Smoothing capacitor charging method for backup power supply, and backup power supply

Abstract

This backup power supply: causes both a charge converter for charging a battery block of a plurality of power supply units (BBU) and a discharge converter for causing the battery block to be in a discharging state to be in an operating state; and charges a smoothing capacitor connected to the output side of each BBU by DC supplied from a DC bus (DCbus) via the charge converter and the discharge converter which are in the operating state.

Description

Charging method for smoothing capacitor of backup power supply and backup power supply

[0001] The present invention relates to a method and apparatus for charging a smoothing capacitor of a backup power supply used as an uninterruptible power supply or an emergency power supply.

[0002] Backup power supplies equipped with secondary batteries are used in servers and data centers as backup power sources in the event of a power outage or emergency. Backup power supply devices are designed to keep the built-in secondary battery fully charged and on standby to reliably supply power to the system and protect data during a momentary power outage or other power outage.

[0003] This type of backup power supply is connected to a direct current bus line (DC bus) to which power from a commercial power source is supplied via a power supply circuit, and the DC bus is configured to supply power to systems (loads) such as servers and data centers. This configuration allows power to be supplied from the backup power supply when the power supply from the commercial power source is interrupted due to a power outage or other reason. Typically, an emergency generator is also connected in addition to the backup power supply, and the backup power supply is configured to supply power from the time of the power outage until power is supplied from the generator. Generally, the DC bus and the secondary battery built into the backup power supply are connected via a DC / DC converter, and a smoothing capacitor is provided on the output side (DC bus side) of the DC / DC converter.

[0004] In recent years, the increasing sophistication of servers and data centers has led to the need for high-output DC / DC converters, which in turn has led to a demand for larger-capacity smoothing capacitors. Large-capacity smoothing capacitors can effectively suppress voltage fluctuations and ripples, but they pose a problem: when attempting to quickly charge the DC bus from a discharged state after a power outage, the inrush current becomes extremely large. To suppress the inrush current, it is generally necessary to charge the smoothing capacitor via a current-limiting resistor, but as the capacity of smoothing capacitors increases, the charging time for the smoothing capacitor tends to become longer.

[0005] To charge a smoothing capacitor connected to a DC bus, conventional power supply units (hereinafter referred to as BBUs: Battery Backup Units) have a charging switch between the smoothing capacitor and the DC bus that charges the smoothing capacitor while limiting the charging current. A semiconductor switching element such as an FET is used for the charging switch. If the charging switch is switched on to charge the smoothing capacitor directly from the DC bus, an excessively large charging current will flow momentarily. Therefore, the charging switch cannot directly connect the DC bus to the smoothing capacitor. To reduce the instantaneous excessive current, a current-limiting resistor is connected in series with the semiconductor switching element to limit the inrush current of the smoothing capacitor. A current-limiting resistor can increase its electrical resistance to reduce excessive inrush current, but it also reduces the charging current, resulting in a longer charging time for the smoothing capacitor. Conversely, a current-limiting resistor with a low electrical resistance can quickly charge the smoothing capacitor, but it can also have issues such as damage to the semiconductor switching element due to the instantaneous inrush current. Furthermore, the current limiting resistor generates Joule heat in proportion to the square of the charging current, which makes it difficult to design for heat dissipation.

[0006] Thus, a backup power supply is required to start up in a short time (ideally within 10 milliseconds) in the event of a commercial power outage and to supply power to the DC bus in place of the commercial power supply. Therefore, if the smoothing capacitor is charged during a power outage, it will be difficult to start up within 10 milliseconds due to the charging time and heat generation issues mentioned above. On the other hand, a battery block that has been removed from the backup power supply for maintenance or the like must be connected to the DC bus, and then the smoothing capacitor must be charged so that it can be connected to the DC bus and begin supplying power.

[0007] Japanese Patent Application Laid-Open No. 2003-61209

[0008] A technology for charging a large-capacity smoothing capacitor connected to a power line has been developed (see Patent Document 1). Patent Document 1 discloses a vehicle power supply system that includes a main battery, an auxiliary battery that charges and discharges at a lower voltage than the main battery, an inverter circuit that receives voltage from the main battery via a main contactor, a smoothing capacitor connected in parallel between the main battery and the inverter circuit, and a DC / DC converter connected between the auxiliary battery and the smoothing capacitor, and that precharges the smoothing capacitor using power from the auxiliary battery. This configuration eliminates the need for a current-limiting resistor, even when charging a large-capacity smoothing capacitor, thereby suppressing inrush current and solving the problem of heat generation. However, unlike in-vehicle power supplies, backup power supplies used as uninterruptible power supplies or emergency power sources generally do not have an auxiliary battery such as a 12V lead-acid battery. Therefore, applying these technologies to backup power supplies requires a dedicated circuit or power supply to charge the smoothing capacitor, resulting in a complex circuit configuration.

[0009] A method for charging a smoothing capacitor according to an embodiment of the present invention relates to a method for charging a smoothing capacitor in a hot-swap backup power supply in which multiple power supply units (BBUs: Battery Backup Units) are detachably connected to a direct current bus line (DC bus). The BBU of the backup power supply that charges the smoothing capacitor in this method includes a battery block, a discharge DC / DC converter (hereinafter referred to as the "discharge converter") that stabilizes the output voltage of the battery block and outputs it to the DC bus, a smoothing capacitor connected to the output side of the discharge converter, a main switch connected between the battery block and the discharge converter and the charge converter, a charge switch that connects the smoothing capacitor to the DC bus, a charge DC / DC converter (hereinafter referred to as the "charge converter") that charges the battery block with power from the DC bus, and a control circuit that controls the main switch, the charge switch, the discharge converter, and a charge converter. The control circuit turns off the main switch and the charge switch, and while the control circuit keeps the main switch and the charge switch off, charges the smoothing capacitor with charging current from the DC bus via the charge converter and the discharge converter. The charge converter and discharge converter may be set to an operating state, and the smoothing capacitor may be charged by the output from the DC bus via the operating charge converter and discharge converter, regardless of the output from the battery block.

[0010] The backup power supply of the present invention is a hot-swap backup power supply consisting of multiple BBUs detachably connected to a direct current bus line (DC bus). Each BBU includes a battery block, a discharge converter that stabilizes the output voltage of the battery block and outputs it to the DC bus, a smoothing capacitor connected to the output side of the discharge converter, a main switch connected between the battery block, the discharge converter, and the charge converter, a charge switch connected between the DC bus and the smoothing capacitor, a charge converter that charges the battery block with power from the DC bus, and a control circuit that controls the main switch, charge switch, discharge converter, and charge converter. When a BBU that has been disconnected from the DC bus is reconnected to the DC bus, the control circuit turns off the main switch and charge switch to disconnect the smoothing capacitor from the DC bus and activates the charge converter and discharge converter, so that the smoothing capacitor is charged with output from the DC bus via the active charge converter and discharge converter, regardless of the output from the battery block.

[0011] The method for charging a smoothing capacitor in a backup power supply and the backup power supply of the present invention are characterized by the ability to quickly charge the smoothing capacitor without providing a dedicated circuit.Furthermore, the method for charging a smoothing capacitor in a backup power supply and the backup power supply of the present invention are characterized by the ability to efficiently charge the smoothing capacitor in a short time with little heat generation.

[0012] FIG. 1 is a circuit diagram of a backup power supply according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a charging current A that charges a power supply capacitor from a direct current bus line (DCbus) when a charging converter in an operating state in the backup power supply of FIG. 1 is in charge. FIG. 3 is a circuit diagram showing a charging current B that charges a smoothing capacitor by starting a discharge converter while maintaining charging current A from the DCbus via an operating charge converter and discharge converter in the backup power supply of FIG. 1. FIG. 4 is a circuit diagram showing a charging current C that charges the smoothing capacitor to the DCbus voltage when the charging switch in an on state charges the smoothing capacitor to the DCbus voltage after the discharge converter is turned off in the backup power supply of FIG. 1. FIG. 5 is a circuit diagram showing an example of a non-isolated DC / DC converter.

[0013] The present invention will be described in detail below with reference to the drawings. In the following description, terms indicating specific directions or positions (e.g., "upper," "lower," and other terms including these terms) will be used as necessary. However, the use of these terms is intended to facilitate understanding of the invention with reference to the drawings, and the meaning of these terms does not limit the technical scope of the present invention. Furthermore, parts that appear with the same reference numerals in multiple drawings indicate the same or equivalent parts or members.

[0014] Furthermore, the embodiments shown below are specific examples of the technical concept of the present invention and are not intended to limit the present invention thereto. Furthermore, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described below are intended as examples and are not intended to limit the scope of the present invention thereto. Furthermore, the content described in one embodiment or example can also be applied to other embodiments or examples. Furthermore, the sizes and positional relationships of components shown in the drawings may be exaggerated for clarity of explanation.

[0015] A method for charging a smoothing capacitor according to an embodiment of the present invention is a method for charging a smoothing capacitor in a hot-swap backup power supply in which multiple power supply units (BBUs: Battery Backup Units) are detachably connected to a direct current bus line (DC bus). Each of the multiple BBUs includes a battery block, a discharge converter that stabilizes the output voltage of the battery block and outputs it to the DC bus, a smoothing capacitor connected to the output side of the discharge converter, a main switch connected between the battery block and the discharge and charge converters, a charge switch that connects the smoothing capacitor to the DC bus, a charge converter that charges the battery block with power from the DC bus, and a control circuit that controls the main switch, the charge switch, and the discharge and charge converters. The control circuit detects that the BBU is connected to the DC bus, turns off the main switch and the charge switch, activates the charge converter and the discharge converter, and charges the smoothing capacitor with output from the DC bus via the charge converter and the discharge converter, regardless of the output from the battery block.

[0016] The method for charging the smoothing capacitor of the backup power supply described above has the advantage that the smoothing capacitor can be charged efficiently because the charge converter and discharge converter are in an operating state and the smoothing capacitor is charged by the DC bus output, regardless of the output from the battery block.

