VOLTAGE COMPENSATED ACTIVE CELL BALANCING

• US 20140306662A1
• Filed: 04/04/2014
• Published: 10/16/2014
• Est. Priority Date: 04/05/2013
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: KIM, Dave Daekyum, MILLIKEN, Robert Jon
• Granted Patent: US 9,774,206 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: H01M 2010/4271 Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A monitoring device includes an input terminal configured to receive an input signal from a battery system management (BSM); an output terminal configured to output cell parameters used to determine an open cell voltage associated with one of a plurality of cells within the battery stack connected to the monitoring circuit based on the input signal received from the BSM; a processor; and a memory storing executable instructions for causing the processor to: measure a cell voltage associated with the one of the plurality of cells within the battery stack; measure a voltage drop associated with a measured balancing current; calculate the open cell voltage by adjusting the measured cell voltage based on the measured voltage drop; and balance the battery stack based on the calculated open cell voltage, wherein balancing and calculating the open cell voltage are performed concurrently.

Claims

1. A monitoring device configured to monitor an open cell voltage during battery stack balancing, the monitoring device comprising:

an input terminal configured to receive an input signal from a battery system management (BSM);

an output terminal configured to output cell parameters used to determine an open cell voltage associated with one of a plurality of cells within the battery stack connected to the monitoring device based on the input signal received from the BSM;

a processor; and

a memory storing executable instructions for causing the processor to;

measure a cell voltage associated with the one of the plurality of cells within the battery stack;

measure a voltage drop associated with a measured balancing current;

calculate the open cell voltage by adjusting the measured cell voltage based on the measured voltage drop; and

balance the battery stack based on the calculated open cell voltage, wherein balancing and calculating the open cell voltage are performed concurrently.

2. The monitoring device of claim 1, wherein the monitoring device is between the BSM and the battery stack and further includes:

an integrated power switch; and

an analog multiplexer configured to provide on the output terminal a measurable parameter based on the input signal received on the input terminal, the measuring parameter includes a cell voltage of the one of the plurality of the cells within the battery stack with balancing enabled, the cell voltage with balancing disabled, a voltage proportional to balancing current, a voltage proportional to internal die temperature of the monitoring device, and/or a handshake voltage.

3. The monitoring device of claim 2, wherein the handshake voltage determines the accuracy of measurement readings by the BSM.

4. The monitoring device of claim 1, further comprising a current sense amplifier for measuring a balancing current, wherein memory further stores executable instructions for causing the processor to actively monitor the balancing current of the monitoring device and calculating the voltage drop based on the monitored balancing current to avoid overcharging or undercharging the one of the plurality of the cells during balancing.

5. The monitoring device of claim 1, wherein the monitoring device includes a monolithic flyback DC/DC converter.

6. The monitoring device of claim 1, wherein the memory further stores executable instructions for causing the processor to:

activate the monitoring device on a first negative edge of an input signal received on the input terminal,

initiate a time window defining a window of time within which the monitoring device is active,

count number of negative pulses on the input terminal during the time window,

output a handshake voltage on the output terminal corresponding to a last known count of the negative pulses on the input terminal, and

output a voltage proportional to a cell parameter based on the number of negative pulses counted once the time window expires.

7. The monitoring device of claim 1, wherein the monitoring device is connected to the battery stack via a single-wire battery connection in which a ground connection of the monitoring device to the battery stack shares a common path with a Vcell connection of another monitoring device to the battery stack.

8. The monitoring device of claim 7, wherein the memory further stores executable instructions for causing the processor to calculate the open cell voltage based on a following formula:

V_n,A=V_n,B+I_n·

(R<sub>n−

1,A</sub>+R_n,B)−

I<sub>n−

1</sub>·

R<sub>n−

1,B</sub>−

I_n+1·

R_n,A+(I_n−

I_MOD)·

R_n,CELL

where;

V_n,A is the open cell voltage associated with the one of the plurality of cells,

V_n,B is the measured cell voltage by the monitoring device for one of the plurality of cells,

R<sub>n−

1,A</sub> and R<sub>n−

1,B</sub> are resistances associated with a line connecting a ground terminal of the monitoring device with a negative terminal of the cell,

R_n,A and R_n,B are resistances associated with a line connecting a Vcell pin of the monitoring circuit with a plus terminal of the cell,

R_n,CELL is a resistance accounting for all impedances not having a shared path with a cell below and a cell above the one of the plurality of cells,

I_n is a balancing current associated with the one of the plurality of cells,

I<sub>n−

1</sub> is a balancing current associated with the cell below the one of the plurality of cells,

I_n+1 is a balancing current associated with the cell above the one of the plurality of cells, and

I_MOD is the current simultaneously flowing through the plurality of cells.

9. The monitoring device of claim 1, wherein the monitoring device is connected to the battery stack via a two-wire battery connection in which a ground connection of the monitoring device to the battery stack does not share a common path with a Vcell connection of a second monitoring device to the battery stack, the second monitoring circuit being adjacent and below the monitoring circuit.

10. The monitoring device of claim 9, wherein the memory further stores executable instructions for causing the processor to calculate an impedance associated with the monitoring circuit based on a following formula:

11. The monitoring device of claim 10, wherein the memory further stores executable instructions for causing the processor to calculate the open cell voltage based on the following formula with two-wire battery connections:

V_n,A=V_n,B+I_n·

R_n+(I_n−

I_MOD)·

R_n,CELL·

I<sub>n−

1</sub>·

R<sub>n−

1</sub>,

where;

V_n,A is the open cell voltage associated with the one of the plurality of cells,

V_n,B is the measured cell voltage by the monitoring device for the one of the plurality of cells,

R_n is the impedance associated with a V_CELL pin of monitoring device connected to the one of the plurality of cells,

R<sub>n−

1</sub> is an impedance associated with a monitoring device connected to a cell below the one of the plurality of cells,

R_n,CELL is the DCR and connection resistance of one of the plurality of cells,

I_n is a balancing current associated with the one of the plurality of cells,

I<sub>n−

1</sub> is a balancing current associated with the cell below the one of the plurality of cells, and

I_MOD is the current simultaneously flowing through the plurality of cells.

12. The monitoring device of claim 1, the memory further stores executable instructions for causing the processor to measure a voltage droop associated with the one of the plurality of cells and calculate the open cell voltage based on the voltage droop and the voltage drop.

13. The monitoring device of claim 1, wherein the voltage droop is added to the voltage drop in calculating the open cell voltage after threshold amount time of the monitoring device associated with the one of the plurality of cells turns ON.

14. A system comprising:

a plurality of modules, each module including a battery stack, a monitoring circuit of claim 1 for balancing one of the plurality of cells of the battery stack, and a module system management for measuring the open voltage, wherein measuring the open cell voltage and balancing the cell are performed concurrently;

a module-to-stack balancer coupled to the plurality of modules and including a plurality of balancers each associated with one of the plurality of modules, the module-to-stack balancer configured to balance a voltage or stored charge among the modules.

15. An IR compensated active cell balancing method comprising steps of:

receiving an input signal at an input terminal of a monitoring device and from a battery system management (BSM);

responsive to the input signal, activating the monitoring device for balancing one of the plurality of cells within a battery stack coupled to the monitoring device;

measuring a cell voltage associated with one of the plurality of cells;

measuring a voltage drop associated with a measured balancing current;

calculating via a processor an open cell voltage associated with the one of the plurality of cells by adjusting the measured cell voltage based on the measured voltage drop; and

balancing the battery stack based on the processor calculated open cell voltage, wherein balancing and calculating the open cell voltage are performed concurrently.

16. The method of claim 15, further comprising providing on the output terminal a measurable parameter based on the input signal received on the input terminal, wherein the measuring parameter includes a cell voltage of the one of the plurality of the cells within the battery stack with balancing enabled, the cell voltage with balancing disabled, a voltage proportional to balancing current, a voltage proportional to internal die temperature of the monitoring device, and/or a handshake voltage.

17. The method of claim 15, further comprising:

actively monitoring the balancing current of the monitoring device; and

calculating the voltage drop based on the monitored balancing current to avoid overcharging or undercharging the one of the plurality of the cells during balancing.

18. The method of claim 15, wherein the monitoring device includes a monolithic flyback DC/DC converter.

19. The method of claim 15, wherein activating the monitoring device includes activating the monitoring device on a first negative edge of an input signal received on the input terminal, the method further comprising:

initiating a time window defining a window of time within which the monitoring device is active;

counting number of negative pulses on the input terminal during the time window; and

outputting a handshake voltage on the output terminal corresponding to a last known count of the negative pulses on the input terminal; and

outputting a voltage proportional to a cell parameter based on the number of negative pulses counted once the time window has expired.

20. The method of claim 15, wherein calculating the open cell voltage includes calculating the open voltage based on the following formula:

V_n,A=V_n,B+I_n·

(R<sub>n−

1,A</sub>+R_n,B)−

I<sub>n−

1</sub>·

R<sub>n−

1,B</sub>−

I_n+1·

R_n,A+(I_n−

I_MOD)·

R_n,CELL,

where;

V_n,A is the open cell voltage associated with the one of the plurality of cells,

V_n,B is the measured cell voltage by the monitoring device for the one of the plurality of cells,

R<sub>n−

1,A</sub> and R<sub>n−

1,B</sub> are resistances associated with a line connecting a ground terminal of the monitoring device with a negative terminal of the cell,

R_n,A and R_n,B are resistances associated with a line connecting a Vcell pin of the monitoring circuit with a plus terminal of the cell,

R_n,CELL is a resistance accounting for all impedances not having a shared path with a cell below and a cell above the one of the plurality of cells,

I_n is a balancing current associated with the one of the plurality of cells,

I<sub>n−

1</sub> is a balancing current associated with the cell below the one of the plurality of cells,

I_n+1 is a balancing current associated with the cell above the one of the plurality of cells, and

I_MOD is the current simultaneously flowing through the plurality of cells in a module including the monitoring device and the BSM.

21. The method of claim 15, further comprising calculating an impedance associated with the monitoring circuit for calculating the open cell voltage based on the following formula:

22. The method of claim 21, wherein calculating the open cell voltage includes calculating the open voltage based on the following formula:

V_n,A=V_n,B+I_n·

R_n+(I_n−

I_MOD)·

R_n,CELL−

I<sub>n−

1</sub>·

R<sub>n−

1</sub>,

where;

V_n,A is open cell voltage associated with the one of the plurality of cells,

V_n,B is a measured cell voltage by the monitoring device for the one of the plurality of cells,

R_n is the impedance associated with the Vcell pin of monitoring device connected to the one of the plurality of cells,

R<sub>n−

1</sub> is an impedance resistance associated with a monitoring device connected to a cell below the one of the plurality of cells,

R_n,CELL is the DCR and connection resistance of one of the plurality of cells,

I_n is a balancing current associated with the one of the plurality of cells,

I<sub>n−

1</sub> is a balancing current associated with the cell below the one of the plurality of cells, and

I_MOD is the current simultaneously flowing through the plurality of cells in a module including the monitoring device and the BSM.

23. A monitoring device comprising:

an input terminal configured to receive an input signal from a battery system management (BSM);

an output terminal configured to output cell parameters used to determine an open cell voltage associated with one of a plurality of cells within the battery stack connected to the monitoring circuit based on the input signal received from the BSM;

a processor; and

a memory storing executable instructions for causing the processor to;

measure a cell voltage associated with the one of the plurality of cells within the battery stack;

measure a voltage drop associated with a measured balancing current;

calculate the open cell voltage by adjusting the measured cell voltage based on the measured voltage drop;

calculate capacity associated with the one of the plurality of cells;

calculate stored charge of the one of the plurality of cells based on the calculated capacity;

balance the battery stack based on the calculated stored charge, wherein balancing and calculating the open cell voltage are performed concurrently.

24. The monitoring device of claim 23, wherein the memory further stores executable instructions for causing the processor to calculate the capacity based on a following formula:

25. The monitoring device of claim 24, wherein to calculate the open cell voltage, the memory further stores executable instructions to calculate a first open cell voltage and a second open cell voltage and to calculate the percentage change in the SOC, the memory further stores executable instructions to utilizes a look-up table configured to correlate the first open cell voltage with a first percentage SOC and the second open cell voltage with the second percentage SOC such that the difference between the first percentage SOC and the second percentage SOC corresponds to the percentage change in the SOC.

26. The monitoring device of claim 25, the memory further stores executable instructions for causing the processor to calculate the capacity based on a following formula:

Q_n=% SOC_n·

Capacity_n,

where;

% SOC_n represents percentage SOC of the one of the plurality of cells, and

Capacity_n represents capacity of the one of the plurality of cells.