JPH0993945A - Power factor improving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the power factor of a plurality of DC-DC converters with a relatively simple construction. SOLUTION: An AC voltage is rectified by the rectifiers 11 and 12 of a plurality of DC-DC converters 101 and 102 and the rectified voltages are inputted to capacitors 21 and 22 respectively. The terminal voltages of the capacitors 21 and 22 are applied to series circuits composed of the primary windings of transformers 31 and 32 and switching devices 41 and 42 . Controllers 61 and 62 control the ON's/OFF's of the switching devives 41 and 42 to stabilize the output DC voltages of rectifying/smoothing circuits 51 and 52 which are connected to the secondary windings of the transformers 31 and 32 . Further, a controller 8 which compares the AC voltage with a set voltage Vr and switches the AC voltage applied to the rectifiers 11 and 12 with a switching circuit 7 and makes the timings of the charging currents of the capacitors 21 and 22 corresponding to the DC-DC converters 101 and 102 different from each other is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a plurality of DC-DCs.
The present invention relates to a power factor correction circuit for a converter. In a DC-DC converter in which an AC voltage is rectified by a rectifier circuit and applied to a capacitor, and the terminal voltage of this capacitor is applied to the primary winding of a transformer and a switching element, when the voltage exceeds the terminal voltage of the capacitor. The charging current flows according to the output voltage of the rectifier circuit. This charging current has a peak waveform that is significantly different from the AC voltage waveform. Therefore, there is a problem that the power factor becomes low due to the inclusion of harmonic components in addition to the fundamental wave component of the AC voltage, and improvement of this power factor is desired.

[0002]

BACKGROUND ART FIG. 4 is an explanatory view of a conventional example, 31 _1,
31 ₂ is a rectifier circuit, 32 ₁ and 32 ₂ are capacitors, 33
₁ , 33 ₂ are transformers, 34 ₁ , 34 ₂ are switching elements, 35 ₁ , 35 ₂ are rectifying and smoothing circuits, 36 ₁ , 36 ₂
Is an output control circuit, 37 is a load, and 40 ₁ and 40 ₂ are DC-
A DC converter is shown, showing a case where they are connected in parallel.

The DC-DC converters 40 ₁ and 40 ₂ are
By the respective rectifier circuits 31 _1, 31 ₂ rectifies an AC voltage is applied to the capacitor 32 _1, 32 _2, capacitors 32
The terminal voltages of ₁ , 32 ₂ are supplied to the primary windings of the transformers 33 ₁ , 33 ₂ and the switching element 3 such as a field effect transistor.
It is applied to the series circuit with 4 ₁ , 34 ₂ and the transformer 33 ₁ ,
The induced voltage of the secondary winding of 33 ₂ is rectified and smoothed by the rectifying and smoothing circuits 35 ₁ , 3
5 ₂ rectifies and smoothes, supplies a DC voltage to the load 37, compares the output DC voltage with the set reference voltage in the output control circuits 36 ₁ and 36 ₂ , and switches the switching element 34 according to the error voltage. The ON period of ₁ and 34 ₂ is controlled to stabilize the output DC voltage supplied to the load 37.

When the power consumption of the load 37 is small,
Although one DC-DC converter is used, when the power consumption of the load 37 is large or the reliability is increased as a redundant configuration, a configuration in which a plurality of DC-DC converters are connected in parallel as shown in the drawing is used. Has been adopted. If the voltage supplied to the load 37 is very high, multiple DC
The input side of the -DC converter is connected in parallel, and the output side is connected in series.

[0005]

The DC-DC converters 40 ₁ and 40 ₂ convert the AC voltage into rectifier circuits 31 ₁ and 31 _2.
Capacitor 32 ₁ and rectified by, 32 ₂ has an input-side configuration for charging a current flowing at that time, the capacitor 32 _1, 32 rectifier circuit 31 from the terminal voltage of the _{2 1,} 31 ₂
When the rectified output voltage of is high. That is, as shown in the operation explanatory view of the conventional example of FIG. 5, when the AC voltage has the waveform shown in (a), the rectified output voltages of the rectifier circuits 31 ₁ and 31 ₂ become those shown in (b). And the capacitors 32 ₁ ,
The terminal voltage of 32 ₂ is as shown in (c), and the primary windings of the transformers 33 ₁ and 33 ₂ and the switching elements 34 ₁ and
34 ₂ in series circuit.

