JP7406870B2 - Charging control circuit - Google Patents

Description

The present invention relates to a charging control circuit.

In recent years, out of consideration for the global environment, engine-driven vehicles driven by internal combustion engines, ie, engines, are being replaced by electric vehicles driven by motors. In particular, lithium ion secondary batteries with high energy density are often used as battery power sources for driving motors.

Japanese Patent Application Publication No. 2017-225241

It is an important issue to take measures to prevent overcharging in charging control circuits for electric vehicles equipped with a plurality of battery modules that accommodate a large number of lithium ion secondary battery cells.

The present invention has been made in view of this background, and an object of the present invention is to provide a technology that allows safe charging.

The main invention of the present invention for solving the above problems is a charging control circuit, including a charging circuit, a constant current discharging circuit that discharges at a constant current that does not exceed an upper limit current, the charging circuit and the constant current discharging circuit. a battery module connected in parallel to the battery cell group; a second energization cutoff element that irreversibly energizes or cuts off the charging current, and when at least one of the battery modules is overcharged, the second energization cutoff element of the overcharged battery module The charging current is cut off using one current cutoff element, and if the first current cutoff element fails to cut off the charging current, the second current cutoff element of all the battery modules is used to cut off the charging current, and the second current cutoff element of all the battery modules is used to cut off the charging current. If the interruption by the second energization interruption element fails, the battery module group is discharged using the constant current discharge circuit.

Other problems disclosed in the present application and methods for solving the problems will be made clear by the section of the embodiments of the invention and the drawings.

According to the present invention, charging can be performed safely.

1 is a circuit block diagram schematically showing the configuration of a battery module 3 according to the present embodiment. FIG. FIG. 2 is a circuit block diagram schematically showing the configuration of a charging control circuit 103 according to the present embodiment. FIG. 2 is a circuit block diagram schematically showing the configuration of a charging circuit 104 according to the present embodiment. 2 is a flowchart diagram schematically showing control of the main controller 9 of the charging control circuit 104 according to the present embodiment. FIG.

In a lithium ion secondary battery, during charging, lithium ions are electrically separated from the positive electrode active material in the lithium ion secondary battery cell into the electrolyte, while during discharging, the lithium ions are released from the electrolyte into the electrolyte. It has an operating principle in which a current flows due to the movement of electrons as they are electrically inserted into the positive electrode active material, and a redox reaction occurs within the positive electrode active material as the lithium ions are electrically removed or inserted. is said to occur.

In addition, the process of ignition during overcharging of the lithium ion secondary battery is such that lithium ions are released from the positive electrode active material in the lithium ion secondary battery cell during overcharging when an overvoltage is applied to the lithium ion secondary battery cell. When a large amount of active oxygen is extracted and the crystal lattice structure of the positive electrode active material collapses, electrically unstable active oxygen is released from the positive electrode active material into the electrolyte, and the active oxygen comes into contact with the flammable electrolyte. It is said to ignite and cause a chain reaction.

The positive electrode active material of a lithium ion secondary battery is typically composed of lithium cobalt oxide, lithium manganate, or lithium nickel oxide. During charging, lithium ions are transferred to the positive electrode according to the redox reaction within the positive electrode active material. A phenomenon in which lithium ions are electrically desorbed from the active material into the electrolytic solution, and a phenomenon in which a large amount of lithium ions are desorbed from the positive electrode active material into the electrolysis during overcharging, resulting in the release of active oxygen. Focusing on one thing, it can be said that charging is similar to a substantial reduction reaction in an oxidation-reduction reaction, and in particular, it can be said that the overcharged state is substantially similar to an excessive reduction reaction. On the contrary, during discharge, it can be said that the phenomenon is similar to the above-mentioned substantial oxidation reaction, that is, the phenomenon in which the positive electrode active material substantially takes in oxygen.

Therefore, for the purpose of increasing safety during overcharging, it is required to suppress the reaction in which the positive electrode active material releases active oxygen during overcharging, that is, the substantial excessive reduction reaction. In addition, even if the charging control circuit is equipped with a safety mechanism for double protection against overcharging, if the double protection fails, for example, the CID provided inside the lithium ion secondary battery cell Even if the existence of a safety mechanism that cuts off the charging current by stripping the welding point using the increase in internal pressure due to the gas generated by electrolysis of the electrolytic solution due to overvoltage is positioned as a safety protection measure as triple protection, the above CID is When flooded, the sealing part is electrolytically corroded, and the high-pressure gas that has increased internal pressure escapes from the electrolytically eroded sealing part to the outside of the battery cell, failing to strip the welding point, resulting in continued overcharging and ignition. Sometimes. Furthermore, when using a laminated lithium ion secondary battery cell that cannot incorporate a CID, the failure of the double overcharge protection will inevitably lead to ignition, even if the probability of failure of the double overcharge protection is low. The damage caused in the event of a fire is severe. Therefore, from a risk assessment perspective, it is necessary to ensure safety by taking into consideration even when double protection fails.

