[0001] The present disclosure relates, in general, to power supply charging and discharging systems. In particular, the present disclosure relates to methods and systems for active cell and module balancing for a battery of an electric vehicle.
BACKGROUND
[0002] Background description includes information that may be useful in understanding the present subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
[0003] Modern high-voltage (HV) batteries, such as large lithium-ion batteries, often include multiple battery cells connected in series. Unfortunately, the actual output voltage provided by each individual battery cell in the HV battery may vary slightly because of production tolerances, uneven temperature distribution and differences in the ageing characteristics of particular cells. During the charging cycle, if there is a degraded cell in the chain with a diminished capacity, there is a danger that once it has reached its full charge it will be subject to overcharging until the rest of the cells in the chain reach their full charge. The result is temperature and pressure build up and possible damage to the cell. With every charge - discharge cycle the weaker cells will get weaker until the battery fails. During discharging, the weakest cell will have the greatest depth of discharge and will tend to fail before the others. It is even possible for the voltage on the weaker cells to be reversed as they become fully discharged before the rest of the cells also resulting in early failure of the cell. In some systems, voltage

detection circuitry can be used to determine the output voltage of each battery cell, and a voltage balancing system can be used to compensate for variations in the output voltages of the each battery cells.
[0004] Consider battery cells connected in series in an electric vehicle, where each battery cell is ideally designed to provide an output voltage of 3 V. Voltage detection circuitry may determine that one of the battery cells actually has an output voltage of 3.1V. In such scenario, a conventional active voltage balancing system identifies battery cells having an output voltage below 3V, and evenly supply extra 0.1V to the identified battery cells till the output voltage of the battery cells is substantially balanced. Then, a direct current-to-direct current (DC-DC) step-down converter is used to charge a low-voltage (LV) battery from the high-voltage (HV) battery. In this scenario, since electrical energy is supplied to the LV battery after cell balancing and conversion, two-level electrical energy losses are observed in the conventional active voltage balancing system. The first level is contributed by isolated boost converter of slave BMS, and the second level is contributed by step-down DC-DC converter used for LV lines. This results in significant energy being lost from the battery cells, which shortens the operational life of the HV battery. Also, active cell balancing circuits require more complex, larger footprint solutions, hence, are generally costly.
[0005] Accordingly, there is a need for methods and systems for active cell and module balancing for a battery of an electric vehicle so as to minimize the line losses during the supply of the electrical energy.
OBJECTS OF THE DISCLOSURE
[0006] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0007] A general object of the present disclosure is to provide methods and systems for active cell and module balancing for a battery of an electric vehicle so as to minimize the line losses during supply of the electrical energy.

[0008] An object of the present disclosure is to reduce the electrical energy losses during active battery cell balancing.
[0009] Another object of the present disclosure is to run auxiliary loads for performing active battery cell balancing.
[0010] Another object of the present disclosure is to deliver the electrical energy from the cell balancing on a low voltage line with the improvement in battery efficiency.
[0011] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY
[0012] This summary is provided to introduce concepts related to methods and systems for active cell and module balancing for a battery of an electric vehicle. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0013] The present disclosure relates to a method for active cell balancing for an electric vehicle battery. The method includes the step of: identify a battery cell having an output voltage above a threshold value at a master battery management system (BMS) based on a digital voltage data received from a slave BMS; communicating a control signal from the master BMS to the slave BMS; controlling a switch, corresponding to the identified battery cell, in a switch controller of the slave BMS based on the received control signal from the master BMS; and activating, by the slave BMS, an isolated boost direct current to direct current (DC-DC) converter to convert electrical energy of the identified battery

