Battery control methods and circuits, and energy storage to grid connection systems
A method measures a power characteristic at the one or more storage batteries, and controls the one or more batteries to selectively act as a generator to supply power to the power grid or to act as a load to draw power from the power grid in response to a predetermined disturbance in the power characteristic being detected. A system includes a battery charging circuit, a battery to grid circuit and a controller that monitors a power characteristic at the one or more storage batteries, and controls the one or more batteries to selectively act as a generator to supply power to the power grid or to act as a load to draw power from the power grid in response to a predetermined disturbance in the power characteristic being detected.
1. A method for regulating the power transfer between one or more storage batteries and a power grid, the method comprising locally measuring a power characteristic at the one or more storage batteries, and locally controlling the one or more batteries to selectively act as a generator to supply power to the power grid or to act as a load to draw power from the power grid in response to a predetermined disturbance in the power characteristic being detected.
2. The method of claim 1 , wherein the power characteristic comprises a local frequency at the one or more storage batteries and the predetermined disturbance comprises a frequency disturbance.
3. The method of claim 2 , wherein the controlling comprises controlling the battery to act as a generator to supply power when a first predetermined frequency deviation in the local frequency is detected, and the controlling the battery to act as a load to draw power from the connected power grid when a second predetermined frequency deviation in the local frequency is detected.
4. The method of claim 2 , further comprising locally releasing the battery or batteries from power regulation control when the local frequency is stable.
5. The method of claim 2 , wherein the frequency disturbance is determined as a function of the first derivative of the change in local frequency.
6. The method of claim 2 , wherein the controlling comprises controlling the battery or batteries to have a battery power output linearly dependent on frequency deviation, with ramp limits of ±3 kW at ±100 mHz according to:
P
=
{
-
3
kW
,
if
Δ
f
<
-
100
mHz
h
·
Δ
f
kW
,
if
-
100
mHz
<
Δ
f
<
100
mHz
3
kW
,
if
Δ
f
>
100
mHz
(
1
)
where h=X kW/Hz is a control parameter and Δf is the frequency deviation from its nominal value, and wherein h=˜30 kW/Hz.
7. The method of claim 2 , wherein said controlling comprises controlling the battery or batteries to have a battery power output dependent upon a tanh, or a sigmoid function.
8. The method of claim 2 , wherein the controlling comprises controlling the battery or batteries to have a battery power output linearly dependent on frequency deviation, with ramp limits of a first predetermined power and a fraction of that power according to:
P
=
{
-
first
predetermined
kW
,
if
Δ
f
<
-
fraction
mHz
h
kW
/
Hz
·
Δ
f
kW
,
if
-
fraction
mHz
<
Δ
f
<
fraction
mHz
first
predetermined
kW
,
if
Δ
f
>
fraction
mHz
(
1
)
where h kW/Hz is a control parameter and Δf is frequency deviation from its nominal value.
9. The method of claim 8 , wherein the one or more storage batteries comprises a plug-in electrical vehicle or a home battery.
10. A system for connecting one or more storage batteries to a power grid, the system comprising a battery to grid circuit and a local controller that monitors a power characteristic at the one or more storage batteries, and controls the one or more batteries to selectively act as a generator to supply power to the power grid or to act as a load to draw power from the power grid in response to a predetermined disturbance in the power characteristic being detected, wherein the controller comprises a battery charging circuit that controls the battery to act as a generator to supply power when a first predetermined frequency deviation in the local frequency is detected, and controls the battery to act as a load to draw power from the connected power grid when a second predetermined frequency deviation in the local frequency is detected.
11. The system of claim 10 , wherein the battery to grid circuit comprises a pulse-width modulation signal generator, a grid-tie inverter sub circuit connecting the signal generator with a transformer as its main supply and a referent sine wave generator, the power of the battery to grid circuit depends on the PWM frequency that is regulated by the controller, and a second transformer that powers the battery or batteries and returns power to the power grid.
12. The system of claim 10 , wherein the power characteristic comprises a local frequency at the one or more storage batteries and the predetermined disturbance comprises a frequency disturbance.
13. The system of claim 12 , further comprising releasing the battery or batteries from power regulation control when the local frequency is stable.
14. The system of claim 12 , wherein the frequency disturbance is determined as a function of the first derivative of the change in local frequency.
15. The system of claim 12 , wherein the controlling comprises controlling the battery or batteries to have a battery power output linearly dependent on frequency deviation, with ramp limits of ±3 kW at ±100 mHz according to:
P
=
{
-
3
kW
,
if
Δ
f
<
-
100
mHz
h
·
Δ
f
kW
,
if
-
100
mHz
<
Δ
f
<
100
mHz
3
kW
,
if
Δ
f
>
100
mHz
(
1
)
where h=X kW/Hz is a control parameter and Δf is the frequency deviation from its nominal value, h=˜30 kW/Hz.
16. The system of claim 12 , wherein said controlling comprises controlling the battery or batteries to have a battery power output dependent upon a tanh, or a sigmoid function.
17. The system of claim 12 , wherein the controlling comprises controlling the battery or batteries to have a battery power output linearly dependent on frequency deviation, with ramp limits of a first predetermined power and a fraction of that power according to:
P
=
{
-
first
predetermined
kW
,
if
Δ
f
<
-
fraction
mHz
h
kW
/
Hz
·
Δ
f
kW
,
if
-
fraction
mHz
<
Δ
f
<
fraction
mHz
first
predetermined
kW
,
if
Δ
f
>
fraction
mHz
(
1
)
where h kW/Hz is a control parameter and Δf is frequency deviation from its nominal value.
18. The system of claim 17 , further comprising releasing the battery or batteries from power regulation control when the local frequency is stable.
19. The system of claim 10 , wherein the one or more storage batteries comprises a plug-in electrical vehicle or a home battery.