JP2018129896A - Battery Management Unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery management unit capable of accurately measuring the voltages of battery cells included in a battery system while suppressing a relative error.SOLUTION: A battery management unit 3 for measuring voltages of a plurality of battery cells of a secondary battery 100 that is formed of serially connected the battery cells, comprises a capacitor C which is one capacitor, photo MOS relays 10 which are provided correspondingly between terminals of the battery cells, which are independently connected in series to the capacitor C, and which turn ON/OFF the corresponding connections, and a microcomputer 3a which controls the ON/OFF of the photo MOS relays 10. The microcomputer 3a charges the capacitor C by separately turning ON the photo MOS relays 10 of the battery cells 1 to 7, carries out an operation of turning off the photo MOS relays 10 when the terminal voltage of the capacitor C reaches a saturation state, and of obtaining the terminal voltage of the charged capacitor C. This operation is sequentially carried out for each of the battery cells so that the voltage of each of the battery cells is measured.SELECTED DRAWING: Figure 1

Description

  In a battery system in which battery cells are connected in series to increase the voltage and used as an energy source, the present invention detects the voltage of each battery cell and controls the voltage and current applied during charging and discharging according to the state of the battery cell The present invention also relates to a battery management unit for improving the safety and long life of the battery system.

  In recent years, electrical energy is temporarily stored using a battery such as a photovoltaic power generation panel (also called a solar cell panel or PV), an EV (electrically driven vehicle), or a power storage device, and the stored electrical energy is used. The spread of portable equipment that temporarily stores electrical energy using small batteries such as various information terminals and uses the stored electrical energy is rapidly progressing.

  However, the battery output voltage is 1.2V for nickel-metal hydride, 2V for lead-acid batteries, and less than 4V for lithium-ion batteries, which is too low for use with a single battery. Therefore, these battery cells are connected in series. There are many devices that are configured as a battery and are designed to increase power by setting a high voltage of at least 12V and a high voltage of about 360V.

  At the time of charging / discharging such an assembled battery, the current that flows during both charging and discharging is the same in any battery cell, and the voltages of the individual battery cells corresponding to the current usually take different values. Therefore, even if the battery voltage of the whole assembled battery is observed, the voltage of each battery cell is different, and a certain battery cell may exceed the allowable value as a battery cell. Battery cells that exceed the permissible value can cause battery system disasters such as swelling, heat generation, smoke generation, and explosion. Moreover, in the state connected to load, even if the voltage of a certain battery cell falls abnormally, it may be covered with another battery voltage and the supply of power to the load may be forced. In such a case, the corresponding battery cell may be in an overdischarged state and may lead to electrode destruction. At the next charging time, the corresponding battery cell causes overcharge prior to other battery cells, and various battery systems. It becomes a hazard.

  In order to prevent the hazards of various battery systems as described above, the voltage of each battery cell (single cell) that is a constituent element of the battery system is constantly monitored, and the individual data of the voltage and the appropriateness based on the data are determined. Such control is indispensable for extending the life of the battery system and ensuring safety. Therefore, a battery management system (BMS: Battery management system) is conventionally used as a device that monitors the voltage of each battery cell (single cell) of the battery system and performs predetermined control on the battery system. The battery management system has a battery management unit (BMU) as a unit that measures the voltage and temperature of each battery cell included in the battery system and monitors and controls (protects) the battery system. .

  Various methods for measuring the voltage of individual battery cells of a battery system by a battery management system have been made in the past (see, for example, Patent Document 1).

  For example, FIG. 6 shows a general basic circuit for measuring a battery cell voltage by the resistance division method. However, the voltage measurement method using this basic circuit inevitably involves measurement errors. Specifically, in this basic circuit, when the error of each resistor is the same, the error is larger in the battery cell located in the upper part of the figure. For example, if the resistance has an error of 1%, the cell 1 has an error of 37 mV and the cell 7 has an error of 259 mV. Further, in the resistance division method, the energy loss of the battery cell due to the division resistance varies in principle depending on the individual battery cell. Therefore, the resistance division method has a drawback that a large amount of charge (SOC) varies over time. In addition, when a conventional BMU is connected to this basic circuit, it is necessary to always pass a current in order to detect the voltage of the battery cell (see FIG. 7A), which wastes power. Moreover, since the electric current which flows through each battery cell differs, the variation in the charge amount (SOC) of a battery cell by connecting BMU arises (refer FIG.7 (b)).

