Power conversion device

Abstract

A power conversion device (1) comprises: a first switch (10) having a first terminal connected to a first power supply line (21) and a second terminal connected to a second power supply line (22); and a suppression circuit (15) connected in parallel to the first switch (10). The first switch (10) is driven at a predetermined switching frequency (fsw). In the suppression circuit (15), a sub-resonance circuit (13) and a second switch (14) are connected in series. The resonance frequency of the sub-resonance circuit (13) is set to a value higher than the switching frequency (fsw). A first ground capacitor (C31) is provided between a first terminal (D) of the first switch (10) and a ground potential (GND), and a second ground capacitor (C32) is provided between the first terminal (D) of the second switch (14) and the ground potential (GND). The capacitances of the first ground capacitor (C31) and the second ground capacitor (C32) are substantially equal.

Description

Power Conversion Device

[0001] The present invention relates to a power conversion device.

[0002] A voltage-resonant power conversion circuit including a class E circuit can perform low-loss switching by using zero-voltage switching, which turns on the switch of the class E circuit when the voltage across the switch is zero. This allows the switch's drive frequency to be increased, making it possible to miniaturize passive components such as the inductor and capacitor of the LC series resonant circuit of the class E circuit. However, using voltage resonance increases the voltage between the switch's terminals. This requires the use of switching elements with high voltage resistance, which increases the cost of the switch and increases conduction loss.

[0003] In light of this, a voltage resonant power conversion circuit is known that suppresses the peak voltage between the terminals of a switch by adding an LC series resonant circuit having a resonant frequency higher than the switching frequency of the switch in parallel with the switch as a peak voltage suppression circuit (see Patent Document 1). This enables the switching element to have a lower withstand voltage, resulting in lower costs and suppression of conduction loss.

[0004] JP 2017-184500 A

[0005] However, in the power conversion circuit of Patent Document 1, when a peak voltage suppression circuit is applied to a voltage-resonant power conversion circuit including a class E circuit in which the input voltage fluctuates, the peak voltage suppression circuit operates even in a region where there is sufficient margin for the device's withstand voltage. As a result, current always flows through the peak voltage suppression circuit, increasing power consumption and reducing the efficiency of the power conversion circuit, resulting in constant losses. Furthermore, the increased power consumption increases heat generation in the switch, requiring an increase in the size of a cooler to cool the switch.

[0006] Furthermore, in the power conversion circuit of Patent Document 1, the switches of the class E circuit are operated at the same switching frequency as the resonant frequency of the LC series resonant circuit of the class E circuit, so high-frequency electromagnetic noise is generated when the switching elements operate. Furthermore, there is an imbalance between the parasitic capacitance between the high-potential power line and the ground potential and the parasitic capacitance between the low-potential power line and the ground potential, which reduces the symmetry of the impedance to ground, causing electromagnetic noise to leak outside the power conversion circuit. This requires the use of multiple noise filters to combat the electromagnetic noise, which increases the circuit size and costs.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a power conversion device that can suppress the peak voltage of the voltage between the terminals of a switch, thereby improving efficiency and suppressing noise.

[0008] A power conversion device according to one aspect of the present invention includes a first switch having a first terminal connected to a first power supply line and a second terminal connected to a second power supply line, and a suppression circuit connected in parallel to the first switch. The first switch is driven at a predetermined switching frequency. The suppression circuit includes a sub-resonant circuit and a second switch connected in series. The resonant frequency of the sub-resonant circuit is set to a value higher than the switching frequency. The first terminal of the sub-resonant circuit is connected to a first terminal of the first switch, the first terminal of the second switch is connected to a second terminal of the first switch, and the second terminal of the sub-resonant circuit is connected to a second terminal of the second switch. A first grounded capacitor is provided between the first terminal of the first switch and a ground potential, and a second grounded capacitor is provided between the first terminal of the second switch and a ground potential. The first grounded capacitor and the second grounded capacitor have approximately the same capacitance.

[0009] According to the present invention, it is possible to provide a power conversion device that can suppress the peak voltage between the terminals of a switch, improve efficiency, and suppress noise at the same time.

