JP2011101571A - Ac-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC-DC converter for directly switching an AC current, which is improved so as to suppress an even number harmonic current in an AC current switching circuit by matching the currents of a positive half-wave and a negative half-wave of an AC current. <P>SOLUTION: In an AC-DC converter including an AC power supply 1, a reactor 2, first to fourth diodes 3 to 6 which constitute a bridge rectifier, a first capacitor 7, and a load 8, a first switch element 9, and a second switch element 10 are connected to a first diode 3 and a second diode 4 in parallel, respectively. A first resistance 11 is inserted into a first capacitor 7 in series, and detection circuits 13 and 14 for detecting voltages at both ends of the first resistance 11 are added. An oscillation control circuit 12 is added to turn on the first switch element 9 and the second switch element 10 simultaneously in synchronization with output signals from the detection circuits 13 and 14, and to maintain an on-period constant at least during one AC period of the AC power supply 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching power supply, and more particularly to an AC-DC converter that directly switches an alternating current.

  As a conventional means of an AC-DC converter for directly switching an alternating current, there is a circuit example shown in FIG. 5 (Japanese Patent Laid-Open No. 2000-208290). In FIG. 5, MOSFET 109 and diode 105 constitute switching means for the positive half-wave supplied from AC power supply 101, and MOSFET 110 and diode 106 constitute switching means for the negative half-wave. The reactor 102 and the capacitor 107 function as a common part regardless of positive or negative.

  In the AC positive half-wave, the MOSFET 109 is repeatedly turned on and off to accumulate excitation energy in the reactor 102. When the MOSFET 109 is off, the excitation energy is released to charge the capacitor 107. The AC power source 101 is supplied with an excitation current and a current due to the release of excitation energy. Since the on and off widths are controlled so that the average value thereof is proportional to the instantaneous value of the alternating voltage at that time, the current is proportional to the voltage. That is, a high power factor can be obtained. A high power factor can be obtained in the same way even in the negative half-wave of alternating current. Further, by directly switching the alternating current, a diode for rectifying the alternating current can be omitted, and the efficiency is improved.

However, even if a high power factor is obtained if the AC positive half-wave current is not equal to the negative half-wave current, even-order harmonic currents are generated, exceeding the limit value of the harmonic current regulation. In addition, the common mode choke coil responsible for attenuating the switch noise by the even harmonic current is saturated and the attenuation effect is impaired.
The conventional example shown in FIG. 5 has a disadvantage that even-order harmonics are easily generated.

  An object of the present invention is to provide an AC-DC converter that directly switches an alternating current, which is improved so that even-order harmonics are not generated by matching alternating current positive and negative half-wave currents. It is said.

  Accordingly, the invention described in claim 1 comprises a first diode and a second diode, which are connected in reverse to each other with a common anode connected to both ends of a series circuit of the AC power supply and the reactor, in series with the AC power supply. Both ends of the series circuit are connected to each other, and both ends of the series circuit composed of a third diode and a fourth diode connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode. The first capacitor is connected between the connection point of the first diode and the second diode, the connection point of the third diode and the fourth diode, and a load is connected to both ends of the first capacitor. In the connected AC-DC converter, the first switch element is connected in parallel to the first diode, and the second switch element is connected in parallel to the second diode. Insert a first resistor in series with the first capacitor, add a detection circuit that outputs a signal when the voltage across the first resistor drops to a predetermined value, and synchronize with the signal output by the detection circuit Thus, an oscillation control circuit is added which simultaneously turns on the first switch element and the second switch element and keeps the on period constant for at least one AC cycle of the AC power supply.

