JP2008159298A - Power source system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source system excellent in reliability, capable of utilizing an alkaline storage battery for a long service life as a main power source in the real usage environment of an HEV. <P>SOLUTION: The power source system is equipped with: a main source comprising an alkaline storage battery; a charging/discharging circuit controlling the charge and discharge of the main source; a voltage sensor detecting the voltage of the main source; an SOC detector sequentially checking a charging level from the voltage detected by the voltage sensor; and a controller recognizing the charging level checked by the SOC detector as a management-required condition when the charging level is not less than A1 and its variation is not more than A2, and setting the level below A1 by discharging the main source using the charging/discharging circuit when the management-required condition continues longer than a predetermined time T1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply system using an alkaline storage battery as a main power source, and more particularly to a technique for optimizing the storage state of an alkaline storage battery and extending its life.

  Demand for alkaline storage batteries such as nickel metal hydride storage batteries is increasing mainly in hybrid vehicles (hereinafter abbreviated as HEV) and industrial applications (emergency power supply, etc.). Especially in HEV, since the alkaline storage battery, which is an auxiliary power source, requires continuous assistance in driving the motor (discharge), the charge depth (hereinafter referred to as SOC, 100% when fully charged and 0% when fully discharged) is defined. (Numericalization) is often increased (specifically, SOC = 80%).

By the way, deterioration accompanying the charge / discharge cycle is mentioned as one of the life deterioration factors of the alkaline storage battery using nickel hydroxide as the positive electrode active material. This is due to a phenomenon in which low-density γ-NiOOH is generated in the active material by repeated charge and discharge, and the positive electrode swells while taking in the electrolytic solution, thereby depleting the electrolytic solution in the separator. Such deterioration is likely to occur when SOC is used in the range of 0 to 100%. Therefore, it is desirable to use SOC in the range of about 20 to 80% particularly in HEV applications where a long life is required. (For example, Patent Document 1).
JP-A-11-187777

  However, even if the upper limit value of the SOC is set to 80%, low density γ-NiOOH is generated depending on the situation, and as a result, deterioration due to swelling of the positive electrode occurs. Specifically, although there is no problem when the alkaline storage battery is repeatedly charged and discharged in a short time, if the alkaline storage battery is stored without being charged and discharged in a state where the SOC of the alkaline storage battery is close to 80%, the above-described problem occurs frequently. Since it is common not to use HEV for a long period of time, it is necessary to avoid adverse effects caused by behavior different from experimental data obtained by repeated charging and discharging in a short time.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly reliable power supply system that can extend the life of an alkaline storage battery as a main power supply in an HEV actual use environment.

  In order to solve the above problems, a power supply system of the present invention includes a main power source made of an alkaline storage battery, a charge / discharge circuit that controls charging and discharging of the main power source, a voltage sensor that detects the voltage of the main power source, and a voltage sensor. The SOC detection unit that sequentially reads the charging depth from the voltage detected by the battery, and the state in which the charging depth read by the SOC detection unit exceeds A1 and the variation range of the charging depth is A2 or less is recognized as a management required state. And a control unit that reduces the charging depth to A1 or less by discharging the main power source using the charging / discharging circuit when it continues beyond the predetermined time T1.

  When the main power supply is not used, the fluctuation range of the SOC becomes small. Therefore, the fluctuation range of the charging depth is recognized as a management requirement state in which the main power source is placed in the storage state, and this management requirement state is When the main power supply is forcibly discharged using the charge / discharge circuit when it continues beyond a predetermined time, deterioration due to swelling of the positive electrode can be suppressed, and the life of the main power supply can be extended.

  As described above, according to the present invention, the life of the alkaline storage battery as the main power source can be extended, and thus the reliability of the power supply system in HEV applications can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  The first invention sequentially determines a main power source composed of an alkaline storage battery, a charge / discharge circuit for controlling charging and discharging of the main power source, a voltage sensor for detecting the voltage of the main power source, and a charging depth from the voltage detected by the voltage sensor. The SOC detection unit to be read and the state where the charge depth read by the SOC detection unit exceeds A1 and the fluctuation range of the charge depth is A2 or less are recognized as the management required state, and this management required state has continued for a predetermined time T1. The present invention relates to a power supply system including a control unit that sometimes lowers the charging depth to A1 or less by discharging a main power supply using a charge / discharge circuit.

  FIG. 1 is a block diagram showing an example of the configuration of the power supply system of the present invention. A main power source 1 made of an alkaline storage battery is connected in parallel with the CPU 2. The CPU 2 includes a voltage sensor that detects the voltage of the main power source 1, an SOC detection unit that sequentially reads the charging depth from the voltage detected by the voltage sensor, and the main power source that is discharged according to the charging depth read by the SOC detection unit. And a control unit.

