JP2016123148A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a loss can be reduced by introducing a switching element or a diode formed from a wide band gap semiconductor in a switching power supply but since cost of the wide band gap semiconductor element is extremely high relatively to a silicon semiconductor element under the present circumstances and thoughtless introduction may result in increase of cost.SOLUTION: The switching power supply is configured to convert AC power supplied from an AC power source 2 into DC power and comprises: booster parts 4-7 including smoothing means 8 to which a DC load 3 is connected and which smooths the DC power, reactors L1-L4, backflow prevention diodes d1-d4 and switching means Q1-Q4; and a control part 11 which performs ON/OFF drive control on the switching means. The switching means in at least one booster part is formed from the wide band gap semiconductor element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device (converter device) that performs a converter operation for converting alternating current power into direct current power, and particularly relates to a technique applicable to a power supply device using a wide band gap semiconductor.

  A conventional switching power supply device that converts AC power to DC power generally uses a booster circuit composed of a reactor, a diode, and a switching element to realize a power factor improvement function for input power and a boost function for output voltage. Met. A representative example is a switching power supply device using a so-called boost chopper circuit.

  The conventional standard step-up chopper circuit has a rectifier diode bridge for full-wave rectification of AC power, a reactor with one end connected to the positive output of the rectifier diode bridge, and a reverse flow prevention with an anode connected to the other end of the reactor. Diode, a switching element connected between the anode of the reverse current blocking diode and the negative output of the rectifying diode bridge, and connected between the cathode of the reverse current blocking diode and the negative output of the rectifying diode bridge An electrolytic capacitor is provided, and a DC voltage is extracted from between terminals of the electrolytic capacitor while increasing the power factor of the power source by appropriately turning on and off the switching element.

  A so-called bridgeless power factor correction circuit has been proposed as an applied form of the boost chopper circuit. In this bridgeless power factor correction circuit, a booster composed of a reactor, a switching element, and a diode is connected to each of the two power lines of the AC power supply, and the output voltage of the two boosters is smoothed by an electrolytic capacitor, so that the switching element is appropriately On and off control, the power factor of the power supply is increased, and a DC voltage is extracted from between the terminals of the electrolytic capacitor. Since this bridgeless power factor correction circuit has one diode reduced in the current path from the AC power supply to the DC voltage output as compared with the above-described standard step-up chopper circuit, the conduction loss for one diode is suppressed. be able to. For this reason, the loss which arises in a switching power supply device can be reduced, and the power conversion efficiency can be improved (for example, refer patent document 1).

  In the bridgeless boost type converter, the switching element of the booster is a bidirectionally conductive element such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and is used as a parasitic diode of the MOSFET. It has also been known to realize so-called synchronous rectification in which the MOSFET is turned on at the timing of current flow to further suppress the loss of one parasitic diode in the booster (see, for example, Patent Document 2).

  In addition, as a means for further suppressing loss of electronic equipment such as a switching power supply device, a wide band gap semiconductor element has been introduced. The diodes and switching elements used in switching power supply devices are generally semiconductor elements formed of silicon (hereinafter abbreviated as Si), but the semiconductor elements are made of silicon and wide band gap semiconductors. (As a typical example, it is known that the conduction loss and switching loss of an element can be reduced by replacing with silicon carbide (hereinafter abbreviated as SiC) and gallium nitride (hereinafter abbreviated as GaN).

Japanese Patent Laying-Open No. 2012-175833 (FIG. 2) JP 2010-154582 (paragraph 0048)

  Loss can be reduced by introducing switching elements and diodes made of wide bandgap semiconductors in switching power supply devices, but wide bandgap semiconductor elements are currently much more expensive than silicon semiconductor elements and are introduced unnecessarily. There is a problem in that doing so leads to a significant cost increase of the switching power supply device.

  The present invention has been made to solve the above-described problems, and a first object of the present invention is to obtain a switching power supply device that can suppress the manufacturing cost of the device while utilizing a wide band gap semiconductor element. That is. A second object of the present invention is to obtain a switching power supply device that realizes a control operation capable of suppressing loss of the switching power supply device.

  The switching power supply device of the present invention is a switching power supply device that converts AC power supplied from an AC power source into DC power, and is connected to a DC load, smoothing means for smoothing the DC power, and one end of the AC power source. Connected to the other end of the reactor, and a cathode connected to the positive terminal of the smoothing capacitor, an anode of the reverse current blocking diode, and a negative electrode of the smoothing capacitor A plurality of boosting units having switching means connected between side terminals; and a control unit for controlling on / off driving of the switching means, wherein at least one of the boosting unit switching means is a wide band gap semiconductor. It is formed by an element.

  Since the switching power supply device of the present invention is provided with a plurality of boosting sections to reduce the current flowing through each switching element, an element formed of a wide band gap semiconductor having a small current capacity is used as the switching means. It is possible to reduce the cost of the entire switching power supply device compared to the case where all switching means are elements made of silicon semiconductors, and to take advantage of the low loss of wide band gap semiconductor elements, and to convert power A switching power supply device with high efficiency can be obtained.

1 is a diagram showing a system configuration including a switching power supply device in Embodiment 1. FIG. Application pattern of wide band gap semiconductor element and silicon semiconductor element in the boosting section. FIG. 3 is a diagram showing a specific configuration example of a system configuration including a switching power supply device according to the first embodiment. Switching pattern (asynchronous rectification operation) explanatory diagram in Embodiment 1 Switching pattern (asynchronous rectification operation + interleave operation) explanatory diagram in the first embodiment Operation flow diagram of switching operation according to load in the first embodiment Switching pattern (synchronous rectification operation) explanatory drawing in Embodiment 1 FIG. 5 is a diagram showing a system configuration including a switching power supply device in a second embodiment. Switching pattern (asynchronous rectification operation) explanatory diagram in Embodiment 2 Operation flow diagram of switching operation according to load in embodiment 2

Embodiment 1.
The configuration and operation of the switching power supply according to Embodiment 1 will be described with reference to the drawings. FIG. 1 shows a system configuration including the switching power supply device of the present embodiment. This system is connected to an AC power source (AC) 2, a switching power source device 1 that converts AC power supplied from the AC power source 2 into DC power and outputs it, and an output of the switching power source device 1. And a DC load 3 that consumes DC power. The AC power supply 2 supplies AC power to the switching power supply device 1 via two power supply lines (L side and N side). As an example of the DC load 3, a combination of an inverter and a motor driven by the inverter is assumed.

  Next, the configuration of the switching power supply device 1 will be described. The switching power supply device 1 includes a booster 4 and a booster 5 connected in parallel to the L-side power line of the AC power supply 2, a booster 6 and a booster 7 connected in parallel to the N-side power line of the AC power supply 2, A smoothing capacitor 8 that is a smoothing means that smoothes DC power provided at the outputs of the four boosting units 4 to 7, and an output voltage detection unit 9 that detects a DC output voltage Vout that is a voltage across the terminals of the smoothing capacitor 8. , A current detection unit 10 that detects a load current flowing through the DC load 3, and a control unit 11 that controls the boosting units 4 to 7 based on the voltage and current detected by the output voltage detection unit 9 and the current detection unit 10. Is done. The current detection unit 10 can be composed of, for example, a shunt resistor and a means for detecting a voltage between terminals of the shunt resistor. An electrolytic capacitor can be used as the smoothing capacitor 8. Further, the negative electrode side terminal of the smoothing capacitor 8 is GND-connected (grounded) so that the reference potential of the DC output voltage Vout is set to GND.

  The step-up unit 4 includes a reactor L1, one end connected to the L-side power line, an anode connected to the other end of the reactor L1, and a cathode connected to the positive-side terminal of the smoothing capacitor 8, a backflow prevention diode d1, a backflow prevention The switching element Q1 is connected between the anode of the working diode d1 and the negative terminal of the smoothing capacitor 8, and the diode D1 is connected in reverse parallel to the switching element Q1.

  Each of the boosting units 5 to 7 has the same configuration as that of the boosting unit 4, the boosting unit 5 includes a reactor L2, a diode d2, a switching element Q2, and a diode D2, and the boosting unit 6 includes a reactor L3, a diode d3, and a switching element Q3. , The diode D3, and the boosting unit 7 includes a reactor L4, a diode d4, a switching element Q4, and a diode D4.

  In the boosters 4 to 7, the switching elements Q1 to Q4 and the diodes d1 to d4 are elements formed of a wide band gap semiconductor or a silicon semiconductor element. Examples of the wide band gap semiconductor include SiC (silicon carbide), GaN (gallium nitride), and diamond. There are three configurations (configurations A, B, and C) shown in FIG. 2 as application patterns of the wide band gap semiconductor element and the silicon semiconductor element in the boosters 4 to 7.

  In the configuration A, an SiC-MOSFET is used as the switching element Qn, and an SiC-diode is used as the diode dn. In the configuration B, an Si-IGBT is used as the switching element Qn, and an SiC-diode is used as the diode dn. -Use Si-diodes for IGBT and diode dn. Here, n = 1 to 4, corresponding to the boosting units 4 to 7, respectively.

  The diodes D1 to D4 are diodes connected in antiparallel to the switching elements Q1 to Q4, respectively. When the switching element Qn is a SiC-MOSFET, a parasitic diode of the switching element Qn (SiC-MOSFET) may be used as the diode Dn, or an external SiC-diode is connected in antiparallel to the switching element Qn. But you can. When an external SiC diode is not added as the diode Dn, the number of parts can be reduced, which is advantageous in terms of cost. When an external SiC diode is added as the diode Dn, an SiC diode having better characteristics than the parasitic diode can be used. In the following description of the operation, the diode Dn is described as a parasitic diode. When the switching element Qn is a Si-IGBT, the diode Dn is an external Si-diode or an external SiC-diode connected in reverse parallel to the switching element Qn.

  Two or more types of configurations A to C are applied to the four boosting units 4 to 7 as a whole. Thereby, the SiC device is applied to at least one of the switching element and the backflow prevention diode.

  The control unit 11 adjusts the on / off timing of the switching elements Q1 to Q4 of the boosting units 4 to 7 based on the voltage and current detected by the output voltage detection unit 9 and the current detection unit 10, and performs switching based on this timing. The elements Q1 to Q4 are individually turned on / off. Hereinafter, a specific configuration example of the boosters 4 to 7 will be described.

  The switching power supply device 20 of FIG. 3 includes the booster 4 and the booster 6 in the switching power supply device 1 of FIG. 1 with the configuration A of FIG. 2 (switching elements Q1 and Q3 are SiC-MOSFETs, and diodes d1 and d3 are SiC-diodes). And the configuration C of FIG. 2 (the switching elements Q2 and Q4 are Si-IGBTs and the diodes d2 and d4 are Si-diodes) is applied to the boosting unit 5 and the boosting unit 7, respectively. In FIG. 3, the same or corresponding parts as in FIG. Further, in order to make it easy to see that the diodes d1 and d3 are SiC semiconductors, symbols of normal diode elements are enclosed in an ellipse and displayed.

  The control unit 11 performs on / off control of the switching elements Q1 to Q4, so that (A) asynchronous rectification operation, (B) asynchronous rectification operation + interleave operation, and (C) switching operation according to load + asynchronous will be described below. Since each operation of the rectification operation and (D) switching operation according to the load + synchronous rectification operation can be performed, the operations will be described in order.

<(A) Asynchronous rectification operation>
The operation of asynchronous rectification will be described with reference to (a) the voltage waveform of the AC power supply 2 and (b) the switching pattern examples of the switching elements Q1 to Q4 in FIG. Note that the asynchronous rectification means that synchronous rectification is not performed by the switching elements Q1 and Q3 (both are SiC-MOSFETs) of the switching power supply device 20.

  Since AC power is supplied from the AC power supply 2 to the switching power supply device 1, the L-side power line is in a higher potential than the N-side power line (abbreviated as “L-side power line is at high potential”), and N. The state where the side power supply line is at a higher potential than the L side power supply line (abbreviated as when the N side power supply line is at a high potential) is periodically repeated. For this reason, the operation will be described separately when the L-side power line is at a high potential and when the N-side power line is at a high potential.

  First, the operation when the L-side power supply line is at a high potential will be described. This corresponds to the operation in the state where the voltage of the AC power supply 2 is a positive value in FIG. When the L-side power supply line is at a high potential, a current flows from the L side of the AC power supply 2 to the switching power supply device 20 via the L-side power supply line, and this current is divided into the booster 4 and the booster 5. At this time, the control unit 11 causes the switching element Q1 and the switching element Q2 to repeat the ON state and the OFF state simultaneously as in the switching pattern shown in FIG. 4B, and the switching element Q3 and the switching element Q4 maintain the OFF state. To do.

  When the switching element Q1 and the switching element Q2 are in the OFF state by the control of the control unit 11, in the boosting unit 4, a current flows through the path of the reactor L1 → the diode d1 → the smoothing capacitor 8 and the DC load 3, and in the boosting unit 5, the reactor L2 → Diode d 2 → Current flows through the path of the smoothing capacitor 8 and the DC load 3. The current flowing through the smoothing capacitor 8 and the DC load 3 reaches the AC power supply 2 through the diode D3 → the reactor L3 → the N-side path of the AC power supply 2 or the diode D4 → the reactor L4 → the N-side path of the AC power supply 2. In this way, a current flows through a path from the L side of the AC power supply 2 to the N side of the AC power supply 2 via the smoothing capacitor 8 and the DC load 3, charging the smoothing capacitor 8 and supplying power to the DC load 3. Is done. Since the switching element Q3 is in the off state, the operation is asynchronous rectification, and no current flows through the switch portion of the switching element Q3, and a current flows through the diode D3, which is a parasitic diode.

  On the other hand, when the switching element Q1 and the switching element Q2 are in the ON state by the control of the control unit 11, the current flows in the path of the reactor L1 → the switching element Q1 in the boosting unit 4, and the reactor L2 → the switching element Q2 in the boosting unit 5 Current flows through the path. The current flowing out of the switching element Q1 or the switching element Q2 is the diode D3 of the booster 6 → reactor L3 → the N-side path of the AC power supply 2, or the diode D4 of the booster 7 → reactor L4 → the N-side of the AC power supply 2. It reaches the AC power supply 2 by the route. Thereby, energy is accumulated in the reactor L1 and the reactor L2. When the switching element Q1 and the switching element Q2 are simultaneously switched to the OFF state by the control of the control unit 11 in a state where this energy is accumulated, the energy accumulated in the reactor L1 and the reactor L2 flows to the smoothing capacitor 8 and the terminal of the smoothing capacitor 8 The DC output voltage Vout, which is an inter-voltage, is boosted. Note that the switching element Q3 and the switching element Q4 must be kept off while the L-side power supply line is at a high potential.

  Next, an operation when the N-side power supply line is at a high potential will be described. This corresponds to the operation in the state where the voltage of the AC power supply 2 is a negative value in FIG. When the N-side power supply line is at a high potential, a current flows from the N side of the AC power supply 2 to the switching power supply device 20 via the N-side power supply line, and this current is divided into the booster 6 and the booster 7. At this time, the control unit 11 causes the switching element Q3 and the switching element Q4 to repeat the ON state and the OFF state simultaneously as in the switching pattern shown in FIG. 4B, and the switching element Q1 and the switching element Q2 maintain the OFF state. To do.

  When the switching element Q3 and the switching element Q4 are in the OFF state by the control of the control unit 11, in the boosting unit 6, current flows through the path of the reactor L3 → the diode d3 → the smoothing capacitor 8 and the DC load 3, and in the boosting unit 7, the reactor L4 → Diode d 4 → Current flows through the path of the smoothing capacitor 8 and the DC load 3. The current flowing through the smoothing capacitor 8 and the DC load 3 reaches the AC power source 2 through a path on the L side of the diode D1 → the reactor L1 → the AC power source 2 or a path on the L side of the diode D2 → the reactor L2 → the AC power source 2. In this way, a current flows through the path from the N side of the AC power supply 2 to the L side of the AC power supply 2 via the smoothing capacitor 8 and the DC load 3 to charge the smoothing capacitor 8 and supply power to the DC load 3. Is done. Since the switching element Q1 is in the off state, the operation is asynchronous rectification, and current does not flow through the switch portion of the switching element Q1, but current flows through the diode D1, which is a parasitic diode.

  On the other hand, when the switching element Q3 and the switching element Q4 are in the ON state by the control of the control unit 11, the current flows in the path of the reactor L3 → the switching element Q3 in the boosting unit 6, and the reactor L4 → the switching element Q4 in the boosting unit 7 Current flows through the path. The current flowing out of the switching element Q3 or the switching element Q4 is a path on the L side of the diode D1 → reactor L1 → AC power source 2 of the boosting unit 4 or a diode D2 of the boosting unit 5 → reactor L2 → the L side of the AC power source 2. It reaches the AC power supply 2 by the route. Thereby, energy is accumulated in the reactor L3 and the reactor L4. When the switching element Q3 and the switching element Q4 are simultaneously switched to the OFF state under the control of the control unit 11 in a state where this energy is stored, the energy stored in the reactor L3 and the reactor L4 flows to the smoothing capacitor 8 and the terminal of the smoothing capacitor 8 The DC output voltage Vout, which is an inter-voltage, is boosted. Note that the switching element Q1 and the switching element Q2 must be kept off while the N-side power supply line is at a high potential.

  As described above, when the L side power line of the AC power supply 2 is at a high potential, the switching element Q1 and the switching element Q2 are simultaneously turned on / off, the switching element Q3 and the switching element Q4 are turned off, and the N side power line is When the potential is high, the switching element Q3 and the switching element Q4 are simultaneously turned on / off, and the switching element Q1 and the switching element Q2 are turned off, thereby realizing a boost converter function by an asynchronous rectification operation.

  A SiC device is more expensive than a Si device, and especially a device having a large current capacity increases the price difference from the Si device. In the switching power supply device 20 shown in FIG. 3, since the boosting unit is paralleled, the current flowing through each switching element Qn can be reduced. For this reason, if SiC devices having a small current capacity are used as the switching elements Q1 and Q3, and the diodes d1 and d3, the cost of the entire switching power supply apparatus can be reduced as compared with the case where all the devices are made of Si semiconductors. A switching power supply with high power conversion efficiency can be obtained while making use of the advantages of low loss of the SiC device while reducing the power consumption.

<(B) Asynchronous rectification operation + interleave operation>
The operation combining the asynchronous rectification operation and the interleave operation will be described with reference to (a) the voltage waveform of the AC power supply 2 in FIG. 5 and (b) the switching pattern examples of the switching elements Q1 to Q4.

  As in the switching pattern shown in FIG. 5B, the control unit 11 controls the switching element so that the ON state of the switching element Q1 and the switching element Q2 is alternately repeated when the L-side power supply line is at a high potential. When the line is at a high potential, the switching element is controlled so that the ON state of the switching element Q3 and the switching element Q4 is alternately repeated. Such a switching operation is called an interleave operation.

  In addition, the switching elements that are not performing the interleaving operation are kept off. Specifically, when the L-side power supply line is at a high potential, the switching elements Q3 and Q4 are turned off, and when the N-side power supply line is at a high potential, the switching elements Q1 and Q2 are turned off. For this reason, when the L-side power supply line is at a high potential, the switching element Q3 is in an off state, so that an asynchronous rectification operation is performed, and no current flows through the switch portion of the switching element Q3, and a current flows through the parasitic diode D3. Further, when the N-side power supply line is at a high potential, the switching element Q1 is in an off state, so that an asynchronous rectification operation is performed, and no current flows through the switch portion of the switching element Q1, and a current flows through the parasitic diode D1.

  By performing the operation combining the asynchronous rectification operation and the interleave operation as described above, (a) in addition to the effect at the time of the asynchronous rectification operation, the switching frequency viewed from the AC power supply 2 side is equivalently increased. The effect that reactor L1-L4 can be reduced in size is acquired.

<(C) Switching operation according to load + Asynchronous rectification operation>
The switching power supply device 20 of FIG. 3 applies the configuration A (the switching elements Q1 and Q3 are SiC-MOSFETs and the diodes d1 and d3 are SiC-diodes) to the boosting unit 4 and the boosting unit 6, respectively. 7 is applied with the configuration C of FIG. 2 (the switching elements Q2 and Q4 are Si-IGBTs and the diodes d2 and d4 are Si-diodes), respectively. That is, the booster 4 and the booster 6 are configured to include SiC devices, and the booster 5 and the booster 7 are configured only of Si devices. Therefore, as described below, the switching pattern of the switching element Qn may be made variable according to the load state of the DC load 3.

  Specific control contents will be described based on the operation flow of FIG. First, a load condition determination threshold (Pth) is set in the control unit 11 (step S1). A storage unit (not shown) may be provided in the control unit 11, and a determination threshold value (Pth) may be held in advance in this storage unit, or an instruction from another device or device (not shown) Alternatively, the determination threshold value (Pth) may be set in the control unit 11 based on an instruction from a microcomputer (not shown) for overall device management provided in the switching power supply device 20. In the following description, a case where the determination threshold (Pth) is defined by a power value will be described.

  Next, the control unit 11 calculates the power consumption (Pm) at the DC load 3 based on the output voltage and the load current detected by the output voltage detection unit 9 and the current detection unit 10. This power consumption (Pm) corresponds to the load state of the DC load 3 detected by the control unit 11 (step S2).

  Next, the control unit 11 compares the detected load state (Pm) of the DC load 3 with the determination threshold value (Pth) of the load state, and when the load state (Pm) of the DC load 3 is equal to or less than the determination threshold value (Pth). (Pm ≦ Pth) is determined to be a “low load state”, and the process proceeds to step S4. When the load state (Pm) is larger than the determination threshold value (Pth) (Pm> Pth), it is determined to be a “high load state”. The process proceeds to step S5.

  In step S4, since the load is low, only switching elements Q1 and Q3 of boosting unit 4 and boosting unit 6 whose switching elements are SiC devices are switched (switching element Q1 is turned on / off when the L-side power line is at high potential. When the N-side power supply line is at a high potential, the switching element Q3 is turned on / off.) The switching elements Q2 and Q4 of the booster 5 and booster 7 are always turned off so as not to perform the switching operation. On the other hand, in step S5, since the load is high, all the switching elements Q1 to Q4 of the boosters 4 to 7 are turned on / off (the switching elements Q1 and Q2 are turned on / off when the L-side power line is at a high potential, When the N-side power supply line is at a high potential, the switching elements Q3 and Q4 are driven on / off).

  The switching pattern of the switching elements Q1 to Q4 in the high load state may be the switching pattern of the asynchronous rectification operation of FIG. 4B or the switching pattern of the interleave operation of FIG.

  Then, by repeatedly executing the flow of steps S2 to S4, the switching operation of the switching elements Q1 to Q4 of the boosters 4 to 7 corresponds to the load state even when the load state of the DC load 3 changes from moment to moment. Can be switched.

  For example, when the air conditioner equipped with the switching power supply device 20 is operated under an intermediate heating condition, the DC load 3 is in a low load state. Therefore, only the boosting units 4 and 6 including the SiC device are operated and operated under the rated condition. If the load state of the DC load 3 exceeds a predetermined threshold value and becomes a high load state, the boosting units 5 and 7 constituted only by the Si device can be operated together.

  As described above, when the DC load 3 is in a low load state, only the step-up units 4 and 6 including the SiC device are operated. Therefore, switching is performed while a current is mainly applied to the SiC device having a small loss characteristic. By reducing the number of switching times of the elements Q1 and Q3, the power conversion loss of the switching power supply device 20 can be suppressed. A SiC device is more expensive than a Si device, but a smaller current capacity can reduce the cost of the SiC device. Since the switching power supply device 20 described here suppresses the use location of the SiC device and reduces the current rating of the switching element by paralleling the boosting unit, it is possible to use a SiC device having a low current capacity. did. This makes it possible to reduce the loss while suppressing the cost of the entire switching power supply device.

  It should be noted that switching operation control according to such a load is a loss of equipment when applied to equipment that has a large ratio of low-load operation time to operation time, for example, a switching power supply installed in an air conditioner or the like. It is more effective by reduction.

<(D) Switching operation according to load + Synchronous rectification operation>
In the above “(C) switching operation according to load + asynchronous rectification operation”, the switching element Qn uses an asynchronous rectification switching pattern. However, when the DC load 3 is low in load, the switching pattern may be a synchronous rectification pattern. . The switching operation of synchronous rectification when the DC load 3 is low will be described with reference to (a) the voltage waveform of the AC power supply 2 and (b) the switching pattern examples of the switching elements Q1 to Q4 in FIG.

  First, the operation when the L-side power supply line is at a high potential will be described. This corresponds to the operation in the state where the voltage of the AC power supply 2 is a positive value in FIG. The switching element Q2 and the switching element Q4 that are Si-IGBTs are always turned off over the entire period of the power supply cycle of the AC power supply 2. Further, when the L-side power supply line is at a high potential, the switching element Q3, which is a SiC-MOSFET, maintains the on state. When the L-side power line is at a high potential, the current flowing from the L side of the AC power supply 2 to the switching power supply device 20 flows to the boosting unit 4. Since switching unit Q2 is always in the off state and boosting unit 5 is not performing a boosting operation, a reverse voltage is applied to diode d2 and no current flows through boosting unit 5.

  When the switching element Q1, which is a SiC-MOSFET, is turned on by the control unit 11, a current flows in the path of the reactor L1 → the switching element Q1 in the boosting unit 4, and the current flowing out of the switching element Q1 The switch part of the switching element Q3 → reactor L3 → the path on the N side of the AC power supply 2 or the diode D4 of the boosting unit 7 → the reactor L4 → the AC power supply 2 through the path on the N side of the AC power supply 2. Thereby, energy is accumulated in the reactor L1.

  Thereafter, when the switching element Q1 is turned off, in the boosting unit 4, a current flows through the path of the reactor L1, the diode d1, the smoothing capacitor 8, and the DC load 3, and the output voltage is boosted by the energy accumulated in the reactor L1. The current flowing through the DC load 3 is synchronously rectified while the switching element Q3 is turned on, so that the switching element Q3 → the reactor L3 → the path on the N side of the AC power supply 2 or the diode D4 → reactor L4 → The AC power supply 2 is reached through a path on the N side of the AC power supply 2.

  Thus, when the L-side power supply line is at a high potential, in the current path from the L side to the N side of the AC power supply 2, the current flows through the switch portion of the switching element Q3 without passing through the diode D3 that is a parasitic diode. Since the loss of the MOSFET is smaller than that of the diode, the conduction loss for one diode can be reduced by the synchronous rectification operation.

  When the N-side power supply line is at a high potential, the roles of the booster 4 and the booster 6 are opposite to those when the L-side power supply line is at a high potential. That is, as shown in the switching pattern of FIG. 7B, the switching element Q1 is kept on, energy is stored in the reactor L3 when the switching element Q3 is on, and stored in the reactor L3 when the switching element Q3 is off. The generated energy flows to the DC load 3 side, and the voltage can be boosted. Also in this case, the conduction loss for one diode can be reduced by the synchronous rectification operation of the switching element Q1.

  Note that when the DC load 3 is in a high load state, the current flowing through the DC load 3 increases. Therefore, if the current returning from the DC load 3 to the AC power supply 2 is concentrated on one SiC-MOSFET element, element destruction occurs. It is not preferable because of concern. Therefore, by performing the synchronous rectification operation only when the DC load is in a low load state, the power conversion loss of the switching power supply device 20 during the low load operation can be further suppressed.

Further, the DC load 3 may be switched to an interleave operation as a switching pattern in a high load state as in the case of “(C) switching operation according to load + asynchronous rectification operation”.

  In the above description, the configuration example in which the configuration A of FIG. 2 is applied to the boosting unit 4 and the boosting unit 6 and the configuration C is applied to the boosting unit 5 and the boosting unit 7 in the switching power supply device 1 of FIG. However, the combination in which the configurations A, B, and C of FIG. 2 are applied to each of the boosters 4 to 7 is not limited to this.

  In addition, in the switching power supply device 1 of FIG. 1, two boosters are provided for each of the L-side power line and the N-side power line of the AC power supply 2, but each power supply line is provided with three or more boosters. May be.

Embodiment 2.
The configuration and operation of the switching power supply device according to the second embodiment will be described with reference to the drawings. FIG. 8 shows a system configuration including the switching power supply device of this embodiment. In FIG. 8, the same or corresponding parts as those in FIG. This system is connected to an AC power source (AC) 2, a switching power source device 30 that converts AC power input from the AC power source 2 into DC power and outputs it, and an output of the switching power source device 30. And a DC load 3 that consumes power. The switching power supply device 30 is different from the switching power supply device 1 described in the first embodiment in the configuration of the boosting unit.

<(A) Asynchronous rectification operation>
The boosting unit of the switching power supply 30 includes a boosting unit 31 connected to the L-side power supply line of the AC power supply 2 and a boosting unit 32 connected to the N-side power supply line. The step-up unit 31 includes a reactor L5 whose one end is connected to the L-side power line, an anode connected to the other end of the reactor L5, and a cathode connected to the positive-side terminal of the smoothing capacitor 8 and a reverse current blocking diode d5. The switching element Q5 is a SiC-MOSFET connected between the anode of the working diode d5 and the negative terminal of the smoothing capacitor 8, and the switching element Q6 is a Si-IGBT connected in parallel to the switching element Q5. The switching element Q5 has a MOSFET parasitic diode D5. The backflow prevention diodes d5 and d6 are SiC-diodes or Si-diodes, respectively.

  Here, the parallel connection of the switching element Q5 and the switching element Q6 means that the drain terminal of the switching element Q5 (SiC-MOSFET) and the collector terminal of the switching element Q6 (Si-IGBT) are connected, and the switching element Q5 (SiC-MOSFET). ) And the emitter terminal of the switching element Q6 (Si-IGBT) are connected to each other.

  The boosting unit 32 has the same configuration as the boosting unit 31, and includes a reactor L6, a backflow blocking diode d6, a switching element Q7 that is a SiC-MOSFET, a switching element Q8 that is a Si-IGBT, and a switching element Q7 (SiC-MOSFET). The switching element Q7 and the switching element Q8 are connected in parallel.

  The control unit 11 performs on / off control of the switching elements Q5, Q6, Q7, and Q8 based on the load current and the output voltage detected by the current detection unit 10 and the output voltage detection unit 9, respectively. As a result, a boosted voltage is generated in the smoothing capacitor 8 connected to the output terminals of the booster 31 and the booster 32.

  Next, the operation of the control unit 11 will be described with reference to (a) the voltage waveform of the AC power supply 2 and (b) switching pattern examples of the switching elements Q5 to Q8 in FIG. First, the operation when the L-side power supply line is at a high potential will be described. This corresponds to the operation in the state where the voltage of the AC power supply 2 is a positive value in FIG. When the L-side power line is at a high potential, a current flows from the L side of the AC power supply 2 to the boosting unit 31 of the switching power supply 30. At this time, the control unit 11 performs control so that the switching element Q5 and the switching element Q6 repeat the ON state and the OFF state simultaneously as in the switching pattern shown in FIG. 9B. On the other hand, switching element Q7 and switching element Q8 are controlled to maintain the off state.

  When the switching element Q5 and the switching element Q6 are simultaneously OFF, the current from the L side of the AC power supply 2 flows through the path of the reactor L5 → the diode d5 → the smoothing capacitor 8 and the DC load 3, and the smoothing capacitor 8 and the DC load 3 The current flowing out from the diode D7 → the reactor L6 → the AC power supply 2 through the N-side path of the AC power supply 2. In this way, the current flows through the path from the L side of the AC power source 2 to the N side of the AC power source 2 via the smoothing capacitor 8 and the DC load 3, so that charging of the smoothing capacitor 8 and the DC load 3 are performed. Power is supplied. Since switching element Q7 is in an off state, asynchronous rectification is performed, and a current flows through diode D7, which is a parasitic diode of switching element Q7.

  On the other hand, when the switching element Q5 and the switching element Q6 are simultaneously turned on by the control of the control unit 11, a current flows through a path on the N side of the reactor L5 → switching elements Q5, Q6 → diode D7 → reactor L6 → AC power supply 2. . Thereby, energy is accumulated in the reactor L5. When the switching element Q5 and the switching element Q6 are simultaneously switched to the OFF state under the control of the control unit 11 in a state where this energy is accumulated, the energy accumulated in the reactor L5 flows to the smoothing capacitor 8, and the voltage between the terminals of the smoothing capacitor 8 is A certain DC output voltage Vout is boosted.

  Next, an operation when the N-side power supply line is at a high potential will be described. This corresponds to the operation in the state where the voltage of the AC power supply 2 is negative in FIG. When the N-side power supply line is at a high potential, current flows from the N-side of the AC power supply 2 to the boosting unit 32 of the switching power supply 30. At this time, the control unit 11 controls the switching element Q7 and the switching element Q8 to repeat the on state and the off state simultaneously as in the switching pattern shown in FIG. 9B. On the other hand, switching element Q5 and switching element Q6 are controlled to maintain the off state. As a result, the DC output voltage Vout, which is the voltage across the smoothing capacitor 8, is boosted in the same manner as when the N-side power supply line is at a high potential.

  As described above, when the L side power line of the AC power source 2 is at a high potential, the switching element Q5 and the switching element Q6 are simultaneously turned on / off, the switching element Q7 and the switching element Q8 are turned off, and the N side power line is When the potential is high, the switching element Q7 and the switching element Q8 are simultaneously turned on / off, and the switching element Q5 and the switching element Q6 are turned off to realize a boost converter function by an asynchronous rectification operation.

  In the switching power supply device 30 shown in FIG. 8, since the switching elements in the boosting units 31 and 32 are arranged in parallel, the current flowing through each switching element Qn can be reduced. For this reason, a SiC device with small current capacity can be used for switching element Q5 and switching element Q7, and the cost of a SiC device can be reduced.

  Further, since the SiC device is applied to a part of the switching element and the diode, the number of used elements of the SiC device can be reduced as compared with the case where all the devices are wide band gap semiconductors. Thus, while reducing the cost of the entire switching power supply device, it is possible to take advantage of the low loss of the SiC device and obtain a switching power supply device with high power conversion efficiency.

<(B) Switching operation according to load>
The control unit 11 may make the switching pattern of the switching element Qn variable according to the load state of the DC load 3. Specific control contents will be described based on the operation flow of FIG.

  Steps S11 to S13 are basically the same as steps S1 to S3 in the operation flow (FIG. 6) described in the first embodiment. In step S13, the control unit 11 compares the detected load state (Pm) of the DC load 3 with the determination threshold value (Pth) of the load state, and the load state (Pm) of the DC load 3 is equal to or less than the determination threshold value (Pth). It is determined that (Pm ≦ Pth) is a “low load state”, and the process proceeds to step S14. If the load state (Pm) is larger than the determination threshold value (Pth) (Pm> Pth), it is determined as a “high load state”. The process proceeds to step S15.

  In step S14, since the load is low, only switching elements Q5 and Q7, which are SiC devices, are switched (switching element Q5 is turned on / off when the L-side power line is at a high potential, and switching is performed when the N-side power line is at a high potential. The element Q7 is driven on and off.) The switching elements Q6 and Q8, which are Si devices, are always turned off so as not to perform the switching operation. A specific switching pattern of the switching elements Q5 and Q7 may be an asynchronous rectification switching pattern (switching patterns of the switching elements Q5 and Q7 in FIG. 9B).

  On the other hand, in step S15, since the load is high, all the switching elements Q5 to Q8 are turned on / off (the switching elements Q5 and Q6 are turned on / off when the L-side power line is at a high potential, and the N-side power line is high). When the potential is applied, the switching elements Q7 and Q8 are turned on and off.) (Switching patterns of the switching elements Q5 to Q8 in FIG. 9B).

  In the operation in the low load state in step S14, the switching elements Q5 and Q7 may be synchronously rectified. Thus, when the L-side power supply line is at a high potential, current flows through the switch portion of the switching element Q7 in the current path from the L side to the N side of the AC power supply 2 without passing through the diode D7 that is a parasitic diode. When the N-side power line is at a high potential, current flows through the switch portion of the switching element Q5 in the current path from the N side to the L side of the AC power supply 2 without passing through the diode D5 that is a parasitic diode. Since the loss of the MOSFET is smaller than that of the diode, the conduction loss for one diode can be reduced by the synchronous rectification operation. Similarly, when the N-side power line is at a high potential, the conduction loss for one diode can be reduced by the synchronous rectification operation.

  As described above, since only the switching element of the SiC device is switched when the DC load 3 is in a low load state, the switching elements Q1, Q3 are made to flow while focusing current on the SiC device having a small loss characteristic. By reducing the number of times of switching, power conversion loss of the switching power supply device 20 can be suppressed. A SiC device is more expensive than a Si device, but a smaller current capacity can reduce the cost of the SiC device. The switching power supply device 30 described here can reduce the current rating of each switching element by controlling the location where the SiC device is used and paralleling the switching element, and can use a SiC device having a low current capacity. did. This makes it possible to reduce the loss while suppressing the cost of the entire switching power supply device.

  It should be noted that switching operation control according to such a load is a loss of equipment when applied to equipment that has a large ratio of low-load operation time to operation time, for example, a switching power supply installed in an air conditioner or the like. It is more effective by reduction.

DESCRIPTION OF SYMBOLS 1 Switching power supply apparatus 2 AC power supply 3 DC load 4-7 Boosting part 8 Smoothing capacitor 9 Output voltage detection part 10 Current detection part 11 Control part 20 Switching power supply apparatus 30 Switching power supply apparatuses 31-32 Boosting part L1-L6 Reactors Q1-Q8 Switching elements D1-D5, D7 Diode (parasitic diode)
d1 to d6 Backflow prevention diode

Claims (10)

A switching power supply device that converts AC power supplied from an AC power source into DC power,
Smoothing means connected to a DC load and smoothing the DC power;
A reactor having one end connected to the AC power supply; an anode connected to the other end of the reactor; a cathode connected to the positive terminal of the smoothing capacitor; and an anode of the reverse current blocking diode; A plurality of boosting units having switching means connected between the negative electrode side terminals of the smoothing capacitor;
A control unit that controls on / off drive of the switching means,
The switching power supply device characterized in that at least one of the booster switching means is formed of a wide band gap semiconductor element.   The at least one of the boosting units is connected to one power supply line of the AC power supply, and the other boosting unit is connected to the other power supply line of the AC power supply. Switching power supply. The control unit determines a low load state when a load state of a DC load connected to the smoothing unit is equal to or less than a predetermined threshold value, and determines a high load state when the load state is greater than the threshold value,
When the load state of the DC load is a low load state, only the switching unit or the switching unit of the boosting unit in which the diode is formed of a wide band gap semiconductor element is turned on / off, and the other switching units of the boosting unit are turned off. Drive
3. The switching power supply device according to claim 1, wherein when the load state of the DC load is a high load state, the switching units of all the boosting units are driven on and off. 4. An output voltage detection unit that detects an output voltage that is a voltage between terminals of the smoothing unit, and a current detection unit that detects a load current flowing in a DC load connected to the smoothing unit,
The switching power supply apparatus according to claim 3, wherein the determination of the load state of the DC load is performed using electric power calculated based on the detected output voltage and load current.   The switching power supply according to any one of claims 1 to 4, wherein the switching means of the boosting unit is a MOSFET or a combination of an IGBT and a diode connected in antiparallel to the IGBT. apparatus.   5. The switching power supply device according to claim 1, wherein the switching unit of the boosting unit is a MOSFET and an IGBT connected in parallel.   7. The switching power supply device according to claim 5, wherein the control unit performs synchronous rectification control on the MOSFET when a load state of the DC load is a low load state. 8.   6. The switching power supply device according to claim 1, wherein the control unit performs interleave control of switching means of the boosting unit.   9. The switching power supply device according to claim 1, wherein at least one of the backflow blocking diodes is formed of a wide band gap semiconductor element.   The switching power supply according to any one of claims 1 to 9, wherein the wide band gap semiconductor is silicon carbide (SiC), gallium nitride (GaN), or diamond.

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