JP4989695B2 - AC / DC converter and equipment - Google Patents

Description

  The present invention relates to an AC / DC converter that suppresses a harmonic current contained in an input current from an AC power source and controls a DC voltage, and an apparatus including the AC / DC converter.

  As a conventional AC / DC converter, two switching elements are provided, and the two switching elements are simultaneously operated by a low-frequency PWM to control the input current in a substantially sinusoidal shape to suppress the harmonic current, thereby reducing the voltage of the DC voltage. It is known to improve the power factor by controlling the value to an arbitrary value by feedback control. In this conventional example, the power factor is improved by operating the switching element at a low frequency PWM of 5 kHz or less to make the input current substantially sinusoidal. In order to control the output DC voltage to an arbitrary value and make the input current approximately sinusoidal, DC voltage control is performed with the control value of the reference voltage and the detected voltage, and the converter voltage with a sinusoidal waveform based on this control A command is generated and the input current is controlled based on the voltage difference from the power supply voltage. Thereby, the harmonic current can be drastically reduced and the power factor can be improved. In addition, since the output DC voltage can be controlled to an arbitrary voltage value by feedback control, it is less expensive than high-frequency PWM control, and the reactor can be made smaller than switch control once or several times in a power supply half cycle ( For example, see Patent Document 1).

  In addition, there is also known a device that uses a super junction structure MOSFET as a switching element and performs soft switching in which a capacitor is connected in parallel with the switching element. This conventional example is a technique for reducing energization loss by using an element called a super junction MOSFET (hereinafter referred to as SJ-MOSFET), and uses a super junction structure having a large stray capacitance between MOSFET terminals. Thus, the capacitor used for soft switching is replaced with this stray capacitance. Thereby, a capacitor | condenser can be abbreviate | omitted (for example, refer patent document 2).

  Furthermore, the power MOSFET has a super junction structure so that a power supply with high efficiency, small size, and low noise can be realized, and the recovery characteristic of the built-in diode, which is a drawback of the super junction structure, is poor and the recovery loss is large. In order to improve the above, it is known to reduce the loss of recovery by parallelizing Schottky barrier diodes which are unipolar elements (see, for example, Patent Document 3).

International Publication No. 2009/028053 (pages 3 to 13, FIGS. 1 and 3 to 8) Japanese Patent Laid-Open No. 2000-156978 (pages 2 to 3, FIGS. 1 to 2) Japanese Patent Laid-Open No. 2006-24690 (pages 3 to 5, FIG. 1)

  However, in the conventional example described in Patent Document 1, although it is a low-frequency PWM, since it always performs a PWM operation, there is less loss than the high-frequency PWM control method, but the switch operation is performed once or several times in a power supply half cycle. There is a problem that the loss is larger than that of the AC / DC converter.

In addition, the super junction has a low on-resistance due to its structure, so that conduction loss can be reduced. On the other hand, since the stray capacitance between the terminals of the MOSFET is large, there is a problem in that recovery characteristics are poor.
However, in the conventional example described in Patent Document 2, consideration is not given to improving the recovery characteristics by utilizing the stray capacitance.

  The conventional example described in Patent Document 3 attempts to improve recovery characteristics by connecting a Schottky barrier diode in parallel to an SJ-MOSFET. However, the built-in diode and the Schottky barrier diode are connected in parallel. However, the MOSFET semiconductor itself is not improved.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a highly efficient AC / DC converter with little loss and a device including the AC / DC converter.

An AC / DC converter according to the present invention includes a rectifier connected to an AC power source via a reactor, two capacitors connected in series between output terminals of the rectifier, and a first diode that is a parasitic diode. possess the, the FET is a device having a super junction structure, among the current flowing through the first diode, a second diode for blocking the current so as not to flow through the forward current of the first diode The two sets of bidirectional switches are configured by connecting the input terminals of the rectifiers provided in each of the two sets of bidirectional switches. Connected in series, connecting the connection point of the two sets of bidirectional switches and the connection point of the two capacitors, the control means is a current flowing from the AC power supply The reactive current is extracted, and the two sets of bidirectional switches are operated so that the reactive current becomes zero. When at least one FET is turned off, the current flowing from the AC power source to the rectifier from the turned-off FET is It is a commutation.

