KR20110054681A - Battery cell voltage monitoring circuit - Google Patents

Abstract

PURPOSE: A battery cell voltage monitoring circuit is provided to protect a battery by maintain the balance between battery cells through monitoring the voltage of the battery cell. CONSTITUTION: A battery cell voltage monitoring circuit includes a battery pack(110), analog multiplexers(120, 122), a differential amplifier(130), and a MICOM(140). The battery cells of the battery pack are connected in series. The analog multiplexer is connected to a detection line leaded from the detection point of the battery cell through a photocoupler. The differential amplifier outputs the detection voltage.

Description

Battery cell voltage monitoring circuit

The present invention relates to a circuit for monitoring the voltage of a battery cell, and more particularly, to monitor the voltage of each battery cell connected in series to maintain balancing between battery cells and to protect in case of emergency. The circuit operates to protect the battery, minimizes battery power consumption when detecting the voltage of the battery cells to extend the battery life, and is isolated with a photo coupler between the high potential battery pack voltage and the supervisory circuit. The present invention relates to a battery cell voltage monitoring circuit providing circuit safety.

Background Art Conventionally, in an electric vehicle such as a hybrid car, a battery pack formed by connecting a plurality of secondary batteries in series as a power source for a driving motor is mounted. In such a battery pack, since it is usually necessary to generate a high voltage of 200 to 300 V, for example, as a lithium-based secondary battery having an output of about 3.6 V, 60 to 80 cells are connected in series. As a NiMH-based secondary battery having an output of about 1.2 V per cell, about 200 cells are connected in series to form a battery pack.

In such a battery pack, it is preferable that the state of charge of all the secondary batteries is equal. For example, when one secondary battery has a charge rate of 70% and the other secondary battery has a charge rate of 50%, the amount of electricity that can be charged is 30% since the secondary battery having a charge rate of 70% is fully charged. If the battery is charged more than%, the secondary battery, which had a charge rate of 70%, will have a charge rate of more than 100%, and its life will be significantly shortened. As a result, the lifespan as a battery pack is also shortened.

However, lithium ion batteries and lithium polymer batteries used in electric vehicles, hybrid cars, or battery packs for storing electricity have excellent charge and discharge characteristics, and are lighter and smaller in volume than other types of batteries. It offers many advantages, but when it is used in series, the performance of one cell becomes poor, so it is impossible to charge and discharge, and there is a risk of fire and explosion. There is a disadvantage that can not be used.

Accordingly, by reading the voltage of each of the battery unit cells (Reading) to maintain the cell balancing (Cell Balancing) during the use of the battery pack, and protects the circuit in case of emergency in order to prevent changes in the characteristics of the unit cell and accidents It uses BMS (Battery Management System) to prevent battery damage and prolong battery life.

For this function, the BMS must detect the correct cell voltage and consume less battery power. Therefore, the most important of the BMS functions is the accurate cell voltage reading function, and it is necessary to reduce the voltage loss of the battery pack when performing this function.

However, when the battery is not used for a long time, the battery is often discharged due to the BMS.

SUMMARY OF THE INVENTION An object of the present invention for solving the above-described problems is to monitor the voltage of each battery cell to maintain balance between battery cells, and in case of emergency protection circuitry to protect the battery and to extend the life of the battery cells. The present invention provides a battery cell voltage monitoring circuit which minimizes battery power consumption when detecting a voltage, and insulates a photocoupler between a battery pack voltage of a high potential and a monitoring circuit so that the circuit operates stably.

Battery cell voltage monitoring circuit according to the present invention for achieving the above object, the battery pack is connected to one or more battery cells in series; An analog multiplexer having respective detection lines drawn out from each detection point for each of the battery cells, respectively, through respective photo couplers; A differential amplifier for differentially amplifying the value output from the analog multiplexer and outputting a detection voltage; And a microcomputer that calculates the detected voltage output from the differential amplifier as data.

The apparatus may further include a cell monitor switch configured to turn on or off the operation of all photo couplers connected to the respective battery cells under the control of the microcomputer.

In addition, the cell monitor switch may use a PNP transistor or an NPN transistor.

In addition, as the cell monitor switch is turned on, power is applied to all the photo couplers, and each of the photo couplers is turned on, so that each battery power is supplied from the detection point to each of the battery cells through the respective detection lines. It is delivered to the photo coupler of, and is transmitted from each photo coupler to each of the analog multiplexer through the respective detection line, multiplexed in the analog multiplexer, each detection voltage is transmitted to the microcomputer through the differential amplifier.

In addition, a voltage divider is connected to both ends of each photo coupler connected to each of the battery cells.

In addition, the microcomputer has an ADC function for converting the detected voltage in the analog form into data in the digital form.

The microcomputer performs a correction operation by software on the data of the detected voltage.

According to the present invention, a battery circuit voltage detection circuit having a simple circuit and easy configuration and high durability can be implemented.

In addition, you can easily change the desired number of battery cells.

In addition, the circuitry is isolated, ensuring stability even at high voltages in the battery pack.

In addition, since the battery cell voltage is sensed only when the cell monitor switch is turned on using the cell monitor switch and the photo coupler, the battery pack power consumption can be greatly reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating a battery cell voltage monitoring circuit according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the battery cell voltage monitoring circuit 100 according to the present invention includes a battery pack 110 in which one or more battery cells of a battery unit are connected in series; Analog multiplexers 120 and 122 connected to respective detection lines drawn from respective detection points for each battery cell through respective photo couplers PC; A differential amplifier 130 for differentially amplifying the values output from the analog multiplexers 120 and 122 and outputting a detected voltage; And a micom 140 that calculates the detected voltage output from the differential amplifier 130 as data.

In addition, a cell monitor switch 150 for turning on or turning off all photo couplers PC connected to each of the battery cells under the control of the microcomputer 140. More).

In this case, the cell monitor switch 150 may use a PNP transistor or an NPN transistor.

In addition, voltage dividers Ra and Rb are connected to both ends of each photo coupler PC connected to each of the battery cells.

In addition, the microcomputer 140 has an analog to digital converter (ADC) function for converting an analog voltage into a digital data.

Meanwhile, although FIG. 1 illustrates one battery pack in which 14 cells are connected in series in one embodiment, the number of cell connections may be changed according to the purpose of use.

In addition, although the battery and the sensing unit are insulated with a photo coupler for safety and noise prevention, when the insulation is not required, it can be replaced with a transistor.

In addition, distribution resistors Ra and Rb for voltage sensing of each battery cell are connected to each battery cell. Therefore, when the cell monitor switch Q1 is turned on, the voltage (VS0 to VS14) dropped to the division resistor Rb of each cell is read and inputted to the analog mux U1 and U2. After addressing voltage difference, differential amplification is performed by differential amplifier (OP Amp U3) and applied to Micom U4 ADC (Analog to Digital Converter) to read voltage value.

In an embodiment of the present invention, the output voltage of each battery cell can be, for example, 20 V and the input range of the power supply voltage can be within +5 V. Therefore, the voltage at the point where three battery cells are connected in series can be, for example, 60V. In this case, the partial pressure ratio by the pair of voltage divider resistors can be assumed to be 0.083 (= 5 V / 60 V).

2 is a flowchart illustrating an operation of a battery cell voltage monitoring circuit according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the battery cell voltage monitoring circuit 100 according to the present invention applies a turn on signal, for example, a high level signal, from the microcomputer 140 to the cell monitor switch 150 (S210).

Accordingly, as shown in FIG. 1, as the high level signal is applied to the base side and turned on in the cell monitor switch 150 including the NPN type transistor, current flows from the collector side to the emitter side. 150 is turned on (S220).

In this case, the turn on time of the cell monitor switch 150 may be adjusted as a program of the microcomputer 140.

As the cell monitor switch 150 is turned on, a + 5V power is applied to all the photo couplers PC connected to each battery cell, so that each photo coupler PC is turned on (S230).

In the case of each photo coupler PC, as the light emitting diode in the photo coupler receives + 5V power and emits light, the photo transistor in the photo coupler receives the photo transistor and turns on to operate the photo coupler PC. Done.

Accordingly, each battery power is transmitted from the detection point for each battery cell to each photo coupler through each detection line, and from each photo coupler to each of the analog multiplexers 120 and 122 through each detection line ( S240).

Subsequently, the analog multiplexers 120 and 122 multiplex the voltages applied from the respective photo couplers and transmit them to the differential amplifier 130 (S250).

Accordingly, the differential amplifier 130 differentially amplifies each detected voltage and transfers the detected voltages to the microcomputer 140 (S260).

The microcomputer 140 converts the received analog voltage into a digital form and calculates the data as data (S270).

Here, when the voltage of the battery cell is V, the voltage VS dropped to the distribution resistor Rb may be obtained as in Equation 1 below.

In Equation 1, VSn represents a voltage dropped to the distribution resistor Rb of each battery cell, and V represents a voltage of the battery cell.

For example, if the battery cell voltage is 4.2V, the voltage dropped to the distribution resistor Rb is VS14 = Rb / Ra + Rb x (4.2x14), VS13 = Rb / Ra + Rb x (4.2x13),. .., VS1 = Rb / Ra + Rb x (4.2x1).

Therefore, the sensing voltage BATn across each cell can be obtained as shown in Equation 2.

That is, the voltage between both ends of BAT.14 = VS14-VS13, the voltage between both ends of BAT.13 = VS13-VS12, ..., the voltage between both ends of BAT.1 = VS1-VS0.

