JP3211380B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at a high frequency, and a power conversion device used for a power supply of various electronic devices.

[0002]

2. Description of the Related Art Heretofore, as this type of power converter, for example, an apparatus using a push-pull inverter shown in FIG. 7 has been known. In this configuration, an input terminal of a full-wave rectifier circuit 2 is connected to an AC power supply 1, and a smoothing capacitor 3 is connected in parallel to an output terminal of the full-wave rectifier circuit 2. A push-pull inverter 4 is connected to the smoothing capacitor 3.

The push-pull inverter 4 is connected in series with the first
The winding 5a and the second winding 5b, and the first winding 5a and the second
A transformer 5 having a third winding 5c magnetically coupled to the winding 5b is provided, and a connection point between the first winding 5a and the second winding 5b is connected to a positive terminal of the smoothing capacitor 3. First
The non-connection end of the winding 5a is connected to the first switching element 6 and the first switching element 6.
Connected to the negative terminal of the smoothing capacitor 3 via a first half-wave switch circuit 8 having a parallel circuit of
The non-connection end of the second winding 5b is connected to the negative terminal of the smoothing capacitor 3 via a second half-wave switch circuit 11 having a parallel circuit of the second switching element 9 and the second diode 10. The first and second switching elements 6 and 9 have polarities such as transistors, and have opposite polarities to the first and second diodes 7 and 10, respectively. The anodes of the first and second diodes 7 and 10 are connected to the negative terminal of the smoothing capacitor 3.

A capacitor 1 is connected to a third winding 5c of a transformer 5.
2 and a load 14 are connected via a choke coil 13 in series. Note that a discharge lamp or the like is used as the load.

In this device, when the power supply 1 is turned on, a DC voltage is generated across the smoothing capacitor 3 by the full-wave rectifier circuit 2 and the smoothing capacitor 3. Then, the first and second switching elements 6 and 9 are alternately turned on and off at a high frequency by driving means (not shown). Assuming now that the first switching element 6 is turned on and the second switching element 9 is turned off, the first winding 5a → the first winding 5a
Current flows in the direction of the switching element 6 of the first winding 5
DC voltage from both ends of the smoothing capacitor 3 is applied to a.

At the same time, a voltage corresponding to the turns ratio is generated in the third winding 5c, and a current flows in the direction of the reactor 13 → the load 14 → the capacitor 12.

Next, first and second switching elements 6, 9
Is turned on and off, this time, the second winding 5b → the second winding
Current flows in the direction of the switching element 9 of the second winding 5
DC voltage is applied to b between both ends of the smoothing capacitor 3.

As a result, a voltage in the third winding 5c is generated in a direction opposite to that of the third winding 5c.
→ Current flows in the direction of the reactor element 13.

In this way, AC power is supplied to the load 14.

[0010]

In such a conventional apparatus, the input voltage waveform from the AC power supply 1 is a sine wave as shown in FIG. The waveform is equal to the charging current and has a very large peak value during the charging period of the smoothing capacitor 3 as shown in FIG. The charging current does not flow except during the charging period in which the input voltage is lower than the voltage across the smoothing capacitor 3. Therefore, the input current waveform is a discontinuous waveform having a pause. Therefore, there is a problem that current harmonics and current distortion occur.

Another problem is that the effective value increases because the power factor of the input current is poor.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power converter capable of making the input current waveform a sine wave or a waveform close thereto, thereby preventing current harmonics and current distortion from occurring and improving the power factor. .

[0013]

SUMMARY OF THE INVENTION The present invention provides a rectifier circuit having an input terminal connected to an AC power supply, a capacitor connected between output terminals of the rectifier circuit, a first winding, and a first winding. A transformer having a second winding magnetically coupled to the first winding, a third winding magnetically coupled to the second winding, and a first winding of the transformer connected in series to an output terminal of the rectifier circuit. is, this flowing a first switching element and the reverse current
Preparative a first switch circuit having a diode that can,
Connected in series with the second winding of the transformer, the second having a diode <br/> over de of the first switching element can be passed the second switching element and the reverse current to the switching operation to alternately and the switch circuit, connected to the smoothing capacitors connected in parallel with the series circuit of the second winding and the second switch circuit of the transformer, via a capacitor and a reactor element in series with the third winding of the transformer Load and equipment
The capacity of the capacitor connected between the output terminals of the rectifier circuit makes the input current waveform from the power supply continuous.
It is set to such a value .

[0014]

In the present invention having such a configuration, the capacitor connected between the output terminals of the rectifier circuit and the first of the transformer are connected.
The winding draws a current from the power supply to the circuit side when the input voltage becomes relatively low, so that the input current waveform becomes a continuous waveform.

Further, the capacity of the capacitor depends on the input from the power supply.
Since the value of the current waveform is set to be continuous, the rise in the voltage across the first winding of the transformer, which occurs when the first switching element is turned on, can be appropriately suppressed. Also at the point, the input current waveform from the power supply is made a continuous waveform.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an input terminal of a full-wave rectifier circuit 22 composed of a diode bridge is connected to an AC power supply 21, and a capacitor 2 is connected to an output terminal of the full-wave rectifier circuit 22.
3 and a first switching element 25 composed of a first winding 24a of a transformer 24, a transistor and the like.
And a series circuit of a first half-wave switch circuit 27 having a parallel circuit of a first diode 26. The transformer 24 includes the first winding 24a in addition to the first winding 24a.
a and the first winding 24 magnetically coupled to
a, a third winding 24c magnetically coupled to the second winding 24b.

A second switching element 28, such as a transistor, is connected to a second winding 24b of the transformer
A second half-wave switch circuit 30 having a parallel circuit of the diode 29 is connected in series, and its second winding 24b and the second
The smoothing capacitor 31 is connected in parallel to a series circuit with the half-wave switch circuit 30 of FIG.

A capacitor 32 and a choke coil 33 as a reactor element are provided on the third winding 24c of the transformer 24.
Are connected in series to a load 34 such as a discharge lamp.

The switching elements 25 and 28 of the half-wave switch circuits 27 and 30 are alternately turned on and off at a high frequency by driving means (not shown). The anodes of the first and second diodes 26 and 29 are connected to the negative terminal of the smoothing capacitor 31. The first and second switching elements 25 and 28 and the first and second diodes 26 and 29 are connected in parallel with opposite polarities.

Next, the operation of this embodiment will be described.

When the AC power supply 21 is turned on, the switching elements 25 and 28 of the half-wave switch circuits 27 and 30 are alternately turned on and off at a high frequency by the driving means, and high-frequency magnetic energy corresponding to the switching is generated. ,
High frequency power is supplied to the load 34 from the third winding 24c.

At this time, the DC component of the power transmitted to the third winding 24 c is removed by the capacitor 32, and the AC waveform becomes a smooth waveform by the choke coil 33.

This operation will be described more specifically.
2 turns on and off at the timing shown in FIG. 2A, and the second switching element 28 turns on and off at the timing shown in FIG. 28 is t1-t2, t3-t4
2A and 2B, the current I24a shown in FIG. 2C flows through the first winding 24a of the transformer 24, and the current I24a shown in FIG.
The current I24b shown in (d) flows. For example, now, the first switching element 25 is turned on, and the second switching element 2
When the switch 8 is turned off, a current I24a flows through the first winding 24a and the first switching element 25, and the current I24a linearly increases as shown in FIG.

Next, when the first switching element 25 is turned off at a certain point in time t1, the current I flowing through the first winding 24a is turned off.
24a is stopped instantly. At this time, the magnetic energy stored at this time is cut off the path on the primary side of the transformer 24, so that the magnetic energy is discharged by flowing through the path of the second winding 24b. Thereby, the diode 29, the second winding 2
4b, a current I24b flows through the path of the smoothing capacitor 31 to charge the smoothing capacitor 31. At this time, the magnitude of the current I24b flowing through the second winding 24b decreases linearly.

If the second switching element 28 is turned on at the time t2 while the current is flowing through the diode 29, the voltage across the second switching element 28 is zero, so that switching loss may occur. Absent.

Then, when the second switching element 28 is turned on, the smoothing capacitor 31 charged in the previous period from t1 to t2 acts as a power source to operate the secondary circuit.
Accordingly, the direction of the current I24b flowing through the second winding 24b is reversed at a certain point in time and increases linearly.

Next, at time t3, the second switching element 28
Is turned off, the current I24b flowing through the second winding 24b is instantaneously stopped, and a resonance voltage is generated at both ends of the second switching element 28 as shown in FIG. At this time, since there is no current flow path in the secondary side circuit,
Magnetic energy is stored in the transformer 24.

This magnetic energy is supplied to the first winding 24
a, the capacitor 23, and the diode 26 circulate, and the current I24 flowing through the first winding 24a at this time.
a decreases linearly. The capacitor 23 shown in FIG.
A current I23 shown in (g) flows.

If the first switching element 25 is turned on at time t4 while the current is flowing through the diode 26, the voltage between both ends of the first switching element 25 becomes zero as shown in FIG. Therefore, no switching loss occurs.

Thereafter, this operation is repeated, and AC power is supplied to the load 34.

In such an operation, a sine wave AC voltage V1 waveform as shown in FIG. 3 between both ends of the capacitor 23.
A voltage V2 waveform as shown in FIG. That is, this voltage waveform is a waveform in which a voltage waveform from the output terminal of the full-wave rectifier circuit 22 is superimposed on an oscillating voltage generated by a closed circuit including the first winding 24a of the transformer 24 and the capacitor 23.