[0010] FIG. 1 is a circuit diagram showing an example of the configuration of a power conversion device according to a first embodiment. FIG. 2A is a waveform diagram schematically showing the relationship between the input voltage V1 of the power conversion device according to the first embodiment and the inter-terminal voltage Vt of the first switch. FIG. 2B is a waveform diagram showing the inter-terminal voltage Vt1 of the first switch of the power conversion device according to the first embodiment and the inter-terminal voltage Vt2 of the first switch of the power conversion device of the comparative example in region B of FIG. 2A. FIG. 2C is a waveform diagram showing the inter-terminal voltage Vt1 of the first switch of the power conversion device according to the first embodiment and the inter-terminal voltage Vt2 of the first switch of the power conversion device of the comparative example in region C of FIG. 2A. FIG. 3 is a circuit diagram showing an example of the configuration of a power conversion device according to a second embodiment. FIG. 4 is a circuit diagram showing an example of the configuration of a power conversion device according to a third embodiment. FIG. 5 is a circuit diagram showing an example of the configuration of a power conversion device according to a fourth embodiment.

[0011] The embodiments will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0012] First Embodiment The configuration of a power conversion device 1 according to the first embodiment will be described with reference to Fig. 1. The power conversion device 1 according to the first embodiment is a voltage-resonant class E inverter circuit serving as a power factor correction circuit. The power conversion device 1 converts AC power from an AC power supply Vac connected as an external power supply 2 into AC power with a high-frequency switching frequency fsw, and outputs the AC power to an external load 3. The AC power supply Vac is, for example, a commercial power supply with an effective voltage of 100 V and a frequency of 50 Hz or 60 Hz. The switching frequency fsw is, for example, a high frequency of about 100 kHz to several tens of MHz.

[0013] The power conversion device 1 includes input terminals T1 and T2, a rectifier 19, power supply lines 21 and 22, input inductors L01 and L02, a first switch 10, main resonant circuits 11 and 12, an output capacitor C0, a suppression circuit 15, ground capacitors C31 and C32, and output terminals T3 and T4. The suppression circuit 15 includes a sub-resonant circuit 13 and a second switch 14 connected in series. The suppression circuit 15 also includes a control unit 16 that controls the on / off of the first switch 10 and the second switch 14. An external power supply 2 is connected in parallel to the first input terminal T1 and the second input terminal T2. An external load 3 is connected in parallel to the first output terminal T3 and the second output terminal T4.

[0014] The power conversion device 1 is provided with a voltmeter 17 for measuring an input voltage V1 input between the first input terminal T1 and the second input terminal T2, and an ammeter 18 for measuring an input current I1 flowing between the external power supply 2 and the power conversion device 1. The values ​​of the input voltage V1 measured by the voltmeter 17 and the input current I1 measured by the ammeter 18 are transmitted to the control unit 16. Note that a configuration may be adopted in which either the voltmeter 17 or the ammeter 18 is provided.

[0015] The input terminals of a rectifier 19 are connected in parallel to the pair of first input terminal T1 and second input terminal T2. The rectifier 19 full-wave rectifies the input voltage V1 and outputs a DC voltage with a full-wave rectified waveform between the positive output terminal + and the negative output terminal −. The positive output terminal + serves as a first power supply terminal on the high potential side, and the negative output terminal − serves as a second power supply terminal on the low potential side. A first power supply line 21 is provided between the positive output terminal + and the first output terminal T3, and a second power supply line 22 is provided between the negative output terminal − and the second output terminal T4. The first power supply line 21 is the high potential side power supply line, and the second power supply line 22 is the low potential side power supply line.

[0016] The first terminal D of the first switch 10 is connected to a first power supply line 21, and the second terminal S of the first switch 10 is connected to a second power supply line 22. A first input inductor L01 is provided on the first power supply line 21, connecting the positive output terminal + of the rectifier 19 and the first terminal D of the first switch 10. A second input inductor L02 is provided on the second power supply line 22, connecting the negative output terminal − of the rectifier 19 and the second terminal S of the first switch 10. The first input inductor L01 and the second input inductor L02 function as choke inductors. The inductances of the first input inductor L01 and the second input inductor L02 are approximately equal. Note that the configuration is not limited to one in which both the first input inductor L01 and the second input inductor L02 are provided, and a configuration in which either the first input inductor L01 or the second input inductor L02 is provided may also be used.