As shown in FIG. 1, the battery module 3 reversibly inputs a charging current input to a high voltage rated battery cell group 1H in which a plurality of lithium ion secondary battery cells are connected in series. Alternatively, a semiconductor current cutoff element FET6 as a first current cutoff element to be stopped and a self-fusing fuse SCP7 as a second current cutoff element to irreversibly input or cut off are connected to the terminal 8 through series. The module controller, that is, the primary protection IC 4 detects the voltage of the battery cell group 1H or the current of the battery cell group 1H, that is, the voltage appearing across the shunt resistor 6, and turns on the FET 6 according to the detection result. Or, it is turned off to control the input or stop of the charging current input to the terminals 8 and the like. Further, the secondary protection IC 5 is driven independently of the primary protection IC 4, detects the voltage of the battery cell group 1H, and turns on the FET 10 in accordance with the detection result or the instruction signal 9 from the primary protection IC 4. The heater in the SCP 7 is energized and heated to self-fuse the fuse element in the SCP 7, irreversibly cutting off the charging current.

As shown in FIG. 2, the charging control circuit 103 connects a plurality of battery modules 3 in series to form a battery module 3 group, and connects the battery module 3 group to the charging circuit 11. The charging circuit 11 connects the power input cable 10 to a commercial power source, inputs an AC voltage, converts it to a desired DC voltage, applies the DC voltage to the 3 groups of battery modules, and supplies a charging current to the 3 groups of battery modules. input, and the battery cell group 1H in the battery module 3 is charged.

As shown in FIG. 3, the charging control circuit 104 has a configuration in which a constant current discharging circuit 12 is added to the charging control circuit 103 and connected in parallel to three groups of battery modules. The main controller 9 controls the constant current discharge circuit 12 using a control signal 13 according to a flow chart described later.

Next, the control of the main controller 9 of the charging circuit 104 will be explained using the flowchart shown in FIG.

In Step 1, the main controller 9 of the charging control circuit 104 communicates with the 3 groups of battery modules using the insulating communication signal 3 to control the battery cell group in at least one battery module 3 among the 3 groups of battery modules. It is detected whether the voltage of 1H exceeds a predetermined voltage 1 or not. When it is determined that the voltage of the battery cell group 1H exceeds the predetermined voltage 1, the process moves to Step 2, instructs all the battery modules 3 to turn off the FETs 6, and turns off the charging current to all the battery modules 3. Stop. In Step 3, the main controller 9 communicates with the 3 groups of battery modules using the insulating communication signal 3 so that the voltage of the battery cell group 1H in at least one battery module 3 among the 3 groups of battery modules is It is detected whether or not a predetermined voltage 2 higher than the predetermined voltage 1 has been exceeded. When it is determined that the voltage of the battery cell group 1H exceeds the predetermined voltage 2, the process proceeds to Step 4, in which all the battery modules 3 are operated to turn on the FETs 10 in the battery modules 3 to irreversibly cut off the SCP 7. using the insulating communication signal 3 to cut off the charging current to all of the battery modules 3.

In Step 5, the main controller 9 communicates with the 3 groups of battery modules using the insulating communication signal 3 so that the voltage of the battery cell group 1H in at least one battery module 3 among the 3 groups of battery modules is It is detected whether or not a predetermined voltage 3 higher than the predetermined voltage 1 and the predetermined voltage 2 has been exceeded. When it is determined that the voltage of the battery cell group 1H exceeds the predetermined voltage 3, the process moves to Step 6, and uses the communication signal 13 to turn on the constant current discharge circuit 12 so that the upper limit current is not exceeded for the battery module 3 group. Discharge is performed at a predetermined constant current.

Note that the current upper limit value of the constant current discharge is set with a sufficient margin for the current value that does not lead to ignition due to overcurrent discharge, and the predetermined voltage 3 is set at the positive electrode in the lithium ion secondary battery cell. Safety can be steadily ensured by setting the voltage slightly lower than the voltage at which active oxygen is released from the active material.

