Description

The EXDC2 model was developed in line with the references [1] [2]. Figure 1 shows the architecture of the EXDC2 model [2]. EXDC2 is similar to DC2A, the regulator output limits are proportional to the machine terminal voltage.

Mask and Parameters

AVR parameters

Expanding the "EXDC2 diagram" displays the block diagram in the parameters window.

Name	Description	Unit
Tr	Regulator input filter time constant	s
Ka	Voltage regulator gain	-
Ta	Regulator time constant	s
Tb	Voltage regulator time constant	s
Tc	Voltage regulator time constant	s
Kf	Excitation control system stabilizer gain	-
Tf1	Excitation control system stabilizer time constant	s
Vrmax	Maximum voltage regulator output	pu
Vrmin	Minimum voltage regulator output	pu

Exciter Parameters

Expanding the "Exciter diagram" displays the block diagram in the parameters window.

Name	Description	Unit	Variable = {Possible Values}
Te	Exciter time constant	s	Te >= 0.04
Ke*	Exciter constant related to self-excited field	-	-
Se1, Se2	Exciter saturation factor at the corresponding Vex	pu	-
Efd1, Efd2	Exciter voltage for the exciter saturation function	pu	-

*When the user specifies Ke as 0, in the initialization, the model automatically calculates a Ke using the following equation and the initial Efd [2]

Initial value tab

Name	Description	Unit	Variable = {Possible Values}
Efd0	Exciter output voltage initial value	pu	--

The parameter Efd0 can be set manually, 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”, then Efd0 shall be set as “=SM1.EfdInit” if a thermal machine or a hydraulic machine is used, and as "=SM1.EFD_Init" if a pu standard or pu fundamental machine is used.

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

Inputs and Outputs and Additional Signals Available for Monitoring

Inputs

Name	Description	Unit
Vc1	Signal proportional to compensated terminal voltage (refer to the load compensator block documentation) If the load compensator block is not used upstream from the exciter block, then Vc1 is equal to Vt	pu
Vref	Voltage regulator reference voltage	pu
Vs	Combined PSS and possibly discontinuous control output after any limits or switching, as summed with terminal voltage and reference signals	pu
Vuel*	Underexcitation limiter output	pu
Voel*	Overexcitation limiter output	pu

*Vuel and Voel is normally an input to this excitation system but the user has the option to use a fixed constant value directly in the mask by choosing internal in the mask option.

Outputs

Name	Description	Unit
Efd	Exciter output voltage	pu

References

[1] I. C. Report, "Excitation System Models for Power System Stability Studies," in IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 2, pp. 494-509, Feb. 1981.

[2] PSS®E 34.2.0 Model Library. NY, USA: Siemens Industry, Inc., 2017.