JP2011055592A - Secondary cell and method for charging and discharging the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary cell which charges and discharges for reducing the variable SOC without wasting electric energy. <P>SOLUTION: A secondary cell configured by connecting a plurality of unit cells 20 and charging and discharging circuits 30 in series includes; charging and discharging circuits (a chopper circuit, a smoothing capacitor, and a control circuit) which are correspondingly provided to the unit cells 20 and output a predetermined voltage by discharging unit cells 20 or charging the unit cells 20 with a predetermined charge current; and control units (a switch 40, an operational amplifier 50, an A/D converting circuit 60, and an MPU70) which estimate the state of charge (SOC) of the unit cells 20 and operate the charging and discharging circuits 30 so that the discharge power from a unit cell 20 higher in charging rate may be larger at discharge than the discharge power from a unit cell 20 lower in charging rate and that the charge power to a unit cell 20 higher in charging rate may be smaller at discharge than the charge power to a unit cell 20 lower in charging rate based on the estimated charging rate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a chargeable / dischargeable secondary battery used for an electric vehicle, a hybrid vehicle, and the like, and a charge / discharge method thereof.

  As a conventional technique, a battery device described in Patent Document 1 is known. A battery device constituted by a chargeable / dischargeable secondary battery is constituted by connecting a plurality of unit cells (unit cells) such as lithium ion batteries in series. Since the unit cells vary, the charge rate (SOC: State of Charge) of each unit cell differs even when charging / discharging with the same current. When the variation in the SOC of the unit cell becomes large, a unit cell that is overdischarged or overcharged is generated, and there is a possibility that problems such as cell breakage or capacity reduction may occur.

  Therefore, in the technique disclosed in Patent Document 1, the voltage of the unit cell is measured by an A / D converter, and the SOC is estimated. When the SOC variation is large, the discharge circuit connected in parallel to the unit cell having a high SOC is turned on to discharge, thereby correcting the SOC variation.

  As shown in FIG. 6, the conventional battery system as a whole has a DC / DC converter 200 connected to the output side of the battery device 100, and a load 80 is required by the DC / DC converter 200 during discharging. The battery device 100 supplies power to the load 80 by stepping up or down to a certain voltage. At the time of charging, the voltage supplied from the load 80 side by the DC / DC converter 200 is stepped up or down to a constant voltage to charge the battery device 100.

JP 2000-92732 A

  In the above-described conventional technology, the variation in SOC is corrected by discharging electric energy stored in a unit cell having a high SOC by a discharge circuit. However, discharging means that electric energy is consumed as heat, resulting in a waste of electric energy and a problem that efficiency of using electric energy is lowered.

  An object of the present invention is to provide a secondary battery and a charge / discharge method thereof that can charge / discharge while reducing variation in SOC without wasting electric energy.

  In order to solve the above-described problem, one embodiment of the present invention is a secondary battery configured by connecting a plurality of units each including a unit cell and a charge / discharge circuit in series, and is provided corresponding to each unit cell. A charge / discharge circuit that discharges from each unit cell and outputs a predetermined discharge voltage or charges each unit cell with a predetermined charging current, and estimates the charging rate of each unit cell Based on the charged rate, the discharge power from the unit cell with a high charge rate is higher than the discharge power from the unit cell with a low charge rate during discharge, and the charge power to the unit cell with a high charge rate is higher during charge. And a control unit that operates the charge / discharge circuit so as to be smaller than the charge power to the unit cell having a low charge rate.

  Another aspect of the present invention is a secondary battery charge / discharge method configured by connecting a plurality of units each including a unit cell and a charge / discharge circuit in series, and estimating a charge rate of each unit cell. In addition, based on the estimated charging rate, discharging is performed such that the discharging power from the unit cell having a high charging rate is larger than the discharging power from the unit cell having a low charging rate. Each unit cell is charged so that the charging power to the unit cell with a high rate is smaller than the charging power to the unit cell with a low charging rate.

  According to the present invention, there is an effect that charging and discharging can be performed while reducing variation in SOC without wasting electric energy.

It is a block diagram which shows the battery system in this Embodiment. It is a circuit diagram which shows the power converter circuit in this Embodiment. It is a block diagram which shows the modification 1 of this Embodiment. It is a block diagram which shows the modification 2 of this Embodiment. It is a block diagram which shows the modification 3 of this Embodiment. It is a block diagram which shows the conventional battery system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a battery system composed of secondary batteries in the embodiment of the present invention. The secondary battery constituting the battery device 100A is configured by connecting a plurality (N) of unit cells 20 such as lithium ion batteries in series to a load 80 via a charge / discharge circuit 30 that is a DC / DC converter. The A current sensor 90 is introduced between the load 80 and the battery device 100 </ b> A, and the load current IG measured by the current sensor 90 is input to the MPU 70. A differential amplifier 50 is connected to both ends of the unit cell 20 via the switch 40 in order to perform voltage measurement, and the voltage amplified by the differential amplifier 50 is supplied to the MPU (Micro Processing) via the A / D conversion circuit 60. Unit) 70. Further, the MPU 70 is connected to each charge / discharge circuit 30 through a signal line SL, and needs a value of a terminal current (charge / discharge current of each unit cell) I1 of each charge / discharge circuit 30 and a voltage V2 between terminals on the load side. Is input and stored in response to.

  The charging / discharging circuit 30 only needs to be configured to determine the output voltage on the load side during discharging and to determine the charging current on the unit cell side during charging according to an instruction from the MPU 70. For example, what is shown by Unexamined-Japanese-Patent No. 2005-295671 is applicable.

  FIG. 2 shows a circuit example to which the configuration shown in the above publication is applied. The charge / discharge circuit 30 includes a chopper circuit 1, two smoothing capacitors C 1 and C 2 arranged individually at input / output terminals thereof, and a control circuit 11.

The chopper circuit 1 includes a power supply side half bridge circuit 2, a load side half bridge circuit 3,
A reactor 4 is provided.

  The power supply side half bridge circuit 2 includes a power supply side switching element 6 of the upper arm whose high potential side electrode terminal is connected to the positive terminal of the unit cell 20, and a low potential side of the unit cell 20 connected in series to the switching element 6. The power supply side switching element 7 of the lower arm connected to the negative electrode terminal of the unit cell 20 is provided with an electrode terminal.

  The load-side half-bridge circuit 3 has a high-potential side main electrode terminal opposite to the unit cell 20 of the charge / discharge circuit 30 corresponding to the high-potential side terminal of the load 80 or the negative terminal of the adjacent unit cell 20 connected in series. The load-side switching element 9 of the upper arm connected to the low-potential side terminal that is the terminal of the (load side), the low-potential side main electrode terminal connected in series to the switching element 9 and the negative terminal of the unit cell 20; Connected to the low potential side terminal of the load 80 or the high potential side terminal which is the terminal (load side) opposite to the unit cell 20 of the charge / discharge circuit 30 corresponding to the positive terminal of the unit cell 20 adjacent in series. Load-side switching element 10 of the lower arm.

  Each switching element 6, 7, 9, 10 is subjected to switching control by the control circuit 11. The control circuit 11 acquires these detected values from the current sensor A1 or the voltage sensor V2, transmits them to the MPU 70 as necessary, and calculates and sets the parameter values calculated and set by the MPU 70 according to these values. The chopper circuit 1 is controlled so that the detection values of the sensors match.

  Here, the chopper circuit 1, the two smoothing capacitors C1 and C2, and the control circuit 11 constitute a charge / discharge circuit according to the present invention, and the MPU 70 constitutes a control unit according to the present invention.

Hereinafter, the operation of the present embodiment will be described.
First, the MPU 70 estimates the charging rate (SOC) of each unit cell 20 from the voltage of each unit cell 20 detected via the A / D conversion circuit 60. During discharge (discharge mode) in which the load is driven by the secondary battery, the MPU 70 obtains the optimum output voltage (load side output) of the charge / discharge circuit 30 from the SOC of each unit cell 20, and sets the charge / discharge circuit 30. Set to the control circuit 11 to be configured. When the charging rate of the i-th unit cell 20 among the N unit cells 20 is SOCi, the output voltage (discharge voltage) on the load side of the charge / discharge circuit 30 is V2i, and the supply voltage to the load is VL. ,

VL = ΣV2i
V2i / VL = SOCi / ΣSOCi

  V2i is calculated so that the above holds, and the discharge voltage is set in the control circuit 11 of each charge / discharge circuit 30. Then, the control circuit 11 controls the switching elements 6, 7, 9, and 10 so that the discharge voltage of each charge / discharge circuit 30 becomes the set discharge voltage.

  With this configuration, the output voltage of the charge / discharge circuit 30 connected to the unit cell 20 having a high SOC is set higher than that of the unit cell 20 having a low SOC, so that the power discharged from the unit cell 20 having a high SOC is more SOC. The unit cell 20 having a low value becomes larger than the electric power discharged, and the discharge is performed in the direction of reducing the variation in the SOC.

  On the other hand, at the time of charging using the load as a generator (charging mode), the MPU 70 detects the total charging current IG via the current sensor 90. The charging rate of the N unit cells 20 is SOCi (i = 1 to N), the charging voltage supplied from the outside is VG, the charging current to the battery side of each charging / discharging circuit 30 is I1i, and each unit cell When the voltage of 20 is V1i and the average conversion efficiency of the charge / discharge circuit 30 is η (%),

VG × IG × η / 100 = Σ (V1i × I1i)
I1i / (ΣI1i / N) = 2−SOCi / Σ (SOCi / N)

  I1i is obtained so that the following holds, and the charging current (I1i) is set in the control circuit 11 of each charge / discharge circuit 30. Then, the control circuit 11 controls the switching elements 6, 7, 9, and 10 so that the charging current to each unit cell becomes the set charging current.