As mentioned above, the phenomenon in which the crystal lattice structure of the positive electrode active material collapses during overcharging and the active oxygen is released from the positive electrode active material into the electrolyte is essentially a phenomenon in the redox reaction within the positive electrode active material. It can be said that this is similar to an excessive reduction reaction, and conversely, during discharging, it can be said that it is similar to an oxidation reaction that is the opposite of the reduction reaction, that is, a phenomenon in which the positive electrode active material takes in oxygen into its interior in a temporal manner.

The state leading to the above-mentioned Step 4 is a state in which the primary protection IC 4 of at least one battery module 3 among the 3 battery module groups fails to detect overvoltage of the battery cell group 1H in Step 1, or Even if the FETs 6 of all the battery modules 3 in the module 3 group are turned off, the charging current fails to cut off due to a short-circuit failure of the FET 6, etc., and charging continues. The control plays the role of double protection to compensate for the failure of the primary protection against overcharging in Steps 1 and 2, and furthermore, the state leading to Step 6 is caused by the secondary protection IC 5 in the battery module operating normally due to some factor. In other words, double protection has failed, and at this stage, a large amount of lithium ions are extracted from the positive electrode active material in the lithium ion secondary battery cell, and active oxygen is about to be released. It can be said that the state is similar to an excessive reduction reaction, and the moment the constant current discharge by the constant current discharge circuit 12 starts, the reaction within the positive electrode active material is reversed from the reduction reaction to the oxidation reaction, and the positive electrode activity is A stage immediately before the lithium ions electrically released from the substance into the electrolyte are electrically inserted into the positive electrode active material, and the amount of active oxygen that has begun to be released from the positive electrode active material reaches the ignition condition of the electrolyte. In this case, the lithium ions released into the electrolytic solution are inserted back into the positive electrode active material, and a state similar to an oxidation reaction occurs, that is, the active oxygen is taken into the positive electrode active material, and the active oxygen is absorbed into the positive electrode active material. is substantially absorbed, while at a stage before the active oxygen begins to be released from the positive electrode active material, the discharge is equivalent to preventing the overvoltage state from continuing and suppressing the release of active oxygen in advance. It can be said that it becomes a state.

In the event that the double protection against overcharging fails due to the above-mentioned mechanism state substantially similar to absorbing active oxygen or the mechanism substantially similar to suppressing the release of active oxygen, Ignition of a laminated lithium ion secondary battery cell without a CID or a lithium ion secondary battery in which the CID does not operate normally can be avoided.

As explained above, when charging a car equipped with a large number of lithium-ion secondary battery cells, when the lithium-ion secondary battery cells are overcharged, the positive electrode active material is transferred to the electrolyte within the battery cell, which can cause a fire. It is possible to substantially absorb or suppress released active oxygen to avoid ignition of the lithium ion secondary battery cell, and from a risk assessment perspective, it is possible to achieve high safety even assuming the failure of double protection against overcharging.

Although the present embodiment has been described above, the above embodiment is for facilitating understanding of the present invention, and is not for construing the present invention in a limited manner. The present invention may be modified and improved without departing from the spirit thereof, and the present invention also includes equivalents thereof.

3 Battery module 9 Main controller 103 Charging control circuit 104 Charging circuit

Claims (2)

charging circuit;
A constant current discharge circuit that discharges at a constant current that does not exceed the upper limit current,
a battery module connected in parallel to the charging circuit and the constant current discharging circuit;
Equipped with
The battery module includes:
A battery cell group,
a first energization interrupting element that reversibly supplies or interrupts charging current to the battery cell group;
a second energization interrupting element that irreversibly supplies or interrupts the charging current to the battery cell group;
Equipped with
When at least one of the battery modules becomes overcharged, the charging current is cut off using the first energization cutoff element of the overcharged battery module;
If the first current cutoff element fails to cut off the charging current, the second current cutoff element of all the battery modules is used to cut off the charging current;
discharging the battery module group using the constant current discharge circuit if the second current cutoff element fails to cut off the battery;
Charging control circuit. The charging according to claim 1, wherein a voltage threshold for starting discharge by the constant current discharging circuit is higher than a voltage threshold for overcharge cutoff by the first energization cutoff element and a voltage threshold for overcharge cutoff by the second energization cutoff element. control circuit.

Images