JP3713429B2 - Offline UPS system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an offline UPS (Uninterruptible Power Supply) system.
[0002]
[Prior art]
FIG. 3 is a circuit diagram showing an example of a conventional offline UPS system. In FIG. 3, the offline UPS system 1 includes a power switch 2, a bypass circuit 3, an output switching relay switch 4, an AC / DC converter 5, a battery 6, a DC / AC inverter 7, an output terminal 8, and a control circuit 9. . This off-line UPS system is different from the on-line system in which the inverter is fed both during normal times and during power outages, during normal times it outputs the AC voltage of the commercial AC power supply 10, and in the event of a power outage or the like, the AC voltage from the DC / AC inverter 7 is output. This is an off-line uninterruptible power supply that switches to output the.
[0003]
The commercial AC power supply 10 is supplied to the contact 4 b of the output switching relay switch 4 through the power switch 2 and the bypass circuit 3, and is applied to the AC / DC converter 5. The DC voltage from the battery 6 is converted into an AC voltage by the DC / AC inverter 7 and supplied to the contact 4 c of the output switching relay switch 4.
[0004]
The control circuit 9 is composed of, for example, a microcomputer, monitors the input voltage from the commercial AC power supply 10 applied to the voltage monitoring port P1 via the power switch 2, and determines the common terminal of the output switching relay switch 4 according to the state of the input voltage. A control signal for switching and controlling 4a is output from the output port P2.
[0005]
In the above-described configuration, during normal operation, the control circuit 9 switches the common terminal 4a of the output switching relay switch 4 to the contact 4b side based on detection of the input voltage from the commercial AC power supply 10. Accordingly, the AC voltage of the commercial AC power supply 10 is supplied to the output terminal 8 via the bypass circuit 3 and the output switching relay switch 4. Further, the battery 6 is charged by applying the AC voltage of the commercial AC power supply 10 after being converted into a DC voltage by the AC / DC converter 5.
[0006]
On the other hand, at the time of a power failure of the commercial AC power supply 10, the control circuit 9 detects that the input voltage from the commercial AC power supply 10 has decreased, and controls the common terminal 4a of the output switching relay switch 4 to switch to the contact 4c side. To do. As a result, an AC voltage obtained by converting the DC voltage of the battery 6 by the DC / AC inverter 7 is supplied to the output terminal 8.
[0007]
FIG. 4 is a flowchart showing the above-described operation. First, the control circuit 9 converts the input voltage from the commercial AC power supply 10 into a monitoring voltage level (step S21), and then checks the input voltage value Vin (step S22). Next, it is determined whether or not the input voltage value Vin is equal to or higher than the threshold value Vth (Vth <Vin) (step S23).
[0008]
If the answer to step S23 is yes, the control circuit 9 switches and maintains the output switching relay switch 4 to the bypass circuit 3 side (step S24), and performs a commercial operation for supplying the AC voltage of the commercial AC power supply 10 to the output terminal 8. This is performed (step S25).
[0009]
On the other hand, if the answer to step 23 is no (for example, if the input voltage value Vin drops due to, for example, a power failure of the commercial AC power supply 10), the control circuit 9 sets the output switching relay switch 4 to the DC / AC inverter 7 side. (Step S26), and an inverter operation is performed in which the AC voltage obtained by converting the DC voltage of the battery 6 by the DC / AC inverter 7 is supplied to the output terminal 8 (step S27).
[0010]
In this way, the offline UPS system performs a commercial operation operation in which the AC voltage from the commercial AC power supply 10 is supplied to the output terminal 8 when normal, and performs an inverter operation in which power is supplied from the DC / AC converter 7 during a power failure. Works as an uninterruptible power supply system.
[0011]
[Problems to be solved by the invention]
In the offline UPS system described above, an overcurrent may occur due to an inrush current of a load (not shown) connected to the output terminal 8 or an output short circuit. When such an overcurrent occurs, the input voltage drops due to the influence of the power supply impedance. As a result, the control circuit 9 detects a drop in the input voltage, and from the commercial operation by the commercial AC power supply 10 to the DC / AC inverter 7. Switch to inverter power feeding.
[0012]
However, when the output switching relay switch 4 is switched while an overcurrent is flowing, arcing or chattering may occur between the contacts, which may cause deterioration of the contacts of the output switching relay switch 4 or contact welding. . Further, there is a problem that the commercial AC power supply 10 is short-circuited with the DC / AC inverter 7 due to the arc between the contacts, which may cause the semiconductor elements constituting the DC / AC inverter 7 to be destroyed.
[0013]
In view of the above-described problems, an object of the present invention is to provide an off-line UPS system that prevents deterioration and welding of relay contacts and destruction of semiconductor elements.
[0014]
[Means for Solving the Problems]
In view of the above-described object, the offline UPS system of the present invention includes an AC / DC converter that converts an AC voltage from a commercial AC power source into a DC voltage, a battery that is charged with the DC voltage from the AC / DC converter, and a battery. DC / AC inverter that converts DC voltage from AC to AC voltage, bypass circuit that bypasses AC voltage from commercial AC power supply, AC voltage from bypass circuit and AC voltage from DC / AC inverter are selectively output Switching means, an output terminal for supplying an alternating voltage selected by the switching means, and an alternating current input voltage from a commercial alternating current power source is monitored, and when a drop in alternating current input voltage is detected, the switching means is connected to the bypass circuit side. And a control circuit for controlling switching from the DC to AC inverter side. The control circuit includes output current detection means for detecting the output current at the output terminal, and operates to maintain the switch means on the bypass circuit side when the AC input voltage is lowered and the output current is in an overcurrent state.
[0015]
Thereby, deterioration and welding of the contact of the switch means and destruction of the semiconductor element of the DC / AC converter can be prevented.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of an offline UPS system according to the present invention. In FIG. 1, the same components as those of the conventional apparatus of FIG.
[0017]
In the offline UPS system shown in FIG. 1, in addition to monitoring the input voltage of the commercial AC power supply 10 using the same components as those in the conventional system shown in FIG. 3, the control circuit 9 monitors the output current flowing through the output terminal 8 and outputs it. The switching condition is characterized by an output overcurrent added in addition to an input voltage abnormality.
[0018]
That is, the control circuit 9 includes a current monitoring port P3 as output current detection means for monitoring the output current flowing through the output terminal 8.
[0019]
In the above-described configuration, during normal operation, the control circuit 9 switches and maintains the common terminal 4a of the output switching relay switch 4 as the switch means to the contact 4b side based on detection of the input voltage and output current within the normal range. are doing. Therefore, the AC voltage of the commercial AC power supply 10 is supplied to the output terminal 8 via the bypass circuit 3 and the output switching relay switch 4.
[0020]
On the other hand, when the output current from the output terminal 8 is in an overcurrent state, the control circuit detects that the output current is in the overcurrent state at the current monitoring port P3, and at the same time, as described above, The voltage monitoring port P1 detects that the input voltage has dropped due to the influence. In this case, the control circuit 9 does not switch the common terminal 4a of the output switching relay switch 4 to the contact 4c side, but maintains it on the contact 4b side. As a result, the commercial operation in which the AC voltage of the commercial AC power supply 10 is supplied to the output terminal 8 is maintained.
[0021]
In addition, when it is detected that the input voltage from the commercial AC power supply 10 is reduced and the output current is not in an overcurrent state (for example, including a power failure), the control circuit 9 outputs the output switching relay. The common terminal 4a of the switch 4 is switched to the contact 4c side. As a result, an AC voltage obtained by converting the DC voltage of the battery 6 by the DC / AC inverter 7 is supplied to the output terminal 8.
[0022]
FIG. 2 is a flowchart showing the operation of the above-described offline UPS system. First, the control circuit 9 converts the input voltage from the commercial AC power supply 10 into a monitoring voltage level (step S1), and then checks the input voltage value Vin (step S2). Next, it is determined whether or not the input voltage value Vin is equal to or higher than the threshold value Vth (Vth <Vin) (step S3).
[0023]
If the answer to step 3 is no (that is, an input voltage drop state such as during a power failure), then the control circuit 9 converts the output current at the output terminal 8 to a monitoring current level (step S4), Next, the output current value Iout is confirmed (step S5). Next, it is determined whether or not the output current value Iout is equal to or greater than the threshold value Ith (Ith <Iout) (step S6).
[0024]
If the answer to step S6 is yes (that is, the output overcurrent state), or if the answer to step S3 is yes, the control circuit 9 switches and maintains the output switching relay switch 4 to the bypass circuit 3 side (step S7). Then, commercial operation for supplying the AC voltage of the commercial AC power supply 10 to the output terminal 8 is performed (step S8).
[0025]
On the other hand, if the answer to step 6 is no, the control circuit 9 switches the output switching relay switch 4 to the DC / AC inverter 7 side (step S9), and the alternating current obtained by converting the DC voltage of the battery 6 by the DC / AC inverter 7 is used. An inverter operation for supplying a voltage to the output terminal 8 is performed (step S10).
[0026]
In this way, the offline UPS system performs a commercial operation operation in which the AC voltage from the commercial AC power supply 10 is supplied to the output terminal 8 during normal operation and overcurrent, and the output switching relay switch 4 performs switching operation during a power failure. Thus, it works as an uninterruptible uninterruptible power supply apparatus that performs an inverter operation for supplying power from the DC / AC converter 7. Therefore, since the output change-over relay switch 4 does not change over at the time of overcurrent, it is possible to prevent contact deterioration of the output change-over relay switch 4 and welding and destruction of the semiconductor element of the DC / AC converter 7.
[0027]
As described above, the embodiment of the present invention has been described. However, the present invention is not limited to this, and various modifications and applications are possible.
[0028]
For example, in the above-described embodiment, the relay switch is used as the switch means for selectively outputting the AC voltage from the bypass circuit 3 and the AC voltage from the DC / AC inverter 7, but other switch elements are used. You can also
[0029]
Further, the offline UPS system of the present invention further includes an overload protection device, for example, stops the UPS operation at 110 to 120% overload power, and maintains commercial operation at 400 to 600% output overcurrent. It can be set as the structure to do.
[0030]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the deterioration of the contact of a switch and the welding at the time of overcurrent and destruction of the semiconductor element of a DC / AC converter can be prevented.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of an offline UPS system according to the present invention.
FIG. 2 is a flowchart showing an operation of the offline UPS system of FIG.
FIG. 3 is a circuit diagram showing an example of a conventional offline UPS system.
4 is a flowchart showing the operation of the offline UPS system of FIG.
[Explanation of symbols]
1 Commercial AC power supply 3 Bypass circuit 4 Output switching relay switch (switch means)
5 AC / DC converter 6 Battery 7 DC / AC inverter 8 Output terminal 9 Control circuit P3 Current monitoring port (output current detection means)

Claims (1)

An AC / DC converter that converts an AC voltage from a commercial AC power source into a DC voltage, a battery that is charged with a DC voltage from the AC / DC converter, and a DC / AC that converts the DC voltage from the battery into an AC voltage Inverter, bypass circuit for bypassing AC voltage from commercial AC power supply, switch means for selectively outputting AC voltage from bypass circuit and AC voltage from DC / AC inverter, selected by switch means When the AC input voltage from the commercial AC power supply is monitored and a drop in the AC input voltage is detected, the switch means is connected from the bypass circuit side to the DC / AC inverter. An offline UPS system having a control circuit for switching control to the side,
The control circuit includes output current detection means for detecting an output current at the output terminal, and maintains the switch means on the bypass circuit side when the AC input voltage is reduced and the output current is in an overcurrent state. An off-line UPS system that operates.

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