Patent Description:
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.

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.

<CIT> discloses a power supply control apparatus for a motor vehicle and it has a drive controller that regulates supply of control signal based on detected current in a FET after adjustment process which is based on the FET temperature.

<CIT> relates to an apparatus and a method for current detection.

<CIT> relates to a semiconductor device, an in-vehicle valve system and a solenoid driver that control a solenoid valve mounted on a vehicle such as a car.

<CIT> relates to a motor-control system <NUM>.

<CIT> relates to a current detector and a current limiter.

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.

According to the invention, battery current measuring devices, battery current measuring methods and battery packs as defined by the appended claims are proposed.

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.

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 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> 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>, 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 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, <NUM> V.

The digital signal converted by the A/D converter is transmitted to the microcontroller unit (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>, 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 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 temperature-resistance 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.

<FIG> is a block diagram of a battery current measuring device <NUM> according to an embodiment of the present invention.

The battery current measuring device <NUM> includes a switching element <NUM>, a voltage measurement unit <NUM>, a voltage amplification unit <NUM>, an A/D converter <NUM>, a temperature compensation unit <NUM>, and a current calculation unit <NUM>.

The switching element <NUM> is formed in the charge/discharge path between the battery and the output terminal of the battery. The switching element <NUM> 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 <NUM> 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 <NUM> measures the voltage across the switching element <NUM>. Here, the voltage measurement unit <NUM> is configured to measure the voltage across the switching element <NUM> as an analog value, such as an analog front end. The voltage measurement unit <NUM> transmits the measured voltage signal across the switching element to the voltage amplification unit <NUM>. The voltage across the switching element <NUM> may be amplified in the voltage amplification unit <NUM> without the voltage measurement unit <NUM>.

The voltage amplification unit <NUM> amplifies the voltage across the switching element applied directly from the switching element <NUM> or through the voltage measurement unit <NUM>. The amplified voltage of the switching element <NUM> is transmitted to the A/D converter <NUM>.

The A/D converter <NUM> receives the amplified voltage signal of the switching element <NUM>. The A/D converter <NUM> converts the receive voltage signal of the switching element <NUM> into a digital signal. That is, the A/D converter <NUM> converts the voltage across the switching element into a digital value. The A/D converter <NUM> uses a reference voltage that changes with temperature in converting the received voltage signal of the switching element <NUM> into a digital signal.

Specifically, the switching element <NUM> has a large change in resistance value with temperature. As the temperature of the switching element <NUM> is higher, the resistance becomes greater. Therefore, the switching element <NUM> 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 <NUM> and derive an accurate voltage value, the temperature compensation unit <NUM> 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 <NUM>, 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 <NUM> 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 <NUM> is a voltage that is changed according to a temperature rather than a fixed voltage, for example, <NUM> V. Diodes, which are semiconductor elements such as the switching element <NUM>, 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 <NUM>.

At this time, in order to allow the diode to operate in the environment of the same temperature as the switching element <NUM>, the diode is disposed on the same copper plate as the switching element <NUM> and is disposed close to the switching element <NUM>.

As described above, the temperature compensation unit <NUM> is connected to the A/D converter <NUM> 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 <NUM>. That is, the reference voltage is changed depending on the diode structure and the temperature.

Specifically, the temperature compensation unit <NUM> includes a diode structure in which a plurality of diodes are connected in series and in parallel. That is, the temperature compensation unit <NUM> includes a diode structure capable of compensating for the resistance change according to the temperature change of the switching element. One end of the temperature compensation unit <NUM> is connected to the power supply voltage, and the other end is connected to the A/D converter <NUM>. That is, the diode structure is connected in series between the power supply voltage and the A/D converter <NUM> so that the reference voltage generated by the temperature compensation unit <NUM> is applied to the A/D converter <NUM>.

Since the diode is also a semiconductor device such as the switching element <NUM>, the resistance value changes with temperature like the switching element <NUM>. In addition, since the resistance varies depending on the type of the switching element <NUM>, 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 <NUM> 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 <NUM>. Furthermore, the temperature compensation unit is disposed close to the switching element.

The A/D converter <NUM> receives the amplified measurement voltage of the switching element <NUM> received from the voltage amplification unit <NUM>, converts the amplified voltage signal of the switching element <NUM> into a digital signal using the reference voltage determined by the temperature compensation unit <NUM>, and transmits it to the current calculation unit <NUM>.

The current calculation unit <NUM> calculates the battery current using the digital signal received from the A/D converter <NUM>, and calculates and computes battery information, such as the degeneration degree of the battery and the battery capacity, using the calculated battery current.

<FIG> 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 and have a wide range of resistance changes with temperature. The voltage measurement unit <NUM> measures the voltage across the switching element <NUM> (S300). The voltage measurement unit <NUM> transmits the measured voltage signal across the switching element to the voltage amplification unit <NUM>. The voltage across the switching element <NUM> may be amplified by the voltage amplification unit <NUM> immediately without the voltage measurement unit <NUM>.

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 <NUM> transmitted to the voltage amplification unit <NUM> is amplified by the voltage amplification unit (S302). The amplified voltage signal of the switching element <NUM> is transmitted to the A/D converter <NUM> (S304).

The A/D converter <NUM> receiving the amplified voltage signal of the switching element <NUM> receives a reference voltage from the temperature compensation unit <NUM> (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 <NUM> 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 <NUM> to change the reference voltage value of the A/D converter, the voltage of the switching element <NUM> 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 <NUM> so that the reference voltage transmitted to the A/D converter <NUM> may be changed according to the 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 <NUM> is a reference voltage that is changed according to a temperature rather than a fixed voltage, for example, <NUM> V. Diodes, which are semiconductors such as the switching element <NUM>, 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 <NUM>.

As described above, the temperature compensation unit <NUM> is connected to the A/D converter <NUM> 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 <NUM>.

The A/D converter <NUM> converts the measured voltage signal of the switching element <NUM> 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 <NUM> transmits the converted digital signal to the current calculation unit <NUM> (S310).

The current calculation unit <NUM> receiving the digital signal calculates the current of the switching element <NUM> using the received digital signal to estimate the battery current, and obtains battery information using the estimated battery current.

<FIG> 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>, 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 <NUM> is also affected by the 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 <NUM> mΩ when the temperature of the MOSFET is <NUM>, the current will be a/(<NUM>*<NUM>-<NUM>)A, and when the temperature of MOSFET is <NUM>, since the resistance is <NUM> mΩ , the current will be a/(<NUM>*<NUM>-<NUM>)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> 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>, for example, if the current flows at <NUM> mA, a voltage drop of <NUM> mV is made at <NUM>, a voltage drop of about <NUM> mV is made at <NUM>, a voltage drop of about <NUM> mV is made at <NUM>, and a voltage drop of about <NUM> mV is made at <NUM>.

Thus, for example, if the input voltage of the diode structure is <NUM> V, by forward voltage drop of the diode, the reference voltage inputted to the A/D converter <NUM> is <NUM> V at <NUM>, is about <NUM> V at <NUM>, is about <NUM> V at <NUM>, and is about <NUM> V at <NUM>.

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> is an implementation example according to an embodiment of the present invention.

As shown in <FIG>, 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 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 temperature-resistance curve as the MOSFET. Accuracy is determined by how similar this temperature-resistance curve is.

<FIG> 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 operational amplifier (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, <NUM> 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> 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 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-resistance 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> is a configuration diagram of a battery current measuring device according to another embodiment of the present invention.

The configuration of <FIG> is the same as that of <FIG> except for the configuration in which a subtractor <NUM> is added and the configuration in which a temperature compensation unit <NUM> is connected to the subtractor. Therefore, the description will be mainly focused on the configuration different from that of <FIG>.

The voltage across the measured switching element <NUM> is amplified, and the amplified voltage signal is inputted to the first input terminal of the subtractor <NUM>. In addition, the output voltage signal of the temperature compensation unit <NUM> is inputted to the second input terminal of the subtractor <NUM>.

Here, the temperature compensation unit <NUM> is configured to compensate for the voltage value changed according to the resistance change caused by the temperature change of the switching element <NUM>, and has the same temperature-resistance curve as the switching element <NUM>. Thus, like the output voltage signal of the voltage amplification unit <NUM> that changes with the temperature of the switching element <NUM>, the output voltage signal of the temperature compensation unit <NUM> also changes with the temperature. Therefore, as a result, the difference between the voltage signals inputted to the first input terminal and the second input terminal of the subtractor <NUM> always remains constant. Accordingly, the output voltage signal of the subtractor <NUM> also remains constant regardless of the voltage change of the switching element <NUM> with temperature.

The output voltage signal of the subtractor <NUM> is inputted to the A/D converter <NUM>, and the A/D converter <NUM> converts the output voltage signal received from the subtractor <NUM> into a digital signal using the fixed reference voltage and transmits the converted digital signal to the current calculation unit <NUM>.

The configuration of <FIG> is the same as that of <FIG> 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>.

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> is a flowchart illustrating a battery current measuring method according to another embodiment of the present invention.

The voltage measurement unit <NUM> measures the voltage across the switching element <NUM> (S <NUM>).

The measured voltage signal at both ends of the switching element <NUM> is amplified by the voltage amplification unit <NUM> (S1110). Here, the voltage across the switching element may be amplified by the voltage amplification unit <NUM> immediately without the voltage measurement unit <NUM>.

The voltage signal at both ends of the switching element <NUM> amplified by the voltage amplification unit <NUM> is received at the first input terminal of the subtractor (<NUM>).

Meanwhile, the output voltage signal of the temperature compensation unit <NUM> connected to the other input terminal of the subtractor <NUM> is inputted to the second input terminal of the subtractor <NUM> (S1130).

As described above, the temperature compensation unit <NUM> is configured to compensate for the voltage value changed according to the resistance change caused by the temperature change of the switching element <NUM>, and has the same temperature-resistance curve as the switching element <NUM>. Thus, like the output voltage signal of the voltage amplification unit <NUM> that changes with the temperature of the switching element <NUM>, the output voltage signal of the temperature compensation unit <NUM> 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 <NUM> changes with temperature, the output voltage signal of the subtractor <NUM> also remains constant.

The output voltage signal of the subtractor <NUM> is inputted to the A/D converter <NUM> (S1140).

The A/D converter <NUM> converts the inputted output voltage signal of the subtractor <NUM> into a digital signal using a fixed reference voltage, for example, <NUM> V (S <NUM>), and transmits the digital signal to the MCU (S1160).

Claim 1:
A battery current measuring device comprising:
a switch (<NUM>) configured to control charging and discharging of a battery:
an A/D converter (<NUM>) configured to convert a voltage value across the switch into a digital value;
a temperature compensation unit (<NUM>) having a diode structure capable of compensating for a resistance change according to a change of temperature of the switch; and
a controller (<NUM>) configured to calculate a current flowing through the switch based on the digital value of the voltage value,
wherein the A/D converter is configured to convert the voltage value across the switch into the digital value using a reference voltage inputted from the temperature compensation unit, wherein the switch (<NUM>) is a MOSFET,
wherein the battery current measuring device is installed on a substrate, and wherein the temperature compensation unit (<NUM>) and the MOSFET (<NUM>) are formed on a same layer of the substrate.