ST2A Excitation System

Implements IEEE type ST2A excitation system model

Library

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks / Machines / Excitation Systems

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.

Parameters

Controllers Tab

Low-pass filter time constant: The time constant Tr of the first-order system representing the stator terminal voltage transducer. Default is 20e-3.
Voltage regulator gain and time constant: The gain Ka and time constant Ta of the first-order system representing the main regulator. Default is [120 0.15].
Voltage regulator output limits: The voltage regulator output limits VRmin and VRmax, in p.u. Default is [0 1.0].
Damping filter gain and time constant: The gain Kf and time constant Tf of the first-order system representing the derivative feedback. Default is [0.05 1.0].

Exciter and Rectifier Tab

Exciter gain and time constant: The gain Ke and time constant Te of the first-order system representing the exciter. Default is [1.0 0.5].
Current circuit gain coefficient KI: The current circuit gain coefficient. Default is 8.0.
Potential circuit gain coefficient Kp: The potential circuit gain coefficient. Default is 4.88.
Direct axis synchronous machine reactance: Enter the value of the Xd reactance of the controlled Synchronous Machine block. Default is 1.56.
Rectifier loading factor Kc: The rectifier loading factor, proportional to commutating reactance. Default is 1.82.

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. Default is [1 1].
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. Default is 1.
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. Default is 0.

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).