[0017] In another embodiment of the present invention, a method for charging a smoothing capacitor of a backup power supply has a circuit configuration in which the BBU has a power supply capacitor connected to the output side of the charging converter, and when the BBU is reconnected to the DC bus, the control circuit turns off the main switch to cut off output from the battery block, turns off the charging switch to disconnect the smoothing capacitor from the DC bus, and further turns the discharge converter to a non-operating state and the charging converter to an operating state to charge the input-side power supply capacitor via the operating charging converter, and then turns both the charging converter and the discharging converter to an operating state to charge the smoothing capacitor with output from the DC bus via the operating charging converter and discharging converter.

[0018] In another embodiment of the present invention, a method for charging a smoothing capacitor in a backup power supply can charge the smoothing capacitor using a charge converter and a discharge converter that are in an operating state, and then turn on the charge switch to maintain the smoothing capacitor at the same potential as the DC bus.

[0019] In another embodiment of the method for charging a smoothing capacitor of a backup power supply according to the present invention, the discharge converter of the BBU can be a non-isolated DC / DC converter, thereby improving power efficiency at low cost.

[0020] In another embodiment of the method for charging a smoothing capacitor of a backup power supply according to the present invention, the output power of the charging converter can be set to 1 / 10 or less of the output power of the discharging converter.

[0021] In another embodiment of the present invention, a method for charging a smoothing capacitor of a backup power supply includes a generator that supplies power to a DC bus, and when the commercial power supply fails, an operating discharge converter supplies power to the DC bus before the generator starts up, and after the generator starts up, power can be supplied from the generator to the DC bus.

[0022] A backup power supply in another embodiment of the present invention is a hot-swap backup power supply made up of a plurality of BBUs detachably connected to a direct current bus line (DC bus), the BBUs comprising: a battery block; a discharge converter that stabilizes the output voltage of the battery block and outputs it to the DC bus; a smoothing capacitor connected to the output side of the discharge converter; a main switch connected between the battery block and the discharge converter and the charge converter; a charge switch that connects the DC bus to the smoothing capacitor; a charge converter that charges the battery block with power from the DC bus; and a control circuit that controls the main switch, charge switch, discharge converter, and charge converter; and when the BBU is reconnected to the DC bus, the control circuit turns off the main switch and charge switch and sets the charge converter and discharge converter to operating states, so that the smoothing capacitor is charged with output from the DC bus via the charge converter and discharge converter regardless of the output of the battery block.

[0023] In another embodiment of the backup power supply of the present invention, the BBU has a circuit configuration in which a power supply capacitor is connected to the output side of the charging converter, and when charging the smoothing capacitor, the main switch and charging switch are turned off and the discharging converter is in a non-operating state, so that the power supply capacitor is charged by the output of the DC bus regardless of the output of the battery block, and then both the charging converter and the discharging converter are turned on, so that the smoothing capacitor can be charged by the output from the DC bus.

[0024] In another embodiment of the backup power supply of the present invention, after the smoothing capacitor is charged by the charge converter and discharge converter in operation, the charge switch is turned on to maintain the smoothing capacitor at the same potential as the DC bus.

[0025] In a backup power supply according to another embodiment of the present invention, the discharge converter of the BBU can be a non-isolated DC / DC converter.

[0026] In a backup power supply according to another embodiment of the present invention, the output power of the charging converter can be 1 / 10 or less of the output power of the discharging converter.

[0027] A backup power supply in another embodiment of the present invention is equipped with a generator that supplies power to a DC bus, and in the event of a power outage, a discharge converter supplies power to the DC bus until the generator starts up, and after the generator starts up, power can be supplied from the generator to the DC bus.

[0028] 1 to 4, a backup power supply 1 has a plurality of battery backup units (BBUs) 3 detachably connected to a direct current bus line (DC bus) 2. The backup power supply 1 is a hot-swap power supply in which each BBU 3 can be detached. In the hot-swap backup power supply 1, each BBU 3 is disconnected from the DC bus 2, then reset and reconnected to the DC bus 2, while the DC bus 2 is maintained at its operating voltage.

[0029] 1 includes a power supply circuit 4 of an AC / DC converter that converts AC from the commercial power supply into DC, supplying power to the DC bus 2 when the commercial power supply is not interrupted, and a generator 5 that supplies power to the DC bus 2 after the BBU 3 has supplied power during a power outage. Typically, the generator 5 outputs AC, and as shown in the figure, it is configured to supply power to the DC bus 2 via a power supply circuit 20 that converts AC to DC. This configuration makes it possible to protect a system connected to the DC bus 2 during a power outage or other such event.

[0030] The BBU 3 may be configured with a hot-swap function. A hot-swap BBU 3 can maintain the DC bus 2 of the entire system at its operating voltage while the battery block 6 is removed for maintenance. However, a BBU 3 removed from the backup power supply will experience a drop in voltage as the smoothing capacitor 9 gradually discharges. This is because if a BBU 3 with a smoothing capacitor 9 with a reduced voltage is directly connected to the DC bus 2, an excessive current will instantaneously flow from the DC bus 2 to the smoothing capacitor 9 with a reduced voltage. The inrush current can be resolved by charging the smoothing capacitor 9 of the removed BBU 3 to the DC bus 2 voltage and then connecting it to the DC bus 2.

