JPH09107681A - Dc uniterruptible power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a DC uninterruptible power supply apparatus whose circuit configuration is simple, which is miniaturized and which is low-cost. SOLUTION: A main circuit is constituted of an AC power supply 1, of diodes 2, 3, 4, of reactors 6, 7, of semiconductor switches 8, 9, of diodes 10, 11 and of capacitors 12, 13. A control circuit outputs a positive DC voltage and a negative DC voltage in such a way that the semiconductor switches 8, 9 are turned on or off by a PWM control operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC uninterruptible power supply device that rectifies a commercial power source to supply power to a load when the commercial power source is healthy, and supplies power to the load from the DC power source when the commercial power source fails.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a conventional example of a DC uninterruptible power supply of this type. In FIG. 5, the main circuit of the DC uninterruptible power supply is a commercial power supply 1, a diode 2,
3, reactors 6 and 7, semiconductor switches 8 and 9 such as IGBTs, diodes 10 and 11, smoothing capacitors 12 and 13, DC power supplies 21 and 22, and switches 23 and 24, Further, the control circuit 100 of the DC uninterruptible power supply device includes a power failure detection means 101 including a rectifier and a comparator, a commercial polarity determination means 102 including a comparator, a logic circuit, a PWM control circuit, a gate drive circuit, and the like. It is composed of semiconductor switch control means 103. Here, the terminal voltage of the DC power supply 21 is an arbitrary voltage lower than the set voltage across the capacitor 12, and the terminal voltage of the DC power supply 22 is an arbitrary voltage lower than the set voltage across the capacitor 13.

The operation of the DC uninterruptible power supply system shown in FIG. 5 will be described below. When the voltage of the commercial power source 1 is a specified value, for example, 85% or more of the rated voltage, that is, the power failure detection means 10
When 1 does not output the power failure signal (this state is called when the commercial power source 1 is healthy), the switch 22 and the switch 24 are turned off, and power is supplied from the commercial power source 1 to the load of the apparatus.

At this time, the polarity of the voltage of the commercial power source 1 is discriminated by the commercial polarity discriminating means 102, and when the semiconductor switch control means 103 has the positive polarity (the polarity shown in the figure), the semiconductor switch 8 is turned to the negative polarity (the opposite to that shown in the figure). When the polarity is set, the semiconductor switch 9 is turned on / off. The semiconductor switch 9 having the positive polarity and the semiconductor switch 8 having the negative polarity may be either on or off.

When the commercial power source 1 is healthy and the voltage polarity of the commercial power source 1 is positive, the semiconductor switch control means 103
Thus, when the semiconductor switch 8 is turned on, the voltage of the commercial power supply 1 is applied to the reactor 6, and the current flowing through the reactor 6 increases. The current at this time flows through the path of commercial power supply 1 → diode 2 → reactor 6 → semiconductor switch 8 → commercial power supply 1. When the semiconductor switch control means 103 turns off the semiconductor switch 8, the differential voltage between the voltage of the capacitor 12 and the voltage of the commercial power supply 1 is applied to the reactor 6 in the opposite direction to that when the semiconductor switch 8 is on, and the current decreases. . At this time, the current is commercial power source 1 → diode 2 → reactor 6 → diode 10 → capacitor 12 →
The energy of the reactor 6 is transmitted to the capacitor 12 by flowing through the path of the commercial power source 1. By controlling the on / off time ratio of the semiconductor switch 8, the current from the commercial power source 1 can be controlled to an arbitrary instantaneous value.
Further, this allows the voltage across the capacitor 12 to be set to an arbitrary value higher than the peak value of the voltage of the commercial power supply 1.

Next, when the commercial power source 1 is healthy, the commercial power source 1
When the voltage polarity is negative, the semiconductor switch control means 103 causes the diode 3, the reactor 7, the semiconductor switch 9, the diode 11, and the capacitor 13 to operate in the same manner as described above, and the energy of the reactor 7 is transmitted to the capacitor 13. When the commercial power supply 1 drops below the specified value, the power failure detection circuit 101 outputs a power failure signal (this state is referred to as a power failure of the commercial power supply 1) and the switches 23 and 24 are turned on.

