JP2001346340A - Ac power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of the cost increase of the device caused by the requirement of a plurality of current detectors when an interruptible power supply is constituted of a commercial power supply and an inverter. SOLUTION: An AC power supply 1 is connected to a load 3 via a first switch 4. An inverter 2 is connected to the load 3 via a second switch 6. The power supplying line 20 of the AC power supply 1 and the power supplying line 21 of the inverter 2 are magnetically connected to a common core 15. The synthesized current output of the two lines 20, 21 is obtained from the current detecting winding 16 of the core 15. The output of the current detector 11 is inputted into a comparator 23 to compare with an overcurrent reference voltage Vr1, controlling the inverter 2 to an 'OFF' state if the detected current is judged to be an overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply device for supplying power to a load using a commercial AC power supply and an inverter.

[0002]

2. Description of the Related Art A conventional uninterruptible power supply (UPS) comprises a commercial AC power supply 1 connected to a pair of AC power supply terminals 1a and 1b and a DC-AC converter or inverter 2 as shown in FIG.
Thus, power is supplied to the common load 3. More specifically, a pair of AC power supply terminals 1a, 1b
Is connected to the load 3 via the first switch 4 and the fuse 5. A pair of output terminals 2a and 2b of the inverter 2
Is connected to the load 3 via the second switch 6.
The first switch 4 has first, second, third and fourth contacts a.
1, a2, a3, a4 and the first and second movable contacts b1
, B2. The second switch 6 is the fifth, sixth,
It has seventh and eighth contacts a5, a6, a7, a8 and third and fourth movable contacts b3, b4. First and second
Switches 4 and 6 operate in opposite directions. That is, the first
When the first and second movable contacts b1 and b2 of the switch 4 are in contact with the first to fourth contacts a1 to a4, the third and fourth movable contacts b3 of the second switch 6 , B4
Are separated from the fifth to eighth contacts a5 to a8. The first and second switches 4 and 6 are controlled by a switch control circuit 7. In the case of FIG. 1, the switch control circuit 7
The first switch 4 is turned off when the power outage is detected,
The second switch 6 is turned on. When the AC power supply 1 returns to normal, the second switch 6 is turned off and the first switch 4 is turned on. It should be noted that the second switch 6 can be always turned on and the first switch 4 can be turned on when the inverter 2 fails.

By the way, first and second switches 4 and 6
It is difficult to instantaneously change the on / off state of the device.
For example, when the second switch 6 is turned off and the first switch 4 is turned on, even after the first switch 4 is turned on, the movable contacts b3 and b4 of the second switch 6 and the contact a5 are turned on. To a8 may be kept electrically connected by an arc. In such a case, at the same time when power is supplied from the AC power supply 1 to the load 3, the inverter 2 is connected in parallel to the AC power supply 1, and a cross current flows. Further, when the second switch 6 is turned on and the first switch 4 is turned off, if the turn-off of the first switch 4 is delayed by an arc or the like, power is supplied from the inverter 2 to the load 3 at the same time. A cross current flows from the inverter 2 to the AC power supply 1 side. If the cross current is large, the inverter 2 may be damaged. Therefore, in the conventional AC power supply device, as shown in FIG. 1, the first, second, and third current detectors 8a,
8b, 8c, or the first and second current detectors 8a, 8b, or the second and third current detectors 8b, 8c, and the load 3 Current I0 flowing through the first and second current detectors 8 is detected.
The current I1 of the AC power supply 1 and the current I2 of the inverter 2 are detected at a and 8b, and an overcurrent of the inverter 2 due to a cross current or the like is detected, and a stop command is given to the shutdown terminal 9 of the inverter 2 at the time of the overcurrent. The third current detector 8c is used for generating an alarm or the like when the load current I0 becomes larger than a predetermined value or for current control.

[0004]

By the way, if a plurality of current detectors 8a, 8b, 8c are provided as shown in FIG.
The state of each part can be reliably detected, and the inverter 2
Can be satisfactorily protected, but inevitably increases the cost of the AC power supply device.

[0005] Therefore, an object of the present invention is to reduce the cost of an AC power supply device.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the above object, the present invention provides an AC power supply terminal for supplying AC power to a load, and an AC power supply terminal between the AC power supply terminal and the load. A first switch provided in the power supply, an inverter for supplying power to the load, and an inverter provided between the inverter and the load and operated or controlled in the reverse of on / off of the first switch. The second formed
And a current detector for collectively detecting a current flowing from the AC power supply terminal to a line for supplying power to the load and a current flowing from the inverter to a line for supplying power to the load. The present invention relates to an AC power supply device characterized in that:

It is desirable that an overcurrent detection circuit be provided to control the inverter to be open when the overcurrent is detected, as viewed from the AC power supply side. It is desirable to provide a means for notifying an overcurrent state as described in claim 3.

[0008]

According to the invention of each claim, the first current when the power is supplied to the load only by the AC power supply by one current detector, and the current is supplied to the load only by the inverter. The second current and the sum of the load current and the cross current can be detected, and the cost of the AC power supply device can be reduced. According to the invention of claim 2, protection of the inverter can be easily achieved. Further, according to the third aspect of the invention, the load state can be easily monitored.

[0009]

Embodiments and Examples Next, an AC power supply device according to embodiments and examples of the present invention will be described with reference to FIGS. However, in FIG. 2, substantially the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The AC power supply device of FIG. 2 omits the first, second and third current detectors 8a, 8b and 8c from the circuit of FIG. 1, and provides a common current detector 11 in place of this. ,
First and second overcurrent detection circuits 12 and 13 and notification means 1
4 and the other components are the same as those shown in FIG.

The current detector 11 according to the present invention comprises a magnetic core 15, a detection coil 16, a rectifier 17, and an output resistor 1
8 A pair of power supply lines 19 of the AC power supply 1,
One of the lines 20 and the other of the pair of power supply lines 21 and 22 of the inverter 2 pass through the magnetic core 15. Therefore, lines 20, 21
Acts on the core 15 as a one-turn winding. Of course, two power supply lines 20, 21 may be wound around the core 15. The lines 19, 2 on the AC power supply side
0 and the lines 21 and 22 on the inverter side are connected to each other and also to the load 3.

The rectifier circuit 17 has four diodes D1, D
2, a full-wave rectifier circuit in which D3 and D4 are bridge-connected. The current detection winding 1 is connected to the AC input terminal of the rectifier circuit 17.
6, and an output resistor 18 is connected to the DC output terminal. Therefore, a voltage Vi corresponding to the absolute value of the current of the winding 16 is obtained in the resistor 18. This voltage Vi is called a current detection value.

The first overcurrent detection circuit 12 includes a first comparator 23 and a first reference voltage source 24. One input terminal (negative terminal) of the first comparator 23 is connected to the current detector 11, the other input terminal (positive terminal) is connected to the first reference voltage source 24, and this output terminal is connected to the inverter. 2 is connected to the shutdown terminal 9. The first reference voltage source 24 supplies a first reference voltage Vr1 having a higher level than the current detection value Vi corresponding to the rated load current when the power is normally supplied from the AC power supply 1 or the inverter 2 to the load 3. appear. Therefore, the first comparator 23 detects the current detection value Vi
Generates a low-level output when the voltage becomes higher than the first reference voltage Vr1, thereby controlling the inverter 2 to a shutdown state.

The second overcurrent detecting circuit 13 is for alarming purposes and comprises a second comparator 25 and a second reference voltage source 26. One input terminal (positive terminal) of the second comparator 25 is connected to the current detection circuit 11, and the other input terminal (negative terminal) is connected to the second reference voltage source 26. The second reference voltage source 26 generates a second reference voltage Vr2 having a value between the current detection value Vi corresponding to the rated current of the load 3 and the first reference voltage Vr1. The second comparator 25 generates a high-level output, that is, an alarm output when the current detector Vi becomes higher than the second reference voltage Vr2, and notifies the alarm means 14 of the output.
Send to The notification means 14 comprises, for example, an overcurrent notification buzzer, and notifies the buzzer when a relatively low overcurrent level state continuously occurs.

FIG. 3 shows the inverter 2 of FIG. 2 in detail. The inverter 2 includes a storage battery 30, a conversion circuit 31, a filter 32, a control circuit 33, and a charging circuit. Storage battery 30 is charged to a predetermined voltage by charging circuit 34. The charging circuit 34 converts the voltage of the commercial AC power supply 1 shown in FIG. 2 into a predetermined DC voltage and charges the storage battery 30.

Between a pair of terminals of the storage battery 30, first, second, third and fourth switches Q1, Q2, Q3, Q3 comprising semiconductor switches such as transistors, FETs, IGBTs, etc.
Q4 is bridged. That is, a series circuit of the first and second switches Q1, Q2 and a series circuit of the third and fourth switches Q3, Q4 are connected in parallel to the storage battery 30. The interconnection point P1 of the first and second switches Q1, Q2 and the interconnection point P2 of the third and fourth switches Q3, Q4 are connected to the inverter output terminals 2a, 2b via a high frequency component removing filter 32. Have been. Note that the filter 32 may include an output transformer. An inverter output voltage having the same frequency as the frequency (for example, 50 Hz) of the commercial AC power supply 1 is generated between the pair of output terminals 2a and 2b.

The control circuit 33 is a known circuit that alternately turns on and off the first and second switches Q1 and Q2 and alternately turns on and off the third and fourth switches Q3 and Q4. , A reference sine wave voltage generating circuit 35, a sawtooth wave generator 36, an error amplifier 37, a comparator 38, a control signal forming circuit 39, and a shutdown switch 40.
The control circuit 33 is substantially the same as, for example, the specification and drawings of Japanese Patent Application No. 11-60417 except for a shutdown switch 40, and is substantially the same as a part of a three-phase control circuit disclosed in Japanese Patent Application Laid-Open No. 11-41982. Therefore, the detailed description will be omitted, and will be briefly described. The reference sine wave voltage generating circuit of FIG. 3 generates a sine wave voltage of, for example, 50 Hz in synchronization with the voltage of the AC power supply 1 of FIG. Error amplifier 37
Corrects the amplitude of the reference sine wave voltage with the detected value of the inverter output voltage so that the output voltage of the inverter 2 is kept constant. The sawtooth generator 36 has a frequency (for example, 20 to 100 kHz) sufficiently higher than the frequency of the output voltage of the inverter 2.
Generates a sawtooth wave voltage, that is, a carrier. The comparator 38 generates a PWM pulse by comparing the sawtooth voltage of the sawtooth voltage generator 36 with the output sine wave of the error amplifier 37. The gate signal forming circuit 39 outputs the control signal Vg for the first to fourth switches Q1 to Q4 according to the output of the comparator 38 and the phase inversion signal.
1, Vg2, Vg3 and Vg4 are formed as schematically shown in FIG. 4 and supplied to the control terminals of the first to fourth switches Q1 to Q4. The shutdown switch 40 is provided between the power supply terminal 41 of the control signal forming circuit 39 and the control signal forming circuit 39, and is turned off when a low-level signal is input to the shutdown terminal 9, and is turned off from t1 to t1 in FIG. As shown in the period t2, generation of the control signals Vg1, Vg2, Vg3, Vg4 is prohibited. During the period from t1 to t2, all of the first to fourth switches Q1 to Q4 are turned off, and the load 3 or the AC power supply 1 is turned off.
The inverter 2 is open when viewed from the side. A switch equivalent to the shutdown switch 40 is connected to each switch Q.
1 to Q4 control signal lines, and switches Q1 to Q4
May be turned off.

[0018]

Next, the current detection by the current detector 11 will be described in detail. The AC power supply device of FIG.
There is a possibility of taking third and fourth modes.

The first mode is a mode in which the first switch 4 is turned on and the second switch 6 is turned off, and power is supplied to the load 3 by the AC power supply 1. This first
In the mode period, the AC power source 1 which is the same as the load current I0
Current I1 is detected by the current detector 11 and the current detection value V
i is the value shown in the following equation. Vi = KI1 = KI0 (K is a constant)

The second mode is when the first switch 4 is controlled to change from on to off and at the same time when the second switch 6 is controlled to change from off to on, or when the second switch 6 is changed from on to off. First switch 4 while controlling
Is a mode in which the AC power supply 1 serves as a power supply and a current flows through the load 3 and the inverter 2 when the power supply is switched from off to on. In this case, the AC power supply 1, the line 19 and the load 3
At the same time as the load current I0 flows through the circuit composed of the AC power supply 1, the line 19, the line 21, the inverter 2, the line 22, and the line 20, the cross current In flows through the circuit composed of the AC power supply 1, the line 19, the line 21, and the line 22. The magnetic flux proportional to the current I0 + In flowing through the line 20 and the current I flowing through the line 21
A sum with a magnetic flux proportional to n is generated, and a current detection value Vi represented by the following equation is obtained. Vi = K (Io + 2In) The detected current value Vi in the second mode is larger than the normal load current I0. When the current detection value Vi becomes higher than the voltage Vr1 of the first reference voltage source 24, the output of the comparator 23 goes low, and the control signal of the inverter 2 is shut down as shown at t1 to t2 in FIG. You. As a result, the inverter 2 is opened, and the cross current component 2In
Disappears. When the overcurrent condition is removed at t2, the control signal becomes valid again, for example, the second and third switches Q2
, Q3 are turned on. But still the first switch 4
Alternatively, if the conduction state of the second switch 6 due to an arc or the like is not resolved and both the first and second switches 2 and 4 are in the on state, a cross current occurs again, and the output of the comparator 23 becomes low. And the inverter 2 is again shut down from time t3. 4, t1 to t2, t3 to t4,
As shown after t5 to t6 and t7, the repetition of the shutdown operation of the inverter 2 is at most a half cycle of the voltage of the AC power supply 1. That is, when the current of the AC power supply 1 becomes zero, the arc of the first switch 4 or the second switch 6 is extinguished. Therefore, the operation shifts to a normal operation thereafter.

The third mode is a mode in which the first switch 4 is off and the second switch 6 is on, and the current I 2 of the inverter 2 is supplied to the load 3. This third
Current detection value V obtained from current detector 11 in the mode of
i can be expressed by the following equation. Vi = KI2 = KI0

In the fourth mode, when the first and second switches 4 and 6 are switched, the inverter 2 serves as a power supply and the load 3
And a mode in which current flows through the AC power supply 1. This fourth
In the first mode, a load current I0 flows through a circuit including the inverter 2, the line 21, the load 3, and the line 22, and a circuit including the inverter 2, the line 21, the line 19, the AC power supply 1, the line 20, and the line 22. Cross current In
Flows. Therefore, the current detection value Vi in the fourth mode can be expressed by the following equation. Vi = K (I0 + 2In) Since the detected current value Vi is larger than the rated load current as in the second mode, when the level of the cross current In is large, the output of the first comparator 23 becomes low, Inverter 2 is shut down.

In the circuit of FIG. 2, at least the load current I0 is detected in any of the first to fourth modes. Accordingly, if the load current I0 increases due to short-circuiting of the load 3 while power is being supplied from the inverter 2 to the load 3, the output of the first overcurrent detector 12 becomes low, and the inverter 2 is turned off. Is done. If the load current I0 increases due to short-circuiting of the load 3 while power is being supplied from the AC power supply 1 to the load 3, the fuse 5 as a circuit interrupting means is blown and the power supply is stopped. Since the power capacity of AC power supply 1 is sufficiently larger than the power capacity of inverter 2, AC power supply 1 is sufficiently protected by fuse 5.

The second overcurrent detection circuit 13 generates a second reference voltage Vc whose current detection value Vi is lower than the first reference voltage Vr1.
When r2 is exceeded, an alarm output is generated, and this is
Send to Thus, it is possible to notify the user of the overload state.

As is apparent from the above, the UP of this embodiment
According to the S-type AC power supply device, one current detector 11 can detect both that the current I0 of the load 3 is excessive and that the cross current is excessive. Therefore, it is possible to reduce the number of current detectors and reduce the cost of the AC power supply device. Further, in this embodiment, when the overcurrent occurs, the control signals Vg1 to Vg4 of the inverter 2 are stopped and the inverter 2 is opened, so that the protection of the inverter 2 can be achieved quickly and easily, and the normal operation can be achieved. Can be returned quickly. Further, since the alarm signal is formed based on the output of one current detector 11, the signal can be easily formed.

[0026]

[Modifications] The present invention is not limited to the above embodiment, and for example, the following modifications are possible. (1) The first and second switches 4, 6 can be single-sided switches that turn on / off only one of the pair of power lines. (2) The first and second switches 4 and 6 can be controllable semiconductor switches such as transistors and thyristors. Further, the first and second switches 6 can be manually operated. (3) The inverter 2 can be modified to a half-bridge type inverter. (4) Instead of forming the current detector 11 by CT, it can be formed by a Hall element or the like. When forming with a ball element, the magnetic flux of lines 20 and 21 is applied to one ball element. (5) The inverter 2 can be continuously turned off by the low-level output of the first comparator 23. That is, it can be continuously turned off after t1 in FIG. (6) In the embodiment, the inverter 2 is always in the operating state, but can be brought into the operating state only when the inverter 2 supplies power to the load 3. (7) In the embodiment, the first switch 4 is always on,
Although the second switch 6 is off, the second switch 6 can be normally turned on and the first switch 4 can be turned on when the inverter 2 is abnormal. (8) The control signals Vg1 to Vg1 of the inverter 2 are controlled so as to keep the load current or the voltage constant by the output of the current detector 11.
Vg4 pulse width control can also be performed. (9) Although the rectifier 17 is used for the current detector 11, the rectifier 17 can be omitted by using a window comparator for the overcurrent detection circuit 12.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional AC power supply device.

FIG. 2 is a circuit diagram showing an AC power supply device according to an embodiment of the present invention.

FIG. 3 is a circuit diagram illustrating the inverter of FIG. 2 in detail.

FIG. 4 is a waveform diagram showing a control signal of a switch of the inverter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Inverter 4, 6 1st and 2nd switch 11 Current detector 12 Overcurrent detection circuit

Claims (3)

[Claims] An AC power supply terminal for supplying AC power to a load; a first switch provided between the AC power supply terminal and the load; and an inverter for supplying power to the load. A second switch provided between the inverter and the load and configured to be operated or controlled in a manner opposite to the on / off state of the first switch; and power from the AC power supply terminal to the load. An AC power supply device, comprising: a current detector for detecting a current flowing in a line for supplying power to the line and a current flowing in a line for supplying power from the inverter to the load at a time. 2. An overcurrent detection circuit connected to the current detector, wherein the inverter is open when viewed from an AC power supply in response to a signal indicating an overcurrent obtained from the overcurrent detection circuit. 2. A control means for controlling the distance between the first and second parts.
An AC power supply as described. 3. An alarm overcurrent detection circuit connected to the current detector, and means for notifying an overcurrent state in response to an overcurrent signal obtained from the alarm overcurrent detection circuit. The AC power supply device according to claim 1 or 2, further comprising: