The Battery ESS (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. Battery ESS (Generic) component in the Schematic Editor core library
component
component dialog window
component parameters
Property tabs:
1 - General
2 - Battery
3 - Grid codes
4 - Conv. Extras
5 - Grid Extras
Battery ESS (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. Battery ESS (Generic) block diagram
High level control contains:
PQ Control block - Contains regulators for active and reactive power control.
The PQ Control block receives power references and measured powers after the transformer
(grid side) and calculates refererence output currents. These current references are fed
to the low level control logic. This control block is active in the grid following mode
of operation.
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.
Low level control subsystem main parts:
Currents and Voltage/Frequency control block - Contains regulators for inner
current and voltage control loops. Input signals to the Currents Control block are
reference currents and measured currents before the transformer (converter side). The
input signal to the Voltage Control block is the reference voltage and measured voltage
before the transformer (converter side).
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.
Battery ESS (Generic) power stage
The power
stage is shown in Figure 2. The main
elements include the average model of the inverter, the input L filter, the 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. Battery ESS (Generic) power stage
Battery ESS (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 50 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 battery energy storage input signals and their order.
All these signals are also defined in the corresponding Battery ESS (Generic)
UI subsystem with built-in Probe components (for
output signals) and SCADA Input components (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. The Battery ESS (Generic) UI
subsystem is located in the same place in the Schematic Editor library as the Battery
ESS (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. Battery ESS (Generic) user interface inputs
Number
Input
Description
Signal range
Default value
0
Enable
A digital input that enables the converter. The converter is enabled when the
input value is high.
0 or 1
0
1
Converter mode
An analog input that sets the operation mode of the converter. Available modes
and their respective codes are:
grid following mode (code 0)
droop (code 1)
isochronous (code 2)
0 or 1 or 2
0
2
Reset alarms
A digital input that resets alarms if the converter is in a fault
0 or 1
0
3
Pref
An analog input that is the active power reference. This reference is active in
grid following and droop mode. [pu]
0
4
Qref
An analog input that sets the reactive power reference. This reference is
active in grid following and droop mode. [pu]
0
5
Frequency droop offset
An analog input that sets the offset for frequency in frequency droop control
mode. [pu]
0
6
Frequency droop coeff
An analog input that sets the frequency droop coefficient for the frequency
droop control mode [%]
[0, 100]
2
7
Voltage droop coeff
An analog input that sets the voltage droop coefficient for the voltage droop
control mode [%]
[0, 100]
4
8
Vrms_ref
An analog input that sets the voltage reference. This reference is active in
isochronous mode of operation. [pu]
> 0
1
9
Fref
An analog input that sets the frequency reference. This reference is active in
the isochronous mode of operation. [pu]
> 0
1
10
Max SOC
An analog input that sets the maximum allowed state of charge of the battery.
[%]
[55.0, 95.0]
90
11
Min SOC
An analog input that sets the minimum allowed state of charge of the battery.
[%]
[5.0, 45.0]
10
12
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
13
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
14
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
15
Fref rate of change
An analog input that sets the rate of change of the frequency reference
ramping. [pu/s]
>= 0.0001
0.02
16
LVRT enable
Digital input that enables the LVRT unit. The LVRT unit is enabled when the
input value is high.
0 or 1
0
17
LVRT Q contribution
An analog input that specifies additional reactive power contribution per
percent of voltage drop in the case of a LVRT event. [%]
>= 0
2
18
LVRT P set
An analog input that defines the active power reference in the case of a LVRT
event. [pu]
Digital input that enables the VoltVAr unit. The VoltVAr unit is enabled when
the input value is high.
0 or 1
0
26
HzWatt enable
Digital input that enables the HzWatt unit. The HzWatt unit is enabled when the
input value is high.
0 or 1
0
27
VoltWatt enable
Digital input that enables the VoltWatt unit. The VoltWatt unit is enabled when
the input value is high.
0 or 1
0
28
Voltage droop offset
An analog input that sets the offset for voltage in voltage droop control mode.
[pu]
0
29-49
reserved_ins
Inputs that are not used.
0
* If the values for inputs 19 to 24 are all zeroes, default values will be used.
Table 3. Battery ESS (Generic) user interface outputs
Number
Output
Description
0
Enable_fb
A digital output describing the converter enable/disable state. The converter
is enabled if the output is high.
1
Converter_mode_fb
An analog output describing which control mode the converter operates in.
2
Pref_fb_kW
An analog output with the instantaneous value of the applied power reference in
the converter. [kW]
3
Qref_fb_kVAr
An analog output with the instantaneous value of the applied reactive power
reference in the converter. [kVAr]
4
Pnom_kW
An analog output with the value of nominal active power of the converter. [kW]
5
Qnom_kVAr
An analog output with the value of nominal reactive power of the converter.