cell from high voltage side to low voltage side and to supply the converted low voltage electrical energy to loads of slave BMS.
[0014] In an aspect, the method further includes supplying the converted low voltage electrical energy to loads of slave BMS.
[0015] In an aspect, the method further includes deactivating the isolated boost DC-DC converter when the output voltage of the identified battery cell is ascertained within the threshold value.
[0016] In an aspect, the step of identification of the battery cell having an output voltage above a threshold value, includes further steps of monitoring values of output voltage of each battery cell of a plurality of battery cells using a voltage detection circuitry of the slave BMS; converting the monitored values into digital voltage data by a printed circuit board (PCB) control circuit of the slave BMS, and communicating the digital voltage data, of the monitored values of the output voltage of each battery cell, to the master BMS.
[0017] The method as claimed in claim 1, wherein the method step of monitoring values of the output voltage of each battery cell, includes sequentially monitoring each battery cell of a plurality of battery cells.
[0018] The present disclosure further includes a system for active cell balancing for an electric vehicle battery. The system includes a master battery management system (BMS) to identify a battery cell having an output voltage above a threshold value based on a digital voltage data. The system further includes a slave BMS communicatively coupled to the master BMS. The slave BMS is to receive a control signal from the master BMS for the identified battery cell having an output voltage above a threshold value; control a switch, corresponding to the identified battery cell, in a switch controller based on the received control signal; and activate an isolated boost direct current to direct current (DC-DC) converter: to convert electrical energy of the identified battery cell from high voltage side to low voltage side, and to supply the converted low voltage electrical energy to loads of slave BMS.

[0019] In an aspect, the slave BMS supplies the converted low voltage
electrical energy to loads of slave BMS.
[0020] In an aspect, the slave BMS deactivates the isolated boost DC-DC
converter when the output voltage of the identified battery cell is ascertained
5 within the threshold value.
[0021] In an aspect, the slave BMS is to monitor values of output voltage of
each battery cell of a plurality of battery cells using a voltage detection circuitry
of the slave BMS; convert the monitored values into digital voltage data by a
printed circuit board (PCB) control circuit of the slave BMS, and communicate
10 the digital voltage data, of the monitored values of the output voltage of each
battery cell, to the master BMS.
[0022] In an aspect, the voltage detection circuitry monitors the values of the
output voltage of each battery cell by sequentially monitoring each battery cell of a plurality of battery cells.
15 [0023] Various objects, features, aspects, and advantages of the inventive
subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0024] It is to be understood that the aspects and embodiments of the
20 disclosure described above may be used in any combination with each other.
Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0025] The foregoing summary is illustrative only and is not intended to be in
any way limiting. In addition to the illustrative aspects, embodiments, and features
25 described above, further aspects, embodiments, and features will become apparent
by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
6

[0026] The illustrated embodiments of the subject matter will be best
understood by reference to the drawings, wherein like parts are designated by like
numerals throughout. The following description is intended only by way of
example, and simply illustrates certain selected embodiments of devices, systems,
5 and methods that are consistent with the subject matter as claimed herein,
wherein:
[0027] FIG. 1 illustrates an exemplary architecture of a battery management
system (BMS), in accordance with an embodiment of the present disclosure; and
[0028] FIG. 2 illustrates a method of implementing the battery management
10 system to perform active cell balancing of an electric vehicle battery, in
accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0029] The detailed description of various exemplary embodiments of the
15 disclosure is described herein with reference to the accompanying drawings. It
should be noted that the embodiments are described herein in such details as to
clearly communicate the disclosure. However, the amount of details provided
herein is not intended to limit the anticipated variations of embodiments; on the
contrary, the intention is to cover all modifications, equivalents, and alternatives
20 falling within the spirit and scope of the present disclosure as defined by the
appended claims.
[0030] It is also to be understood that various arrangements may be devised
that, although not explicitly described or shown herein, embody the principles of
the present disclosure. Moreover, all statements herein reciting principles, aspects,
25 and embodiments of the present disclosure, as well as specific examples, are
intended to encompass equivalents thereof.
[0031] The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of example embodiments. As
7

used herein, the singular forms “a”, “an” and “the” are intended to include the
plural forms as well, unless the context clearly indicates otherwise. It will be
further understood that the terms “comprises”, “comprising”, “includes” and/or
“including,” when used herein, specify the presence of stated features, integers,
5 steps, operations, elements and/or components, but do not preclude the presence
or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0032] It should also be noted that in some alternative implementations, the
functions/acts noted may occur out of the order noted in the figures. For example,
10 two figures shown in succession may, in fact, be executed concurrently or may
sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0033] Unless otherwise defined, all terms (including technical and scientific
terms) used herein have the same meaning as commonly understood by one of
15 ordinary skill in the art to which example embodiments belong. It will be further
understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
20 [0034] Embodiments and/or implementations described herein relate to
methods and systems for active cell and module balancing for a battery of a vehicle. FIG. 1 illustrates an exemplary battery management system (BMS) 100, according to an embodiment of the present disclosure. The BMS 100 includes a plurality of slaves 102 connected to a master BMS 104. Each of the slaves 102
25 includes a voltage detection circuitry (not shown in FIG. 1) and a printed circuit
board (PCB) control circuit 106. The voltage detection circuitry is in communication with a respective battery stack module M1, M2, and the PCB control circuit 106. The PCB control circuit 106 may be thought of as an accurate voltmeter and is configured to convert the measured analog voltage output of the
8

battery cells in the battery stack module (M1, M2) to a digital data that can be read by a processing unit or a microprocessor.
[0035] The voltage detection circuitry, in one specific example, includes an
LT8584. However, communication between the PCB control circuit 106 and the
5 voltage detection circuitry is not limited to the scheme used by the LT8584 and
other types of communication between the voltage detection circuitry and the PCB control circuit 106 may be used.
[0036] The PCB control circuit 106, in one specific example, includes
LTC680x family of voltage monitoring ICs having 12 channels for measuring 12
10 battery cells in the battery stack module (M1, M2) and several General Purpose
Input/Output (“GPIO”) channels that may be configured as analog or digital inputs or outputs. Each of the 12 channels of the PCB control circuit 106 includes two pins, out of which the first pin is dedicated for reading battery cell measurement parameters from the voltage detection circuitry and the second pin is
15 dedicated for enabling and communicating with other components of the BMS
100.
[0037] In accordance with the present disclosure, the voltage detection
circuitry may be an active balancing circuit. Being an active balancing circuit, the voltage detection circuitry is inserted between the battery stack module (M1, M2)
20 and the PCB control circuit 106, and includes an output pin and an input pin. The
input pin is connected to the first pin of the PCB control circuit 106 and is configured to receive the enabling signal from the second pin of the PCB control circuit 106. The output pin of the voltage detection circuitry is connected to the first pin of the PCB control circuit 106 and is configured to provide various
25 measurements to the PCB control circuit 106 via the second pin of the PCB
control circuit 106.
[0038] Further, the voltage detection circuitry is configured to monitor the
output voltage of each battery cell during battery stack/module balancing, loading and charging. To illustrate one specific example, assume that there is a weak
9

battery cell, which is aged more than the other cells in the battery stack module
(M1, M2). During the charging process, the weak battery cell is likely to get
charged and sometimes overcharged before the other battery cells because it has a
lesser capacity to retain charge due to erosion. When the charge of the weak
5 battery cell reaches above a certain threshold value, without the voltage detection
circuitry, the charging operation may be discontinued to avoid overcharging the
weak battery cell and damaging the battery stack module (M1, M2). As a result,
the weak battery cell may be charged within an acceptable threshold value but the
remaining battery cells in the battery stack module (M1, M2) may be
10 undercharged.
[0039] Instead of discontinuing the charging operation, the voltage detection
circuitry monitors values of the output voltage of each battery cell of a plurality of battery cells of the respective battery pack modules (M1, M2) and provides the same to the PCB control circuit 106 to convert the monitored values into digital
15 voltage data. This digital voltage data is then communicated from the slave BMS
102 to the master BMS 104 over communication lines 108. The master BMS 104 identifies a weak battery cell having an output voltage above a threshold value based on the received digital voltage data, and in response, communicates a control signal to the slave BMS 102. The control signal is processed at the PCB
20 control circuit 106 to control a switch, corresponding to the identified weak
battery cell, in a switch controller 110 of the slave BMS 102.
[0040] Once the respective switch associated with the identified weak battery
cell is controlled, the slave BMS 102 actives an isolated boost direct current to direct current (DC-DC) converter 112. The isolated boost DC-DC converter 112
25 then converts electrical energy of the identified weak battery cell from identified
weak cell of high voltage side to low voltage side, and supplies the converted low voltage electrical energy to loads of slave BMS to meet the energy requirement of PCB control circuit 106 of slave BMS 102. The isolated boost DC-DC converter 112 may continue this process until all weak battery cells are discharged up to an
30 acceptable threshold value.
10

