Description

The CHP model features a generator that comes from an internal library in HYPERSIM, a control for the CHP and an exciter. The control of the CHP handles the model of the CHP outputting the necessary mechanical torque for the generator and the voltage reference for the exciter, as the control allows to perform droop and select between reactive power control or voltage reference control. The diagram is shown in Figure 1.

The control of the CHP comprises of a gas turbine that feeds a steam turbine. The gas turbine and steam turbine combination include a heat recovery steam generator (HRSG). The model of the mechanical drive train of the plant is illustrated in Figure 2. The speed/load control regulates the amount of fuel to be supplied to the gas turbine to control the torque produced by the gas turbine. Figure 3 illustrates the fuel valve, compressor and gas turbine.

The HRSG and steam turbine control is displayed in Figure 5. It models the produced mechanical torque from the steam turbine.

Figure 1 CHP Overall diagram

Mask and Parameters

General Combined-Cycle Plant Data Parameters

Name	Description	Unit
Snom	Nominal electrical power of generator	VA
Pnom	Nominal mechanical power of turbine	W
Vnom	Nominal voltage	V_rmsLL
Fnom	Nominal frequency	Hz
PratedST	Nominal steam turbine power	VA
PratedGT	Nominal gas turbine power	VA
Plan Configuration	In this parameter is selected the configuration of the power plant. GT+ST_GEN: the generator is at the end and it is driven by the gas and steam turbine. GT+GEN+ST: The generator is between the two turbines, and it is driven by both. GT_GEN: The generator is only driven by the gas turbine.	-
H_GT	Inertia parameter for gas turbine	pu
H_ST	Inertia parameter for steam turbine	pu
D_GT	Shaft spring constant for gas turbine	pu torque/rad
D_ST	Shaft spring constant for steam turbine	pu torque/rad
K_GT	Shaft mutual damping for gas turbine	pu torque/ pu dw
K_ST	Shaft mutual damping for steam turbine	pu torque/pu dw

Synchronous Generator Parameters

Name	Description	Unit
Xd	Direct synchronous reactance	pu
Xd’	Direct transient reactance	pu
Xd’’	Direct sub-transient reactance	pu
T’do	Direct axis transient time constant	s
T’’do	Direct axis sub-transient time constant	s
Xq	Quadrature synchronous reactance	pu
Xq’	Quadrature transient reactance	pu
Xq’’	Quadrature sub-transient reactance	pu
T’qo	Quadrature axis transient time constant	s
T’’qo	Quadrature axis sub-transient time constant	s
Saturation	Saturation (1 = Yes, 0 = No)	-
EU, EL, SGU, SGL	Parameters used to generate saturation curve. See Figure 9	pu
Ra	Armature resistance	pu
XI	Armature leakage reactance	pu
H	Mass inertia constant	s
D	Damping coefficient	pu

Gas Turbine Speed/Load Control Data Parameters

Name	Mode	Description	Unit
Max Limit		Governor set point maximum limit	pu
Min Limit		Governor set point minimum limit	pu
Rate Limiter		Governor set point rate limiter	pu/s

W	Grid connected	Referring to Figure 3, 1/W corresponds to the droop	-
W	Grid forming / Speed control	In this mode W is part of the proportional and integral gain in the speed control, which is a PI control. *	-
Y	Grid connected	Referring to Figure 3, Y corresponds to the time constant of the transfer function	-
Y	Grid forming / Speed control	This constant is part of the proportional and integral gain in the speed control. *	-
X	Grid forming / Speed control	Referring to Figure 3, this constant is part of the proportional gain in the speed control. *	-
Control Limiter		Limiter of the acceleration controller	pu/s
Ksp		Acceleration controller gain	-
Accel Control		Enabled or disabled action of the acceleration controller	-
Tt		Temperature constant of the temperature controller	°C
Ttemp		Time constant of the temperature controller	s
Temp Control		Enabled or disabled action of the temperature controller	-
Min Fuel		Fuel demand minimum limit	pu
Max Fuel		Fuel demand maximum limit	pu
Rated Exhaust Temp		Gas turbine rated exhaust temperature	°C

Gas Turbine Data parameters

The fuel valve, compressor and gas turbine model data parameters are as follows:

Name	Description	Unit
a	Valve positioner gain	-
b	Valve positioner constant	-
c	Valve positioner constant	-
Tf	Fuel system time constant	s
Kf	Fuel system gain	-
Krs	Radiation shield gain	-
Trs	Radiation shield time constant	-
Ttc	Thermocouple time constant	-
Etd	Turbine and exhaust transport delay	-
Ecr	Combustion reaction time delay	-
Tcd	Compressor discharge time constant	s
MinFuel	Rated fuel for self-sustained no load conditions	pu

