WO2014203715A1 - Secondary-cell discharge circuit, balance correction circuit, and power storage device - Google Patents

Abstract

[Problem] To provide a secondary-cell discharge circuit or the like which is capable of definitively preventing the overdischarge of a secondary cell. [Solution] This discharge circuit (1) for a secondary cell (B) is equipped with: a discharge element (R) connected between the terminals of the secondary cell (B); a switching element (S) for controlling the current flowing through the discharge element (R) and connected in series to the discharge element (R) between the terminals of the secondary cell (B); and one or more unidirectional elements (D) having a forward-direction-voltage threshold at or above the discharge cut-off voltage of the secondary cell (B), and connected in series to the discharge element (R) and the switching element (S) between the terminals of the secondary cell (B). The unidirectional element (D) is configured, for example, by using a diode (d) or a light-emitting diode (led). It is possible, for example, to use the discharge circuit (1) in a balance correction circuit (70) for correcting the cell balance of a battery comprising a plurality of secondary cells (B1-Bn).

Description

Secondary battery discharge circuit, balance correction circuit, and power storage device

The present invention relates to a discharge circuit for a secondary battery, a balance correction circuit, and a power storage device, and more particularly to a technique for preventing overdischarge of the secondary battery.

Secondary batteries such as lithium ion batteries and lithium polymer batteries, when the discharge progresses and the battery voltage becomes an overdischarge state below the discharge end voltage, the internal constituent material changes, and the performance deteriorates or cannot be recharged. Further, if the secondary battery that has been over-discharged is used as it is, there is a risk of fire or explosion. Therefore, a mechanism for reliably preventing overdischarge is indispensable for such secondary batteries.

Regarding a mechanism for preventing overdischarge, for example, Patent Document 1 discloses a charge / discharge for controlling a secondary battery module having a plurality of lithium ion secondary batteries and an assembled battery in which the secondary battery modules are connected in parallel. In the secondary battery system comprising the control means, when the voltage of the lithium ion secondary battery module being discharged becomes lower than a predetermined discharge stop voltage, the charge / discharge control means discharges the lithium ion secondary battery module being discharged. Is stopped and discharge from another lithium ion secondary battery module is started.

JP 2012-156025 A

Some products that use secondary batteries are intentional as shown in FIG. 8, such as a balance correction circuit that corrects the cell balance of a rechargeable flash unit (electronic flash unit) or an assembled battery composed of a plurality of secondary batteries. Some have a circuit (discharge circuit 80) that performs a proper discharge.

Here, in the discharge circuit 80, for example, when the connection between the secondary battery B and the discharge element R cannot be released due to a short circuit failure of the switch element S or a failure of the control circuit C, the discharge from the secondary battery B is performed. There is a possibility that the current supply to the element R continues and the secondary battery B is overdischarged. Therefore, a mechanism for reliably preventing overdischarge of the secondary battery B is indispensable for such a discharge circuit 80.

The present invention has been made in view of such a background, and an object thereof is to provide a secondary battery discharge circuit, a balance correction circuit, and a power storage device that can reliably prevent overdischarge of the secondary battery. And

In order to achieve the above object, one of the present invention is a discharge circuit for a secondary battery, a discharge element connected between terminals of the secondary battery, and the secondary battery in series with the discharge element. Connected between the terminals of the secondary battery, a switch element for controlling a current flowing through the discharge element, and connected between the terminals of the secondary battery in series with the discharge element and the switch element, and more than a discharge end voltage of the secondary battery And one or more unidirectional elements having a forward voltage threshold.

Another one of the present invention is the discharge circuit, wherein the unidirectional element includes one or more diodes connected in series.

Another one of the present invention is the above discharge circuit including one or more light emitting diodes connected in series. In this case, the light emitting diode may function as a discharge element.

Another aspect of the present invention is the discharge circuit, wherein the unidirectional element includes one or more diodes and one or more light emitting diodes connected in series. To do.

Another one of the present invention is a balance correction circuit, the discharge element connected between the respective terminals of the secondary battery of the assembled battery consisting of a plurality of secondary batteries connected in series, A switch element connected in series with each of the discharge elements and controlling a current flowing through each of the discharge elements; and a forward voltage greater than or equal to the discharge end voltage of the secondary battery connected in series with each of the discharge elements and the switch elements. A plurality of discharge circuits configured to include one or more unidirectional elements having a threshold value, a voltage sensor for measuring a voltage of each of the plurality of secondary batteries, and each of the plurality of secondary batteries A control circuit for turning on and off each of the switch elements in accordance with a measurement value of the voltage sensor in order to equalize the voltage.

Another one of the present invention is a power storage device, which includes the secondary battery and the discharge circuit.

Another one of the present invention is a power storage device, which includes the assembled battery and the balance correction circuit.

The other problems disclosed in the present application and the solutions thereof will be clarified by the description of the mode for carrying out the invention and the drawings.

According to the present invention, it is possible to reliably prevent overdischarge of the secondary battery.

It is an example of the discharge circuit 1 of a secondary battery. It is a figure explaining the forward direction threshold voltage of a diode. FIG. 6 is a diagram showing another example of the discharge circuit 1 of the secondary battery (when the unidirectional element D is configured by a plurality of unidirectional elements D (1) to D (n) connected in series). It is a figure which shows another example (when the light emitting diode led is used as the unidirectional element D) of the discharge circuit 1 of a secondary battery. FIG. 6 is a diagram showing another example of the discharge circuit 1 of the secondary battery (when the unidirectional element D is configured by a plurality of light emitting diodes led (1) to led (n) connected in series). Another example of the discharge circuit 1 of the secondary battery (one or more diodes d (1) to d (n) connected in series and one or more light emitting diodes led (1) to led It is a figure which shows (when it is comprised combining (n)). This is a balance correction circuit 70 shown as an application example of the discharge circuit 1. 2 is an example of a discharge circuit 80;

Cross-reference of related applications This application claims priority based on Japanese Patent Application No. 2013-127813 filed on Jun. 18, 2013, the contents of which are incorporated herein by reference.

Hereinafter, embodiments of the present invention will be described. In the following description, the same or similar parts may be denoted by the same reference numerals and redundant description may be omitted.

FIG. 1 shows a discharge circuit 1 of a secondary battery B shown as an embodiment. As shown in the figure, the discharge circuit 1 includes a discharge element R connected between the positive and negative terminals of the secondary battery B, and a discharge element R connected in series between the positive and negative terminals of the secondary battery B. A switch element S for controlling the flowing current, a discharge element R, a unidirectional element D connected between the positive and negative terminals of the secondary battery B in series with the switch element S, and a control circuit C for turning on and off the switch element S are provided.

The terminals T + and T− connected to the positive and negative terminals of the secondary battery B have loads that operate using the energy of the secondary battery B (eg, heating elements, motors, electronic circuits of rechargeable flash furnaces (electronic flash furnaces)) , The load when the secondary battery B is used as an auxiliary power source for supplying power to a load in a general home or factory, etc.), a current supply source for supplying a charging current to the secondary battery B (for example, a charger, a regeneration circuit) ) Etc. are connected.

The secondary battery B is a secondary battery having a predetermined discharge end voltage, and is, for example, a lithium ion battery or a lithium ion polymer battery. In the following description, the end-of-discharge voltage means that the secondary battery B is overdischarged (the battery voltage of the secondary battery B cannot maintain the secondary battery B in a normal state (the performance deterioration of the secondary battery B or The lowest voltage that is guaranteed not to reach a value (which causes a failure to recharge) or the like (a voltage that can lead to overdischarge when the battery voltage of the secondary battery B is less than the discharge end voltage) ).

The switch element S is an element that controls a current flowing through the discharge element R. For example, a bipolar transistor (pnp type, npn type), a field effect transistor (Field-EffectｎTransistor) (p channel type, n channel type), a relay Such as a mechanical switch. The switch element S is turned on / off by the control circuit C. In the present embodiment, a case where the switch element S is a pnp type transistor will be described as an example.

The discharge element R is an element that promotes discharge of the secondary battery B by converting electric energy stored in the secondary battery B into heat energy or the like, and is, for example, a resistance element.

The unidirectional element D is a semiconductor element having a forward voltage threshold equal to or higher than the discharge end voltage of the secondary battery B, and is, for example, a diode (including a case where a transistor functions as a diode by diode connection). In the following description, the forward voltage threshold value refers to the lowest voltage (minimum voltage required for moving the carrier) that allows the unidirectional element D to be energized in the forward direction. When the voltage applied to the unidirectional element D becomes less than the forward voltage threshold, the current flowing through the unidirectional element D is minute or zero. For reference, FIG. 2 shows the relationship between the forward voltage and forward current of the diode (VI characteristics) and the relationship between these and the forward threshold voltage.

