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Combined Heat and Power (CHP)


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

NameDescriptionUnit

Snom

Nominal electrical power of generator

VA

Pnom

Nominal mechanical power of turbine

W

Vnom

Nominal voltage

VrmsLL

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

NameDescriptionUnit

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

-


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

-


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

NameDescription
PCCNetwork connection; supports 3-phase connection

Inputs

NameDescriptionUnits
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
Mode0 -Grid-connected PQ, 1- Grid-connected PV, 2- Grid forming, 3- Fixed frequency/Q control.-

Outputs

None


Sensors

NameDescriptionUnits
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
VceMeasurement of the VCE fuel demand for the gas turbinepu
WfMeasurement of the WF fuel flow supplied by the gas turbine and used by the steam turbinepu
Tx_measExhaust temperature measurement°C
Tm_STMechanical torque output produced by the steam turbinepu
Tm_GTMechanical torque output produced by the gas turbinepu
PmTotal generated mechanical power pu
TmGenerated torquepu
TxExhaust temperature measurement supplied by the gas turbine and used by the steam turbine°C
Vref_excReference voltage of the exciterpu
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
Mode0 -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 

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