1. A battery current measuring device comprising: a switching element configured to control charging and discharging of a battery: an A/D converter configured to convert a voltage value across the switching element into a digital value; a temperature compensation unit having a diode structure capable of compensating for a resistance change according to a change of temperature of the switching element; and a current calculation unit configured to calculate a current flowing through the switching element based on the digital value of the voltage value, wherein the A/D converter converts the voltage value of the switching element into the digital value using a reference voltage inputted from the temperature compensation unit.

2. The battery current measuring device of claim 1, wherein the diode structure of the temperature compensation unit comprises a plurality of diodes, wherein a number and connection configuration of the plurality of diodes are determined so as to have a temperature-resistance curve matching a temperature-resistance curve of the switching element.

3. The battery current measuring device of claim 2, further comprising a voltage amplification unit configured to amplify the voltage value before applying the voltage value across the switching element to the A/D converter.

4. The battery current measuring device of claim 2, wherein the reference voltage is changed according to the diode structure and the temperature.

5. The battery current measuring device of claim 1, wherein the temperature compensation unit is disposed close to the switching element.

6. The battery current measuring device of claim 1, wherein the switching element is a MOSFET. 21

7. The battery current measuring device of claim 6, wherein the temperature compensation unit is formed on a same layer as a layer on which the MOSFET is formed on a substrate on which the battery current measuring device is installed.

8. A battery current measuring method comprising: receiving a voltage across a switching element for controlling charging and discharging of a battery; generating a reference voltage for compensating for a resistance change according to a temperature change of the switching element; converting the voltage of the switching element into a digital value using the generated reference voltage; and calculating a current flowing through the switching element based on the digital value.

9. The battery current measuring method of claim 8, wherein the reference voltage is generated by a diode structure including a plurality of diodes, wherein a number and connection configuration of the plurality of diodes are determined so as to have a temperature-resistance curve matching a temperature-resistance curve of the switching element.

10. The battery current measuring method of claim 8, wherein the diode structure is disposed close to the switching element.

11. A battery pack comprising: a battery capable of being charged and discharged; a switching element configured to control charging and discharging of the battery: an A/D converter configured to convert a voltage value across the switching element into a digital value; a temperature compensation unit having a diode structure capable of compensating 22 for a resistance change according to a temperature change of the switching element; and a current calculation unit configured to calculate a current flowing through the switching element based on the digital value of the voltage value, wherein the A/D converter converts the voltage value of the switching element into the digital value using a reference voltage inputted from the temperature compensation unit.

12. A battery current measuring device comprising: a switching element configured to control charging and discharging of a battery: an A/D converter configured to convert a voltage across the switching element into a digital value; a temperature compensation unit including a diode structure that has a temperatureresistance curve matching the switching element and is capable of compensating for a resistance change according to a temperature change of the switching element; a subtractor configured to receive the voltage across the switching element and an output of the temperature compensation unit and output a constant voltage signal; and a current calculation unit configured to calculate a current flowing through the switching element based on the digital value of the voltage, wherein the A/D converter converts the voltage signal inputted from the subtractor into the digital value using a fixed reference voltage.

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“BATTERY CURRENT MEASURING DEVICE AND
METHOD”
LG ENERGY SOLUTION, LTD., of Tower 1, 108, Yeouidaero,
Yeongdeungpo-gu, Seoul 07335, Republic of Korea
The following specification particularly describes the invention and the manner in which
it is to be performed.
2
[SPECIFICATION]
[TITLE OF INVENTION]
BATTERY CURRENT MEASURING DEVICE AND METHOD
[TECHNICAL FIELD]
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of Korean Patent Application No.
10-2019-0001151, filed on January 4, 2019, the entire contents of which are hereby
incorporated by reference.
Technical field
The present invention relates to a battery current measuring device and method. In
particular, the present invention relates to a device and method for measuring battery
current without using a shunt resistor.
[BACKGROUND ART]
The charge/discharge current of the battery must be measured to calculate/compute
not only the output but also battery information such as battery degeneration information
and battery capacity. In addition, precise measurement accuracy is required in order to
accurately calculate the battery information, and in order to meet this, conventionally, a
battery current is measured using a precision resistor such as a shunt.
However, since these shunt resistors also occupy a large volume and add cost,
assembly processes, and the like, a better solution is required.
[DISCLOSURE OF THE INVENTION]
[TECHNICAL PROBLEM]
As a means for measuring the current of the battery, an object of the present
invention is to obtain an efficient battery current measuring means without using a shunt
resistor that occupies a large volume and adds cost and assembly process.