The control circuit C is a circuit (an analog circuit, a digital circuit, an integrated circuit (IC chip), etc.) that controls the switching element S to control the discharge of the secondary battery B. For example, when the switch element S is configured using a bipolar transistor, the control circuit C controls the base voltage of the switch element S to turn on and off the switch element S. For example, when the switch element S is configured using a field effect transistor, the control circuit C controls the gate voltage of the switch element S to turn on and off the switch element S.

In the discharge circuit 1 having the above configuration, for example, even when the coupling between the secondary battery B and the discharge element R cannot be released due to a short circuit failure of the switch element S or a failure of the control circuit C, the discharge proceeds. Accordingly, the battery voltage of the secondary battery B gradually decreases, and the discharge of the secondary battery B automatically stops when the battery voltage of the secondary battery B becomes equal to the forward voltage threshold value of the unidirectional element D. Therefore, it is possible to reliably prevent the secondary battery B from being overdischarged. The discharge circuit 1 can be configured by adding a unidirectional element D to a general discharge circuit including a switch element S, a control circuit C, and a discharge element R. A mechanism for reliably preventing overdischarge can be realized simply and at low cost. In recent years, power storage devices capable of storing large amounts of electricity have attracted attention against the background of environmental problems and power demand problems, and power storage devices used in such applications are particularly required to have high reliability and safety. By adding the discharge circuit 1 to a power storage device (battery pack) configured using the secondary battery B, the reliability and safety of the power storage device can be improved simply and at low cost.

As shown in FIG. 3, the unidirectional element D may be configured using a plurality of the same or different unidirectional elements D (1) to D (n) connected in series. In this case, the discharge of the secondary battery B stops when the battery voltage of the secondary battery B becomes equal to the sum of the forward voltage thresholds of the unidirectional elements D (1) to D (n). Therefore, the discharge stop voltage of the secondary battery B can be freely set by changing the number and type of the unidirectional elements D (1) to D (n). The secondary battery B can be handled flexibly. In addition, if the number and type of unidirectional elements D (1) to D (n) are appropriately selected, the discharge of the secondary battery B can be prevented from being stopped at an unnecessarily high voltage ( The forward voltage threshold value of the unidirectional element D can be brought close to the discharge end voltage), and the performance of the secondary battery B can be sufficiently obtained.

As shown in FIG. 4, the unidirectional element D may be configured using a light emitting diode led. Further, as shown in FIG. 5, the unidirectional element D may be configured using a plurality of light emitting diodes led (1) to led (n) connected in series. Thus, when a light emitting diode is used as the unidirectional element D, the state of discharge can be easily confirmed visually. In this case, the unidirectional element D may function as a pilot lamp. In addition, since light emitting diodes have a higher forward voltage threshold than other types of diodes such as general-purpose rectifying diodes, various types of discharge end voltages differ by configuring the unidirectional element D using light emitting diodes. The secondary battery B can be flexibly handled.

In addition, since the light-emitting diode consumes relatively larger power than other types of diodes, the light-emitting diode used as the unidirectional element D can function as a discharge element that replaces the discharge element R or assists the discharge element R. It is. When the light emitting diode is replaced with the discharge element R as in the former case, the number of components of the discharge circuit 1 can be reduced and the manufacturing process can be simplified. Further, when the light emitting diode functions as a discharge element that assists the discharge element R as in the latter case, the consumption of energy during discharge can be distributed between the discharge element R and the unidirectional element D. The reliability of R and the unidirectional element D can be improved.

Also, as shown in FIG. 6, the unidirectional element D connects one or more diodes d (1) to d (n) and one or more light emitting diodes led (1) to led (n) in series. You may comprise by. By doing so, the degree of freedom in setting the discharge stop voltage is increased, and it is possible to flexibly cope with various secondary batteries B having different discharge end voltages. The connection order is not limited to that shown in FIG.

