Control device of energy storage system
A control device of an energy storage system is provided. The control device includes a voltage calculation unit calculating the difference between a reference voltage and a measured voltage; frequency calculation unit calculating the difference between a reference frequency and a measured frequency; a power reserve margin (PRM) calculating a ratio of reserve power to the maximum consumption of power; and a power calculation unit using, as input values, coefficients calculated at the voltage calculation unit, the frequency calculation unit and the PRM calculation unit, and calculating a switch control value of an energy storage system by further using a difference in reactive power and active power.
1. A control device of an energy storage system, the control device comprising:
a power conversion system (PCS) control unit configured to calculate a control value for charging and discharging the energy storage system; and
a charging and discharging device configured to adjust charged and discharged amounts of energy of the energy storage system,
wherein the PCS control unit comprises:
a voltage calculation unit configured to calculate a difference between a reference voltage supplied to a system and a measured voltage received from the system;
a frequency calculation unit configured to calculate a difference between a reference frequency supplied to the system and a measured frequency received from the system;
a power reserve margin (PRM) calculation unit configured to calculate a PRM based on a ratio of reserve power to a maximum power consumption of the energy storage system;
a power calculation unit configured to receive coefficients calculated by the voltage calculation unit, the frequency calculation unit and the PRM calculation unit and to calculate a switch control value of the energy storage system by using a difference between reactive power and active power;
a PRM difference calculation unit configured to calculate a difference between a value calculated by the PRM calculation unit and a reference PRM value;
an operation coefficient calculation unit configured to calculate an energy ratio of the energy storage system corresponding to the difference calculated by the difference calculation unit and to calculate a switch operation coefficient according to the charged amount of the energy storage system; and
an operation control unit configured to adjust the charged and discharged amounts of energy of the energy storage system based on the calculated switch operation coefficient.
2. The control device according to claim 1 , wherein the PRM is calculated as a ratio of the reserve power P leftover to a difference between the maximum power consumption P load and an output of a distributed power supply P DG and an output power of the energy storage system P ESS according to the following equation:
PRM
(
%
)
=
P
leftover
(
t
)
P
load
(
t
)
-
P
DG
(
t
)
-
P
ESS
(
t
)
×
100.
3. The control device of claim 2 , wherein the PRM calculation unit is further configured to calculate P ESS based on a reference PRM PRF ref , an efficiency coefficient N ESS , and a proportional factor Ka according to the following equation:
P
ESS
=
{
P
load
(
t
)
-
P
DG
(
t
)
-
100
·
P
leftover
(
t
)
PRM
ref
(
%
)
}
·
Ka
n
ESS
_P
CS
.
4. The control device according to claim 3 , wherein the PRM calculation unit is further configured to calculate a ratio of a sum of a difference between a maximum energy supply amount P G and P load and amounts of energy stored in the distributed power supply and the energy storage system to P load according to the following equation:
PRM
(
%
)
=
P
G
(
t
)
-
P
load
(
t
)
+
P
DG
(
t
)
+
P
ESS
(
t
)
P
load
(
t
)
×
100.
5. The control device according to claim 4 , wherein the PRM calculation unit is further configured to convert output power of the energy storage system into a value for amounts of energy according to the following equation:
P
ESS
=
[
{
1
+
PRM
ref
(
%
)
}
·
P
load
100
-
P
G
(
t
)
-
P
DG
(
t
)
]
·
Kb
n
ESS
_P
CS
.
6. The control device according to claim 1 , wherein the PRM calculation unit is further configured to:
determine a maximum amount of power supplied based on an output of a distributed power supply and an output of the energy storage system; and
calculate the PRM using a corresponding reserve power amount.
7. The control device according to claim 1 , further comprising a droop control unit configured to calculate voltage and frequency values as part of the PRM calculation.
8. The control device according to claim 1 , wherein the operation control unit is further configured to stop discharging the energy storage system when the charged amount is less than or equal to a reference amount.
9. The control device according to claim 1 , wherein:
the PRM difference calculation unit is further configured to calculate a difference between a ratio and the reference PRM value; and
the ratio is of a sum of a difference between a maximum energy supply amount and the maximum power consumption and amounts of energy stored in a distributed power supply and the energy storage system to the maximum power consumption.