[TECHNICAL SOLUTION]
A battery current measuring device according to an embodiment of the present
invention includes: a switching element configured to control charging and discharging of
a battery: an A/D converter configured to convert a voltage value across the switching
element into a digital value; a temperature compensation unit having a diode structure
3
capable of compensating for a resistance change according to a change of temperature of
the switching element; and a current calculation unit configured to calculate a current
flowing through the switching element based on the digital value of the voltage value, and
the A/D converter converts the voltage value of the switching element into the digital value
using a reference voltage inputted from the temperature compensation unit.
According to one feature of this embodiment, the diode structure of the temperature
compensation unit includes a plurality of diodes, and a number and connection
configuration of the plurality of diodes are determined so as to have a temperatureresistance
curve matching a temperature-resistance curve of the switching element.
According to another feature of this embodiment, the battery current measuring
device further includes a voltage amplification unit configured to amplify the voltage value
before applying the voltage value across the switching element to the A/D converter.
According to another feature of this embodiment, the reference voltage is changed
according to the diode structure and the temperature.
According to another feature of this embodiment, the temperature compensation
unit is disposed close to the switching element.
According to another feature of this embodiment, the switching element is a
MOSFET.
According to another feature of this embodiment, the temperature compensation
unit is formed on a same layer as a layer on which the MOSFET is formed on a substrate
on which the battery current measuring device is installed.
A battery current measuring method according to an embodiment of the present
invention includes: receiving a voltage across a switching element for controlling charging
and discharging of a battery; generating a reference voltage for compensating for a
resistance change according to a temperature change of the switching element; converting
the voltage of the switching element into a digital value using the generated reference
voltage; and calculating a current flowing through the switching element based on the
digital value.
A battery pack according to an embodiment of the present invention includes: a
battery capable of being charged and discharged; a switching element configured to control
4
charging and discharging of the battery: an A/D converter configured to convert a voltage
value across the switching element into a digital value; a temperature compensation unit
having a diode structure capable of compensating for a resistance change according to a
temperature change of the switching element; and a current calculation unit configured to
calculate a current flowing through the switching element based on the digital value of the
voltage value, and the A/D converter converts the voltage value of the switching element
into the digital value using a reference voltage inputted from the temperature compensation
unit.
A battery current measuring device according to an embodiment of the present
invention includes: a switching element configured to control charging and discharging of
a battery: an A/D converter configured to convert a voltage across the switching element
into a digital value; a temperature compensation unit including a diode structure that has a
temperature-resistance curve matching the switching element and is capable of
compensating for a resistance change according to a temperature change of the switching
element; a subtractor configured to receive the voltage across the switching element and an
output of the temperature compensation unit and output a constant voltage signal; and a
current calculation unit configured to calculate a current flowing through the switching
element based on the digital value of the voltage, and the A/D converter converts the
voltage signal inputted from the subtractor into the digital value using a fixed reference
voltage.
[ADVANTAGEOUS EFFECTS]
The present invention is to measure the current of the battery using a
semiconductor switch to turn on/off the battery without using a shunt resistor so that the
volume can be reduced and it is more efficient in terms of cost and production process.
[BRIEF DESCRIPTION OF THE DRAWINGS]
FIG. 1 is a view briefly comparing a conventional battery current measuring device
with a battery current measuring device according to an embodiment of the present
invention.
FIG. 2 is a block diagram of a battery current measuring device according to an
embodiment of the present invention.
5
FIG. 3 is a flowchart illustrating a battery current measuring method according to
an embodiment of the present invention.
FIG. 4 is a graph illustrating a change in resistance according to a temperature
change of a MOSFET.
FIG. 5 is a graph showing a change in current and voltage according to the
temperature of a diode.
FIG. 6 is an implementation example according to an embodiment of the present
invention.
FIG. 7 is an exemplary configuration diagram of a battery current measuring device
using a conventional shunt resistor.
FIG. 8 is a configuration diagram of a battery current measuring device according
to an embodiment of the present invention.
FIG. 9 is a configuration diagram of a battery current measuring device according
to another embodiment of the present invention.
FIG. 10 is a configuration diagram of a battery current measuring device according
to another embodiment of the present invention.
FIG. 11 is a flowchart illustrating a battery current measuring method according to
another embodiment of the present invention.
[MODE FOR CARRYING OUT THE INVENTION]
Hereinafter, some embodiments of the present invention will be described in detail
through exemplary drawings. It should be noted that, in assigning reference numerals to
components of each drawing, although the components are displayed on different drawings,
like reference numerals refer to like components. Additionally, in describing the inventive
concept, detailed descriptions of well-known configurations or functions will be omitted if
it is determined that they would obscure the subject matter of the inventive concept.
In order to solve the problem of the above-mentioned shunt resistor, the present
invention includes a method and device that can measure current using essential
components of the battery to measure the current of the battery without using a shunt
resistor.
In general, a switching element for controlling charging and discharging by turning
6
on/off a battery must be essentially present, and the switching element is composed of a
semiconductor device such as a MOSFET.
Since the resistance of semiconductor devices such as MOSFETs is generally
similar to shunt resistors, although there is the method of measuring the current through the
conventional method, semiconductors have not been used to measure practically accurate
currents because of the large magnitude of change in resistance with temperature.
However, the present invention includes the diode configuration as described below,
thereby making it possible to accurately measure the current of the battery by
supplementing the difficulty of accurate current measurement according to the resistance
change of the MOSFET with temperature. Hereinafter, the configuration of the present
invention will be described in more detail.
Here, the type of battery is not particularly limited, and for example, the battery
may be composed of a lithium ion battery, a lithium polymer battery, a nickel cadmium
battery, a nickel hydrogen battery, a nickel zinc battery, and the like.
In addition, a plurality of battery cells are formed of a battery module connected in
series and/or parallel, and at least one battery module is combined with a Battery
Management System (BMS) to form a battery pack.
The BMS estimates the state of the battery and manages the battery using the
estimated state information.
Hereinafter, the battery cell or battery module will be referred to simply as a battery.
FIG. 1 is a view briefly comparing a conventional battery current measuring device
with a battery current measuring device according to an embodiment of the present
invention.
In FIG. 1, the view on the left side is a simplified diagram of a battery current
measuring device for measuring current of a battery using a conventional shunt resistor.
In order to measure the battery current, a shunt resistor is connected in series on
one side of the battery, and the BMS calculates the battery current by measuring the
voltage across the connected shunt resistor. Hereinafter, the battery current measuring
method through the shunt resistor will be described in more detail.
A shunt resistor is connected in series on one side of the battery and the voltage
7
across the shunt resistor is measured by a voltage measurement unit. The voltage across the
shunt resistor is amplified by the voltage amplification unit because of its small size.
The voltage amplified by the voltage amplification unit is converted to a digital
value through an analog to digital (A/D) converter. In this case, the reference voltage of the
A/D converter may be a fixed value, for example, 5 V.
The digital signal converted by the A/D converter is transmitted to the MCU. In the
MCU receiving the digital signal, the current of the battery is calculated using the received
digital signal.
Here, the voltage measurement unit, the voltage amplification unit, the A/D
converter, and the MCU are included in the Battery Management System (BMS).
In addition to the shunt resistor, a switching element for controlling charging and
discharging of the battery is located on the current path between the battery and the output
terminal. The switching element is generally a semiconductor device, preferably a
MOSFET. The switching element receives the control signal from the BMS to perform
charging and discharging of the battery.
In FIG. 1, the view on the right side is a simplified diagram of a battery current
measuring device according to an embodiment of the present invention.
The battery current measuring device according to an embodiment of the present
invention does not include a shunt resistor unlike a conventional battery current measuring
device.
However, a battery current is calculated by using a switching element, for example,
a MOSFET, for controlling charging and discharging of the battery.
That is, in embodiments of the present invention, the voltage across the MOSFET
is measured by the voltage measurement unit. However, MOSFETs are semiconductor
devices, and the resistance changes greatly with the change in temperature. The MOSFET
is directly connected to the battery because it performs charging/discharging control of the
battery, and because of the heat generated during battery charging/discharging, MOSFETs
are also affected by battery heat. Therefore, it is difficult to accurately measure the voltage
of the MOSFET as the resistance changes due to the heat of the MOSFET.
Therefore, the present invention includes a separate temperature compensation unit
8
to compensate for the resistance change caused by the heat of the MOSFET. This will be
described later.
The voltage measured across the MOSFET is amplified by the voltage
amplification unit. The amplified signal is converted into a digital signal by the A/D
converter. That is, the A/D converter converts the voltage across the switching element into
a digital value.
However, as described above, in order to compensate for the resistance change
caused by the temperature change of the MOSFET, the reference voltage of the A/D
converter is changed. In order to change the reference voltage of the A/D converter, a diode
structure is connected to the A/D converter. The diode structure may be composed of a
single or a plurality of diodes.
In addition, since the resistance may vary depending on the type and number of
MOSFET devices and their connection configurations, the diode connected to the A/D
converter is selected to have the same voltage drop characteristic as the MOSFET, or a
plurality of diodes are connected in series and in parallel to allow the temperature curve to
be the same as that of the MOSFET. That is, the plurality of diodes have a temperatureresistance
curve that matches the temperature-resistance curve of the MOSFET which is
the switching element. Here, as the temperature curve is more similar to that of the
MOSFET, the accuracy of the current measurement becomes higher.
For more accurate measurements with the same temperature curve as the MOSFET,
a plurality of diodes connected to the A/D converter are placed on the same copper plate as
the MOSFET and placed close to the MOSFET to create an environment with a
temperature that is identical to a temperature that affects the MOSFET.
The digital signal converted by the A/D converter is transmitted to the MCU which
is a current calculation unit. The MCU receiving the digital signal from the A/D converter
converts the digital signal to the current flowing through the switching element again. The
charge/discharge current of the battery can be calculated from the current flowing through
the switching element. Battery state information such as battery degeneration degree and
capacity is calculated/computed by using the battery charge/discharge current converted in
the MCU.
9
FIG. 2 is a block diagram of a battery current measuring device 200 according to an
embodiment of the present invention.
The battery current measuring device 200 includes a switching element 201, a
voltage measurement unit 202, a voltage amplification unit 204, an A/D converter 206, a
temperature compensation unit 208, and a current calculation unit 210.
The switching element 201 is formed in the charge/discharge path between the
battery and the output terminal of the battery. The switching element 201 is controlled to
be On/Off based on the control signal of the BMS, thereby supplying the power stored in
the battery to the outside or charging the battery with external power. In the embodiments
of the present invention, the switching element 201 may be, for example, a MOSFET, but
is not limited thereto and any switching element may be applied as long as the switching
element changes resistance depending on temperature.
The voltage measurement unit 202 measures the voltage across the switching
element 201. Here, the voltage measurement unit 202 is configured to measure the voltage
across the switching element 201 as an analog value, such as an analog front end. The
voltage measurement unit 202 transmits the measured voltage signal across the switching
element to the voltage amplification unit 204. The voltage across the switching element
201 may be amplified in the voltage amplification unit 204 without the voltage
measurement unit 202.
The voltage amplification unit 204 amplifies the voltage across the switching
element applied directly from the switching element 201 or through the voltage
measurement unit 202. The amplified voltage of the switching element 201 is transmitted
to the A/D converter 206.
The A/D converter 206 receives the amplified voltage signal of the switching
element 201. The A/D converter 206 converts the receive voltage signal of the switching
element 201 into a digital signal. That is, the A/D converter 206 converts the voltage across
the switching element into a digital value. The A/D converter 206 uses a reference voltage
that changes with temperature in converting the received voltage signal of the switching
element 201 into a digital signal.
Specifically, the switching element 201 has a large change in resistance value with
10
temperature. As the temperature of the switching element 201 is higher, the resistance
becomes greater. Therefore, the switching element 201 is difficult to measure the correct
voltage because the resistance is changed under the influence of the temperature change
according to the heat generation of the battery. In order to supplement the characteristics of
the switching element 201 and derive an accurate voltage value, the temperature
compensation unit 208 including a plurality of diodes is connected to a reference voltage
input terminal of the A/D converter.
The diode has a different voltage drop for a fixed current value as the temperature
changes. Therefore, by using the diode type, number and connection configuration having
a temperature-resistance curve similar to the resistance change curve with the temperature
change of the switching element 201, it changes the reference voltage value of the A/D
converter. As a result, it is possible to derive a more accurate voltage of the switching
element 201 which is not affected by temperature.
That is, according to the present invention, the reference voltage applied to the A/D
converter for measuring the voltage across the switching element 201 is a voltage that is
changed according to a temperature rather than a fixed voltage, for example, 5 V. Diodes,
which are semiconductor elements such as the switching element 201, have a forward
voltage drop with temperature. Thus, the reference voltage changed through this diode
compensates for the resistance change with temperature of the switching element 201.
At this time, in order to allow the diode to operate in the environment of the same
temperature as the switching element 201, the diode is disposed on the same copper plate
as the switching element 201 and is disposed close to the switching element 201.
As described above, the temperature compensation unit 208 is connected to the A/D
converter 206 to apply a reference voltage, and is configured to compensate for voltage
values, which change with resistance changes due to temperature changes in the switching
element 201. That is, the reference voltage is changed depending on the diode structure and
the temperature.
Specifically, the temperature compensation unit 208 includes a diode structure in
which a plurality of diodes are connected in series and in parallel. That is, the temperature
compensation unit 208 includes a diode structure capable of compensating for the
11
resistance change according to the temperature change of the switching element. One end
of the temperature compensation unit 208 is connected to the power supply voltage, and
the other end is connected to the A/D converter 206. That is, the diode structure is
connected in series between the power supply voltage and the A/D converter 206 so that
the reference voltage generated by the temperature compensation unit 208 is applied to the
A/D converter 206.
Since the diode is also a semiconductor device such as the switching element 201,
the resistance value changes with temperature like the switching element 201. In addition,
since the resistance varies depending on the type of the switching element 201, the type
and number of diodes included in the diode structure and the connection configuration are
adjusted to make the temperature-resistance curve the same. At this time, the accuracy of
the measured voltage is determined by how similar the temperature-resistance curve of the
switching element 201 and the temperature-resistance curve of the diode structure are.
Meanwhile, the diode structure may include a single diode, and in this case, the single
diode is selected to have the same voltage drop characteristic to compensate for the voltage
change with the temperature of the entire switching element 201. Furthermore, the
temperature compensation unit is disposed close to the switching element.
The A/D converter 206 receives the amplified measurement voltage of the
switching element 201 received from the voltage amplification unit 204, converts the
amplified voltage signal of the switching element 201 into a digital signal using the
reference voltage determined by the temperature compensation unit 208, and transmits it to
the current calculation unit 210.
The current calculation unit 210 calculates the battery current using the digital
signal received from the A/D converter 206, and calculates and computes battery
information, such as the degeneration degree of the battery and the battery capacity, using
the calculated battery current.
FIG. 3 is a flowchart illustrating a battery current measuring method according to
an embodiment of the present invention.
A switching element that controls the charging and discharging of the battery, for
example, a MOSFET, is connected to the battery. MOSFETs are semiconductor devices
12
and have a wide range of resistance changes with temperature. The voltage measurement
unit 202 measures the voltage across the switching element 201 (S300). The voltage
measurement unit 202 transmits the measured voltage signal across the switching element
to the voltage amplification unit 204. The voltage across the switching element 201 may be
amplified by the voltage amplification unit 204 immediately without the voltage
measurement unit 202.
Here, in relation to the measured voltage, in order to compensate for the resistance
change due to the temperature change of the switching element, the reference voltage of
the A/D converter is changed. In order to change the reference voltage of the A/D converter,
a diode structure is connected to the A/D converter. The diode structure may be composed
of a single or a plurality of diodes. This will be described later.
The voltage signal of the switching element 201 transmitted to the voltage
amplification unit 204 is amplified by the voltage amplification unit (S302). The amplified
voltage signal of the switching element 201 is transmitted to the A/D converter 206 (S304).
The A/D converter 206 receiving the amplified voltage signal of the switching
element 201 receives a reference voltage from the temperature compensation unit 208
(S306). That is, the reference voltage is set to compensate for the resistance change
according to the temperature change of the switching element by the temperature
compensation unit.
Specifically, the temperature compensation unit 208 includes a single or a plurality
of diodes. The diode has a different voltage drop for a fixed current value as the
temperature changes. Therefore, by using a diode having a temperature-resistance curve
similar to the temperature-resistance curve with the change of temperature of the switching
element 201 to change the reference voltage value of the A/D converter, the voltage of the
switching element 201 can be derived to a more accurate voltage value that is not affected
by temperature.
The voltage drop of the input voltage is made according to the temperature by the
diode included in the temperature compensation unit 208 so that the reference voltage
transmitted to the A/D converter 206 may be changed according to the temperature.
That is, according to the present invention, the reference voltage applied to the A/D
13
converter for measuring the voltage across the switching element 201 is a reference voltage
that is changed according to a temperature rather than a fixed voltage, for example, 5 V.
Diodes, which are semiconductors such as the switching element 201, have a forward
voltage drop with temperature. Thus, the reference voltage changed through this diode
compensates for the resistance change with temperature of the switching element 201.
At this time, in order to allow the diode to operate in the environment of the same
temperature as the switching element 201, the diode is disposed on the same copper plate
as the switching element 201 and is disposed close to the switching element 201.
As described above, the temperature compensation unit 208 is connected to the A/D
converter 206 to apply a reference voltage, and is configured to compensate for voltage
values, which change with resistance changes due to temperature changes in the switching
element 201.
The A/D converter 206 converts the measured voltage signal of the switching
element 201 into a digital signal by using the applied reference voltage (S308). That is, the
amplified voltage is converted into a digital value by using the reference voltage set by the
A/D converter.
The A/D converter 206 transmits the converted digital signal to the current
calculation unit 110 (S310).
The current calculation unit 110 receiving the digital signal calculates the current of
the switching element 201 using the received digital signal to estimate the battery current,
and obtains battery information using the estimated battery current.
FIG. 4 is a graph illustrating a change in resistance according to a temperature
change of a MOSFET.
As the MOSFET has a resistance change with temperature as in the graph shown in
FIG. 4, due to the changing resistance of the MOSFET, the current cannot be calculated
accurately through V=I*R.
That is, even if the voltage across the MOSFET is measured equally, the calculated
current will change with temperature because the resistance of the MOSFET changes with
temperature. The MOSFET is directly connected to the battery because it controls the
charging/discharging of the battery, and the switching element 201 is also affected by the
14
heat generated during a battery charging/discharging process. Therefore, it is difficult to
accurately measure the voltage of the MOSFET as the resistance changes due to the heat of
the MOSFET.
For example, even if the measured voltage across the MOSFET is a V, since the
resistance is 0.6 mΩ when the temperature of the MOSFET is 60℃, the current will be
a/(0.6*10-3)A, and when the temperature of MOSFET is 140℃, since the resistance is 0.8
mΩ , the current will be a/(0.6*10-3)A. That is, since the resistance changes according to
the temperature of the MOSFET, even if the measured voltage is the same, the resistance
may vary depending on the temperature and thus the calculated current may be different.
In order to compensate for this, the present invention includes a separate
temperature compensation unit to compensate for the voltage change according to the
resistance change due to the heat of the MOSFET.
FIG. 5 is a graph showing a change in current and voltage according to the
temperature of a diode.
The forward voltage drop of the diode varies according to the temperature when the
same current flows. Referring to the graph of FIG. 5, for example, if the current flows at
200 mA, a voltage drop of 100 mV is made at 150°C, a voltage drop of about 140 mV is
made at 125°C, a voltage drop of about 190 mV is made at 100°C, and a voltage drop of
about 230 mV is made at 75 °C.
Thus, for example, if the input voltage of the diode structure is 5 V, by forward
voltage drop of the diode, the reference voltage inputted to the A/D converter 206 is 4.9 V
at 150°C, is about 4.86 V at 125°C, is about 4.81 V at 100°C, and is about 4.77 V at 75°C.
By using the characteristics of such a diode, it can be implemented as a single diode
using a diode having a temperature curve most similar to that of the MOSFET, and a
plurality of diodes can also be connected in series to compensate for the changed voltage
values at the MOSFETs.
FIG. 6 is an implementation example according to an embodiment of the present
invention.
As shown in FIG. 6, the diode is disposed close to the MOSFET. In addition, the
layer directly below the MOSFET layer, on which the MOSFET is disposed, extends under
15
the diode so that the MOSFET and the diode are located on the same layer.
This is to reduce the temperature deviation by allowing the MOSFET and the diode
to be disposed on the same layer.
In addition, since the resistance varies depending on the MOSFET device type and
the number of parallels, the diode is also selected as a device with the same voltage drop
characteristics as the MOSFET, or connected in series to have the same temperatureresistance
curve as the MOSFET. Accuracy is determined by how similar this temperatureresistance
curve is.
FIG. 7 is an exemplary configuration diagram of a battery current measuring device
using a conventional shunt resistor.
A shunt resistor is connected in series between the battery and the output terminal,
and the voltage across the shunt resistor is small so that it is amplified by the voltage
amplification unit.
The voltage amplified in the voltage amplification unit, for example, an Op amp, is
converted to a digital value through an analog to digital (A/D) converter. In this case, the
reference voltage may be a fixed value, for example, 5 V.
The digital signal converted by the A/D converter is transmitted to the MCU. In the
MCU receiving the digital signal, it is converted to a current value again using the received
digital signal.
FIG. 8 is a configuration diagram of a battery current measuring device according
to an embodiment of the present invention.
Battery current is measured using a switching element that controls charging and
discharging of the battery, for example, a MOSFET. The MOSFET is a semiconductor
device, and it is difficult to measure the accurate voltage due to a large change in resistance
with the change of temperature.
After amplifying the voltage of the MOSFET through the OP amp, the amplified
signal is converted into a digital signal in the A/D converter.
However, as described above, the MOSFET is difficult to accurately measure the
voltage due to the large width of the resistance change with the temperature change.
Therefore, in order to compensate for this, the reference voltage of the A/D converter is
16
changed. In order to change the reference voltage of the A/D converter, a diode structure is
connected to the A/D converter. The diode structure may be composed of a single or a
plurality of diodes.
In addition, since the resistance may vary depending on the type and number of
MOSFET devices and their connection configurations, the diode connected to the A/D
converter is selected to have the same voltage drop characteristic as the MOSFET, or a
plurality of diodes are connected in series and in parallel to allow the temperatureresistance
curve to be same as that of the MOSFET. Here, as the temperature-resistance
curve is more similar to that of the MOSFET, the accuracy of the current measurement
becomes higher.
The digital signal converted by the A/D converter is transmitted to the MCU. The
MCU receiving the digital signal from the A/D converter calculates the digital signal as a
current again. Battery state information such as battery degeneration degree and capacity is
calculated/computed by using the battery charge/discharge current converted in the MCU.
FIG. 9 is a configuration diagram of a battery current measuring device according
to another embodiment of the present invention.
The configuration of FIG. 9 is the same as that of FIG. 2 except for the
configuration in which a subtractor 906 is added and the configuration in which a
temperature compensation unit 908 is connected to the subtractor. Therefore, the
description will be mainly focused on the configuration different from that of FIG. 2.
The voltage across the measured switching element 201 is amplified, and the
amplified voltage signal is inputted to the first input terminal of the subtractor 906. In
addition, the output voltage signal of the temperature compensation unit 908 is inputted to
the second input terminal of the subtractor 906.
Here, the temperature compensation unit 908 is configured to compensate for the
voltage value changed according to the resistance change caused by the temperature
change of the switching element 201, and has the same temperature-resistance curve as the
switching element 201. Thus, like the output voltage signal of the voltage amplification
unit 904 that changes with the temperature of the switching element 201, the output
voltage signal of the temperature compensation unit 908 also changes with the temperature.
17
Therefore, as a result, the difference between the voltage signals inputted to the first input
terminal and the second input terminal of the subtractor 906 always remains constant.
Accordingly, the output voltage signal of the subtractor 906 also remains constant
regardless of the voltage change of the switching element 201 with temperature.
The output voltage signal of the subtractor 906 is inputted to the A/D converter 910,
and the A/D converter 910 converts the output voltage signal received from the subtractor
906 into a digital signal using the fixed reference voltage and transmits the converted
digital signal to the current calculation unit 912.
FIG. 10 is a configuration diagram of a battery current measuring device according
to another embodiment of the present invention.
The configuration of FIG. 10 is the same as that of FIG. 8 except for the
configuration in which a subtractor is added and the configuration in which a temperature
compensation unit is connected to the subtractor. Therefore, the description will be mainly
focused on the configuration different from that of FIG. 8.
After amplifying the measured MOSFET voltage through the OP amp, the
amplified signal is inputted to the subtractor. However, since the MOSFET has a large
change in resistance due to temperature change, in order to compensate for this, the other
input terminal of the subtractor is connected with a diode structure which is a temperature
compensation unit.
The diode structure connected to the subtractor includes a single or a plurality of
diodes, and the diode structure has the same temperature-resistance curve as the MOSFET.
Therefore, the difference between the output voltage signal of the diode structure inputted
to the subtractor and the voltage across the MOSFET always remains constant, so that the
output of the subtractor also remains constant.
The voltage signal outputted from the subtractor is inputted to the A/D converter,
and the A/D converter converts the voltage signal outputted from the subtractor into a
digital signal using a fixed reference voltage.
FIG. 11 is a flowchart illustrating a battery current measuring method according to
another embodiment of the present invention.
The voltage measurement unit 902 measures the voltage across the switching
18
element 201 (S1100).
The measured voltage signal at both ends of the switching element 201 is amplified
by the voltage amplification unit 904 (S1110). Here, the voltage across the switching
element may be amplified by the voltage amplification unit 904 immediately without the
voltage measurement unit 902.
The voltage signal at both ends of the switching element 201 amplified by the
voltage amplification unit 904 is received at the first input terminal of the subtractor
(S1120).
Meanwhile, the output voltage signal of the temperature compensation unit 908
connected to the other input terminal of the subtractor 906 is inputted to the second input
terminal of the subtractor 906 (S1130).
As described above, the temperature compensation unit 908 is configured to
compensate for the voltage value changed according to the resistance change caused by the
temperature change of the switching element 201, and has the same temperature-resistance
curve as the switching element 201. Thus, like the output voltage signal of the voltage
amplification unit 904 that changes with the temperature of the switching element 201, the
output voltage signal of the temperature compensation unit 908 also changes with the
temperature.
Therefore, the difference between the both signals inputted to the subtractor always
remains constant. Accordingly, even though the voltage of the switching element 201
changes with temperature, the output voltage signal of the subtractor 906 also remains
constant.
The output voltage signal of the subtractor 906 is inputted to the A/D converter 910
(S1140).
The A/D converter 910 converts the inputted output voltage signal of the subtractor
906 into a digital signal using a fixed reference voltage, for example, 5 V (S1150), and
transmits the digital signal to the MCU (S1160).
Although the present invention has been described above by limited embodiments
and drawings, the present invention is not limited thereto, and it will be apparent to those
skilled in the art that the present invention may be implemented in various ways within the
19
equivalent scope of the technical spirit of the present invention and the claims to be
described below.
20
We Claim:
1. A battery current measuring device comprising:
a switching element configured to control charging and discharging of a battery:
an A/D converter configured to convert a voltage value across the switching
element into a digital value;
a temperature compensation unit having a diode structure capable of compensating
for a resistance change according to a change of temperature of the switching element; and
a current calculation unit configured to calculate a current flowing through the
switching element based on the digital value of the voltage value,
wherein the A/D converter converts the voltage value of the switching element into
the digital value using a reference voltage inputted from the temperature compensation unit.
2. The battery current measuring device of claim 1, wherein the diode
structure of the temperature compensation unit comprises a plurality of diodes,
wherein a number and connection configuration of the plurality of diodes are
determined so as to have a temperature-resistance curve matching a temperature-resistance
curve of the switching element.
3. The battery current measuring device of claim 2, further comprising a
voltage amplification unit configured to amplify the voltage value before applying the
voltage value across the switching element to the A/D converter.
4. The battery current measuring device of claim 2, wherein the reference
voltage is changed according to the diode structure and the temperature.
5. The battery current measuring device of claim 1, wherein the temperature
compensation unit is disposed close to the switching element.
6. The battery current measuring device of claim 1, wherein the switching
element is a MOSFET.
21
7. The battery current measuring device of claim 6, wherein the temperature
compensation unit is formed on a same layer as a layer on which the MOSFET is formed
on a substrate on which the battery current measuring device is installed.
8. A battery current measuring method comprising:
receiving a voltage across a switching element for controlling charging and
discharging of a battery;
generating a reference voltage for compensating for a resistance change according
to a temperature change of the switching element;
converting the voltage of the switching element into a digital value using the
generated reference voltage; and
calculating a current flowing through the switching element based on the digital
value.
9. The battery current measuring method of claim 8, wherein the reference
voltage is generated by a diode structure including a plurality of diodes,
wherein a number and connection configuration of the plurality of diodes are
determined so as to have a temperature-resistance curve matching a temperature-resistance
curve of the switching element.
10. The battery current measuring method of claim 8, wherein the diode
structure is disposed close to the switching element.
11. A battery pack comprising:
a battery capable of being charged and discharged;
a switching element configured to control charging and discharging of the battery:
an A/D converter configured to convert a voltage value across the switching
element into a digital value;
a temperature compensation unit having a diode structure capable of compensating
22
for a resistance change according to a temperature change of the switching element; and
a current calculation unit configured to calculate a current flowing through the
switching element based on the digital value of the voltage value,
wherein the A/D converter converts the voltage value of the switching element into
the digital value using a reference voltage inputted from the temperature compensation unit.
12. A battery current measuring device comprising:
a switching element configured to control charging and discharging of a battery:
an A/D converter configured to convert a voltage across the switching element into
a digital value;
a temperature compensation unit including a diode structure that has a temperatureresistance
curve matching the switching element and is capable of compensating for a
resistance change according to a temperature change of the switching element;
a subtractor configured to receive the voltage across the switching element and an
output of the temperature compensation unit and output a constant voltage signal; and
a current calculation unit configured to calculate a current flowing through the
switching element based on the digital value of the voltage,
wherein the A/D converter converts the voltage signal inputted from the subtractor
into the digital value using a fixed reference voltage.