[0017] In the first embodiment, an N-channel MOSFET is used as the first switch 10, but this is not limiting and a semiconductor switching element such as an IGBT can be used. In the first embodiment, the first terminal D of the first switch 10 is the drain, the second terminal S is the source, and the control electrode is the gate.

[0018] A control electrode of the first switch 10 is connected to the control unit 16. The first switch 10 is driven at the switching frequency fsw when a control signal of the switching frequency fsw is input from the control unit 16 to the control electrode.

[0019] An output capacitor C0 serving as a shunt capacitor is connected in parallel to the first terminal D and the second terminal S of the first switch 10. Note that the output capacitor C0 may be a capacitor of a separate component, or may not be a capacitor of a separate component by utilizing the parasitic capacitance of the first switch 10.

[0020] The first power supply line 21 is provided with a first main resonant circuit 11 connecting the first terminal D of the first switch 10 and the first output terminal T3. The first main resonant circuit 11 is an LC series resonant circuit in which an inductor L11 and a capacitor C11 are connected in series. The second power supply line 22 is provided with a second main resonant circuit 12 connecting the second terminal S of the first switch 10 and the second output terminal T4. The second main resonant circuit 12 is an LC series resonant circuit in which an inductor L12 and a capacitor C12 are connected in series. The resonant frequency fr1 of the first main resonant circuit 11 and the second main resonant circuit 12 is set to a value corresponding to the switching frequency fsw, i.e., a value approximately equal to the switching frequency fsw. Note that the configuration is not limited to providing both the first main resonant circuit 11 and the second main resonant circuit 12, and a configuration in which either the first main resonant circuit 11 or the second main resonant circuit 12 is provided may also be used.

[0021] A suppression circuit 15 is connected in parallel to the first switch 10. The breakdown voltage Vr of a typical semiconductor switching element is approximately 650 V, and semiconductor switching elements with a breakdown voltage Vr higher than 650 V are expensive. Furthermore, the inter-terminal voltage Vt of the first switch 10 becomes, for example, approximately four times the absolute value of the input voltage V1 due to voltage resonance of the main resonant circuits 11 and 12. Therefore, there is a possibility that the peak voltage of the inter-terminal voltage Vt of the first switch 10 may exceed the breakdown voltage Vr of the semiconductor switching element. The suppression circuit 15 suppresses the peak voltage of the inter-terminal voltage Vt of the first switch 10, for example, to prevent the peak voltage of the inter-terminal voltage Vt from exceeding the breakdown voltage Vr of the semiconductor switching element.

[0022] The suppression circuit 15 has a sub-resonant circuit 13 and a second switch 14 connected in series. The sub-resonant circuit 13 functions as a peak suppression circuit for suppressing the peak voltage of the inter-terminal voltage Vt of the first switch 10. The sub-resonant circuit 13 is an LC series resonant circuit in which an inductor L2 and a capacitor C2 are connected in series. The resonant frequency fr2 of the sub-resonant circuit 13 is set to a value higher than the switching frequency fsw. For example, the resonant frequency fr2 of the sub-resonant circuit 13 is set to a value two or three times the switching frequency fsw. The second switch 14 is a switch for switching the operation of the sub-resonant circuit 13 on and off. When the second switch 14 is off, the parallel connection between the first switch 10 and the sub-resonant circuit 13 is disconnected, and the operation of the sub-resonant circuit 13 is turned off. When the second switch 14 is on, the first switch 10 and the sub-resonant circuit 13 are connected in parallel, and the operation of the sub-resonant circuit 13 is turned on.

[0023] In the first embodiment, the first terminal of the sub-resonant circuit 13 is connected to the first terminal D of the first switch 10, the first terminal D of the second switch 14 is connected to the second terminal S of the first switch 10, and the second terminal of the sub-resonant circuit 13 is connected to the second terminal S of the second switch 14. In the first embodiment, an N-channel MOSFET is used as the second switch 14, but this is not limited thereto, and a semiconductor switching element such as an IGBT can be used. In the first embodiment, the first terminal D of the second switch 14 is the drain, the second terminal S is the source, and the control electrode is the gate. The control electrode of the second switch 14 is connected to the control unit 16. The control unit 16 controls the on and off of the second switch 14.

