JP2012222852A - Ac-dc power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC-DC power conversion device that reduces a power loss in current detection and implements a compact and inexpensive power supply device.SOLUTION: The AC-DC power conversion device includes: a first series circuit in which a first rectifying element, a first self-turnoff switching element, and a current detector are connected in series; a second series circuit in which a second rectifying element and a second self-turnoff switching element are connected in series; a capacitor connected further in parallel with a parallel circuit in which the series circuits are connected in parallel; a first reactor having one end connected to a first junction connecting the rectifying element and the self-turnoff switching element of the first series circuit; and a second reactor having one end connected to a second junction connecting the rectifying element and the self-turnoff switching element of the second series circuit. An AC voltage is applied between the respective other ends of the first and second reactors, and a DC voltage is taken out from both ends of the capacitor.

Description

  The present invention relates to an AC-DC power converter, and more particularly to an AC-DC that converts an AC voltage into a DC voltage while improving the harmonic content contained in the input power factor and input current using a self-extinguishing switching element. The present invention relates to a current detection technique suitable for a power converter.

  Conventionally, a current detection circuit applied to an AC-DC power converter that converts an AC voltage into a DC voltage while improving an input power factor and a harmonic content rate included in an input current is known (for example, Patent Documents). 1). The current detection circuit disclosed in Patent Document 1 is shown in FIG. 5 and the operation of the main circuit will be described.

  In the circuit shown in FIG. 5, when the polarity of the AC power source 6 is positive (the tip of the arrow shown in FIG. 5 is positive and the root of the arrow is negative, the same applies hereinafter), when the switching element 1a is turned on, the AC power source 6 → reactor The current increases in the path of 5a → switching element 1a → shunt resistor 10 → shunt resistor 11 → body diode 2b of the switching element 2a → reactor 5b → AC power source 6.

  Next, when the switching element 1a is turned off, the current is commutated through the path of the reactor 5a → the diode 3 → the capacitor 7 → the shunt resistor 11 → the body diode 2b of the switching element 2a → the reactor 5b → the AC power source 6 → the reactor 5a. Then, the energy held by reactors 5a and 5b is transferred to capacitor 7 and the current is reduced.

  Even when the power supply voltage is negative (when the tip of the arrow shown in FIG. 5 is negative and the root of the arrow is positive, the same applies hereinafter), the same operation is performed by turning the switching element 2a on and off due to the symmetry of the circuit.

  Therefore, driving the switching elements 1a and 2a with an appropriate control signal (gate signal) improves the power factor and harmonic content while controlling the input current in a sine wave shape with less distortion, and boosts the voltage across the capacitor. The generated DC voltage can be generated.

  By the way, as described above, in order to control the AC input current to a waveform with a high power factor and less distortion, it is necessary to detect a current value to be controlled. Further, in order to prevent the power conversion device from being damaged by an overcurrent, a protection function is required such as detecting the value of the current flowing through the circuit and stopping the device when an excessive current flows.

  Patent Document 1 discloses a method in which respective voltages generated in the shunt resistors 10 and 11 are rectified and synthesized by an adder circuit and used as an input current detection signal. Specifically, in the circuit shown in FIG. 5, when the input voltage is positive, the voltage generated in the shunt resistor 11 is used as a detection signal, and when the input voltage is negative, the voltage generated in the shunt resistor 10 is used as a detection signal. At this time, a bidirectional current flows through the shunt resistors 10 and 11 through the above-described path. Therefore, depending on the polarity of the input voltage, power loss occurs on the shunt resistor side that is not used for current detection.

  Further, a circuit using a switching element as shown in FIG. 5 generates noise along with the switching operation. If this is superimposed on the current detection signal, malfunctions such as malfunction may occur. For this reason, it is desirable that the current detection signal has a voltage value as high as possible and the ratio to noise is relatively small. For this purpose, the resistance value of the shunt resistors 10 and 11 may be increased, but at the same time, the power loss generated in the shunt resistors 10 and 11 also increases. For this reason, overheating and enlargement of the shunt resistors 10 and 11 are caused, and as a result, the efficiency of the entire power conversion device is lowered.

  Of course, other current detection means that do not use a shunt resistor include a Hall CT and a current transformer. However, the hall CT is generally more expensive than the shunt resistor and has drawbacks such as an increase in size and the need for power supply. Furthermore, since a magnetic material is used, the hall CT overheats when a current containing a high frequency component flows. There is a concern. On the other hand, the current transformer has a drawback that applicable conditions are limited because current below a certain frequency cannot be detected.

  Therefore, a power supply circuit that solves these problems is known (see, for example, Patent Document 2). This power supply circuit is configured as shown in FIG. The main circuit operation in this power supply circuit will be outlined. First, when the polarity of the AC power supply 6 is positive, when the switching element 1a is turned on, the current increases in the path of the AC power supply 6 → reactor 5a → switching element 1a → shunt resistor 10 → diode 9 → reactor 5b → AC power supply 6. Next, when the switching element 1a is turned off, the current is commutated in the path of the reactor 5a → the diode 3 → the capacitor 7 → the diode 9 → the reactor 5b → the AC power supply 6 → the reactor 5a, and the energy stored in the reactors 5a and 5b is transferred to the capacitor The transfer current decreases.

  Even when the power supply voltage is negative, the same operation can be performed by turning on / off the switching element 2a due to the symmetry of the circuit. Therefore, one shunt resistor can be reduced as compared with FIG. 5, and power loss in the shunt resistor when the switching element is off can be suppressed.

JP 2003-333855 A JP 2006-25579 A

  However, in the power supply circuit disclosed in Patent Document 2 described above, for example, when the input voltage is positive, all of the current flowing through the above-described path flows through the diode 9 (diode 8 in the case of negative polarity). For this reason, the power loss in the diodes 8 and 9 increases. That is, the power loss in the diode (current × forward voltage drop) is larger than the power loss (resistance × current square) in the shunt resistor of several mΩ to several tens mΩ. In order to withstand this large power loss, it is necessary to increase the current capacity of the diodes 8 and 9, which causes a new problem that the cost of the power conversion device increases and the conversion efficiency of the entire device decreases.

  In general, a switching element such as a MOSFET incorporates a body diode. For this reason, if it is set as the structure of patent document 2 (FIG. 6), it is necessary to integrate two circuits (a part of the broken line shown in FIG. 6) of a switching part and a diode as one package. Then, as described above, the power loss in the diode portion increases, and the temperature of the entire package also increases. For this reason, the new problem that the loss of a switching part also increases arises.

  The present invention has been made to solve such problems, and provides an AC-DC power conversion device that reduces power loss associated with current detection and realizes downsizing and cost reduction of a power supply device. Objective.

In order to achieve the above-described object, an AC-DC power converter according to the present invention includes a first series circuit in which a first rectifier element, a first self-extinguishing switching element, and a current detector are connected in series. A second series circuit in which a second rectifying element and a second self-extinguishing switching element are connected in series; a capacitor further connected in parallel to a parallel circuit in which these series circuits are connected in parallel; A first reactor having one end connected to a first connection point connecting the rectifying element of the series circuit and the self-extinguishing switching element; and the rectifying element and the self-extinguishing switching element of the second series circuit And a second reactor having one end connected to a second connection point connecting the first and second reactors, and applying an AC voltage between the other ends of the first and second reactors, Both ends It is characterized by taking out the al DC voltage. Preferably, the current detector is a resistance element.

  Therefore, the power converter described above can detect the current flowing in the power supply circuit with one shunt resistor. In other words, the AC-DC power converter of the present invention can reduce the shunt resistance, which was conventionally required to two, to one, so that not only can the number of parts be reduced, but the size and cost of the device can be reduced, and the shunt can be reduced. It is possible to achieve an excellent effect that it is possible to reduce power loss generated in the resistor.

It is a circuit diagram which shows the principal part structure of the alternating current-direct current power converter device which concerns on Example 1 of this invention. It is a block diagram which shows an example of a current detection circuit. It is a figure which shows an example of the waveform of the alternating voltage and alternating current input into the alternating current-DC power converter device shown in FIG. It is a circuit diagram which shows the principal part structure of the alternating current-direct current power converter device which concerns on Example 2 of this invention. The circuit diagram which shows an example of the conventional AC-DC power converter device. The circuit diagram which shows an example of another conventional AC-DC power converter device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 1 to 4 show an example of an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 5 denote the same components, and the basic configuration is shown in FIG. It is the same as the conventional one.

The feature of the first embodiment is that the current flowing through the circuit can be detected with only one current detector, thereby reducing the size and increasing the efficiency of the AC-DC power converter. .
The AC-DC power converter according to the first embodiment of the present invention having such characteristics will be described in detail.

  In FIG. 1, 1a and 2a are MOSEFTs of first and second self-extinguishing switching elements, respectively. Reference numerals 3 and 4 denote diodes of the first and second rectifying elements, respectively. The anode of the diode 3 is connected to the drain of the MOSFET 1, and one end of a resistance element (shunt resistor) 10 that is a current detector is connected to the source of the MOSFET 1 to constitute a first series circuit.

  Further, the anode of the diode 4 is connected to the drain of the MOSFET 2 to constitute a second series circuit. The MOSFETs 1a and 2a are configured such that body diodes 1b and 2b are connected between their drains and sources.

  These first and second series circuits are connected in parallel. More specifically, the cathodes of the diodes 3 and 4 are connected to a direct current positive polarity DC line P, and the other end of the shunt resistor 10 and the source of the MOSFET 2a are connected to a direct current negative polarity direct current line N. A DC smoothing capacitor 7 is connected between the DC lines P and N.

  Further, one end of reactors 5a and 5b is connected to a connection point between diode 3 and MOSFET 1a in the first series circuit and a connection point between diode 4 and MOSFET 2a in the second series circuit, respectively. An AC power source 6 is connected to the other ends of these reactors 5a and 5b.

  In the AC-DC power converter of the present invention configured as described above, a current value converted into a voltage value detected by the shunt resistor 10 is applied to a current detection circuit (not shown in FIG. 1) described later. . Then, the current value detected by the current detection circuit is given to a gate control unit (not shown), and the MOSFETs 1a and 2a are subjected to switching control.

FIG. 2 is a block diagram illustrating an example of a current detection circuit. In this figure, 20 is a voltage detection circuit, 21 is a sample hold unit, and 22 is a control unit (gate drive unit).
The bidirectional current flowing through the shunt resistor 10 is detected by the voltage detection circuit 20. The voltage detection circuit 20 may be configured using, for example, a general differential amplifier circuit or a shunt resistor amplifier IC.

  In addition, when the control part 22 of a back | latter stage is comprised with a microcomputer, a negative voltage cannot be input into the analog input terminal (A / D conversion input) with which a microcomputer is provided. For this reason, an offset voltage is superimposed on the output signal of the sample hold unit 21 to prevent a negative voltage from being input to the microcomputer (the external reference function of the amplifier IC constituting the voltage detection circuit 20 may be used), Alternatively, it is converted into a positive voltage by a full-wave rectifier circuit.

  As described above, when the input voltage is positive, the current flowing through the shunt resistor has a pulse-like waveform. Therefore, the sample hold unit 21 samples the detection value output from the voltage detection circuit 20 in synchronization with the ON period of the MOSFET 1a. & Hold. Since the technique of sampling and holding in synchronization with the on / off timing of the MOSFET 1a is known, the description thereof is omitted. In addition, since the A / D conversion is necessary particularly when the control is performed by a microcomputer or the like, the operation of sample → A / D conversion → control calculation → result output is originally performed. Just synchronize. In this case, it goes without saying that the sample and hold function of the A / D converter built in the microcomputer can be used.