FIG. 7 shows a balance correction circuit 70 that corrects the cell balance of an assembled battery composed of a plurality of secondary batteries B1 to Bn, as an application example of the discharge circuit 1. The balance correction circuit 70 includes a plurality of discharge circuits 1 (discharge circuit 1 shown in FIG. 1) provided for each of the secondary batteries B1 to Bn. More specifically, the balance correction circuit 70 is connected between the respective terminals of the secondary batteries B1 to Bn of the assembled battery composed of the plurality of secondary batteries B1 to Bn connected in series. The switch elements S1 to Sn that are connected in series to the discharge elements R1 to Rn and control the current flowing through the discharge elements R1 to Rn, respectively, and the discharge elements R1 to Rn and the switch elements S1 to Sn are connected in series, Each of the secondary batteries B1 to Bn includes one or more unidirectional elements D1 to Dn each having a forward voltage threshold value equal to or higher than a discharge end voltage. The secondary batteries B1 to Bn are provided with voltage sensors M1 to Mn for measuring the respective battery voltages.

The control circuit C turns on and off the switches S1 to Sn in accordance with the battery voltages of the secondary batteries B1 to Bn input from the voltage sensors M1 to Mn, thereby causing a mediating element (not shown) between the secondary batteries B1 to Bn. Energy is transferred via an inductor, a transformer, etc., thereby equalizing the battery voltages of the secondary batteries B1 to Bn. Examples of circuits that perform such operations are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-185229 and 11-176483.

In the balance correction circuit 70 having the above configuration, for example, even when the switch elements S1 to Sn are short-circuited or the control circuit C is faulty, the secondary batteries B1 to Bn are each discharged twice. When the battery voltages of the secondary batteries B1 to Bn become equal to the forward voltage threshold values of the unidirectional elements D1 to Dn respectively provided, the batteries are automatically stopped. Therefore, any secondary battery B1 to Bn does not overdischarge.

The configuration of the discharge circuit 1 used in the balance correction circuit 70 is not necessarily limited to the discharge circuit 1 shown in FIG. 1. For example, all or part of the discharge circuit 1 included in the balance correction circuit 70 is shown in FIGS. Any one of the circuits shown in FIG. When the discharge circuit 1 shown in FIGS. 4 to 6 is used, the state of discharge of each of the secondary batteries B1 to Bn constituting the assembled battery can be easily confirmed visually.

The balance correction circuit 70 is, for example, a power storage device (an electric vehicle, a hybrid vehicle, an electric motorcycle, a railway vehicle, a lift, a power storage device for system linkage, a personal computer, a notebook computer, a mobile phone, a smartphone using an assembled battery. , PDA devices, etc.). The balance correction circuit 70 may be provided separately from the assembled battery, or may be integrated with the assembled battery to constitute a power storage device (battery pack) or the like.

The above description is intended to facilitate understanding of the present invention and is not intended to limit the present invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.

1 discharge circuit, B secondary battery, R discharge element, D unidirectional element, d diode, led light emitting diode, C control circuit, 60 balance correction circuit

Claims (8)

1. A discharge element connected between terminals of the secondary battery;
   A switch element connected between the terminals of the secondary battery in series with the discharge element and controlling a current flowing through the discharge element;
   A unidirectional element connected in series with the discharge element and the switch element between the terminals of the secondary battery and having a forward voltage threshold equal to or higher than a discharge end voltage of the secondary battery. Secondary battery discharge circuit.
2. 2. The discharge circuit according to claim 1, wherein the unidirectional element includes one or more diodes connected in series.
3. 2. The discharge circuit according to claim 1, wherein the unidirectional element includes one or more light emitting diodes connected in series.
4. 2. The secondary battery according to claim 1, wherein the unidirectional element includes one or more diodes and one or more light emitting diodes connected in series. Discharge circuit.
5. 5. The discharge circuit according to claim 3 or 4, wherein the light emitting diode functions as the discharge element.
6. A discharge element connected between respective terminals of the secondary battery of the assembled battery composed of a plurality of secondary batteries connected in series, connected in series with each of the discharge elements, and controls a current flowing through the discharge element. A switching element that is connected to each other in series with the discharge element and the switch element, and includes one or more unidirectional elements having a forward voltage threshold equal to or higher than a discharge end voltage of the secondary battery. A plurality of discharge circuits;
   A voltage sensor for measuring a voltage of each of the plurality of secondary batteries;
   A balance correction circuit comprising: a control circuit that turns on and off each of the switch elements in accordance with a measurement value of the voltage sensor in order to equalize the voltages of the plurality of secondary batteries.
7. A power storage device comprising the secondary battery according to any one of claims 1 to 5 and the discharge circuit.
8. A power storage device comprising the assembled battery according to claim 6 and the balance correction circuit.

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