JPH03178563A - Dc power supply - Google Patents

Abstract

PURPOSE:To convert an input current to a sine wave, to reduce harmonic components, and to improve its power factor by providing two switching elements to hold a choke coil therebetween, and using the elements according to a high or low input voltage. CONSTITUTION:A reference sine wave voltage Vr is output from the output voltage of a rectifier 2. A voltage Vii is formed from a current Ii of a current transformer 1 and a current from a diode 11. A current I3 of a choke coil 3 is controlled by ON/OFF of an FET 9, an FET 4 by using the voltages Vr, Vii. That is, the FET 9 is held ON in a zone in which the momentary value of an AC power supply is lower than an output voltage E0, only the FET 4 is switched, and the current Ii is fallen between the upper limit and the lower limit of the reference value. The FET 4 is held ON in a zone in which the momentary value of the AC power supply is higher than the voltage E0, only the FET 9 is switched, and the sum of the current Ii and the current of the diode 11 is fallen between the upper limit and the lower limit of the reference value.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides the following advantages by converting the input terminal into an approximate sine wave.
The present invention relates to a DC power supply device that can obtain a controlled output voltage by reducing harmonic components of an input terminal and improving the power factor.

[Conventional technology]

For a DC power supply device that obtains DC output from an AC power supply, simply using a rectifier is not preferable because the input current waveform is intermittent and the power factor and efficiency are low. Therefore, a DC power supply device has been proposed that reduces harmonic components of the input current and improves the power factor by approximately converting the input current into a sine wave.

In other words, connect a double wave rectifier to the input AC power supply.

The main circuit has a main circuit configuration in which a choke coil and a switching element are connected to the output, and DC power is supplied to the choke coil through a diode. The control method includes means for obtaining the difference voltage between the proportional value of the voltage of the load and the reference voltage, and means for multiplying by the proportional value of the absolute value of the voltage of the input AC power supply. The switching element of the main circuit is driven by a voltage comparator having a history characteristic using the proportional value of the absolute value and the above multiplied signal.

Therefore, by means of obtaining the difference voltage between the proportional value of the voltage of the load and the reference voltage, a control signal corresponding to the desired output setting value can be obtained. Then, input statement i is multiplied by a proportional value of the absolute value of the voltage of the power source.

A reference sine wave voltage whose amplitude can be controlled is obtained. and,
Compare the voltage proportional to the current magnitude of the choke coil in the main circuit with its reference sine wave voltage.

A voltage comparator having a rotation width approximately proportional to the reference sine wave voltage drives the switching element of the main circuit so as to limit the current variation width of the choke coil within its history width.

[Problem to be solved by the invention]

However, although such conventional DC power supplies can make the input current waveform almost similar to the voltage waveform, since they are configured with a step-up chopper, the output voltage can be adjusted to the peak value of the expected maximum value of the input voltage. Since it has to be designed higher, it becomes difficult to design a converter connected to the next stage of the rectifier circuit.

In other words, if the input voltage of the converter is high, it is necessary to use switching elements with high withstand voltage.

Not only does the switching speed become slow, switching loss increases, and conduction loss increases, but it also becomes expensive and has problems such as noise during switching and the need to provide a large insulation distance during printed wiring.

[Means to solve the problem]

The present invention solves one or more of the above problems.

A step-up chopper and a step-down chopper are combined, and the output voltage is lowered below the peak value of the input voltage, and the step-up chopper is operated during the period when the input voltage is lower than the output, and the step-down chopper is operated during the period when the input voltage is higher than the output.

〔Example〕

FIG. 1 is a connection diagram of an embodiment of a DC power supply device according to the present invention. In the figure, an AC power supply 10 is connected to the AC input side of a diode bridge rectifier circuit 2 via a line filter 14 and a current transformer l.

A FET 9, which is a first switching element, is connected between the DC output terminals of the rectifier circuit 2. Choke coil 3. A series circuit of FET4, which is the second switching element, is
A series circuit of a diode 5 and a smoothing capacitor C1 is connected to both ends of the smoothing capacitor Ct, and a DC voltage is taken out from both ends of the smoothing capacitor Ct and supplied to a load RL connected to an output terminal 12.13. A diode 11 and a current transformer 517 connected in a 3 m series are connected between the connection point of FET 9 and the choke coil 3 and the connection point of FET 4 and the smoothing capacitor C1, and the current of the diode H is detected by the current transformer 17. There is.

Here, the pulsating voltage that is the output of the rectifier circuit 2 is connected to the resistor R1,
The valence group divided by R2, the output voltage, and the basic voltage source 16
The value 0 amplified by the error amplifier 6 is applied to the multiplier 7.
It is extracted as a reference sine wave voltage Vr. The amplitude of this reference sine wave voltage Vr can be controlled depending on the load condition, making it possible to control the energy. Next, the proportional value of the input current detected by the current transformer l is passed through the rectifier circuit 15 to obtain its absolute value, and the current of the diode 11 is detected by the current transformer 17 and rectified by the diode 21. Superimpose the values.

These corresponding voltages 'Shi,' across resistor R6
to occur.

A hysteresis width approximately proportional to the AC input voltage value is created using resistors R7 and R8 and a comparator 8 for this voltage value, and the drive output signal transitions at a threshold within the hysteresis width. In other words, the comparator 8 compares it with the reference sine wave voltage V'' and, for example, as shown in FIG. 1.
When the current proportional value v, ゛C reaches the upper limit value of the reference sine wave voltage Vr at =12, the drive of the FET 4 is cut off. Energy is accumulated in the choke coil 3 during the section where the FET 4 is on, and when the FET 9 is turned off, the energy accumulated in the choke coil 3 is released and supplied to the load RL via the diode 5.

Such switching of the FET 4 makes the input voltage waveform a continuous high-frequency triangular waveform, and the envelope of the current drop value and the envelope of the current peak value each become a sine wave. Therefore, t=0.1=T corresponding to the trough of the AC input voltage waveform
The switching frequency near /2 is the peak of the waveform t=
The switching frequency becomes higher compared to the switching frequency near t2.

Input AC? ! ! Since the current waveform of each cycle is a triangular wave superimposed on the lower limit value of a sine wave, the average value of 'tM l i becomes the center of the P-P value of the triangular waveform, and becomes a sine waveform. Furthermore, by attenuating the modulated frequency components using a manually operated filter, high frequency components are reduced and the power factor is improved.

During the period in which the instantaneous absolute values 1e, f of the AC and wide electric current FIIO are lower than the output voltage Eo, that is, in the section shown in FIG. 2, the output voltage E detected by the resistor R4° and the resistor R5°
The proportional value of the input voltage ei detected by the resistor R1" and the resistor 1WR2° is determined by the comparator I8.
, the logic circuit 22 generates a 0 signal, and the logic circuit 23 generates a signal according to the signal of the comparator 8.

This causes the drive circuit 20 to generate one signal.

The drive circuit 19 generates a signal according to the on/off signal of the comparator 8 described above. Therefore, the FET 4 is switched on and off while the FET 9 remains conductive, so that the input terminal falls within the range between the upper limit and the lower limit set to the reference value, which is a proportional value of the AC manual pressure.

In the period B, during which the instantaneous absolute value 1e, I of the AC power supply lO is higher than the output voltage Eo, conversely, the second switching element, FET4, is kept off, and the first switching element, FET9, is switched, Control is performed so that the sum of the input current and the current of the second diode 11 falls within the range of the upper and lower limits set for the reference value mentioned above.

FIG. 2 shows operating waveforms, and further details will be explained with reference to FIG. 1. During period A when Ie and l are smaller than Eo, when FET4, which is the second switching element, conducts during boost chopper operation, current flows in the closed loop of AC power supply 10c + rectifier 2 → FET9 = => choke coil 3180FET4eO rectifier 2 → AC power supply lO. , the current i at that time will rise with a slope of l e + "K if the inductance value of the choke coil 3 is L and the capacitance of the smoothing capacitor C1 is sufficiently large. lot is the current of the choke coil 3 immediately before turning on, and is the lower limit value. be.

When the input current increases and reaches the upper limit value, FET4 is turned off and AC power source 10 rectifier 2=>FET9 choke coil 3 diode 5 smoothing capacitor C1=! > Rectifier 2 = + Current flows in the closed loop of AC power supply lO, and the current at that time is.

do.

1o2 is the current in the choke coil immediately before turning off, which is the upper limit value. When the input current decreases and reaches the lower limit value, the switching element 6 is made conductive, and this operation is repeated to make the input current waveform similar to the input voltage waveform. Note that the capacitor C2 has a small capacity for use as a high frequency filter, and has no effect on the fundamental wave component of the AC power source IO. During period B when the input voltage rises and becomes larger than the output voltage, the second switching element FET4 is kept off in step-down chopper operation, and the first switching element FET9 is made conductive, so that the AC power supply 10- 0 rectifier 2<F ET9
<Choke coil 3 Diode 5 Smoothing capacitor C1 → Rectifier 2 = 0 Current flows in a closed loop of AC power supply lO, and current i is the current value of the previous choke coil 5. When the input current increases and reaches an upper limit value, the first switching element is turned off. Then the input current is cut off.

What is the energy stored in choke coil 3?

Choke coil 3=0 diode 5 Smoothing capacitor C1==5th diode → Current flows through the closed loop of choke coil 3. This current i is.

104 is the current value of the choke coil 3 immediately before turning off.

When the choke coil decreases and reaches the lower limit value, the FET 9, which is the first switching element, is made conductive again. FET9
Since the input current is cut off during the period when is off, the input current, which had been within the range of the upper and lower limits of the reference value, will deviate from the range, and the current of choke coil 3 in Figure 2 will change. The waveform is obtained by subtracting the current flowing through the diode 11 from .

However, from equations (3) and (4), the duty ratio in period B is expressed as □/rfiH, and the average duty ratio in period B is a fairly large value, and the fundamental wave component obtained by removing the high frequency component from the input current is near the peak. The waveform becomes slightly distorted.

The current detection means is not limited to the current transformer 1, but may be any other method as long as it can detect the current of the choke coil 3. For example, a method of inserting a low resistance in series with the choke coil 3 may be used. In addition, the electric current i%t13 of the choke coil 3 is the electric current 14 of the switch cable 4 and the electric current 1 of the flywheel diode 5.
5, choke coil 3 and switch element 4
It is also possible to insert a DC variable mW or low resistance into each of the signals and add those signals.

Further, the voltage detection means can also be obtained directly from the AC power source IO via a rectifier circuit. In that case, it is necessary to insert a small transformer or an optical coupling element between them as an insulating means.

A similar effect can be obtained by switching the polarities of the rectifier circuit 2, FET 4.9, and diodes 5 and 11. The diode 5 is not limited to a normal diode, but may be a Schottky diode as long as it is a unidirectional switching element.For the FET 4.9, a switching element such as a bipolar transistor or an IGBT can be used in addition to a field effect transistor.

〔Effect of the invention〕

As described above, in the present invention, by combining a step-up chopper and a step-down chopper, the step-up chopper operates during the period when the input voltage is lower than the output voltage, and the step-down chopper operates during the period when the input terminal is higher than the output voltage. The output voltage can be made lower than the peak value of the maximum input terminal, the withstand voltage of the switching element of the converter connected to the secondary stage can be lowered, and troubles caused by high voltage can be avoided.

Furthermore, since the present invention constantly monitors the instantaneous values of the input voltage and output voltage, and at the same time monitors the input current and the instantaneous current of diode 9, there is no need for a special startup circuit such as an inrush prevention circuit or a soft start circuit. It also has the effect of providing sufficient protection against instantaneous interruptions in the input AC power supply and output short circuits.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the DC power supply device according to the present invention, and FIG. 2 shows waveform diagrams of various parts for explaining its operation. ■--Current transformer, 2... Rectifier circuit, 3... Choke coil 4... FET, 5... Diode, 6...
error amplifier. 7... Multiplier, 8... Comparator, 9... FE
T1O...AC power supply, +1...diode. 12, 13... Output terminal, 14... Line filter. 15... Rectifier circuit, +6... Reference voltage source, 17
···Current transformer. 18... Comparator, 19.20... Drive circuit. 21...Diode, 22.23...-Logic circuit.

Claims (1)

[Claims] A first switching element, a choke coil, and a second switching element are connected between the output terminals of a diode bridge that full-wave rectifies an AC voltage.
A series circuit of switching elements is connected, a series body of a first rectifier diode and a smoothing capacitor is connected to both ends of the second switching element, and a connection point between the first switching element and the choke coil is connected to the connection point of the first switching element and the choke coil. A second switching element is connected between the second switching element and the connection point of the smoothing capacitor.
In a DC power supply device that connects a diode and extracts a DC voltage from both ends of the smoothing capacitor, the first switching element is made conductive during a period in which the output voltage of the diode bridge is lower than the voltage of the smoothing capacitor, and the The second switching element is switched to control the input current so that it falls within a range with an upper limit value and a lower limit value set to a reference value proportional to the input voltage waveform, and the output voltage of the diode bridge is the voltage of the smoothing capacitor. During the higher period, the second switching element is turned off, and the sum of the absolute value of the current of the second diode and the input current is within a range with an upper limit value and a lower limit value set to a reference value proportional to the input voltage waveform. A DC power supply device characterized by controlling switching of a first switching element so that the first switching element is controlled.