According to the present invention, an AC / DC converter includes a rectifier connected to an AC power source via a reactor, two capacitors connected in series between output terminals of the rectifier, and a first diode that is a parasitic diode. was closed in the interior, the FET is a device having a superjunction structure, the one of the current flowing through the first diode, the second breaking current so as not to flow through the forward current of the first diode Two sets of bidirectional switches composed of diodes and control means, and the two sets of bidirectional switches by connecting the input terminals of the rectifiers provided in each of the two sets of bidirectional switches. The switches are connected in series, the connection point of the two sets of bidirectional switches and the connection point of the two capacitors are connected, and the control means When the two sets of bidirectional switches are operated so that the reactive current becomes zero and at least one FET is turned off, the current flowing from the AC power source to the rectifier from the turned off FET Therefore, since the current does not flow to the first diode (parasitic diode) built in the FET, the low on-resistance of the FET (SJ-MOSFET) is not required. Therefore, it is possible to construct a suitable circuit configuration without any demerits. Therefore, since the current loss generated when the semiconductor element flows is reduced by using the low on-resistance characteristics of the FET, a highly efficient AC / DC converter can be obtained.

1 is a circuit block diagram showing a first embodiment of an AC / DC converter according to the present invention. It is a circuit diagram in the ideal state for demonstrating the principle of operation of the alternating current direct current converter in Embodiment 1 of this invention. It is a block diagram which shows the structure of the control means in Embodiment 1 of the alternating current direct current converter which concerns on this invention. It is a block diagram which shows the structure of the other control means in Embodiment 1 of the alternating current direct current converter which concerns on this invention. It is a circuit block diagram which shows Embodiment 2 of the alternating current direct current converter which concerns on this invention. It is a circuit block diagram which shows Embodiment 3 of the alternating current direct current converter which concerns on this invention.

Embodiment 1 FIG.
FIG. 1 is a circuit block diagram showing Embodiment 1 of an AC / DC converter according to the present invention. As shown in FIG. 1, the AC / DC converter includes an AC power source 1, a rectifier 2, a first switch unit 3, a second switch unit 4, a reactor 5, a first capacitor 6, a second capacitor 7, a DC unit. It consists of a load 8.
The rectifier 2 is for rectifying the AC of the AC power source 1. One of the first switch means 3 is connected to the input terminal of the rectifier 2. One of the second switch means 4 is connected to the other input terminal of the rectifier 2. The reactor 5 is inserted between the AC power source 1 and the first switch means 3 or the second switch means 4. One of the first capacitors 6 is connected to the output terminal of the rectifier 2. One of the second capacitors 7 is connected to the other output terminal of the rectifier 2. The DC load 8 is connected to the output of the rectifier 2, and the first switch means 3, the second switch means 4, the first capacitor 6, the second capacitor 7, and the other end of each of them are both It is connected.

  Moreover, the control means 20 which operates the 1st switch means 3 and the 2nd switch means 4 is comprised, and the control means 20 is the detection value (DC voltage Vdc) of the DC voltage detector 21 and the input current detector 22. The first switch means 3 and the second switch means 4 are operated based on the input current Is) and the power supply phase signal θ from the power supply zero cross detector 23.

A diode 10 and a resistor 12 are connected in parallel with the first capacitor 6, and a diode 11 and a resistor 13 are connected in parallel with the second capacitor 7, and the diode 10 and the diode 11 are connected to the first capacitor 6 and the second capacitor 6. The polarity is opposite to that of the capacitor 7.
The diode 10 and the diode 11 are provided to prevent the voltage of the capacitor 6 and the voltage of the capacitor 7 from being reversed in polarity, and the resistor 12 and the resistor 13 are the voltage of the capacitor 6 and the voltage of the capacitor 7. It is provided to suppress unbalance.

Further, the first switch means 3 is a bidirectional switch means composed of an SJ-MOSFET 3a and a diode rectifier 3b, and the second switch means 4 is also a bidirectional switch means composed of an SJ-MOSFET 4a and a diode rectifier 4b. It is. Note that the super junction structure of the SJ-MOSFET is a structure having a P layer deeper than that of a normal MOSFET, which is also disclosed in FIG. 1 of Patent Document 3, and the deep P layer is in wide contact with the n layer. It is known to have a high voltage resistance while having a low on-resistance.
In order to associate with the claims, the SJ-MOSFET constitutes an FET, the parasitic diode built in the structure of the SJ-MOSFET constitutes a first diode, and the diode rectifier constitutes a second diode. To do.

FIG. 2 is a circuit configuration diagram in an ideal state for explaining the operation principle of the AC / DC converter according to Embodiment 1 of the present invention.
Next, the operation principle of the AC / DC converter according to Embodiment 1 will be described with reference to FIGS. In FIG. 1, the voltage across the AC power supply 1 is Vs, and the current flowing through the reactor 5 is I. The AC power source 1 and the reactor 5 in FIG. 2 are the same as those shown in FIG. 1, and the AC / DC converter is a virtual AC power source 9. A virtual AC power supply 9 as shown in FIG. 2 is realized by operating the two switch means 3 and 4 in a complementary manner. Here, the voltage across the virtual AC power supply 9 is Vc *.

  The current I flowing through the reactor 5 is determined by the voltage difference between the voltage of the AC power supply 1 and the voltage of the virtual AC power supply 9. If the voltage Vc * output from the virtual AC power supply 9 is output in a sine wave shape, the current flowing through the reactor 5, in other words, the input current flows as a sine wave, and the harmonic current is suppressed. Further, when the phase difference between the input current and the AC power supply 1 becomes zero, the power factor becomes 100%. Therefore, the amplitude | Vc * | in the virtual AC power supply 9 and the phase difference φ between the AC power supply 1 are appropriately set. If controlled to output a sinusoidal voltage, the harmonics of the input current can be suppressed and power factor improvement can be realized.

  FIG. 3 shows an example of a control block capable of controlling the DC voltage between the output terminals of the rectifier 2 to an arbitrary command value and further controlling the voltage Vc * of the virtual AC power supply 9.

FIG. 3 is a block diagram showing the configuration of the control means 20 in Embodiment 1 of the present invention.
Next, the internal configuration of the control means 20 will be described with reference to FIG. In order to control the DC voltage Vdc detected by the DC voltage detector 21 to a DC voltage command value Vdc * which is a predetermined value set in advance, a difference between the detected value of the DC voltage and the command value is input to the PI controller 30. . The PI controller 30 outputs a current command value Ip * to control the DC voltage to a predetermined value.

  The instantaneous value Is of the input current detected by the input current detector 22 and the power supply phase θ detected by the power supply zero cross detector 23 are input to the PQ converter 31. The PQ converter 31 separates the active power component (P-axis component) of the input current and the reactive power component (Q-axis component) of the input current, and the reactive power component Iq is 0 so that the power source power factor becomes 100%. And the active power component Ip is controlled by the PI controller 34 so as to become the output value Ip * of the PI controller 30.

  The inverse PQ converter 35 inversely converts the output Vp * of the PI controller 33 and the output Vq * of the PI controller 34 at the power supply phase θ. As a result, the power factor is 100%, in other words, the reactive power component of the current is 0, and the command value Vc * of the voltage across the virtual AC power supply 9 that is a preset DC voltage is obtained.

FIG. 4 shows an example of another configuration of the control means 20. FIG. 4 utilizes the property that the voltage-current vector relationship is orthogonal when the power factor described in Patent Document 1 is 100%, and a detailed description thereof is described in Patent Document 1.
In addition, w shown in FIG. 4 represents an angular velocity.

