JP2000278954A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter which does not cast a burden upon a system side by charging a battery using energy of both of two capacitors always equally, and also materializes the continuance of stable operation of an inverter by having a battery charge function, and also, having a balance function of two capacitors to unbalanced load, and further is inexpensive by constituting the circuit so as to communize some of these functions. SOLUTION: When a system power source 10 is normal, capacitors 8 and 9 are charged each by the switching of switches 40 and 41, and a battery 11 is charged by a switch 42. When the system power source 10 is abnormal, relays 24 and 48 are switched to charge the capacitors 8 and 9 each by the switching of the switches 40 and 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, and more particularly to an uninterruptible power supply capable of supplying power to a load even when a power failure occurs in a system power supply. The present invention relates to an apparatus having a function corresponding to charge / discharge of a battery and an unbalanced load.

[0002]

2. Description of the Related Art FIG. 20 shows, for example, pp. 149-152, No. 9 of the 1997 National Conference of the Institute of Electrical Engineers of Japan. 6
FIG. 9 is a circuit diagram of the conventional uninterruptible power supply shown in “Trial production of new circuit type single-phase UPS”. In the figure, 1 is a load, 2 is a capacitor, 3 is a reactor, 4 and 5 are switches, and 6 and 7 are diodes connected in anti-parallel to the switches 4 and 5, respectively. 7 constitute an inverter 26. Reference numerals 8 and 9 denote capacitors, reference numeral 10 denotes a system power supply (AC power supply), reference numeral 11 denotes a battery which is an energy source for supplying energy to the load 1 when the system power supply 10 fails, and reference numeral 12 denotes a reactor. 15 is a switch, 16, 17, 1
8, 19, 20, 21, 22, 25 are diodes, 23
Is a reactor, 24 is a relay, and 26 is an inverter.

Next, the operation of the conventional uninterruptible power supply will be described. First, when the system power supply 10 is normal, that is, when no power failure occurs, the relay 24 is connected to A in FIG. At this time, energy to be supplied from the system power supply 10 to the load 1 is obtained. For this reason, when the system power supply 10 is at a positive voltage (voltage in the direction of the arrow), the switch 13 is turned on and off,
When the switch 13 is turned on, the system power supply 10-relay 24-reactor 12-diode 16-switch 1
A current is accumulated in the reactor 12 in the direction of the arrow in the figure through the path of the 3-system power supply 10. Next, by turning off the switch 13, the system power supply 10-relay 2
4-Reactor 12-Diode 20-Capacitor 8-
The energy stored in the reactor 12 moves to the capacitor 8 through the path of the system power supply 10.
In this way, when the system power supply 10 has a positive voltage, the capacitor 8 is charged by turning the switch 13 on and off.

When the system power supply 10 is at a negative voltage (voltage in the opposite direction of the arrow), the switch 14 is turned on and off. When the switch 14 is on, the system power supply 10-switch 14-diode 17- A current is accumulated in the reactor 12 in a direction opposite to the arrow in the figure through the path of the diode 18, the reactor 12, the relay 24, and the system power supply 10. Next, by turning off the switch 14, the system power supply 10-capacitor 9-diode 2
The energy stored in the reactor moves to the capacitor 9 through the path of 5-diode 18-reactor 12-relay 24-system power supply 10. Thus, when the system power supply 10 has a negative voltage, the switch 9 is turned on and off to charge the capacitor 9.

The energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by an inverter 26 using the switches 4 and 5 and the diodes 6 and 7. Further, the reactor 3 and the capacitor 2
Constitutes a filter for removing high-frequency voltage components generated by the inverter 26, and a sine wave voltage that does not include high-frequency components is applied to the voltage applied to the load 1.

When the switch 15 is turned on, the battery 11 is charged by two charging paths. That is, when the system power supply 10 has a positive voltage and the capacitor 8 is charged from the system power supply 10, the switch 15-reactor 23-battery 11-diode 19-capacitor 8-diode 21-switch 15 By the path, current is accumulated in the reactor 23 from the capacitor 8 and charges the battery 11. When the switch 15 is turned off, the reactor 23-
The battery 11 is continuously charged by the energy of the reactor 23 through the path of the battery 11-diode 22-reactor 23. On the other hand, when the system power supply 10 has a negative voltage and the capacitor 9 is connected to the system power supply 1
During the period from 0 to charging, the capacitors 8 and 9 pass through the reactor 2 via the path of the switch 15 -reactor 23 -battery 11 -diode 25 -capacitor 9 -capacitor 8 -diode 21 -switch 15.
The current is accumulated in the battery 3 and the battery 11 is charged. Although the diode 25 is in the opposite direction, when the switch 14 is off (a period in which the capacitor 9 is charged from the system power supply 10), the current flows through the above-described path because the diode 25 is in a conductive state.

Next, when a power failure occurs in the system power supply 10, the relay 24 is connected to B in the figure. At this time, when the switches 13 and 14 are simultaneously turned on, the battery 11-relay 24-reactor 12-diode 16-switch 13-switch 14-diode 17-
Through the path of the battery 11, a current flows through the reactor 12 in the direction of the arrow in the figure, and energy is stored in the reactor 12. Next, for example, when only the switch 14 is turned off, the battery 11-the relay 24-the reactor 12
The energy of the reactor 12 moves to the capacitor 9 and charges the capacitor 9 through the path of the diode 16, the switch 13, the capacitor 9, the diode 25, and the battery 11. Similarly, when only the switch 13 is turned off, the battery 11-relay 24-reactor 12-diode 20-capacitor 8-switch 14-
The energy of the reactor 12 moves to the capacitor 8 through the path between the diode 17 and the battery 11 to charge the capacitor 8.

The energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by an inverter 26 constituted by the switches 4 and 5 and the diodes 6 and 7. Further, the reactor 3 and the capacitor 2
Constitutes a filter for removing high-frequency voltage components generated by the inverter 26, and a sine wave voltage that does not include high-frequency components is applied to the voltage applied to the load 1.

In this way, even if a power failure occurs in the system power supply 10, power can be constantly supplied to the load 1. Further, since the battery 11 has a function of charging, the battery can be recharged after the system power supply returns from the power failure state and becomes normal. The amount of charge of each of the capacitors 8 and 9 depends on whether the switch 13 or the switch 13
14 can be controlled by turning on and off, even if the load 1 is a load that generates an unbalanced current as shown in FIG. Can be controlled.