  Also, if the divided resistance value is increased in order to reduce the load amount on the battery cell for measurement, the accuracy of the voltage measurement value is reduced.If the divided resistance value is decreased in order to obtain accuracy, the load amount is increased. The variation of the battery cells increases and the accuracy is high, but the battery itself has a self-variation in the amount of charge (SOC). Therefore, there is a demand for a technique for accurately measuring the voltage of each battery cell included in the battery system while suppressing a relative error.

JP 2014-116992 A

  Accordingly, the present invention has been made in view of the above problems, and provides a battery management unit capable of accurately measuring the voltage of each battery cell included in the battery system while suppressing relative errors. With the goal.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in the battery management unit of claim 1,
A battery management unit for measuring a voltage for each battery cell of a battery system configured by connecting a plurality of battery cells in series,
One capacitor,
A first switching element provided correspondingly between the terminals of each battery cell, connected in series independently to the capacitor, and ON / OFF the connection;
A control circuit for controlling ON / OFF of the first switching element;
The control circuit includes:
The capacitor is charged by turning on the first switching element for each battery cell, and when the terminal voltage of the capacitor reaches a saturated state, the first switching element is turned off. An operation for acquiring a terminal voltage is executed, and the voltage for each battery cell is measured by sequentially performing this operation for each battery cell.

In the battery management unit of claim 2,
The battery cell is provided with a balancing means for comparing the voltage of each battery cell, and discharging or charging each battery cell independently as necessary to level the SOC level of each battery cell.

In the battery management unit of claim 3,
The control circuit includes:
The charging voltage of the charging power source for charging the battery system is controlled in accordance with the voltage of each battery cell to optimize the charging and discharging operations of the entire battery system.

  According to the battery management unit of the present invention, it is possible to accurately measure individual battery cells included in the battery system while suppressing relative errors.

  As a result, it is possible to prevent the occurrence of abnormal phenomena such as a decrease in battery system charging capability, heat generation, smoke generation, and ignition due to variations in constituent battery cells, which is the greatest concern in the application of battery systems. In addition, there is a concern that the entire battery system has a reduced capacity and a short life due to one characteristic defect of the constituent battery cells, and a system configuration that can prevent these concerns is realized.

The block diagram which shows typically the structure of the charging device provided with the battery management system which has a battery management unit which concerns on one Embodiment of this invention. The block diagram which shows the structure of a microcomputer. The figure which shows the cell voltage detection circuit which is a basic circuit of a floating capacitor system. The sequence diagram which shows an example of operation | movement of a capacitor charge, voltage detection, and microcomputer arithmetic processing. Explanatory drawing explaining the feature of a battery management unit. The figure which shows an example of the measurement circuit of the battery cell voltage by a resistance division system. Explanatory drawing explaining the problem of a resistance division system.

Next, a charging device 1 including a battery management system (BMS) having a battery management unit according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The charging device 1 stores electric power generated by various energy sources E in a secondary battery 100 that is an example of a battery system via a charging power source 2 and supplies electric power from the secondary battery 100 to a load 200. is there. The charging device 1 is electrically connected to a load 200 that operates using electric power stored in the secondary battery 100. Examples of the energy source E include PV, wind power, geothermal heat, and the like. Examples of the load 200 include a power source such as a motor, various devices, an illumination device such as an electric light, a display device for information, and the like.
In addition, the battery system in the present embodiment is a battery pack that is formed into a pack and modularized by a series connection of a plurality of battery cells to form an assembled battery.

  Here, the secondary battery 100 in the present embodiment refers to a battery that can be repeatedly charged and discharged, and converts electrical energy into chemical energy and stores it, and conversely converts the stored chemical energy into electrical energy. A battery that can be used. Examples of the secondary battery 100 include a nickel-cadmium battery, a nickel-hydrogen metal battery, a lithium ion battery, and a lead battery. Among these, as the secondary battery 100, a lithium ion battery with a high energy density is particularly preferable.

As shown in FIG. 1, the charging device 1 includes an energy source E, a charging power source 2, a battery management unit (hereinafter referred to as BMU) 3 that monitors and controls the secondary battery 100, a balance mechanism 4, a current detection / The protection circuit 5 and the display means 6 are mainly provided. The charging device 1 is electrically connected to a secondary battery 100 that is a battery system and a load 200. The BMU 3 is electrically connected to the charging power source 2, the balance mechanism 4, the current detection / protection circuit 5, the display means 6, the secondary battery 100, the load 200, and the like.
In addition, each structure of the secondary battery 100 connected to the charging apparatus 1 demonstrated in this embodiment, BMU3 with which the charging apparatus 1 is equipped, and BMU3 should just be a structure which can implement | achieve the function demonstrated in this embodiment, It can be changed as appropriate.

  The charging power source 2 is a power source that supplies a charging voltage to the secondary battery 100. The charging power source 2 has a transformer and a rectifier circuit that converts AC power into DC, and the converted DC power is supplied to the secondary battery 100 via the BMU 3.

  The BMU 3 includes a microcomputer (hereinafter referred to as a microcomputer) 3a that is an example of a control circuit (processor) that mainly executes arithmetic operations / commands, a charging voltage control unit 3b that controls charging voltage and the like, and a secondary battery 100. And a cell voltage detection circuit 3c for detecting the voltage of each battery cell. The BMU 3 measures the voltage for each battery cell of the secondary battery 100.

The microcomputer 3a is electrically connected to the charging voltage control unit 3b and the cell voltage detection circuit 3c. As shown in FIG. 2, the microcomputer 3a includes a microprocessing unit (hereinafter referred to as MPU) 40 as a central processing unit, a read only memory (hereinafter referred to as ROM) 41 as storage means, and a random access memory (hereinafter referred to as RAM). 42, a switching control unit 43 that controls ON / OFF of switching elements (a photo MOS relay 10 that is a first switching element and a capacitor relay 11 that is a second switching element) included in the cell voltage detection circuit 3c, and a time A timer 44 that is a measuring unit, a counter 45 that is a counting unit, a current detection unit 46 that detects a current value energized in the secondary battery 100 via a charging current detection unit (not shown), and the secondary battery 100 Battery voltage monitoring unit 47 for monitoring the voltage value (battery cell voltage) between terminals of each battery cell, A / D And an A / D converter 48 or the like having a conversion function. In the ROM 41, various processing programs processed in the charging device 1 (for example, the voltage of each battery cell included in the secondary battery 100 is detected, and the voltage and current applied during charging and discharging are controlled according to the state. And the like are stored. The microcomputer 3a is a control circuit that has the switching control unit 43 and controls ON / OFF of switching elements (a photo MOS relay 10 that is a first switching element and a capacitor relay 11 that is a second switching element described later). is there.
Details of the operation executed in the cell voltage detection circuit 3c will be described later.

  The balance mechanism 4 is a balance unit having a function of maintaining a voltage balance between the battery cells of the secondary battery 100, and includes, for example, an IC chip that incorporates the function. The balance mechanism 4 is operated by the microcomputer 3a of the BMU 3. The balance mechanism 4 compares the voltages of a plurality of battery cells, and discharges or charges each battery cell independently as necessary to level the SOC (State of Charge) level of each battery cell. is there.

  The current detection / protection circuit 5 is a protection circuit for detecting the current value of the charging current and stopping overcharge and overdischarge. The current detection / protection circuit 5 measures the voltage with an electronic circuit, and stops charging when the voltage becomes a certain value or more. Similarly, in the case of overdischarge, the discharge is stopped when the voltage becomes a certain value or less. The current detection / protection circuit 5 is operated by the microcomputer 3a of the BMU 3.

  The display means 6 displays the state of charge (SOC, etc.) of the secondary battery 100, the total voltage of the battery, the voltage of each battery cell, etc. in real time. The display means 6 is composed of, for example, a predetermined display device or a PC (personal computer) LCD.

  The secondary battery 100 is an example of a battery system in which a plurality of battery cells (single cells serving as a basis for battery reaction) are connected in series to increase the voltage and use it as an energy source. The secondary battery 100 is an assembled battery in which a plurality of battery cells (seven in this embodiment) are connected in series, and a plurality of battery cells are electrically stacked to increase the voltage. Examples of the secondary battery 100 include a lithium ion battery.

[Cell voltage detection circuit]
Next, the voltage detection method and data processing method of each battery cell of the secondary battery 100 by BMS3 are demonstrated.

  The cell voltage detection circuit 3c is a measurement circuit that measures the voltages of a plurality of battery cells. The capacitor C, which is one high-precision capacitor, and a plurality of capacitors C that are independently connected in series to the capacitor C and turn on / off the connection. (In this embodiment, it is composed of seven photo MOS relays 10, 10,...) That are first switching elements. The capacitor C is provided on the secondary side of the plurality of battery cells. The capacitor C is connected to the A / D converter 48 of the microcomputer 3a via the capacitor relay 11.

The photo MOS relay 10 is a semiconductor relay that can be switched ON / OFF by an optical signal.
In the present embodiment, the photo MOS relay 10 which is a semiconductor relay is used as the first switching element, but there is no particular limitation, and other types of switching elements may be used.

  As shown in FIG. 3, the secondary battery 100 that is a battery system is configured by connecting a plurality of battery cells (of the same specification, but shown as cells 1 to 7 for convenience in FIG. 3 and the like) in series. Yes. The plurality of battery cells 1 to 7 are provided with a plurality of photo MOS relays 10, 10... Corresponding to each of the battery cells 1 to 7. In principle, the photo MOS relay 10 is mounted on each of the positive and negative electrodes of the individual battery cells 1 to 7 to be measured, and a pair of switches of the photo MOS relay 10 are turned on / off according to instructions from the microcomputer 3a. It has a function of conducting / non-conducting at the same time and operates in pairs.

  Next, a battery cell voltage detection method (also referred to as a floating capacitor method in this embodiment) will be described more specifically with reference to FIG.

[First process: Capacitor charging process]
First, in response to an instruction signal from the microcomputer 3a, a pair of switches of the photo MOS relay 10 attached to one of the plurality of photo MOS relays 10, 10. Is turned on and the battery cell 1 is in a conductive state. Thereby, the capacitor C for voltage detection is charged (charged), the terminal voltage V _C of the capacitor C changes with time, and the relationship of the following expression (1) is established. Capacitor C passes through a time until saturation (this time elapses from a time constant (T0) determined by the sum of the capacitance (C) of capacitor C, the internal resistance (r0) of photo MOS relay 10 and buffer resistance (R)). The terminal voltage V _C of the capacitor C becomes the voltage of the battery cell of reference 1 represented by V ₁ . Next, it progresses to a battery cell voltage calculation process.

Here, in the above equation (1), t is the elapsed time, and T0 is the time constant described above.

[Second Process: Battery Cell Voltage Calculation Step]
Subsequently, after the photo-MOS relay 10 to OFF (non-conducting state) when the terminal voltage V _C of the capacitor C becomes a voltage V ₁ of the battery cell of the code 1, and a pair of switch capacitors relay 11 in the ON state Then, the capacitor C is connected to the A / D converter 48 of the microcomputer 3a. Inside the microcomputer 3a, the terminal voltage V _{C of the} capacitor C (the voltage V 1 of the battery cell with reference numeral ₁ ) is A / D converted (digital calculation), and the memory cell designated as the voltage V ₁ of the battery cell with the reference numeral 1 (for example, , RAM 42).

After the calculation is completed, the capacitor charging step and the battery cell voltage calculation step described above are applied to the battery cell of reference numeral 2, and the voltage V2 of the battery cell of reference numeral ₂ is measured and stored in the memory.

  The same process is continued for the number of battery cells (seven in the present embodiment), and the process returns to the battery cell of reference numeral 1 again to continue the process. That is, the voltage of each battery cell constituting the secondary battery 100 is sequentially detected and monitored cyclically at a certain time interval.

  In this way, the capacitor charging step as the first process and the battery cell voltage calculation step as the second process are executed in a chain, and measurement of all the battery cells constituting the battery system is performed. It is possible to make the microcomputer 3a recognize all the voltage values of the battery cells constituting the.

  The above-described process is activated by the ON / OFF switching operation of the corresponding photo MOS relay 10, but the time control is performed by a signal from the microcomputer 3a. FIG. 4 shows a timing chart of charging of the capacitor C and signal transmission to the microcomputer 3a. In FIG. 4, the horizontal axis corresponds to time (msec), and the vertical charge relay corresponds to each photoMOS relay 10.

  In this way, the microcomputer 3a charges the capacitor C by turning on the photo MOS relay 10 for each battery cell, and turns off the photo MOS relay 10 when the terminal voltage of the capacitor C reaches a saturated state. The operation of acquiring the terminal voltage of the charged capacitor C is executed, and this operation is sequentially performed for each battery cell to measure the voltage for each battery cell.

Further, the microcomputer 3a operates the current detection / protection circuit 5 based on the result of all the voltage values of the battery cells, and charges if one of the battery cells constituting the secondary battery 100 exceeds a specified limit voltage. Has a battery protection function that stops immediately and stops discharge immediately when a predetermined lower limit voltage is reached. Further, an interruption relay that cuts off the power supply to the load 200 is attached as an equipment of the secondary battery 100, and a stop signal from the microcomputer 3a for stopping them is applied as a driving signal for the interruption relay to cut off the electric power. A configuration is also possible.
That is, the microcomputer 3a controls the charging voltage of the charging power source 2 for charging the secondary battery 100 according to the voltage of each battery cell, and optimizes the charging and discharging operation of the entire secondary battery 100. Can be

  In addition, the microcomputer 3a observes the degree of voltage variation of each battery cell, adjusts the current intensity of charging, reduces the discharge current, and automatically adjusts the adaptability of the load power according to the battery power, Abnormal operation of the secondary battery 100 can be prevented. As a result, according to BMU3, the function aiming at the safety | security of a battery and prolonging a lifetime becomes realizable.

Furthermore, for example, when each battery cell is configured with a fixed resistance load via a control relay, the voltage of the other battery cell can be matched with the minimum value of the battery cell, and so-called passive cell balance function is provided. It is also possible to make it.
In addition, passive cell balance is discharging a high voltage battery cell and uniting with a low voltage battery cell.

In addition, for example, when each battery cell is provided with an independent power supply via a control relay, it is possible to perform supplementary charging to match the voltage of the other battery cell with the maximum value of the battery cell, and so-called active cell balance function is provided. It is also possible to make it.
The active cell balance means charging a low voltage battery cell and adjusting it to a high voltage battery cell.

  Next, the feature of the battery cell voltage detection method using the above-described floating capacitor method will be described with reference to FIG.

Feature 1) As shown in FIG. 5A, the voltage of each battery cell can be measured one by one with an accurate value.
According to the battery cell voltage detection method by the floating capacity method, the voltage of each battery cell (battery cells indicated by reference numerals 1 to 7) is measured individually with a tester. Thereby, the measurement error by the position of a battery cell does not arise like the conventional resistance division system mentioned above.

Feature 2) When BMU3 is stopped, the current consumption is completely zero.
That is, as shown in FIG. 5B, since all the switches are in the OFF state, no current flows. Thus, no current flows when the BMU 3 is not operating. Therefore, waste of power can be suppressed as compared with the conventional BMU described above.

Feature 3) Since the circuit configuration of each battery cell is the same, there is no variation due to BMU3.
That is, as shown in FIG.5 (c), it is because the electric current which flows from each battery cell is the same.

  In this way, the cell voltage detection circuit 3c has been devised in terms of circuit so as to perform measurement independently as if it were measured with an insulated voltmeter.

  The cell voltage detection circuit 3c is a circuit intended to provide a method for connecting and measuring only arbitrary battery cells to the measurement circuit when the measurement of the battery cells constituting the secondary battery 100 is intended. It is. As a result, measurement is performed by the same measurement circuit, and measurement errors are eliminated. In addition, relative relative errors do not occur when the load amount due to measurement is the same as the measurement time. Therefore, in the BMU 3, the configured battery cells 1 to 7 can be measured with the same accuracy and with the same instrument under the same conditions.

  As described above, according to the BMU 3, it is possible to accurately measure individual battery cells included in the secondary battery 100 while suppressing a relative error.

  As a result, it is possible to prevent the occurrence of abnormal phenomena such as a decrease in charging capacity of the secondary battery 100 due to variations in the constituent battery cells, heat generation, smoke generation, and ignition, which is the greatest concern in the application of the secondary battery 100. . In addition, there is a concern that the overall capacity of the secondary battery 100 may be reduced due to one characteristic defect of the constituent battery cells, and the life of the secondary battery 100 may be shortened. Thus, a system configuration capable of protecting these concerns is realized.

  To summarize the present invention, the battery cells are made of the same material, in the same environment, even if produced in the same production process, from a microscopic point of view, and even a slight difference in history thereafter greatly differs in the life of the battery. Show properties. This can be imitated as a creature.

  Therefore, for charging a battery system constituted by a combination of battery cells having different personalities, it is an indispensable provision to inject proper power while monitoring the state of each battery cell. The status monitoring according to the method of the present invention does not involve any inconvenience due to the installation of the mechanism itself without the accuracy of the monitoring itself and the unbalanced cell load associated with the monitoring mechanism.

  On the other hand, generally speaking, a battery charger is charged by converting AC input power to DC and applying a voltage that matches the battery voltage. Completion of charging obtains a termination signal from the battery (ie, a signal that no more energy injection can be tolerated anymore) and stops application.

  The signal generation method and the like have already been established as existing technologies, but the present invention is applied and developed by extending this overall control to individual battery cells that are further configured.

Here, the function of the BMU 3 according to this embodiment described above is as follows.
1) All voltages (potentials) of the constituent battery cells are acquired by the method described above.
2) When the voltage indicating the maximum voltage reaches the allowable maximum voltage defined by the battery type, charging is stopped.
3) Alternatively, the battery cell continues to be charged, but the voltage rising tendency becomes slower than the amount of charge, and charging is stopped if the calculation result shows that the amount of charge does not increase even if charging is continued further.
Although not described above, functions that can be added to the BMU 3 are as follows.
4) Stop charging when the battery temperature reaches the specified upper limit.
5) Stop charging when the charging current decreases to the specified value.

  Further, the most important point regarding discharge is that one of the constituent battery cells must be avoided to be below the allowable lower limit voltage. The entire voltage measurement can only be detected as the sum of the voltages of individual battery cells. Even if the voltage is 48 V, for example, in an appropriate voltage range, this 48 V may be covered by another battery cell even if the voltage of a certain battery cell falls below the allowable lower limit voltage.

  When the voltage of the battery cell is lower than the allowable voltage, the crystal gap of the negative electrode in the cell is out of balance and swells. Appears to exhibit a so-called “battery bulge” phenomenon. Due to this swelling, the crystal of the negative electrode breaks down and the number of active material sites decreases, resulting in a decrease in charge capacity. (The same phenomenon occurs during overcharge and this also appears as a bulge.)

  In order to prevent this overdischarge phenomenon, a mechanism that constantly monitors and controls the voltage of the configured battery cell is indispensable. Specifically, when the voltage reaches the lower limit of setting, a mechanism for shutting off is provided, or current control is performed. A mechanism for controlling the discharge current may be provided by providing a mechanism.

  As described above, the present invention is excellent in that the voltage of each battery cell at an accurate and appropriate time is detected and a control mechanism based on the data is constructed.

1 Charging Device 3 Battery Management Unit (BMU)
3a Microcomputer (control circuit)
10 Photo MOS relay (first switching element)
11 Capacitor relay (second switching element)
C capacitor (capacitor)

Claims (3)

A battery management unit for measuring a voltage for each battery cell of a battery system configured by connecting a plurality of battery cells in series,
One capacitor,
A first switching element provided correspondingly between the terminals of each battery cell, connected in series independently to the capacitor, and ON / OFF the connection;
A control circuit for controlling ON / OFF of the first switching element,
The control circuit includes:
The capacitor is charged by turning on the first switching element for each battery cell, and when the terminal voltage of the capacitor reaches a saturated state, the first switching element is turned off. A battery management unit that performs an operation of acquiring a terminal voltage and measures a voltage for each battery cell by sequentially performing the operation for each of the battery cells.   The battery device includes a balance unit that compares the voltage of each battery cell, discharges or charges each battery cell independently as needed, and equalizes the SOC level of each battery cell. Item 6. The battery management unit according to Item 1. The control circuit includes:
The charging and discharging operations of the entire battery system are optimized by controlling a charging voltage of a charging power source for charging the battery system according to a voltage of each of the battery cells. The battery management unit according to claim 1 or 2.