[0024] The control unit 16 is a general-purpose computer equipped with a CPU (Central Processing Unit), a memory, and an input / output unit. A computer program (control program) is installed in the control unit 16. By executing the computer program, the control unit 16 performs various functions.

[0025] The power conversion device 1 is a voltage-resonant class E inverter circuit in which a first switch 10 repeatedly turns on and off at a high-frequency switching frequency fsw and a high-voltage inter-terminal voltage Vt, thereby generating an AC current having the same frequency as the switching frequency fsw.

[0026] In a circuit configured like the power conversion device 1, the higher the switching frequency fsw, the smaller the inductance required for the passive components inductors L11 and L12 and the capacitance required for capacitors C11 and C12, allowing for a more compact circuit. Furthermore, during the off-period of the first switch 10, zero voltage switching (ZVS) can be performed by using the current of the main resonant circuits 11 and 12 to zero the inter-terminal voltage Vt of the first switch 10 before turning it on, thereby eliminating turn-on loss. Performing ZVS reduces losses even when the switching frequency fsw is increased, potentially enabling a more compact power conversion device 1. However, voltage resonance increases the inter-terminal voltage Vt of the first switch 10. Therefore, the first switch 10 must have a high breakdown voltage Vr, which increases the cost of the first switch 10 and increases conduction loss.

[0027] Therefore, a sub-resonant circuit 13, which is an LC series resonant circuit, is connected in parallel with the first switch 10 as a peak voltage suppression circuit having a resonant frequency fr2 that is two or three times the switching frequency fsw. This makes it possible to reduce the component of the inter-terminal voltage Vt of the first switch 10 that corresponds to the second or third harmonic of the switching frequency fsw, and to reduce the inter-terminal voltage Vt applied when the first switch 10 is off. This makes it possible to reduce the withstand voltage of the first switch 10, reduce costs, and suppress conduction loss.

[0028] In a voltage-resonant power conversion device 1 including a class E circuit in which the input voltage V1 fluctuates, if the first switch 10 and the sub-resonant circuit 13 are directly connected in parallel, the sub-resonant circuit 13 will operate even in a region where the withstand voltage of the first switch 10 is sufficiently high. This causes losses to occur constantly in the sub-resonant circuit 13. As a result, the efficiency of the power conversion device 1 will deteriorate, and heat generation will increase, requiring an enlarged cooler.

[0029] Therefore, in the first embodiment, as described above, the suppression circuit 15, in which the sub-resonant circuit 13 and the second switch 14 are connected in series, is connected in parallel with the first switch 10. The control unit 16 determines the value of the inter-terminal voltage Vt of the first switch 10 based on at least one of the input voltage V1 observed by the voltmeter 17 and the input current I1 observed by the ammeter 18, and switches the second switch 14 on and off according to the determined value of the inter-terminal voltage Vt.

[0030] For example, when the second switch 14 is off, the control unit 16 controls the second switch 14 to switch from off to on when it determines that the voltage Vt across the first switch 10 exceeds the threshold voltage Vth. Furthermore, when the second switch 14 is on, the control unit 16 controls the second switch 14 to switch from on to off when it determines that the voltage Vt across the first switch 10 is below the threshold voltage Vth.

[0031] With this configuration, when the inter-terminal voltage Vt exceeds the threshold voltage Vth, the sub-resonant circuit 13 operates, thereby suppressing the peak voltage of the inter-terminal voltage Vt. Furthermore, when the inter-terminal voltage Vt is below the threshold voltage Vth, the sub-resonant circuit 13 does not operate. In other words, in a region where the withstand voltage of the first switch 10 is sufficiently large, the sub-resonant circuit 13 does not operate, thereby improving the efficiency of the power conversion device 1 and ultimately enabling the size of a cooler used in the power conversion device 1 to be reduced.

[0032] Furthermore, the power conversion device 1 according to the first embodiment is provided with a first grounded capacitor C31 that connects the first terminal D of the first switch 10 to the earth line 23, and a second grounded capacitor C32 that connects the first terminal D of the second switch 14 to the earth line 23. The earth line 23 is connected to the earth potential GND. The capacitances of the first grounded capacitor C31 and the second grounded capacitor C32 are approximately equal. Furthermore, the product of the inductance of the first input inductor L01 and the capacitance of the first grounded capacitor C31 is approximately equal to the product of the inductance of the second input inductor L02 and the capacitance of the second grounded capacitor C32.

[0033] Of the electromagnetic noise, the amount of common-mode noise is proportional to the difference between the product of the inductance of the first input inductor L01 and the capacitance of the first grounded capacitor C31 and the product of the inductance of the second input inductor L02 and the capacitance of the second grounded capacitor C32. By making the product of the inductance of the first input inductor L01 and the capacitance of the first grounded capacitor C31 and the product of the inductance of the second input inductor L02 and the capacitance of the second grounded capacitor C32 approximately equal, the difference described above becomes small (almost zero). This improves the symmetry of the impedance to ground between the first power supply line 21 and the second power supply line 22, suppresses the outflow of common-mode noise, and suppresses noise of harmonic components of the switching frequency fsw.

[0034] In this way, in the power conversion device 1 according to the first embodiment, the peak voltage of the inter-terminal voltage Vt of the first switch 10 can be suppressed, improving efficiency and simultaneously suppressing noise.

[0035] Next, the operation of the power conversion device 1 will be described using FIGS. 2A to 2C. FIG. 2A is a waveform diagram schematically illustrating the relationship between the input voltage V1 of the power conversion device 1 and the inter-terminal voltage Vt of the first switch 10. FIG. 2B is a waveform diagram illustrating the inter-terminal voltage Vt1 of the first switch 10 of the first embodiment and the inter-terminal voltage Vt2 of the first switch 10 of the comparative example in region B of FIG. 2A. FIG. 2C is a waveform diagram illustrating the inter-terminal voltage Vt1 of the first switch 10 of the first embodiment and the inter-terminal voltage Vt2 of the first switch 10 of the comparative example in region C of FIG. 2A. In the first embodiment, when the inter-terminal voltage Vt1 exceeds the threshold voltage Vth, the second switch 14 is turned on to operate the sub-resonant circuit 13, and when the inter-terminal voltage Vt1 falls below the threshold voltage Vth, the second switch 14 is turned off to prevent the sub-resonant circuit 13 from operating. In contrast to this, in the comparative example, the second switch 14 is always turned on, and the sub-resonant circuit 13 remains in operation, regardless of the value of the inter-terminal voltage Vt2.

[0036] In Fig. 2A, the terminal voltage Vt of the first switch 10 is shown as a waveform that appears to be full-wave rectified with respect to the sinusoidal input voltage V1 with an effective value of 100 V and a frequency of 50 Hz. However, in reality, as shown in Figs. 2B and 2C, the terminal voltages Vt1 and Vt2 increase in proportion to the input voltage V1 when the first switch 10 is driven at the switching frequency fsw due to voltage resonance of the main resonant circuit 11, which is an LC series resonant circuit. In Figs. 2A to 2C, Vr is the element breakdown voltage of the first switch 10, and Vth is the threshold voltage at which the operation of the second switch 14 is switched.

[0037] 2B , in region B where the inter-terminal voltage Vt exceeds the threshold voltage Vth, the inter-terminal voltage Vt1 of the first embodiment and the inter-terminal voltage Vt2 of the comparative example have the same waveform, with the peak voltages suppressed by the operation of the sub-resonant circuit 13. In this way, in the region where the inter-terminal voltage Vt exceeds the threshold voltage Vth, the inter-terminal voltage Vt can be reduced in both the first embodiment and the comparative example. Therefore, even when the input voltage V1 is large, the inter-terminal voltage Vt can be made smaller than the element breakdown voltage Vr of the first switch 10.

[0038] 2C , in region C where the inter-terminal voltage Vt is below the threshold voltage Vth, the peak voltage of the inter-terminal voltage Vt1 in the first embodiment is not suppressed because the sub-resonant circuit 13 is not operating. In contrast, the inter-terminal voltage Vt2 in the comparative example has a waveform in which the peak voltage is suppressed by the operation of the sub-resonant circuit 13. Thus, in the region where the inter-terminal voltage Vt is below the threshold voltage Vth, the comparative example always generates losses due to the operation of the sub-resonant circuit 13. In contrast, in the first embodiment, the sub-resonant circuit 13 is not operating, so no losses are generated by the sub-resonant circuit 13.

[0039] As in the first embodiment, when the inter-terminal voltage Vt falls below the threshold voltage Vth and the second switch 14 is turned off, the capacitor C2 of the sub-resonant circuit 13 and the parasitic capacitance Cp of the second switch 14 are connected in series to form a composite capacitance Cs. This composite capacitance Cs and the inductor L2 of the sub-resonant circuit 13 form a composite resonant circuit. The resonant frequency fr3 of this composite resonant circuit must be set higher than the resonant frequency fr2 of the sub-resonant circuit 13, which is two or three times the switching frequency fsw, to nullify the peak suppression effect of the composite resonant circuit. To achieve this, the capacitance of the capacitor C2 of the sub-resonant circuit 13 must be set to a value greater than the parasitic capacitance Cp of the second switch 14.

[0040] For this reason, in the first embodiment, the capacitance of the capacitor C2 of the sub-resonant circuit 13 is set to a value larger than the parasitic capacitance Cp of the second switch 14. As a result, when the second switch 14 is turned off, it is possible to nullify the peak suppression effect of the composite resonant circuit formed by the composite capacitance Cs, which is formed by the capacitor C2 of the sub-resonant circuit 13 and the parasitic capacitance Cp of the second switch 14 connected in series, and the inductor L2.

[0041] As described above, in the power conversion device 1 according to the first embodiment, the peak voltage of the inter-terminal voltage Vt of the first switch 10 can be suppressed, thereby improving efficiency and simultaneously suppressing noise. Furthermore, by suppressing noise, the number of noise filter stages can be reduced, enabling the power conversion device 1 to be made smaller and less expensive.

[0042] Second Embodiment Next, the configuration of a power conversion device 1A according to a second embodiment will be described with reference to Fig. 3. The power conversion device 1A according to the second embodiment differs from the power conversion device 1 according to the first embodiment shown in Fig. 1 in that a DC power supply Vdc is connected as the external power supply 2 and the rectifier 19 is omitted. The first input terminal T1 serves as a first power supply terminal on the high potential side, and the second input terminal T2 serves as a second power supply terminal on the low potential side. A first power supply line 21 extends between the first input terminal T1, which is the first power supply terminal on the high potential side, and the first output terminal T3, and a second power supply line 22 extends between the second input terminal T2, which is the second power supply terminal on the low potential side, and the second output terminal T4.

[0043] The DC power supply Vdc is, for example, a rechargeable secondary battery such as a lithium-ion battery. The rest of the configuration of the power conversion device 1A according to the second embodiment is the same as the configuration of the power conversion device 1 according to the first embodiment, and therefore detailed description thereof will be omitted. Since the DC voltage of the DC power supply Vdc fluctuates depending on the charging and discharging status, the input voltage V1 also fluctuates.

[0044] For this reason, the second embodiment is provided with a voltmeter 17 for measuring the input voltage V1 input between the first input terminal T1 and the second input terminal T2, and an ammeter 18 for measuring the input current I1 flowing between the external power supply 2 and the power conversion device 1. The values ​​of the input voltage V1 measured by the voltmeter 17 and the input current I1 measured by the ammeter 18 are transmitted to the control unit 16. The control unit 16 determines the value of the inter-terminal voltage Vt of the first switch 10 based on the input voltage V1 observed by the voltmeter 17 and the input current I1 observed by the ammeter 18, and switches the second switch 14 on and off in accordance with the determined value of the inter-terminal voltage Vt.

[0045] The second embodiment also provides the same effects as the first embodiment, namely, suppressing the peak voltage of the inter-terminal voltage Vt of the first switch 10, improving efficiency, and simultaneously suppressing noise. Furthermore, suppressing noise allows for a reduction in the number of noise filter stages, thereby enabling the miniaturization and cost reduction of the power conversion device 1A.

[0046] Third Embodiment Next, the configuration of a power conversion device 1B according to a third embodiment will be described with reference to Fig. 4. The power conversion device 1B according to the third embodiment differs from the power conversion device 1A according to the second embodiment shown in Fig. 3 in that an EMI filter 20 is mounted downstream of the input terminals T1 and T2. In the third embodiment, the positive output terminal + of the EMI filter 20 serves as a first power supply terminal on the high potential side, and the negative output terminal − of the EMI filter serves as a second power supply terminal on the low potential side. A first power supply line 21 extends between the positive output terminal +, which is the first power supply terminal on the high potential side, and the first output terminal T3, and a second power supply line 22 extends between the negative output terminal −, which is the second power supply terminal on the low potential side, and the second output terminal T4.

[0047] The EMI filter is an LC filter formed by combining a common mode choke coil, an X capacitor, and a Y capacitor. When the inductance of the common mode choke coil of the EMI filter is sufficiently larger than the inductance of the input inductors L01 and L02 serving as choke coils, the following occurs. That is, the product of the inductance of the common mode choke coil and the capacitance of the first grounded capacitor C31 is approximately equal to the product of the inductance of the common mode choke coil and the capacitance of the second grounded capacitor C32, improving the symmetry of the impedance to ground. Therefore, the choke coils connected to the first switch 10 may be consolidated into either the first input inductor L01 or the second input inductor L02. In the power conversion device 1A configured as shown in FIG. 3, the first input inductor L01 is implemented, and the second input inductor L02 is omitted.

[0048] The third embodiment differs from the first embodiment in that the external power supply 2 is a DC power supply Vdc, an EMI filter is implemented, and the second input inductor L02 is omitted, but the same effects as those of the first embodiment can be obtained. As a result, the third embodiment also suppresses the peak voltage of the inter-terminal voltage Vt of the first switch 10, improving efficiency and suppressing noise. Furthermore, suppressing noise allows the number of noise filter stages to be reduced, thereby enabling the power conversion device 1B to be made smaller and more cost-effective.

[0049] Fourth Embodiment Next, the configuration of a power conversion device 1C according to a fourth embodiment will be described with reference to Fig. 5. The power conversion device 1C according to the fourth embodiment has the same circuit configuration as the power conversion device 1A according to the second embodiment shown in Fig. 3, but differs in the following respects.

[0050] In the fourth embodiment, the first switch 10 is provided with an insulating first heat conduction member (not shown), the second switch 14 is provided with an insulating second heat conduction member (not shown), and these heat conduction members are cooled by a heat dissipation member 30 serving as a cooler connected to the earth potential GND. The first grounded capacitor C31 is a parasitic capacitance formed between the first terminal of the first switch 10 and the first heat conduction member, and the second grounded capacitor C32 is a parasitic capacitance formed between the first terminal of the second switch 14 and the second heat conduction member. As a result, in the power conversion device 1C according to the fourth embodiment, it is possible to reduce the number of capacitor components used in the circuit, thereby reducing costs, and to obtain heat dissipation properties for the first switch 10 and the second switch 14.

[0051] The fourth embodiment also provides the same advantageous effects as the first embodiment, suppressing the peak voltage of the inter-terminal voltage Vt of the first switch 10, improving efficiency, and simultaneously suppressing noise. Furthermore, suppressing noise allows for a reduction in the number of noise filter stages, enabling the power conversion device 1C to be made smaller and more cost-effective.

[0052] Each of the functions described in the above embodiments may be implemented by one or more processing circuits, including programmed processors, electrical circuits, and even devices such as application specific integrated circuits (ASICs), or circuit components arranged to perform the described functions.

[0053] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. From this disclosure, various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art.

[0054] REFERENCE SIGNS LIST 1, 1A, 1B, 1C Power conversion device 2 External power supply 3 External load 10 First switch 11 First main resonant circuit 12 Second main resonant circuit 13 Sub-resonant circuit 14 Second switch 15 Suppression circuit 16 Control unit 17 Voltmeter 18 Ammeter 19 Rectifier 20 EMI filter 21 First power supply line 22 Second power supply line 23 Earth line 30 Heat dissipation member C0 Output capacitor C11, C12, C2 Capacitor C31 First grounded capacitor C32 Second grounded capacitor L01 First input inductor L02 Second input inductor L11, L12, L2 Inductor T1 First input terminal T2 Second input terminal T3 First output terminal T4 Second output terminal

Claims

1. A power conversion device comprising: a first power supply line connecting a first power supply terminal and a first output terminal; a second power supply line connecting a second power supply terminal and a second output terminal; a first switch having a first terminal connected to the first power supply line and a second terminal connected to the second power supply line; and a suppression circuit connected in parallel to the first switch, wherein the first switch is driven at a predetermined switching frequency, and the suppression circuit has a sub-resonant circuit and a second switch connected in series, the resonant frequency of the sub-resonant circuit being set to a value higher than the switching frequency, a first terminal of the sub-resonant circuit being connected to the first terminal of the first switch, a first terminal of the second switch being connected to the second terminal of the first switch, and a second terminal of the sub-resonant circuit being connected to the second terminal of the second switch, a first grounded capacitor being provided between the first terminal of the first switch and a ground potential, and a second grounded capacitor being provided between the first terminal of the second switch and the ground potential, and the first grounded capacitor and the second grounded capacitor having approximately the same capacitance.

2. The power conversion device according to claim 1, further comprising an input inductor provided at least one between the first power supply terminal and the first terminal of the first switch, and between the second power supply terminal and the second terminal of the first switch.

3. The power conversion device according to claim 2, wherein the input inductor comprises: a first input inductor provided between the first power supply terminal and the first terminal of the first switch; and a second input inductor provided between the second power supply terminal and the second terminal of the first switch, and wherein the inductances of the first input inductor and the second input inductor are approximately equal.

4. The power conversion device according to any one of claims 1 to 3, further comprising a control unit that controls the on and off of the first switch and the second switch, wherein the control unit drives the first switch at the switching frequency and controls the second switch to be switched on and off according to the voltage between the terminals of the first switch.

5. The power conversion device according to claim 4, wherein the control unit observes at least one of an input voltage and an input current, and determines the value of the inter-terminal voltage based on the observed value of at least one of the input voltage and the input current.

6. The power conversion device according to claim 4 or 5, wherein the control unit switches the second switch from off to on when it determines that the inter-terminal voltage exceeds a threshold voltage while the second switch is off, and switches the second switch from on to off when it determines that the inter-terminal voltage is below the threshold voltage while the second switch is on.

7. A power conversion device according to any one of claims 1 to 6, further comprising: a main resonant circuit provided between the first terminal and the first output terminal of the first switch and / or between the second terminal and the second output terminal of the first switch; and an output capacitor connected in parallel to the first switch, wherein the resonant frequency of the main resonant circuit is approximately equal to the switching frequency.

8. The power conversion device according to claim 7, wherein the main resonant circuit comprises: a first main resonant circuit provided between the first terminal and the first output terminal of the first switch; and a second main resonant circuit provided between the second terminal and the second output terminal of the first switch, and the resonant frequencies of the first main resonant circuit and the second main resonant circuit are approximately equal to the switching frequency.

9. The power conversion device according to any one of claims 1 to 8, wherein the resonant frequency (fr2) of the auxiliary resonant circuit is set to two or three times the switching frequency.

10. The power conversion device according to any one of claims 1 to 9, wherein the sub-resonant circuit is an LC series resonant circuit in which an inductor and a capacitor are connected in series.

11. The power conversion device according to claim 10, wherein the capacitance of the capacitor of the sub-resonant circuit is set to a value greater than the parasitic capacitance of the second switch.

12. A power conversion device according to any one of claims 1 to 11, further comprising: a first heat conduction member provided in the first switch and connected to the earth potential; and a second heat conduction member provided in the second switch and connected to the earth potential, wherein the first grounded capacitor is a parasitic capacitance between the first terminal of the first switch and the first heat conduction member, and the second grounded capacitor is a parasitic capacitance between the first terminal of the second switch and the second heat conduction member.

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