[kVAr]
6
Snom_kVA
An analog output with the value of nominal apparent power of the converter.
[kVA]
7
Vnom_LL_V
An analog output with the value of nominal converter's voltage. [V]
8
Fnom_Hz
An analog output with the value of nominal converter's frequency. [Hz]
9
Vrms_ref_fb_V
An analog output with feedback information about the RMS value of the reference
voltage. [V]
10
Fref_fb_Hz
An analog output with feedback information about the reference frequency value. [Hz]
11
Vgrid_rms_meas_kV
An analog output reporting the RMS value of the grid voltage, measured at the
grid side of the transformer. [kV]
12
Fmeas_Hz
An analog output reporting the value of the grid voltage frequency. [Hz]
13
Pmeas_kW
An analog output reporting the instantaneous value of the three-phase active power
output of the converter. [kW]
14
Pa_meas_kW
An analog output reporting the instantaneous value of the phase A active power
output of the converter. [kW]
15
Pb_meas_kW
An analog output reporting the instantaneous value of the phase B active power
output of the converter. [kW]
16
Pc_meas_kW
An analog output reporting the instantaneous value of the phase C active power
output of the converter. [kW]
17
Qmeas_kVAr
An analog output reporting the instantaneous value of the three-phase reactive power
output of the converter. [kVAr]
18
Qa_meas_kVAr
An analog output reporting the instantaneous value of the phase A reactive
power output of the converter. [kVAr]
19
Qb_meas_kVAr
An analog output reporting the instantaneous value of the phase B reactive
power output of the converter. [kVAr]
20
Qc_meas_kVAr
An analog output reporting the instantaneous value of the phase C reactive
power output of the converter. [kVAr]
21
Smeas_kVA
An analog output reporting the instantaneous value of the three-phase apparent power
output of the converter. [kVA]
22
PFmeas
An analog output reporting the value of the converter output power factor.
23
Vconv_rms_meas_V
An analog output reporting the RMS value of the converter voltage, measured at
the converter side of the transformer. [V]
24
SOC
An analog output reporting the state of charge value of the battery. [%]
25
SOH
An analog output reporting the state of health value of the battery. [%]
Note: This functionality is not currently supported. Value is set to 0.
26
Vbatt_V
An analog output reporting the instantaneous value of DC voltage at the output of
the battery. [V]
27
Ibatt_A
An analog output reporting the instantaneous value of DC current at the output of
the battery. [A]
28
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.
29
state
An analog output reporting the code of the state of the converter.
30
alarm_msg
An analog output reporting the value of the alarm message. In order for the converter to
return to normal operation after the alarm has been triggered, all alarms must be reset.
31
Batt_cap_nom_Ah
An analog output reporting the value of the nominal battery capacity. [Ah]
32
Lvrt_active_status
A digital output that signals the status of the LVRT unit. If high, the LVRT
unit is active and contributing active and reactive power to the grid, otherwise it
is not active.
33-49
reserved_outs
Outputs that are not used.
Table 4. Battery ESS (Generic) external inputs
Number
Input
Description
Signal range
0
Initial SOC
Defines initial state of charge of the battery at simulation start.
[%]
[0, 100]
1
Initial SOH
Defines initial state of health of the battery at simulation start. This
value reduces nominal battery capacity. [%]
(0, 100]
Note: In order preserve backward compatibility, 0 values are internally substituted with 100.
2-4
reserved_exts
Inputs that are not used.
Table 5. Battery ESS (Generic) UI subsystem
Figure 3. Battery ESS (Genric) UI
Figure 4. Battery ESS (Generic) UI internals
Battery ESS (Generic) operational states
Table 6. Main state machine states
Code
Decription
1
Starting up state – Represents the state of the
converter between the moment signal activation is triggered and the moment when the
converter starts operating, e.g. system checking and synchronization time.
2
Running state - Represents the operational state of the converter.
3
Disabled state - Reports if the converter is not enabled/operational.
4
Fault state – Represents the state of the converter if it encounters a fault.
It is necessary to reset the alarms once the converter enters this state.
Table 7. Faults/Alarm messages
Code
Description
0
None of the alarms have been triggered
1
Over current protection. Input phase currents are greater than the
maximum specified value.
2
Grid voltage out of range. Grid voltage is outside the specified range.
This protection is active in grid following mode. If the voltage restores, the fault
will be automatically reset.
3
Grid frequency out of range. Grid frequency is outside the specified
range. This protection is active in grid following mode. If the frequency restores,
the fault will be automatically reset.
4
Over power protection. Measured apparent power is greater than the
maximum allowed apparent power.
