Electric vehicle battery monitoring system
Systems and methods for monitoring and controlling a battery are disclosed. Systems can include a battery having an output voltage and an output current when delivering power, a load driven by power delivered from the battery, battery output voltage and current sensing circuits, and processing circuitry coupled to the battery output voltage and current sensing circuits. The processing circuitry may be configured to obtain sensed battery output voltage and current values, and to estimate values for at least three battery state parameters by concurrently fitting the voltage and current values to at least two different equations.
1. A battery powered apparatus comprising:
a battery comprising one or more electrochemical cells, the battery having an output voltage and an output current when delivering power;
a load driven by power delivered from the battery;
a battery output voltage sensing circuit;
a battery output current sensing circuit; and
processing circuitry coupled to the battery output voltage sensing circuit and the battery output current sensing circuit, the processing circuitry configured to obtain sensed battery output voltage values and sensed battery output current values at defined intervals and to estimate values for at least three battery state parameters of a plurality of battery state parameters at particular times when the battery is delivering power to the load, the plurality of battery state parameters including an open circuit voltage (V oc ), a series resistance (R s ), a first resistance (R 1 ), a first capacitance (C 1 ), a second resistance (R 2 ), and a second capacitance (C 2 ), wherein each of the at least three battery state parameters varies over time as the battery is used to drive the load;
wherein estimating the at least three battery state parameters comprises concurrently fitting sensed battery output voltage values and sensed battery output current values and/or data derived using the sensed battery output voltage values and sensed battery output current values to at least two different equations, wherein each of the at least two different equations are defined at least in part by different subsets of the at least three battery state parameters.
2. The battery powered apparatus of claim 1 , wherein one or more of the at least two different equations is a linear equation with a slope and an intercept defined at least in part by one or more of the at least three battery state parameters.
3. The battery powered apparatus of claim 1 , wherein estimating comprises storing current estimated values for the at least three battery state parameters, obtaining additional sensed battery output voltage values and sensed battery output current values, and updating the current estimates of the at least three battery state parameters based at least in part on the additional sensed battery output voltage values and sensed battery output current values.
4. The battery powered apparatus of claim 1 , wherein the estimation of at least one of the battery state parameters is dependent on the estimated value of at least one other battery state parameter.
5. The battery powered apparatus of claim 1 , wherein the processing circuitry is configured to estimate values of at least six battery state parameters and wherein the at least two different equations include at least three linear equations.
6. The battery powered apparatus of claim 5 , wherein the three linear equations comprise:
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wherein R s , V oc , R 1 , C 1 , R 2 , and C 2 are components of a battery equivalent circuit, wherein R 1 and C 1 are components of a first series RC circuit and R 2 and C 2 are components of a second series RC circuit and wherein equations (2) and (3) are solved over a predetermined sampling time interval.
7. The battery powered apparatus of claim 1 , wherein the at least three battery state parameters comprise an open circuit voltage of a battery equivalent circuit.
8. The battery powered apparatus of claim 7 , wherein the processing circuitry is further configured to estimate a charge state of the battery based at least in part on the estimated open circuit voltage of the equivalent circuit.
9. A method of operating a battery powered apparatus, the method comprising:
driving a load of the apparatus with a battery;
sensing the output voltage and output current of the battery at defined intervals while driving the load;
using the sensed battery output voltage values and sensed battery output current values to estimate values for at least three battery state parameters of a plurality of battery state parameters at particular times when the battery is driving the load, wherein each of the at least three battery state parameters varies over time as the battery is used to drive the load, the plurality of battery state parameters including an open circuit voltage (V oc ), a series resistance (R s ), a first resistance (R 1 ), a first capacitance (C 1 ), a second resistance (R 2 ), and a second capacitance (C 2 ), wherein the estimating the at least three battery state parameters comprises fitting sensed battery output voltage values and sensed battery output current values and/or data derived from the sensed battery output voltage values and sensed battery output current values to at least two different equations, wherein each of the at least two different equations are defined at least in part by different subsets of the at least three battery state parameters.
10. The method of claim 9 , wherein one or more of the at least two different equations is a linear equation with a slope and an intercept defined at least in part by one or more of the at least three battery state parameters.
