Documentation

DC2A Excitation System

Implements IEEE type DC2A excitation system model

Library

sps_avr

Description

This block models a field controlled dc-commutator exciter with continuously acting voltage regulators supplied from the generator or auxiliaries bus voltage. The voltage regulator output limits are proportional to terminal voltage Vt.

This block is an adaptation of the DC2A 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.

Transient gain reduction lead and lag time constants

The time constants Tb and Tc of the first-order system representing the lead-lag compensator.

Exciter and Rectifier Tab

Exciter gain and time constant

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

Field voltage values

The exciter saturation function is defined as a multiplier of exciter alternator output voltage to represent the increase in exciter excitation requirements due to saturation [1]. The saturation function is determined by specifying two voltage points, Efd1 and Efd2 in p.u, on the air-gap line and Constant Resistance Load Saturation curve, and providing the corresponding two saturation multipliers SeEfd1 and SeEfd2

Typically, the voltage Efd1 is a value near the expected exciter maximum output voltage. The Efd2 value is about 75% of Efd1.

Exciter saturation function values

The exciter saturation function is defined as a multiplier of exciter alternator output voltage to represent the increase in exciter excitation requirements due to saturation. The saturation function is determined by specifying two voltage points, Efd1 and Efd2 in p.u., on the air-gap line and Constant Resistance Load saturation curve, and providing the corresponding two saturation multipliers SeEfd1 and SeEfd2.

SeEfd1 and SeEfd2 multipliers are equal to A-B / B, A is the value of exciter field current on the Constant Resistance Load saturation curve corresponding to the selected Efd voltage, and B the value of exciter field current on the air-gap line corresponding to the selected Efd voltage [1].

If you do not want to model the saturation effect, set SeVe1 and SeVe2 values to zero.

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..

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.

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 DC2A from the Block Choice menu to control the Synchronous Machine block using the DC2A 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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