Backup power supply and method for controlling backup power supply

Abstract

Provided is a backup power supply that efficiently supplies power under the control of a microcomputer. The backup power supply is charged by a rectifier for generating power of a predetermined voltage, and supplies power to a load device operating with power supplied from the rectifier when the supplied power is insufficient. The backup power supply includes a secondary battery to be charged with power from the rectifier, a control unit for controlling charging and discharging of the secondary battery, and an input / output voltage detection unit for detecting the output voltage from the rectifier. The control unit stops charging of the secondary battery or reduces a charging current flow of the secondary battery when the output voltage drops to a first threshold voltage or less.

Description

DESCRIPTION Title of the Invention: BACKUP POWER SUPPLY AND METHOD FOR CONTROLLING BACKUP POWER SUPPLY Technical Field

[0001] The present invention relates to a backup power supply and a method for controlling the backup power supply. Background Art

[0002] Conventionally, combination of a rechargeable battery and a rectifier has been used in fields requiring backup devices using rechargeable batteries. Further, lead batteries have been widely used as rechargeable batteries.

[0003] When a rectifier has no room in the allowable power thereof and a larger amount of current flows instantaneously through a load device, the rectifier may be overloaded, which reduces the output voltage of the rectifier instantaneously. When the output voltage of the rectifier drops due to overload, it may be detected as a trouble of the load device or occurrence of a low voltage in a crossing gate.

[0004] Therefore, when the output power of the rectifier drops, a lead battery is electrically connected to the load device and discharges to the load device, thereby continuing the operation of the load device. Summary of the Invention Problems to be solved by the Invention

[0005] In recent years, there has been a tendency to use, as a backup power supply, a light-weight, compact, and long-life battery instead of a lead battery. Further, such a battery is equipped with a control board in order to perform highly functional control, and requires control using a microcomputer or the like.

[0006] An object of the present invention is to provide a backup power supply and a method for controlling the same that perform efficient power supply under the control of a microcomputer. Means for Solving the Problems

[0007] In order to achieve the above object, according to a first aspect of the present invention, the invention is characterized by a backup power supply to be charged by a rectifier for generating power of a predetermined voltage, the backup power supply suppling power to a load device operated with power supplied from the rectifier, when the power supplied from the rectifier to the load device is insufficient, comprising: a secondary battery configured to be charged with power from the rectifier; a control unit configured to control charging and discharging of the secondary battery; and an output voltage detection unit configured to detect an output voltage from the rectifier. When the output voltage drops to or below a first threshold voltage lower than the predetermined voltage, the control unit performs at least one of reducing a charging current for charging the secondary battery and stopping charging of the secondary battery.

[0008] According to a second aspect of the present invention, the invention is characterized by a backup power supply charged by a rectifier for suppling power to a load device operated with power supplied from the rectifier outputting power of a predetermined voltage, when the power supplied from the rectifier to the load device is insufficient, comprising: a secondary battery configured to be charged with power from the rectifier; a control unit configured to control charging and discharging of the secondary battery; an output voltage detection unit for detecting an output voltage from the rectifier; and a battery voltage detection unit for detecting a battery voltage across the secondary battery. When the output voltage drops to or below a third threshold voltage lower than the predetermined voltage and the output voltage is lower than the battery voltage, the control unit allows the secondary battery to discharge to the load device during a first time period. When the output voltage returns to the predetermined voltage after elapse of the first time period, the control unit stops discharge from the secondary battery to the load device.

[0009] According to a third aspect of the present invention, the invention is characterized by a method for controlling a backup power supply for suppling power to a load device operated with power supplied from a rectifier outputting power of a predetermined voltage, when the power supplied from the rectifier to the load device is insufficient. The method includes: charging the backup power supply by the rectifier; and stopping charging of the backup power supply when an output voltage from the rectifier drops to or below a first threshold voltage lower than the predetermined voltage.

