SM ST4C

Discrete-time or continuous-time synchronous machine ST4C static excitation system with an automatic voltage regulator

Since R2020a

• 

Libraries:
Simscape / Electrical / Control / SM Control

Description

The SM ST4C block implements a synchronous-machine-type ST4C static excitation system model in conformance with IEEE 421.5-2016^[1].

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

You can 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) property to 0. To configure the integrator for discrete time, set the Sample time (-1 for inherited) property to a positive, nonzero value, or to -1 to inherit the sample time from an upstream block.

The SM ST4C block comprises of four major components:

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

• The Voltage Measurement Transducer 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. This voltage error is then passed through a voltage regulator to produce the field voltage.

• The Power Source component models the power source for the controlled rectifier when it is independent from the terminal voltage.

This diagram shows the overall structure of the ST4C excitation system model:

In the diagram:

• V_T and I_T are the measured terminal voltage and current of the synchronous machine.

• V_C1 is the current-compensated terminal voltage.

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

• V_REF is the reference terminal voltage.

• V_S is the power system stabilizer voltage.

• V_B is the exciter field voltage.

• E_FD and I_FD are the field voltage and current, respectively.

The following sections describe each of the major parts of the block in detail.

Current Compensator and Voltage Measurement Transducer

The current compensator is modeled as:

$$V_{C1}=V_T+I_T\sqrt{R_C^2+X_C^2},$$

where:

• R_C is the load compensation resistance.

• X_C is the load compensation reactance.

The voltage measurement transducer is implemented as a Low-Pass Filter block with the time constant T_R. Refer to the documentation for the Low-Pass Filter block for the exact discrete and continuous implementations.

Excitation Control Elements

This diagram illustrates the overall 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 the power switch selector (V_S) voltages. For more information about using limiters with this block, see Field Current Limiters.

• There are two Take-over Logic subsystems. The subsystems model 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.

• The PI_R subsystem models a PI controller that functions as a control structure for the automatic voltage regulator and allows the representation of an equipment retrofit with a modern digital controller. The minimum and maximum anti-windup saturation limits for the block are V_PImin and V_PImax, respectively.

• The PI_M subsystem models a PI controller and replaces the Lead-Lag block in SM ST3C. The minimum and maximum anti-windup saturation limits for the block are V_Mmin and V_Mmax, respectively.

• An inner field voltage control loop is utilized to linearize the exciter control characteristic and it is composed of the gains K_M and K_G and the time constants T_M and T_G. The minimum and maximum anti-windup saturation limits for the Low-Pass Filter block are V_Amin and V_Amax, respectively.

Field Current Limiters

You can use various field current limiters 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:

• The summation point as part of the automatic voltage regulator (AVR) feedback loop

• The take-over point to override the usual behavior of the AVR

If you are using the stator current limiter at the summation point, use the single input V_SCLsum. If you are using the stator current limiter at the take-over point, use both the overexcitation input, V_SCLoel, and the underexcitation input, V_SCLuel.

Power Source

It is possible to adopt a different representation of the power source for the controlled rectifier by selecting the relevant option in the Power source selector parameter. The power source for the controlled rectifier can be either derived from the terminal voltage (Position A: power source derived from generator terminal voltage) or it can be independent of the terminal voltage (Position B: power source independent of generator terminal conditions).

This diagram shows a model of the exciter power source utilizing a phasor combination of the terminal voltage, V_T, and terminal current, I_T:

Ports

Input

V_REF — Voltage reference

scalar

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

Data Types: single | double

V_S — Input from stabilizer

scalar

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

Data Types: single | double

V_T — Terminal voltage

scalar

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

Data Types: single | double

I_T — Terminal current

scalar

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

Data Types: single | double

V_OEL — Overexcitation limit signal

scalar

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

V_UEL — Underexcitation limit signal

scalar

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

V_SCLsum — Summation point stator current limit signal

scalar

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 (V_SCL) to Summation point.

Data Types: single | double

V_SCLoel — Take-over stator current limit (OEL)

scalar

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

V_SCLuel — Take-over stator current limit (UEL)

scalar

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

Ifd_pu — Measured field current

scalar

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

Data Types: single | double

Output

Efd_pu — Field voltage

scalar

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

Data Types: single | double

Parameters

General

Initial field voltage, Efd0 (pu) — Initial output voltage

1 (default) | real number

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

Initial terminal voltage, Vt0 (pu) — Initial terminal voltage

1 (default) | real number

Initial per-unit terminal voltage.

Initial terminal current, It0 (pu) — Initial terminal current

1 (default) | real number

Initial per-unit terminal current.

Sample time (-1 for inherited) — Block sample time

-1 (default) | 0 | positive scalar

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

Resistive component of load compensation, R_C (pu) — Compensation resistance

0 (default) | positive number

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 component of load compensation, X_C (pu) — Compensation reactance

0 (default) | positive number

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.

Regulator input filter time constant, T_R (s) — Regulator time constant

0 (default) | positive number

Equivalent time constant for the voltage transducer filtering.

Control

Voltage regulator proportional gain, K_PR (pu) — Regulator proportional gain

10.75 (default) | positive number

Proportional gain associated with the voltage regulator PI control block.

Voltage regulator integral gain, K_IR (pu/s) — Regulator integral gain

10.75 (default) | positive number

Integral gain associated with the voltage regulator PI control block.