  Since the first switch element and the second switch element are turned on at the same time and maintain a constant ON period for at least one cycle of the AC power supply, the ON period is maintained in the positive half cycle and the negative half cycle. There is no difference. In addition, the charging current flowing through the first capacitor during the off period has a current waveform having a negative slope determined by the voltage across the first capacitor, the instantaneous value of the voltage of the AC power supply, and the inductance of the reactor. Since the voltage of the AC power supply is a sine wave and has a positive and negative shape, the first switch element and the second switch element are simultaneously turned on at the time when the voltage across the first resistor reaches a predetermined value, so that the off period It is possible to prevent the difference between the positive half cycle and the negative half cycle.

  According to the second aspect of the present invention, a reactor is connected in series to an AC power source, and a series of first and second diodes connected in opposite directions with an anode common to both ends of a series circuit of the AC power source and the reactor. Both ends of the circuit are connected to each other, and both ends of a series circuit composed of a third diode and a fourth diode, which are connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode, respectively Connect the first capacitor between the connection point of the first diode and the second diode and the connection point of the third diode and the fourth diode, and connect the load across the first capacitor. In the AC-DC converter, the first switch element is connected in parallel to the first diode, the second switch element is connected in parallel to the second diode, A series circuit composed of a second capacitor and a second resistor is connected in parallel to the switch element, and a series circuit composed of a third capacitor and a third resistor is connected in parallel to the second switch element. When either the voltage across the resistor or the voltage across the third resistor falls to a predetermined value, a detection circuit is added to output a signal, and the first switch is synchronized with the signal output from the detection circuit An oscillation control circuit was added to turn on the element and the second switch element at the same time and keep the on period constant for at least one AC cycle of the AC power supply.

Since the first switch element and the second switch element are turned on at the same time and maintain a constant ON period for at least one AC cycle of the AC power supply, the ON period is used in the positive half cycle and negative half cycle of AC. There is no difference.
The voltage across the first switch element and the voltage across the second switch element are substantially zero during the on-period, but when turned off, one switch element has a voltage substantially equal to the voltage across the first capacitor. The drop voltage of the diode connected in parallel is applied to the other. The voltage applied to one switch element after turn-off falls to the instantaneous value of the AC power supply voltage when the exciting energy of the reactor is completely discharged, so that the current flowing in the series circuit of the capacitor and resistor connected in parallel to the switch element Changes and the voltage across the resistor drops. Since the voltage of the AC power supply is a sine wave and has the same shape, the voltage at both ends of the second resistor or the voltage at both ends of the third resistor drops to become a predetermined value at the time when the first switch element and the second switch By simultaneously turning on the elements, it is possible to prevent a difference between the positive half cycle and the negative half cycle in the off period. That is, even-order harmonic current does not occur.

  According to a third aspect of the present invention, a reactor is connected in series to an AC power source, and a series composed of a first diode and a second diode connected in opposite directions with an anode common to both ends of a series circuit of the AC power source and the reactor. Both ends of the circuit are connected to each other, and both ends of a series circuit composed of a third diode and a fourth diode, which are connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode, respectively. Connect the first capacitor between the connection point of the first diode and the second diode and the connection point of the third diode and the fourth diode, and connect the load across the first capacitor. In the AC-DC converter, the first switch element is connected in parallel to the first diode, the second switch element is connected in parallel to the second diode, and A fourth resistor is inserted in series in the parallel circuit of the diode and the first switch element, and a fifth resistor is inserted in series in the parallel circuit of the second diode and the second switch element. A detection circuit that outputs a signal when the voltage at both ends or the voltage across the fifth resistor falls to a predetermined value is added, and the first switch element and the second switch are synchronized with the signal output from the detection circuit An oscillation control circuit was added to turn on the elements at the same time and keep the ON period constant for at least one AC cycle of the AC power supply.

Since the first switch element and the second switch element are turned on at the same time and maintain a constant ON period for at least one cycle of the AC power supply, the ON period is maintained in the positive half cycle and the negative half cycle. There is no difference.
In the off-period, a current passing through the first diode or the second diode flows, so that a voltage is generated across either the fourth resistor or the fifth resistor.

  The current is a current waveform having a negative slope determined by the voltage across the first capacitor, the instantaneous value of the voltage of the AC power supply, and the inductance of the reactor. Since the voltage of the AC power supply is positive and negative, the AC switching power supply is also positive during the off period by simultaneously turning on the first switch element and the second switch element at the time when the voltage across the first resistor reaches a predetermined value. It is possible to prevent the difference between the half cycle and the negative half cycle.

According to the present invention, it is possible to suppress even-order harmonic currents that are likely to occur in an AC-DC converter that generates a DC voltage by switching an AC current.
The Harmonic Current Suppression Guidelines (issued by the Agency for Natural Resources and Energy) stipulates that second harmonics should be suppressed to 2% or less of the fundamental wave component for lighting equipment, so the present invention is an effective means for clearing the guidelines. obtain.

  Further, since the even-order harmonic current is suppressed, the conventional problem of saturating the common mode choke coil can be solved, so that no circuit measures are required for the problem, and an economic effect due to the reduction of parts can be expected.

  FIG. 2 is a circuit diagram showing an embodiment of the invention as set forth in claim 1;   It is a circuit diagram which shows the Example of invention of Claim 2.   It is a circuit diagram which shows the Example of invention of Claim 3.   It is a wave form diagram which shows the electric current waveform of the alternating current power supply of FIG.   It is a circuit diagram which shows an example of the conventional system.

  The best mode for carrying out the invention will be described with reference to the drawings of the embodiments.

  FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the first switch element 9 and the second switch element 10 are simultaneously turned on and off by the output pulse of the oscillation control circuit 12. When the first switch element 9 and the second switch element 10 are in the ON state, the current of the AC power source 1 flows only in the reactor 2 and accumulates excitation energy in the reactor 2. Since the on-period maintains a constant value for at least one period of the alternating current cycle, the positive half-wave of the alternating current and the negative half-wave subsequent thereto are the same on-period.

  When the first switch element 9 and the second switch element 10 are turned off, the excitation energy of the reactor 2 is any two diodes in the bridge rectifier circuit formed by the AC power source 1 and the first diode 3 to the fourth diode 6. And flows through the first capacitor 7 and the first resistor 11 and is discharged.

  This current has a peak value of the current value of the reactor 2 immediately before the turn-off, and the slope is a value obtained by dividing the difference between the voltage across the first capacitor 7 and the instantaneous value of the AC voltage of the AC power source 1 by the inductance of the reactor 2. The current decreases.

  The voltage across the first resistor 11 also decreases, but when the voltage becomes smaller than the value of the reference power supply 13, the output terminal of the comparator 14 sucks, and the oscillation control circuit 12 receiving the signal receives the first signal. A pulse for turning on the switch element 9 and the second switch element 10 is output.

  During the ON period, a constant value is maintained in both the positive half wave and the negative half wave of the AC voltage, so that the peak current of the reactor 2 immediately before the turn-off is proportional to the instantaneous value of the AC voltage. The slope descending from the peak current is proportional to the difference between the instantaneous value of the voltage of the first capacitor 7 and the AC voltage.

  Since the voltage of the AC power supply is a sine wave, if the above condition is satisfied, the current of the same waveform is obtained in the positive half wave and the negative half wave. That is, even-order harmonic current does not flow.

  FIG. 2 is a circuit diagram showing an embodiment of the second aspect of the present invention. In the figure, the first switch element 9 and the second switch element 10 are simultaneously turned on and off by the output pulse of the oscillation control circuit 12. When the first switch element 9 and the second switch element 10 are in the ON state, the current of the AC power source 1 flows only in the reactor 2 and accumulates excitation energy in the reactor 2. Since the on-period maintains a constant value for at least one period of the alternating current cycle, the positive half-wave of the alternating current and the negative half-wave subsequent thereto are the same on-period.

  When the first switch element 9 and the second switch element 10 are turned off, the excitation energy of the reactor 2 is any two diodes in the bridge rectifier circuit formed by the AC power source 1 and the first diode 3 to the fourth diode 6. And flows through the first capacitor 7.

  While the exciting energy of the reactor 2 is released, a voltage substantially equal to the voltage across the first capacitor 7 is applied to both ends of the first switch element 9 or both ends of the second switch element 10. When it is completely discharged, the voltage drops to the instantaneous value of the AC voltage of the AC power source 1. The voltage drop is detected by the series circuit of the second capacitor 18 and the second resistor 20 or the series circuit of the third capacitor 19 and the third resistor 21. When the decreasing voltage becomes smaller than the value of the reference power supply 13, the comparator 14 or the comparator 15 sucks and the oscillation control circuit 12 receiving the signal turns on the first switch element 9 and the second switch element 10. Is output.

  Since the first switch element 9 and the second switch element 10 are turned on after the excitation energy of the reactor 2 becomes zero, the current flowing through the AC power source 1 rises from zero ampere, and the excitation energy Since the turn-on is at the same time as the end of the discharge, the waveform shown in FIG. 4 is obtained.

  Switching in which the excitation energy becomes zero every cycle as shown in the waveform of FIG. 4 and the time during which the excitation energy is zero is called a critical mode. In the critical mode, the alternating current and the alternating voltage are similar. It becomes a shape and the power factor becomes 1.

  In the embodiment of FIG. 1 and FIG. 3 to be described later, it is possible to make the voltage close to the critical mode by selecting a value of the reference power supply 13 as close to zero as possible.

FIG. 3 is a circuit diagram showing an embodiment of the third aspect of the present invention.
In the figure, the first switch element 9 and the second switch element 10 are simultaneously turned on and off by the output pulse of the oscillation control circuit 12. When the first switch element 9 and the second switch element 10 are in the ON state, the current of the AC power source 1 flows only in the reactor 2 and accumulates excitation energy in the reactor 2. Since the on-period maintains a constant value for at least one period of the alternating current cycle, the positive half-wave of the alternating current and the negative half-wave subsequent thereto are the same on-period.

When the first switch element 9 and the second switch element 10 are turned off, the excitation energy of the reactor 2 is any two diodes in the bridge rectifier circuit formed by the AC power source 1 and the first diode 3 to the fourth diode 6. And flows through the first capacitor 7 and either the fourth resistor 16 or the fifth resistor 17.
This current has a peak value of the current value of the reactor 2 immediately before the turn-off, and the slope is a value obtained by dividing the difference between the voltage across the first capacitor 7 and the instantaneous value of the AC voltage of the AC power source 1 by the inductance of the reactor 2. The current decreases.
The voltage at both ends of the fourth resistor 16 or the voltage at both ends of the fifth resistor 17 also falls, but when the voltage becomes smaller than the value of the reference power supply 13, the output terminal of the comparator 14 is sucked, Upon receiving the signal, the oscillation control circuit 12 outputs a pulse for turning on the first switch element 9 and the second switch element 10.

  During the ON period, a constant value is maintained in both the positive half wave and the negative half wave of the AC voltage, so that the peak current of the reactor 2 immediately before the turn-off is proportional to the instantaneous value of the AC voltage. The slope descending from the peak current is proportional to the difference between the instantaneous value of the voltage of the first capacitor 7 and the AC voltage.

  Since the voltage of the AC power supply is a sine wave, if the above condition is satisfied, the current of the same waveform is obtained in the positive half wave and the negative half wave. That is, even-order harmonic current does not flow.

  In the embodiment shown in FIGS. 1 to 3, MOSFETs are applied to the first switch element 9 and the second switch element 10, so that the first diode 3 and the second diode 4 are replaced with MOSFET body diodes. It is also possible.

  In the embodiment shown in FIGS. 1 to 3, the voltage detecting circuit for the voltage drop of the reference power supply 13 and the comparators 14 and 15 is implemented. However, an equivalent circuit may be constituted by a transistor.

  The method of directly switching the alternating current can reduce the loss due to the diode, but the conventional method has a weak countermeasure against even-order harmonic current. The AC-DC converter of the AC current switching system that suppresses even-order harmonic current of the present invention has a high industrial applicability.

DESCRIPTION OF SYMBOLS 1,101 AC power source 2,102 Reactor 3, 4, 5, 6, 105, 106 Diode 7, 107 Capacitor 8, 108 Load 9, 10, 109, 110 MOSFET
11 Resistor 12 Oscillation Control Circuit 13 Reference Power Supply 14, 15 Comparator 16, 17 Resistor 18, 19 Capacitor 20, 21 Resistor 103, 104 Oscillation Control Circuit

Claims (3)

  A reactor is connected in series to an AC power source, and both ends of a series circuit composed of a first diode and a second diode connected in opposite directions with an anode common to both ends of the series circuit of the AC power source and the reactor, respectively. And both ends of a series circuit composed of a third diode and a fourth diode connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode, A first capacitor is connected between a connection point between the first diode and the second diode and a connection point between the third diode and the fourth diode, and a load is applied to both ends of the first capacitor. In the connected AC-DC converter, a first switch element is connected in parallel with the first diode, and a second switch is connected in parallel with the second diode. A detecting circuit that outputs a signal when the voltage across the first resistor drops to a predetermined value, and a first resistor is inserted in series with the first capacitor. The first switch element and the second switch element are simultaneously turned on in synchronization with a signal output from the detection circuit, and the ON period is kept constant for at least one AC cycle of the AC power supply. An AC-DC converter characterized by adding an oscillation control circuit.   A reactor is connected in series to an AC power source, and both ends of a series circuit composed of a first diode and a second diode connected in opposite directions with an anode common to both ends of the series circuit of the AC power source and the reactor, respectively. And both ends of a series circuit composed of a third diode and a fourth diode connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode, A first capacitor is connected between a connection point between the first diode and the second diode and a connection point between the third diode and the fourth diode, and a load is applied to both ends of the first capacitor. In the connected AC-DC converter, a first switch element is connected in parallel with the first diode, and a second switch is connected in parallel with the second diode. A switch circuit is connected, a series circuit composed of a second capacitor and a second resistor is connected in parallel with the first switch element, and a third capacitor and a third switch are connected in parallel with the second switch element. Connecting a series circuit composed of resistors, and adding a detection circuit that outputs a signal when either the voltage across the second resistor or the voltage across the third resistor falls to a predetermined value, and Oscillation that simultaneously turns on the first switch element and the second switch element in synchronization with a signal output from the detection circuit and keeps the ON period constant for at least one AC cycle of the AC power supply. An AC-DC converter characterized by adding a control circuit.   A reactor is connected in series to an AC power source, and both ends of a series circuit composed of a first diode and a second diode connected in opposite directions with a common anode are connected to both ends of the series circuit of the AC power source and the reactor. And both ends of a series circuit composed of a third diode and a fourth diode connected in opposite directions with a common cathode at both ends of the series circuit of the first diode and the second diode, A first capacitor is connected between a connection point between the first diode and the second diode and a connection point between the third diode and the fourth diode, and a load is applied to both ends of the first capacitor. In the connected AC-DC converter, a first switch element is connected in parallel with the first diode, and a second switch is connected in parallel with the second diode. A fourth resistor is inserted in series with the parallel circuit of the first diode and the first switch element, and is connected in series with the parallel circuit of the second diode and the second switch element. And a detection circuit that outputs a signal when the voltage across the fourth resistor or the voltage across the fifth resistor falls to a predetermined value is added. An oscillation control circuit for simultaneously turning on the first switch element and the second switch element in synchronization with a signal to be output and maintaining an on period constant for at least one AC cycle of the AC power supply; An AC-DC converter characterized by being added.

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