The charging current of the capacitors 32 ₁ and 32 ₂ is when the rectified output voltage is higher than the terminal voltage, for example, as shown in (d). Therefore, the alternating current has a pulse shape as shown in (e). This is one D
Even in the case of C-DC converter, a plurality of DC-DC
Similar AC current flows even when the converters are operated in parallel. The power factor is large in the case where a current having a waveform close to a sine wave of an AC voltage flows, and is smaller as more harmonic currents different from the sine wave are included. When such a device having a small power factor is connected to an AC power source, the efficiency on the AC power source side is reduced, and therefore it is desired to improve the power factor.

[0007] Therefore, between the AC power supply choke coil so as to suppress the peak of the alternating current waveform shown in (e) of FIG. 5 and the rectifying circuit 31 _1, 31 _2, or rectifying circuit 31 _1, It is conceivable to connect between 31 ₂ and capacitors 32 ₁ and 32 ₂ . However, since a relatively large choke coil is required, there is a problem that the DC-DC converter becomes large and the cost increases.

There is also known a power factor correction circuit that switches the charging currents of the capacitors 32 ₁ and 32 ₂ at high speed in response to an AC voltage waveform and brings the envelope of the charging currents closer to a sine wave (for example, (Kaisho 63-154064)
However, compared to the choke coil and the main switching element, a switching element that performs a switching operation at a high speed is required, which causes a problem of cost increase. The present invention
The purpose is to improve the power factor with a relatively simple structure.

[0009]

SUMMARY OF THE INVENTION A power factor correction circuit of the present invention.
Is an AC voltage rectifier circuit 1₁, 1₂Rectified by
Densa 2₁, 2₂Input to this capacitor 2₁, 2₂
The terminal voltage of the transformer 3 ₁, 3₂Primary winding and switch
Element 4₁, 4₂This is applied to the series circuit of
Ching element 3₁, 3₂The on / off control of the transformer
Three₁, 3₂Rectifying and smoothing circuit 5 connected to the secondary winding of₁, 5
₂DC-DC converters that stabilize the output DC voltage of the
Data 10₁, 10₂AC voltage in the power factor correction circuit of
And a set voltage are compared, and a plurality of DC-DC converters 1
0₁, 10₂Corresponding rectifier circuit 1₁, 1₂Via conde
Sensor 2₁, 2₂The timing of the current flowing into the
The control circuit 8 and the switching circuit 7 are provided.

[0010] A plurality of DC-DC converter 10 _1, 10
_2, for example one of the DC-DC converter 10 _1, when in response to the conventional example as well as the full-wave rectified voltage of the rectifier circuit 1 ₁ charging current flows in pulse-like to the capacitor 2 _1, another DC-DC The converter 10 ₂ controls the switching circuit 7 by the control circuit 8 so that the charging current of the capacitor 2 ₂ due to the full-wave rectified voltage of the rectifying circuit 1 ₂ flows at a timing different from the charging current flowing in the capacitor 2 ₁ . Therefore, the alternating current from the alternating current power supply is
Since the timings are different for the DC converters 10 ₁ and 10 ₂ , it is possible to approximate a sine wave as a whole,
Power factor can be improved.

[0011] Also input to the capacitor 2 _1, 2 ₂ AC voltage is rectified by the rectifier circuit ₁ 1, 1 _2, and the capacitor 2 _1, 2 ₂ of the terminal voltage transformer 3 _1, 3 ₂ of the primary winding It is applied to the series circuit with switching elements 4 ₁ and 4 ₂ ,
A plurality of DC-s that stabilize the output DC voltage of the rectifying and smoothing circuits 5 ₁ and 5 ₂ connected to the secondary windings of the transformers 3 ₁ and 3 ₂ by the on / off control of the switching elements 3 ₁ and 3 _2.
In the power factor correction circuit of the DC converters 10 ₁ and 10 ₂ , a plurality of DC-DCs are compared by comparing the AC voltage with the set voltage.
Converter 10 _1, 10 ₂ corresponding rectifier circuits ₁ 1, 1 ₂ from the transformer 3 _1, 3 ₂ of the primary winding and the switching element 4
Switching the full-wave rectified voltage applied to ₁ and 4 ₂
And a control circuit and a switching circuit for different the timing of the current flowing into the capacitor 2 _1, 2 ₂ through the rectifier circuit 1 _1, 1 ₂ of the plurality of DC-DC converter 10 _1, 10 ₂ corresponding.

The full-wave rectified voltage of the rectifier circuits 1 ₁ and 1 ₂ is applied to the capacitors 2 ₁ and 2 ₂ via a switching circuit,
The timings at which the charging currents of the capacitors 2 ₁ and 2 ₂ flow are controlled to be different depending on the switching circuit. As a result, the alternating current from the alternating current power source can generate a plurality of DC-Ds.
Since the timing is different for each of the C converters 10 ₁ and 10 ₂ , the sine wave can be approximated as a whole, and the power factor can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 is an explanatory view of an embodiment of the present invention, shows a case in which the two DC-DC converters 10 _1, 10 _2, 1 _1, 1 ₂ rectifier circuit, 2 ₁ , 2 ₂
Is a capacitor, 3 ₁ , 3 ₂ is a transformer, 4 ₁ , 4 ₂ is a switching element such as a field effect transistor, 5 ₁ ,
5 ₂ is a rectifying / smoothing circuit including a rectifying diode, a smoothing choke coil, a smoothing capacitor, etc., 6 ₁ and 6 ₂ are switching elements 4 by comparing the output DC voltage with a set reference voltage.
An output control circuit for controlling the ON period of ₁ and 4 _2, a switching circuit 7 including a thyristor, 8 a control circuit, 9
Is a comparison circuit, 11 ₁ , 11 ₂ , 12 ₁ and 12 ₂ are output terminals, and 13 and 14 are input terminals for AC voltage.

[0014] A plurality of DC-DC converter 10 _1, 10
The input side of ₂ is connected in parallel and the input terminals 13, 1 are connected to the AC power supply.
4 is connected, the capacitors 2 ₁ and 2 ₂ are charged by the full-wave rectified voltage of the rectifier circuits 1 ₁ and 1 ₂ , and the terminal voltages of the capacitors 2 ₁ and 2 ₂ are changed to the primary voltages of the transformers 3 ₁ and 3 ₂ . It is applied to the series circuit of the winding and the switching elements 4 ₁ and 4 ₂ and the ON time of the switching elements 4 ₁ and 4 ₂ is controlled by the control circuits 6 ₁ and 6 ₂ to transform the transformers 3 ₁ and 3 _2.
The stabilized DC voltage is output from the rectifying and smoothing circuits 5 ₁ and 5 ₂ connected to the secondary winding of the.

The output sides of the DC-DC converters 10 ₁ and 10 ₂ are connected in parallel or in series to form a load (not shown).
Supply a stabilized DC voltage to. The switching circuit 7, which can be connected between the plurality of DC-DC converter 10 _1, 10 ₂ input to the corresponding terminals 13 and 14 and the rectifying circuit ₁ 1, 1 _2, in which case, a plurality of DC
It can be omitted for one of the DC-DC converters. In this embodiment, the case where the DC-DC converter 10 _{1 is} omitted is shown. Further, the switching circuit 7 shows a case in which thyristors are connected in parallel in opposite directions, but it can be composed of a triac or the like capable of passing a current in both directions.

Further, the control circuit 8 includes a comparison circuit 9 and the like, and compares the alternating voltage with the positive and negative polarity set voltage Vr, and turns on the switching circuit 7 when the alternating voltage is lower than the set voltage Vr. Therefore, at the DC-DC converter 10 _2, an AC voltage to the rectifier circuit 1 ₂ at the timing not the peak point of the positive and negative polarity of the AC voltage is applied, the charging current rectified voltage is applied to the capacitor 2 ₂ Flowing.

FIG. 2 is a diagram for explaining the operation of an embodiment of the present invention, in which the AC voltage applied to the input terminals 13 and 14 from the AC power source has a sine waveform shown by V ₁ in (a). The AC voltage V ₁ is applied to the rectifier circuit 11 of the DC-DC converter 10 ₁ on _one side to be full-wave rectified, and a charging current flows through the capacitor 2 ₁ in the vicinity of the peak voltage of the AC voltage V _1. . Therefore, the alternating current flows at the timing shown by A ₁ .

[0018] Also in the rectifier circuit 1 ₂ of the other DC-DC converter 10 ₂ is blocked peak voltage near the AC voltages V ₁ by the switching circuit 7, a waveform of V ₂ of (b). The AC voltage V ₂ is full-wave rectified is applied to the capacitor 2 ₂ by the rectifier circuit 1 _2, the AC voltage V ₂
Since the charging current corresponding to (3) flows, the alternating current has a bimodal characteristic like A _{2 in} (c). Therefore, as shown in (d), the sum of the alternating current A ₁ in (a) and the alternating current A _{2 in} (c) is supplied from the alternating current power source,
As is clear from comparison with the waveform of the alternating current A ₁ , it is possible to approximate a sine wave, so that the power factor can be improved.

Since the capacitor 2 ₁ is charged in the vicinity of the peak point of the full-wave rectified voltage and the capacitor 2 ₂ is charged in the full-wave rectified voltage deviated from the vicinity of the peak point, the respective capacitors 2 ₁ , 2 ₂ are charged. Although a slight difference occurs in the terminal voltage, the switching elements 4 ₁ , 4 due to the control circuits 6 ₁ , 6 ₂
4 by controlling the _second on-time, it is possible to stabilize the output DC voltage to a predetermined value.

FIG. 3 is an explanatory view of another embodiment of the present invention, in which the same reference numerals as those in FIG. 1 indicate the same parts, 7A is a field effect transistor forming a switching circuit, and 8A is a control circuit. This embodiment shows a case where a switching circuit is connected between a rectifier circuit and a capacitor, and it is possible to provide a switching circuit corresponding to the DC-DC converters 10 ₁ and 10 ₂ as in the above-described embodiments, It can be omitted for one DC-DC converter in.

Further, the control circuit 8A, similarly to the control circuit 8 of the above-described embodiment, is configured to include a comparison circuit for comparing the AC voltage with the set voltage Vr, and switches at a position deviated from the vicinity of the peak point of the AC voltage. is intended to turn on the field effect transistor 7A as an element, in this case, as compared full-wave rectified voltage of the rectifier circuit 1 ₂ and the set voltage, it can be configured to perform on-control of the field effect transistor 7A Is.

Also in this embodiment, the capacitors 2 ₁ ,
Since the timing of the charging current of 2 ₂ is different,
The timings of the alternating currents flowing from the alternating current power supply to the rectifier circuits 1 ₁ and 1 ₂ are also different, and the sum of the alternating currents is close to a sine wave, and the power factor can be improved.

In each of the above-mentioned embodiments, a single-stone DC is used.
-The case where two DC converters are operated in parallel is shown, but the present invention is also applicable to other configurations, such as a Futaki type DC-DC converter, and the input side of two or more DC-DC converters. By connecting in parallel and comparing the alternating voltage with different set voltages, the charging current of the capacitor by the full-wave rectified voltage is controlled to flow at different timings, and the alternating current from the alternating current power source is made to approach a sine wave. Power factor can be improved.

[0024]

As described above, according to the present invention, the input sides of the plurality of DC-DC converters 10 ₁ and 10 ₂ are connected in parallel, and the AC voltage and the set voltage are compared with each other so that the plurality of DC
-DC converter 10 _1, 10 ₂ corresponding rectifier circuits ₁ 1,
The waveform of the alternating current from the alternating current power source is made to be close to a sine wave by differentiating the timings of the charging currents of the capacitors 2 ₁ and 2 ₂ due to the full wave rectified voltage of 1 ₂ and the existing multiple DC-DC converters. Even in the power supply device including the above, there is an advantage that the power factor can be improved by providing the control circuit 8 and the switching circuit 7 having a relatively simple configuration.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of one embodiment of the present invention.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional example.

FIG. 5 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

1 ₁ , 1 ₂ Rectifier circuit 2 ₁ , 2 ₂ Capacitor 3 ₁ , 3 ₂ Transformer 4 ₁ , 4 ₂ Switching element 5 ₁ , 5 ₂ Rectifier smoothing circuit 6 ₁ , 6 ₂ Output control circuit 7 Switching circuit 8 Control circuit 9 Comparison Circuit 10 ₁ , 10 ₂ DC-DC converter

Claims (2)

[Claims] 1. An AC voltage is rectified by a rectifier circuit and input to a capacitor, a terminal voltage of the capacitor is applied to a series circuit of a primary winding of a transformer and a switching element, and ON / OFF control of the switching element is performed. In a power factor correction circuit of a plurality of DC-DC converters for stabilizing an output DC voltage of a rectifying and smoothing circuit connected to a secondary winding of the transformer, the plurality of DC-DC converters are compared by comparing the AC voltage with a set voltage. DC-
A switching circuit and a control circuit for switching the AC voltage applied to the rectifier circuit corresponding to the DC converter and different in the timing of the current flowing into the capacitor via the rectifier circuits corresponding to the plurality of DC-DC converters. A power factor correction circuit characterized by being provided. 2. An AC voltage is rectified by a rectifier circuit and input to a capacitor, a terminal voltage of the capacitor is applied to a series circuit of a primary winding of a transformer and a switching element, and the ON / OFF control of the switching element is performed. In a power factor correction circuit of a plurality of DC-DC converters for stabilizing an output DC voltage of a rectifying and smoothing circuit connected to a secondary winding of the transformer, the plurality of DC-DC converters are compared by comparing the AC voltage with a set voltage. DC-
A full-wave rectified voltage applied to the primary winding of the transformer and the switching element is switched from the rectifier circuit corresponding to the DC converter and flows into the capacitor through the rectifier circuits corresponding to the plurality of DC-DC converters. A power factor correction circuit comprising a control circuit and a switching circuit that make the timings of currents different from each other.