Thyristor bridge firing control equivalent time constant, T_A (s) — Regulator lag time constant for first lead-lag block

0.02 (default) | positive number

Equivalent time constant in the thyristor bridge firing control.

Maximum regulator output, V_Rmax (pu) — Upper limit of regulator output

1 (default) | real number

Maximum per-unit output voltage of the regulator.

Minimum regulator output, V_Rmin (pu) — Lower limit of regulator output

-0.87 (default) | real number

Minimum per-unit output voltage of the regulator.

Forward proportional gain of inner loop field regulator, K_PM (pu) — Inner loop forward proportional gain

1 (default) | positive number

Per-unit forward proportional gain of the PI control block in the inner loop field regulator.

Forward integral gain of inner loop field regulator, K_IM (pu/s) — Inner loop forward integral gain

0 (default) | positive number

Forward integral gain of the PI control block in the inner loop field regulator.

Maximum output of field current regulator, V_Mmax (pu) — Upper limit of field current regulator output

99 (default) | real number

Maximum per-unit output voltage of the field current regulator.

Minimum output of field current regulator, V_Mmin (pu) — Lower limit of field current regulator output

-99 (default) | real number

Minimum per-unit output voltage of the field current regulator.

Maximum exciter output, V_Amax (pu) — Upper limit of exciter output

99 (default) | real number

Maximum per-unit output voltage of the exciter.

Minimum exciter output, V_Amin (pu) — Lower limit of exciter output

-99 (default) | real number

Minimum per-unit output voltage of the exciter.

Feedback gain of field current regulator, K_G (pu) — Feedback gain of field current regulator

0 (default) | positive number

Per-unit feedback gain of the field current regulator.

Feedback time constant of field current regulator, T_G (s) — Feedback time constant of field current regulator

0 (default) | positive number

Per-unit feedback time constant of the field current regulator.

Maximum feedback voltage for field current regulator, V_Gmax (pu) — Maximum feedback voltage for field current regulator

99 (default) | positive number

Maximum per-unit feedback voltage for the field current regulator.

Alternate PSS input locations (V_S) — PSS input location

Summation point before take-over UEL (default) | Summation point after take-over UEL

Power system stabilizer input.

Alternate OEL input locations (V_OEL) — OEL input location

Unused (default) | Summation point at voltage error | Take-over at voltage regulator input | Take-over at inner-loop output

Overexcitation limiter input location:

• If you select Summation point at voltage error, V_OEL is an input of the Summation Point Logic subsystem.

• If you select Take-over at voltage regulator input, V_OEL is an input of the Take-over Logic subsystem.

• If you select Take-over at inner-loop output, V_OEL is an input of the Take-over Logic 1 subsystem.

Alternate UEL input locations (V_UEL) — UEL input location

Unused (default) | Summation point at voltage error | Take-over at voltage regulator input | Take-over at inner-loop output

Underexcitation limiter input location:

• If you select Summation point at voltage error, V_UEL is an input of the Summation Point Logic subsystem.

• If you select Take-over at voltage regulator input, V_UEL is an input of the Take-over Logic subsystem.

• If you select Take-over at inner-loop output, V_UEL is an input of the Take-over Logic 1 subsystem.

Alternate SCL input locations (V_SCL) — SCL input location

Unused (default) | Summation point at voltage error | Take-over at voltage regulator input | Take-over at inner-loop output

Stator current limiter input location:

• If you select Summation point, use the V_SCLsum input port.

• If you select any of the Take-over options, use the V_SCLoel and V_SCLuel input ports.

Exciter

Rectifier loading factor proportional to commutating reactance, K_C (pu) — Rectifier loading factor

0.113 (default) | positive number

Rectifier loading factor proportional to the commutating reactance.

Potential circuit (voltage) gain coefficient, K_P (pu) — Potential circuit voltage gain coefficient

9.3 (default) | positive number

Per-unit voltage gain coefficient in the power source circuit.

Dependencies

To enable this parameter, set Power source selector to Position A: power source derived from generator terminal voltage.

Compound circuit (current) gain coefficient, K_I (pu) — Potential circuit current gain coefficient

0 (default) | positive number

Per-unit current gain coefficient in the power source circuit.

Dependencies

To enable this parameter, set Power source selector to Position A: power source derived from generator terminal voltage.

Reactance associated with potential source, X_L (pu) — Potential source reactance

0.124 (default) | positive number

Per-unit reactance in the power source circuit.

Dependencies

To enable this parameter, set Power source selector to Position A: power source derived from generator terminal voltage.

Potential circuit phase angle (degrees) — Potential circuit phase angle

0 (default) | positive number

Phase angle of the power source circuit, in degrees.

Dependencies

To enable this parameter, set Power source selector to Position A: power source derived from generator terminal voltage.

Maximum available exciter voltage, V_Bmax (pu) — Exciter voltage upper limit

11.63 (default) | positive number

Maximum per-unit available exciter voltage value.

Power source selector — Power source selector

Position A: power source derived from generator terminal voltage (default) | Position B: power source independent of generator terminal conditions

Position of the power source selector, specified as Position A: power source derived from generator terminal voltage or Position B: power source independent of generator terminal conditions.

References

[1] IEEE Recommended Practice for Excitation System Models for Power System Stability Studies. IEEE Std 421.5-2016. Piscataway, NJ: IEEE-SA, 2016.

Extended Capabilities

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

Version History

Introduced in R2020a