11. The method of claim 9 , wherein estimating comprises storing current estimated values for the at least three battery state parameters, obtaining additional sensed battery output voltage values and sensed battery output current values, and updating the current estimates of the at least three battery state parameters based at least in part on the additional sensed battery output voltage values and sensed battery output current values.
12. The method of claim 9 , wherein the estimation of at least one of the battery state parameters is dependent on the estimated value of at least one other battery state parameter.
13. The method of claim 9 , further comprising estimating values for at least six battery state parameters using at least three linear equations.
14. The method of claim 9 , further comprising using three linear equations for the at least two different equations, the three linear equations comprising:
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wherein R s , V oc , R 1 , C 1 , R 2 , and C 2 are components of a battery equivalent circuit, wherein R 1 and C 1 are components of a series RC circuit and R 2 and C 2 are components of a second series RC circuit and wherein equations (2) and (3) are solved over a predetermined sampling time interval.
15. The method of claim 9 , wherein the at least three battery state parameters comprise an open circuit voltage of a battery equivalent circuit.
16. The method of claim 15 , further comprising estimating a charge state of the battery based on the estimated open circuit voltage of the equivalent circuit.
17. An electric vehicle with a battery monitoring system, the vehicle comprising:
a battery;
a powertrain comprising at least one electric motor driven by the battery;
a battery output voltage sensing circuit;
a battery output current sensing circuit; and
processing circuitry coupled to the battery output voltage sensing circuit and the battery output current sensing circuit, the processing circuitry configured to obtain sensed battery output voltage values and sensed battery output current values at defined intervals and to estimate values for at least three battery state parameters of a plurality of battery state parameters at particular times when the battery is delivering power to the powertrain, wherein each of the at least three battery state parameters varies over time as the battery is used to drive the powertrain, the plurality of battery state parameters including an open circuit voltage (V oc ), a series resistance (R s ), a first resistance (R 1 ), a first capacitance (C 1 ), a second resistance (R 2 ), and a second capacitance (C 2 ), wherein estimating the at least three battery state parameters comprises concurrently fitting sensed battery output voltage values and sensed battery output current values and/or data derived from the sensed battery output voltage values and sensed battery output current values to at least two different equations, wherein each of the at least two different equations are defined at least in part by different subsets of the at least three battery state parameters.
18. The electric vehicle of claim 17 , comprising powertrain control circuitry that is configured to receive the estimated battery state parameters and control the powertrain based at least in part on the estimated battery state parameters.
19. The electric vehicle of claim 17 , wherein the processing circuitry is configured to estimate values of six of the plurality of battery state parameters using three linear equations, and wherein the three linear equations comprise:
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V
s
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=
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s
(
I
b
)
+
V
oc
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1
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1
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2
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+
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,
(
3
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wherein R s , V oc , R 1 , C 1 , R 2 , and C 2 are components of a battery equivalent circuit, wherein R 1 and C 1 are components of a series RC circuit and R 2 and C 2 are components of a second series RC circuit and wherein equations (2) and (3) are solved over a predetermined sampling time interval.
20. The electric vehicle of claim 17 , wherein the battery performance parameters comprise an open circuit voltage of a battery equivalent circuit, and wherein the processing circuitry is further configured to estimate a charge state of the battery pack based at least in part on the estimated open circuit voltage of the equivalent circuit.
21. The electric vehicle of claim 20 , wherein the processing circuitry is further configured to calculate a vehicle range estimate and deliver the vehicle range estimate to a user of the vehicle on a display located within the vehicle.
22. The electric vehicle of claim 20 , wherein the battery performance parameters further comprise at least one resistance and at least one capacitance of the battery equivalent circuit.
23. The electric vehicle of claim 22 , wherein the processing circuitry is further configured to estimate an instantaneous power limit of the battery pack in real time based on the estimated battery state parameters.
24. The electric vehicle of claim 23 , further comprising updating a pedal map of the electric vehicle based on the estimated instantaneous power limit.
25. The electric vehicle of claim 17 , wherein the battery performance parameters comprise a series resistance of a battery equivalent circuit.
26. The electric vehicle of claim 25 , wherein the processing circuitry is further configured to compare the series resistance to a predetermined threshold and notify a user of the vehicle that battery maintenance is necessary when the series resistance exceeds the predetermined threshold.
27. The battery powered apparatus of claim 1 , wherein the processing circuitry does not include using an extended Kalman filter to estimate values for at least three battery state parameters.