[0031] The hot-swap backup power supply 1 has multiple BBUs 3 detachably connected to a direct current bus line (DC bus) 2. Each BBU 3 includes a battery block 6, a discharge converter (hereinafter referred to as the discharge converter) 7 that operates during a power outage to stabilize the output voltage of the battery block 6 and output it to the DC bus 2, a smoothing capacitor 9 connected to the output side of the discharge converter (hereinafter referred to as the charge converter) 7 to suppress fluctuations in the output voltage, a charge switch 10 that connects the charged smoothing capacitor 9 to the DC bus 2, a charge converter 8 that charges the battery block 6 with power from the DC bus 2 and maintains the battery block 6 in a charged state, a control circuit 11 that controls the charge switch 10, the discharge converter 7, and the charge converter 8, and a main switch 19 that is provided between the battery block 6 and the discharge converter 7 and charge converter 8. The main switch 19 is provided to prevent excess leakage current from reducing the remaining battery capacity of the battery block 6.

[0032] When BBU 3, which has been disconnected from backup power supply 1 (i.e., from DCbus 2), is reconnected to DCbus 2, control circuit 11 maintains charge switch 10 in the OFF state, maintains smoothing capacitor 9 in a state where it is not connected to DCbus 2, and operates charge converter 8 and discharge converter 7 to charge smoothing capacitor 9 with charging current from DCbus 2 via charge converter 8 and discharge converter 7, thereby maintaining smoothing capacitor 9 at the voltage of DCbus 2. In this way, while control circuit 11 controls main switch 19 and charge switch 10 to the OFF state, smoothing capacitor 9 is charged with charging current from DCbus 2 via charge converter 8 and discharge converter 7. Thereafter, control circuit 11 switches charge switch 10 to the ON state, maintaining smoothing capacitor 9 at the voltage of DCbus 2. Note that during this time, main switch 19 is controlled to be OFF.

[0033] The backup power supply 1 described above switches the discharge converter 7 of each BBU 3 to an active state when it detects a commercial power outage. The active discharge converter 7 supplies power from the battery block 6 to the DC bus 2. With each battery unit supplying power to the DC bus 2, the voltage of the DC bus 2 is maintained constant, allowing power to be continuously supplied to the load during a power outage. At this time, the output capacitor of the discharge converter is charged in advance, thereby shortening the startup time of the discharge converter.

[0034] Backup power supply 1 detects a power outage in the AC commercial power supply and supplies power from each BBU 3 to DC bus 2, thereby maintaining the supply of power to loads such as servers even during a power outage. When the AC commercial power supply is not interrupted, backup power supply 1 supplies power to the load from the commercial power supply's power supply circuit 4 via DC bus 2. When the commercial power supply fails, power cannot be supplied from the commercial power supply's power supply circuit 4 to DC bus 2, so when backup power supply 1 detects a power outage, it supplies power from BBU 3 to DC bus 2 to prevent a voltage drop on DC bus 2.

[0035] In the event of a power outage, the backup power supply 1 shown in the circuit diagram of Figure 1 first supplies power from the battery block 6 to the DC bus 2, and then supplies power from the generator 5 to the DC bus 2. The battery block 6 can switch the discharge converter 7 into an operating state to supply power to the DC bus 2, or switch the generator 5 into an operating state to supply power to the DC bus 2. However, while the discharge converter 7 can start up quickly and quickly supply power to the DC bus 2 after detecting a power outage, the generator 5 takes time to start up and requires a startup time before it can output the specified voltage to the DC bus 2.

[0036] When a power outage occurs and the voltage on DC bus 2 drops, the load will no longer operate normally, so when the backup power supply 1 shown in FIG. 1 detects a power outage, it starts the generator 5 while supplying power from BBU 3 to DC bus 2. It takes several minutes for the generator 5 to start. The BBU 3 continues to supply power to DC bus 2 for several minutes until the generator 5 starts up normally.

[0037] The BBU3 is required to supply power to the DC bus2 quickly (preferably within 10 milliseconds) after detecting a power outage, preventing a voltage drop on the DC bus2 and maintaining the load in operation. The voltage drop on the DC bus2 after a power outage is affected by the capacitance of the smoothing capacitor 9 connected to the DC bus2, the capacitance of the electrolytic capacitor connected to the DC bus, and the current consumption of the load. The capacitance of the electrolytic capacitor connected to the DC bus is the total capacitance of the smoothing capacitor and the electrolytic capacitor connected to the DC bus. The voltage drop on the DC bus2 after a power outage can be delayed by increasing the total capacitance of the electrolytic capacitor and the electrolytic capacitor on the load input side.

[0038] The voltage of DC bus 2, to which the electrolytic capacitor is connected, is set so that there is no voltage drop in order to start the discharge converter within 10 milliseconds after a commercial power outage and protect the load system.

[0039] Since backup power supply 1 detects a power outage and starts supplying power to DC bus 2 with a short delay (ideally within 10 milliseconds), BBU 3 that has been disconnected from DC bus 2 also needs to have its smoothing capacitor 9 charged in advance after being reconnected so that it can supply power to battery block 6 in the event of a power outage. When BBU 3 with smoothing capacitor 9 that has been disconnected from DC bus 2 and whose voltage has dropped is connected to DC bus 2, backup power supply 1 in Figure 1 charges smoothing capacitor 9 of BBU 3 that has been reconnected to DC bus 2 with the voltage of DC bus 2 via charge converter 8 and discharge converter 7, so that BBU 3 can quickly supply power to DC bus 2 from the reconnected BBU 3 in the event of a power outage.

[0040] (Battery Block 6) The battery block 6 connects multiple battery cells in series or parallel, and sets the output voltage and charge / discharge capacity to optimal values. The battery block 6 can increase the output voltage by connecting battery cells in series, the output current by connecting them in parallel, and the charge / discharge capacity by increasing the number of cells connected in parallel with DC. The battery cells can use non-aqueous secondary batteries such as lithium-ion batteries, which can increase the volume and charge / discharge capacity relative to the volume. However, all secondary batteries currently in use or to be developed in the future, such as all-solid-state batteries, can be used for the battery cells.

[0041] (Discharge converter 7, charge converter 8) The discharge converter 7 and charge converter 8 are CVCC (constant voltage constant current characteristic) DC / DC converters that control the output voltage to a constant voltage and set the maximum value of the output current. The discharge converter 7 and charge converter 8 can be non-insulated types.

[0042] The maximum output power of the discharge converter 7 is set to, for example, 1 / 10 or less, preferably 1 / 20 or less. This is because the discharge power of the battery block 6 is significantly greater than the charge power. The battery block 6 supplies large amounts of power during a power outage by discharging for a short time, such as a few minutes, but does not necessarily need to be fast-charged. Because fast charging can cause battery degradation, the charge time is set significantly longer than the discharge time. This is also the reason why the BBU does not use a bidirectional converter between the battery and the DC bus, but instead provides separate charge and discharge converters. This configuration makes it possible to pre-charge the smoothing capacitor without incurring the cost of additional circuitry.

[0043] Note that if a bidirectional converter is provided instead of the discharge converter 7 and charge converter 8, there is a problem in that the capacitor on the battery block side cannot be charged by the DC bus. In such a configuration, typically, the capacitor provided on the battery block side of the bidirectional converter is charged by charging from the battery block.

[0044] Furthermore, the above backup power supply 1 charges the smoothing capacitor 9 via the charge converter 8 and the discharge converter 7, so that the smoothing capacitor can be charged in advance in preparation for a power outage with higher efficiency and less heat generation than the conventional method of limiting the charging current of the smoothing capacitor using a current limiting resistor or the like.

[0045] 5 shows a circuit diagram of a discharge converter, which is a non-isolated DC / DC converter. The non-isolated DC / DC converter shown in this circuit diagram includes a semiconductor switching element 13, such as a power MOSFET, that is switched on and off at a predetermined cycle, a control circuit 11 that switches the semiconductor switching element 13 on and off, an inductor 14 that switches the direction of current flowing through the semiconductor switching element 13, and a smoothing capacitor 9 connected to the output side. The control circuit 11 detects the voltage of the smoothing capacitor 9, i.e., the output voltage, and controls the duty ratio for switching the semiconductor switching element 13 on and off to control the current flowing through the inductor 14, i.e., by adjusting the ratio of the on and off times of the semiconductor switching element 13, the voltage of the smoothing capacitor 9 is maintained at a constant voltage. When the output voltage becomes higher than the set voltage, which is the voltage of DC bus 2, control circuit 11 shortens the on time relative to the off time, i.e., reduces the duty ratio, shortens the conduction time of inductor 14, and reduces the output voltage to the set voltage, and conversely, when the voltage of smoothing capacitor 9 becomes the set voltage inductor of the duty ratio, increases the duty ratio and lengthens the conduction time of inductor 14, thereby controlling the output voltage to the set voltage. Furthermore, control circuit 11 detects the output current, and when the output current exceeds the set value, controls the duty ratio for switching semiconductor switching element 13 on and off so that the output current becomes the maximum set current, thereby controlling the output current not to exceed the maximum set current.

[0046] Discharge converter 7, a non-isolated DC / DC converter shown in Figure 5, can pass current from the input side to the output side by individually controlling the on state of semiconductor switching elements 13. This means that charge converter 8 can be operated, discharge converter 7 can be maintained in a pass-through state, and smoothing capacitor 9 can be charged with the output current of charge converter 8. However, if discharge converter 7 is maintained in a pass-through state and smoothing capacitor 9 is charged, there is a problem that excessive charging current will flow through switching element 13 and inductor 14 of discharge converter 7 if smoothing capacitor 9 is discharged and the voltage is low. This is because the on resistance of the switching element of discharge converter 7 in the on state is extremely small, and the internal resistance of discharged smoothing capacitor 9 is also extremely small. Excessive charging current flowing through switching element 13 and inductor 14 of discharge converter 7 can damage the switching element of discharge converter 7 and inductor 14.

[0047] In backup power supply 1 of the present invention, both the DC / DC converters of charge converter 8 and discharge converter 7 are in an operating state, and smoothing capacitor 9 is charged with the DC output of DC bus 2. Since the charging current output from charge converter 8 is supplied to smoothing capacitor 9 via discharge converter 7 in an operating state to charge smoothing capacitor 9, even when smoothing capacitor 9 is discharged and reaches a low voltage, smoothing capacitor 9 is not charged with an excessive current that passes through discharge converter 7.

[0048] 1 to 4 is connected to the input side of the discharge converter 7 and the output side of the charge converter 8, with the power supply capacitor 12 connected. When the BBU 3 is reconnected to the DC bus 2, in the process preceding the switching of both the charge converter 8 and the discharge converter 7 to the operating state, the control circuit 11 switches the discharge converter 7 to the non-operating state and the charge converter 8 to the operating state, and the operating charge converter 8 charges the input-side power supply capacitor 12. The non-operating discharge converter 7 switches its switching element to the off state, preventing current pass-through from the input side to the output side, and charges the power supply capacitor 12 with the current output from the charge converter 8. The operating charge converter 8 charges the power supply capacitor 12 to the charging voltage of the battery block 6. With power supply capacitor 12 charged to or nearly to the voltage of DCbus2, charge converter 8 and discharge converter 7 are put into operation, and while charge converter 8 charges power supply capacitor 12, discharge converter 7 converts the voltage of power supply capacitor 12 to the voltage of DCbus2 and outputs it, thereby charging smoothing capacitor 9 to the voltage of DCbus2.

[0049] As shown in Fig. 2, the above backup power supply 1 maintains the switching element of the discharge converter 7 in the OFF state and charges the power supply capacitor 12 using the charge converter 8 without passing through. With the power supply capacitor 12 in a charged state, as shown in Fig. 3, the discharge converter 7 is put into an operating state and charges the smoothing capacitor 9. The above backup power supply 1 has the advantage of being able to stably and quickly charge the smoothing capacitor 9 because the charge converter 8 charges the power supply capacitor 12 and maintains the input voltage of the discharge converter 7 at a constant voltage while charging the smoothing capacitor 9. After the smoothing capacitor 9 has been charged to a predetermined voltage, as shown in Fig. 4, the first semiconductor switching element 16 is put into the ON state and the smoothing capacitor 9 is charged to the voltage of the DC bus 2 via the current limiting resistor 15.

[0050] (Smoothing capacitor 9, power supply capacitor 12) The smoothing capacitor 9 is a capacitor connected to the output side of the discharge converter 7 to suppress fluctuations and ripples in the output voltage. Since the smoothing capacitor 9 can suppress fluctuations and ripples in the output voltage more effectively by increasing its capacitance, an electrolytic capacitor with a large capacitance, for example, an electrolytic capacitor with a capacitance of several hundred μF to several thousand μF or more, is used.

[0051] (Charging switch 10) The charging switch 10 of the backup power supply 1 in FIGS. 1 to 4 is a parallel circuit consisting of a first charging switch consisting of a series circuit in which a first semiconductor switching element 16 is connected in series with a current limiting resistor 15, and a second charging switch consisting of a second semiconductor switching element 17 to which the current limiting resistor 15 is not connected. When smoothing capacitor 9 is charged to a predetermined voltage, this charging switch 10 first turns on first semiconductor switching element 16 to make the voltage of smoothing capacitor 9 equal to that of DCbus2, and then switches second semiconductor switching element 17 to the on state to maintain the voltage of smoothing capacitor 9 at the voltage of DCbus2. Therefore, without using charging converter 8 and discharging converter 7 to charge smoothing capacitor 9 to the voltage of DCbus2, at the timing to charge smoothing capacitor 9 to a voltage approximate to the voltage of DCbus2, for example, a voltage that is 80% of the voltage of DCbus2, first semiconductor switching element 16 is switched on to charge smoothing capacitor 9 to the voltage of DCbus2, and then second semiconductor switching element 17 is switched on to maintain the voltage of smoothing capacitor 9 at the voltage of DCbus2. Therefore, backup power supply 1 equipped with this charging switch 10 can shorten the time it takes for charging converter 8 and discharging converter 7 to charge smoothing capacitor 9, and charge switch 10 can maintain the voltage of smoothing capacitor 9 at the voltage of DC bus 2.

[0052] (Control circuit 11) Control circuit 11 controls the on / off of charge switch 10 and controls the operating states of charge converter 8 and discharge converter 7 to supply DC power to DC bus 2 from each BBU 3 connected to DC bus 2. Control circuit 11 inputs an on or off signal to the gates of MOSFETs that are semiconductor switching elements 16 and 17 of charge switch 10 to control the on / off of semiconductor switching elements 16 and 17. Control circuit 11 detects that the voltage of smoothing capacitor 9 has risen to the voltage of DC bus 2 or to a voltage that is close to a preset DC bus 2 voltage, and switches semiconductor switching element 17 of charge switch 10 to the on state.

