Voltage regulator reference set point, in per-unit representation, specified as a scalar.

Data Types: single | double

Input from the power system stabilizer, in per-unit representation, specified as a scalar.

Data Types: single | double

Terminal voltage magnitude, in per-unit representation, specified as a scalar.

Data Types: single | double

Terminal current magnitude, in per-unit representation, specified as a scalar.

Data Types: single | double

Input from the overexcitation limiter, in per-unit representation, specified as a scalar.

Dependencies

  • To ignore the input from the overexcitation limiter, set Alternate OEL input locations (V_OEL) to Unused.

  • To use the input from the overexcitation limiter at the summation point, set Alternate OEL input locations (V_OEL) to Summation point.

  • To use the input from the overexcitation limiter at the take-over point, set Alternate OEL input locations (V_OEL) to Take-over.

Data Types: single | double

Input from the underexcitation limiter, in per-unit representation, specified as a scalar.

Dependencies

  • To ignore the input from the underexcitation limiter, set Alternate UEL input locations (V_UEL) to Unused.

  • To use the input from the underexcitation limiter at the summation point, set Alternate UEL input locations (V_UEL) to Summation point.

  • To use the input from the underexcitation limiter at the take-over point, set Alternate UEL input locations (V_UEL) to Take-over.

Data Types: single | double

Input from the stator current limiter when using the summation point, in per-unit representation, specified as a scalar.

Dependencies

  • To ignore the input from the stator current limiter, set Alternate SCL input locations (V_SCL) to Unused.

  • To use the input from the stator current limiter at the summation point, set Alternate SCL input locations to Summation point.

Data Types: single | double

Input from the stator current limiter that prevents field overexcitation when using the take-over point, in per-unit representation, specified as a scalar.

Dependencies

  • To ignore the input from the stator current limiter, set Alternate SCL input locations (V_SCL) to Unused.

  • To use the input from the stator current limiter at the take-over point, set Alternate SCL input locations (V_SCL) to Take-over.

Data Types: single | double

Input from the stator current limiter that prevents field underexcitation when using the take-over point, in per-unit representation, specified as a scalar.

Dependencies

  • To ignore the input from the stator current limiter, set Alternate SCL input locations (V_SCL) to Unused.

  • To use the input from the stator current limiter at the take-over point, set Alternate SCL input locations (V_SCL) to Take-over.

Data Types: single | double

Measured per-unit field current of the synchronous machine, specified as a scalar.

Data Types: single | double

Output

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Per-unit field voltage to apply to the field circuit of the synchronous machine, returned as a scalar.

Data Types: single | double

Parameters

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General

Initial per-unit voltage to apply to the field circuit of the synchronous machine.

Time between consecutive block executions. During execution, the block produces outputs and, if appropriate, updates its internal state. For more information, see What Is Sample Time? and Specify Sample Time.

For inherited discrete-time operation, set this parameter to -1. For discrete-time operation, set this parameter to a positive integer. For continuous-time operation, set this parameter to 0.

If this block is in a masked subsystem or a variant subsystem that supports switching between continuous operation and discrete operation, promote this parameter to ensure correct switching between the continuous and discrete implementations of the block. For more information, see Promote Block Parameters on a Mask.

Pre-Control

Resistance used in the current compensation system. Set this parameter and Reactance component of load compensation, X_C (pu) to 0 to disable current compensation.

Reactance used in the current compensation system. Set this parameter and Resistive component of load compensation, R_C (pu) to 0 to disable current compensation.

Equivalent time constant for the voltage transducer filtering.

Control

Gain of the regulator.

Equivalent lag time constant in the fist Lead-Lag (Discrete or Continuous) block of the voltage regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the first Lead-Lag (Discrete or Continuous) block of the voltage regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Equivalent lag time constant in the second Lead-Lag (Discrete or Continuous) block of the voltage regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the second Lead-Lag (Discrete or Continuous) block of the voltage regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Equivalent lag time constant in the first Lead-Lag (Discrete or Continuous) block of the underexcitation limiter regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the first Lead-Lag (Discrete or Continuous) block of the underexcitation limiter regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Equivalent lag time constant in the second Lead-Lag (Discrete or Continuous) block of the underexcitation limiter regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the second Lead-Lag (Discrete or Continuous) block of the underexcitation limiter regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Equivalent lag time constant in the first Lead-Lag (Discrete or Continuous) block of the overexcitation limiter regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the first Lead-Lag (Discrete or Continuous) block of the overexcitation limiter regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Equivalent lag time constant in the second Lead-Lag (Discrete or Continuous) block of the overexcitation limiter regulator. Set this parameter to 0 when the additional lag dynamics are negligible.

Equivalent lead time constant in the second Lead-Lag (Discrete or Continuous) block of the overexcitation limiter regulator. Set this parameter to 0 when the additional lead dynamics are negligible.

Maximum per-unit regulator output.

Minimum per-unit regulator output.

Overexcitation limiter input location.

Underexcitation limiter input location.

Stator current limiter input location, specified as one of these options:

  • Summation point — Use the V_SCLsum input port.

  • Take-over — Use the V_SCLoel and V_SCLuel input ports.

Exciter

Per-unit rectifier loading factor. This value is proportional to the commutating reactance.

Equivalent time constant of the firing control for the thyristor bridge, in seconds.

References

[1] IEEE Std 421.5-2016 (Revision of IEEE Std 421.5-2005). "IEEE Recommended Practice for Excitation System Models for Power System Stability Studies." Piscataway, NJ: IEEE, 2016.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023a

See Also

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