In this state, the semiconductor switch control means 10
When the semiconductor switch 8 is turned on by 3, the DC power source 21
→ switch 23 → reactor 6 → semiconductor switch 8 → current flows through the path of the DC power source 21, and when the semiconductor switch control means 103 turns off the semiconductor switch 8,
A current flows through the path of DC power supply 21 → switch 23 → reactor 6 → diode 10 → capacitor 12 → DC power supply 21, and the energy of reactor 6 is transmitted to capacitor 12. Similarly, when the semiconductor switch 9 is turned on / off, energy is transferred to the capacitor 13.

In FIG. 5, the semiconductor switch control means 103 does not depend on whether the energy transmitted to the capacitor 12 and the energy transmitted to the capacitor 13 are supplied from the commercial power supply 1 or the DC power supplies 21 and 22.
The so-called PWM control for controlling the on / off time ratio of the semiconductor switch 8 to the semiconductor switch 9 can be independently controlled. Therefore, even when loads having different capacities are connected between the terminals P and M and between the terminals M and N shown in FIG. 5, the positive DC output voltage, that is, the voltage between the terminals P and M, A negative DC output voltage, that is, a voltage between the terminals M and N can always be maintained at a constant value, and a DC uninterruptible power supply with positive and negative outputs can be provided.

[0009]

As the switches 23 and 24 shown in FIG. 5, mechanical switches such as electromagnetic contactors and relays or semiconductor switches are used. However, when the mechanical switches are used, it takes time to operate. Because it costs, commercial power source 1
The DC output voltage of the device decreases during the period from the detection of the power failure to the time when the mechanical switch actually turns on. In order to suppress this voltage drop, it is necessary to increase the capacitance of the capacitors 12 and 13, which causes a problem that the device becomes large.

When a semiconductor switch that operates at high speed is used instead of the mechanical switch, a so-called gate drive circuit for controlling ON / OFF of the semiconductor switch is required, which complicates the device. There was also a problem. An object of the present invention is to provide a DC uninterruptible power supply device that solves the above problems.

[0011]

[Means for Solving the Problems] In a DC uninterruptible power supply device that rectifies the commercial power source to supply power to the load when the commercial power source is healthy, and supplies power to the load from the DC power source when the commercial power source fails
According to the first aspect of the present invention, a series connection circuit of a first diode and a second diode and a series connection circuit of a third diode and a DC power source are connected in parallel, and a first semiconductor switch and a second semiconductor switch are connected in series. And connecting the parallel connection point of the parallel connection circuit and both ends of the series connection circuit of the semiconductor switch via the first and second reactors, respectively, and connecting the first capacitor and the second capacitor in series. The semiconductor switch and the first capacitor are connected via the fourth diode, the second semiconductor switch and the second capacitor are connected via the fifth diode, and one end of the commercial power supply is connected to the first diode and the second diode. The other end of the commercial power supply, the connection point of the first semiconductor switch and the second semiconductor switch, and the connection point of the first capacitor and the second capacitor are connected in parallel with each other. And a control circuit for controlling the main circuit of the DC uninterruptible power supply, wherein both ends of the first capacitor are positive side DC output and both ends of the second capacitor are negative. Side DC output.

According to a second aspect, in the first aspect,
In the control circuit, a commercial polarity discriminating unit that discriminates the voltage polarity of the commercial power source and outputs a positive or negative commercial signal, and a power failure detecting unit that detects a power failure of the commercial power source and outputs a power failure signal And an internal polarity signal generating means for alternately generating positive polarity or negative polarity internal signals at a predetermined cycle,
A semiconductor switch control means for turning on or off each of the first and second semiconductor switches, wherein the semiconductor switch control means outputs the second signal when the commercial power source is healthy and a positive commercial signal is output. When the semiconductor switch is turned off, the first semiconductor switch is turned on / off by the PWM control based on the set value of the voltage across the first capacitor, and when the commercial power source is healthy and a negative commercial signal is output. , The first semiconductor switch is turned off, the second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor, and when the commercial power supply is out of power, a positive internal signal is output. The second semiconductor switch is turned on, the first semiconductor switch is turned on based on the set value of the voltage across the first capacitor. It is turned on and off by the PWM control,
When the commercial power source is out of power and the negative internal signal is output, the first semiconductor switch is turned on, and the second semiconductor switch is turned on by PWM control based on the set value of the voltage across the second capacitor. Turn off.

A third invention is the same as the first invention,
In the control circuit, a commercial polarity discriminating unit that discriminates the voltage polarity of the commercial power source and outputs a positive or negative commercial signal, and a power failure detecting unit that detects a power failure of the commercial power source and outputs a power failure signal And an internal polarity signal generating means for alternately generating positive polarity or negative polarity internal signals at a predetermined cycle,
A commercial signal and an internal signal are input, the commercial signal is selected and output when the commercial signal changes within a predetermined time period, and the internal signal is selected when the commercial signal does not change within the predetermined time period. And a polarity selecting means for outputting
Semiconductor switch control means for turning on or off each of the second semiconductor switches, and when the commercial power source is healthy and the output of the polarity selection means is a positive commercial signal or internal signal by the semiconductor switch control means, The semiconductor switch is turned off, and the first semiconductor switch is set to the first
It is turned on / off by PWM control based on the set value of the voltage across the capacitor, and when the commercial power source is healthy and the output of the polarity selection means is a negative commercial signal or internal signal, the first semiconductor switch is turned off. , The second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor, and when the commercial power source is in a power failure and the output of the polarity selecting means is a positive commercial signal or an internal signal. , The second semiconductor switch is turned on, the first semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor, the commercial power supply is in the power failure, and the output of the polarity selection means is negative. In the case of the commercial signal or the internal signal, the first semiconductor switch is turned on and the second semiconductor switch is set to the voltage across the second capacitor. Turning on or off by PWM control based on.

A fourth aspect of the present invention is the power outage power supply device according to the first aspect, wherein an electromagnetic contactor is inserted into and connected to one end of the commercial power source, and the control circuit comprises:
A commercial polarity discriminating means for discriminating the voltage polarity of the commercial power source and outputting a positive polarity or negative polarity commercial signal; a power failure detecting means for detecting a power failure of the commercial power source and outputting a power failure signal;
A timer means for measuring a predetermined time period from the time when the power failure signal is output, an internal polarity signal generating means for alternately generating a positive polarity or negative polarity internal signal at a predetermined cycle, a commercial signal and an internal signal. Polarity selecting means for inputting and selecting and outputting the commercial signal when the commercial signal is changing within a predetermined time period, and for selecting and outputting the internal signal when the commercial signal is not changing within the predetermined time period. A semiconductor switch control means for turning on or off each of the first and second semiconductor switches, and an electromagnetic contactor is turned on when the commercial power source is healthy by the output of the power failure detection means, and an electromagnetic contactor when the commercial power source is black. The contactor is released, and the semiconductor switch control means turns off the second semiconductor switch when the commercial power source is healthy and the output of the polarity selection means is a positive commercial signal or internal signal. 1 a semiconductor switch is turned on and off by the PWM control based on the set value of the voltage across the first capacitor, when the output of the and polarity selection means and the commercial power source is at the time of sound is negative polarity of the commercial signal or the internal signal,
The first semiconductor switch is turned off, and the second semiconductor switch is set to PW based on the set value of the voltage across the second capacitor.
When the commercial power supply is turned off by the M control, the timer means does not reach a predetermined time limit when the commercial power source is in a power failure, and the output of the polarity selection means is a positive commercial signal or an internal signal, the second
Turning on / off the semiconductor switch at a predetermined on / off ratio, and turning on / off the first semiconductor switch by PWM control based on the set value of the voltage across the first capacitor;
When the commercial power source is out of power and the timer means does not reach a predetermined time limit and the output of the polarity selecting means is a negative commercial signal or an internal signal, the first semiconductor switch is turned on / off at a predetermined on / off ratio. Then, the second semiconductor switch is turned on / off by the PWM control based on the set value of the voltage across the second capacitor, the timer means reaches a predetermined time limit when the commercial power source is out of power, and the output of the polarity selecting means is positive. In the case of a power-supply commercial signal or internal signal, the second semiconductor switch is turned on, and the first semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor. When the timer means reaches a predetermined time limit and the output of the polarity selecting means is a negative commercial signal or internal signal, the first semiconductor switch is turned on and the second semiconductor switch is turned on. Turning on or off by PWM control based conductor switches to the set value of the voltage across the second capacitor.

According to the first to fourth aspects of the invention, when the commercial power source fails, positive and negative direct currents are supplied to the load of the apparatus by the two DC power sources and the two switches shown in the above-mentioned conventional example. On the other hand, positive and negative direct currents can be supplied to the load by the series connection circuit of one DC power source and the diode, the internal polarity signal generating means of the control circuit, and the semiconductor switch control means.

[0016]

1 is a circuit configuration diagram of a DC uninterruptible power supply showing an embodiment of the present invention. The main circuit of the DC uninterruptible power supply is a commercial power supply 1, a diode 2,
3, 4, DC power supply 5, reactors 6, 7 and IGB
Semiconductor switches 8 and 9 such as T and diodes 10 and 1
1, the smoothing capacitors 12 and 13, and the control circuit 20.
0, 300, or 400, and the terminal voltage of the DC power supply 5 is set to an arbitrary voltage lower than both the voltage across the capacitor 12 and the voltage across the capacitor 13 to be set.

[0017]

FIG. 2 is a circuit configuration diagram of a DC uninterruptible power supply device showing a first embodiment of the present invention. Components having the same functions as those of the conventional example shown in FIG. The description will be omitted, and the description will focus on functions different from those in FIG. That is, in FIG. 2, the control circuit 200 includes the power failure detection means 10
1, a commercial polarity discriminating means 102, a semiconductor switch controlling means 201 including a logic circuit, a PWM control circuit, a gate driving circuit, and the like, and an internal polarity including an astable multivibrator that outputs a square wave of 50 to 60 Hz. It is composed of the signal generating means 202.

The operation of the DC uninterruptible power supply system shown in FIG. 2 will be described below. When the commercial power source 1 is healthy, that is, when the power outage detection unit 101 does not output a power outage signal, and the voltage polarity of the commercial power source 1 detected by the commercial polarity determination unit 102 is positive (polarity shown), the semiconductor switch The control means 201 turns on / off the semiconductor switch 8 and turns off the semiconductor switch 9. Further, in the above-mentioned state, when the voltage polarity of the commercial power source 1 detected by the commercial polarity discriminating means 102 has a negative polarity (a polarity opposite to that shown in the drawing), the semiconductor switch control means 201 turns on / off the semiconductor switch 9, The switch 8 is turned off. The method of turning on / off the semiconductor switch 8 or 9 to control the voltage across the capacitor 12 or 13 to a set value is the same as in the conventional example shown in FIG.

At the time of power failure of the commercial power supply 1, when the internal polarity signal output by the internal polarity signal generating means 202 is positive, the semiconductor switch control means 201 turns on / off the semiconductor switch 8 and turns on the semiconductor switch 9. The current path when the semiconductor switch 8 is on is the DC power supply 5 → diode 4 → reactor 6 → semiconductor switch 8 → semiconductor switch 9 → reactor 7 → DC power supply 5, and when the semiconductor switch 8 is turned off, the current is the DC power supply. 5
→ Current flows through the path of diode 4 → reactor 6 → diode 10 → capacitor 12 → semiconductor switch 9 → reactor 7 → DC power supply 5. That is, when the internal polarity signal is positive, power is supplied only to the capacitor 12. Similarly, when the internal polarity signal is negative, the semiconductor switch control means 201 turns on / off the semiconductor switch 9 and turns on the semiconductor switch 8. In this case, power is supplied only to the capacitor 13. Therefore, FIG.
In the same way as the conventional circuit shown in 1,
The positive-side output and the negative-side output can be individually controlled regardless of the power supply from the DC power supply 5.

In the circuit configuration shown in FIG. 2, for example, when a positive AC voltage is present in the AC power supply 1 when the semiconductor switch 8 is on, the commercial power supply 1 turns the reactor 6 into
Will be short circuited for up to half a cycle through
At this time, the current from the commercial power supply 1 may have a very large value. Further, since the diode 4 is inserted in the discharging direction of the DC power supply 5, it is needless to say that the DC power supply may be on the negative electrode side, not limited to the example of FIG.

Therefore, the DC uninterruptible power supply of the first embodiment is premised on the application only when the voltage of the AC power supply 1 is equal to or higher than the specified value, or when there is no voltage (0V). FIG.
2 is a circuit configuration diagram of a DC uninterruptible power supply showing a second embodiment of the present invention, and those having the same functions as those of the first embodiment shown in FIG. Will be omitted, and the description will focus on the functions different from those in FIG.

That is, in FIG. 3, the control circuit 300 includes a power failure detection means 101, a commercial polarity discrimination means 102, an internal polarity signal generation means 202, and a semiconductor switch control means including a logic circuit, a PWM control circuit, a gate drive circuit and the like. 301 and a polarity selecting means 302 including a logic circuit and a timer circuit. The polarity selecting means 302 shown in FIG. 3 inputs a commercial signal output from the commercial polarity determining means 102 and an internal signal output from the internal polarity signal generating means 202, and incorporates a change in the commercial signal into a timer. The output of the polarity selecting means 302 is monitored by a circuit and has a function of operating so as to switch from the commercial signal to the internal signal when the commercial signal does not change, for example, after half a cycle of the commercial power source 1 or more. .

The operation of the DC uninterruptible power supply system shown in FIG. 3 will be described below. When the commercial power source 1 is healthy, the same operation as in the first embodiment described above is performed, and it is determined that the commercial power source 1 is in the power failure state and the change of the commercial signal monitored by the polarity selecting means 302 is normal. If so, the semiconductor switch control means 301 turns on or turns on each of the semiconductor switches 8 and 9 in response to the commercial signal in the same mode as when the commercial power source 1 is healthy. For example, when the semiconductor switch 8 is on, the DC power supply 5 → diode 4 → reactor 6 → semiconductor switch 8 → semiconductor switch 9 → reactor 7 → DC power supply 5
The current supplied from the DC power supply 5 along the
There is a current supplied from the commercial power supply 1 in the path of the diode 2, the reactor 6, the semiconductor switch 8 and the commercial power supply 1, but any current decreases when the semiconductor switch 8 is off. That is, the ON / OFF time ratio of the semiconductor switch 8 is set to the above PW based on the voltage across the capacitor 12.
Performed by M control.

Next, when the commercial power source 1 is in a power failure and it is judged that the change of the commercial signal monitored by the polarity selecting means 302 is abnormal, that is, when the voltage of the AC power source 1 becomes extremely low (almost). 0 V), which is an operation based on the internal signal, and operates in the same manner as in the first embodiment. FIG.
It is a circuit block diagram of the DC uninterruptible power supply which shows the 3rd Example of this invention, The same code | symbol is attached | subjected to the thing which has the same function as the 1st, 2nd Example shown in FIG. The description will be omitted, and the description will focus on the functions different from those in FIGS.

That is, in FIG. 4, an electromagnetic contactor 31 is provided in the main circuit of the DC uninterruptible power supply, and the control circuit 3
00 is a power failure detection means 101 and commercial polarity determination means 102
Internal polarity signal generating means 202 and polarity selecting means 30
2, a semiconductor switch control unit 401 including a logic circuit, a PWM control circuit, a gate drive circuit, and the like, and a timer unit 402.

The operation of this DC uninterruptible power supply is such that the output of the power failure detecting means 101 closes the electromagnetic contactor 31 when the commercial power supply 1 is healthy, and opens the electromagnetic contactor 31 when the commercial power supply 1 fails. I have to. At this time, the time (about 20 milliseconds) until the power failure detection means 101 outputs the power failure signal and actually opens the electromagnetic contactor 31 is controlled by the timer means 402 by the semiconductor switch control means 401 when the commercial power supply 1 fails. The operation of the second embodiment is not performed.

That is, as described in the description of the first embodiment, when the commercial power source 1 has a power failure and a voltage is present in the commercial power source 1 while the device is operating according to the internal signal, the commercial power source 1 is When short-circuited for a maximum of half cycles via the reactor 6 or the reactor 7, and when the second embodiment is applied, the commercial power supply 1 is in a power failure and the voltage of the commercial power supply 1 is much higher than the rated voltage. Even when the voltage is low and slight, when the semiconductor switches 8 and 9 are switched at a high frequency of several kHz or more based on the PWM control, reactors 6 and 7 having small inductance values are used. A large current can flow to. Further, when used in an environment with a large amount of noise or the like, the sensitivity of the commercial polarity discriminating means 102 is not increased so much, and at this time, even if the commercial detection becomes impossible, a certain voltage may still exist. There is. Under such a condition, a current exceeding the rating may flow from the AC power supply 1 when operating according to the internal signal.

In order to prevent these, in the third embodiment, when the voltage of the AC power supply 1 becomes less than the specified value, the AC power supply 1 is disconnected by the electromagnetic contactor 31. Since it takes time to complete the interruption of the electromagnetic contactor 31, the above-mentioned problem may occur. Therefore, during the period until the completion of the cutoff, an increase in current is prevented by the output of the timer means 402, for example, when the internal signal has a positive polarity, the semiconductor switch 9 is turned off for a short fixed time within one switching cycle of the PWM control. However, after the interruption is completed, that is, after the measurement by the timer means 402 is completed, the same operation as in the second embodiment is performed.

[0029]

According to the first to third embodiments of the present invention, positive and negative direct currents can be supplied to a load by a series connection circuit of a single direct current power source and a diode when a commercial power source fails to operate. Only one DC power supply was needed instead of two, and it is possible to reduce the size and cost of the DC uninterruptible power supply. Moreover, since a mechanical switch or a semiconductor switch for switching the DC power supply is not required, the structure is simplified and the operation reliability is improved.

Further, according to the third embodiment, since the short circuit phenomenon of the commercial power source is avoided by providing the electromagnetic contactor, it is provided for protecting the commercial power source and the main circuit of the DC uninterruptible power supply. No need for fuses. Further, as the AC power source, a private power generation facility such as a diesel generator may be used in addition to the commercial power source.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a DC uninterruptible power supply showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a DC uninterruptible power supply showing a first embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a DC uninterruptible power supply showing a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of a DC uninterruptible power supply showing a third embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a DC uninterruptible power supply device showing a conventional example.

[Explanation of symbols]

1 ... Commercial power supply, 2, 3, 4 ... Diode, 5 ... DC power supply, 6, 7 ... Reactor, 8, 9 ... Semiconductor switch, 1
0, 11 ... Diodes, 12, 13 ... Capacitors, 2
1, 22 ... DC power supply, 23, 24 ... Switch, 31 ... Electromagnetic contactor, 100, 200, 300, 400 ... Control circuit, 101 ... Blackout detection means, 102 ... Commercial polarity determination means, 103, 201, 301, 401 ... semiconductor switch control means, 202 ... internal polarity signal generation means, 302 ... polarity selection means, 402 ... timer means.

Claims (4)

[Claims] 1. A direct current uninterruptible power supply device for rectifying a commercial power source to supply power to a load when the commercial power source is healthy, and for supplying power to the load from the DC power source when the commercial power source has a power failure. Series connection circuit of
A third diode and a series connection circuit of a DC power source are connected in parallel, a first semiconductor switch and a second semiconductor switch are connected in series, and a parallel connection point of the parallel connection circuit and both ends of the series connection circuit of the semiconductor switch are connected. Are respectively connected via the first and second reactors, the first capacitor and the second capacitor are connected in series, the first semiconductor switch and the first capacitor are connected via the fourth diode, and the second semiconductor switch And a second capacitor are connected via a fifth diode, one end of the commercial power supply is connected to a coupling point of the first diode and the second diode, the other end of the commercial power supply, the first semiconductor switch and the second semiconductor A main circuit of a direct current uninterruptible power supply device in which a connection point with a switch and a connection point between a first capacitor and a second capacitor are connected in parallel to each other; And a control circuit for controlling the circuit, the two ends of the first capacitor and the positive side DC output, a DC uninterruptible power supply, characterized in that the two ends of the second capacitor and the negative side DC output. 2. The DC uninterruptible power supply according to claim 1, wherein the control circuit includes a commercial polarity discriminating means for discriminating a voltage polarity of the commercial power source and outputting a positive or negative commercial signal. A power failure detecting means for detecting a power failure of the commercial power source and outputting a power failure signal; an internal polarity signal generating means for alternately generating a positive polarity or a negative polarity internal signal at a predetermined cycle; Semiconductor switch control means for turning on or off each semiconductor switch, and when the commercial power source is healthy and a positive commercial signal is output, the second semiconductor switch is turned off by the semiconductor switch control means, The first semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor, and when the commercial power source is healthy, a negative commercial signal is output. When the power is supplied, the first semiconductor switch is turned off, the second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor, and the commercial power source is in a power failure and has a positive polarity. When the internal signal is being output, the second semiconductor switch is turned on, the first semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor, and the commercial power source is in a power failure and When a negative polarity internal signal is being output, the first semiconductor switch is turned on, and the second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor. Uninterruptible power system. 3. The DC uninterruptible power supply according to claim 1, wherein the control circuit includes a commercial polarity discriminating means for discriminating a voltage polarity of the commercial power source and outputting a positive or negative commercial signal. , A power failure detecting means for detecting a power failure of the commercial power source and outputting a power failure signal, an internal polarity signal generating means for alternately generating a positive polarity or a negative polarity internal signal at a predetermined cycle, a commercial signal and an internal signal Polarity selection to input and to select and output the commercial signal when the commercial signal is changing within the predetermined time period, and to select and output the internal signal when the commercial signal is not changing within the predetermined time period Means and semiconductor switch control means for turning on and off each of the first and second semiconductor switches, the semiconductor switch control means ensures that the commercial power source is healthy and the output of the polarity selection means is positive. When sex commercial signal or the internal signal, the second semiconductor switch is turned off, on-the PWM control based the first semiconductor switch to the set value of the voltage across the first capacitor
When the commercial power supply is healthy and the output of the polarity selection means is a negative commercial signal or internal signal, the first semiconductor switch is turned off and the second semiconductor switch is turned off by the voltage across the second capacitor. The second semiconductor switch is turned on and off by the PWM control based on the set value, and when the commercial power source is in a power failure and the output of the polarity selecting means is a positive commercial signal or an internal signal, the first semiconductor switch is turned on. The first semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor, and when the commercial power source is in a power failure and the output of the polarity selection means is a negative commercial signal or an internal signal. Is turned on, and the second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor. DC uninterruptible power supply. 4. The DC uninterruptible power supply according to claim 1, wherein an electromagnetic contactor is inserted and connected to one end of the commercial power supply, and the control circuit determines the voltage polarity of the commercial power supply. And a commercial polarity discriminating means for outputting a positive or negative commercial signal, a power failure detecting means for detecting a power failure of the commercial power source and outputting a power failure signal, and a predetermined time period from when the power failure signal is output. A timer means for measuring, an internal polarity signal generating means for alternately generating a positive polarity or a negative polarity internal signal at a predetermined cycle, a commercial signal and an internal signal are input, and the commercial signal is output within a predetermined time period. Polarity selecting means for selecting and outputting a commercial signal when the commercial signal is changing and for outputting the internal signal when the commercial signal is not changing within the predetermined time period, and turning on each of the first and second semiconductor switches. Or And a semiconductor switch control means for turning on the electromagnetic contactor when the commercial power source is healthy, and releasing the electromagnetic contactor when the commercial power source has a power failure, by the output of the power failure detection means. When the power source is healthy and the output of the polarity selection means is a positive commercial signal or internal signal, the second semiconductor switch is turned off, and the first semiconductor switch is controlled by PWM control based on the set value of the voltage across the first capacitor. on·
When the commercial power supply is healthy and the output of the polarity selection means is a negative commercial signal or internal signal, the first semiconductor switch is turned off and the second semiconductor switch is turned off by the voltage across the second capacitor. The second semiconductor switch is turned on / off by PWM control based on a set value, and when the commercial power supply is out of power, the timer means does not reach a predetermined time limit and the output of the polarity selection means is a positive commercial signal or an internal signal. The predetermined on
The first semiconductor switch is turned on and off at an off ratio, the first semiconductor switch is turned on and off by PWM control based on the set value of the voltage across the first capacitor, the commercial power source is out of power, and the timer means does not reach a predetermined time limit. When the output of the polarity selecting means is a negative commercial signal or an internal signal, the first semiconductor switch is turned on / off at a predetermined on / off ratio, and the second semiconductor switch is set to the set value of the voltage across the second capacitor. The second semiconductor switch is turned on when the commercial power source is in a power failure and the timer means reaches a predetermined time limit and the output of the polarity selecting means is a positive commercial signal or an internal signal. , First
The semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the first capacitor, the timer means reaches a predetermined time limit when the commercial power source is out of power, and the output of the polarity selecting means is a negative commercial signal. Alternatively, when the signal is an internal signal, the first semiconductor switch is turned on, and the second semiconductor switch is turned on / off by PWM control based on the set value of the voltage across the second capacitor.