Now, after the second switching element 28 is turned on and a predetermined current flows from the smoothing capacitor 31,
Is turned off, the magnetic energy stored in the transformer 24 is transferred to the third winding 2 of the transformer 24.
4c to the load 34.

However, at this time, a part of the magnetic energy is generated by the back electromotive force induced in the first winding 24a.
A current flows through a closed circuit of the capacitor 4a, the capacitor 23, and the first diode 26. This current decreases with time from a certain peak value. Further, when the current becomes zero at a certain time, the first winding 24a tries to keep the current flowing, so that a back electromotive force is generated in the first winding 24a in a direction in which the first switching element 25 side has a high potential.

As a result, the voltage across the capacitor 23 tends to be lower than the input voltage, so that current is drawn from the AC power supply 21 to the first winding 24a side of the transformer 24.

Next, when the first switching element 25 shifts to the ON state, a current starts flowing in a direction of discharging the electric charge stored in the capacitor 23. This allows the transformer 2
4, the direction of the current flowing through the first winding 24a is reversed.
The potential at both ends of the winding 24a increases. That is, the potential at both ends of the capacitor 23 increases.

Therefore, the circuit composed of the first winding 24a and the first switching element 25 operates as if the input voltage is high despite the low input voltage.

With such an operation, the input current I1 is reduced as shown in FIG.
A continuous waveform as shown in FIG. Since the waveform of the input current I1 is substantially triangular, the input current I1 is controlled by controlling in such a direction as to suppress the peak.
The waveform of the input current I close to a sine wave as shown in FIG.
It can be 1 'waveform.

By doing so, the problems of input current distortion and harmonics can be significantly improved, and the power factor can be improved. To realize this, it is necessary to set the capacitance of the capacitor 23 to a value limited by the switching frequency of each half-wave switch circuit 27, 30 and the circuit constant of each part.

Further, since the peak of the current can be suppressed low, the line shape of the wiring can be narrowed.

For example, if the input voltage from the AC power supply 21 is A
When a load of about 200 W is used as the load 34, the first and second windings 24a and 24b of the transformer 24 are 100 turns, the third winding 24c is 220 Dahn, and the choke coil is a circuit constant of each part. 3
3 for 180 turns and the capacity of the smoothing capacitor 31 for 200 turns.
μF, the capacitance of the capacitor 32 is 0.22 μF, and the switching frequency f of each half-wave switch circuit 27, 30 is about 45 KHz. In order to make the input current waveform continuous, the capacitance of the capacitor 23 is about 0.022 μF. I just need.

Next, the capacity of the capacitor 23 is set to 0.022 μm.
A case where the value is smaller than F and a case where the value is larger than F will be described.

For example, when the capacity of the capacitor 23 is 0.01 μm
When F, the impedance of the capacitor 23 increases, so after the first switching element 25 is turned off,
Although the current flowing through the capacitor 23 decreases, the voltage V2 across the capacitor 23 increases as shown in FIG.

Accordingly, when the first switching element 25 is turned on, the voltage applied to the first winding 24a is equal to the voltage between both ends of the capacitor 23. Therefore, even if the input voltage is low, it is as if the input voltage is low. Act as if it were higher. However, if the capacity of the capacitor 23 is small, the capacitor 2 generated when the input voltage becomes low
3, the voltage between both ends becomes too large,
Since the input voltage at this portion works as if it increased sharply, the input current I1 is accordingly reduced as shown in FIG.
As shown in (c), when the input voltage is substantially zero, a sharp rise occurs, and the problems of input current distortion and harmonics cannot be solved.

For example, when the capacity of the capacitor 23 is set to 0.0
If it is set to 33 μF, the impedance of the capacitor 23 becomes small, so that the current flowing through the capacitor 23 increases after the first switching element 25 is turned off, and the voltage V2 across the capacitor 23 becomes as shown in FIG. Lower.

Therefore, when the input voltage is low,
1, the voltage applied to the first winding 24a when the first switching element 25 is turned on is insufficient, and the input voltage is close to zero to some extent during the idle period. And the waveform of the input current I1 is not continuous as shown in FIG. 5 (c). Therefore, also in this case, the problems of input current distortion and harmonics cannot be solved.

In the above example, the capacity of the capacitor 23 is set to 0.0
Although the case where the capacitance is changed from 22 μF to 0.01 μF or 0.033 μF has been described, the waveform of the input current I1 does not become continuous when the capacitance of the capacitor 23 changes from 0.022 μF to about several tens nF. .

Next, another embodiment of the present invention will be described with reference to the drawings.

