POWER FACTOR IMPROVING CONVERTER, AND POWER SUPPLY DEVICE INCLUDING POWER FACTOR IMPROVING CONVERTER

Abstract

Provided are a plurality of circuit blocks each including: a first series circuit including a first rectifying element and a first switching element which are connected in series; a second series circuit including a second rectifying element and a second switching element which are connected in series; and a capacitor, wherein output terminals are connected to both ends of the first series circuit, both ends of the second series circuit, and both ends of the capacitor. Input terminals of the respective circuit blocks are connected in series. An AC power source is connected thereto via a choke, thereby solving the problem.

Claims

1. A power factor improving converter comprising: a plurality of circuit blocks each including a first series circuit including a first rectifying element and a first switching element which are connected in series, a second series circuit including a second rectifying element and a second switching element which are connected in series, and a capacitor wherein one input terminal is connected to a connecting point of the first rectifying element and the first switching element, an other input terminal is connected to a connecting point of the second rectifying element and the second switching element, and output terminals are connected to both ends of the first series circuit, both ends of the second series circuits, and both ends of the capacitor; at least one choke inserted into a series circuit formed by connecting the other input terminal and the one input terminal of adjacent ones of the plurality of circuit blocks; a plurality of loads each connected to output terminals of one of the plurality of circuit blocks; and an AC power supply connected to the series circuit including the at least one choke inserted and formed by connecting the other input terminal and the one input terminal of the adjacent ones of the plurality of circuit blocks.

2. The power factor improving converter according to claim 1, wherein the first switching element and the second rectifying element are replaced with each other.

3. The power factor improving converter according to claim 1, wherein the first rectifying element is replaced with a third switching element, and the second rectifying element is replaced with a fourth switching element.

4. The power factor improving converter according to claim 1, wherein a MOSFET are used as the switching element.

5. The power factor improving converter according to claim 1, wherein a parallel connection circuit including an IGBT and a rectifying element is used as the switching element.

6. A power supply device comprising: a power factor improving converter including: a plurality of circuit blocks each including a first series circuit including a first rectifying element and a first switching element which are connected in series, a second series circuit including a second rectifying element and a second switching element which are connected in series, and a capacitor wherein one input terminal is connected to a connecting point of the first rectifying element and the first switching element, an other input terminal is connected to a connecting point of the second rectifying element and the second switching element, and output terminals are connected to both ends of the first series circuit, both ends of the second series circuits, and both ends of the capacitor; at least one choke inserted into a series circuit formed by connecting the other input terminal and the one input terminal of adjacent ones of the plurality of circuit blocks; a plurality of loads each connected to output terminals of one of the plurality of circuit blocks; and an AC power supply connected to the series circuit including the at least one choke inserted and formed by connecting the other input terminal and the one input terminal of the adjacent ones of the plurality of circuit blocks; and a plurality of isolated converters including, as the plurality of loads, a plurality of primary circuits each connected to the output terminals of one of the plurality of circuit blocks, wherein DC outputs, on a secondary side, of respective ones of the plurality of isolated converters are connected to each other.

7. The power supply device according to claim 6, wherein each of the plurality of isolated converters is operated by shifting respective phases thereof from each other.

8. A power supply device comprising: a power factor improving converter including: a plurality of circuit blocks each including a first series circuit including a first rectifying element and a first switching element which are connected in series, a second series circuit including a second rectifying element and a second switching element which are connected in series, and a capacitor wherein one input terminal is connected to a connecting point of the first rectifying element and the first switching element, an other input terminal is connected to a connecting point of the second rectifying element and the second switching element, and output terminals are connected to both ends of the first series circuit, both ends of the second series circuits, and both ends of the capacitor; at least one choke inserted into a series circuit formed by connecting the other input terminal and the one input terminal of adjacent ones of the plurality of circuit blocks; a plurality of loads each connected to output terminals of one of the plurality of circuit blocks; and an AC power supply connected to the series circuit including the at least one choke inserted and formed by connecting the other input terminal and the one input terminal of the adjacent ones of the plurality of circuit blocks; and a plurality of isolated converter including, as the plurality of loads, a plurality of primary circuits each connected to the output terminals of one of the plurality of circuit blocks, wherein secondary windings of transformers of respective ones of the plurality of isolated converters are connected in series, and a series circuit including the secondary windings are connected to a rectifying and smoothing circuit.

9. The power supply device according to claim 8, wherein each of the plurality of primary circuits of the plurality of isolated converters includes: a converter configured to convert a DC voltage into an AC pulse voltage; a resonant circuit connected to the converter; and the primary winding of the transformer connected to the resonant circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows one example of an n-level power factor improving converter of the present invention.

[0026] FIG. 2 shows one example of a 3-level power factor improving converter of the present invention.

[0027] FIG. 3 shows an equivalent circuit of FIG. 2 focusing on a change in voltage of a choke.

[0028] FIG. 4 shows a waveform of a current of a choke of a conventional circuit.

[0029] FIG. 5 shows a waveform of a current of a choke of the present invention.

[0030] FIG. 6 shows a waveform of a voltage of the choke of the conventional circuit.

[0031] FIG. 7 shows a waveform of a voltage of the choke of the present invention.

[0032] FIG. 8 shows a choke current waveform and a choke voltage waveform of the conventional circuit.

[0033] FIG. 9 shows a choke current waveform and a choke voltage waveform of the present invention.

[0034] FIG. 10 shows an example of a 4-level power factor improving converter of the present invention.

[0035] FIG. 11 shows an equivalent circuit of FIG. 10 focusing on a change in voltage of the choke.

[0036] FIG. 12 shows an example where an isolated converter is connected as a load of FIG. 2.

[0037] FIG. 13 shows an example where an isolated converter is connected as the load of FIG. 2.

[0038] FIG. 14 shows an example where an isolated converter is connected as the load of FIG. 2.

[0039] FIG. 15 shows a circuit diagram of a conventional power factor improving converter.

[0040] FIG. 16 shows an equivalent circuit of FIGS. 15, 17, 18, and 19 focusing on a change in voltage of the choke.

[0041] FIG. 17 shows a circuit diagram of a conventional power factor improving converter.

[0042] FIG. 18 shows a circuit diagram of a conventional power factor improving converter.

[0043] FIG. 19 shows a circuit diagram of a conventional power factor improving converter.

MODE FOR CARRYING OUT THE INVENTION

[0044] A mode for carrying out the present invention is apparent if the following description of preferred examples is read with reference to the accompanying drawings. However, the drawings are exclusively for the illustration purpose and do not limit the technical scope of the present invention.

[0045] An n-level power factor improving converter of the present invention (n is an integer of 3 or more) includes an AC power supply 1, a choke 2, (n−1) circuit blocks 5, and loads 3 each connected to output terminals of one of the circuit blocks 5, as shown in FIG. 1.

[0046] Each circuit block 5 includes a first series circuit including a diode 11 and a MOSFET 31, a second series circuit including a diode 12 and a MOSFET 32, and a capacitor 51. A drain of the MOSFET 31 and an anode of the diode 11 are connected, and a drain of the MOSFET 32 and an anode of the diode 12 are connected. One input terminal is connected to a connecting point of the diode 11 and the MOSFET 31, and the other input terminal is connected to a connecting point of the diode 12 and the MOSFET 32. A cathode of the diode 11 and a cathode of the diode 12 are connected to one end of the capacitor 51, a source of the MOSFET 31 and a source of the MOSFET 32 are connected to the other end of the capacitor 51, and further each load 3 is connected via the output terminals to both ends of the capacitor 51.

[0047] The input terminals of the respective circuit blocks 5 are connected in series. Specifically, the AC power supply 1 is connected via the choke 2 between one input terminal of the first circuit block 5 and the other input terminal of the (n−1)-th circuit block 5. The other input terminal and one input terminal of the adjacent circuit blocks 5 are connected. For example, the other input terminal of the first circuit block 5 and one input terminal of the second circuit block 5 are connected. Here, “adjacent” need not be “physically adjacent” and “formally adjacent” suffices.

[0048] In the mode for carrying out the present invention and later-described examples, description is given with respect only to the configuration that the circuit block 5 includes the first series circuit including the diode 11 and the MOSFET 31, the second series circuit including the diode 12 and the MOSFET 32, and the capacitor 51, wherein the drain of the MOSFET 31 and the anode of the diode 11 are connected, and the drain of the MOSFET 32 and the anode of the diode 12 are connected.

[0049] However, without being limited thereto, for example, a configuration may be such that the cathode of the diode 11 and the source of the MOSFET 31 are connected, and the cathode of the diode 12 and the source of the MOSFET 32 are connected. In this case, the drain of the MOSFET 31 and the drain of the MOSFET 32 are connected to the other end of capacitor 51, and the anode of the diode 11 and the anode of the diode 12 are connected to one end of the capacitor 51.

[0050] Additionally, a configuration may be such that the first series circuit is a series circuit including two diodes, and the second series circuit is a series circuit including two MOSFETs. Further, a configuration may be such that both the first series circuit and the second series circuit are series circuits each including two MOSFETs.

Example 1

Configuration of Example 1

[0051] FIG. 2 shows an example of the present invention where the number of levels n is 3. This converter includes the AC power source 1, the choke 2, the two circuit blocks 5, and the loads 3 each connected to the output terminals of one of the circuit blocks 5.

[0052] Each circuit block 5 includes the first series circuit including the diode 11 and the MOSFET 31, the second series circuit including the diode 12 and the MOSFET 32, and the capacitor 51. The drain of the MOSFET 31 and the anode of the diode 11 are connected, and the drain of the MOSFET 32 and the anode of the diode 12 are connected. One input terminal is connected to the connecting point of the diode 11 and the MOSFET 31, and the other input terminal is connected to the connecting point of the diode 12 and the MOSFET 32. The cathode of the diode 11 and the cathode of the diode 12 are connected to one end of the capacitor 51, the source of the MOSFET 31 and the source of the MOSFET 32 are connected to the other end of the capacitor 51, and further each load 3 is connected via the output terminals to both ends of the capacitor 51.

[0053] The input terminals of the first circuit block 5 and the input terminals of the second circuit block 5 are connected in series. Specifically, the AC power supply 1 is connected via the choke 2 between one input terminal of the first circuit block 5 and the other input terminal of the second circuit block 5. Additionally, the other input terminal of the first circuit block 5 and one input terminal of the second circuit block 5 are connected.

Operation of Example 1

[0054] In the thus-configured power factor improving converter of Example 1, an output voltage of each circuit block 5 is assumed to be controlled to be Vo/2. Since the configuration of each circuit block 5 is similar to that of the circuit of FIG. 18, the voltage between the input terminals of each circuit block 5 is selectable from the states of 0 and ±Vo/2 by on-off of the MOSFETs 31 and 32. Since the input terminals of each circuit block 5 are connected in series, as a whole, the voltage is selectable from the states of 0, ±Vo/2, and ±Vo.

[0055] Accordingly, an equivalent circuit of FIG. 2 focusing on a change in voltage of the choke 2 will be a circuit shown in FIG. 3. This is the same as shown in FIG. 16, as a circuit, but values of the variable voltage source 4 differ therefrom such that coefficients of the voltage Vo include not only 0 and 1, but also newly-added ½. It is referred to as a “three-level” because there are such three voltage levels.

[0056] Thus, the coefficients of the voltage Vo including not only 0 and 1, but also newly-added ½, thereby enabling a reduction in voltage applied to the choke 2. For example, it is preferable that 0 and ½ are selected when the instantaneous value of the AC power supply 1 is low, while ½ and 1 are selected when the instantaneous value of the AC power supply 1 is high.

[0057] Additionally, the switching of the voltage between the input terminals is performed by shifting the phase, thereby enabling an increase in apparent frequency for the choke 2.

[0058] For example, when 0 and ½ are selected, it is preferable to switch, as follows. [0059] First circuit block: 0 Second circuit block 2: 0 [0060] First circuit block: ½ Second circuit block 2: 0 [0061] First circuit block: 0 Second circuit block 2: 0 [0062] First circuit block: 0 Second circuit block 2: ½ Although each circuit block 5 is subject to the switching once, switching as a whole is performed twice such as 0, ½, 0, ½.

[0063] Accordingly, the inductance required to achieve the same ripple current decreases.

[0064] A waveform of a current of the choke 2 of the conventional circuit is shown in FIG. 4, while a waveform of a current of the choke 2 of Example 1 is shown in FIG. 5. The current waveform shown here is a simulation result in a case where the input voltage is 240V, the output voltage is 400V (each 200V in Example 1), the load resistance is 24Ω ohms (each 12Ω in Example 1), and the switching frequency is 90 kHz. The difference is the inductance of the choke which is 100 μH in the conventional circuit, and 25 μH in Example 1.

[0065] Although both the current waveform shown in FIG. 4 and the current waveform shown FIG. 5 are displayed at 20 A/div and 2 msec/div, it is understandable that both indicate substantially the same ripple current despite the difference in inductance. In this example, the inductance was reduced to ¼, thus enabling substantial miniaturization of the choke.

[0066] A waveform of a voltage of the choke 2 of the conventional circuit is shown in FIG. 6, while the waveform of a voltage of the choke 2 of Example 1 is shown in FIG. 7. In the conventional circuit, the input voltage and (input voltage−output voltage) are applied to the choke 2, so that the voltage of ±400V is applied at the maximum. On the other hand, in Example 1, the input voltage and (input voltage−the output voltage÷2) are applied when the input voltage is low, while (input voltage−output voltage÷2) and (input voltage−the output voltage) are applied when the input voltage is high, so that the voltage is suppressed to ±200V.

[0067] Waveforms obtained by enlarging the waveforms shown in FIGS. 4, 5, 6, and 7 from 6 msec by 2 switching cycles are shown in FIG. 8 and FIG. 9. FIG. 8 is a waveform of the conventional circuit where the applied voltage is high, and there is a change in voltage once per cycle. On the other hand, FIG. 9 is a waveform of Example 1 where the applied voltage is kept low, there are changes in voltage twice in one cycle. Thus, as a choke, the applied voltage decreases and the frequency increases, and therefore the inductance required to achieve the same ripple current decreases.

[0068] Additionally, since the voltage of Vo/2 is applied to each of the MOSFETs 31 and 32, dV of Equation 1 becomes ±Vo/2, and the common mode current becomes ½ of that of the conventional circuit. Accordingly, it is possible to reduce more common mode noise than the conventional circuit can, thereby enabling the miniaturization of the noise filter.

Effect of Example 1

[0069] By the above action, it is possible to, by use of the circuit of the present invention, miniaturize the choke and also miniaturize the noise filter.

Example 2

Configuration of Example 2

[0070] FIG. 10 shows an example of the present invention where the number of levels n is 4. This converter includes the AC power source 1, the choke 2, the three circuit blocks 5, and the loads 3 each connected to the output terminals of one of the circuit blocks 5.

[0071] Each circuit block 5 includes the first series circuit including the diode 11 and the MOSFET 31, the second series circuit including the diode 12 and the MOSFET 32, and the capacitor 51. The drain of the MOSFET 31 and the anode of the diode 11 are connected, and the drain of the MOSFET 32 and the anode of the diode 12 are connected. One input terminal is connected to the connecting point of the diode 11 and the MOSFET 31, and the other input terminal is connected to the connecting point of the diode 12 and the MOSFET 32. The cathode of the diode 11 and the cathode of the diode 12 are connected to one end of the capacitor 51, while the source of the MOSFET 31 and the source of the MOSFET 32 are connected to the other end of the capacitor 51, and further each load 3 is connected via the output terminals to both ends of the capacitor 51.

[0072] The input terminals of the three circuit blocks 5 are connected in series. Specifically, the AC power supply 1 is connected via the choke 2 between one input terminal of the first circuit block 5 and the other input terminal of the third circuit block 5. Additionally, the other input terminal of the first circuit block 5 and one input terminal of the second circuit block 5 are connected. Further, the other input terminal of the second circuit block 5 and one input terminal of the third circuit block 5 are connected.

Operation of Example 2

[0073] In the thus-configured power factor improving converter of Example 2, an output voltage of each circuit block 5 is assumed to be controlled to be Vo/3. Since the configuration of each circuit block 5 is similar to that of the circuit of FIG. 18, the voltage between the input terminals of each circuit block 5 is selectable from the states of 0 and ±Vo/3 by on-off of the MOSFETs 31 and 32. Since the input terminals of each circuit block 5 are connected in series, as a whole, the voltage is selectable from the states of 0, ±Vo/3, ±Vo×⅔, and ±Vo.

[0074] Accordingly, an equivalent circuit of the circuit shown in FIG. 10 focusing on a change in voltage of the choke 2 will be a circuit shown in FIG. 11. This is the same as the circuit shown in FIG. 16, as a circuit, but values of the variable voltage source 4 differ therefrom such that coefficients of the voltage Vo include not only 0 and 1, but also newly-added ⅓ and ⅔. It is referred to as a “four-level” because there are such four voltage levels.

[0075] Thus, the coefficients of the voltage Vo including not only 0 and 1, but also newly-added ⅓ and ⅔, thereby enabling a reduction in voltage applied to the choke. For example, it is preferable that 0 and ⅓ are selected when the instantaneous value of the AC power supply 1 is low, while ⅓ and ⅔ are selected when the instantaneous value of the AC power supply 1 is mediate, while ⅔ and 1 are selected when the instantaneous value of the AC power supply 1 is high.

[0076] Additionally, the switching of the voltage between the input terminals is performed by shifting the phase, thereby enabling an increase in apparent frequency for the choke 2.

[0077] For example, when 0 and ⅓ are selected, it is preferable to switch, as follows.

TABLE-US-00001 First circuit block: 0 Second circuit block: 0 Third circuit block: 0 First circuit block: ⅓ Second circuit block: 0 Third circuit block: 0 First circuit block: 0 Second circuit block: 0 Third circuit block: 0 First circuit block: 0 Second circuit block: ⅓ Third circuit block: 0 First circuit block: 0 Second circuit block: 0 Third circuit block: 0 First circuit block: 0 Second circuit block: 0 Third circuit block: ⅓

[0078] Although each circuit block 5 is subject to the switching once, switching as a whole is performed three times such as 0, ⅓, 0, ⅓, 0, ⅓.

[0079] Accordingly, the inductance required to achieve the same ripple current decreases.

[0080] Thus, since the fact that the coefficients of the voltage Vo include not only 0 and 1, but also newly-added ⅓ and ⅔ is equal to that as a choke, the applied voltage decreases and the frequency increases, the inductance required to achieve the same ripple current decreases. This is similar to Example 1. However, since the voltage amplitude of Vo has been reduced from ½ to ⅓, and the number of switching has been increased from twice to three times, the required inductance further decreases in Example 2 than in Example 1.

[0081] Additionally, since the voltage of Vo/3 is applied to each of the MOSFETs, dV of Equation 1 becomes ±Vo/3, and the common mode current becomes ⅓ of that of the conventional circuit. Accordingly, it is possible to reduce more common mode noise in Example 2 than in Example 1, thereby enabling the miniaturization of the noise filter.

Effect of Example 2

[0082] By the above action, it is possible to, by use of the circuit of the present invention, miniaturize the choke and also miniaturize the noise filter.

Example 3

Configuration of Example 3

[0083] In Example 3, as the loads for the respective circuit blocks 5 of the circuit shown in FIG. 2, primary sides of full-bridge converters 6 (hereinafter referred to as “converters 6”) are respectively connected, as in a circuit shown in FIG. 12, and outputs of the respective converters 6 are connected to each other and to the load 3.

[0084] In each converter 6, inputs of a bridge circuit including a MOSFET 33, a MOSFET 34, a MOSFET 35, and a MOSFET 36 are connected to the output terminals of each circuit block 5. Outputs of this bridge circuit are connected to a primary winding of a transformer 61. A secondary winding of the transformer 61 is connected to a rectifying circuit including a diode 13, a diode 14, a diode 15, and a diode 16 which are bridged. Outputs of the rectifying circuit are connected to a smoothing circuit including a choke 8 and a capacitor 52.

Operation of Example 3

[0085] The converter 6, by the MOSFET 33, the MOSFET 34, the MOSFET 35, and the MOSFET 36, provides a positive and negative voltage to the primary winding of the transformer 61. Then, a voltage which appears in the secondary winding of the transformer 61 is rectified by the diode 13, the diode 14, the diode 15, and the diode 16. Then, the voltage and current are smoothed by the choke 8 and the capacitor 52.

[0086] Additionally, in such a case where the outputs of the plurality of converters 6 are connected to each other, it is known that the ripple current of the capacitor 52 can be reduced by shifting the phases with each other to drive the converters, which are generally called multi-phase converters.

Effect of Example 3

[0087] Thus, the outputs of the respective converters 6 are connected with each other, thereby realizing, as a whole, a single-input single-output isolated converter with the power factor improving function.

[0088] Additionally, each converter 6 is driven while shifting the phases of each converter 6, thereby enabling a reduction in ripple current of the capacitor 52, and thus enabling the miniaturization of the capacitor 52.

[0089] Here, although the example of the full-bridge converter has been taken in the Example 3, a circuit type of the converter 6 is not limited thereto as long as the converter 6 is an isolated converter, thereby still achieving the same effect that, as a whole, a single-input single-output isolated converter with the power factor improving function can be realized by connecting the outputs of the respective converters 6.

[0090] Additionally, although the example of the parallel connection has been taken as the method of connecting the outputs of the respective converters 6, even if this is replaced with a series connection, it is still possible to achieve the same effect that, as a whole, a single-input single-output isolated converter with the power factor improving function can be realized by connecting the outputs of the respective converters 6.

Example 4

Configuration of Example 4

[0091] FIG. 13 shows another example of converters to be connected as the loads for the respective circuit blocks. Here, the same components as those of the circuit shown in FIG. 12 are represented by the same symbols.

[0092] In each converter, inputs of the bridge circuit including the MOSFET 33, the MOSFET 34, the MOSFET 35, and the MOSFET 36 are connected to the output terminals of each circuit block 5. Outputs of this bridge circuit are connected to primary windings of a transformer 62 and a transformer 63. Secondary windings of the transformers 62 and 63 are connected in series. The series circuit including the secondary windings is connected to a rectifying circuit including a diode 17, a diode 18, a diode 19, and a diode 20 which are bridge-configured. Outputs of the rectifying circuit are connected to a smoothing circuit including a choke 9 and a capacitor 53.

Operation of Example 4

[0093] Operation on the primary side is similar to that of the circuit shown in FIG. 12. The MOSFET 33, the MOSFET 34, the MOSFET 35, and the MOSFET 36 provide a positive and negative voltage to the primary windings of the transformers 62 and 63. Then, voltages which appear in the secondary windings of the transformers 62 and 63 are added by the series connection thereof. Then, the added voltages are rectified by the diode 17, the diode 18, the diode 19, and the diode 20. Then, the voltage and current are smoothed by the choke 9 and the capacitor 53.

Effect of Example 4

[0094] Since the voltages of the primary windings of the transformers 62 and 63 are selectable from the voltages of 0 and ±Vo/2, voltages obtained by turn ratio conversion of 0, ±Vo/2, and ±Vo appear in the series circuit including the secondary windings of the transformers 62 and 63. Here, Vo is a value obtained by adding the output voltages of the respective circuit blocks 5.

[0095] Accordingly, the same act as described with respect to the power factor improving converter appears, thereby enabling the miniaturization of the choke 9.

[0096] Here, although the example of the circuit using the four MOSFETs in the bridge configuration as the primary circuit of the converter has been taken in Example 4, another circuit may be used as long as a positive and negative voltage can be provided to the primary windings of the transformer 62 and 63, thereby achieving the same effect that the chokes 9 can be miniaturized.

Example 5

Configuration of Example 5

[0097] FIG. 14 shows another example of converters to be connected as the loads for the respective circuit blocks. Example 5 differs from Example 4 in that resonance circuits 7 are added, and chokes 9 are short-circuited.

Operation of Example 5

[0098] In the thus-constructed isolated DC/DC converter, outputs of two bridge circuits each including the MOSFET 33, the MOSFET 34, the MOSFET 35, and the MOSFET 36 are made equal, and the voltages of the secondary windings of the transformer 62 and 63 become half the voltage of the capacitor 53. Then, when an output of one bridge circuit is made zero, the voltage of the secondary winding of the other transformer 63 becomes equal to the voltage of the capacitor 53, and the voltage of the secondary winding of the one transformer 62 becomes zero. This makes it possible to switch the voltage of the resonant circuit 7 in a multilevel.

Effects of Example 5

[0099] Since it is possible to switch the voltage of the resonant circuit in a multilevel, the duty of each level is controlled, thereby enabling a control at a fixed frequency in spite of the resonant converter.

[0100] Additionally, the voltage of the resonant circuit is switched in a multilevel, thereby enabling the use of the rectifier diode always in the current discontinuous mode even if a ratio of the input voltage and the output voltage varies. As a result of this, the recovery current does not flow through the rectifier diode, thereby reducing the surge voltage and resulting in low noise.

[0101] Here, although the example using MOSFETs as the switching elements has been taken in the above description, the same effect can be achieved even if a parallel circuit including an IGBT and an antiparallel diode is used.

INDUSTRIAL APPLICABILITY

[0102] According to the present invention, the multilevel converter technology is applicable to non-isolated power factor improving converters, and particularly, is applicable to cascade multi-cell multilevel converters.

DESCRIPTION OF REFERENCE NUMERALS

[0103] 1 AC power supply [0104] 2 choke [0105] 3 load [0106] 4 variable voltage source [0107] 5 circuit block [0108] 6 full-bridge converter [0109] 7 resonance circuit [0110] 8, 9 choke [0111] 11-28 diode [0112] 31-41 MOSFET [0113] 51-54 capacitor [0114] 61-63 transformer