The Diesel Genset (Generic) component, shown in Table 1, is a Schematic Editor library block from the
Distributed Energy Resources section, of the Microgrid
library. It is capable of operating in isochronous, droop and grid following mode.
Table 1. Diesel Genset (Generic) component in the Schematic Editor core library
component
component dialog window
component parameters
Property tabs:
1 - General
2 - DG
3 - Extras
Diesel Genset (Generic) block diagram
The
component consists of two main parts: a high level control subsystem and a low level control
subsystem with a power stage and necessary measurements included. Figure 1. Diesel Genset (Generic) block diagram
High level control contains:
Ramping elements - Limit the ROC (rate of change) of the active power
reference, reactive power reference, voltage reference, and frequency reference. The
rate of change for each function is configured through a corresponding input signal.
Frequency droop functionality - Calculates frequency reference signal when
droop control mode is activated. This control unit is described in the documentation for
the Frequency droop unit in DER generic
components.
Voltage droop functionality - Calculates voltage references signal when droop
control mode is activated. This control unit is described in Voltage droop unit in DER generic components.
Main state machine - Controls and checks overall functionality of the plant.
Operational plant states are described in Main state machine
states table.
Low level control subsystem main parts:
Synchronization control block - Consists of required logic and controller to
synchronize the genset to an existing power grid with respect to voltage magnitude and
frequency.
PQ Control block - Contains regulators for active and reactive power control when
the diesel generator is connected to the grid. The PQ Control block receives power
references and measured powers after the transformer (grid side). This control block is
active in grid following mode of operation.
Voltage/Frequency control - Contains regulators for direct control of the
generator voltage and frequency output. Inputs signals to control block are the reference
and measured values of the generator stator (before transformer) voltage and frequency.
This control block is active when the genset is working under grid forming or droop
control operating modes.
Fault state machine - Checks all measurements, signals the fault state, and sends
an alarm message. It also immediately opens the MCB (main circuit breaker) on any detected
fault. A list of implemented faults is shown in Faults/Alarm messages
table.
Diesel Genset (Generic) power stage
The power
stage is shown in Diesel Genset
(Generic) power stage. The main elements include the VBR model of the synchronous
generator, transformer and the MCB that connects the plant to the grid. The transformer can be
excluded from the power stage if it is not necessary. Power stage elements are parametrized
from the component dialog box.
Figure 2. Diesel Genset (Generic) power stage
Diesel Genset (Generic) inputs and outputs
This
component has one user interface input, one user interface output and one external input. The
user interface input and user interface output are each arrays of 40 elements, while the
external input is an array of 5 elements. Table 2 describes the input signals and their order,
while Table 3 describes the output
signals and their order. Lastly, Table 4 describe the external diesel generator input signals and their order.
All these signals are also defined in the
corresponding Diesel Genset (Generic) UI subsystem with built-in Probes (for output signals) and SCADA Inputs
(for input signals), as shown in Table 5.
These signals were split and joined by a properly configured DER (Generic) Output Split and DER (Generic) Control Join components.
Diesel Genset (Generic) UI
subsystem is located in the same place in the Schematic Editor library as the
Diesel Genset (Generic) component, and it can be unlinked from the library and adopted to
the specific needs. Unit [pu] is associated to nominal values, which are either inserted as
general tab
parameters or derived from them.
Table 2. Diesel Genset (Generic) user interface inputs
Number
Input
Description
Signal range
Default value
0
Enable
A digital input that enables the genset operation. The Genset is enabled when
the input value is high.
0 or 1
0
1
Reset alarms
A digital input that resets alarms if the Genset is in a fault
0 or 1
0
2
Pref
An analog input that is the active power reference. This reference is active in
grid following and droop mode. [pu]
0
3
Qref
An analog input that sets the reactive power reference. This reference is
active in grid following and droop mode. [pu]
0
4
Operation mode
An analog input that sets the operation mode of the Genset. Available modes and
their respective codes are:
grid following mode (code 2)
droop (code 0)
isochronous (code 1)
0 or 1 or 2
0
5
Vrms_ref
An analog input that sets the voltage reference. This reference is active in
isochronous mode of operation. [pu]
> 0
1
6
Fref
An analog input that sets the frequency reference. This reference is active in
the isochronous mode of operation. [pu]
> 0
1
7
Frequency droop offset
An analog input that sets the offset for frequency in frequency droop control
mode. [pu]
0
8
Frequency droop coeff
An analog input that sets the frequency droop coefficient for the frequency
droop control mode [%]
[0, 100]
2
9
Voltage droop coeff
An analog input that sets the voltage droop coefficient for the voltage droop
control mode [%]
[0, 100]
4
10
Pref rate of change
An analog input that sets the rate of change of the active power reference
ramping. [pu/s]
>= 0.001
0.1
11
Qref rate of change
An analog input that sets the rate of change of the reactive power reference
ramping. [pu/s]
>= 0.001
0.1
12
Vrms_ref rate of change
An analog input that sets the rate of change of the voltage reference ramping.
[pu/s]
>= 0.001
0.1
13
Fref rate of change
An analog input that sets the rate of change of the frequency reference
ramping. [pu/s]
Relative timeout period for the Over current
protection. [pu] **Absolute timeout period in seconds is equal to this
input value divided by nominal frequency.
Synchronisation time limit for the Synch timeout
error. [s]
> 0
20
19
Voltage droop offset
An analog input that sets the offset for voltage in voltage droop control mode.
[pu]
0
20-39
reserved_ins
Inputs that are not used.
0
* If the values for inputs 14 to 18 are all zeroes, default values will be used.