  The function of the control unit will be further described in detail. When the SOC read by the SOC detection unit is higher than the predetermined value A1 and the fluctuation range of the SOC is smaller than the predetermined value A2, the control unit recognizes the main power supply 1 as a management required state that should be forcibly discharged. When the management state continues beyond the predetermined time T1, the control unit discharges the main power source 1 using the charge / discharge circuit to make the charging depth A1 or less. Here, the charge / discharge circuit includes switches 5 and 6 that open and close according to a command from a control unit included in the CPU 2, a generator 3 connected to the switch 5, and a load 4 connected to the switch 6.

  An example of the SOC behavior of the power supply system used for HEV is shown in FIG. The regenerative energy from the combustion energy or the brake is converted into electric energy by the generator 3. In the actual use state, both the switches 5 and 6 are turned on, and charging is performed in which the current from the generator 1 is supplied to the main power source 1 according to the amount of electricity to be supplied to the load 4, and the current is generated by the generator 3 and the main power source 1. Are frequently repeated to the load 4 (corresponding to rapid start, acceleration, climbing, etc.). However, when the HEV is in an unused state (for example, when the vehicle is stopped), the main power supply 1 is left unattended regardless of the SOC value. Here, as shown in FIG. 2A, when the SOC is in a required management state where the SOC is larger than the predetermined value A1, and this required management state continues beyond the predetermined time T1, as described above, the low density γ -NiOOH is easily generated, and there is a concern about deterioration of the main power source 1 due to swelling of the positive electrode. In the power supply system of the present invention, if it is detected that the fluctuation range of the SOC is smaller than the predetermined value A2 (that is, the unused state), the control unit commands, and only the switch 6 is turned on while the switch 5 is turned off. As shown in 2 (b), the SOC of the main power supply 1 is lowered to a predetermined value A1 or less using the load 4. By this operation, it is possible to avoid a region where γ-NiOOH is easily generated at the positive electrode, so that deterioration of the main power supply 1 can be suppressed.

  The configuration illustrated in FIG. 1 is an example, and the voltage sensor, the SOC detection unit, and the control unit may be configured separately.

The second invention is characterized in that A1 is set to 20 to 70% based on the first invention. If A1 is made excessively small, the stored electric energy is extremely reduced and the role as a power source is lowered. On the other hand, if A1 is excessively increased, the deterioration due to the generation of γ-NiOOH described above cannot be prevented sufficiently.

  The third invention is characterized in that A2 is set to 0 to 2% based on the first invention. It is not preferable to treat the SOC variation in which A2 exceeds 2% as an unused state because it becomes difficult to distinguish the actual usage state.

  The fourth invention is characterized in that T1 is set to 1 to 3 hours based on the first invention. If T1 is excessively small, even a short pause in the actual use state will be mistaken as an unused state. On the other hand, if T1 is excessively increased, the above-described production of γ-NiOOH is promoted, which is not preferable.

  A nickel hydride storage battery or a nickel cadmium storage battery can be selected as the alkaline storage battery constituting the main power source 1. Both positive electrodes have nickel hydroxide as the active material, and cobalt, cobalt compounds, light rare earth compounds, zinc oxide, etc. are added as additives, and then filled into the three-dimensional metal porous body or the two-dimensional metal porous body. Sintered into a structure. The negative electrode is a hydrogen storage alloy in the case of a nickel metal hydride storage battery, and in the case of a nickel cadmium storage battery, cadmium is used as an active material, and a carbon material and various binders are added as additives and then filled into a three-dimensional metal porous body. Alternatively, it is configured by being applied to a two-dimensional metal porous body. An electrode group is formed by winding or laminating the positive electrode and the negative electrode through a separator typified by a polyolefin non-woven fabric. After inserting the electrode group into a cylindrical or rectangular battery case, An alkaline storage battery is configured by injecting an electrolytic solution.

  Examples of the present invention will be described in detail below. Needless to say, the present invention is not limited to this embodiment.

(Example 1)
A long positive electrode using nickel hydroxide as an active material and a long negative electrode using a hydrogen storage alloy as an active material are wound through a separator made of a sulfonated polypropylene non-woven fabric, and the electrode group is Configured. This electrode group was inserted into a cylindrical battery case having an inner diameter of 30 mm and a length of 60 mm, and an electrolyte mainly composed of potassium hydroxide was injected and sealed to obtain a nickel hydride storage battery having a nominal capacity of 6 Ah. This nickel metal hydride storage battery was connected in series in 12 cells to serve as the main power source.

  A power supply system similar to that shown in FIG. 1 is configured using this main power supply. If the SOC fluctuation range A2 is 1% or less as a condition for forced discharge, the power supply system is continued as it is, and when the power supply is left for 2 hours. (T1 = 2 hours) It was input to the control section so that discharging was performed until SOC reached 50% at 3A (A1 = 50%). This power supply system is referred to as Example 1.

(Examples 2 to 5)
A power supply system configured in the same manner as in Example 1 was implemented except that A1 was 15% (Example 2), 20% (Example 3), 70% (Example 4), and 75% (Example 5). Examples 2 to 5.

(Examples 6 to 7)
Except that T1 was set to 3 hours (Example 6) and 3.5 hours (Example 7), the power supply system configured in the same manner as Example 1 is referred to as Examples 6-7.

(Comparative example)
A power supply system configured in the same manner as in Example 1 is used as a comparative example except that the forced discharge as shown in Example 1 is not performed.

  The power supply system described above was evaluated by the following method. The results are shown in (Table 1).

(Discharge capacity measurement)
Each power supply system was charged for 1.6 hours at 3 A from a completely discharged state (SOC 80%), and after the power supply was brought into a management-required state, it was left in a 45 ° C. environment for 10 hours. In addition, about each Example, forced discharge was performed according to each setting condition during this leaving. Further, after being left standing, discharging was performed at 3A until reaching 12V. This charge / discharge cycle was repeated 300 times, and the value obtained by dividing the finally obtained discharge capacity α by the theoretical capacity β obtained by multiplying A1 by 6 Ah is shown in Table 1 as a measure of life characteristics.

本発明に示す強制放電を行わなかった比較例は、寿命特性が極端に低下した。これは放置中に正極でγ−ＮｉＯＯＨが顕著に生成したためである。この比較例に対し、各実施例は良好な寿命特性を示した。ただしＡ１が高い実施例５は寿命特性がやや低下した。またＡ１が低い実施例２については、寿命特性は良好なものの、ＳＯＣ自体が低すぎるので残存容量が低いという課題が生じた。よって強制放電後のＳＯＣであるＡ１は２０〜７０％が好ましいことが判る。また、強制放電を実施してもＴ１が長い実施例７については放電容量がやや低下した。よって要管理状態と認定して強制放電を実施するまでの時間Ｔ１は３時間以下が好ましいことが判る。

The comparative example in which the forced discharge shown in the present invention was not performed had extremely deteriorated life characteristics. This is because γ-NiOOH was remarkably generated at the positive electrode during standing. In contrast to this comparative example, each example exhibited good life characteristics. However, in Example 5 where A1 was high, the life characteristics were slightly deteriorated. Moreover, about Example 2 with low A1, although the lifetime characteristic was favorable, since the SOC itself was too low, the subject that residual capacity was low arose. Therefore, it can be seen that A1 which is the SOC after the forced discharge is preferably 20 to 70%. Moreover, even if forced discharge was implemented, about Example 7 with long T1, discharge capacity fell a little. Therefore, it can be seen that the time T1 from the recognition of the management required state to the forced discharge is preferably 3 hours or less.

  In addition to this example, it was confirmed that if the SOC fluctuation range A2 exceeds 2%, forced discharge is performed during weak charge / discharge in the actual use state. Therefore, A2 is preferably 0 to 2%. Similarly, when T1 was set to less than 1 hour, a short pause in the actual use state was mistaken as an unused state, and it was confirmed that forced discharge was performed. Therefore, it is preferable that the time T1 from the recognition of the management required state to the forced discharge is 1 hour or more.

The block diagram which shows an example of a structure of the power supply system of this invention (A) The figure which shows an example of the behavior of SOC of the conventional power supply system, (b) The figure which shows an example of the behavior of SOC of the power supply system of this invention

Explanation of symbols

1 Main power 2 CPU
3 External power supply 4 Load 5 Switch 6 Switch

Claims (4)

A main power source comprising an alkaline storage battery;
A charge / discharge circuit for controlling charging and discharging of the main power source;
A voltage sensor for detecting the voltage of the main power supply;
An SOC detector that sequentially reads the charging depth from the voltage detected by the voltage sensor;
When the state of charge depth read by the SOC detection unit exceeds A1 and the variation range of the charge depth is A2 or less is recognized as a management required state, the charge / discharge is performed when the management required state continues for a predetermined time T1. A control unit that reduces the charging depth to A1 or less by discharging the main power supply using a circuit;
Having a power system. The power supply system according to claim 1, wherein the A1 is 20 to 70%. The power supply system according to claim 1, wherein the A2 is 0 to 2%. The power supply system according to claim 1, wherein the T1 is set to 1 to 3 hours.

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