JPH06197556A - Power conversion device - Google Patents

Abstract

PURPOSE:To reduce harmonic components from the input current of a push-pull type power conversion device and, at the same time, to obtain a high power factor. CONSTITUTION:In a power converter in which a push-pull type inverter circuit composed of an output transformer, switching element, capacitor, etc., are connected to a full-wave rectifier circuit 23 which performs full-wave rectification on AC power through a choke coil 28, a serial circuit of a choke coil 29, smoothing capacitor 30, choke coils 31 and 32, and diodes 33 and 34 are connected between the positive side of the output terminal of the circuit 23 and an arbitrary position of the primary winding of the output transformer. In addition, a diode 35 is connected between the output terminals of the circuit 23 through the coil 29 and capacitor 30 connected in series and a serial circuit of a capacitor 36 and choke coil 37 is connected in parallel with the choke coil 27. Moreover, a capacitor 38 is connected in parallel with a serial circuit of the coil 29, capacitor 30, and diode 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a push-pull type power conversion device.

[0002]

2. Description of the Related Art A power conversion device of this type is known as shown in FIG. This is because the input terminal of the full-wave rectifier circuit 2 is connected to the AC power source 1, and the positive terminal of the output terminal of the full-wave rectifier circuit 2 has a midpoint t1 of the primary winding 3p of the output transformer 3.
, The primary winding 3p of the output transformer 3 via the switching elements 5 and 6 on the negative side of the output terminal of the full-wave rectifier circuit 2, and the common choke coil 4 respectively.
Connect each end of. 1 of the output transformer 3
A capacitor 7 is connected in parallel to the next winding 3p to form a push-pull type inverter circuit.

The positive terminal of the output terminal of the full-wave rectifier circuit 2 is connected to the anode of the diode 10 via the smoothing capacitor 8 and the choke coil 9 in series, and the diode 12 is connected via the smoothing capacitor 8 and the choke coil 11 in series. Connected to the anode of. Each diode 10,
The cathode 12 is connected to symmetrical winding positions t2 and t3 on the side of the end of the primary winding 3p of the output transformer 3 with respect to the midpoint t.

The positive side of the output terminal of the full-wave rectifier circuit 2 is connected to the cathode of the diode 13 via the smoothing capacitor 8, and the anode of the diode 13 is connected to the negative side of the output terminal of the full-wave rectifier circuit 2. ing. Full wave rectifier circuit 2
The capacitor 14 is connected between the output terminals of.

Then, each filament electrode 15a, 15 of the fluorescent lamp 15 is loaded as a load on the secondary winding 3s of the output transformer 3.
b is connected.

In this power converter, an AC power source 1
Therefore, when a sinusoidal AC voltage E as shown in (a) of FIG. 7 is applied, a full-wave rectified output is generated at the output terminal of the full-wave rectifier circuit 2.

When the full-wave rectified output is higher than the voltage of the smoothing capacitor 8, the smoothing capacitor 8 and the choke coil 9 and the diode 10 are connected in series from the positive electrode side of the output terminal of the full-wave rectifying circuit 2 to the choke coil 11. 1 of output transformer 3 via series circuit with diode 12
A current flows through the next winding 3p, and the smoothing capacitor 8 is charged.

When the full-wave rectified output is below the voltage of the smoothing capacitor 8, the input current is stopped and the smoothing capacitor 8
Will be discharged. The discharge at this time is diode 1
Through 3.

Therefore, the input current IIN from the AC power supply 1 at this time has a waveform in which a zero level section is generated in the middle as shown in FIG. 7B, and the voltage V14 generated across the capacitor 14 is as shown in FIG. The voltage waveform shown in (c) of 7 is obtained.

[0010]

In such a power converter, since the input current IIN has a discontinuous waveform forming a zero level section in the middle, the input current contains a lot of harmonic components. For example, when an AC voltage of 50HZ is applied, the input current only needs to have a 50HZ component, but due to the discontinuous waveform, especially the third, fifth, seventh, ninth, etc. odd harmonic components Many will be included. When a power conversion device containing a lot of such harmonic components is used, there is a risk of adversely affecting substation equipment and other equipment.

Therefore, the present invention is to provide a power converter which can reduce the harmonic component of the input current in the push-pull type and can obtain a high power factor.

[0012]

According to the present invention, the middle point of the primary winding of an output transformer is connected to the positive electrode side of the output terminal of a full-wave rectification circuit for full-wave rectifying an AC power source, and the full-wave rectification is performed. Connect each terminal of the primary winding of the output transformer to the negative side of the output terminal of the circuit through a switching element respectively, and connect the positive side of the output terminal of the full-wave rectifier circuit and the middle point of the primary winding of the output transformer. The first inductance in series with the negative terminal of the output terminal of the full-wave rectifier circuit and each switching element, and the first capacitor is connected in parallel to the primary winding of the output transformer. Then, in a power conversion device including a push-pull type inverter circuit that alternately switches each switching element to output an AC voltage to the secondary winding of the output transformer, Output Circuit including a series circuit of at least a second inductance, a smoothing capacitor, and a first diode connected with the cathode on the primary winding side, connected between the primary winding of the And a second diode connected between the output terminal of the full-wave rectifier circuit and a second inductor and a smoothing capacitor in series, with the anode on the negative side of the output terminal, and the first diode connected in parallel with the first inductance. A series circuit of the inductance 3 and the second capacitor, and a third capacitor connected in parallel to the series circuit of the second inductance, the smoothing capacitor and the second diode are provided.

[0013]

In the present invention having such a structure, when the switching elements are alternately turned on and off, a resonance voltage is generated in the parallel circuit of the primary winding of the output transformer and the first capacitor. That is, the inverter circuit oscillates.

When the input voltage is high, the input voltage is applied to the inverter circuit as it is, and when the input voltage is low, the smoothing capacitor is discharged to maintain the applied voltage.

When the input voltage becomes lower than the voltage of the smoothing capacitor, vibration energy is transmitted from the inverter circuit side by the series circuit of the third inductance and the second capacitor, and the voltage of the third capacitor vibrates.

Due to this vibration, even if the input voltage is lower than the original voltage of the third capacitor, the input current is drawn from the power source side, and the input current can be shaped like a sine wave.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 21 is an AC power supply, and a capacitor 22 for absorbing harmonics is connected to the AC power supply 21 and an input terminal of a full-wave rectifier circuit 23 is connected.

The midpoint t1 of the primary winding 24p of the output transformer 24 is connected to the positive side of the output terminal of the full-wave rectification circuit 23, and the switching element 25 is connected to the negative side of the output terminal of the full-wave rectification circuit 23. 26, and each end of the primary winding 24p of the output transformer 24 is connected via a choke coil 27, which is a first inductance, in common. The primary winding 24p of the output transformer 24
A capacitor 28 is connected in parallel with the above to form a push-pull type inverter circuit.

The positive electrode side of the output terminal of the full-wave rectifier circuit 23 is commonly connected via a series circuit of a choke coil 29 and a smoothing capacitor 30 which are second inductances, and further via choke coils 31 and 32 individually. Are connected to the anodes of the diodes 33 and 34, respectively.

The diode 33 has its cathode connected to an arbitrary winding position t2 located at one end side connected to the switching element 25 with respect to the midpoint t1 of the primary winding 24p of the output transformer 24, and the diode 33 34 has its cathode connected to an arbitrary winding position t3 located on the other end side connected to the switching element 26 with respect to the midpoint t1 of the primary winding 24p of the output transformer 24.

The choke coil 29 and the smoothing capacitor 30 are connected to the positive electrode side of the output terminal of the full-wave rectifier circuit 23.
Are connected in series to the cathode of the second diode 35. The anode of the second diode 35 is connected to the negative side of the output terminal of the full-wave rectifier circuit 23.

The choke coil 27 includes a second capacitor 36 and a choke coil 3 which is a third inductance.
The series circuit with 7 is connected in parallel.

A third capacitor 38 is connected in parallel to the series circuit of the choke coil 29, the smoothing capacitor 30 and the second diode 35.

The secondary winding 2 of the output transformer 24
Each filament electrode 39 of the fluorescent lamp 39 as a load on 4s
a and 39b are connected.

In the embodiment having such a structure, when the switching elements 25 and 26 are alternately turned on and off, the output transformer 2 is turned off in the off section of the switching element 25.
A half-wave sinusoidal resonance voltage is generated by the parallel circuit of the primary winding 24p of No. 4 and the capacitor 28, and the primary winding 24p of the output transformer 24 is generated in the off section of the switching element 26.
A half-wave sinusoidal resonance voltage is generated by the parallel circuit of the capacitor 28 and the capacitor 28.

This resonance energy is transmitted to the secondary winding 24s of the output transformer 24, a high frequency high voltage is applied to the fluorescent lamp 39, and the filament electrodes 39a and 39b.
Is preheated and the fluorescent lamp 39 is turned on.

At this time, when the voltage applied to the inverter circuit is high, the input voltage is applied as it is,
When the input voltage is low, the voltage is maintained by discharging the smoothing capacitor 30.

When the input voltage becomes lower than the voltage of the smoothing capacitor 30, the vibration energy is transmitted from the inverter circuit side by the series circuit of the second capacitor 36 and the choke coil 37, and the voltage of the third capacitor 38. Vibrates. Due to this vibration, the input voltage is
The current can be drawn even when the voltage is lower than the voltage of the capacitor 38.

For example, if a 50 HZ sine wave voltage E as shown in FIG.
A voltage V38 as shown in FIG. 2 (c), which vibrates at a high frequency in the valley of the voltage, is generated at both ends of the capacitor 38 due to the vibration from the inverter circuit side. As a result, the input current is drawn even in the valley portion where the input voltage is lower than the original voltage of the third capacitor 38, so that the input current reaches the zero point.

Therefore, by appropriately setting the magnitude of the vibration energy, the input current IIN has a shape close to a sine wave as shown in FIG. 2 (b).

As described above, since the input current can have a waveform close to a continuous sine wave, harmonic components can be sufficiently reduced. Moreover, since the phase of the input voltage and the phase of the input current can be made substantially equal, the power factor is high.

Next, another embodiment of the present invention will be described with reference to the drawings. The same parts as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In the configuration shown in FIG. 3, a capacitor 40 for absorbing harmonics is connected between the output terminals of the full-wave rectifier circuit 23,
A third capacitor 38 is connected in parallel to the capacitor 40 via a diode 41, and the choke coil 27
Is connected in series between the positive terminal of the output terminal of the full-wave rectifier circuit 23 and the midpoint t1 of the primary winding 24p of the output transformer 24 via the diode 41, and the choke coil 27
A series circuit of a second capacitor 36 and a choke coil 37 is connected in parallel.

Even in this way, when the input voltage becomes lower than the voltage of the smoothing capacitor 30, the vibration energy is transmitted from the inverter circuit side by the series circuit of the second capacitor 36 and the choke coil 37, whereby the first Since the voltage of the capacitor 38 of No. 3 oscillates and the input current can be drawn in, the same effect as in the above-described embodiment can be obtained.

In FIG. 4, the capacitor 40 and the diode 41 are omitted in FIG.

Even in this way, when the input voltage becomes lower than the voltage of the smoothing capacitor 30, the vibration energy is transmitted from the inverter circuit side by the series circuit of the second capacitor 36 and the choke coil 37, so that Since the voltage of the capacitor 38 of No. 3 oscillates and the input current can be drawn in, the same effect as in the above-described embodiment can be obtained.

In FIG. 5, the choke coils 31 and 32 and the diodes 33 and 34 in FIG. 4 are omitted,
Instead, a series circuit of the choke coil 29, the smoothing capacitor 30, and the diode 42 which is the first diode is connected in parallel to the choke coil 27.

Even in this way, when the input voltage becomes lower than the voltage of the smoothing capacitor 30, the vibration energy is transmitted from the inverter circuit side by the series circuit of the second capacitor 36 and the choke coil 37. Since the voltage of the capacitor 38 of No. 3 oscillates and the input current can be drawn in, the same effect as in the above-described embodiment can be obtained.

In each of the above embodiments, the output transformer 2
A description has been given of the case where a fluorescent lamp, which is a load, is directly connected to the secondary winding, but the present invention is not limited to this. For example, a rectifying circuit and a smoothing circuit are connected to the secondary winding to rectify and smooth the secondary side output. Alternatively, the DC output may be provided and the DC output may be supplied to the load.

[0041]

As described above, according to the present invention, in the push-pull type power converter, the harmonic component of the input current can be reduced and a high power factor can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram showing voltage and current waveforms at various parts in the embodiment.

FIG. 3 is a circuit configuration diagram showing another embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing another embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing still another embodiment of the present invention.

FIG. 6 is a circuit configuration diagram showing a conventional example.

FIG. 7 is a diagram showing voltage and current waveforms of respective parts in the conventional example.

[Explanation of symbols]

 21 ... AC power supply 23 ... Full-wave rectification circuit 24 ... Output transformer 25, 26 ... Switching element 27 ... Choke coil (first inductance) 28 ... First capacitor 29 ... Choke coil (second inductance) 30 ... Smoothing capacitor 33, 34 ... 1st diode 35 ... 2nd diode 36 ... 2nd capacitor 37 ... Choke coil (3rd inductance) 38 ... 3rd capacitor

Claims (1)

[Claims] 1. A midpoint of a primary winding of an output transformer is connected to a positive side of an output terminal of a full-wave rectifier circuit for full-wave rectifying an AC power source, and a negative side of an output terminal of the full-wave rectifier circuit is connected to the positive side. Each end of the primary winding of the output transformer is connected via a switching element respectively, and between the positive side of the output terminal of the full-wave rectification circuit and the midpoint of the primary winding of the output transformer, or A first inductor is inserted in series between the negative electrode side of the output terminal of the full-wave rectifier circuit and each of the switching elements, and a first capacitor is connected in parallel to the primary winding of the output transformer, 2 switching of the output transformer is performed by alternately switching the switching elements.
In a power converter including a push-pull type inverter circuit that outputs an AC voltage to a secondary winding, in a positive side of an output terminal of the full-wave rectifier circuit and an arbitrary winding position of a primary winding of the output transformer. A circuit including a series circuit of at least a second inductance, a smoothing capacitor, and a first diode connected with the cathode on the primary winding side, and the output terminal of the full-wave rectification circuit. A second diode connected through a second inductance and a smoothing capacitor in series with the anode on the negative electrode side of the output terminal; a third inductance connected in parallel with the first inductance; and a second capacitor. A series circuit and a third capacitor connected in parallel to the series circuit of the second inductance, the smoothing capacitor and the second diode are provided. Power converter for.