AC1A Excitation System

Implements IEEE type AC1A excitation system model

Library

Simscape / Electrical / Specialized Power Systems / Electrical Machines / Synchronous Machine Control

Description

This block models an ac alternator driving a diode rectifier to produce the field voltage Vf required by the Synchronous Machine block. A non-controlled voltage regulator provides a voltage in p.u. with a lower limit of zero imposed by the diode rectifier.

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 [400 0.02].
Voltage regulator internal limits: The voltage regulator internal limits VAmin and VAmax, in p.u. Default is [-14.5 14.5].
Voltage regulator output limits: The voltage regulator output limits VRmin and VRmax, in p.u. Default is [-5.43 6.03].
Damping filter gain and time constant: The gain Kf and time constant Tf of the first-order system representing the derivative feedback. Default is [0.03 1.0].
Transient gain reduction lead and lag time constants: The time constants Tb and Tc of the first-order system representing the lead-lag compensator. Default is [0 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 0.80].

Exciter alternator 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,Ve1 and Ve2 in p.u., on the air-gap line and no-load saturation curve and providing the corresponding two saturation multipliers SeVe1 and SeVe2. Default is [4.18 3.14].

Typically, the voltage Ve1 is a value near the expected exciter maximum output voltage, Ve2 value is about 75% of Ve1 [1].

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 [1]. The saturation function is determined by specifying two voltage points, Ve1 and Ve2 in p.u., on the air-gap line and no-load saturation curve and providing the corresponding two saturation multipliers SeVe1 and SeVe2. Default is [0.10 0.03].

SeVe1 and SeVe2 multipliers are equal to C-B / B, C is the value of exciter field current on the no-load saturation curve corresponding to the specified Ve voltage, and B is the value of exciter field current on the air-gap line corresponding to the selected Ve voltage [1].

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

Demagnetizing factor Kd

The gain Kd represents the demagnetizing factor, a function of exciter alternator reactances. Default is 0.38.

Rectifier loading factor Kc

The gain Kc represents the rectifier loading factor proportional to the commutating reactance. Default is 0.20.

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].
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.
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.

Examples

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 AC1A from the Block Choice menu to control the Synchronous Machine block using the AC1A 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).

Version History

Introduced in R2012b