Table 3. Diesel Genset (Generic) user interface outputs
Number
Output
Description
0
Enable_fb
A digital output describing the Genset enable/disable state. The Genset is
enabled if the output is high.
1
Pref_fb_kW
An analog output with the instantaneous value of the applied power reference in
the Genset. [kW]
2
Qref_fb_kVAr
An analog output with the instantaneous value of the applied reactive power
reference in the Genset. [kVAr]
3
Vrms_ref_fb_V
An analog output with feedback information about the RMS value of the reference
voltage. [V]
4
Fref_fb_Hz
An analog output with feedback information about the reference frequency value.
[Hz]
5
Pnom_kW
An analog output with the value of the nominal active power of the Genset. [kW]
6
Qnom_kVAr
An analog output with the value of the nominal reactive power of the Genset.
[kVAr]
7
Snom_kVA
An analog output with the value of the nominal apparent power of the Genset.
[kVA]
8
Fmeas_Hz
An analog output reporting the value of the grid voltage frequency. [Hz]
9
Vgrid_rms_meas_kV
An analog output reporting the RMS value of the grid voltage, measured at the
grid side of the transformer. [kV]
10
Pmeas_kW
An analog output reporting the instantaneous value of the three-phase active
power output of the Genset. [kW]
11
Qmeas_kVAr
An analog output reporting the instantaneous value of the three-phase reactive
power output of the Genset. [kVAr]
12
Smeas_kVA
An analog output reporting the instantaneous value of the three-phase apparent
power output of the Genset. [kVA]
13
PFmeas
An analog output reporting the value of the Genset output power factor.
14
Vgen_rms_meas_V
An analog output reporting the RMS value of the Genset voltage, measured at the
Genset side of the transformer. [V]
15
Gen_speed_RPM
Generator speed. [RPM]
16
MCB_status
A digital output reporting the information about the state of the main circuit
breaker (contactor). The contactor is closed if the value is high.
17
state
An analog output reporting the code of the state of the Genset.
18
alarm_msg
An analog output reporting the value of the alarm message. In order for the
Genset to return to normal operation after the alarm has been triggered, all alarms
must be reset.
19
Converter_mode_fb
Analog output describing the control mode that the converter is operating
in.
20-39
reserved_outs
Outputs that are not used.
Table 4. Diesel Genset (Generic) external inputs
Number
Input
Description
Signal range
0-4
reserved_exts
Inputs that are not used.
Table 5. Diesel Genset (Generic) UI subsystem
Figure 3. Diesel Genset (Genric) UI
Figure 4. Diesel Genset (Generic) UI internals
Diesel Genset (Generic) operational states
Table 6. Main state machine states
Code
Decription
1
Sync up state – Represents the state of the genset between the moment of
enabling signal activation and the moment when converters starts operating, e.g.
synchronization time.
2
Running state – Represents the state in which the genset is operating
normally in one of the control modes.
3
Disabled state – Represents the state when the genset is disabled and
disconnected.
4
Fault state – Represents the state in which genset goes if fault
occured. It is necessary to reset the alarms once genset is in this state.
Table 7. Faults/Alarm messages
Code
Description
0
None of the alarms have been triggered
1
Over current protection. This fault state is triggered when the stator
current magnitude exceeds the maximum value for the specified timeout number of
cycles of the nominal frequency.
2
Grid voltage out of range. Is triggered when the grid voltage is lower
than the specified value. This protection is active in grid following mode.
3
Rotor unstable. This fault is triggered when the rotor delta angle
(phase angle between the generator back-emf and stator voltage) exceeds 75 degrees.
This fault is only active in grid following mode.
4
Sync timeout. This fault is triggered if the genset fails to reach
synchronism with the grid within a specified time duration.
5
Frequency drift is trigged when the generator speed goes outside
specified bound with respect to the speed in which synchronization is achieved.
e.g., this fault often happens when grid is disconnected and the machine is actively
providing power output, resulting in excess energy which causes accelertion or
deceleration.
Component dialogue box and parameters
The Diesel Genset (Generic) component dialogue box consists of four tabs for specifying
parameters of the component. Unit [pu] is associated to nominal values, which are inserted
as general tab
parameters or derived from them.
Tab: "1 - General"
In this component tab, the general parameters of the Diesel Gneset and the grid can be
specified.Figure 5. Diesel Genset (Generic) "1 - General" parameters.
Diesel Genset nominal line voltage (transformer's primary side). [V]
Nominal frequency
fnom
Diesel Genset Nominal frequency. [Hz]
Include transformer
include_transformer
Include the transformer in the Diesel Genset power stage model.
Nominal grid line voltage
Vnom_sec_LL
Nominal line voltage of the grid (transformer's secondary side). [V]
Tab: "2 - DG"
In this component tab, parameters that are related to the
Generator system part of the Diesel Genset can be specified.
Figure 6. Diesel Genset (Generic) "2 - DG" parameters.
In this component tab, additional parameters that are related to the
Diesel Genset can be specified.
Figure 7. Diesel Genset (Generic) "3 - Extras" parameters.
The value of the shunt resistances that are used for the measurement of phase
voltages at the converter input. The position of shunts is shown in Diesel Genset
(Generic) power stage image. [pu]
Faster execution rate
Tfast
The Faster execution rate at which part of the inner signal processing of the
component will be executed. Should be approximately 5 to 10 times faster than the
Slower execution rate. [s]
Slower execution rate
Tslow
The Slower execution rate, at which part of the inner signal processing of
the component will be executed. This execution rate is inherited by the connected
UI subsystem. Should be approximately 5 to 10 times slower than the Faster
execution rate. [s]
Example
Overall behavior and control methodologies can be better understood with the use of the
given example:
