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ST2A Excitation System

Implements IEEE type ST2A excitation system model

Library

sps_avr

Description

This block models a compound source rectifier excitation system. It utilizes both terminal voltage, Vt, and terminal current, It, to form a model of the exciter power source.

This block is an adaptation of the ST2A excitation system of the IEEE® 421 standard, copyright IEEE 2005, all rights reserved.

Dialog Box and Parameters

Controllers Tab

Low-pass filter time constant

The time constant Tr of the first-order system representing the stator terminal voltage transducer.

Voltage regulator gain and time constant

The gain Ka and time constant Ta of the first-order system representing the main regulator.

Voltage regulator output limits

The voltage regulator output limits VRmin and VRmax, in p.u.

Damping filter gain and time constant

The gain Kf and time constant Tf of the first-order system representing the derivative feedback.

Exciter and Rectifier Tab

Exciter gain and time constant

The gain Ke and time constant Te of the first-order system representing the exciter.

Current circuit gain coefficient KI

The current circuit gain coefficient.

Potential circuit gain coefficient Kp

The potential circuit gain coefficient.

Direct axis synchronous machine reactance

Enter the value of the Xd reactance of the controlled Synchronous Machine block.

Rectifier loading factor Kc

The rectifier loading factor, proportional to commutating reactance.

Initial Values Tab

Initial values of terminal voltage and field voltage

The initial values of terminal voltage Vt0 and field voltage Efd0, both in p.u. Initial terminal voltage is normally set to 1 pu. The Vt0 and Efd0 values can be determined using the Powergui Load Flow tool.

Initial value of terminal current

The initial value of terminal current It0, in p.u. This value can be determined using the Powergui Load Flow tool.

Sample time

Specify a value greater than zero to discretize the block at the given sample time. Set to -1 to inherit the simulation type and sample time parameters of the Powergui block.

Ports

Vref

The reference value of the stator terminal voltage, in p.u.

Vt

The measured value in p.u. of the stator terminal voltage of the controlled Synchronous Machine block.

It

It The measured value in p.u. of the stator terminal current of the controlled Synchronous Machine block.

Ifd

The measured value in p.u. of the stator field current of the controlled Synchronous Machine block.

Vstab

Connect this input to a power system stabilizer to provide additional stabilization of power system oscillations. When you do not use this option, connect to a Simulink ground block. The input is in p.u.

Efd

The field voltage to apply to the Vf input of the controlled Synchronous Machine block. The output is in p.u.

Example

The power_machines example contains a Configurable Subsystem block that allows you to select between seven types of excitation systems to control the terminal voltage of the Synchronous Machine block. This configurable block refers to the power_machines_lib example library that contains seven pretuned excitation system blocks that fit simulation requirements for this example.

Right-click the EXCITATION configurable block, then select ST2A from the Block Choice menu to control the Synchronous Machine block using the ST2A Excitation System block.

References

[1] "IEEE Recommended Practice for Excitation System Models for Power System Stability Studies." IEEE Standard, Vol. 421, No. 5, 2005 (Revision of IEEE 521.5-1992).

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