[0010] According to a fourth aspect of the present invention, the invention is characterized by a method for controlling a backup power supply charged by a rectifier for supplying power to a load device operated with power supplied from the rectifier when the power supplied from the rectifier to the load device is insufficient, the rectifier outputting power of a predetermined voltage. The method includes: supplying power from the backup power supply to the load device over a first period of time on a condition that an output voltage of the backup power supply is higher than an output voltage from the rectifier when the output voltage from the rectifier drops to or below a third threshold voltage lower than the predetermined voltage. Advantageous Effects of the Invention

[0011] According to the present invention, when an amount of the power supplied from the rectifier to the load device operating with power supplied from the rectifier is insufficient, the backup power quickly supplies an amount of power corresponding to the insufficient amount of power from the secondary battery to the load device, which enables the load device to continue the operation. Brief Description of the Drawings

[0012] FIG. 1 is a circuit diagram of a backup power supply according to an embodiment. FIG. 2 is a graph showing a time change of the voltage at an input / output part of the backup power supply. FIG. 3 is a graph showing a time change of the voltage at the input / output part of the backup power supply. FIG. 4 is a graph showing a time change of the voltage at the input / output part of the backup power supply. FIG. 5 is a graph showing a time change of the voltage at the input / output part of the backup power supply. Embodiments for Carrying out the Invention

[0013] A backup power supply 1 according to an embodiment of the present invention will be described with reference to FIG. 1. It goes without saying that the present invention is not limited to the embodiment described below, and various modifications are possible within the scope of the claims.

[0014] <Configuration of Backup Power supply> As shown in FIG. 1, the backup power supply 1 is connected to a power supply line L that electrically connects a rectifier 2 and a load device 3. The rectifier 2 is an AC-DC converter that uses external commercial power to generate and output DC power of a normal voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. In the present embodiment, the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> is in the range of 26.2 V to 28.8 V. The load device 3 is a device which is supplied with power by the rectifier 2 to operate. In the present embodiment, for example, in the case of a railroad crossing device, the load device 3 is a crossing gate installed at a railroad crossing, and opens and closes a rod attached to the crossing gate according to traveling of trains. The load device 3 has a rated voltage of 24 V.

[0015] The backup power supply 1 includes an input / output part 11, a secondary battery 12, a DC-DC converter 13, a constant current control circuit 14, and a control unit 15. The input / output part 11 is connected to the power supply line L through which power is supplied from rectifier 2 to load device 3. When the backup power supply 1 is charged, an output voltage from the rectifier 2 is applied to the input / output part 11. On the other hand, when the backup power supply 1 supplies power to the load device 3 as a backup power supply, a battery voltage Vb of the secondary battery 12 becomes a voltage at the input / output part 11.

[0016] The secondary battery 12 includes a plurality of alkaline secondary battery cells connected in series or in parallel. The plurality of alkaline secondary battery cells is nickel-hydrogen secondary battery cells. In the present embodiment, the secondary battery 12 includes twenty alkaline secondary battery cells connected in series, and discharges power of a battery voltage Vb of 20.0 to 28.8 V according to a charge capacity.

[0017] The DC-DC converter 13 is a boost type voltage converter for boosting the output voltage Vo of the rectifier 2 to a voltage which enables the secondary battery 12 to be fully charged, and outputs the boosted voltage to the secondary battery 12 via the constant current control circuit 14.

[0018] A charging switch 16 for turning on / off charging of the secondary battery 12 is provided between the constant current control circuit 14 and one electrode of the secondary battery 12. Further, a discharging switch 17 for turning on / off discharging of the secondary battery 12 is provided between the other electrode of the secondary battery 12 and the input / output part 11. Note that a diode D is connected between the discharging switch 17 and the input / output part 11. The anode of the diode D is connected to the other electrode of the secondary battery 12, and the cathode of the diode D is connected to the input / output part 11.

[0019] The control unit 15 has a microcomputer, and includes an input / output voltage detection unit 18 for detecting a voltage Vi at the input / output part 11, and a battery voltage detection unit 19 for detecting the battery voltage Vb of the secondary battery 12. The control unit 15 controls switching of the charging switch 16 and the discharging switch 17 in accordance with the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 and the battery voltage <semantics>Vb<annotation encoding="application / x-tex">V_b< / annotation>< / semantics> of the secondary battery 12. Since the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 is equal to the output voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> of the rectifier 2, the control unit 15 monitors the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11, which enables the backup power supply 1 to get to know the operation states of the rectifier 2 and the load device 3.

[0020] <Operation of Backup Power supply> (1) Stop of charging of backup power supply The operation of the backup power supply 1 will be described with reference to FIGS. 2 to 5.

