Power supply device

Abstract

To provide a power supply device capable of suppressing a deterioration of an energy storage element.SOLUTION: A power supply device includes first wiring and second wiring in which a DC current is input, third wiring, a power storage element, a first switching element, a second switching element, and a third switching element. The first switching element controls a current flowing between the first wiring and the third wiring. The power storage element is connected to either one of the second wiring and the third wiring. The second switching element causes the current to flow from the power storage element to the other one of the second wiring and the third wiring, and controls the current flowing from the other wiring to the power storage element. The third switching element is connected to the second switching element in series, causes the current to flow from the other wiring to the power storage element, and controls the current flowing from the power storage element to the other wiring.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a power supply device. [Background technology]

[0002] Induction heating devices require a large amount of power to inductively heat the workpiece. If all of the required power is to be received from an external source, it is necessary to establish a power receiving system that matches the maximum amount of power required, which is costly. Therefore, it has been considered to provide an energy bank unit in the power supply device of the induction heating device and to supply part of the power from the energy bank unit. However, there is a problem with the energy bank unit, in that it deteriorates quickly if it is used frequently or if an overcurrent flows through it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-351352 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of an embodiment of the present invention is to provide a power supply device that can reduce the frequency and amount of power consumed by charging and discharging the storage elements used in the energy bank section, thereby suppressing deterioration of the storage elements. [Means for solving the problem]

[0005] A power supply device according to an embodiment of the present invention includes a first wiring and a second wiring for receiving a direct current, a third wiring, a storage element, a first switching element, a second switching element, and a third switching element. The first switching element controls a current flowing between the first wiring and the third wiring. The storage element is connected to one of the second wiring and the third wiring. The second switching element flows a current from the storage element to the other of the second wiring and the third wiring, and controls a current flowing from the other wiring to the storage element. The third switching element is connected in series to the second switching element, flows a current from the other wiring to the storage element, and controls a current flowing from the storage element to the other wiring. Effect of the Invention

[0006] According to an embodiment of the present invention, by controlling the charging and discharging of an energy storage element with a small number of power semiconductors, it is possible to realize a power supply device that can reduce the frequency and amount of power consumed by charging and discharging, thereby suppressing deterioration of the energy storage element. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing a power supply device according to a first embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing the power storage element section of the power supply device according to the first embodiment. [Diagram 3] FIG. 3 is a timing chart showing the operation of the power supply device according to the first embodiment, with the horizontal axis representing time and the vertical axis representing output current. [Figure 4] FIG. 4 is a circuit diagram showing the operation of the power supply device during the charging period. [Diagram 5] FIG. 5 is a circuit diagram showing the operation of the power supply device during an output period without limiter operation. [Figure 6] FIG. 6 is a circuit diagram showing the operation of the power supply device during an output period with limiter operation. [Figure 7]FIG. 7 is a block diagram showing a high-frequency induction heating device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] <First embodiment> First, the power supply device according to this embodiment will be described in brief. FIG. 1 is a block diagram showing a power supply device according to the present embodiment. The power supply device 1 according to this embodiment is, for example, a power supply for an induction heating device.

[0009] As shown in Fig. 1, the power supply device 1 according to this embodiment is provided with a converter section 50, a power storage element section 60, and an inverter section 70. An AC current I0 is input to the power supply device 1 from outside the power supply device 1. The AC current I0 is, for example, a current derived from a commercial power source. The AC current I0 may be a three-phase current or a single-phase current. The AC current I0 is input to the converter section 50 of the power supply device 1.

[0010] The converter unit 50 converts the AC current I0 into a DC current I1. The configuration of the converter unit 50 is not particularly limited. For example, the converter unit 50 may be configured with a diode, a thyristor, or other electronic components.

[0011] The DC current I1 output from the converter section 50 is input to the storage element section 60. When no output is required, the storage element section 60 charges the storage element 10 with the DC current I1. When output is required, the storage element section 60 outputs the DC current I1 as is, or combines the DC current I1 with the DC current I2 output from the storage element 10 and outputs the result. In other words, when the output of the power supply device 1 is DC current I3, I3=I1+I2. The DC current I2 may be zero.

[0012] The DC current I3 output from the power storage element unit 60 is input to the inverter unit 70. The inverter unit 70 converts the DC current I3 into an AC current I4 and outputs it. The configuration of the inverter unit 70 is not particularly limited. For example, it may be configured with a full bridge circuit made up of four power semiconductors, or may be configured with other circuits. As described above, the power supply device 1 receives an AC current I0 as input and outputs an AC current I4.

[0013] Next, the power storage element section 60 will be described in detail. FIG. 2 is a circuit diagram showing the power storage element section of the power supply device according to this embodiment. As shown in FIG. 2, the energy storage element section 60 includes an energy storage element 10, a first wiring 11, a second wiring 12, a third wiring 13, a first switching element 21, a second switching element 22, a third switching element 23, a fourth switching element 24, a first reactor 31, a second reactor 32, and a freewheel diode 40.

[0014] The first switching element 21, the second switching element 22, the third switching element 23, and the fourth switching element 24 are power semiconductors. In Fig. 2, the symbol R denotes a load to which an AC current I4 is input from the power supply device 1.

[0015] A positive electrode potential is applied to the first wiring 11 from the converter unit 50, and a negative electrode potential is applied to the second wiring 12 from the converter unit 50. As a result, a direct current I1 is input from the converter unit 50 to the first wiring 11 and the second wiring 12. The first wiring 11, the first switching element 21, the third wiring 13, the fourth switching element 24, and the second reactor 32 are connected in series in this order from the positive electrode of the converter unit 50 toward the positive electrode of the load R. The second wiring 12 is connected from the negative electrode of the converter unit 50 to the negative electrode of the load R.

[0016] The second switching element 22, the third switching element 23, the first reactor 31, and the energy storage element 10 are connected in series in this order from the third wiring 13 toward the second wiring 12. In addition, a freewheel diode 40 is connected between the second wiring 12 and the third wiring 13. The anode of the freewheel diode 40 is connected to the second wiring 12, and the cathode of the freewheel diode 40 is connected to the third wiring 13. The freewheel diode 40, the second reactor 32, and the load R form a loop-shaped current path via the inverter unit 70.

[0017] The positive electrode of the energy storage element 10 is connected to the first reactor 31 , and the negative electrode of the energy storage element 10 is connected to the second wiring 12 . The energy storage element is an element that has at least a pair of electrodes and an electrolyte and has a function of being capable of repeated charging and discharging. The energy storage element may be a power storage device, and one cell may be a power storage device or a battery cell. Alternatively, one cell may be a battery pack.

[0018] Examples of the storage element include secondary batteries such as lithium ion secondary batteries, lead storage batteries, lithium ion polymer secondary batteries, nickel hydrogen storage batteries, nickel cadmium storage batteries, nickel iron storage batteries, nickel-zinc storage batteries, and silver oxide-zinc storage batteries, liquid circulation type secondary batteries such as redox flow batteries, zinc-chlorine batteries, and zinc-bromine batteries, mechanical charge type secondary batteries such as aluminum-air batteries, air-zinc batteries, and air-iron batteries, and high temperature operation type secondary batteries such as sodium-sulfur batteries and lithium-iron sulfide batteries. The storage element may be replaced with or used in combination with a capacitor with high capacity density such as an electric double layer capacitor or a lithium ion capacitor.

[0019] In the first switching element 21, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) section 21m and a diode section 21d are connected in anti-parallel. The MOSFET section 21m controls the current flowing from the first wiring 11 to the third wiring 13. The diode section 21d allows a current to flow from the third wiring 13 to the first wiring 11, but does not allow a current to flow from the first wiring 11 to the third wiring 13.

[0020] In the first switching element 21, the MOSFET section 21m and the diode section 21d are configured as an integral part and do not exist physically independent. The "MOSFET section 21m" and the "diode section 21d" are expedient concepts used when expressing the function of the first switching element 21 in a circuit diagram. In the first switching element 21, even if the MOSFET section 21m is off, a reverse current can flow through the diode section 21d. The same is true for the second switching element 22, the third switching element 23, and the fourth switching element 24.

[0021] In the second switching element 22, a MOSFET section 22m and a diode section 22d are connected in inverse parallel. The MOSFET section 22m controls the current flowing from the third wiring 13 to the third switching element 23. The diode section 22d allows a current to flow from the third switching element 23 to the third wiring 13, but does not allow a current to flow from the third wiring 13 to the third switching element 23. In other words, the second switching element 22 controls the on / off of the current flowing from the third wiring 13 to the third switching element 23, and allows a current to flow from the third switching element 23 to the third wiring 13 unconditionally.

[0022] In the third switching element 23, a MOSFET section 23m and a diode section 23d are connected in anti-parallel. The MOSFET section 23m controls the current flowing from the first reactor 31 to the second switching element 22. The diode section 23d allows a current to flow from the second switching element 22 to the first reactor 31, but does not allow a current to flow from the first reactor 31 to the second switching element 22. In other words, the third switching element 23 controls the on / off of the current flowing from the first reactor 31 to the second switching element 22, and allows a current to flow from the second switching element 22 to the first reactor 31 unconditionally.

[0023] In the fourth switching element 24, a MOSFET section 24m and a diode section 24d are connected in anti-parallel. The MOSFET section 24m controls the current flowing from the third wiring 13 to the load R. The diode section 24d allows a current to flow from the load R to the third wiring 13, but does not allow a current to flow from the third wiring 13 to the load R. In other words, the fourth switching element 24 controls the on / off of the current flowing from the third wiring 13 to the load R, and allows a current to flow unconditionally from the load R to the third wiring 13.

[0024] The first reactor 31 is connected between the third switching element 23 and the energy storage element 10, and smoothes the current flowing therebetween by its self-inductance. The second reactor 32 is connected between the fourth switching element 24 and the load R, and smoothes the current flowing therebetween by its self-inductance.

[0025] Next, the operation of the power supply device according to this embodiment will be described. FIG. 3 is a timing chart showing the operation of the power supply device according to this embodiment, with the horizontal axis representing time and the vertical axis representing output current. In addition, in Figure 3, the rated value I 0-MAX is shown by a dashed line. FIG. 4 is a circuit diagram showing the operation of the power supply device during the charging period. FIG. 5 is a circuit diagram showing the operation of the power supply device during an output period without limiter operation. FIG. 6 is a circuit diagram showing the operation of the power supply device during an output period with limiter operation.

[0026] The limiter operation is when the current flowing through the first switching element 21 exceeds the rated value I 0-MAX When the current flowing through the first switching element 21 is about to exceed the rated value I 0-MAX This operation limits the power receiving capacity so that it does not exceed 100%. This allows the power receiving capacity to be controlled and reduced.

[0027] 3, when the power supply device 1 operates, a charging period T1, an output period T2 without limiter operation, and an output period T3 with limiter operation are realized in response to a request from the load R. Table 1 shows the states of the switching elements 21-24 in each of the periods T1-T3. Note that in the following explanation, only the current flowing from the positive electrode of the converter unit 50 to the positive electrode of the storage element 10 or the positive electrode of the load R will be explained.

[0028] [Table 1]

[0029] In the charging period T1, the output current required by the load R is zero. At this time, the first switching element 21 is "on" (conducting), the second switching element 22 is "PWM" (pulse width control), the third switching element 23 is "off" (non-conducting), and the fourth switching element 24 is also "off." Note that "pulse width control" is a method of controlling the magnitude of the overall current by repeating a conductive period and a non-conducting period at a constant cycle and controlling the ratio between the time width of the conductive period and the time width of the non-conducting period.

[0030] As a result, as shown in Fig. 4, the DC current I1 input from the converter unit 50 flows into the energy storage element 10 via the MOSFET unit 21m of the first switching element 21, the MOSFET unit 22m of the second switching element 22, the diode unit 23d of the third switching element 23, and the first reactor 31. In addition, the amount of current flowing into the energy storage element 10 is controlled by the PWM of the second switching element 22. The current that has been made into a pulsating current by the PWM of the second switching element 22 is smoothed by the first reactor 31. In this manner, the energy storage element 10 is charged. At this time, the energy storage element unit 60 does not output a current to the inverter 70.

[0031] During the output period T2 when the limiter is not operating, the rated input current I 0-MAX The following output current is required. At this time, the first switching element 21 is set to "on", the second switching element 22 is set to "off", the third switching element 23 is also set to "off", and the fourth switching element 24 is set to "PWM".

[0032] 5, the energy storage element 10 is separated from the current path, and the DC current I1 input from the converter unit 50 is supplied to the inverter unit 70 via the MOSFET unit 21m of the first switching element 21, the MOSFET unit 24m of the fourth switching element 24, and the second reactor 32. The amount of current flowing to the inverter unit 70 is controlled by PWM of the fourth switching element 24. The inverter 70 converts the DC current I1 into an AC current I4 and supplies it to the load R. In this way, during the period T2, the entire output current of the power supply device 1 is supplied by power supplied from outside, and the energy storage element 10 is not charged or discharged.

[0033] During the output period T3 with the limiter operating, the rated input current I 0-MAX At this time, the first switching element 21 is set to "PWM", the second switching element 22 is set to "OFF", the third switching element 23 is set to "ON", and the fourth switching element 24 is set to "PWM".

[0034] 6, the DC current I2 discharged from the energy storage element 10 is supplied to the inverter unit 70 via the first reactor 31, the MOSFET unit 23m of the third switching element 23, the diode unit 22d of the second switching element 22, the MOSFET unit 24m of the fourth switching element 24, and the second reactor 32. In addition, the DC current I1 input from the converter unit 50 is supplied to the inverter unit 70 via the MOSFET unit 21m of the first switching element 21, the MOSFET unit 24m of the fourth switching element 24, and the second reactor 32.

[0035] As a result, the DC current I3 obtained by combining the DC current I2 output from the energy storage element 10 and the DC current I1 input from the converter unit 50 is output to the inverter unit 70. At this time, the amount of current supplied to the inverter unit 70 is controlled by the PWM of the fourth switching element 24. The current made into a pulsating current by the PWM of the fourth switching element 24 is smoothed by the second reactor 32. In addition, the DC current I1 is smoothed to a rated value I 0-MAX This controls the converter 50 to the rated value I 0-MAX It is possible to avoid flowing a current exceeding 100%. The inverter 70 converts the DC current I3 output from the energy storage element unit 60 into an AC current I4 and supplies it to the load R. In this manner, during the period T3, the output current required by the load R is realized by using both the external power supply means and the energy storage element 10.

[0036] Further, the return current of the load R flows from the second wiring 12 through the inverter unit 70 and the freewheel diode 40 to the third wiring 13.

[0037] Next, the effects of this embodiment will be described. According to this embodiment, by providing the power storage element 10 in the power supply device 1, it is possible to realize the required output current by using both the external power supply means and the power storage element 10. As a result, the rated value I 0-MAXcan be made smaller than the maximum value of the output current, thereby reducing the capacity and cost of the power receiving equipment. For example, when the AC current I0 is generated by a commercial power source, the rated value of the commercial power source can be reduced.

[0038] Furthermore, according to this embodiment, by controlling each switching element, the storage element 10 is charged in the charging period T1, and discharged in the output period T3 with the limiter operating, but the storage element 10 is not charged or discharged in the output period T2 without the limiter operating. This reduces the number of times the storage element 10 is discharged, and deterioration of the storage element 10 can be suppressed.

[0039] Furthermore, according to this embodiment, when charging the energy storage element 10 during the charging period T1, the second switching element 22 is set to "PWM", so that the current flowing into the energy storage element 10 can be controlled and overload charging does not occur. In addition, the current that has been made into a pulsating current by the PWM of the second switching element 22 can be smoothed by the first reactor 31. This also makes it possible to suppress deterioration of the energy storage element 10.

[0040] Furthermore, in this embodiment, when the current required by the load R can be supplemented by only the DC current I1 from the converter 50, the discharge of the storage element 10 is stopped. On the other hand, the storage element 10 is discharged only when the DC current I1 from the converter 50 is insufficient to meet the current required by the load R. Therefore, the discharge current from the storage element 10 can also be reduced.

[0041] <Second embodiment> The second embodiment is an example in which the power supply device 1 according to the first embodiment is used as a power supply for a high-frequency induction heating device. High frequency refers to a frequency of, for example, 1 kHz or higher. FIG. 7 is a block diagram showing the high-frequency induction heating device according to this embodiment.

[0042] 7, the high-frequency induction heating device 100 according to this embodiment is provided with a power supply device 1, a matching device 103, a transformer 104, and a coil 105. The coil 105 is disposed near the workpiece 200.

[0043] The configuration of the power supply device 1 is as described in the first embodiment. That is, the power supply device 1 is provided with a converter unit 50, a power storage element unit 60, and an inverter unit 70. A matching device 103, a transformer 104, and a coil 105 correspond to a load R shown in FIG.

[0044] An AC current I0 is input from the outside to the converter section 50 of the power supply device 1. The AC current I0 is supplied from a commercial power source, for example. The converter section 50 converts the AC current I0 into a DC current I1 and outputs it to the first wiring 11 and the second wiring 12 of the storage element section 60. The inverter section 70 receives a DC current I3 from the storage element section 60, converts it to an AC current I4, and outputs it. The frequency of the AC current I4 is 1 kHz or higher.

[0045] An AC current I4 is input to the matching box 103. The matching box 103 is matched to the AC current I4 and passes the AC current I4. A matching capacitor for resonance is also provided in the matching box 103, and the AC current I4 flows at a resonance frequency determined by the matching capacitor and the coil 105. The output current of the matching box 103 is input to the transformer 104, which converts the voltage and current of the input current and outputs it to the coil 105. The coil 105 inductively heats the workpiece 200.

[0046] In the high-frequency induction heating device 100, a large current output is required in a short time. For example, after a part of the workpiece 200 is heated by outputting 1000 kW of power for 0.2 to 0.3 seconds, the workpiece 200 is moved relative to the coil 105, and another part of the workpiece 200 is heated by outputting 1000 kW of power for 0.2 to 0.3 seconds. When the workpiece 200 is heated, the power supply device 1 uses a direct current I1 input from the converter unit 50 and a direct current I2 discharged from the storage element 10 of the storage element unit 60 in combination. When the workpiece 200 is moved, the output of the power supply device 1 is stopped. The time required to move the workpiece 200 is, for example, 10 to 20 seconds. In this way, when the power supply device 1 is used as a power source for the high-frequency induction heating device 100, the charging period T1 shown in FIG. 3 is 10 to 20 seconds, and the output period T3 with the limiter operation is 0.2 to 0.3 seconds. That is, the output period T3 with the limiter operating is extremely short compared to the charging period T1.

[0047] It is preferable to use a lithium ion capacitor as the energy storage element 10. Although the lithium ion capacitor has a smaller capacity than a lithium ion battery, it can instantly discharge a large current. For example, the energy storage element 10 can be configured by connecting multiple lithium ion capacitors in parallel.

[0048] According to this embodiment, by using a lithium ion capacitor for the energy storage element 10, a power supply device suitable for the high frequency induction heating device 100 can be realized. Also, as described in the first embodiment, the rated value of the commercial power source used for the high frequency induction heating device 100 can be reduced. This allows a significant reduction in the power receiving capacity. Furthermore, deterioration of the energy storage element 10 can be suppressed. Other configurations, operations, and effects of this embodiment are similar to those of the first embodiment described above.

[0049] The above-described embodiments are examples of the present invention, and the present invention is not limited to these embodiments. For example, the present invention also includes embodiments in which some components are added, deleted, or modified in the above-described embodiments.

[0050] For example, in Fig. 2, an example is shown in which the first switching element 21, the fourth switching element 24, and the second reactor 32 are connected to the positive electrode of the converter unit 50, but this is not limiting, and at least one element may be connected to the negative electrode of the converter unit 50. Also, in Fig. 2, an example is shown in which the second switching element 22, the third switching element 23, the first reactor 31, and the storage element 10 are connected in this order from the positive electrode side to the negative electrode side, but this is not limiting. These elements may be connected in any order as long as they are connected in series.

[0051] Further, in each of the above-described embodiments, an example has been shown in which the power supply device is used as a power source for an induction heating device, but the present invention is not limited to this, and the power supply device may be used for any purpose.

[0052] The present invention includes the following aspects.

[0053] (Appendix 1) a first wiring and a second wiring for receiving a direct current; The third wiring, a first switching element that controls a current flowing between the first wiring and the third wiring; an energy storage element connected to one of the second wiring and the third wiring; a second switching element that causes a current to flow from the storage element to the other of the second wiring and the third wiring and controls the current flowing from the other wiring to the storage element; a third switching element connected in series to the second switching element, causing a current to flow from the other wiring to the storage element and controlling a current flowing from the storage element to the other wiring; A power supply unit comprising:

[0054] (Appendix 2) 2. The power supply device according to claim 1, further comprising a first reactor connected between the storage element and the second switching element.

[0055] (Appendix 3) 3. The power supply device according to claim 1, further comprising a fourth switching element that controls a current flowing between the third wiring and a load.

[0056] (Appendix 4) 4. The power supply device according to claim 3, further comprising a second reactor connected between the fourth switching element and the load.

[0057] (Appendix 5) 5. The power supply device according to claim 1, wherein the power storage element is a lithium ion capacitor.

[0058] (Appendix 6) a first period in which the first switching element is turned on, the second switching element is pulse-width controlled, and the third switching element is turned off; a second period in which the first switching element is turned on, the second switching element is turned off, and the third switching element is turned off; a third period in which the first switching element is pulse-width controlled, the second switching element is turned off, and the third switching element is turned on; 6. The power supply device according to claim 1, which achieves the above object.

[0059] (Appendix 7) Further, a fourth switching element is provided to control a current flowing between the third wiring and a load. In the first period, the fourth switching element is turned off; In the second period, the fourth switching element is subjected to pulse width control, 7. The power supply device according to claim 6, wherein in the third period, the fourth switching element is subjected to pulse width control.

[0060] (Appendix 8) a converter unit that outputs the DC current to the first wiring and the second wiring; an inverter unit that converts a direct current input from the first wiring and the third wiring into an alternating current and outputs the alternating current to the load; 2. The power supply device of claim 1, further comprising:

[0061] (Appendix 9) 9. The power supply device according to any one of claims 1 to 8, which is a power supply for a high-frequency induction heating device. [Explanation of symbols]

[0062] 1 Power supply 10 Energy storage element 11 1st wiring 12 2nd wiring 13 Third wiring 21 First switching element 21m MOSFET section 21d Diode section 22 Second switching element 22m MOSFET section 22d Diode section 23 Third switching element 23m MOSFET section 23d Diode section 24 Fourth switching element 24m MOSFET section 24d Diode section 31 First reactor 32 Second reactor 40 Freewheeling Diode 50 Converter section 60 Storage element section 70 Inverter section 100 High frequency induction heating device 103 Matching box 104 Transformer 105 Coil 200 Work I0 alternating current I1 DC current I2 DC current I3 DC current I4 alternating current I 0-MAX Rated value R load T1 Charging Period T2 Output period without limiter operation T3 Output period with limiter operation

Claims

1. a first wiring and a second wiring to which a direct current is input; A third wiring; a first switching element that controls a current flowing between the first wiring and the third wiring; an energy storage element connected to one of the second wiring and the third wiring; a second switching element that causes a current to flow from the storage element to the other of the second wiring and the third wiring and controls the current flowing from the other wiring to the storage element; a third switching element connected in series to the second switching element, for causing a current to flow from the other wiring to the storage element and for controlling a current flowing from the storage element to the other wiring; A power supply unit comprising:

2. The power supply device according to claim 1 , further comprising a first reactor connected between the storage element and the second switching element.

3. The power supply device according to claim 1 , further comprising a fourth switching element that controls a current flowing between the third wiring and a load.

4. The power supply device according to claim 3 , further comprising a second reactor connected between the fourth switching element and the load.

5. 2. The power supply device according to claim 1, wherein the power storage element is a lithium ion capacitor.

6. a first period in which the first switching element is turned on, the second switching element is pulse-width controlled, and the third switching element is turned off; a second period in which the first switching element is turned on, the second switching element is turned off, and the third switching element is turned off; a third period in which the first switching element is pulse-width controlled, the second switching element is turned off, and the third switching element is turned on; The power supply device according to claim 1 .

7. a fourth switching element that controls a current flowing between the third wiring and a load; In the first period, the fourth switching element is turned off; In the second period, the fourth switching element is subjected to pulse width control, The power supply device according to claim 6 , wherein in the third period, the fourth switching element is subjected to pulse width control.

8. a converter unit that outputs the DC current to the first wiring and the second wiring; an inverter unit that converts a direct current input from the first wiring and the third wiring into an alternating current and outputs the alternating current to the load; The power supply device of claim 1 further comprising:

9. 9. The power supply device according to claim 1, which is a power supply for a high-frequency induction heating device.

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