[0053] Furthermore, control circuit 11 switches on and off switching elements 13 of charge converter 8 and discharge converter 7 at a predetermined cycle to put the DC / DC converters in an operating state, and holds switching elements 13 in an off state to put them in an inoperable state. Control circuit 11 inputs on and off signals alternately at a predetermined cycle to the gates of the MOSFETs that are switching elements 13 of charge converter 8 and discharge converter 7 to put them in an operating state. In the operating state, control circuit 11 controls the duty ratio of the on and on signals input to the gates of the MOSFETs to control the output voltage and output current of each DC / DC converter.

[0054] The flow of charging smoothing capacitor 9 with power from DC bus 2 via charge converter 8 and discharge converter 7 will be described in detail below, based on steps 1 to 4. First, in step 1, control circuit 11 controls main switch 19 between battery block 6 and the discharge path to be in the off state. In step 2, as shown in FIG. 2, control circuit 11 starts charge converter 8 and charges power supply capacitor 12, which is provided on the input side of discharge converter 7, with charging current A. At this time, because main switch 19 between battery block 6 and the discharge path is controlled to be in the off state, power supply capacitor 12 is charged with power from DC bus 2 without using power from battery block 6. In step 3, as shown in FIG. 3, while maintaining the operation of step 2, i.e., charging power supply capacitor 12 with charging current A, discharge converter 7 is started using power from power supply capacitor 12, and smoothing capacitor 9, which is provided on the output side of discharge converter 7, is charged with charging current B. In step 4, control circuit 11 stops discharge converter 8, and connects DC bus 2 to smoothing capacitor 9 via current-limiting resistor 15, as shown in FIG. 4, and smoothing capacitor 9 is charged with charging current C. Step 4 is preferably performed when smoothing capacitor 9 has been charged to a certain extent and the voltage of smoothing capacitor 9 has approached the voltage of DC bus 2. Steps 2 and 3 may be configured to be performed substantially simultaneously. However, in order to stabilize the operation of discharge converter 7, it is preferable to perform step 3 when power supply capacitor 12 is charged to a certain extent, but there is no problem if there is a timing when the control of step 2 and the control of step 3 are performed at the same time.

[0055] Furthermore, if the BBU 3 is configured to be hot-swappable, it may be necessary to precharge the power supply capacitor 12 or the smoothing capacitor 9 while the charge remains therein. When considering such a situation, the operation of step 3 is particularly important. When the discharge converter 7 is configured as shown in FIG. 5 , it is possible to operate the discharge converter 7 so that the input current to the discharge converter 7 is output in a pass-through manner, unlike the procedure of the embodiment of the present invention. At the initial startup, i.e., when hot swapping is not anticipated and the smoothing capacitor 9 is to be charged without any charge remaining in the power supply capacitor 12 or the smoothing capacitor 9, the charge converter 8 can be started, and then the discharge converter 7 can be set to pass-through, allowing the charge converter 8 to charge the power supply capacitor 12 and the smoothing capacitor 9 (this corresponds to a configuration in which step 3 is omitted).

[0056] However, when the BBU 3 is configured to be hot-swappable, as in the embodiment of the present invention, it is not possible to charge the power supply capacitor 12 and the smoothing capacitor 9 using this type of control. Specifically, if the discharge converter 7 is set to pass-through mode while charge remains in the power supply capacitor 12 or the smoothing capacitor 9, the pass-through occurs when there is a difference between the input and output voltages of the discharge converter 7. This voltage difference can cause an inrush current to flow through the discharge converter 7, potentially resulting in a breakdown of the discharge converter 7. In particular, with the assumed circuit configuration, the voltage of the power supply capacitor 12 may be higher than the voltage of the smoothing capacitor 9 due to the difference in the natural discharge rates of the power supply capacitor 12 and the smoothing capacitor 9. In such a situation, it is effective to charge the smoothing capacitor 9 using the procedure of the embodiment of the present invention shown in Figures 3-5. Specifically, according to the procedure of the embodiment of the present invention, when Step 1 is performed, the power supply capacitor 12 can be charged by the charge converter 8 even if the voltage of the power supply capacitor 12 is equal to the voltage of the battery block 6 or has decreased due to natural discharge. When step 2 is executed, even if the voltage of smoothing capacitor 9 is equal to the voltage of DC bus 2 or has decreased due to natural discharge, it is possible to charge smoothing capacitor 9 by discharge converter 7. As described above, according to the procedure of the embodiment of the present invention, even if charge remains in power supply capacitor 12 and smoothing capacitor 9, it is possible to charge smoothing capacitor 9 while preventing inrush current.

[0057] The method for charging a smoothing capacitor of a backup power supply and the backup power supply of the present invention can be effectively used as a device that supplies power to a load during a power outage to maintain the load in an operating state.

[0058] REFERENCE SIGNS LIST 1 Backup power supply 2 DC bus (direct current bus line) 3 BBU (Battery backup unit) 4 Power supply circuit 5 Generator 6 Battery block 7 Discharge converter 8 Charging converter 9 Smoothing capacitor 10 Charging switch 11 Control circuit 12 Power supply capacitor 13 Semiconductor switching element 14 Inductor 15 Current limiting resistor 16 First semiconductor switching element 17 Second semiconductor switching element 19 Main switch 20 Power supply circuit

Claims

1. A method for charging a smoothing capacitor of a backup power supply, wherein the backup power supply is made up of a plurality of power supply units (BBUs: Battery backup units) connected to a direct current bus line (DC bus), and each of the plurality of BBUs comprises: a battery block; a discharge converter connected between the battery block and the DC bus line and outputting the output voltage of the battery block to the DC bus; a charge converter connected between the battery block and the DC bus line, connected in parallel to the discharge converter, and charging the battery block with power from the DC bus line; a smoothing capacitor connected to the output side of the discharge converter; a main switch connected between the battery block, the discharge converter, and the charge converter; a charge switch connected between the smoothing capacitor and the DC bus line; and a control circuit that controls the main switch, the charge switch, the discharge converter, and the charge converter, and wherein the control circuit controls the main switch and the charge switch to an off state, a smoothing capacitor of a backup power supply being charged with a charging current from the DC bus via the charging converter and the discharging converter while the control circuit controls the main switch and the charging switch to be in an off state.

2. A method for charging a smoothing capacitor of a backup power supply as claimed in claim 1, wherein the BBU further comprises an input-side power supply capacitor connected to the output side of the charge converter and to the input side of the discharge converter, and when the BBU is reconnected to the DC bus, the control circuit turns off the charge switch, inactivates the discharge converter, and operates the charge converter to charge the input-side power supply capacitor with the charge converter, and then operates the charge converter and the discharge converter to charge the smoothing capacitor with a charging current from the DC bus via the charge converter and the discharge converter.

3. A method for charging a smoothing capacitor of a backup power supply as claimed in claim 1, wherein after the smoothing capacitor is charged by the charge converter and the discharge converter in operation, the charge switch is turned on to maintain the smoothing capacitor at the same potential as the DC bus.

4. A method for charging a smoothing capacitor of a backup power supply according to claim 1, wherein the discharge converter is a non-isolated DC / DC converter.

5. A method for charging a smoothing capacitor of a backup power supply as set forth in claim 1, wherein the output power of the charging converter is 1 / 10 or less of the output power of the discharging converter.

6. A method for charging a smoothing capacitor of a backup power supply as claimed in claim 1, wherein the backup power supply further comprises a generator that supplies power to the DC bus, and during a commercial power outage, the discharge converter in operation supplies power to the DC bus before the generator starts up, and during a commercial power outage, after the generator has started up, the generator supplies power to the DC bus.

7. A hot-swap backup power supply having a plurality of power supply units (hereinafter referred to as BBUs: Battery backup units) detachably connected to a direct current bus line (DC bus), wherein each of the plurality of BBUs comprises: a battery block; a discharge converter that stabilizes the output voltage of the battery block and outputs it to the DC bus; a smoothing capacitor connected to the output side of the discharge converter; a charge switch connected between the DC bus and the smoothing capacitor; a charge converter that charges the battery block with power from the DC bus; a main switch provided between the battery block and the discharge converter and the charge converter; and a control circuit that controls the main switch, the charge switch, the discharge converter, and the charge converter, wherein, at the timing of reconnection of each of the BBUs to the DC bus, the control circuit turns off the main switch and the charge switch and sets the charge converter and the discharge converter to an operating state, and charges the smoothing capacitor with a charging current from the DC bus via the charge converter and the discharge converter.

8. A backup power supply as claimed in claim 7, wherein the BBU further comprises an input-side power supply capacitor connected to the output side of the charge converter and to the input side of the discharge converter, and wherein the control circuit, at the timing of reconnection of the BBU to the DC bus, turns the charge switch off, puts the discharge converter in a non-operating state, and puts the charge converter in an operating state, thereby charging the power supply capacitor with the charge converter in an operating state, and then, while turning the charge switch off, puts the discharge converter in a non-operating state, and puts the charge converter in an operating state, both the charge converter and the discharge converter are in an operating state, and charges the smoothing capacitor with a charging current from the DC bus via the charge converter and the discharge converter in an operating state.

9. A backup power supply according to claim 7, wherein the control circuit charges the smoothing capacitor with the charge converter and the discharge converter in operation, and then turns on the charge switch to maintain the smoothing capacitor at the same potential as the DC bus.

10. A backup power supply according to claim 7, wherein the discharge converter is a non-isolated DC / DC converter.

11. A backup power supply according to claim 7, wherein the output current of the charging converter is 1 / 10 or less of the output power of the discharging converter.

12. A backup power supply according to claim 7, further comprising a generator that supplies power to the DC bus, wherein, during a power outage, the discharge converter in an operating state supplies power to the DC bus before the generator is started, and after the generator is started, the generator supplies power to the DC bus.

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