FIG. 22 is a circuit diagram of another conventional uninterruptible power supply disclosed in, for example, Japanese Patent Application Laid-Open No. 2-16867, entitled "Power Supply by PWM Control". In FIG.
The same reference numerals are used for the same symbols, and the description thereof is omitted. Reference numerals 30 and 31 denote switches, and reference numerals 32 and 33 denote diodes connected in antiparallel to the switches 30 and 31, respectively.

Next, the operation of the conventional uninterruptible power supply shown in FIG. 22 will be described. First, when the system power supply 10 is normal, that is, when no power failure occurs, the relay 24 is connected to A in the figure. At this time, energy to be supplied from the system power supply 10 to the load 1 is obtained. Therefore, when the system power supply 10 is at a positive voltage (voltage in the direction of the arrow), the switch 31 is turned on and off. When the switch 31 is on, the system power supply 10-relay 24-reactor 12-switch 31 is turned on. −
A current is accumulated in the reactor 12 in the direction of the arrow in FIG. Next, by turning off the switch 31, the system power supply 10
The energy stored in the reactor 12 moves to the capacitor 8 through the path of the relay 24, the reactor 12, the diode 32, the capacitor 8, and the system power supply 10. Thus, when the system power supply 10 has a positive voltage, the switch 8 is turned on and off to charge the capacitor 8.

When the system power supply 10 is at a negative voltage (voltage in the opposite direction of the arrow), the switch 30 is turned on and off. When the switch 30 is on, the system power supply 10-capacitor 8-switch 30- Reactor 1
A current is accumulated in the reactor 12 in a direction opposite to the arrow in the figure through the path of the 2-relay 24 and the system power supply 10.
Next, by turning off the switch 30, the system power supply 10-capacitor 9-diode 33-reactor 12
The energy stored in the reactor moves to the capacitor 9 through the path of the relay 24 and the system power supply 10. Thus, when the system power supply 10 has a negative voltage, the switch 9 is turned on and off to charge the capacitor 9.

The energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by an inverter 26 by the switches 4 and 5 and the diodes 6 and 7. Further, the reactor 3 and the capacitor 2
Constitutes a filter for removing a high-frequency voltage component generated by the inverter, and a sine wave voltage containing no high-frequency component is applied to the voltage applied to the load 1.

Next, when a power failure occurs in the system power supply 10, the relay 24 is connected to B in the figure. At this time, when the switch 31 is turned on, the battery 11-relay 24-reactor 12-switch 31-battery 1
Through the first path, a current flows through the reactor 12 in the direction of the arrow in the figure, and energy is stored in the reactor 12. Next, when the switch 31 is turned off, the battery 11-relay 24-reactor 12-diode 32-
The energy of the reactor 12 moves to the capacitors 8 and 9 through the path of the capacitor 8-the capacitor 9-the battery 11 to charge the capacitors 8 and 9 at once.

The energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by an inverter including the switches 4 and 5 and the diodes 6 and 7. The reactor 3 and the capacitor 2 constitute a filter for removing a high-frequency voltage component generated by the inverter, and a sine wave voltage that does not include a high-frequency component is applied to the voltage applied to the load 1. In this manner, power can be constantly supplied to the load 1 even if a power failure occurs in the system power supply 10.

[0016]

The conventional uninterruptible power supply is configured as described above. In the uninterruptible power supply shown in FIG. 20, two charging paths are used for charging the battery 11 as described above. Occurs. That is, system power supply 1
0 is a negative voltage, and the capacitor 9 is connected to the system power supply 1
During the period from 0 to charging, the diode 25 is in an open state, and as shown in FIG. 23, when the switch 15 is turned on, the switch 15 -the reactor 23 -the battery 11
The battery 11 is charged through the path of the diode 25, the capacitor 9, the capacitor 8, the diode 21, and the switch 15. At this time, the charging current i ₂₃ to the battery 11 flowing through the reactor 23 is
-Diode 25-Diode 18-Reactor 12-
Diode 2 is connected by the route of relay 24-system power supply 10.
5 is smaller than the charging current i ₂₅ to the capacitor 9 flowing to the capacitor 5, the current i finally flowing to the diode 25
₂₅ becomes i ₂₅ −i ₂₃ (> 0), and all the charging current i ₂₃ flows to the diode 25. Therefore, capacitors 8 and 9
Is used equally for charging the battery 11.

On the other hand, the battery 1 flowing through the reactor 23
Charging current i ₂₃ to 1 is greater than the charging current i ₂₅ to the capacitor 9 to flow to the diode 25, the current i ₂₅ flowing through the final diode 25, i ₂₅ -i ₂₃ (<
0), it is only part of the charge current i ₂₃ diode 25
And the remaining current (i ₂₃ -i ₂₅ ) that could not flow to the diode 25 is changed to the switch 15 -reactor 23 -battery 11 -diode 19 -capacitor 8-
The current flows through the diode 19 through the path of the diode 21 and the switch 15 to charge the battery 11. Thus, some of the charging current i ₂₃ to the battery 11 flowing through the reactor 23 flows through the diode 25, the energy of the capacitor 8 and 9 are used to charge the evenly battery 11, the remaining current of the capacitor 8 Only energy will be used to charge the battery 11.

During the period when the system power supply 10 is at a positive voltage and the capacitor 8 is charged from the system power supply 10, the current flowing through the diode 25 is zero, and when the switch 15 is turned on, the switch 15- Reactor 23-battery 11-diode 19-capacitor 8-
Through the path of the diode 21 and the switch 15, the charging current i23 flows using the capacitor 8 as a supply source, and only the energy of the capacitor 8 is used for charging the battery 11.

As described above, in the uninterruptible power supply shown in FIG. 20, two charging paths, a path flowing through the diode 25 and a path flowing through the diode 19, occur depending on the magnitude of the current flowing through the diode 25. In the case of the charging path through the diode 19, only the energy of the capacitor 8 is used for charging the battery 11. At this time, since the energy of the capacitor 8 decreases, the switch 13 is turned on and off so that the energy from the system power supply 10 charges the capacitor 8 more. For example, when the load 1 is not loaded, as a result, FIG. A current as shown in FIG. Therefore, even when the load 1 is not loaded, the battery 11 is charged as shown in FIG.
Since the current shown in Fig. 4 flows through the grid, it places a burden on the power receiving transformer on the grid side, and in some cases, causes the transformer to be demagnetized, causing an overcurrent on the grid side and causing a system fault. There was a problem that it could be.

The uninterruptible power supply shown in FIG. 22 does not have a function of charging the battery 11, so that a separate charger must be provided. When a power failure occurs in the system power supply 10 and the capacitors 8 and 9 are charged from the battery 11, the capacitors 8 and 9 are not configured to be charged independently. During operation, if the load 1 generates an unbalanced current as shown in FIG. 21, the voltages of the capacitors 8 and 9 cannot be controlled to desired voltage values, respectively. This causes instability, and consequently, the continuation of operation by the inverter 26 becomes impossible. In order to solve such a problem, as shown in FIG. 25, a battery charger including a switch 100, a diode 107, and a reactor 106, and switches 101 and 102, a diode 10
The capacitor voltage balance circuit 110 including the reactors 3 and 104 and the reactor 105 may be separately connected, but there is a problem that the number of switches and reactors increases and the cost increases.

The present invention has been made in order to solve the above-mentioned problems, and does not impose a burden on the system side by charging a battery by always using the energy of both capacitors equally. An object is to obtain a power conversion device.

Also, by having a battery charging function and a capacitor balancing function for an unbalanced load,
It is an object of the present invention to obtain an inexpensive power converter by realizing stable operation continuation of an inverter and further configuring a circuit to partially share these functions.

[0023]

According to a first aspect of the present invention, there is provided a power converter for converting AC power from a system power supply into DC power and storing the DC power in two capacitors connected in series. And an inverter circuit that converts DC power converted by the converter circuit into AC power and supplies the AC power to a load. One of an input terminal of the converter circuit and one of an output terminal of the inverter circuit are connected to the second terminal. In the power converter connected to the interconnection point of the two capacitors, the converter circuit uses the energy of the two capacitors evenly when the power storage means and the system power supply have no voltage abnormality. A power storage control means for storing power; and a circuit for switching the energy of the power storage means when the voltage of the system power supply is abnormal. A discharge control means for discharging the capacitor and a DC power converted from the system power supply to the two capacitors; and a discharge control means for discharging the energy of the power storage means to the two capacitors. Voltage control means for controlling the potential at the connection point.

Further, in the power converter according to the second configuration of the present invention, in the first configuration, the converter circuit has a first reactor connected to one end of an AC power supply and a first reactor for functioning as a DC power supply. And a series circuit of a second capacitor, each of which is connected between an output terminal of the first reactor and both ends of the series circuit of the first and second capacitors, and has opposite directions to the AC power supply. A first and a second diode, and a first and a second diode connected in parallel with a series circuit of the first and second capacitors via the first and the second diode;
A series circuit of first and second switches having the same direction, connecting an interconnection point of the first and second capacitors, an interconnection point of the first and second switches, and the other end of the AC power supply. Connection means, a series circuit of a third switch, a second reactor, and a battery connected in parallel with the first and second capacitors, a third switch connected in parallel with the second reactor and the battery, A third diode having an opposite direction, an input terminal of the first reactor, a first relay for switching and connecting to one end of the AC power supply and one end of the battery, and the other end of the battery; A second relay connected to one end of the series circuit of the first and second capacitors and one end of the series circuit of the first and second switches, and when the AC power supply has no abnormal voltage, First The relay is switched to the AC power supply side, the second relay is switched to the series circuit side of the first and second capacitors, and if the AC power supply has a voltage abnormality, the first relay is switched to the battery side and the second relay is switched to the battery side. Relays of the first and second
Is switched to the series circuit side of the switch.

Further, in the power converter according to the third configuration of the present invention, in the first configuration, the converter circuit includes a first reactor connected to one end of an AC power supply and a first reactor for functioning as a DC power supply. And a series circuit of a second capacitor, each of which is connected between an output terminal of the first reactor and both ends of the series circuit of the first and second capacitors, and has opposite directions to the AC power supply. First and second switches, connection means for connecting an interconnection point of the first and second capacitors to the other end of the AC power supply, one end of which is connected to a series circuit of the first and second capacitors and the first switch. A series circuit of a third switch, a second reactor, and a battery, connected between the second switch and the other end, connected between the series circuit of the first and second capacitors and the second switch;
A fourth switch connected in parallel to the second reactor and the battery and having a direction opposite to that of the third switch, and an input terminal of the first reactor connected to one end of the AC power supply and one end of the battery. A first relay to switch and connect,
A second relay configured to switch and connect one end of the second reactor to one end of the battery and an interconnection point of the first and second capacitors, and when there is no voltage abnormality in the AC power supply, The first relay is switched to the AC power supply side, and the second relay is switched to the battery side. If the AC power supply has a voltage abnormality, the first relay is switched to the battery side, and the second relay is switched to the first battery. And switching to the interconnection point side of the second capacitor.

Further, in the power converter according to the fourth configuration of the present invention, in the third configuration, the voltage control means converts the DC power converted from the system power into two when the voltage of the system power is normal. When storing power in the two capacitors, there is provided switching means for storing each capacitor independently, and the sum of the voltages of the two capacitors and the potential of the interconnection point of the two capacitors are detected. A difference from a desired set value is calculated, the difference is amplified by a first controller, and a first current command value obtained by multiplying a sine coincident with the phase of the system power supply is further calculated. A difference between the potential and a desired set value is calculated, and the difference is calculated as a second
A second current command value is amplified by the controller of the above, and further multiplied by the absolute value of the sine that matches the phase of the system power supply,
The sum of the first current command value and the second current command value,
A control circuit for setting a command value of a current flowing to the system power supply is provided, and a current flowing to the system power supply follows the command value of the current by the switching means.

[0027] In the power converter according to the fifth configuration of the present invention, in the fourth configuration, the voltage control means discharges energy of the power storage means to the two capacitors when the voltage of the system power supply is abnormal. Sometimes it has switching means for discharging each capacitor independently,
A control circuit for controlling the voltage of one of the two capacitors by the switching means so that the potential at the interconnection point of the two capacitors becomes a desired set value.

In the power converter according to a sixth aspect of the present invention, in the fourth aspect, the voltage control means discharges energy of the power storage means to the two capacitors when the voltage of the system power supply is abnormal. A switching means for discharging each capacitor independently, and detecting a load current flowing through a load so that a potential at an interconnection point of the two capacitors becomes a desired set value. And a control circuit for controlling a current corresponding to the load current to flow through the two capacitors.

Further, in the power converter according to the seventh configuration of the present invention, in the fourth configuration, the voltage control means discharges energy of the power storage means to the two capacitors when the voltage of the system power supply is abnormal. A switching means for discharging each capacitor independently, and detecting a load current flowing through a load so that a potential at an interconnection point of the two capacitors becomes a desired set value. And a control circuit for controlling a DC current included in the load current to flow through the two capacitors.

Further, in the power converter according to the eighth configuration of the present invention, in any of the first to seventh configurations, when storing without using the power converter, the capacitor is not charged by the power storage means. The circuit is switched as described above.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a power conversion device according to Embodiment 1 of the present invention. The same reference numerals as those in the conventional device denote the same components, and a description thereof will be omitted. 40 to 42 are switches, 43 to 47 are diodes, 48 is a relay, and 49 is a reactor.

Next, the operation of the apparatus shown in FIG. 1 will be described.
First, when the system power supply 10 is normal, that is, when a power failure occurs.
When there is no life, relays 24 and 48 are connected to A in the figure.
Continued. At this time, from the system power supply 10 to the load 1
Get the energy to supply. For this purpose, the above system
Voltage of the power supply 10₁Is a positive voltage (voltage in the direction of the arrow)
, The switch 40 is turned on and off, and
When the switch 40 is on, the system power supply 10-relay
24-reactor 12-diode 44-switch 40
-Diagram of the reactor 12 through the path of the system power supply 10
Current i in the direction of _LIs accumulated. Next, switch 40
Is turned off, the system power supply 10-relay 24-relay
Actor 12-diode 44-diode 46-con
The above-mentioned reactor is provided by the path of the
The energy stored in 12 is stored in the capacitor 8
Moving. In this manner, the system power supply 10
In this case, the switch 40 is turned on and off.
Then, the capacitor 8 is charged.

The voltage V of the system power supply 10₁Is negative
When the voltage (voltage in the direction opposite to the arrow) is
Switch 41 is turned on and off, and the switch 41 is turned on.
Has a system power supply 10-switch 41-diode 43-
According to the route of reactor 12-relay 24-system power supply 10.
Thus, a current i in the direction opposite to the arrow shown in FIG. _L
Is accumulated. Next, turn off the switch 41
From the system power supply 10-capacitor 9-diode 47-
Diode 43-reactor 12-relay 24-grid power
Accumulated in the reactor 12 by the path of the source 10
The energy transferred to the capacitor 9. This
The voltage V of the system power supply 10₁Is negative voltage
By turning the switch 41 on and off,
The capacitor 9 is charged. In addition, the system power supply 1 at this time
Voltage V of 0₁And current i_L2 is shown in FIG. (A)
Voltage V₁(B) shows the current i_LIt is a waveform of. Current i
_LIn the switching operation of the switches 40 and 41
The accompanying ripple current is superimposed. This ripple current is
It is removed by an inserted filter (not shown). Also
As shown, the current i_LIs the voltage V₁To be in phase with
Flow out to the system power supply 10 by high power factor control
Harmonic current is suppressed.

As described above, the energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by the inverter 26 including the switches 4 and 5 and the diodes 6 and 7. As shown in FIG. 3, the voltage (a) including the high-frequency voltage component generated by the inverter 26 passes through a filter constituted by the reactor 3 and the capacitor 2, and as a result, the voltage V of the capacitor 2 _Since the waveform of _C is shaped as shown in (b), a sine wave voltage containing no high-frequency component can be applied to the voltage applied to the load 1.

Similarly, the charging operation of the battery 11 when the system power supply 10 is normal, that is, when no power failure occurs, will be described. FIG. 4 shows the charging circuit at this time. The charging voltage of the battery 11 is controlled by the capacitors 8 and 9
Is set to a value smaller than the voltage of When the switch 42 is turned on, the current I _B in the reactor 49 from the capacitor 8 and 9 are accumulated simultaneously charge the battery 11. Next, when the switch 42 is turned off, the reactor 49-the battery 1
The battery 11 is subsequently charged with the energy of the reactor 49 through the path of 1-diode 45.
Therefore, by appropriately controlling the on / off of the switch 42, the voltage of the battery 11 can be charged to a desired value.

Next, when a power failure occurs in the system power supply 10, the relays 24 and 48 are connected to B in FIG. At this time, when the switches 40 and 41 are simultaneously turned on, the battery 11-relay 24-reactor 12-diode 44-switch 40-switch 41-
Through the path from the relay 48 to the battery 11, a current i _L flows in the reactor 12 in the direction of the arrow in the figure, and energy is stored in the reactor 12. Next, for example, when only the switch 41 is turned off, the battery 11-relay 24-
Reactor 12-diode 44-switch 40-capacitor 9-diode 47-relay 48-battery 11
The energy of the reactor 12 moves to the capacitor 9 to charge the capacitor 9 through the path.
Similarly, when only the switch 40 is turned off, the battery 1
1-relay 24-reactor 12-diode 44-diode 46-capacitor 8-switch 41-relay 4
The energy of the reactor 12 moves to the capacitor 8 through the path of the battery 11 to charge the capacitor 8.

The energy stored in the capacitors 8 and 9 as described above is converted from a DC voltage to an AC voltage by the inverter 26 including the switches 4 and 5 and the diodes 6 and 7. As shown in FIG. 3, the voltage (a) including the high-frequency voltage component generated by the inverter 26 passes through a filter constituted by the reactor 3 and the capacitor 2, and as a result, the voltage V of the capacitor 2 The waveform of _C is shown in FIG.
Therefore, a sine wave voltage that does not include a high-frequency component can be applied to the voltage applied to the load 1.

In this manner, power can be constantly supplied to the load 1 even when a power failure occurs in the system power supply 10. Further, since the battery 11 has a function of charging, the battery can be recharged after the system power supply returns from the power failure state and becomes normal. Also, whether the system power supply is normal or abnormal, the amount of charge of each of the capacitors 8 and 9 can be controlled by turning on and off the switches 40 and 41.
However, even if the load generates an unbalanced current as shown in FIG. 21, the voltages of the capacitors 8 and 9 can be controlled to desired voltage values. Also, battery 1
The charging path of No. 1 corresponds to the capacitors 8 and 9 in the circuit of FIG.
Battery 1 to charge the battery evenly
The voltage decrease of the capacitors 8 and 9 due to the charging of 1 is equal to each other, and as the energy supplied from the system for replenishment, the current shown in FIG. Therefore, stable power supply can be performed without imposing a load on a transformer or the like on the system side.

FIG. 5 shows another configuration method of the circuit shown in FIG. In the figure, 90 and 91 are diodes. Although the configuration shown in FIG. 1A is used, the same circuit operation can be realized with the configuration shown in FIG. Further, in the configuration of FIG. 5B, when the system power supply 10 is normal, the energy of the system power supply is stored in the capacitors 8 and 9, but at this time, compared to the configuration of FIG. Since the conduction loss of one diode can be reduced, a power conversion device with higher conversion efficiency can be obtained.

Embodiment 2 FIG. 6 is a circuit diagram showing a power converter according to Embodiment 2 of the present invention. In the figure, the same symbols as those in the conventional example and the first embodiment are the same, and the description thereof is omitted. 50 and 51 are switches,
52 and 53 are diodes, 54 is a relay, and 55 is a reactor.

Next, the operation of the circuit of FIG. 6 will be described.
First, when the system power supply 10 is normal, that is, when no power failure occurs, the relays 24 and 54 are connected to A in FIG. For this reason, when the system power supply 10 is at a positive voltage (voltage in the direction of the arrow), the switch 3
1 when the switch 31 is on,
A current IL is accumulated in the reactor 12 in the direction shown in the figure through the path of the system power supply 10-relay 24-reactor 12-switch 31-capacitor 9-system power supply 10. Next, by turning off the switch 31, the system power supply 1
The energy stored in the reactor 12 is transferred to the capacitor 8 through a path of 0-relay 24-reactor 12-diode 32-capacitor 8-system power supply 10.
Go to Thus, when the system power supply 10 has a positive voltage, the switch 8 is turned on and off to charge the capacitor 8.

When the system power supply 10 is at a negative voltage (voltage in the opposite direction of the arrow), the switch 30 is turned on and off. When the switch 30 is on, the system power supply 10-capacitor 8-switch 30- Reactor 1
A current is accumulated in the reactor 12 in a direction opposite to the direction shown in FIG. Next, when the switch 30 is turned off, the energy stored in the reactor moves to the capacitor 9 through the path of the system power supply 10-the capacitor 9-the diode 33-the reactor 12-the relay 24-the system power supply 10. Thus, when the system power supply 10 has a negative voltage, the switch 9 is turned on and off to charge the capacitor 9.

As described above, the energy stored in the capacitors 8 and 9 is converted from a DC voltage to an AC voltage by the inverter using the switches 4 and 5 and the diodes 6 and 7. The reactor 3 and the capacitor 2 constitute a filter for removing a high-frequency voltage component generated by the inverter, and a sine wave voltage that does not include a high-frequency component is applied to the voltage applied to the load 1.

Further, when the system power supply 10 is normal, the battery 11 is charged by a circuit as shown in FIG. That is, the relay 54 is connected to A in the figure. At this time, when the switch 50 is turned on, the switch 50-the reactor 55-the relay 54-the battery 1
The path of the 1-capacitor 9 capacitor 8 switch 50 to charge the battery 11 with equally energy of the capacitor 8 and 9, a current flows I _B. Turning off the switch 50, the current I _B is the route of the reactor 55 - Relay 54-battery 11 diodes 53- reactor 55, and the current I _B flows to charge the battery 11.

Further, if the system power supply 10 is normal,
And the load 1 is unbalanced as shown in FIG.
The current I as in (b)_OUTIs flowing,
The voltages of the capacitors 8 and 9 are controlled so as to have respective desired voltage values.
Control. That is, when the current shown in FIG.
The discharge of the capacitor 8 is greater than the discharge of the capacitor 9,
Voltage V of capacitor 8_C1And the voltage V of the capacitor 9_C2With
Since a voltage difference is generated between them, a control circuit is provided to
The pressure difference is detected, and as a result, the capacitor 8 is more charged.
The current of the system power supply 10 is shown in FIG.
Control is performed so as to obtain such a current waveform. Specifically in FIG.
An example of a simple control circuit is shown. In the figure, 56 and 57 are additions
, 58 and 59 are subtractors, and 60 and 61 are PI controllers.
Controllers as represented, 62 and 63 are multipliers, 64 is absolute
It is a logarithmic operation circuit. First, two capacitor voltages V_C1,
V _C2Are added by the adder 56, and V_C1And V_C2of
DC voltage command value V which is the command value of the sum voltage_D ^*Compare with
Therefore, the subtractor 58 performs the subtraction. The result of the above subtraction
The result is input to the controller 60 as an error signal,
The controller 60 outputs a signal I corresponding to the error signal.^*Is output.

The control circuit detects the sine value sinθ of the phase of the system power supply 10 by a detector (not shown), and executes the multiplication of the signal I ^* and sinθ by the multiplier 62. As a result of the above multiplication, a sinusoidal signal I ₁ ^* matching the voltage phase of the system power supply 10 is obtained.

The difference voltage between the capacitors 8 and 9 is detected by the subtracter 59 and is input to the controller 61. The controller 61 outputs a signal II ^* according to the difference voltage. Further, the signal sinθ is calculated by the absolute value circuit 6.
4 and the above signal sin by the multiplier 63
The signal II ^* is multiplied by the absolute value of θ. As a result of the above multiplication, a signal I ₂ ^* is obtained. The sum of the signals I ₁ ^* and I ₂ ^* is obtained by the adder 57, and the sum is obtained by the reactor 1.
2 of a current command I _L ^*, thereby switching the switch 30 and 31 so as to follow the I _L ^*. FIG. 10 shows an example of a waveform result.
Shown in In FIG. 10, (a) the voltage V ₁ of the waveform of the system power supply 10, (b) is the signal I ₁ ^* waveform, (c) is the signal I ₂ ^* waveform, (d) is the signal I _L ^* a waveform, the current I _L of the system power source 10 is operated to follow the I _L ^*. Therefore, the capacitor 8 functions to charge the capacitor 8 more, and as a result, the voltages V _C1 and V _C2 are balanced.

Next, when a power failure occurs in the system power supply 10, the relays 24 and 54 are connected to B in FIG. The energy supply path from the battery 11 to the inverter 26 is obtained by the relay 24 as shown in FIG. Hereinafter, a specific operation will be described.
When the switch 31 is turned on, as shown in FIG.
The path of the battery 11 and the relay 24 reactor 12 switches 31- battery 11, current I _L is accumulated in the reactor 12. Next, when the switch 31 is turned off, as shown in FIG.
The energy stored in the reactor 12 moves to the capacitors 8 and 9 and is stored therein by the route of the reactor 12, the diode 32, the capacitor 8, the capacitor 9, and the battery 11. By turning on and off the switch 31 in this manner, the energy of the battery 11 is transferred to the capacitors 8 and 9 and energy is supplied to the inverter 26 and the load 1, and the voltage V _{C1 of the} capacitor 8 and the capacitor 9 voltage V
The sum voltage of _C2 is controlled to a desired value.

In order to stably operate the inverter 26 even when the load 1 has an unbalanced load characteristic as described with reference to FIG. 8, the relay 54, as shown in FIG. The switches 50 and 51 are used and the control circuit shown in FIG. 15 is used to control the voltages of the capacitors 8 and 9 to be stable. That is, the energy of the battery 11 is charged simultaneously with the same energy by the switch 31 and the diode 32 via the reactor 12 and the relay 24 with the same energy. Therefore, when the load 1 has an unbalanced load characteristic, The voltages of the capacitor 8 and the capacitor 9 become unbalanced and are not stable. Therefore, the switches 50 and 51 are controlled by the control circuit, and the capacitors 8 and 9 are controlled.
Is controlled to be stable. FIG. 15 shows a specific control circuit. 15, 70 and 72 are subtracters, 71 and 73 are controllers represented by, for example, a PI controller, 74 is a comparator, 75 is a triangular wave signal, 76 is a NOT circuit, and the control circuit is the capacitor 9. Voltage V _C2
Is controlled to be the command value V _C2 ^* . In the figure, the subtractor 70 calculates an error from the command value of the voltage V _C2 , and the error is input to the controller 71. The controller outputs a signal I _BAL ^* corresponding to the error, and FIG.
Is calculated by the subtracter 72 with respect to the command value of the current _IBAL so that the current _IBAL is equal to the signal _IBAL ^* . The controller 73 outputs a voltage command V according to the error.
_BAL ^* is output, the comparator 74 compares the signal with the triangular wave signal, and compares the result with the ON signal SW50 of the switch 50.
The result inverted by the NOT circuit 76 is used as the ON signal SW51 of the switch 51. By configuring the control circuit in this manner, the voltage V _C2 becomes equal to the command value V
_C2 ^* and is controlled so as to match, it becomes a stable voltage V _C2, since the sum voltage of the voltage V _C1 and V _C2 are controlled to a desired value by the circuit of FIG. 11, as a result the voltage V _C1 is also stable Become.

As described above, even if a power failure occurs in the system power supply 10, power can be constantly supplied to the load 1. Further, since the battery 11 has a function of charging, the battery can be recharged after the system power supply returns from the power failure state and becomes normal. The charge amounts of the capacitors 8 and 9 are determined by turning on and off the switches 30 and 31 when there is no abnormality in the system power supply 10 and the switches 50 and 51 when a power failure occurs in the system power supply 10. , The voltage of the capacitors 8 and 9 can be controlled to desired voltage values even if the load 1 is a load that generates an unbalanced current as shown in FIG. As a result, the inverter 26 can be operated stably. In addition, since the charging path to the battery 11 is charged by using the energy of the capacitors 8 and 9 equally in the circuit of FIG.
24 and 9 have the same amount, and the energy supplied from the system for replenishing this does not flow the current as shown in FIG. 24, and has a positive / negative target current waveform. A stable power supply can be performed without imposing a load on a transformer or the like.

Embodiment 3 FIG. Next, the voltages V _C1 and V _C2
FIG. 16 shows an example of another control circuit for controlling the voltage to be stable.
Shown in In FIG. 16, reference numeral 92 denotes a subtractor, and the other components are the same as those in the second embodiment. Here, by detecting the current I _{OUT of the} load 1 and operating the controller 73 so that the current I _OUT matches the current I _BAL , the voltages V _C1 and V _C2 are stabilized.

More specifically, in FIG.
_{When OUT} is in the direction shown in the figure (positive direction), the current I
_{The OUT} component flows so that only the capacitor 8 is discharged when the switch 4 is turned on, and then only the capacitor 9 is charged when the switch 4 is turned off. Since the switches 4 and 5 of the inverter 26 are operated so as to be alternately turned on and off by pulse width modulation, the operations described above always accompany. When the load 1 has an unbalanced load characteristic and the current I _OUT flows only in a positive direction, the discharging of the capacitor 8 and the charging of the capacitor 9 continue, and as a result, the voltage V _OUT
The voltage of _C1 and V _C2 is not kept stable. To compensate for this, the control circuit shown in FIG. 16, while off each other the switches 50 and 51, by passing the same current I _BAL and the I _OUT to the reactor 55, the current I _OUT positive The current I _BAL
14 also flows in the direction of the arrow shown in FIG. 14. When the switch 50 is on, the capacitor 8 is charged. When the switch 50 is off, the capacitor 9 is discharged. As a result, the charge and discharge amount of each capacitor becomes equal, and the voltage V _C1 and V _C2 stabilize within a predetermined voltage range. Further, the energy supplied to the load collectively charges the capacitors 8 and 9 from the battery 11, so that the voltages V _C1 and V _C2 do not become unstable due to the charging from the battery 11.

Embodiment 4 Further, the voltage V_C1And V_C2
Other control methods for controlling the
You. In the circuit of FIG. 14, as shown in FIG.
Switch 0 and 51 to each other with equal ON width
And let At this time, the voltage V_C1Is the voltage V _C2Greater than
The current I flowing through the reactor 55_BALFigure 1
The above-mentioned reactor 55 flows in the opposite direction of the arrow in FIG.
Is applied with an average voltage. Conversely, voltage V _C1And V_C2Are equal
Sometimes, the average voltage applied to the reactor 55 is zero.
And the current I_BALDoes not flow.

Incidentally, the circuit of FIG. 14 has a path for LC resonance by the reactor 55 and the capacitors 8 and 9. Therefore, the voltage V _C1 becomes the voltage V
_Assuming that the operation start point is greater than _C2 , the current _IBAL is the sum of the DC offset current _IOS and the current component generated by the resonance as shown in FIG. The above current I
_OS is a current caused by the imbalance between the voltages V _C1 and V _C2 . If the load 1 is unbalanced, so that the I _OS appears as a component of the unbalanced current. Further, such a resonance current has a high peak value, and there is a problem that an element having a large current capacity is required to cause current stress on the switches 50 and 51 and the diodes 52 and 53. To solve these problems, only the resonance component current controls the I _BAL to zero, to to flow only I _OS caused by unbalanced loads on the reactor 55 is desired.

FIG. 19 shows a control circuit for realizing the above control method. In the figure, 77 is a controller typified by a PI controller or the like, 78 is a high-pass filter, and 79 is a subtractor. First, only the resonance current component of the detected current I _BAL is extracted by the high-pass filter 78. In order for the control circuit to operate so that the resonance current component becomes zero, first, the subtractor 79 subtracts from the command value (zero), and the subtraction result is input to the controller 77 as an error signal. The controller 77 supplies a voltage command V according to the error.
_BAL ^* is output and compared with the triangular wave signal by the comparator 74, the result is used as the ON signal SW50 of the switch 50, and the result inverted by the NOT circuit 76 is used as the ON signal SW51 of the switch 51. . As a result, the current I _BAL is substantially only a DC current component corresponding to the unbalanced load, and the resonance current as shown in FIG. 18 is suppressed. Thus, the voltages V _C1 and V _C2 are stabilized.

Embodiment 5 In the uninterruptible power supply device according to the first and second embodiments, when the user stores the device without using it for a long period of time, in order to discharge the energy of the capacitors 8 and 9 from the viewpoint of safety, for example, it is not illustrated. A resistor is connected in parallel with the capacitors 8 and 9.
If a circuit is configured so that the battery 11 does not charge the capacitors 8 and 9 during the unused period, useless discharge of the battery 11 due to the resistor can be suppressed. That is, in the circuit of FIG. 1, the relay 24 is connected to A in the figure. FIG.
In this circuit, the relay 24 is connected to A in the figure, and the relay 54 is connected to B in the figure. In this way, since the discharge path from the battery 11 to the capacitors 8 and 9 can be cut off, it is possible to suppress unnecessary discharge of the battery 11 when the device is not used,
An efficient device can be obtained.

[0057]

As described above, according to the first configuration of the present invention, the battery can be charged using the energy of both capacitors at all times evenly, and no burden is imposed on the system side. A power converter can be obtained. In addition, since the battery has a function of charging the battery and a function of balancing the capacitor with respect to an unbalanced load, stable operation of the inverter can be continued.

According to the second and third configurations of the present invention, in addition to the above-described effects, the circuit is configured so as to partially share the function of charging the battery and the function of balancing the capacitor against an unbalanced load. Thus, an inexpensive power converter can be obtained.

According to the fourth configuration of the present invention, when the DC power converted from the system power supply is stored in the two capacitors, the potential at the interconnection point of the two capacitors is stabilized, and Stable operation continuation can be realized.

According to the fifth to seventh configurations of the present invention, when the energy of the power storage means is discharged to the two capacitors, the potential at the interconnection point of the two capacitors is stabilized, and the stable operation of the inverter is achieved. Operation continuation can be realized.

Further, according to the eighth configuration of the present invention, in the power converter of each of the above configurations, it is possible to suppress useless discharge of the battery when the device is not used.
An efficient device can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power converter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a voltage waveform and a current waveform of a system power supply in the power converter according to Embodiment 1 of the present invention.

FIG. 3 is a diagram showing an output voltage of an inverter and a voltage waveform of a capacitor in the power converter according to Embodiment 1 of the present invention.

FIG. 4 is a diagram illustrating a charging operation of a battery in the power converter according to Embodiment 1 of the present invention.

FIG. 5 is a circuit diagram showing a part of another power converter according to Embodiment 1 of the present invention;

FIG. 6 is a circuit diagram showing a power conversion device according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a charging operation of a battery in the power converter according to Embodiment 2 of the present invention.

FIG. 8 is a diagram showing waveforms at the time of an unbalanced load in the power converter according to Embodiment 2 of the present invention.

9 is a diagram showing a control circuit for implementing the current I _L in FIG.

FIG. 10 is a diagram showing voltage and current waveforms in the control circuit of FIG. 9;

FIG. 11 is a diagram illustrating a discharging operation of a battery in a power converter according to Embodiment 2 of the present invention.

FIG. 12 is a diagram illustrating a discharging operation of a battery in a power conversion device according to Embodiment 2 of the present invention.

FIG. 13 is a diagram illustrating a discharging operation of a battery in the power converter according to Embodiment 2 of the present invention.

FIG. 14 is a diagram illustrating an operation of capacitor voltage control at the time of discharging in a power converter according to a second embodiment of the present invention.

FIG. 15 is a diagram showing a control circuit for controlling the capacitor voltage at the time of discharging in the power converter according to Embodiment 2 of the present invention.

FIG. 16 is a diagram showing a control circuit for controlling a capacitor voltage at the time of discharging in a power converter according to Embodiment 3 of the present invention.

FIG. 17 is a diagram illustrating an operation of controlling the capacitor voltage at the time of discharging in the power converter according to Embodiment 4 of the present invention.

FIG. 18 is a diagram illustrating operation of capacitor voltage control at the time of discharging in a power converter according to Embodiment 4 of the present invention.

FIG. 19 is a diagram showing a control circuit for controlling a capacitor voltage at the time of discharging in a power converter according to Embodiment 4 of the present invention.

FIG. 20 is a circuit diagram showing a conventional power converter.

FIG. 21 is a diagram showing a waveform at the time of an unbalanced load.

FIG. 22 is a circuit diagram showing another conventional power converter.

FIG. 23 is a diagram illustrating a charging operation of a battery in a conventional power converter.

FIG. 24 is a diagram showing waveforms during a battery charging operation in a conventional power converter.

FIG. 25 is a circuit diagram showing a device in which a battery charger and a capacitor balance circuit are installed in the conventional power converter shown in FIG.

[Explanation of symbols]

1 load, 2,8,9 capacitor, 3,12,23,
49,55 reactor, 4,5,13-15,30,
31, 40-42, 50, 51 switches, 6, 7, 1
6 to 22, 25, 32, 33, 43 to 47, 52, 5
3, 90, 91 diode, 10 system power supply, 11
Battery, 24, 48, 54 relay, 26 inverter, 56, 57 adder, 58, 59, 70, 72, 7
9,92 subtractor, 60,61,73,77 controller,
62, 63 multiplier, 74 comparator, 75 triangular wave, 7
6 inverter, 78 high-pass filter.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02M 5/453 H02M 5/453 5H750 7/48 7/48 N 7/5387 7/5387 A F term (reference 5G015 GA03 GA06 HA15 JA05 JA22 JA52 5G066 JA02 JB03 5H006 AA02 CA02 CA07 CB04 CB08 CB09 CC01 CC02 CC08 DA02 DB02 DC02 DC05 5H007 AA02 AA08 BB05 BB11 CA01 CB02 CB04 CB12 CB22 CC03 CC07 DB01 EB02 DD07 FF03 FF05 FF08 FF22 FF25 LL20 5H750 BA01 BA07 CC02 CC06 CC08 CC14 CC16 DD01 DD25 FF05

Claims (8)

[Claims] 1. A converter circuit for converting AC power from a system power supply into DC power, storing the DC power in two capacitors connected in series, and converting the DC power converted by the converter circuit into AC power. An inverter circuit for supplying the load to the load, wherein one of the input terminals of the converter circuit and one of the output terminals of the inverter circuit are connected to an interconnection point of the two capacitors. The circuit includes: a power storage unit; a power storage control unit configured to store the power using the energy of the two capacitors evenly when there is no voltage abnormality in the system power supply; and a power storage control unit configured to store a voltage abnormality in the system power supply. Discharging control means for switching the circuit to discharge the energy of the power storage means to the two capacitors, and converting from the system power supply Voltage control means for controlling a potential at an interconnection point of the two capacitors when the stored DC power is stored in the two capacitors and when the energy of the power storage means is discharged to the two capacitors. A power converter characterized by the above-mentioned. 2. A converter circuit comprising: a first reactor connected to one end of an AC power supply; a series circuit of first and second capacitors for functioning as a DC power supply; an output terminal of the first reactor; Via a first and a second diode, and a first and a second diode respectively connected between both ends of a series circuit of the first and second capacitors and having directions opposite to each other with respect to the AC power supply. A series circuit of first and second switches connected in parallel with a series circuit of first and second capacitors and having the same directionality, an interconnection point of the first and second capacitors, and a first and second capacitor; Connecting means for connecting an interconnection point of the switch and the other end of the AC power source; a third means connected in parallel with the first and second capacitors;
A series circuit of a switch, a second reactor and a battery, a third diode connected in parallel to the second reactor and the battery and having a direction opposite to that of the third switch,
A first relay for connecting the input terminal of the first reactor to one end of the AC power supply and one end of the battery, and connecting the other end of the battery to a series circuit of first and second capacitors; A second relay connected to one end and connected to one end of a series circuit of the first and second switches. When the AC power supply has no voltage abnormality, the first relay is connected to the AC power supply side. The second relay is the first
And switching to the series circuit side of the second capacitor, and when the AC power supply has a voltage abnormality, the first relay is connected to the battery side, and the second relay is connected to the series circuit side of the first and second switches. The power converter according to claim 1, wherein the power converter is switched. 3. A converter circuit comprising: a first reactor connected to one end of an AC power supply; a series circuit of first and second capacitors for functioning as a DC power supply; an output terminal of the first reactor; First and second switches connected between both ends of a series circuit of the first and second capacitors and having directions opposite to each other with respect to the AC power supply, and interconnection of the first and second capacitors. Connecting means for connecting a point to the other end of the AC power source, one end of which is a first and a second.
A third switch and a second switch, which are connected between the series circuit of the capacitors of the first and second switches and the other end are connected between the series circuit of the first and second capacitors and the second switch. A series circuit of a reactor and a battery, a fourth switch connected in parallel to the second reactor and the battery and having a direction opposite to that of the third switch, and an input terminal of the first reactor connected to the AC power supply. And a first relay for switching and connecting to one end of the battery and one end of the battery, and a first relay for switching and connecting one end of the second reactor to one end of the battery and an interconnection point of the first and second capacitors. When the AC power supply has no voltage abnormality, the first relay is switched to the AC power supply side, and the second relay is switched to the battery side. The first relay to the battery side,
2. The power converter according to claim 1, wherein the second relay is switched to an interconnecting point between the first and second capacitors. 4. The voltage control means, wherein when the voltage of the system power supply is normal, when the DC power converted from the system power supply is stored in two capacitors, the switching means for storing each capacitor independently. And detecting the sum of the voltages of the two capacitors and the potential of the interconnection point of the two capacitors, calculating the difference between the sum of the voltages and a desired set value, and calculating the difference by a first controller. And a difference between a first current command value multiplied by a sine that matches the phase of the system power supply, a potential at the interconnection point and a desired set value, and the difference is calculated as a second A second current command value is amplified by a controller and further multiplied by an absolute value of a sine that matches the phase of the system power supply, and the sum of the first current command value and the second current command value is calculated. And the command value of the current flowing to the system power supply 4. The power conversion device according to claim 3, further comprising a control circuit for controlling the power supply, wherein a current flowing to the system power supply by the switching means follows a command value of the current. The voltage control means includes switching means for discharging each capacitor independently when discharging the energy of the power storage means to the two capacitors when the voltage of the system power supply is abnormal. 5. A control circuit for controlling a voltage of one of the two capacitors by the switching means so that a potential at an interconnection point of the capacitors has a desired set value. The power converter according to any one of the preceding claims. 6. The voltage control means includes switching means for independently discharging each capacitor when discharging the energy of the power storage means to two capacitors when the voltage of the system power supply is abnormal. A load current flowing through the load is detected so that the potential at the interconnection point of the two capacitors becomes a desired set value, and the switching means controls the current that matches the load current to flow through the two capacitors. The power converter according to claim 4, further comprising a control circuit. 7. The voltage control means includes switching means for independently discharging each of the capacitors when discharging the energy of the power storage means to the two capacitors when the voltage of the system power supply is abnormal. A load current flowing through a load is detected so that a potential at an interconnection point of the two capacitors becomes a desired set value, and a DC component included in the load current flows through the two capacitors by the switching means. 5. The power converter according to claim 4, further comprising a control circuit for controlling the power converter. 8. The power supply according to claim 1, wherein when storing without using the power converter, the circuit is switched so that the capacitor is not charged by the power storage means. Conversion device.