[0041] Similarly, in an alternative implementation, when the battery is being
discharged, the weak battery cell may be discharged more quickly than the other
battery cells in the respective battery stack module (M1, M2). In this scenario, the
slave BMS 102 may control the respective switch of the weak battery cells and
5 controls the isolated boost DC-DC converter 112 to redistribute charge from the
other battery cells in the battery stack modules (M1, M2) until all battery cells are discharged within an acceptable threshold value, allowing all charge in battery stack modules (M1, M2) to be utilized efficiently.
[0042] Thus, with the implementation of the present disclosure, only one-time
10 line loss is present when the electrical energy is converted from high voltage side
to low voltage side. This, in turn, improves the efficiency of the battery cells which enhances the operational life of the battery, specifically high voltage battery of an electric or hybrid vehicle.
[0043] FIG. 2 illustrates a method 200 for active cell balancing for a vehicle
15 battery, according to an embodiment of the present disclosure. The order in which
the method 200 is described is not intended to be construed as a limitation, and
any number of the described method blocks can be combined in any appropriate
order to carry out the method 200 or an alternative method. Additionally,
individual blocks may be deleted from the method 200 without departing from the
20 scope of the subject matter described herein.
[0044] The method 200 begins with identifying a battery cell having an output
voltage above a threshold value. In an aspect, the threshold value can be 3V. The
identifying step includes the process of monitoring values of the output voltage of
each battery cell of a plurality of battery cells using a voltage detection circuitry
25 of the slave BMS 102. Then, the monitored values are converted into digital
voltage data by a printed circuit board (PCB) control circuit 106 of the slave BMS 102. Following the conversion, the digital voltage data, of the monitored values of the output voltage of each battery cell, is communicated to the master BMS 104.
11

[0045] At block 202, the method 200 includes identifying a battery cell having
an output voltage above a threshold value at the master BMS 104 based on the digital voltage data received from the slave BMS 102.
[0046] At block 204, the method 200 includes communicating a control signal
5 from the master BMS 104 to the slave BMS 102.
[0047] At block 206, the method 200 includes controlling a switch,
corresponding to the identified battery cell, in a switch controller 110 of the slave BMS 102 based on the received control signal from the master BMS 104.
[0048] At block 208, the method 200 includes activating, by the slave BMS
10 102, an isolated boost direct current to direct current (DC-DC) converter 112 to
convert electrical energy of the identified battery cell from high voltage side to low voltage side and to supply the converted low voltage electrical energy to loads of slave BMS to meet the energy requirement of PCB control circuit 106 of slave BMS 102.
15 [0049] The method 200 further includes a step of supplying the converted low
voltage electrical energy to loads of slave BMS.
[0050] Also, when the output voltage of the identified battery cell is
ascertained within the threshold value, the slave BMS 102 deactivates the isolated
boost DC-DC converter 112 and activates voltage detection circuitry for
20 sequentially monitoring each battery cell of a plurality of battery cells.
[0051] Thus, with the implementation of the present disclosure, only one-time
line loss is present when the electrical energy is converted from high voltage side
to low voltage side. This, in turn, improves the efficiency of the battery cells
which enhances the operational life of the battery, specifically high voltage
25 battery of an electric or hybrid vehicle.
[0052] The above description does not provide specific details of the
manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out,
12

techniques, known, related art or later developed designs and materials should be employed. Those in the art can choose suitable manufacturing and design details.
[0053] It should be understood, however, that all of these and similar terms
are to be associated with the appropriate physical quantities and are merely
5 convenient labels applied to these quantities. Unless specifically stated otherwise,
as apparent from the discussion herein, it is appreciated that throughout the
description, discussions utilizing terms such as “identifying,” or
“communicating,” or “closing,” or “activating,” or “converting,” or the like, refer
to the action and processes of an electronic control unit, or similar electronic
10 device, that manipulates and transforms data represented as physical (electronic)
quantities within the control unit’s registers and memories into other data similarly represented as physical quantities within the control unit memories or registers or other such information storage, transmission or display devices.
[0054] Further, the terminology used herein is for the purpose of describing
15 particular embodiments only and is not intended to be limiting of the disclosure. It
will be appreciated that several of the above-disclosed and other features and
functions, or alternatives thereof, may be combined into other systems or
applications. Various presently unforeseen or unanticipated alternatives,
modifications, variations, or improvements therein may subsequently be made by
20 those skilled in the art without departing from the scope of the present disclosure
as encompassed by the following claims.
[0055] It will be appreciated that variants of the above-disclosed and other
features and functions, or alternatives thereof, may be combined into many other
different systems or applications. Various presently unforeseen or unanticipated
25 alternatives, modifications, variations, or improvements therein may be
subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
[0056] The claims, as originally presented and as they may be amended,
encompass variations, alternatives, modifications, improvements, equivalents, and
13

substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
5
14

We claim:

A method for cell balancing for an electric vehicle battery, the method comprising:
identifying a battery cell having an output voltage above a threshold value at a master battery management system (BMS) (104) based on a digital voltage data received from a slave BMS (102);
communicating a control signal from the master BMS (104) to the slave BMS (102);
controlling a switch, corresponding to the identified battery cell, in a switch controller (110) of the slave BMS (102) based on the received control signal from the master BMS (104); and
activating, by the slave BMS (104), an isolated boost direct current to direct current (DC-DC) converter (112) to convert electrical energy of the identified battery cell from high voltage side to low voltage side and to supply the converted low voltage electrical energy to loads of slave BMS.
The method as claimed in claim 1, further comprising supplying the converted low voltage electrical energy to loads of slave BMS to meet energy requirement of PCB control circuit 106 of slave BMS 102.
The method as claimed in claim 1, deactivating the isolated boost DC-DC converter (112) when the output voltage of the identified battery cell is ascertained within the threshold value.
The method as claimed in claim 1, wherein identifying the battery cell having an output voltage above a threshold value, comprising:
monitoring values of the output voltage of each battery cell of a plurality of battery cells using a voltage detection circuitry of the slave BMS (102);

converting the monitored values into digital voltage data by a printed circuit board (PCB) control circuit (106) of the slave BMS (102); and
communicating the digital voltage data, of the monitored values of the output voltage of each battery cell, to the master BMS (104). The method as claimed in claim 1, wherein monitoring values of the output voltage of each battery cell comprises sequentially monitoring each battery cell of a plurality of battery cells.
A system (100) for cell balancing for an electric vehicle battery, the system (100) comprising:
a master battery management system (BMS) (104) to identify a battery cell having an output voltage above a threshold value based on a digital voltage data; and
a slave BMS (102), communicatively coupled to the master BMS (104), to:
receive a control signal from the master BMS (104) for the
identified battery cell having an output voltage above a threshold
value;
control a switch, corresponding to the identified battery cell, in a
switch controller (110) based on the received control signal; and
activate an isolated boost direct current to direct current (DC-DC)
converter (112): to convert electrical energy of the identified battery
cell from high voltage side to low voltage side, and to supply the
converted low voltage electrical energy to loads of slave BMS.
The system (100) as claimed in claim 6, wherein the slave BMS (102) supplies the converted low voltage electrical energy to loads of slave BMS to meet energy requirement of PCB control circuit 106 of slave BMS 102.

The system (100) as claimed in claim 6, wherein the slave BMS (102) deactivates the isolated boost DC-DC converter (112) when the output voltage of the identified battery cell is ascertained within the threshold value.
The system (100) as claimed in claim 6, wherein the slave BMS (102) is to:
monitor values of the output voltage of each battery cell of a plurality of battery cells using a voltage detection circuitry;
convert the monitored values into digital voltage data by a printed circuit board (PCB) control circuit (106); and
communicate the digital voltage data, of the monitored values of the output voltage of each battery cell, to the master BMS (104).
). The system (100) as claimed in claim 6, wherein the voltage detection circuitry monitors the values of the output voltage of each battery cell by sequentially monitoring each battery cell of a plurality of battery cells.