JP3306943B2 - Power supply switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for switching between a direct power supply and a UPS output when an uninterruptible power supply (hereinafter referred to as a UPS) detects an overcurrent.

[0002]

2. Description of the Related Art A conventional method of switching between a direct power supply and a UPS output will be described. FIG. 3 is a diagram showing a conventional example of a circuit for switching between a direct power supply and a UPS output, wherein 1 is a direct power supply, 3 is a UPS, 4 is an inverter, 5 is a current transformer,
6 is a load, 7 is a current detector, 8 is a comparator, 9 is a switching level setter, 19 is a switching control device, 30 is an AC switch, 31 is a semiconductor switch, and 32 is a fast-acting fuse.

The direct power supply 1 is connected to the U
The output of the UPS 3 is connected to the output side of the PS 3
, And the output of the UPS 3 is normally supplied to the load 6. When an overcurrent starts flowing to the load 6 due to a short circuit accident or the like on the load side, the overcurrent is detected by the current transformer 5 and the current detector 7. The value detected by the current detector 7 is a comparator 8
Is compared with a switching level preset in the switching level setting device 9. When the detected value exceeds the set value as a result of the comparison by the comparator 8, the switching control device 18 turns on the AC switch 30, and
Power supply from the direct power supply 1 to the load 6 is started. At the same time, an OFF command is output to the inverter 4, the output of the UPS 3 is turned off, and the UPS 3 is protected from an excessive current.

If the overcurrent is settled and the value detected by the current detector 7 falls below the switching level set in the switching level setting unit 9, the switching control unit 19 turns on the AC.
The switch 30 is turned off, and the power supply to the load 6 is switched from the direct power supply 1 to the UPS 3. The AC switch 30 for switching between the output of the UPS 3 and the direct power supply 1 is composed of a series circuit of a semiconductor switch 31 and a fast-blow fuse 32 cooperating with the semiconductor switch 31. As described above, when the current detector 7 detects an overcurrent, the power supply to the load 6 is switched from the output of the UPS 3 to the direct power supply 1. Since the power from the direct power supply 1 is supplied to the load 6 via the AC switch 30, the overcurrent further increases, and the overcurrent is increased by the semiconductor switch 3 in the AC switch 30.
When approaching the overload withstand capability of 1, the fast-blow fuse 32 is blown to protect the semiconductor switch 31.

[0005]

However, since the safe passing current range of the fast-blow fuse which is completely coordinated with the overload withstand capability of the semiconductor switch is considerably low, the overload withstand capability of the direct-feed side is reduced by the fast-blow fuse. When the setting is made in accordance with the above, there is a problem that the overload withstand capability on the direct sending side is set lower than the capability of the semiconductor switch.

Here, when the fast-blow fuse is removed, the overload withstand capability of the direct-feed side can be set to a value corresponding to the capability of the semiconductor switch. Therefore, it is difficult to detect an abnormality of the semiconductor switch. Further, if the power is continuously supplied from the direct transmission side and the overcurrent is stopped, and if the power is switched to the power supply from the UPS, the semiconductor switch cannot be turned off. There was a problem of being damaged up to.

Further, when the semiconductor constituting the AC switch is damaged by the overcurrent, the supply of power to the load has to be temporarily stopped in order to replace the AC switch. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the prior art, and does not use a fast-blow fuse for protecting an AC switch. And U
A method of switching a UPS AC switch that does not overlap with a PS output, and a hybrid that can replace a semiconductor switch that is damaged or possibly damaged by overcurrent without interrupting power supply from a direct power supply. The purpose is to provide an AC switch.

[0008]

In order to achieve the above object, according to the present invention, a power supply source to a load is increased without using a fast-blow fuse for protecting a semiconductor switch.
After switching from S to the direct power supply, an overcurrent flowing in the AC switch is detected. The peak value of the overcurrent is obtained from the overcurrent detection value, and is compared with the peak value of the overload capability of the semiconductor constituting the AC switch. Alternatively, a temporal change of the overcurrent is obtained from the overcurrent detection value, and is compared with the overload withstand capability of the semiconductor constituting the AC switch.

As a result of this comparison, if the detected value exceeds the overload capability of the semiconductor, the semiconductor is determined to be "damaged" or "possibly damaged". The power supply source for the load is not switched from the direct power supply to the UPS output.

[0010]

The peak value of the overcurrent flowing through the AC switch and the AC
By comparing the peak value of the overload withstand capability of the semiconductor constituting the switch, or by comparing the temporal change of the overcurrent flowing in the AC switch with the overload withstand capability of the semiconductor constituting the AC switch, "Damage" or "possibility of damage" is determined.

Even if the overcurrent stops, based on the above determination, the power supply to the load is not switched from the direct power supply to the UPS output. Does not wrap.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG.
FIG. 2 is a diagram showing a first embodiment according to the present invention. In FIG. 1, 10 is a comparator, 11 is an AC switch failure determination level setter, 12 is a memory, 18 is a switching control device, 20 is a hybrid AC switch, 21 is a semiconductor switch, 22 is a mechanical switch, and 23 is a semiconductor switch 21 Are plugs provided at both ends of the mechanical switch 22, and sockets provided at both ends of the mechanical switch 22. In addition,
Those having the same functions as those of the conventional example shown in FIG.

The hybrid AC switch 20 has a configuration in which a plug 23 is inserted into a socket 24, and a semiconductor switch 21 and a mechanical switch 22 are connected in parallel. By turning on / off the semiconductor switch 21, the device functions as an AC switch. The direct power supply is connected to the output side of the UPS 3 via the hybrid AC switch 20, and the output of the UPS 3 is connected to the load 6 via the current transformer 5.
, And the output of the UPS 3 normally supplies power to the load 6.

When a short circuit accident occurs on the load side and an overcurrent starts to flow, the current is transmitted to the current transformer 5 and the current detector 7.
To detect. The value detected by the current detector 7 is compared in the comparator 8 with the switching level set by the switching level setter 9. As a result of the comparison, when the detected value exceeds the switching level, the switching control device 18 fires the AC switch 2 and the power supply from the direct power supply 1 is started. At the same time, the inverter 4 is turned off and protected from excessive current.

Immediately after this, if the overcurrent stops and the value detected by the current detector 7 falls below the switching level set by the switching level setting unit 9, the switching control unit 18 extinguishes the AC switch 2 and turns off the load. 6 is switched from the direct power supply 1 to the inverter 4. The overcurrent detection value input to the comparator 10 is compared with the overload tolerance peak value of the semiconductor constituting the AC switch set in the AC switch failure determination level setting device 11. When the overcurrent continues to flow and further increases, if the overcurrent detection value exceeds the overload withstand peak value, an abnormal signal indicating that “the AC switch may be damaged” is written to the memory 12. The abnormal signal is input to the switching control device 18, and even if the overcurrent stops and the detection value of the current detector 7 falls below the switching level set by the switching level setting device 9, the power supply from the direct power supply 1 is continued. Thus, the inverter 4 is controlled not to be turned on, and at the same time, occurrence of an abnormality is displayed outside.

FIG. 2 is a diagram showing a second embodiment according to the present invention. In the configuration shown in FIG. 2, in order to more accurately determine the abnormality of the AC switch, the comparator 10 shown in FIG.
A memory 1 for storing the output of the current detector 7 as instantaneous current data instead of the switch failure determination level setter 11
3 and a memory 1 for storing a short-time overload withstand curve of a semiconductor constituting an AC switch in advance as tolerance data.
4 and a digital comparator 15.

The memory 13 stores the trend of the instantaneous current at the time of overcurrent as digital data, and compares the digital data with the overload tolerance data of the AC switch stored in the memory 14 by the digital comparator 15. As a result of the comparison by the digital comparator 15, if even one of the instantaneous current data exceeds the predetermined overload tolerance data of the AC switch, it is determined that the AC switch is abnormal and the first embodiment is performed. Similarly to the above, an abnormal signal indicating that “the AC switch may be damaged” is written in the memory 12. The abnormal signal is input to the switching control device 18, and even if the overcurrent stops and the detection value of the current detector 7 falls below the switching level set by the switching level setting unit 9, the power supply from the direct power supply 1 is continued. Thus, the inverter 4 is controlled not to be turned on, and at the same time, occurrence of an abnormality is displayed outside.

Next, the hybrid AC switch will be described. As described above, the hybrid AC switch is a device in which a semiconductor switch 21 and a mechanical switch 22 are connected in parallel using a plug 23 and a socket 24 as in the hybrid AC switch 20 in FIG. Normally (when power is supplied from the UPS 3), both the semiconductor switch 21 and the mechanical switch 22 are off. When an overcurrent occurs due to some factor such as a load side short circuit and the inverter 4 must be turned off, a switching command from the switching control device 18
The semiconductor switch 21 is instantly turned on, and at the same time, the inverter 4 is turned off.

The overcurrent further increases, and the semiconductor switch 2
1 when the overload tolerance is exceeded, that is, when it is determined that the AC switch may be damaged in the first and second embodiments, even after the overcurrent has stopped, the As described above, power supply to the load 3 is continued from the direct power supply without switching the power supply source to the UPS 3. In addition, the semiconductor switch 21 that may be damaged or possibly needs to be replaced with a normal one.

A procedure for replacing the semiconductor switch 21 which may be damaged with a normal one will now be described. First, the mechanical switch 22 is turned on, and then the semiconductor switch 21 that may be damaged is pulled out from the sockets 24 provided at both ends of the mechanical switch 22. Next, after the normal semiconductor switch 21 is inserted into the socket 24, the semiconductor switch 21 is turned on, and the mechanical switch 22 is turned off, thereby replacing the semiconductor switch 21 while power supply to the load is continued. Ends.

At this point, if the overcurrent has stopped, the power supply from the UPS 3 can be restarted by turning off the semiconductor switch 21 and starting the operation of the inverter 4 at the same time.

[0022]

As described above, in the first and second embodiments, it is determined that there is an abnormality in the AC switch.
When an abnormal signal indicating that “the AC switch may be damaged” is written in the memory 12, the occurrence of the abnormality is displayed to the outside, and at the same time, the abnormal signal is input to the switching control device 18. When an abnormal signal is input to the switching control device 18, after the overcurrent has subsided, the control to return from direct power supply to inverter power supply is stopped again, so that the AC switch does not turn off and the direct power supply and the UPS output overlap. Can be avoided.

Further, by providing a current detector and monitoring the load current, it is possible to omit the fast-blow fuse for protecting the semiconductor switch, to reduce the cost, and to possibly damage the AC switch due to an overcurrent. Can be performed easily and accurately.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment according to the present invention.

FIG. 2 shows a second embodiment according to the present invention.

FIG. 3 is a diagram showing a conventional example of a circuit for switching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Direct power supply 2 AC switch 3 UPS 4 Inverter 5 Current transformer 6 Load 7 Current detector 8,10 Comparator 9 Switching level setting device 11 AC switch failure judgment level setting device 12 Memory 13 Instantaneous current data memory 14 AC switch tolerance data memory Reference Signs List 15 digital comparator 18, 19 switching control device 20 hybrid AC switch 21, 31 semiconductor switch 22 mechanical switch 23 insertion plug 24 socket 30 AC switch 32 fast-blow fuse

Claims (3)

(57) [Claims] An apparatus for feeding an electric power to a load by switching between an output of a direct power supply and an output of an uninterruptible power supply by an AC switch connected in series between the direct power supply and the load, wherein a load current flowing through the load is detected. However, if a short circuit accident occurs in the load to which the uninterruptible power supply is supplying power and the load current exceeds a preset switching level, the AC switch is fired and the uninterruptible power supply is turned off. If the power supply to the load is switched from the uninterruptible power supply to the direct power supply and the load current supplied from the direct power supply via the AC switch exceeds the preset AC switch failure determination level setting value, the AC switch is destroyed. been possible there and determines the command to the AC switch-off state is not output even after that the load current becomes a level lower than the switching level, versus the load Te subsequently performed feeding from direct power supply, when the load current supplied through the AC switch from direct power does not exceed the AC switch failure determination level setting value set in advance, the subsequent load current is below the switching level Level A power supply switching method, comprising outputting a command to turn off an AC switch, restarting power supply by the uninterruptible power supply, and restarting power supply to the load by the uninterruptible power supply. 2. The power supply switching method according to claim 1, wherein the AC switch failure determination level setting value is:
A method for switching a power supply device, comprising setting a peak value of short-time overload withstand capability of a semiconductor constituting an AC switch. 3. The switching method for a power supply device according to claim 1, further comprising: a storage device for storing a short-time overload withstand curve of a semiconductor constituting the AC switch;
A method for switching a power supply device, wherein a set value of a C switch failure determination level is a short-time overload tolerance curve stored in the storage device.