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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
Name | Description | Unit |
---|---|---|
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
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 | - |
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
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
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