The circuit configuration of this embodiment is the same as that of FIG. In this embodiment, the capacity of the capacitor 23 and the transformer 2
4, the resonance frequency f determined by the inductance of the first winding 24a is set to a limited resonance frequency determined by a circuit constant or the like in a range that is equal to or slightly lower than the switching frequency fSW.

More specifically, when the input voltage from the AC power supply 21 is set to 200 V AC and a load 34 of about 100 W is used, the capacity of the capacitor 23 is set to 16 μF,
The inductance of the first winding 24a of the transformer 24 is 90
0 μH, the inductance of the second winding 24b is 900 μH
H, the inductance of the third winding 24c is 4.5 mH, the capacitance of the smoothing capacitor 31 is 100 μF,
Is set to 0.22 μF, and the inductance of the choke coil 33 is set to 6 mH. The switching frequency fSW is set to 45 KHz, and the resonance frequency f is set to 42 KHz.

Here, the resonance frequency f = 42 KHz is the voltage resonance generated when the second switching element 28 is turned off, from the moment when the second switching element 28 is turned off when the input voltage is at the minimum. During the period up to the moment when the first switching element 25 is turned on, that is, in FIG.
The resonance frequency is such that the voltage resonance ends substantially equally during the period from t3 to t5. The resonance voltage waveform at this time is as shown in FIG. 6A, and the waveform of the input current I1 is continuous. That is, the waveform is as shown in FIG. Therefore, the problems of input current distortion and harmonics can be greatly improved, and the power factor can be improved.

On the other hand, the capacity of the capacitor 23 is set to 10
When the frequency is set to μF, the resonance frequency f becomes as high as 53 KHz, and the resonance of the resonance voltage waveform ends early as shown in FIG. At this time, the waveform of the input current I1 does not become continuous, but becomes a current waveform which rises rapidly around 0V. That is, the waveform is as shown in FIG.

When the capacitance of the capacitor 23 is set to 33 μF, the resonance frequency f is reduced to 29 KHz, and the resonance voltage waveform has a phenomenon that the resonance does not end within the period from t3 to t5 as shown in FIG. . At this time, the input current I1
Is not continuous and becomes a current waveform having a pause period.
That is, the waveform is as shown in FIG.

In the range where the resonance frequency f determined by the capacitance of the capacitor 23 and the inductance of the first winding 24a of the transformer 24 is equal to or slightly lower than the switching frequency fSW = 45 KHz, it is limited by the circuit constant and the like. By setting the frequency to a certain value, the input current can be made into a continuous waveform, the input current distortion and harmonic problems can be greatly improved, and the power factor can be improved. That is, the same effects as in the above embodiment can be obtained.

[0055]

As described in detail above, according to the present invention, the input current waveform can be a sine wave or a waveform close to the sine wave. An apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 shows ON and OFF states of each switching element in the embodiment.
FIG. 4 is a diagram illustrating an OFF timing and a voltage waveform and a current waveform of each unit.

FIG. 3 is a view showing a voltage waveform and a current waveform of each part in the embodiment.

FIG. 4 is a view showing a voltage waveform and a current waveform of each part when the capacitance of the capacitor is reduced in the embodiment.

FIG. 5 is a diagram showing a voltage waveform and a current waveform of each part when the capacitance of the capacitor is increased in the embodiment.

FIG. 6 is a diagram showing a resonance voltage waveform according to another embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional example.

FIG. 8 is a diagram showing an input voltage waveform and an input current waveform in the conventional example.

[Explanation of symbols]

21 ... AC power supply, 22 ... full-wave rectifier circuit, 23 ... capacitor, 24 ... transformer, 25, 28 ... switching element,
27: first half-wave switch circuit, 30: second half-wave switch circuit, 31: smoothing capacitor, 34: load.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H05B 41/24

Claims (1)

(57) [Claims] A rectifier circuit having an input terminal connected to an AC power supply ; a capacitor connected between output terminals of the rectifier circuit ; a first winding ; a second winding magnetically coupled to the first winding ; and said first winding, a transformer with a third winding which second winding and magnetically coupled; connected with first winding of the transformer to the output terminal of the rectifier circuit via the series, the first Switching element and reverse
First with a diode which can flow direction current
Switch circuit and; are connected in series to a second winding of said transformer, second switching operation alternately with said first switching element
Of switching element and reverse current can flow
A smoothing capacitor connected in parallel to the series circuit of the second winding and the second switch circuit of the transformer; second switch circuit and having that diode to the third winding of the transformer A capacitor and a load connected in series with a reactor element ; and the capacity of the capacitor connected between the output terminals of the rectifier circuit is such that the input current waveform from the power supply is
A power converter characterized by being set to a value that is continuous .