Voltage compensated active cell balancing

Patent metadata

Field	Value
Publication number	US-9774206-B2
Application number	US-201414245390-A
Country	US
Kind code	B2
Filing date	Apr 4, 2014
Priority date	Apr 5, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

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.

First claim

What is claimed is:

1. A monitoring device that determines an open cell voltage during battery stack balancing, the monitoring device comprising:
an input terminal that receives an input signal from a battery system management (BSM);
an output terminal that outputs 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;
the monitoring device having a configuration that:
measures a cell voltage associated with the one of the plurality of cells within the battery stack;
determines a voltage drop associated with a measured balancing current by taking into consideration balancing current associated with the one of the plurality of cells, a cell above the one of the plurality of cells, and a cell below the one of the plurality of cells, and current simultaneously flowing through the plurality of cells;
calculates the open cell voltage during balancing, stack loading, and stack charging by adjusting the measured cell voltage based on the voltage drop; and
actively balances multiple cells in the battery stack based on the calculated open cell voltage, wherein:
the active balancing and the calculating the open cell voltage are performed concurrently, and
the actively balances includes removal of charge from a cell and returning that removed charge to one or more other cells in the stack.

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 that provides 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 the monitoring device actively monitors the balancing current of the monitoring device and calculates 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 monitoring device:
activates the monitoring device on a first negative edge of an input signal received on the input terminal,
initiates a time window defining a window of time within which the monitoring device is active,
counts number of negative pulses on the input terminal during the time window,
outputs a handshake voltage on the output terminal corresponding to a last known count of the negative pulses on the input terminal, and
outputs 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 the ground terminal of the monitoring device to the battery stack shares a common path with a Vcell pin of another monitoring device to the battery stack.

8. The monitoring device of claim 7 , wherein the the open cell voltage is calculated based on the following formula:
V n,A =V n,B +I n ·( R n−1,A +R n,B )− I n−1 ·R n−1,B −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 n−1,A and R n−1,B 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 n−1 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 monitoring device calculates an impedance associated with the monitoring circuit based on the following formula:

R
n

=

V

n
,

MODE
⁢

⁢
0

-

V

n
,

MODE
⁢

⁢
1

-

(

I
n

-

I
MOD

)

·

R

n
,
CELL

I
n

,

where:
V n,MODE0 corresponds to a cell voltage of the one of the plurality of cells with the monitoring device being disabled,
V n,MODE1 corresponds to a cell voltage of one of the plurality of cells with the monitoring device being enabled,

Assignees

• Linear Tech Corp

Inventors

• Kim Dave Daekyum
• Milliken Robert Jon

Classifications

• H02J7/54 Primary

  Passive balancing, e.g. using resistors or parallel MOSFETs · CPC title

• H02J7/0016

  Electricity · mapped topic

• H01M2010/4271

  Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing · CPC title

• H02J7/007 Primary

  Electricity · mapped topic

• G01R31/36 Primary

  Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] · CPC title