5
SOC at critical level. If the SOC is higher than absolute maximum value
or lower than the absolute minimum value of SOC.
Component dialogue box and parameters
The Battery ESS (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 user can specify general parameters of the Battery ESS and the
grid.Figure 5. Battery ESS (Generic) "1 - General" parameters.
Battery ESS nominal line voltage (transformer's primary side). [V]
Nominal frequency
fnom
Battery ESS Nominal frequency. [Hz]
Include transformer
include_transformer
Include the transformer in the Battery ESS power stage model.
Nominal grid line voltage
Vnom_sec_LL
Nominal line voltage of the grid (transformer's secondary side). [V]
Tab: "2 - Battery"
In this component tab, parameters that are related to the Battery system part of the
converter can be specified.Figure 6. Batery ESS (Generic) "2 - Battery" parameters.
In this component tab,
different Grid code parameters can be specified. Currently, LVRT (Low Voltage Ride Through),
VoltVAr, HzWatt, and VoltWatt functionalities are supported. Figure 7. Battery ESS (Generic) "3 - Grid codes" LVRT parameters
Automatically parametrizes voltage and time points according to the chosen
requirements. If the Custom option is selected, voltage and current points become
available for editing.
Allows for defining voltage and reactive power points. Currently, only the
Custom option is supported.
Voltage points
vs_voltvar
VoltVAr curve voltage points.
Reactive power points
qs_voltvar
VoltVAr curve reactive power points.
Preview VoltVAr curve
preview_voltvar
Displays the created VoltVAr curve.
If LVRT and VoltVAr functionalities are both enabled, then the VoltVAr curve has
priority over the LVRT reactive power contribution setting (Q_contribution).
The
VoltVAr curve is linearly extrapolated for voltage values below and above the minimum and
maximum values. Also, the curve is limited by a maximum value of reactive power which can be
produced or stored. This limit is calculated as , where opc_pu is the overpower capability.
Allows for defining frequency and active power points. Currently, only the
Custom option is supported.
Frequency points
fs_hzwatt
HzWatt curve frequency points.
Active power points
ps_hzwatt
HzWatt curve active power points.
Preview HzWatt curve
preview_hzwatt
Displays the created HzWatt curve.
If LVRT and HzWatt functionalities are both enabled, then the HzWatt curve has priority
over the LVRT active power contribution setting.
If the frequency value is below the
minimum value or above the maximum value, then the Grid frequency out of
range error will appear. The HzWatt curve is limited by a maximum value of active
power which can be produced or stored. This limit is calculated as , where opc_pu is the overpower capability.
Allows for defining voltage and active power points. Currently, only the
Custom option is supported.
Voltage points
vs_voltwatt
VoltWatt curve voltage points.
Active power points
ps_voltwatt
VoltWatt curve active power points.
Preview VoltWatt curve
preview_voltwatt
Displays the created VoltWatt curve.
If LVRT and VoltWatt functionalities are both enabled, then the VoltWatt curve has
priority over the LVRT active power contribution setting. But, if HzWatt and VoltWatt
functionalities are both enabled, then the HzWatt curve has priority over the VoltWatt
curve.
The VoltWatt curve is linearly extrapolated for voltage values below and above
the minimum and maximum values. Also, the curve is limited by a maximum value of active
power which can be produced or stored. This limit is calculated as , where opc_pu is the overpower capability.
Tab: "4 - Conv. Extras"
In this component tab, additional parameters that are related to the converter can be
specified.Figure 11. Batery ESS (Generic) "4 - Conv. Extras" parameters.
Input filter impedance. Input filter is a simple L type filter. See the Figure 2. [pu]
Transformer impedance
Zt_n
Determines the transformer impedance. The position of this transformer is
shown in Figure 2.
[pu]
DC link voltage margin
dc_link_margin
Voltage margin over the minimal allowed DC link voltage. This value restricts
the maximum voltage that a converter can generate. [pu]
Overpower capability
opc_pu
Determines the overpower capability of the converter. [pu]
Shunt resistance
Rshunt_pu
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 Figure 2. [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]
Tab: "5 - Grid Extras"
In this component tab,
additional parameters that are related to the grid can be specified.Figure 12. Batery ESS (Generic) "5 - Grid Extras" parameters.
Short circuit apparent power of the grid that the converter is connected to.
This parameter doesn't influence the power stage of the model, only the control
part. Stable operation of the converter can be achived by tuning this parameter.
[pu]
Grid inductive power factor
PFg
Power factor of the grid that the converter is connected to. This power factor
occurs when the grid is short-circuited. This parameter doesn't influence the power
stage of the model, only the control part. Stable operation of the converter can be
achieved by adjusting this parameter. [pu]
Example
Overall behavior and control methodologies can be better understood with the use of the
given example:
