JPH0734629B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power converter that has the function of an uninterruptible power supply using a battery and performs AC-AC power conversion.

[Conventional technology]

Figure 7 shows, for example, Fuji Bulletin Vol58, No.11 (issued in 1985) 6.
It is a circuit block diagram which shows the conventional power converter shown on page 84, In the figure, 1 is an AC input power supply, 2 is a 1st diode rectifier connected to this AC input power supply, 3 is said 1st A capacitor connected to the output side of the diode rectifier 2, 4 is a chopper connected to the output side of the first diode rectifier 2, 5 and 6 are reactors and capacitors connected to the output side of the chopper 4, and 7 is A battery connected in parallel to the capacitor 6, 8 is a first inverter connected to the battery 7 and the capacitor 6, 9 is a first transformer connected to the output side of the first inverter 8, 10 Is a second diode rectifier connected to the output side of the first transformer 9, 11 and 12 are reactors and capacitors connected to the output side of the second diode rectifier 10, and 13 is the aforesaid The second, which is connected to capacitor 12
Inverters, 14 and 15 are reactors and capacitors connected to the output side of the second inverter 13, and 16 is an AC load connected to the capacitor 15.

Next, the operation will be described. First, the AC voltage of the AC input power supply 1 is rectified by the first diode rectifier 2,
The DC voltage smoothed by the capacitor 3 is obtained.
The chopper 4 performs DC-DC power conversion, and controls the voltage of the battery 7 via the reactor 5 and the capacitor 6 that act as a filter. The first inverter 8 is a so-called voltage type inverter, which converts the DC voltage of the battery 7 into an AC voltage, and converts it into DC power again by the second diode rectifier 10 via the transformer 9. The DC output voltage of the second diode rectifier 10 is smoothed by the reactor 11 acting as a filter and the capacitor 12. The second inverter 13 converts the DC voltage of the capacitor 12 into an AC voltage, and an AC load is applied via a reactor 14 and a capacitor 15 which act as a filter.
AC power is supplied to 16. Here, the transformer 9 has a function of insulating between the AC input power supply 1 and the AC load 16. Also, the chopper 4, the first and second inverters 8 and
Power MOSFET is used as a switching element of 13,
Reactors 5,11,14 and capacitors 6,12,15 that act as filters by switching at high frequency
And the transformer 9 is downsized. Also the second inverter
By performing PWM control, 13 supplies an AC output voltage with a small waveform distortion to an AC load 16.

Then, during steady operation, the chopper 4 charges the battery 7 via the first diode rectifier 2 while
It operates so as to supply power to the AC load 16 via the inverters 8 and 13. When the AC input power supply 1 fails, the chopper 4 stops operating and operates to supply power from the battery 7 to the AC load 16 via the first and second inverters 8 and 13.

[Problems to be solved by the invention]

Since the conventional power converter is configured as described above,
The distortion of the current of the AC input power source is large, the power capacity of the chopper 4 is large, and the AC power is obtained through a large number of power converters during steady operation. When it is cut off, the energy of the reactor 11 must be absorbed by the capacitor 12, so the input DC voltage of the second inverter rises sharply and becomes an overvoltage, and there are many problems such as a large number of filters. was there.

The present invention has been made to solve the above problems, and can reduce the current distortion of an AC input power supply, make the power factor 1 and improve the conversion efficiency of a power converter. An object of the present invention is to obtain a power converter capable of suppressing overvoltage of the input DC voltage of the second inverter.

[Means for solving problems]

In the power converter according to the present invention, the conventional chopper is omitted, the first inverter on the input side of the first transformer is configured as a current control type, and the third inverter is provided on the input side of the second inverter. Is provided to charge the battery 7 through the second transformer and the third diode rectifier,
The circuit is configured such that the battery is discharged from the output side of the first diode rectifier through the switch.

[Action]

In the power converter according to the present invention, the first inverter controls the instantaneous waveform of the input current to control the current of the AC input power source in a sine wave shape, and the battery is charged by the third inverter. The operation of the inverter is stopped, and power is supplied from the battery to the AC load via the switch by the first inverter and the second inverter.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In the figure, the same parts as those of FIG. 7 are shown with the same reference numerals, and in FIG. 1, 20 is a reactor connected to the output side of the first diode rectifier 2, and 8a is a series connected to the reactor 20. First inverter 9 which is the first inverter 9
Is connected to the second diode rectifier 10 via, 21 is a third inverter connected to the output side of the second diode rectifier 10, and 22 is connected to the output side of the third inverter 21. A second transformer, 23 is a third diode rectifier connected to the secondary side of the second transformer 22, and 24 is a reactor connected to the output side of the third diode rectifier 23, It is connected to the battery 7. 25 is a switch (for example, a self-extinguishing type semiconductor switch such as a thyristor)
The battery 7 is connected between the battery 7 and the output side of the first diode rectifier 2 in a direction in which the battery 7 is electrically connected to the output side of the first diode rectifier 2.

Next, the operation will be described. First, the switch 25 is turned off during normal operation. Therefore, the AC voltage of the AC input power supply 1 is rectified by the first diode rectifier 2, and the AC power supply of the AC input power supply 1 is the first inverter 8a.
Is controlled by the reactor 20 in a sine wave shape.
The first inverter 8a is a second and a third inverter 13
Unlike 21 and 21, the reactor 20 is provided on the input side to perform current control type PWM control. Subsequently, a specific embodiment of the first inverter 8a will be described below with reference to FIG. FIG. 2 shows an example of the configuration of the first and second diode rectifiers 2 and 10 for the single-phase AC input power supply 1 and the first inverter 8a, which are connected in a single-phase bridge. Also, the third
The operation waveforms of the first inverter 8a shown in FIG. 2 are shown in the figure. The first inverter 8a is switching-controlled at a high frequency, and is instantaneously waveform-controlled in a sine wave in phase with the voltage Va of the AC input power supply 1. Vd represents the waveform of the DC output voltage of the first diode rectifier 2, and the first inverter 8a has a waveform so that the DC output current Id of the first diode rectifier 2 has a waveform similar to this DC output voltage Vd. Control with. For example, with respect to the current reference value Is shown by the broken line in the waveform of FIG. 3 showing the DC output current Id of FIG. ₂ , during the period from time t _{1 to} t ₂ , the arm element of the first inverter 8a (with MOSFET Simultaneously turn on (configured) S ₁ and S ₃ , causing a DC short circuit. This DC output current Id is controlled only by the reactor 20 and increases by ΔI.

Here, L is the inductance of the reactor 20.

When the DC output current Id exceeds the current reference value Is, the arm element
Off the S _3, turns on the arm element S _4. This arm element
During the period t _{2 to} t ₃ in which S ₁ and S ₄ are on, the DC output current Id passes through the first inverter 8a, the first transformer 9 and the second diode rectifier 2 to the capacitor 12 side. Flowing.
So to speak, to operate the energy stored in the reactor 20 during the time period from t ₁ ~t ₂ to emit to the capacitor 12 side during the next time t ₂ ~t _3. t ₂ ~t ₃ period of the DC output current Id
The decrease ΔI _{A of} is as follows.

Here, Vc is the voltage of the capacitor 12, and n is the first transformer 9
Is the winding ratio.

That is, n and Vc must be set so that the output voltage nVc of the first inverter 8a becomes larger than the DC output voltage Vd of the first diode rectifier 2. When the DC output current Id falls below the current reference value Is, the arm element S ₁ is turned off and the arm element S ₂ is turned on. At this time, since the arm elements S ₂ and S ₄ are turned on, the first inverter 8a again causes a DC short circuit, and during the period from time t _{3 to} t ₄ , the DC output current Id is the time (t ₂ −t ₁ ) instead of time (t ₄ −
It rises according to the relational expression obtained by replacing it with t ₃ ). When the DC output current Id exceeds the current reference value Is, the arm element S ₄ is turned off and the arm element S ₃ is turned on. In this case becomes the waveform and opposite polarity when the output current Ii is the time t ₂ ~t ₃ of the first inverter 8a, the first transformer 9 and a second diode rectifier 10
Through the capacitor 12 to the first inverter 8a, an alternating output current Ii is obtained. DC output current Id during the time period from t ₄ ~t ₅ decreases in accordance with equation obtained by replacing the time (t ₅ -t ₄₎ in place of (2) Time in formula (t ₃ -t _2). As described above, the arm element of the first inverter 8a is repeatedly controlled in four switching modes to follow the current reference value and perform waveform control. The current Ia of the AC input power source 1 becomes a sinusoidal AC current waveform due to the rectifying operation of the first diode rectifier 2. As another function of the first inverter 8a, the voltage of the capacitor 12 is controlled to be constant, which changes the magnitude (amplitude) of the current reference value according to the deviation between the voltage reference value of the capacitor 12 and the actual value. This can be performed by changing and following the waveform control by the first inverter 8a.

The second and third inverters 13 and 21 have the same configuration as a normal inverter, and perform an inverter operation of an electric phase control type for an input voltage source by high frequency PWM control. However, the second inverter 13 controls the output voltage in a sine wave shape so that the waveform distortion of the terminal voltage of the AC load 16 is reduced. On the other hand, the third inverter 21 is the battery 7
The charging voltage or charging current of the battery 7 is controlled. Where the third inverter 2
The reason why the charging circuit is configured by the first, second transformer 22 and the third diode rectifier 23 is to electrically insulate the battery 7 and the AC load 16 by the second transformer 22. Further, as another function of the charging circuit, when the AC load is suddenly cut off or the like, and when the input voltage of the second inverter 13 becomes an overvoltage at this time, the third inverter
By 21, the charging current of the battery 7 is controlled to increase, and the input voltage of the second inverter 13 is suppressed.

The power capacity of the third inverter 21 may be small because the charging capacity of the battery 7 is generally about 10% of the output capacity of the second inverter 13.

Next, when the AC input power supply 1 fails, the operation of the third inverter 21 for charging is stopped and the switch 25
(A thyristor is used here is shown). At this time, the voltage of the battery 7 is applied to the output side of the first diode rectifier 2 via the switch 25. The discharge current of the battery 7 is controlled by the first inverter 8a. In this case, the current reference value of the first inverter 8a is switched to a flat DC current reference value for operation.

When the AC input power supply 1 is restored, the current reference value of the first inverter 8a is switched to a sine wave full-wave rectified wave shape and the switch 25 is turned off. Charge it. Switch here 25
When a thyristor is used as the rectifier, the rectifier is turned off when the DC output voltage Vd obtained by rectifying the AC input voltage Va with the first diode rectifier 2 becomes larger than the voltage of the battery 7. Therefore, when the thyristor is used as the switch 25, the voltage of the battery 7 must be set to a value smaller than the peak value of the DC output voltage Vd of the first diode rectifier 2, but the switch 25 is not limited to the thyristor. Arc-extinguishing semiconductor switch (eg GTO, SITH, SI
T, a transistor, etc.), and in this case, the voltage of the battery 7 is not limited.

In the above embodiment, the first, second and third inverters 8
Although the example in which the power MOSFET is used as the arm element of a, 13, 21 has been shown, other self-arc-extinguishing type semiconductor elements may be used. Further, in the above-mentioned embodiment, the case of the single-phase AC input power supply is shown, but even if it is a three-phase input power supply, the same effect as that of the above-mentioned embodiment is obtained. Further, the output of the second inverter 13 may be a single-phase output or a three-phase output. FIG. 4 shows a specific circuit configuration example of a power converter with three-phase input and three-phase output. Three sets of the first diode rectifier 2, the reactor 20, the first inverter 8a, the first transformer 9, and the second diode rectifier 10 are connected to the three-phase AC power supply, The output side of the second diode rectifier 10 is commonly connected to the capacitor 12, and the three sets of the first inverters 8a are separately waveform-controlled so as to flow a three-phase sinusoidal current to the three-phase AC power supply. To do. Second inverter
Reference numeral 13 is composed of a three-phase bridge and generates a three-phase AC output voltage. The third inverter 21 is composed of a single-phase bridge, and constitutes a charging circuit that charges the battery 7 via the second transformer 22, the third diode rectifier 23 and the reactor 24. The switch 25 for discharging the battery 7 is composed of a thyristor 25a and a plurality of diodes.
Is connected to the output side of each positive electrode of the three sets of the first diode rectifiers 2 from the positive electrode of the battery via the thyristor 25a, and from the negative electrode of the battery 7 directly to the three sets of the first diode of the three sets. Is connected to the output side of each negative electrode of the diode rectifier 2 to form a discharge path.

The thyristor 25a may be omitted by replacing the three sets of diodes connected to the output side of the thyristor 25a with thyristors.

FIG. 5 is a circuit configuration diagram showing another embodiment of a three-phase input power converter. In the figure, the first diode rectifier 2a is composed of a three-phase bridge, and reactors 20P and 20N are connected to the positive and negative DC output sides, respectively. First inverter 8a
Are configured by cascade connection of two sets, and are connected between the reactors 20P and 20N. Intermediate point of two sets of first inverters 8a and three-phase AC power supply connected in cascade.
A three-phase AC switch 26 is provided between eu, ev, and ew.
Further, the two sets of the first inverters 8a are commonly connected to the capacitor 12 through the transformer 9 and the second diode rectifier 10, respectively.
It is connected to the. The positive electrode of the battery 7 is connected to the positive electrode terminal of the first diode rectifier 2a via the switch 25, and the negative electrode of the battery 7 is directly connected to the negative electrode terminal of the first diode rectifier 2a. The operation of the first diode rectifier 2a, the first inverter 8a, and the three-phase AC switch 26 will be briefly described with reference to the operation waveform diagram of FIG. The positive and negative output currents I _P and I _N of the first diode rectifier 2a are the positive and negative three-phase half-wave rectified wave shapes of the three-phase AC power supply voltages eu, ev, and ew. Individually with PW
By performing M control and distributing the difference current I _O between both output currents I _P and I _N to the AC input power source through the three-phase AC switch 26,
The current of each phase of the three-phase AC switch 26 and the current of the arm element of the first diode rectifier 2a are combined to form a sinusoidal three-phase current Iu, Iv, Iw of the three-phase AC power supply voltage eu, ev, ew. You are getting alternating current. At the time of a power failure, the three-phase AC switch 26 may be turned off and the discharge current of the battery 7 may be commonly controlled by the two inverters 8a.

In the above embodiment, the second and third diode rectifiers 1
I showed a circuit composed of a single-phase bridge as 0, 23,
An intermediate tap may be provided on the secondary side of the first and second transformers to form a single-phase center tap connection.
Further, the configuration of the third inverter 21 is shown as a single-phase bridge configuration, but even if it is a three-phase bridge configuration, a single-phase half-bridge type, a push-pull type, or the like, the same effect as that of the above-described embodiment is obtained. Play. Although the first inverter 8a has a single-phase bridge structure, it may be a bush-pull type.

In the above embodiment, the AC-AC power conversion is shown, but the second inverter 13 may be omitted and the AC-DC power conversion may be applied.

〔The invention's effect〕

As described above, according to the present invention, the first inverter for performing the waveform control of the input current is provided by providing the mode in which the output side of the first diode rectifier is short-circuited by the direct current via the reactor. Is converted into DC power through the first transformer and the second diode rectifier, the DC power is converted into AC power by the second inverter and supplied to the AC load, and by the third inverter. Second
A charging circuit for charging the battery through the transformer and the third diode rectifier;
Since the circuit is configured so that a switch is provided between the output side of the diode rectifier and the discharge side of the battery, it is possible to reduce the waveform distortion of the current of the AC input power source and to operate at a high power factor, and to maintain a steady state. The efficiency of the power converter during operation can be greatly improved. Further, since the battery charging circuit is provided, there is an effect that stable operation can be performed even in the case of power failure.

[Brief description of drawings]

1 and 2 are circuit configuration diagrams showing a power converter according to an embodiment of the present invention, FIG. 3 is an operation waveform diagram of a main part of the power converter of FIG. 2, FIGS. 4 and 5. Is a circuit configuration diagram of a power converter showing another embodiment of the present invention, FIG. 6 is an operation waveform diagram of a main part of the power converter shown in FIG. 5, and FIG. 7 is a circuit showing a conventional power converter. It is a block diagram. In the figure, 1 is an AC input power source, 2, 10 and 23 are first, second and third diode rectifiers, 8a, 13 and 21 are first, second and third inverters, and 9 and 22 are first. , A second transformer, 7 is a battery, and 25 is a switch. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A first diode rectifier connected to an AC input power source, and a first inverter connected to the output side of the first diode rectifier via a reactor and controlling the current of the reactor to an instantaneous value. A second diode rectifier connected to the output side of the first inverter via a first transformer, and a second inverter connected to the output side of the second diode rectifier and converting to an AC output And a third inverter provided on the output side of the second diode rectifier, and a third diode rectifier connected to the output side of the third inverter via a second transformer. A battery connected to the output side of the third diode rectifier, and a switch provided between the battery and the output side of the first diode rectifier. Power converter for. 2. The power converter according to claim 1, wherein the switch is a self-turn-off type semiconductor switch such as a thyristor.