JP5195388B2 - Power storage device - Google Patents

Description

  The present invention relates to a power storage device that stores power in a power storage unit and discharges it when necessary.

  2. Description of the Related Art In recent years, automobiles (hereinafter referred to as vehicles) equipped with an idling stop function for stopping engine driving when the vehicle is stopped for environmental considerations and fuel efficiency improvement are on the market. In such a vehicle, when a starter that consumes a large current intermittently during use is driven, the voltage of the battery temporarily drops. As a result, the supply voltage to other loads such as audio and car navigation also decreases, and the operation may become unstable.

  Also, regarding vehicle braking, various vehicle braking systems from conventional mechanical hydraulic control to electrical hydraulic control have been proposed, but when the battery becomes abnormal, the vehicle braking system operates. There was a possibility of disappearing.

  On the other hand, for example, Patent Document 1 proposes a power storage device as an auxiliary power source for supplying sufficient power to a load when the voltage of the battery temporarily drops or supplying power to the vehicle braking system when the battery is abnormal. ing. Patent Document 1 is shown as a power supply backup unit that supplies electric power to an electronic control unit of a vehicle braking system among battery devices, particularly when the battery is abnormal.

  FIG. 10 is a block circuit diagram of such a power storage device. For example, a large-capacity electric double layer capacitor is used as a power storage element that stores electric power, and a plurality of these are connected to form a capacitor unit 101 as a power storage unit. The capacitor unit 101 is connected to a charging circuit 103 that controls charging and discharging, and a discharging circuit 105. The charging circuit 103 and the discharging circuit 105 are controlled by the microcomputer 107. The microcomputer 107 is connected to a battery voltage detection means 109 for detecting a battery abnormality, and the battery voltage detection means 109 is connected to an FET switch 111 that supplies power of the capacitor unit 101 in the event of an abnormality.

  The power storage device 113 as the power backup unit configured as described above is connected between the battery 115 and the electronic control unit 117, and is controlled to be started and stopped by the ignition switch 119.

  Since the electronic control unit 117 is a vehicle braking system, the electronic control unit 117 must be continuously driven even when the battery 115 becomes abnormal in order to ensure safety. Therefore, if the battery voltage detection means 109 detects an abnormality of the battery 115, the FET switch 111 is turned on to supply the electric power of the capacitor unit 101 to the electronic control unit 117, thereby responding to the abnormality of the battery 115.

In addition, when the use of the vehicle is finished in a state where the battery 115 is normal, the capacitor unit 101 is in a state where electric power is stored. If this is left as it is when the vehicle is not used, the voltage of the capacitor unit 101 gradually decreases due to self-discharge, but a voltage near the rated voltage is applied to the electric double layer capacitor constituting the capacitor unit 101 for a long period of time. As a result, the electric double layer capacitor deteriorates and the life of the capacitor unit 101 is shortened. In order to avoid this, the microcomputer 107 controls the discharge circuit 105 at the end of use of the vehicle to forcibly discharge the power of the capacitor unit 101. As a result, the life of the power storage device 113 is extended.
JP 2005-28908 A

  According to the power storage device 113 described above, the electronic control unit 117 can surely be continuously driven when the battery 115 is abnormal, so that the safety of the vehicle braking system can be secured and the capacitor unit 101 can be discharged at the end of use for a long life. However, it is necessary to fully charge the capacitor unit 101 every time the vehicle is used, and it takes time to complete the start-up.

  Therefore, in order to shorten the startup time, a configuration in which the power of the capacitor unit 101 is discharged to a voltage that does not cause deterioration of the electric double layer capacitor can be considered. Thereby, start-up can be completed earlier than the capacitor unit 101 is completely discharged.

  In order to realize such an operation, the forced discharge of the capacitor unit 101 is terminated based on a voltage in which the deterioration of the capacitor unit 101 hardly progresses in advance (hereinafter referred to as a non-degraded voltage Vh, which is 6 V here). The voltage value may be obtained as the discharge termination voltage Vd and stored in the microcomputer 107, and discharged by the discharge circuit 105 until the voltage of the capacitor unit 101 reaches the discharge termination voltage Vd at the end of vehicle use.

  However, since the self-discharge characteristics differ depending on the usage state of the capacitor unit 101, there are the following problems depending on the value of the discharge termination voltage Vd.

  First, a case where the discharge termination voltage Vd is close to the predetermined voltage Vm (here, full charge voltage, specifically 13 V) of the capacitor unit 101, that is, forcibly discharging to the discharge termination voltage Vdmax will be described with reference to FIG. While explaining. In FIG. 11, the horizontal axis represents time t, and the vertical axis represents the voltage Vc of the capacitor unit 101.

  In FIG. 11, it is assumed that the use of the vehicle is finished at time t2. Until then, electric power is stored in the capacitor unit 101, so that the voltage Vc is stable at the predetermined voltage Vm.

  Here, the characteristic indicated by the thick solid line in FIG. 11 indicates that the period ts when the capacitor unit 101 reaches the predetermined voltage Vm is short, and the characteristic indicated by the thick dotted line indicates that the period ts is long. Therefore, in the case of the characteristic indicated by the bold solid line, the period ts is from the time t1 to the time t2, and the capacitor unit 101 is being charged before the time t1.

  On the other hand, in the case of the characteristic indicated by the thick dotted line, the period ts is between the times t0 and t2, and the period ts is longer than that in the case of the thick solid line characteristic.

  The characteristics after the forced discharge of the capacitor unit 101 in these two types of states will be described below. It is assumed that the voltage Vc of the capacitor unit 101 is discharged to the discharge termination voltage Vdmax by the discharge circuit 105 from time t2 to time t3. At time t2, voltage Vc decreases by a voltage width ΔV determined by the product of the internal resistance value of capacitor unit 101 and the discharge current. Since the voltage drop rate (slope) from the time t2 to the time t3 is controlled by the discharge circuit 105, the characteristics are almost the same in the case of the thick solid line and the thick dotted line.

  Thereafter, when the voltage Vc reaches the discharge termination voltage Vdmax at time t3, the microcomputer 107 stops the operation of the discharge circuit 105 and ends the forced discharge. As a result, the voltage Vc increases by the voltage width ΔV. Thereafter, the voltage Vc decreases with time due to self-discharge of the capacitor unit 101. At this time, when the period ts is short, the decrease in the voltage Vc due to self-discharge is fast as shown in the characteristic of the thick solid line, and when the period ts is long, the decrease in the voltage Vc due to self-discharge is slow as shown in the characteristic of the thick dotted line. Become. The reason for this will be described later.

  With such characteristics, when the period ts is short, the voltage Vc quickly decreases and approaches the non-degraded voltage Vh (6 V), so that the life of the capacitor unit 101 can be extended. However, when the period ts is long, the voltage Vc gradually decreases, so it does not readily approach the non-degraded voltage Vh (6 V). As a result, there is a problem that the period during which the capacitor unit 101 is in a high voltage state becomes long, and the life cannot be extended.