HRSG and Steam Turbine Parameters

Name	Description	Unit
GTEE	Exhaust energy vector	pu
ST_O	Steam turbine output vector	pu
Tb	Boiler storage time constant	s
Tm	Metal heat capacitance time constant	s
Extra Firing	Supplementary firing energy	pu

Operation Mode Parameters

Name	Description	Unit
Voltage Control
Xc	Droop. By acting in V Regulation mode, the CHP can perform droop (in reactive power-voltage)	-
Kp	Proportional gain PI voltage control	-
Ki	Integral gain PI voltage control	-
Vlim_up_V	Maximum output PI voltage control. The output sets the reference voltage of the exciter	pu
Vlim_lo_V	Minimum output PI voltage control. The output sets the reference voltage of the exciter	pu
Reactive Power Control
Qlim_up	Maximum output reactive power in Q Regulation mode	pu
Qlim_lo	Minimum output reactive power in Q Regulation mode	pu
Kp	Proportional gain PI reactive power control	-
Ki	Integral gain PI reactive power control	-
Vlim_up_Q	Maximum output PI reactive power control. The output sets the reference voltage of the exciter	pu
Vlim_lo_Q	Minimum output PI reactive power control. The output sets the reference voltage of the exciter	pu

Exciter Parameters

The exciter panel description can be found under the exciters section for the type AC1A

Control Exciters

Load Flow Parameters

The load flow parameters are provided by the steady-state solution of the network. They are used to initialize the machines and its controls.

Name	Description	Unit
Voltage	Load flow voltage	pu
Angle	Load flow angle	deg
Active power	Active power	W
Reactive power	Reactive power	Var
Reactive power minimum	Minimal reactive power	Var
Reactive power maximum	Maximum reactive power	Var

Ports, Inputs, Outputs and Signals Available for Monitoring

Ports

Name	Description
PCC	Network connection; supports 3-phase connection

Inputs

Name	Description	Units
Wref	Reference speed or frequency input	pu
Pref	Reference electrical power	pu
Qref	Reference reactive power (the value is used only when the CHP is regulating reactive power)	pu
Vref	Reference voltage (the value is used only when the CHP is regulating voltage)	pu
Mode	0 -Grid-connected PQ, 1- Grid-connected PV, 2- Grid forming, 3- Fixed frequency/Q control.	-

Outputs

None

Sensors

Name	Description	Units
w	Speed	pu
Vtd	Stator voltage d-axis	pu
Vtq	Stator voltage q-axis	pu
Vt	Terminal voltage	pu
Ifd	Field current	pu
Efd	Field voltage	pu
Id	Stator current d-axis	pu
Iq	Stator current q-axis	pu
Vce	Measurement of the VCE fuel demand for the gas turbine	pu
Wf	Measurement of the WF fuel flow supplied by the gas turbine and used by the steam turbine	pu
Tx_meas	Exhaust temperature measurement	°C
Tm_ST	Mechanical torque output produced by the steam turbine	pu
Tm_GT	Mechanical torque output produced by the gas turbine	pu
Pm	Total generated mechanical power	pu
Tm	Generated torque	pu
Tx	Exhaust temperature measurement supplied by the gas turbine and used by the steam turbine	°C
Vref_exc	Reference voltage of the exciter	pu
Wref	Reference speed or frequency input	pu
Pref	Reference electrical power	pu
Qref	Reference reactive power (the value is used only when the CHP is regulating reactive power)	pu
Vref	Reference voltage (the value is used only when the CHP is regulating voltage)	pu
Mode	0 -Grid-connected PQ, 1- Grid-connected PV, 2- Grid forming, 3- Fixed frequency/Q control.	-

More on Synchronous Generator Parameters

The saturation is considered linear from 0 to 0.8 pu of Vt (terminal voltage).

If

where:

a and b are found with some iterations and are:

Modeling Details

The mechanical drive train is illustrated in Figure 2. The user can select between three options for the plant configuration. The first one has coupled the steam turbine and the gas turbine. The generator is placed at one end and it’s driven by the two turbines. The second option the generator is placed between the steam turbine and the gas turbine. The last option is a generator with only a gas turbine without the steam turbine.

Figure 2 Block diagram for the mechanical drive train model.

The models in Figure 3 to Figure 5 are inspired from .

Figure 3 Block diagram for the speed/load temperature & acceleration control.

Figure 4 Block diagam for Fuel valve, compressor & gas turbine model.

From Figure 4 The exhaust temperature calculation is

The gas turbine torque calculation is:

The exhaust flow calculation:

Then:

Figure 5 Block diagram for Heat recovery steam generator & steam turbine model.

Figure 6 shows the diagram for the operation mode of the CHP. The user can select between voltage or reactive power control.

Figure 6 Block diagram for the operation mode.

HYPERSIM Documentation

Combined Heat and Power (CHP)