Description

This model is based on IEEE Std. 412.5 type AC1A excitation system model (1). The AVR is composed of a leadlag compensator and a cascaded first order filter.

Mask and Parameters

AVR Parameters

AC1A AVR Parameters tab

*Vuel and Voel are the usual inputs for this excitation system (see Inputs, Outputs section below), but the user can choose to use a fixed constant value directly in the mask by choosing “internal” in the mask option.
Expanding the "AC1A diagram" displays the block diagram (expanded in AC1A AVR Block diagram) in the parameters window.

AC1A Block Diagram

Name	Description	Unit
Tr	Regulator input filter time constant. This input filter is not part of the standard and there are no typical values recommended. It was added for flexibility.	s
Tb	AVR lead-lag numerator time constant	s
Tc	AVR lead-lag denominator time constant	s
Ka	AVE filter gain	-
Ta	AVR filter time constant	s
Vamax	Maximum filter output	pu
Vamin	Minimum filter output	pu
Vrmax	Maximum voltage regulator output	pu
Vrmin	Minimum voltage regulator output	pu
Kf	Excitation control system stabilizer gain	-
Tf	Excitator control system stabilizer time constant	s

Exciter Parameters

AC1A Exciter Parameters Tab
Expanding the "Exciter diagram" displays the block diagram in the parameters window.

AC1A Exciter Block Diagram

Name	Description	Unit
Te	Exciter time constant	s
Ke	Exciter constant related to self-excited field	-
Kd	Demagnetizing factor	-
Kc	Rectifier loading factor	-
Se1, Se2	Exciter saturation factor at the corresponding Vex	pu
Ve1, Ve2	Exciter voltage for the exciter saturation function	pu

Initial Values

AC1A Initial Values properties tab

Name	Description		Unit
Ifd0	Synchronous machine field current initial value		pu
Efd0	Exciter output voltage initial value		pu

The parameters Ifd0 and Efd0 can be manually set by entering a numerical value. It can also be set automatically, based on load flow calculations, by entering a referenced synchronous machine variable. For instance, if the name of the synchronous machine on which the excitation system is connected is “SM1”:

If a thermal machine or a hydraulic machine is used, Ifd0 shall be set as “=SM1.IfdInit” multiplied by the synchronous machine parameter Xad = Xd – Xl, and Efd0 shall be set as “=SM1.EfdInit”;
If a pu standard or pu fundamental machine is used, Ifd0 shall be set as “=SM1.IF_Init” and Efd0 shall be set as "=SM1.EFD_Init".

Inputs, Outputs and Signals Available for Monitoring

Inputs

Name	Description	Unit
Voel	Over-excitation limiter output*	pu
Vc1	Signal proportional to compensated terminal voltage	pu
Vuel	Under-excitation limiter output*	pu
Vref	Voltage regulator reference voltage	pu
Vs	Is defined as the output voltage of a power system stabilizer (PSS)	pu
Ifd	Synchronous machine field current*	pu

*If a Synch. Machine (Hydraulic or Thermal) from the Network Machines and Generators library is used, the machine observable Ifd must be multiplied by the synchronous machine parameter Xad = Xd – Xl prior to its input to the exciter. This multiplication is not needed if a Synchronous Machine (pu Standard) or (pu Fundamental) is used.

The HYPERSIM® simulation option “Set Initial Conditions” must be checked for the automatic initialization to work properly.

Outputs

Name	Description	Unit
Efd	Exciter output voltage	pu

References

1. “IEEE Recommended Practice for Excitation System Models for Power System Models for
Power System Stability Studies,” IEEE Standard 421.5-2005.