  Then, the case where the discharge termination voltage Vd is separated from the predetermined voltage Vm of the capacitor unit 101, that is, the case where the discharge is forcibly discharged to the discharge termination voltage Vdmin will be described next with reference to FIG. In FIG. 12, the horizontal axis and the vertical axis have the same meaning as in FIG.

  In FIG. 12, the operation from time t0 to t2 is the same as that in FIG. Next, characteristics when the use of the vehicle ends at time t2 and the capacitor unit 101 is forcibly discharged will be described below. From time t2 to t3, the discharge circuit 105 discharges the voltage Vc of the capacitor unit 101 to the discharge termination voltage Vdmin. The slope of the thick solid line is also the case of the thick dotted line as in FIG. Also have almost the same characteristics. Similarly, the voltage Vc decreases by the voltage width ΔV at time t2.

  Thereafter, when the voltage Vc reaches the discharge termination voltage Vdmin at time t3, the forced discharge ends. As a result, the voltage Vc increases by the voltage width ΔV. Thereafter, the voltage Vc decreases with time due to self-discharge of the capacitor unit 101. As in the case of FIG. 11, the rate of decrease at this time is such that when the period ts is short, the voltage Vc decreases rapidly as shown by the characteristic of the thick solid line, and when the period ts is long, it shows the characteristic of the thick dotted line. The decrease in voltage Vc is delayed.

  With such characteristics, when the period ts is long, the voltage Vc gradually decreases and approaches the non-degraded voltage Vh (6 V), so that the life of the capacitor unit 101 can be extended. However, when the period ts is short, the voltage Vc quickly decreases, and thus reaches a voltage lower than the non-degraded voltage Vh (6 V). As a result, the life of the capacitor unit 101 is not shortened, but the voltage Vc of the capacitor unit 101 is reduced more than necessary at the time of restart, so that the start-up time for fully charging the capacitor unit 101 is prolonged. There was a problem.

  Here, the reason why the self-discharge characteristic changes depending on the length of the period ts will be described with reference to FIG. FIG. 13 shows an equivalent circuit diagram of the capacitor. Here, as described above, the capacitor unit 101 has a structure in which a plurality of electric double layer capacitors are connected. Here, however, the connected electric double layer capacitors are combined and treated as equivalent to one capacitor.

  As shown in FIG. 13, the capacitor is considered to be equivalent to a configuration in which a plurality of internal resistance components 121, 122, 123... And capacitance components 131, 132, 133. Here, if the period ts is short, electric power is mainly stored in the capacitive component 131 shown at the top of FIG. 13, and the other capacitive components 132, 133,. This is because the combined resistance value of the internal resistance components 121, 122, 123... Increases as the capacitance components 132, 133. However, the capacity components 132, 133,... Are gradually charged as the period ts becomes longer. Therefore, when the period ts is short, the charging depth is shallow, and when it is long, the depth is deep.

  As a result, in a capacitor with a short period ts, that is, with a shallow charging depth, the capacitance components 132, 133,... Are not charged so much and are mainly charged with the capacitance component 131. The voltage drop becomes faster. On the other hand, in a capacitor with a long period ts, that is, with a deep charging depth, the capacitance components 132, 133,... Are also charged, so that the voltage drop due to self-discharge is delayed.

  From the above, if the discharge termination voltage Vd is set to a value close to the predetermined voltage Vm of the capacitor unit 101, the high voltage application state continues when the vehicle is not used when the period ts during which the capacitor unit 101 is fully charged is long. If the discharge termination voltage Vd is set as a value away from the predetermined voltage Vm, there is a possibility that the deterioration proceeds, and if the period ts is short, the self-discharge proceeds and the voltage Vc decreases more than necessary, and the start-up time There was a problem of becoming longer. This is because the discharge termination voltage Vd is determined as a constant value. Therefore, in the conventional configuration, there is a problem that it is impossible to achieve both the life extension of the capacitor unit 101 and the high-speed activation of the power storage device 113.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a power storage device that can achieve both a long life and high-speed startup of a power storage unit.

In order to solve the conventional problems, a power storage device of the present invention includes a power storage unit including a capacitor, a voltage detection circuit that detects a voltage (Vc) of the power storage unit, and a discharge circuit that forcibly discharges the power storage unit. The voltage detection circuit and a control circuit connected to the discharge circuit, the control circuit forcibly discharging the voltage (Vc) of the power storage unit to a discharge termination voltage (Vd), and then storing the power storage Part is self-discharged, and the discharge termination voltage (Vd) is controlled to increase as the voltage (Vc) of the power storage part decreases rapidly due to the self-discharge of the power storage part. It is.
Further, the control circuit obtains a parameter for changing the self-discharge characteristic of the power storage unit or a parameter value of the self-discharge characteristic, and based on a correlation between the parameter and the discharge termination voltage (Vd), the discharge termination voltage ( Vd) is controlled.
The power storage device includes a power storage unit including a capacitor, a discharge circuit that discharges the power storage unit, and a timer that is connected to the discharge circuit and measures a period (ts) at the start and end of use. And the control circuit controls the discharge circuit to discharge the power storage unit up to a discharge termination voltage (Vd) determined according to the period (ts) after the use ends. Thus, the parameter for changing the self-discharge characteristic is the period (ts).

The power storage device is connected to a power storage unit including a capacitor, a discharge circuit that discharges the power storage unit, a voltage detection circuit that detects a voltage (Vc) of the power storage unit, the discharge circuit, and the voltage detection circuit And a control circuit having a timer for measuring a period (ts) at the start of use and at the end of use. The control circuit is configured to control the power storage unit in the period (ts) after the end of use. The discharge circuit is controlled to discharge the power storage unit to a discharge termination voltage (Vd) determined according to an integrated value (Vt) of the voltage (Vc), and the parameter for changing the self-discharge characteristic is It is an integral value (Vt).

The power storage device is connected to a power storage unit including a capacitor, a discharge circuit that discharges the power storage unit, a voltage detection circuit that detects a voltage (Vc) of the power storage unit, the discharge circuit, and the voltage detection circuit. A voltage per unit time of the power storage unit by detecting at least two points of the voltage (Vc) of the power storage unit detected by the voltage detection circuit after the end of use. The rate of change (Vk) is obtained, the discharge circuit is controlled to discharge the power storage unit to a discharge termination voltage (Vd) determined according to the voltage rate of change (Vk), and the self-discharge characteristic The parameter is the voltage change rate (Vk).

According to the power storage device of the present invention, there is an effect that it is possible to realize a power storage device that can achieve both a long life of the power storage unit and high-speed startup.
Further, since the discharge termination voltage (Vd) is determined according to the period (ts), the voltage (Vc) of the power storage unit due to self-discharge after forced discharge can be brought close to the non-degraded voltage (Vh). As a result, it is possible to avoid a situation where the high voltage application state of the power storage unit continues or self-discharge to the extent that it takes time to start up, and a power storage device capable of achieving both a long life and high speed startup of the power storage unit The effect that can be realized is obtained.

In addition , instead of the period (ts), the discharge termination voltage (Vd) is determined according to the integrated value (Vt) of the voltage (Vc) of the power storage unit in the period (ts), so during the period (ts) Even if the voltage (Vc) of the power storage unit changes, the discharge termination voltage (Vd) is determined according to the integrated value (Vt) corresponding to the energy stored in the power storage unit. Therefore, it is possible to achieve an effect of realizing a power storage device that can achieve both a long life of the power storage unit and high-speed startup by a more accurate discharge termination voltage (Vd).

In addition , according to the power storage device, instead of the period (ts), the discharge termination voltage (Vd) is determined according to the voltage change rate (Vk) of the voltage (Vc) of the power storage unit after the end of use. The discharge termination voltage (Vd) is determined without being affected by the change in the voltage (Vc) of the power storage unit during (ts). Therefore, it is possible to achieve an effect of realizing a power storage device that can achieve both a long life of the power storage unit and high-speed startup by a more accurate discharge termination voltage (Vd).

  The best mode for carrying out the present invention will be described below with reference to the drawings. In the following description, a case where the power storage device is applied as a power backup unit for a vehicle braking system will be described.

(Embodiment 1)
1 is a block circuit diagram of a power storage device according to Embodiment 1 of the present invention. FIG. 2 is a correlation diagram of discharge termination voltage Vd with respect to period ts during which voltage is applied to the power storage unit of the power storage device according to Embodiment 1 of the present invention. FIG. 3 is a time-dependent change figure in the voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 1 of this invention. FIG. 4 is a characteristic diagram of the internal resistance value R with respect to the temperature T of the power storage unit of the power storage device according to Embodiment 1 of the present invention. FIG. 5 is a characteristic diagram of the capacitance value C with respect to the temperature T of the power storage unit of the power storage device according to Embodiment 1 of the present invention. In FIG. 1, thick lines indicate power system wirings, and thin lines indicate signal system wirings.

  In FIG. 1, the power storage device 11 is connected between a main power supply 15 and a load 17. The main power source 15 is a battery, and the load 17 is an electronic control unit of the vehicle braking system.

  The power storage device 11 has the following configuration. First, a charging circuit 19 and a main power supply voltage detection circuit 21 for detecting the voltage Vb of the main power supply 15 are connected to the output of the main power supply 15. A power storage unit 23 is connected to the charging circuit 19. The power storage unit 23 uses an electric double layer capacitor (hereinafter referred to as a capacitor) having a rated voltage of 2.2 V as a power storage element for storing electric power, and a plurality of these capacitors (six in this embodiment 1) are connected in series. To cover the necessary power. Therefore, the predetermined voltage Vm of the power storage unit 23 is 13.2 V (= 2.2 V × 6). The power storage unit 23 is not limited to the above-described configuration, and the number of capacitors may be increased or decreased according to the power specifications required for the load 17 or may be connected in series or in parallel.

  The power storage unit 23 is connected to a voltage detection circuit 25 that detects and outputs the voltage Vc, and is connected to a discharge circuit 27 for arbitrarily discharging the power of the power storage unit 23. The discharge circuit 27 is configured to discharge the power storage unit 23 by consuming electric power as heat by flowing a current from the power storage unit 23 through a built-in discharge resistor (not shown). At this time, the discharge current is controlled to be constant.

  Furthermore, one end of a changeover switch 29 for outputting the electric power to the load 17 is connected to the power storage unit 23. Thereby, supply of the electric power of the power storage unit 23 to the load 17 is controlled.

  The anodes of the first diode 31 and the second diode 33 are connected to the other end of the changeover switch 29 and the main power supply voltage detection circuit 21, respectively. The cathodes of the first diode 31 and the second diode 33 are both connected to the load 17.

  Further, the power storage unit 23 is provided with a temperature sensor 35 for detecting a temperature T in the vicinity thereof.

  The charging circuit 19, the main power supply voltage detection circuit 21, the voltage detection circuit 25, the discharge circuit 27, the changeover switch 29, and the temperature sensor 35 are also connected to a control circuit 37 including a microcomputer and peripheral circuits. From this, the control circuit 37 reads the voltage Vb of the main power supply 15 from the main power supply voltage detection circuit 21, the voltage Vc of the power storage unit 23 from the voltage detection circuit 25, and the temperature T from the temperature sensor 35, respectively. Further, the charging circuit 19 is controlled by transmitting the charging control signal Ccnt, the discharging circuit 27 is transmitted by transmitting the discharging control signal Dcnt, and the on / off of the changeover switch 29 is controlled by transmitting the on / off signal Sof. Further, the control circuit 37 has a function of performing transmission / reception with a vehicle-side control circuit (not shown) by a data signal. Furthermore, the control circuit 37 includes a timer and can measure an arbitrary period.

  Next, the operation of the power storage device 11 will be described.

  First, when an ignition switch (not shown) is turned on to start the vehicle, the engine is driven, and at the same time, the control circuit 37 transmits a charge control signal Ccnt to charge the power storage unit 23 to the charging circuit 19. Thereby, the electric power of the main power supply 15 is charged to the power storage unit 23 with the constant current value I.

  At this time, the control circuit 37 obtains the internal resistance value R and the capacitance value C of the power storage unit 23 as follows.

  First, for the internal resistance value R, the control circuit 37 stops charging while the power storage unit 23 is being charged with the constant current value I, the voltage difference ΔV1 before and after the interruption is obtained by the voltage detection circuit 25, and the voltage difference ΔV1. Is calculated by dividing by a constant current value I. That is, the internal resistance value R is obtained from R = ΔV1 / I. The charging interruption time is determined in advance as the shortest time during which the voltage difference ΔV1 can be detected with high accuracy. In the first embodiment, the charging interruption time is set to 0.1 second.

  Next, for the capacitance value C, while the control circuit 37 is charging the power storage unit 23 with the constant current value I, the voltage detection circuit 25 obtains the change voltage difference ΔV2 during the predetermined time interval Δt in the power storage unit 23 and determines the constant value C. It is obtained by multiplying the current value I by a predetermined time interval Δt and dividing by the change voltage difference ΔV2. That is, the capacitance value C is obtained from C = I · Δt / ΔV2. Note that the predetermined time interval Δt is also determined in advance as the shortest time during which the change voltage difference ΔV2 can be detected with high accuracy, in the same way as the charging interruption time. In the first embodiment, the charging interruption time is set to 0.1 second, similar to the charging interruption time.

  The reason why the internal resistance value R and the capacitance value C of the power storage unit 23 are obtained as described above is that the correlation between the period ts and the discharge termination voltage Vd for determining the discharge termination voltage Vd described later is the internal resistance. This is because it varies depending on the value R and the capacitance value C. Since the internal resistance value R and the capacitance value C vary depending on the ambient temperature of the power storage unit 23 and the degree of deterioration, the discharge termination voltage Vd is corrected by correcting the discharge termination voltage Vd according to the current internal resistance value R and capacitance value C. Can be determined with high accuracy.

  Furthermore, since the degree of progress of deterioration can be understood from the internal resistance value R and the capacitance value C, if any of the internal resistance value R and the capacitance value C exceeds the respective deterioration limit values and deteriorates to a state where it cannot be used as the power storage device 11. By transmitting the deterioration signal as the data signal data to the vehicle-side control circuit, the driver can be warned of the deterioration of the power storage device 11 and can be repaired.

  Even after obtaining the internal resistance value R and the capacitance value C, the control circuit 37 controls the charging circuit 19 to perform charging until full charge while detecting the voltage Vc of the power storage unit 23 by the voltage detection circuit 25. At this time, the control circuit 37 turns off the changeover switch 29 so that the charging current to the power storage unit 23 does not flow to the load 17 side.

  When the power storage unit 23 reaches full charge, the charge is completed, and the charging circuit 19 performs constant voltage control in order to maintain the predetermined voltage Vm (= full charge voltage, which is 13.2 V). The control circuit 37 starts measuring the period ts during which the power storage unit 23 is applied to the predetermined voltage Vm, with the time when the power storage unit 23 reaches the predetermined voltage Vm as the start of use of the power storage device 11. Note that, when the power storage device 11 is used as a power backup system as in the first embodiment, the power storage unit 23 does not supply power to the load 17 as long as the main power supply 15 maintains a normal state. Normally, the period from the time when charging of the power storage unit 23 is completed to the time when the vehicle is finished is measured as a period ts. Thereafter, the control circuit 37 monitors the voltage Vb of the main power supply 15 from the output of the main power supply voltage detection circuit 21.

  In this state, in the unlikely event that the main power supply 15 becomes abnormal while the vehicle is in use, or the power system wiring from the main power supply 15 is disconnected, the power supply from the main power supply 15 to the load 17 is cut off. If this is the case, vehicle braking may not be possible in this state. Therefore, when the control circuit 37 detects a decrease in the voltage Vb of the main power supply 15 due to the abnormality, the control circuit 37 immediately turns on the changeover switch 29 to supply a stable voltage to the load 17. As a result, electric power is supplied from the power storage unit 23 to the load 17 in the direction of the arrow written as the discharge path in FIG. At this time, since the voltage Vb of the main power supply 15 is decreasing, the voltage of the load 17 is lower than the voltage Vc of the power storage unit 23. Accordingly, the first diode 31 is turned on, and the power of the power storage unit 23 is preferentially supplied to the load 17. Thereby, even if the main power supply 15 becomes abnormal, the load 17 can be continuously driven, and the vehicle can be braked. The second diode 33 connected to the main power supply voltage detection circuit 21 is turned off because the voltage Vb of the main power supply 15 is lowered, and the charging circuit 19 includes a backflow prevention means. The power of the power storage unit 23 is not supplied to the main power supply 15.

  Next, the operation at the end of vehicle use, which is a feature of the first embodiment, will be described. As described above, the control circuit 37 measures the period ts from the time when the power storage unit 23 is charged to the predetermined voltage Vm by the charging circuit 19 before the end of use. , The control circuit 37 stops measuring the period ts. Accordingly, the period ts is from when the power storage unit 23 is charged to the predetermined voltage Vm (at the start of use) until the end of use.

  Next, after the use of the vehicle is finished, the control circuit 37 determines the discharge termination voltage Vd according to the period ts as follows.

  First, the control circuit 37 takes in the current temperature T of the power storage unit 23 from the temperature sensor 35. As a result, three parameters for determining the discharge termination voltage Vd with high accuracy, that is, the internal resistance value R, the capacitance value C, and the temperature T are obtained.

  Next, the discharge termination voltage Vd is obtained from FIG. Here, in FIG. 2, the horizontal axis represents the period ts, and the vertical axis represents the discharge termination voltage Vd. In determining the discharge termination voltage Vd, in order to make the voltage Vc of the power storage unit 23 smaller than the non-deteriorated voltage Vh when the vehicle is not in use, the characteristic of the thick solid line in FIG. 11 is used when the period ts is short. The discharge termination voltage Vd is increased as shown by Vdmax, and when the period ts is long, the discharge termination voltage Vd is reduced as shown by Vdmin in order to achieve the characteristics shown by the thick dotted line in FIG. Therefore, as shown in FIG. 2, the discharge termination voltage Vd may be determined to be smaller as the period ts is longer and larger as the period ts is shorter. The non-deteriorated voltage Vh in the first embodiment is defined as an applied voltage of the power storage unit 23 that can ensure the required life (for example, 10 years) of the capacitor when the vehicle is not used. Specifically, the non-deteriorated voltage Vh was 6V. That is, when the voltage Vc of the power storage unit 23 is about 6V when the vehicle is not used, six capacitors are connected in series, so that the applied voltage per capacitor is about 1V. Therefore, the capacitor hardly deteriorates and the power storage device 11 can be used for 10 years, which is the vehicle life.

  Here, when the discharge termination voltage Vd becomes smaller than the non-degraded voltage Vh, the power storage unit 23 further undergoes self-discharge, so that the voltage Vc of the power storage unit 23 increases the non-degraded voltage Vh as shown by a thick solid line in FIG. It takes less time to fully charge the power storage unit 23 at the next startup. In order to avoid this, as shown in FIG. 2, the lower limit value of the discharge termination voltage Vd is set to the non-degraded voltage Vh. Therefore, no matter how long the period ts is, the discharge termination voltage Vd does not become less than the non-deteriorated voltage Vh.

  From the above, basically, the correlation characteristics of FIG. 2 are obtained in advance and stored in a memory built in the control circuit 37, and the discharge termination voltage Vd corresponding to the measured period ts is determined according to the characteristics of FIG. do it.

  However, the correlation in FIG. 2 varies depending on the internal resistance value R, the capacitance value C, and the temperature T described above. That is, the correlation in FIG. 2 shifts upward in FIG. 2 as the internal resistance value R is larger, the capacitance value C is smaller, and the temperature T is higher. Therefore, a plurality of correlations as shown in FIG. 2 are obtained in advance for each combination of the values of the internal resistance value R, the capacitance value C, and the temperature T, for example, by the least square method. The approximate function formula is stored in the memory of the control circuit 37.

  Note that a voltage change of the voltage width ΔV occurs at the start and end of discharge, and this voltage width ΔV is determined by the product of the internal resistance value R and the discharge current as described above. Here, since the discharge current by the discharge circuit 27 is controlled to be constant, the voltage width ΔV corresponding to the deterioration of the capacitor and the change of the internal resistance value R due to the temperature T is obtained in advance and is included. Correlation has been determined.

  Further, as the characteristics of the capacitor, the lower the temperature T, the slower the progress of the deterioration. Therefore, the non-deteriorating voltage Vh may be increased accordingly. Therefore, the correlation may be obtained so as to correct the fluctuation of the non-deteriorated voltage Vh due to the temperature T.

  From the above, since the internal resistance value R, the capacitance value C, and the temperature T are obtained, an approximate function equation stored in the memory is selected according to the combination, and the period ts is substituted into the approximate function equation. Thus, the discharge termination voltage Vd can be determined. Therefore, it is possible to determine the discharge termination voltage Vd with high accuracy by correcting the internal resistance value R, the capacitance value C, and the temperature T. For example, when the power storage device 11 is installed in the vehicle interior and the ambient temperature of the power storage unit 23 is relatively stable, the correction by the temperature T may not be performed. Therefore, it is not always necessary to make corrections using the three parameters of the internal resistance value R, the capacitance value C, and the temperature T.

  In this way, the discharge termination voltage Vd can be obtained. Here, as a representative example, based on FIG. 2, the discharge termination voltage when the period ts is short (referred to as ts1) is Vd1, and when the discharge termination voltage is long (ts2). 3), the change with time of the voltage Vc of the power storage unit 23 after the end of vehicle use will be described with reference to FIG.

  In FIG. 3, the time t0 to t2 are the same as those in FIGS. 11 and 12 in the related art, and thus detailed description thereof is omitted. Here, the period ts1 is between the times t1 and t2, and the period ts2 is the time t0. To t2.

First, the case of the period ts1, that is, the case of the thick solid line in FIG. 3 will be described. Since the period ts1 is shorter than ts2, the charging depth of the power storage unit 23 is shallow and self-discharge is fast . Therefore, the discharge termination voltage Vd1 is set high. As a result, the voltage Vc of the power storage unit 23 detected by the voltage detection circuit 25 reaches the discharge termination voltage Vd1 from time t2 when the use of the vehicle is finished and the control circuit 37 starts forced discharge of the power storage unit 23 by the discharge circuit 27. The period until time t3 is shortened. Immediately after the discharge is started at time t2, the voltage Vc decreases by the voltage width ΔV as in the conventional case. At time t3, the control circuit 37 transmits a discharge control signal Dcnt to the discharge circuit 27 so as to stop the forced discharge. As a result, the voltage Vc increases by the voltage width ΔV. After time t3, as shown in FIG. 3, the voltage Vc of the power storage unit 23 decreases with time due to self-discharge and eventually falls below the non-degraded voltage Vh. Since the discharge termination voltage Vd1 is determined in advance so as to have such a behavior, the progress of deterioration of the power storage unit 23 can be reduced when the vehicle is not used, and a state in which unnecessary discharge is suppressed can be maintained. It is possible to achieve both long life and high-speed startup.

  Next, the case of the period ts2, that is, the case of the thick dotted line in FIG. 3 will be described. Since the period ts2 is longer than ts1, the charging depth of the power storage unit 23 is deep and self-discharge is slow. Accordingly, the discharge termination voltage Vd2 is set low. As a result, the voltage Vc of the power storage unit 23 detected by the voltage detection circuit 25 reaches the discharge termination voltage Vd2 from the time t2 when the use of the vehicle ends and the control circuit 37 starts the forced discharge of the power storage unit 23 by the discharge circuit 27. The period up to time t4 becomes longer. Note that the voltage Vc decreases by the voltage width ΔV at time t2 as in the case where the power storage unit voltage application time is ts1. At time t4, the control circuit 37 stops the forced discharge in the discharge circuit 27, and as a result, the voltage Vc increases by the voltage width ΔV. After time t4, as shown in FIG. 3, voltage Vc of power storage unit 23 decreases with time due to self-discharge and eventually falls below non-degraded voltage Vh. Here, when the thick solid line and the thick dotted line in FIG. 3 are compared, it can be seen that the voltage Vc of the power storage unit 23 behaves substantially equivalently. Since the discharge termination voltage Vd2 is determined in advance so as to achieve such a behavior, as in the case of the period ts1, the deterioration of the power storage unit 23 is reduced when the vehicle is not used, and unnecessary discharge is suppressed. The state can be maintained, and it is possible to achieve both long life and high-speed startup.

  With the above configuration and operation, the discharge termination voltage Vd is determined according to the period ts after the end of use, and the discharge termination voltage Vd is forcibly discharged. Therefore, no matter what the period ts is, When not in use, the progress of deterioration of power storage unit 23 is reduced, and a state in which unnecessary discharge is suppressed can be maintained. Thereby, it is possible to realize a power storage device capable of achieving both a long life and high-speed startup.

  In the first embodiment, the case where the temperature T is substantially constant at the start and end of use of the vehicle has been described. However, if the use time of the vehicle is long, the temperature T at the start and end of use is not necessarily high. It is not always constant. That is, for example, when the vehicle is started in winter, the temperature T at that time is low, and the vehicle is warmed at the end of use of the vehicle. In this case, since the internal resistance value R and the capacitance value C of the power storage unit 23 obtained at the time of starting the vehicle have temperature characteristics, if the discharge termination voltage Vd is obtained using these values at the end of vehicle use, the accuracy deteriorates. In addition, the voltage Vc of the power storage unit 23 at the time of self-discharge may be separated from the non-deteriorated voltage Vh.

  Therefore, in order to obtain the internal resistance value and capacity value (respectively referred to as Re and Ce) at the end of use of the vehicle, the internal resistance value and capacity value (respectively referred to as Rs and Cs) of the power storage unit 23 obtained when the vehicle is started. It is necessary to correct the temperature. Therefore, an example of a temperature correction method for the internal resistance value Re and the capacitance value Ce will be described below.

  First, temperature correction of the internal resistance value Re will be described with reference to FIG. In FIG. 4, the horizontal axis indicates the temperature T, and the vertical axis indicates the internal resistance value R. In general, the internal resistance value R has a characteristic of increasing with the temperature T. FIG. 4 shows a plurality of characteristic lines of temperature T vs. internal resistance value R. This is because the characteristic lines shift upward in FIG. . Therefore, a characteristic line of temperature T vs. internal resistance value R is obtained in advance according to the degree of progress of deterioration and stored in the memory of the control circuit 37.

  Now, consider a case where the vehicle starts at a low temperature and the end of use is a high temperature. At the time of startup, the internal resistance value Rs at the temperature Ts is obtained when the power storage unit 23 is charged as described above. The temperature Ts is detected by the temperature sensor 35. A characteristic line closest to the coordinates (Ts, Rs) in FIG. 4 is selected from the temperature Ts and the internal resistance value Rs thus obtained. In the case of FIG. 4, the second characteristic line (thick line) from the bottom is selected. At this point, when the coordinates (Ts, Rs) reach the uppermost characteristic line in FIG. 4, that is, the deterioration limit characteristic line, it is determined that the power storage unit 23 has deteriorated.

  Next, since the temperature T when the use of the vehicle ends is measured by the temperature sensor 35 as described above, the internal resistance value on the characteristic line (thick line) selected at the start-up at the temperature T (= Te). Re is obtained from FIG. This internal resistance value Re becomes a value after temperature correction.

  Next, temperature correction of the capacitance value Ce will be described with reference to FIG. In FIG. 5, the horizontal axis represents the temperature T, and the vertical axis represents the capacitance value C. In general, the capacitance value C has a characteristic of decreasing with the temperature T. Further, FIG. 5 shows a plurality of characteristic lines of temperature T versus capacitance value C because the characteristic lines shift downward in FIG. 5 as the deterioration progresses from the time of a new product. Therefore, a characteristic line of temperature T vs. capacity value C is obtained in advance according to the degree of progress of deterioration and stored in the memory of the control circuit 37.

  Here, as in the case of the internal resistance value R, a case is considered where the temperature at the start of the vehicle is low and the temperature at the end of use is high. At the time of startup, the capacity value Cs at the temperature Ts is obtained when the power storage unit 23 is charged as described above. The temperature Ts is detected by the temperature sensor 35. A characteristic line closest to the coordinates (Ts, Cs) in FIG. 5 is selected from the temperature Ts and the capacitance value Cs thus obtained. In the case of FIG. 5, the second characteristic line (thick line) from the top is selected. At this time, when the coordinates (Ts, Cs) reach the lowermost characteristic line in FIG. 5, that is, the deterioration limit characteristic line, it is determined that the power storage unit 23 has deteriorated.

  Next, since the temperature T when the use of the vehicle is ended is measured by the temperature sensor 35 as described above, the capacitance value Ce on the characteristic line (thick line) selected at the start-up at the temperature T (= Te). Is obtained from FIG. This capacitance value Ce is a value after temperature correction.

  Next, for each combination of the values of the internal resistance value Re, the capacitance value Ce, and the temperature Te, the internal resistance value Re, the capacitance value Ce, and A characteristic corresponding to the temperature Te is selected. The discharge termination voltage Vd in the period ts is determined based on the characteristics. As a result, even if the temperature changes during use of the vehicle, it is possible to finally determine the discharge termination voltage Vd that has been subjected to temperature correction, and high accuracy can be achieved.

  In addition, as another high accuracy method, the internal resistance value R and the capacitance value C may be obtained at the time of forced discharge after the end of use, instead of being obtained at the time of start-up charging of the power storage unit 23. In this case, the internal resistance value R and the capacitance value C are obtained in the same way as during charging, the former interrupting the discharge to detect the voltage change width, and the latter detecting the slope of the voltage change due to the discharge. To calculate. This eliminates the need for temperature correction of the internal resistance value R and the capacitance value C, and simplifies the control.

  However, in this method, since the discharge termination voltage Vd cannot be determined before the internal resistance value R and the capacitance value C are obtained, the internal resistance value R and the capacitance value C are obtained immediately after the start of the discharge of the power storage unit 23, and the discharge It is necessary to determine the termination voltage Vd. At this time, if there is a case where the discharge termination voltage Vd is very close to the predetermined voltage Vm depending on the configuration or state of the power storage unit 23, the voltage Vc of the power storage unit 23 should be originally set before the discharge termination voltage Vd is determined. There is a possibility that it will fall below the voltage Vd. Therefore, in such a case, it is desirable to obtain the internal resistance value R and the capacitance value C when the power storage unit 23 is charged.

  In the first embodiment, when the power storage unit 23 is charged, the time when the voltage Vc of the power storage unit 23 detected by the voltage detection circuit 25 reaches the predetermined voltage Vm is set as the start of use, and the subsequent period ts is set. Although the measurement is performed, for example, the period ts may be measured by setting the time when an ignition switch (not shown) is turned on to use the vehicle as the start of use. As a result, it is not necessary to use the voltage detection circuit 25 to determine the start of use, and the control is simplified. However, when the period ts is measured as described above, the period until the power storage unit 23 is fully charged is also measured. Here, as described above, since the internal resistance value of the power storage unit 23 increases and the capacity value decreases with deterioration, the period until full charge is shortened. Therefore, since the corresponding error is included in the period ts, from the viewpoint of accuracy, it is desirable to set the time when the voltage Vc of the power storage unit 23 reaches the predetermined voltage Vm as the start of use.

  In power storage device 11 according to the first embodiment, components other than power storage unit 23, discharge circuit 27, and control circuit 37 may be provided outside power storage device 11. As a result, for example, by providing the charging circuit 19 and the voltage detection circuit 25 outside the power storage device 11, the power storage unit 23 is not only charged by the main power supply 15, but also the driving status of the vehicle and the state of the main power supply 15. Depending on the above, it is possible to improve efficiency by switching to or combining with an alternator. Further, by providing main power supply voltage detection circuit 21 outside power storage device 11, the vehicle-side control circuit can share main power supply voltage detection circuit 21. As a result, charging control of the main power supply 15 can be performed according to the voltage Vb of the main power supply 15.

(Embodiment 2)
FIG. 6 is a correlation diagram of discharge termination voltage Vd with respect to integrated value Vt of the voltage applied to the power storage unit of the power storage device in Embodiment 2 of the present invention. FIG. 7 is a time-dependent change figure in the voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 2 of this invention.

  Since the configuration of power storage device 11 in the second embodiment is the same as that in FIG. 1 in the first embodiment, detailed description thereof is omitted. Since the feature of the second embodiment is the operation of determining the discharge termination voltage Vd, the operation will be described focusing on that portion.

  When the use of power storage device 11 is started, control circuit 37 detects voltage Vc of power storage unit 23 at that time with voltage detection circuit 25. Thereafter, the voltage Vc of the power storage unit 23 is continuously detected over a period ts until the use of the power storage device 11 ends, and the integrated value Vt is obtained. Here, the integral value Vt is approximately obtained by detecting and adding the voltage Vc of the power storage unit 23 at a predetermined interval (for example, 1 second).

  The start of use of power storage device 11 is the time when charging of power storage unit 23 is completed as in the first embodiment, and the end of use is the time when a vehicle use end signal is received from the vehicle-side control circuit. It is said.

  Here, in the second embodiment, the integrated value Vt of the voltage Vc of the power storage unit 23 in the period ts is obtained. However, when the power storage device 11 is applied as a power backup unit of the vehicle braking system, it is usually during the period ts. Since voltage Vc of power storage unit 23 is constant at predetermined voltage Vm (= 13.2 V), integrated value Vt is a value proportional to the energy of power storage unit 23. Further, even when the voltage Vc of the power storage unit 23 varies during use of the vehicle, the integrated value Vt becomes a value corresponding to the energy of the power storage unit 23 including the variation.

  Thus, when calculating | requiring the integral value Vt, it is necessary to set it as the time of the charge of the electrical storage part 23 being completed at the time of a use start. The reason is as follows. Temporarily, the use start time is a time point when the ignition switch of the vehicle is turned on and the control circuit 37 is activated. As described above, the power storage unit 23 has a tendency that the internal resistance value R increases and the capacitance value C decreases with deterioration. Therefore, when the power storage unit 23 is charged with constant current, if the power storage unit 23 is not deteriorated, it takes time to fully charge, and if it is deteriorated, the full charge is quickly reached. If this interval is integrated, the deteriorated power storage unit 23 is fully charged earlier, and then the predetermined voltage Vm is maintained, so that the integrated value Vt increases. Since the relationship between the integral value Vt and the discharge termination voltage Vd is an inversely proportional relationship as shown in FIG. 6 described later, the discharge termination voltage Vd becomes lower as the power storage unit 23 deteriorates. As a result, when the power storage unit 23 is discharged by the discharge circuit 27, there is a possibility of excessive discharge. Accordingly, when the integrated value Vt is obtained even when the power storage unit 23 is fully charged, the error of the discharge termination voltage Vd may increase, so the start of use is the time when the charging of the power storage unit 23 is completed. .

  In the second embodiment, the discharge termination voltage Vd is determined from the correlation of FIG. 6 after the use of the vehicle is finished, according to the integrated value Vt obtained as described above. In FIG. 6, the horizontal axis represents the integrated value Vt, and the vertical axis represents the discharge termination voltage Vd. The correlation between the integrated value Vt and the discharge termination voltage Vd is obtained in advance and stored in the control circuit 37 as in the first embodiment.

  Here, as shown in FIG. 6, the integral value Vt is determined so as to decrease as the integral value Vt increases. This is due to the following reason. When the integrated value Vt is large, it corresponds to the fact that a large amount of energy is stored in the power storage unit 23 over the period ts, so that the charging depth becomes deep. Therefore, even if the power storage unit 23 is discharged after the use is completed, the voltage decrease rate is slow. Accordingly, the self-discharge characteristic can be made closer by decreasing the discharge termination voltage Vd as the integrated value Vt is larger. As a result, the correlation between the integrated value Vt and the discharge termination voltage Vd shown in FIG. 6 has the same tendency as the correlation between the period ts and the discharge termination voltage Vd in FIG. Thus, for example, if the integrated value Vt is a small value Vt1, the discharge termination voltage Vd becomes a large value Vd1 from FIG. Similarly, if the integrated value Vt is a large value Vt2, the discharge termination voltage Vd becomes a small value Vd2. The lower limit value of the discharge termination voltage Vd is the non-deteriorated voltage Vh, which is to prevent overdischarge as in the first embodiment.

  When the control circuit 37 determines the discharge termination voltage Vd from the integrated value Vt at the end of vehicle use using the correlation shown in FIG. 6, the control circuit 37 controls the discharge circuit 27 to discharge the power storage unit 23 to the discharge termination voltage Vd. . FIG. 7 shows changes with time in the voltage Vc of the power storage unit 23 at this time. In FIG. 7, the horizontal axis represents time t, and the vertical axis represents the voltage Vc of the power storage unit 23. In FIG. 7, when the integrated value Vt is a small value Vt1, the discharge termination voltage Vd becomes a large value Vd1, and therefore, as shown by a thick solid line, the voltage Vc of the power storage unit 23 from the start of discharge (time t2) is Vd1. Discharge is performed by the discharge circuit 27 until time t3, and then self-discharge occurs. On the other hand, when the integrated value Vt is a large value Vt2, the discharge termination voltage Vd becomes a small value Vd2, so that the voltage Vc of the power storage unit 23 reaches Vd2 from the start of discharge (time t2) as shown by the thick dotted line. Discharge is performed by the discharge circuit 27 until time t4, and then self-discharge occurs. As a result, FIG. 7 is the same as FIG. 3 of the first embodiment, and the self-discharge characteristics can be brought close to the non-degraded voltage Vh.

  With the above configuration and operation, after the end of use, the discharge termination voltage Vd is determined according to the integral value Vt and forcibly discharged to the discharge termination voltage Vd. Therefore, the voltage Vc of the power storage unit 23 during the period ts. Even if fluctuates, it is possible to realize a power storage device that can achieve both a long life of the power storage unit 23 and a high-speed startup of the power storage device 11 with a more accurate discharge termination voltage Vd.

  In the second embodiment, the discharge termination voltage Vd may be corrected by the temperature T, the internal resistance value R, and the capacitance value C of the power storage unit 23 as in the first embodiment.

(Embodiment 3)
FIG. 8 is a time-dependent change figure in the voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 3 of this invention. FIG. 9 is a correlation diagram of discharge termination voltage Vd with respect to voltage change rate Vk at the end of use of the power storage device according to Embodiment 3 of the present invention.

  Since the configuration of power storage device 11 in the third embodiment is the same as that in FIG. 1 in the first embodiment, detailed description thereof is omitted. Since the feature of the third embodiment is the operation of determining the discharge termination voltage Vd, the operation will be described focusing on that portion.

  In the third embodiment, the control circuit 37 does not measure the period ts or the integral value Vt. Therefore, at the start of use, an operation of simply charging the power storage unit 23 is performed. At this time, the internal resistance value R and the capacitance value C of the power storage unit 23 may be obtained by the method described in the first embodiment.

  Next, the operation at the end of use will be described with reference to FIG. In FIG. 8, the horizontal axis represents time t, and the vertical axis represents the voltage Vc of the power storage unit 23.

  In FIG. 8, at time t10, the vehicle is in use. Therefore, the voltage Vc of the power storage unit 23 maintains the predetermined voltage Vm.

  Thereafter, use of the vehicle is terminated at time t11, and the ignition switch is turned off. At this time, the control circuit 37 detects the voltage Vc of the power storage unit 23 by the voltage detection circuit 25 and stops the operation of the charging circuit 19. Thereby, after the end of use, as shown from time t11 to time t12 in FIG. 8, the power storage unit 23 starts self-discharge from the predetermined voltage Vm, and the voltage Vc decreases with time. Thereafter, control circuit 37 detects voltage Vc of power storage unit 23 again at time t12 when voltage change rate measurement period tk stored in advance has elapsed. At this time, if the charging depth of the power storage unit 23 is shallow, as shown by a thick solid line in FIG. The voltage at time t12 in this case is Vc2. On the other hand, when the charging depth is deep, as shown by the thick dotted line in FIG. The voltage at time t12 in this case is Vc1.

  Next, the control circuit 37 calculates the voltage change rate Vk. Specifically, Vk = | Vm−Vc2 | / tk for the thick solid line in FIG. 8, and Vk = | Vm−Vc1 | / tk for the thick dotted line in FIG. Thus, the voltage change rate Vk is obtained as an absolute value without a sign. Hereinafter, the absolute value of the voltage change rate Vk is simply referred to as a voltage change rate Vk. Note that the voltage change rate on the thick solid line in FIG. 8 is Vk2, and the voltage change rate on the thick dotted line in FIG. 8 is Vk1.

  In the operation so far, the control circuit 37 obtains the voltage change rate Vk per unit time of the power storage unit 23 by detecting two points of the voltage Vc of the power storage unit 23 detected by the voltage detection circuit 25 after the end of use. . In order to obtain the voltage change rate Vk, a larger number (three or more points) of the voltage Vc may be detected. When a plurality of voltages Vc are obtained, a plurality of voltage change rates Vk are also obtained. For example, by averaging them, a more accurate voltage change rate Vk can be obtained.

  After obtaining the voltage change rate Vk at time t12, the control circuit 37 determines the discharge termination voltage Vd according to FIG. Here, the horizontal axis of FIG. 9 represents the voltage change rate Vk, and the vertical axis represents the discharge termination voltage Vd. As described above, since the voltage change rate Vk decreases as the charging depth increases, the discharge termination voltage Vd decreases. Therefore, as shown in FIG. 9, the discharge termination voltage Vd is determined so as to increase as the voltage change rate Vk increases. This correlation is obtained in advance and stored in the control circuit 37. Note that the lower limit value of the discharge termination voltage Vd is set to the non-degraded voltage Vh as in the first and second embodiments.

  Here, a specific example will be described. Since the voltage change rate Vk1 described above is smaller than the voltage change rate Vk2, the discharge termination voltage Vd1 with respect to the voltage change rate Vk1 is reduced according to FIG. On the other hand, since the voltage change rate Vk2 is large, the discharge termination voltage Vd2 becomes large.

  Next, at time t12 in FIG. 8, the control circuit 37 controls the discharge circuit 27 to discharge the power storage unit 23 to the discharge termination voltages Vd1 and Vd2 obtained as described above. As a result, when the voltage change rate is large (= Vk2), as shown by the thick solid line in FIG. 8, the power storage unit 23 is discharged until time t13 when the voltage Vc of the power storage unit 23 reaches the discharge termination voltage Vd2, and thereafter Then, the discharge circuit 27 is stopped. Thereby, thereafter, the power storage unit 23 performs self-discharge. When the voltage change rate is small (= Vk1), as shown by the thick dotted line in FIG. 8, the power storage unit 23 is discharged until time t14 when the voltage Vc of the power storage unit 23 reaches the discharge termination voltage Vd1, and then The discharge circuit 27 is stopped. Thereby, thereafter, the power storage unit 23 performs self-discharge. By such an operation, the discharge termination voltage Vd is determined according to the magnitude of the voltage change rate Vk, so that the self-discharge characteristics after time t14 can be brought close to the non-degraded voltage Vh. Note that the voltage Vc of the power storage unit 23 fluctuates by the voltage width ΔV at the start and end of the operation of the discharge circuit 27, which is generated by the internal resistance value R as described in the first embodiment.

  With the above configuration and operation, after termination of use, the discharge termination voltage Vd is determined according to the voltage change rate Vk, and forced discharge is performed up to the discharge termination voltage Vd. A more accurate discharge termination voltage Vd can be determined without being affected by fluctuations. As a result, it is possible to realize a power storage device that can achieve both a long life of the power storage unit 23 and high-speed startup of the power storage device 11.

  In the third embodiment, the discharge termination voltage Vd may be corrected by the temperature T, the internal resistance value R, and the capacitance value C of the power storage unit 23 as in the first embodiment.

  In the first to third embodiments, the discharge control up to the discharge termination voltage Vd is performed based on the voltage Vc of the power storage unit 23. This detects the voltage Vcn (n is the capacitor number) for each capacitor. Then, the discharge control may be performed up to the discharge termination voltage Vdn (n is a capacitor number) determined for each capacitor. In this case, a discharge circuit is provided for each capacitor. However, if a balance circuit is used as the discharge circuit, the voltage balance of each capacitor can be obtained, and discharge control up to the discharge termination voltage Vdn can be achieved. This makes it possible to increase the efficiency of the circuit configuration. In addition, it is desirable that the balance circuit be separated from each capacitor in order to perform self-discharge of each capacitor after discharging to the discharge termination voltage Vdn. Thereby, the overdischarge of each capacitor can be reduced.

  In the first to third embodiments, the electric double layer capacitor is used as the electric storage element in the electric storage unit 23, but this may be another capacitor such as an electrochemical capacitor. In the case where an electrochemical capacitor is used, the deterioration proceeds due to overdischarge. Therefore, the life of the power storage unit 23 can be extended by setting the non-deterioration voltage Vh to be equal to or higher than the overdischarge voltage.

  Further, in the first to third embodiments, the case where the power storage device 11 is used for the power backup system for the electronic control unit of the vehicle braking system has been described. However, the present invention is not limited thereto, and the idling stop, hybrid, electric power steering, electric turbo, etc. It may be used as an auxiliary power source in various systems.

  Since the power storage device according to the present invention can achieve both a long life and high-speed startup of the power storage unit, it is particularly useful as a power storage device for vehicles that stores power in the power storage unit and discharges it when necessary.

1 is a block circuit diagram of a power storage device according to Embodiment 1 of the present invention. Correlation diagram of discharge termination voltage Vd with respect to period ts during which voltage is applied to the power storage unit of the power storage device according to Embodiment 1 of the present invention. Time-dependent change figure in voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 1 of this invention Characteristic diagram of internal resistance value R with respect to temperature T of power storage unit of power storage device in Embodiment 1 of the present invention Characteristic diagram of capacity value C with respect to temperature T of power storage unit of the power storage device according to Embodiment 1 of the present invention Correlation diagram of discharge termination voltage Vd with respect to integral value Vt of the voltage applied to the power storage unit of the power storage device in Embodiment 2 of the present invention. The time-dependent change figure in the voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 2 of this invention The time-dependent change figure in the voltage Vc of the electrical storage part of the electrical storage apparatus in Embodiment 3 of this invention Correlation diagram of discharge termination voltage Vd against voltage change rate Vk at the end of use of the power storage device in Embodiment 3 of the present invention Block diagram of a conventional power storage device The time-dependent change figure in the voltage Vc of the electrical storage part when the discharge termination voltage Vd of the conventional electrical storage apparatus is close to the predetermined voltage Vm Time-dependent change figure in the voltage Vc of the electrical storage part when the discharge termination voltage Vd of the conventional electrical storage apparatus leaves | separates from the predetermined voltage Vm Equivalent circuit diagram of capacitor of conventional power storage device

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Power storage device 19 Charging circuit 23 Power storage part 25 Voltage detection circuit 27 Discharge circuit 35 Temperature sensor 37 Control circuit

Claims (7)

A power storage unit comprising a capacitor;
A voltage detection circuit for detecting a voltage (Vc) of the power storage unit;
A discharge circuit for forcibly discharging the power storage unit;
A control circuit connected to the voltage detection circuit and the discharge circuit,
The control circuit is configured to self-discharge the power storage unit after forcibly discharging the power storage unit voltage (Vc) to a discharge termination voltage (Vd), and the power storage unit by the self-discharge of the power storage unit The power storage device that controls the discharge termination voltage (Vd) to increase as the voltage (Vc) decreases more rapidly . The control circuit obtains a parameter for changing the self-discharge characteristic of the power storage unit or a parameter value of the self-discharge characteristic, and determines the discharge termination voltage (Vd) based on a correlation between the parameter and the discharge termination voltage (Vd). ) Is controlled. 3. The power storage device according to claim 2, wherein the control circuit includes a timer that measures a period (ts) between the start of use and the end of use, and the parameter for changing self-discharge characteristics is the period (ts). The control circuit includes a timer that measures a period (ts) at the start and end of use,
The said control circuit calculates | requires the integral value (Vt) of the voltage (Vc) of the said electrical storage part in the said period (ts), The said parameter which changes a self-discharge characteristic is made into the said integral value (Vt). Power storage device. The control circuit self-discharges the power storage unit after completion of use and before the forced discharge to obtain a voltage change rate (Vk) per unit time of the self-discharge, and sets the parameter of self-discharge characteristics as the voltage The power storage device according to claim 2, wherein the rate of change (Vk) is used. The control circuit uses the internal resistance of power storage unit (R), capacitance (C), or wherein the correlation corrected by at least one taken from a temperature sensor provided in the power storage unit temperature (T) The power storage device according to claim 2. The power storage device according to claim 1, wherein the lower limit value of the discharge termination voltage (Vd) is an applied voltage (non-degraded voltage Vh) of the power storage unit that can ensure a life required for the capacitor.

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