  Next, FIG. 3 is a diagram showing an example of waveforms of the AC voltage and AC current input to the AC-DC power converter described above. Assuming that the current flowing from the MOSFET 1a to the DC line N is positive, when the input AC voltage is positive, when the MOSFET 1a is on, the MOSFET 1a is switched by switching of the control unit, and a pulsed current (positive direction) is generated. Flowing.

  On the other hand, when the input AC voltage is negative, all of the current returning to the AC power source 6 (negative direction) flows. In addition, the current flows through the MOSFET 1a by performing a so-called synchronous rectification operation in which the MOSFET 1a is always turned on during a period in which the AC input voltage is negative. This current is shunted between the body diode 1b and the MOSEFT 1a, but generally the voltage drop at the on-resistance of the MOSFET 1a is lower than the forward voltage drop of the body diode 1b. For this reason, it almost flows to the on-resistance side.

Thus, the AC-DC power converter of the present invention can reduce the power loss in the switching element (MOSFET) as compared with the power supply circuit described in Patent Document 2.
In the AC-DC power converter of the present invention, the number of components can be reduced from the conventional two to one by configuring the current detector and the detection circuit as described above. This makes it possible to reduce the size and cost of the device.

  Next, the form of Example 2 which concerns on the alternating current-DC power converter device of this invention is demonstrated, referring FIG. Example 2 differs from Example 1 described above in that a shunt resistor, which is a current detector, is inserted into the second series circuit. That is, the anode of the diode 3 is connected to the drain of the MOSFET 1a to constitute a first series circuit. Further, the anode of the diode 4 is connected to the drain of the MOSFET 2a, and one end of a resistance element (shunt resistor) 11 that is a current detector is connected to the source of the MOSFET 2a to constitute a second series circuit. The MOSFETs 1a and 2a are configured such that body diodes 1b and 2b are connected between their drains and sources.

  Even in the AC-DC power converter of the second embodiment configured as described above, the shunt resistor 11 has a negative AC input voltage due to the symmetry of the circuit with the power converter of the first embodiment described above. In this case, a pulsed current (positive direction) when the MOSFET 2a is turned on flows, and when the AC input current is positive, all of the current fed back to the AC power supply 6 (negative direction) flows. The current detection circuit may be the same as that in the first embodiment. Therefore, the description is omitted.

  Thus, the AC-DC power converter according to the present invention can reduce the number of parts from two conventional shunt resistors to one, reduce the size and cost of the device, and improve the conversion efficiency of the device. There is a great effect in practical use, such as being able to be enhanced.

1a, 2a Switching element 1b, 2b Body diode 3, 4 Diode 5a, 5b Reactor 6 AC power supply 7 Capacitor 10, 11 Shunt resistor

Claims (3)

A first series circuit in which a first rectifying element, a first self-extinguishing switching element and a current detector are connected in series;
A second series circuit in which a second rectifying element and a second self-extinguishing switching element are connected in series;
A capacitor connected in parallel to a parallel circuit in which these series circuits are connected in parallel;
A first reactor having one end connected to a first connection point connecting the rectifying element of the first series circuit and the self-extinguishing switching element;
A second reactor having one end connected to a second connection point connecting the rectifying element and the self-extinguishing switching element of the second series circuit;
An AC-DC power converter, wherein an AC voltage is applied between the other ends of the first and second reactors, while a DC voltage is taken out from both ends of the capacitor. A first series circuit in which a first rectifying element and a first self-extinguishing switching element are connected in series;
A second series circuit in which a second rectifier element, a second self-extinguishing switching element, and a current detector are connected in series;
A capacitor connected in parallel to a parallel circuit in which these series circuits are connected in parallel;
A first reactor having one end connected to a first connection point connecting the rectifying element of the first series circuit and the self-extinguishing switching element;
A second reactor having one end connected to a second connection point connecting the rectifying element and the self-extinguishing switching element of the second series circuit;
An AC-DC power converter, wherein an AC voltage is applied between the other ends of the first and second reactors, while a DC voltage is taken out from both ends of the capacitor. The AC-DC power converter according to claim 1, wherein the current detector is a resistance element.