In the battery cell voltage monitoring circuit 100 according to the present invention, in order to increase the voltage detection accuracy, the microcomputer 140 can perform a correction operation by software. The microcomputer 140 performs AD conversion by analog-to-digital conversion. In the relationship between the result and the actual voltage, when the AD conversion result is X1, the value Y1 of the voltage V1 can be obtained by multiplying this value by 12 (= 1 / 0.083). An error occurs. Ideally, if the value of X2 is converted to X1 due to the resistance error, the value of the coefficient (X2 / X1) is registered in advance in the microcomputer 140, and based on the following equation (3), the AD conversion result X is correct. The voltage value Y can be obtained.

The values of the coefficients X2 / X1 are individual values for the voltage detection points, and the microcomputer 140 is stored in a nonvolatile memory such as an EEPROM.

By performing this correction operation, the potential of each voltage detection point can be measured accurately, and as a result, the difference calculation by the microcomputer 140 can be performed with high precision. If more accurate correction is required, it may be effective to employ the correction equation of the following equation (4) using two coefficients A and B.

On the other hand, in the battery cell voltage monitoring circuit 100 according to the present invention, the capacitor Cb is connected in parallel to the voltage divider resistor Rb interposed on each voltage branch line, and the low pass filter is provided by the voltage divider resistor Rb and the capacitor Cb. Can be configured. Thereby, the noise component contained in the voltage signal input to the microcomputer 140 can be reduced, and the AD conversion value with high precision can be obtained. When the low pass filter is formed using the partial pressure resistance, the increase in the number of parts is minimal. In addition, in the battery cell voltage monitoring circuit 100 according to the present invention, the differential calculation is performed after AD conversion of all the detection voltages, and thus it is necessary to maintain the detection voltage without changing the detection voltage until all the AD conversion processes are completed. Therefore, the value of the time constant Rb ㅧ Cb of each filter is made constant, and the time constant of each filter is set to be sufficiently longer than the AD conversion time of all cells. Therefore, the time from reaching the steady state after the detection voltage changes can be made constant. In addition, it is possible to suppress the change in the detected voltage until the AD conversion processing of all the channels is completed.

As described above, according to the present invention, the voltage of each battery cell is monitored to maintain the balance between the battery cells, and in case of emergency, a protection circuit is activated to protect the battery and to detect the voltage of the battery cell in order to extend the life of the battery. A battery cell voltage monitoring circuit can be realized that minimizes battery power consumption and insulates the photocoupler between the high potential battery pack voltage and the monitoring circuit so that the circuit operates stably.

As those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features, the embodiments described above are exemplary in all respects and are not intended to be limiting. You must do it. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

The present invention can be applied to a battery pack configured by connecting a lithium ion battery and a lithium polymer battery used in series in an electric vehicle, a hybrid vehicle, or a battery pack for storing electricity.

In addition, it is applicable to a circuit that cannot use the entire battery pack due to one cell having poor characteristics in a battery pack composed of a plurality of battery cells.

In addition, the cell voltage reading function of the BMS function may be applied to a circuit for reducing the voltage loss of the battery pack.

1 is a block diagram illustrating a battery cell voltage monitoring circuit according to an exemplary embodiment of the present invention.

2 is a flowchart illustrating an operation of a battery cell voltage monitoring circuit according to an exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

100: cell voltage monitoring circuit 110: battery pack

120, 122: analog multiplexer 130: differential amplifier

140: microcomputer 150: cell monitor switch

Ra, Rb: Distribution resistor PC: Photo coupler

Claims (7)

A battery pack in which one or more battery cells are connected in series; An analog multiplexer having respective detection lines drawn out from each detection point for each of the battery cells, respectively, through respective photo couplers; A differential amplifier for differentially amplifying the value output from the analog multiplexer and outputting a detection voltage; And A microcomputer (Micom) for calculating the detected voltage output from the differential amplifier as data; Battery cell voltage monitoring circuit comprising a. The method of claim 1, A cell monitor switch for turning on or turning off all photo couplers connected to each of the battery cells according to the control of the microcomputer; Battery cell voltage monitoring circuit further comprising. The method of claim 2, And said cell monitor switch uses a PNP transistor or an NPN transistor. The method of claim 2, As the cell monitor switch is turned on, power is applied to all the photo couplers, and each of the photo couplers is turned on, so that each battery power from the detection point for each of the battery cells passes through each detection line. A battery cell, which is transmitted to a coupler, is transmitted from each photo coupler to each of the analog multiplexers through a respective detection line, multiplexed in the analog multiplexer, and each detected voltage is transmitted to the microcomputer through the comparator. Voltage monitoring circuit. The method of claim 1, A battery cell voltage monitoring circuit, characterized in that a voltage divider is connected across each photo coupler connected to each of the battery cells, respectively. The method of claim 1, And the microcomputer has an analog to digital converter (ADC) function to convert the detected voltage in analog form into data in digital form. The method of claim 1, And the microcomputer performs a correction operation by software on data for the detected voltage.

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