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The battery (storage system) is an element for the storage of electrical energy. In a load flow calculation using profiles, the battery stores or releases energy, according to the specified battery profile. The state of charge depends on the starting value, the storage capacity and the battery profile. During the charging and the discharging processes, the state of charge will not exceed the physical limits.
PARAMETERS
Battery
Parameter |
Default |
Unit |
Description |
Name |
|
|
Name |
C-rate |
0,5 |
/h |
1 hour nominal discharge rate |
Capacity |
0 |
MWh |
Storage capacity |
P |
0 |
MW |
Generation of active power (*) |
Profile |
Default |
|
Name of the load profile for the active power |
SoC |
50 |
% |
Initial State of Charge |
(*) The battery positive power direction is according to the load convention. This implies that a positive P indicate that the battery receives power from the network.
Only the active power P can be used for energy storage.
The voltage dependent behaviour is: constant power.
Profile
Each load flow calculation respects the battery state of charge. The load flow calculation without profile respects the physical limits of a fully charged or discharged battery.
A previously defined load profile can be assigned to the battery. Only in loadflow calculation with profile, the time aspect is taken into account, charging and/or discharging the battery.
The default profile exists of all values of 1 and produces a constant load.
Inverter
Parameter |
Default |
Unit |
Description |
Snom |
|
MVA |
Nominal power of the inverter |
Unom |
node.Unom |
kV |
Nominal voltage of the inverter |
Cos phi |
1 |
|
Cos phi |
Charging efficiency type |
0,1..1 pu: 95 % |
|
Type of the charging efficiency, as function of the input power |
Discharging efficiency type |
0,1..1 pu: 95 % |
|
Type of the discharging efficiency, as function of the output power |
Ik/Inom |
1 |
|
Relation between the short circuit current and the nominal current |
Control
The battery can be equipped with a control to control charging and discharging. A P(U) or P(t) or P(I) control can be selected. The P(U) and P(I) control overrules the generally specified P and profile. The P(t) control overrules these values only when the time is known.
Parameter |
Default |
Unit |
Description |
Sort |
Geen |
|
Sort P control: none, P(U) of P(t) or P(I) |
Begin time |
|
|
Start time of the day as input of the P(t) function |
End time |
|
|
End time of the day as input of the P(t) function |
U |
|
pu |
Input of the P(U) function |
I |
|
pu |
Input of the P(I) function; directional |
P |
|
pu |
Output of the P control in relation to capacity*C-rate; negative is discharging |
Reliability
Parameter |
Default |
Unit |
Description |
Failure frequency |
0 |
per year |
Mean number of occurrences that the battery fails (short circuit) |
Repair duration |
0 |
minutes |
Mean duration of repair or replacement |
Maintenance frequency |
0 |
per year |
Mean number of occurrences that the battery is in maintenance |
Maintenance duration |
0 |
minutes |
Mean duration of maintenance |
Maint. cut-off duration |
0 |
minutes |
Mean duration of cancellation of maintenance in case of emergency |
MODELLING
Load flow
The battery positive power direction is according to the load. This implies that the powers P and Q are positive if the battery draws power from the network. The voltage dependent behaviour is: constant power.
In a load flow calculation without profile the battery behaves like a general load, according to the defined power P and Q, with respect to the state of charge.
The state of charge changes in a load flow calculation with a profile. The value depends on its initial value, the storage capacity and the amount and duration of charging and discharging power. The charging and discharging power are with respect to the network. The actual stored power depends on the battery efficiency.The battery behaves in the following way near the bounds of the SoC:
•at a SoC of 99 % no active power is drawn from the network.
•at a SoC of 1 % no active power is delivered to the network.
Fault analysis
In sequential fault analysis, the battery is modelled as an impedance. This impedance is determined using the pre-fault node voltage and load current, determined in advance by means of a load flow calculation.