[0021] First, a charging stop operation of the backup power supply 1 will be described with reference to FIG. 2. FIG. 2 shows a time change of the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 of the backup power supply 1. In FIG. 2, the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> is a voltage value supplied from the rectifier 2 when the rectifier 2 is in a normal operation. The voltage <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics> is used by the control unit 15 as a first threshold voltage or a fourth threshold voltage in order to turn off the charging switch 16. The turning off the charging switch 16 stops charging of the secondary battery 12. The voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is used for the control unit 15 to determine that power supply has been interrupted in the rectifier 2. The voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is lower than <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics>. The voltage Vr is used as a reference voltage for resuming charging of the secondary battery 12, which is a second threshold voltage. The voltage <semantics>Vr<annotation encoding="application / x-tex">V_r< / annotation>< / semantics> is higher than the voltage <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics>. Both the voltages <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics> and <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> are lower than the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. In the present embodiment, <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics> is set to 24 V, <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is set to 23 V, and <semantics>Vr<annotation encoding="application / x-tex">V_r< / annotation>< / semantics> is set to 24.5 V.

[0022] Referring to FIG. 2, when the rectifier 2 supplies power to the load device 3 at time <semantics>t0<annotation encoding="application / x-tex">t_0< / annotation>< / semantics> in a normal manner, the voltage Vi at the input / output part 11 of the backup power supply 1 is equal to the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. At this time, in the backup power supply 1, the charging switch 16 is turned ON by the control unit 15, so that the secondary battery 12 is charged with the power from the rectifier 2. On the other hand, the control unit 15 turns off the discharging switch 17 so as to prevent the secondary battery 12 from discharging, and is preparation for future discharge.

[0023] Next, at time <semantics>t1<annotation encoding="application / x-tex">t_1< / annotation>< / semantics>, for example, in the case of a railroad crossing device, when the maximum current flow flows through the load device 3 to raise the rod of a crossing gate or the like and then the rectifier 2 is overloaded, the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> starts to drop. At time <semantics>t2<annotation encoding="application / x-tex">t_2< / annotation>< / semantics>, when the output voltage of the rectifier 2 drops below <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics>, the control unit 15 turns off the charging switch 16 to stop charging of the secondary battery 12. However, when the current flowing through the load device 3 returns to normal current after the time t2 because the rod has been fully raised, the voltage Vi turns to increase before voltage Vi drops to the voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics>. The voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is used to determine that a power failure occurs in the rectifier 2. The voltage Vi increases until the voltage Vi reaches the voltage <semantics>Vr<annotation encoding="application / x-tex">V_r< / annotation>< / semantics> at time <semantics>t3<annotation encoding="application / x-tex">t_3< / annotation>< / semantics>, and eventually returns to the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. At time <semantics>t4<annotation encoding="application / x-tex">t_4< / annotation>< / semantics>, for example, when 30 seconds passes after the time <semantics>t3<annotation encoding="application / x-tex">t_3< / annotation>< / semantics>, the control unit 15 switches on the charging switch 16 to resume charging of the secondary battery 12.

[0024] In this way, when the output voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> suddenly drops due to an overload to the rectifier 2, charging of the backup power supply 1 is stopped during the time period from the time <semantics>t2<annotation encoding="application / x-tex">t_2< / annotation>< / semantics> to the time <semantics>t4<annotation encoding="application / x-tex">t_4< / annotation>< / semantics> in order to increase an amount of power to be supplied to the load device 3. Therefore, the rectifier 2 can supply the power scheduled to be supplied to the backup power supply 1 during the time period from the time <semantics>t2<annotation encoding="application / x-tex">t_2< / annotation>< / semantics> to the time <semantics>t4<annotation encoding="application / x-tex">t_4< / annotation>< / semantics> to the load device 3. This operation of the backup power supply 1 can resolve the overload state of the rectifier 2 in a short time. In other words, stopping the charging of the backup power supply 1 for a short time can resolve the overload of the rectifier 2, so that the operation of the load device 3 can be continued.

[0025] The reason why the charging of the secondary battery 12 is resumed after 30 seconds from the time t3 is to avoid occurrence of a trouble in the rectifier 2. Further, in FIG. 2, the control unit 15 stops charging of the secondary battery 12 when the output voltage of the rectifier 2 drops below <semantics>Vc<annotation encoding="application / x-tex">V_c< / annotation>< / semantics>. However, in another embodiment, when the output voltage of the rectifier 2 drops below Vc, the control unit 15 reduces the amount of current to flow through the secondary battery 12 to charge the secondary battery 12, and the rectifier 2 can supply the amount of power corresponding to the reduced amount to the load device 3.

[0026] (2) Discharge of backup power supply Next, discharge control of the backup power supply 1 will be described with reference to FIGS. 3 to 5. FIG. 3 shows a time change of the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 of the backup power supply 1. In FIG. 3, the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> is a voltage output when the rectifier 2 is in a normal operation, and the voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is a voltage which the control unit 15 uses as a third threshold value to determine whether a power failure occurs in the rectifier 2. The voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is lower than <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. In the present embodiment, <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is set to 23 V.

[0027] Referring to FIG. 3, when the rectifier 2 normally supplies power to the load device 3 at time <semantics>t0<annotation encoding="application / x-tex">t_0< / annotation>< / semantics>, the voltage Vi at the input / output part 11 of the backup power supply 1 is equal to the voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>. At this time, in the backup power supply 1, the control unit 15 turns on the charging switch 16, thereby charging the secondary battery 12 with the power from the rectifier 2. On the other hand, the control unit 15 turns off the discharging switch 17 so as to prevent the secondary battery 12 from discharging to the load device 3. The secondary battery 12 is in preparation for future discharge.

[0028] Next, at time <semantics>t11<annotation encoding="application / x-tex">t_{11}< / annotation>< / semantics>, for example, in the case of a railroad crossing device, when the maximum current flows through the load device 3 to raise the rod of a crossing gate or the like and causes the rectifier 2 to be subject to overload, the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> starts to drop. When the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> further drops to the voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> at time <semantics>t12<annotation encoding="application / x-tex">t_{12}< / annotation>< / semantics>, the control unit 15 determines that a power failure has occurred in the rectifier 2. And at time <semantics>t13<annotation encoding="application / x-tex">t_{13}< / annotation>< / semantics> after 200 microseconds from time <semantics>t12<annotation encoding="application / x-tex">t_{12}< / annotation>< / semantics>, the control unit 15 confirms that the battery voltage <semantics>Vb<annotation encoding="application / x-tex">V_b< / annotation>< / semantics> of the secondary battery 12 is higher than <semantics>Vi<annotation encoding="application / x-tex">V_{i}< / annotation>< / semantics>, and then switches the discharging switch 17 from OFF to ON to start discharging of the secondary battery 12. Consequently, the backup power supply 1 starts supplying power to the load device 3. In other words, the backup power supply 1 discharges the secondary battery 12 for 10 seconds from the time <semantics>t13<annotation encoding="application / x-tex">t_{13}< / annotation>< / semantics> to the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics> to supply power to the load device 3. Therefore, the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 becomes equal to the battery voltage Vb of the secondary battery 12 for 10 seconds from the time <semantics>t13<annotation encoding="application / x-tex">t_{13}< / annotation>< / semantics> to the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics>.

[0029] At the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics>, the control unit 15 turns off the discharging switch 17 to detect the output voltage of the rectifier 2. If the output voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> of the rectifier 2 at the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics> has returned to <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>, the control unit 15 maintains the discharging switch 17 in an OFF-state to stop discharging from the secondary battery 12 after the time <semantics>𝗍14<annotation encoding="application / x-tex">\mathsf{t}_{14}< / annotation>< / semantics> . Therefore, power is not suppled from the backup power supply 1 to the load device 3, and the input to the load device 3 is only the power from the rectifier 2. Therefore, the voltage Vi at the input / output part 11 is equal to the output voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> of the rectifier 2.

[0030] In this way, when the rectifier 2 is subject to an overload during the time period from the time <semantics>t11<annotation encoding="application / x-tex">t_{11}< / annotation>< / semantics> to the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics>, the backup power supply 1 supplies power to the load device 3 during the time period from the time <semantics>t13<annotation encoding="application / x-tex">t_{13}< / annotation>< / semantics> to 11 the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics> to compensate for the shortage of power from the rectifier 2 to the load device 3. Accordingly, the operation of the load device 3 can be maintained.

[0031] On the other hand, as shown in FIG. 4, when the detected output power of the rectifier 2 is still equal to or less than the voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> at time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics>, the control unit 15 confirms that the battery voltage Vb is higher than the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at time <semantics>t15<annotation encoding="application / x-tex">t_{15}< / annotation>< / semantics> after 200 microseconds elapsed from the time <semantics>t14<annotation encoding="application / x-tex">t_{14}< / annotation>< / semantics>, and then switches the discharging switch 17 from OFF to ON to start discharging of the secondary battery 12, thereby resuming power supply from the secondary battery 12 to the load device 3. Therefore, the backup power supply 1 supplies power to the load device 3 by discharging the secondary battery 12 for 10 seconds from the time <semantics>t15<annotation encoding="application / x-tex">t_{15}< / annotation>< / semantics> to time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>. As a result, the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 is equal to the battery voltage <semantics>Vb<annotation encoding="application / x-tex">V_b< / annotation>< / semantics> of the secondary battery 12 for 10 seconds from the time <semantics>t15<annotation encoding="application / x-tex">t_{15}< / annotation>< / semantics> to the time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>.

[0032] At the time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>, the control unit 15 turns off the discharging switch 17 to detect the output voltage of the rectifier 2. If the output voltage of the rectifier 2 at the time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics> has returned to <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics>, the control unit 15 continues the OFF-state of the discharging switch 17 to stop discharging from the secondary battery 12 after the time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>. Therefore, the backup power supply 1 does not supply power to the load device 3, and the load device 3 receives only the power from the rectifier <semantics>2<annotation encoding="application / x-tex">2< / annotation>< / semantics>, so that the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 is equal to the output voltage <semantics>V0<annotation encoding="application / x-tex">V_0< / annotation>< / semantics> of the rectifier 2.

[0033] In this way, when the overload condition of the rectifier 2 is not improved even by power supply from the backup power supply 1 to the load device 3 for the first 10 seconds, the time period of power supply from the backup power supply 1 is extended, whereby the operation of the load device 3 can be maintained.

[0034] On the other hand, as shown in FIG. 5, when the control unit 15 detects that the output power of the rectifier 2 is still equal to or less than the voltage <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> at time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>, the control unit 15 determines that a fault which cannot be normally restored within several tens of seconds has occurred in the rectifier 2 and / or the load device 3. The control unit 15 then switches the discharging switch 17 from OFF to ON to resume discharging from the secondary battery 12 at time <semantics>t17<annotation encoding="application / x-tex">t_{17}< / annotation>< / semantics> after 200 microseconds elapsed from the time <semantics>t16<annotation encoding="application / x-tex">t_{16}< / annotation>< / semantics>, thereby supplying power from the backup power supply 1 to the load device 3. In this state, the period for which the voltage at the input / output part 11 is equal to or less than <semantics>Vs<annotation encoding="application / x-tex">V_s< / annotation>< / semantics> is as long as 20 seconds or more. Therefore, after the time <semantics>t17<annotation encoding="application / x-tex">t_{17}< / annotation>< / semantics>, the backup power supply 1 continues the power supply from the load device 3 until the voltage <semantics>Vi<annotation encoding="application / x-tex">V_i< / annotation>< / semantics> at the input / output part 11 exceeds the battery voltage <semantics>Vb<annotation encoding="application / x-tex">V_b< / annotation>< / semantics>. Accordingly, it is possible to continue the operation of the load device 3 despite long-term drop of the output voltage of the rectifier.

[0035] The voltage Vi at the input / output part 11 after the time <semantics>t17<annotation encoding="application / x-tex">t_{17}< / annotation>< / semantics> becomes equal to the battery voltage <semantics>Vb<annotation encoding="application / x-tex">V_b< / annotation>< / semantics> of the secondary battery 12.

[0036] While power is supplied from the backup power supply 1 to the load device 3, the charging of the secondary battery 12 in the backup power supply 1 by the power of the rectifier 2 may be stopped, and the power to be used for charging of the backup power supply 1 may also be supplied to the load device 3.

[0037] In this way, when an overload condition occurs in the rectifier 2, the charging of the backup power supply 1 is stopped. And all the power supplied from the rectifier 2 is supplied to the load device 3, so that the operation of the load device 3 can be continued. When the output voltage of the rectifier 2 further drops, power is also supplied from the backup power supply 1 to the load device 3 to compensate for the power shortage of the load device 3 and maintain the operation of the load device 3. Explanation of Reference Signs

[0038] 1 backup power supply 2 rectifier 3 load device 12 secondary battery 15 control unit 18 input / output voltage detection unit 19 battery voltage detection unit

[0039] The following aspects are also disclosed herein: 1. A backup power supply charged by a rectifier for supplying power to a load device operated with power supplied from the rectifier outputting power of a predetermined voltage, and the backup power supply supplying power to the load device when the power supplied from the rectifier to the load device is insufficient, the backup power supply comprising: a secondary battery configured to be charged with power from the rectifier; a control unit configured to control charging and discharging of the secondary battery; and an output voltage detection unit configured to detect an output voltage from the rectifier, wherein: in response to the output voltage dropping to or below a charge cutoff threshold voltage lower than the predetermined voltage, the control unit performs at least one of reducing a charging current for charging the secondary battery or stopping charging of the secondary battery; and in response to the output voltage dropping to or below a discharge threshold voltage lower than the charge cutoff threshold voltage, the backup power supply supplies the power to the load device. 2. The backup power supply according to aspect 1, wherein the control unit is configured to continue stopping charging of the secondary battery until the output voltage dropped to or under the charge cutoff threshold voltage increases to a charge resumption threshold voltage higher than the charge cutoff threshold voltage and lower than the predetermined voltage. 3. A method for controlling a backup power supply for supplying power to a load device, the load device being operated with power supplied from a rectifier outputting power of a predetermined voltage, and the backup power supply supplying power to the load device when the power supplied from the rectifier to the load device is insufficient as determined by an output voltage from the rectifier dropping to or below a discharge threshold voltage, the method comprising: charging the backup power supply by the rectifier; and stopping charging of the backup power supply when the output voltage from the rectifier drops to or below a charge cutoff threshold voltage lower than the predetermined voltage but higher than the discharge threshold voltage. 4. The method according to aspect 3, further comprising: continuing stopping charging of the backup power supply until the output voltage increases to a charge resumption threshold voltage higher than the charge cutoff threshold voltage and lower than the predetermined voltage after the stopping charging.

Claims

1. A backup power supply charged by a rectifier for supplying power to a load device operated with power supplied from the rectifier outputting power of a predetermined voltage, and the backup power supply supplying power to the load device when the power supplied from the rectifier to the load device is insufficient, the backup power supply comprising: a secondary battery configured to be charged with power from the rectifier; a control unit configured to control charging and discharging of the secondary battery; and an output voltage detection unit configured to detect an output voltage from the rectifier, wherein: in response to the output voltage dropping to or below a charge cutoff threshold voltage lower than the predetermined voltage, the control unit performs at least one of reducing a charging current for charging the secondary battery or stopping charging of the secondary battery; and in response to the output voltage dropping to or below a discharge threshold voltage lower than the charge cutoff threshold voltage, the backup power supply supplies the power to the load device.

2. The backup power supply according to claim 1, wherein the control unit is configured to continue stopping charging of the secondary battery until the output voltage dropped to or under the charge cutoff threshold voltage increases to a charge resumption threshold voltage higher than the charge cutoff threshold voltage and lower than the predetermined voltage.

3. A method for controlling a backup power supply for supplying power to a load device, the load device being operated with power supplied from a rectifier outputting power of a predetermined voltage, and the backup power supply supplying power to the load device when the power supplied from the rectifier to the load device is insufficient as determined by an output voltage from the rectifier dropping to or below a discharge threshold voltage, the method comprising: charging the backup power supply by the rectifier; and stopping charging of the backup power supply when the output voltage from the rectifier drops to or below a charge cutoff threshold voltage lower than the predetermined voltage but higher than the discharge threshold voltage.

4. The method according to claim 3, further comprising: continuing stopping charging of the backup power supply until the output voltage increases to a charge resumption threshold voltage higher than the charge cutoff threshold voltage and lower than the predetermined voltage after the stopping charging.