  With this configuration, the output current of the charge / discharge circuit 30 connected to the unit cell 20 having a high SOC is set lower than that of the unit cell 20 having a low SOC, and the charging current of the unit cell 20 having a low SOC is more SOC. The charging is performed in the direction of reducing the variation in SOC.

  The MPU 70 measures the voltage of the unit cell constantly or appropriately, and when the voltage exceeds a predetermined value during charging or when the voltage falls below a predetermined value during discharging, the unit cell 20 is connected to the series circuit of the unit. The charge / discharge circuit 30 is set so as to be disconnected from the battery. This can be performed, for example, by turning off the switching elements 6 and 7 of the charge / discharge circuit 30 and turning on the switching elements 9 and 10. As a result, the unit cell 20 having an abnormal voltage can be protected.

  In FIG. 1, the changeover switch 40, the differential amplifier 50, and the A / D conversion circuit 60 are connected in this order in order to measure the voltage of the unit cell 20, but as a first modification of the present embodiment, FIG. As shown in FIG. 3, the differential amplifier 50, the changeover switch 40, and the A / D conversion circuit 60 may be connected in this order.

  Furthermore, as a second modification, as shown in FIG. 4, an A / D conversion circuit 60 may be provided for each unit cell 20 in order to measure the voltage of the unit cell 20.

  Further, as a third modification, as shown in FIG. 5, a temperature sensor TH that detects the temperature of the unit cell 20 is provided for each unit cell 20, and the voltage and temperature of the unit cell 20 are measured to change the temperature of the battery capacity. You may make it perform the estimation with respect to the SOC considered, and protection with respect to the temperature of the unit cell 20. FIG. For example, when the temperature of the unit cell 20 exceeds a predetermined temperature, the unit cell 20 can be protected from being disconnected from the series circuit of the unit. Note that the detection signal of the temperature sensor TH is taken into the MPU 70 as a digital value via the A / D conversion circuit 61.

  1 chopper circuit (charge / discharge circuit), 6, 7, 9, 10 switching element, 11 control circuit (control unit), 20 unit cell, 30 charge / discharge circuit, 40 switch, 50 differential amplifier, 60, 61 A / D Conversion circuit, 70 MPU (control unit), 80 load, C1, C2 smoothing capacitor, TH temperature sensor, A1, 90 current sensor, V2 voltage sensor.

Claims (6)

A secondary battery configured by connecting units consisting of a unit cell and a charge / discharge circuit in series,
A charge / discharge circuit that is provided corresponding to each unit cell and discharges from each unit cell to output a predetermined discharge voltage, or charges each unit cell with a predetermined charging current,
In addition to estimating the charging rate of each unit cell, based on the estimated charging rate, the discharging power from the unit cell having a high charging rate is larger than the discharging power from the unit cell having a low charging rate during discharging. And a control unit that operates the charge / discharge circuit so that the charging power to the unit cell having a high charging rate is smaller than the charging power to the unit cell having a low charging rate. The controller is configured such that, during discharging, the charging rate of N unit cells is SOCi (i = 1 to N), and the discharging voltage from each charging / discharging circuit is V2i.
VL = ΣV2i
V2i / VL = SOCi / ΣSOCi
2. The secondary battery according to claim 1, wherein V2i is calculated so as to hold and the discharge voltage of each charge / discharge circuit is controlled. At the time of charging, the control unit sets the charging rate of the N unit cells to SOCi (i = 1 to N), the charging voltage supplied from the outside is VG, the total charging current supplied from the outside is IG, When the charging current to the battery side of the charging / discharging circuit is I1i, the voltage of each unit cell is V1i, and the average conversion efficiency of the charging / discharging circuit is η (%),
VG × IG × η / 100 = Σ (V1i × I1i)
I1i / (ΣI1i / N) = 2−SOCi / (ΣSOCi / N)
3. The secondary battery according to claim 1, wherein I1i that satisfies is obtained, and the charging current I1i of each charging / discharging circuit is controlled.   The said control part monitors the voltage of each unit cell, and isolate | separates the unit cell which became out of the predetermined voltage range from the series circuit which consists of a some unit, The one of Claim 1 thru | or 3 characterized by the above-mentioned. Secondary battery described in 1. A charge / discharge method of a secondary battery configured by connecting a plurality of units each composed of a unit cell and a charge / discharge circuit in series,
In addition to estimating the charging rate of each unit cell, based on the estimated charging rate, the discharging power from the unit cell having a high charging rate is larger than the discharging power from the unit cell having a low charging rate during discharging. Each unit cell is charged so that the charging power to the unit cell with a high charging rate is smaller than the charging power to the unit cell with a low charging rate during charging. Secondary battery charge / discharge method.   6. The method for charging and discharging a secondary battery according to claim 5, wherein the voltage of each unit cell is monitored, and the unit cell outside the predetermined voltage range is separated from the series circuit composed of a plurality of units.

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