Method for estimating battery life in presence of partial charge and discharge cycles
A management framework is disclosed that achieves maximum energy storage device lifetime based on energy storage device life estimation and the price of energy. The management framework includes a battery life estimation from a supercycle model, for a time window between two consecutive full charges of a battery, which allows assessing a worst case scenario impact of all partial cycles within a supercycle on the battery life. The battery life estimation then considers each supercycle as a single discharge unit instead of treating each individual discharge period separately.
1. A method for estimating battery life in power management of a microgrid with an energy storage device that includes charging and discharging modes, comprising:
i) receiving power data from different generation sources, storage state of charge and a storage discharge pattern;
ii) estimating a storage lifetime and determining cost of energy from the energy storage device which includes estimating battery life that considers a supercycle (SC) of a battery as a single discharge unit instead of treating each individual discharge period separately, the supercycle defines a time window between two consecutive full charges of a battery which allows assessing a worst case scenario impact of all partial cycles within a supercycle on the battery life; and
iii) allocating desired power between the energy storage device and a power grid to minimize cost of energy through reduced grid power or feed-in-tariff while maximizing storage lifetime based on a final energy cost; wherein steps i)-iii) are implemented by a computer.
2. The method of claim 1 , wherein the supercycle (SC j ) includes k distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k , respectively and effective ampere hours Ah related to these k discharge events are determined by using the parameters D o D SC j =D o D max,j , where DoD is based on actual depth of discharge.
3. The method of claim 1 , wherein the supercycle (SC j ) includes k distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k , respectively and effective ampere hours Ah related to these k discharge events are determined by using the parameters discharge
I
dischg
,
SC
1
=
I
dischg
,
1
Δ
T
1
+
…
+
I
dischg
,
k
Δ
T
k
Δ
T
k
+
…
+
Δ
T
k
,
where I dischg is based on discharge current.
4. The method of claim 1 , wherein the supercycle of the battery life includes weighting factors for all discharge events within a SC based on a maximum actual depth of dispatch discharge DoD during that SC.
5. The method of claim 1 , wherein the estimated battery life after m supercycles can be estimated as follows:
LF
batt
=
φ
rated
∑
j
=
1
m
L
1
,
j
×
L
2
,
j
×
I
dischg
,
SC
1
×
(
∑
i
=
1
k
Δ
T
i
)
×
T
,
where φ rated is rated charge of life of the battery L 1 and L2 are weighting factors, k and distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k .
6. The method of claim 1 , wherein the supercycle includes multiple periods of partial charges and discharges with different durations and if estimating battery life needs to be carried out at a fixed time-step (Δt) smaller than supercycle SC durations, then for battery charging or standby, in an Lth time-step of a supercycle SC, actual depth of discharge DoD SC j and discharge current I dischg,SC j related to the supercycle SC do not change and follow the relationships DoD SC j (L)=DoD SC j (L−1) and I dischg,SC j =I dischg,SC j (L−1).
7. The method of claim 1 , wherein the supercycle includes multiple periods of partial charges and discharges with different durations and if estimating battery life needs to be carried out at a fixed time-step (Δt) smaller than supercycle SC durations, then for battery discharging, in an Lth time-step of a supercycle SC, actual depth of discharge DoD SC j and discharge current I dischg,SC j related to the supercycle SC parameters do not change and are updated as follows: DoD SC j (L)=maxDoD SC j (L−1) and
I
dischg
,
SC
j
(
L
)
=
I
dischg
,
SC
j
(
L
-
1
)
P
+
I
dischg
,
L
P
+
1
.
8. A system for estimating battery life in power management of a microgrid with an energy storage device that includes charging and discharging modes, comprising:
different generation sources, storage state of charge and a storage discharge pattern providing power data; and
a computer configured for estimating a storage lifetime and determining cost of energy from the energy storage device which includes estimating battery life that considers a supercycle (SC) of a battery as a single discharge unit instead of treating each individual discharge period separately, the supercycle defines a time window between two consecutive full charges of a battery which allows assessing a worst case scenario impact of all partial cycles within a supercycle on the battery life;
wherein the computer allocates desired power between the energy storage device and a power grid to minimize cost of energy through reduced grid power or feed-in-tariff while maximizing storage lifetime based on a final energy cost.
9. The system of claim 8 , wherein the supercycle (SC j ) includes k distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k , respectively and effective ampere hours Ah related to these k discharge events are determined by using the parameters D o D SC j =D o D max,j , where DoD is based on actual depth of discharge.
10. The system of claim 8 , wherein the supercycle (SC j ) includes k distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k , respectively and effective ampere hours Ah related to these k discharge events are determined by using the parameters discharge
I
dischg
,
SC
1
=
I
dischg
,
1
Δ
T
1
+
…
+
I
dischg
,
k
Δ
T
k
Δ
T
k
+
…
+
Δ
T
k
,
where I dischg is based on discharge current.
11. The system of claim 8 , wherein the supercycle of the battery life includes weighting factors for all discharge events within a SC based on a maximum actual depth of dispatch discharge DoD during that SC.
12. The system of claim 8 , wherein the estimated battery life after m supercycles can be estimated as follows:
LF
batt
=
φ
rated
∑
j
=
1
m
L
1
,
j
×
L
2
,
j
×
I
dischg
,
SC
1
×
(
∑
i
=
1
k
Δ
T
i
)
×
T
,
where φ rated is rated charge of life of the battery L 1 and L2 are weighting factors, k and distinct discharge events 1, 2, . . . , k with duration T i , . . . , T k .
13. The system of claim 8 , wherein the supercycle includes multiple periods of partial charges and discharges with different durations and if estimating battery life needs to be carried out at a fixed time-step (Δt) smaller than supercycle SC durations, then for battery charging or standby, in an Lth time-step of a superycle SC, actual depth of discharge DoD SC j , and discharge current I dischg,SC j related to the supercycle SC do not change and follow the relationships DoD SC j (L)=DoD SC j (L−1) and I dischg,SC j (L)=I dischg,SC j (L−1).
14. The system of claim 8 , wherein the supercycle includes multiple periods of partial charges and discharges with different durations and if estimating battery life needs to be carried out at a fixed time-step (Δt) smaller than supercycle SC durations, then for battery discharging, in an Lth time-step of a supercycle SC, actual depth of discharge DoD SC j and discharge current I dischg,SC j related to the supercycle SC parameters do not change and are updated as follows: DoD SC j (L)=maxDoD SC j (L−1) and
I
dischg
,
SC
j
(
L
)
=
I
dischg
,
SC
j
(
L
-
1
)
P
+
I
dischg
,
L
P
+
1
.