  In this way, it is possible to operate the AC / DC converter shown in FIG. 1 with the configuration shown in FIGS. At this time, since the switching operation is always performed with the low-frequency PWM, conduction loss and switching loss accompanying switching occur. Therefore, the conduction loss can be reduced by applying the SJ-MOSFET having a low ON resistance. Furthermore, since it is a low-frequency PWM, for example, if it is 10 kHz or less, the conduction loss is more dominant than the switching loss. Therefore, since the control configuration can realize low-frequency PWM, the low on-resistance, which is an advantage of SJ-MOSEFT, can be used to the maximum extent possible.

  SJ-MOSFETs have the disadvantage of poor recovery characteristics as a compensation for low on-resistance, and thus have not been widely put into practical use. The present invention provides a circuit configuration that can utilize the characteristics of SJ-MOSFETs to the maximum.

  A MOSFET has a parasitic diode formed due to its structure, but in the case of an SJ-MOSFET, the recovery of the parasitic diode is a cause of the drawback. The slow recovery of the parasitic diode means that in the state where the forward current flows through the parasitic diode, the reverse current also flows through the parasitic diode when the current should flow to the transistor side of the MOSFET when the MOSFET is turned on. Represents that.

  An ideal diode instantaneously cuts off the reverse current, but the parasitic diode of the SJ-MOSFET has a slow time until the reverse current is cut off. On the other hand, the parasitic diode of the SJ-MOSFET does not have a diode characteristic even if the recovery is slow. In other words, if the diode characteristic is exhibited, in other words, if the reverse current is cut off, the parasitic diode of the SJ-MOSFET has no adverse effect.

  Therefore, if no current is passed through the parasitic diode of the SJ-MOSFET, there is no occurrence of recovery, and adverse effects due to slow recovery can be eliminated. The state where the current flows through the parasitic diode of the MOSFET is a so-called phenomenon called recirculation, and the current flows as a current path when the transistor is turned off due to phase delay due to inductive load or the like. What is necessary is just to comprise.

  Therefore, description will be made with reference to the circuit configuration of FIG. The first switch means 3 and the second switch means 4 are bidirectional switch means, but the SJ-MOSFET 3a and SJ-MOSFET 4a are connected via diode rectifiers 3b and 4b that cut off current in the reverse direction. Yes. The diode rectifiers 3b and 4b have a function of blocking current from flowing through the parasitic diodes of the SJ-MOSFET 3a and SJ-MOSFET 4a.

  Further, when the SJ-MOSFET 3a or SJ-MOSFET 4a is turned off, when the current flowing through the reactor 5 that is an inductive element continues to flow, since the rectifier 2 is turned on, the parasitic diode of the SJ-MOSFET 3a or SJ-MOSFET 4a Even if no current flows, a current path is secured and commutates to the rectifier 2.

  As described above, according to the first embodiment, current does not flow to the parasitic diode, which can be said to be a defect of the SJ-MOSFET. Therefore, only the merit of the low on-resistance possessed by the SJ-MOSFET can be enjoyed, and a circuit that is suitable if there is no demerit. By constructing the structure, it is possible to reduce the conduction loss generated when the semiconductor element is flowing, and to obtain a highly efficient AC / DC converter. In addition, since the AC / DC converter of the present invention operates at a low frequency PWM, the conduction loss when the semiconductor is on is more dominant than the switching loss due to PWM switching. It is also suitable for the control configuration of the apparatus, and a highly efficient AC / DC converter can be obtained.

Embodiment 2. FIG.
In the first embodiment, the diode rectifier that cuts off the current to the parasitic diode of the SJ-MOSFET is provided in each of the first switch means and the second switch means. However, only one diode rectifier is provided, You may comprise so that a switch means and a 2nd switch means may be shared. This embodiment will be described in the second embodiment.
2 to 4 are also used in the second embodiment.
FIG. 5 is a circuit block diagram showing Embodiment 2 of the AC / DC converter according to the present invention.
In FIG. 5, the first switch means 3 and the second switch means 4 in FIG. 1 are replaced with the first SJ-MOSFET 31a and the second SJ-MOSFET 41a, respectively, and one diode rectifier 14 is connected thereto. Otherwise, the configuration is the same as that of FIG.

  Although the basic circuit of FIG. 5 is not the bidirectional switch means 3 and 4, the operation of the switch elements SJ-MOSFETs 3a and 4a is the same as in FIGS. 1 and 5, and the diode rectifier 14 is a unidirectional flow switch element. Needless to say, the SJ-MOSFETs 3a and 4a are equivalently converted into bidirectional switch means, and thus have the same effect as described above.

  In FIG. 5, a diode rectifier 14 is arranged in a path through which current flows in the parasitic diodes of the SJ-MOSFETs 3a and 4a. Therefore, it can be said that the current does not flow through the parasitic diode. Furthermore, when the SJ-MOSFETs 3a and 4a are turned off, the rectifier 2 is turned on as a current path through which the current in the reactor 5 of the inductive element continues to flow, so that the current path of the reactor is secured and commutated to the rectifier 2.

  As described above, according to the second embodiment, the parasitic diode current blocking element and the commutation element that secures the current path flowing through the inductive element are provided so as not to have a path through which the current flows through the parasitic diode of the SJ-MOSFET. Thus, only the advantage of the low on-resistance of the SJ-MOSFET can be enjoyed.

  Further, when the SJ-MOSFETs 3a and 4a are turned on, the number of diodes in the path through which the current flows is half that in FIG. 1, and the diode conduction loss can be reduced to ½ that of the circuit configuration in FIG. This has the effect of improving the conversion efficiency of the AC / DC converter.

Embodiment 3 FIG.
2 to 4 are also used in the third embodiment.
FIG. 6 is a circuit block diagram showing Embodiment 3 of the AC / DC converter according to the present invention.
6 is the same as the configuration of FIG. 1 except that the first switch means 3 and the second switch means 4 of FIG. 1 are replaced with the first switch means 32 and the second switch means 42, respectively.
The first switch means 32 connects the first SJ-MOSFET 32a and the second SJ-MOSFET 32c in antiparallel, connects the first blocking diode 32b in series with the first SJ-MOSFET 32a, and the second SJ-MOSFET 32a. A bidirectional switch is configured by connecting the blocking diode 32d in series with the second SJ-MOSFET 32c.
The same applies to the configuration of the second switch means 42. The third SJ-MOSFET 42a and the fourth SJ-MOSFET 42c are connected in antiparallel, and the third blocking diode 42b is connected in series with the third SJ-MOSFET 42a. In addition, a bidirectional switch is configured by connecting the fourth blocking diode 42d in series with the fourth SJ-MOSFET 42c.
Thus, instead of the bidirectional switch means composed of the SJ-MOSFET and the diode rectifier, a bidirectional switch is constructed in which two SJ-MOSFETs are connected in antiparallel and a blocking diode is connected in series with the SJ-MOSFET. Thus, the current flowing through the parasitic diode can be cut off, and only the advantage of the low on-resistance of the SJ-MOSFET can be enjoyed.

FIG. 6 shows that the anode terminals of the diodes 3b, 3d, 4b, and 4d are connected to the source terminals of the SJ-MOSFETs 3a, 3c, 4a, and 4c, but the cathode terminal is connected to the drain terminal. Needless to say, even with a simple structure, it is possible to obtain the effect of enjoying only the advantages of the SJ-MOSFET.
Furthermore, although not shown, it goes without saying that the same effect can be obtained by configuring a bidirectional switch in which the sources of two SJ-MOSFETs are connected and a diode is connected in parallel with the SJ-MOSFET. No.
Furthermore, by utilizing the low on-resistance characteristic of the SJ-MOSFET, when the current flows in the reverse direction (in other words, the direction in which the current flows in the parasitic diode), the PWM signal is transmitted between the gate and the source so that the SJ-MOSFET is turned on. Even if the PWM control is configured so that current does not flow through the parasitic diode using the characteristic that current flows in the reverse direction on the FET side instead of the parasitic diode (generally called synchronous rectification characteristics) Needless to say, the effects of

  1, 5, and 6, the N-type channel is described. However, even if the P-type channel is used, the effect of the SJ-MOSFET is not impaired.

As an application example of the present invention, the present invention can be used for a power supply device for a load that consumes power by direct current. In particular, it can be used as a power supply device for an inverter that is a DC / AC converter, and it can be applied to an inverter that drives a permanent magnet motor, realizing energy savings, a low-cost, low-noise AC / DC converter configuration, etc. In addition to refrigerators and washing dryers, it can be applied to household appliances such as refrigerators, dehumidifiers, heat pump water heaters, showcases, and vacuum cleaners, and can also be applied to fan motors, ventilation fans, hand dryers, etc. .
The above products are collectively called equipment.

  DESCRIPTION OF SYMBOLS 1 AC power supply, 2 Rectifier, 3 1st switch means, 3a 1st SJ-MOSFET, 3b 1st diode rectifier, 4 2nd switch means, 4a 2nd SJ-MOSFET, 4b 2nd diode rectifier 5 Reactor, 6 First capacitor, 7 Second capacitor, 8 Load, 14 Diode rectifier, 20 Control means, 31a First SJ-MOSFET, 32 First switch means, 32a First SJ-MOSFET, 32b first blocking diode, 32c second SJ-MOSFET, 32d second blocking diode, 41a second SJ-MOSFET, 42 second switch means, 42a third SJ-MOSFET, 42b third blocking Diode, 42c Fourth SJ-MOSFET, 4 d fourth blocking diode.

Claims (5)

A rectifier connected to an AC power source via a reactor;
Two capacitors connected in series between the output terminals of this rectifier,
A first diode is a parasitic diode possess inside, the FET is a device having a super junction structure, among the current flowing through the first diode, not flow through the forward current of the first diode Two sets of bidirectional switches composed of a second diode that interrupts the current,
Control means,
The two sets of bidirectional switches are connected in series by connecting the input terminals of rectifiers provided in each of the two sets of bidirectional switches, and the connection points of the two sets of bidirectional switches and the two capacitors To the connection point of
The control means extracts a reactive current from a current flowing from the AC power source, operates the two sets of bidirectional switches so that the reactive current becomes zero, and turns off when at least one FET is turned off. An AC to DC converter characterized in that a current flowing from the AC power source is commutated from an FET to the rectifier. A rectifier connected to an AC power source via a reactor;
Two capacitors connected in series between the output terminals of this rectifier,
A first diode is a parasitic diode possess inside, two FET is an element having a super junction structure,
A diode bridge that cuts off a current from flowing through the first diode so as not to pass a forward current of the first diode ;
Switch means configured by connecting the two FETs in series by connecting two outputs of the diode bridge;
Control means,
Connecting the input terminal of the diode bridge and the input terminal of the rectifier constituting the switch means, connecting the connection point of the two FETs and the connection point of the two capacitors;
The control means extracts a reactive current from a current flowing from the AC power supply, operates the switch means so that the reactive current becomes zero, and when at least one FET is turned off, the FET that turns off the rectifier An AC / DC converter characterized in that the current flowing from the AC power source is commutated. A rectifier connected to an AC power source via a reactor;
Two capacitors connected in series between the output terminals of this rectifier,
A first diode is a parasitic diode possess inside, the FET is a device having a super junction structure, among the current flowing through the first diode, not flow through the forward current of the first diode Two sets of bidirectional switches configured by connecting in series a second diode that cuts off the current, and connecting the series circuit in antiparallel,
Control means,
The two sets of bidirectional switches are connected in series, the two sets of bidirectional switches connected in series are connected between the input terminals of the rectifier, and the connection point of the two sets of bidirectional switches and the connection of the two capacitors Connect the dots,
The control means extracts a reactive current from a current flowing from the AC power source, operates the two sets of bidirectional switches so that the reactive current becomes zero, and turns off when at least one FET is turned off. An AC to DC converter characterized in that a current flowing from an AC power source is commutated from an FET to the rectifier.   4. The AC / DC converter according to claim 1, wherein a switching frequency of the FET is set to 10 kHz or less. Apparatus characterized by comprising a AC-DC converter according to any one of claims 1 to 4.

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