Power conversion device

Abstract

In a power converter having a semiconductor switch, common-mode noise is effectively reduced by setting the common-mode inductance value of reactors which are inserted into both lines such that the resonance frequency of the combined capacity of a line-to-ground bypass capacitor and the reactors which are inserted into both lines becomes a predetermined value or more.

Claims

1. A power conversion device comprising: a filter circuit having a line-to-ground bypass capacitor connected between a pair of lines and a ground; a switching circuit having a semiconductor switch; and reactors connected between the filter circuit and the switching circuit, wherein the reactors are two reactors provided in both of the pair of lines, the two reactors sharing a core, and a common-mode inductance value L.sub.1 of the two reactors is set such that a relationship L.sub.1 <t.sub.r.sup.2/4C.sub.1 is satisfied, wherein C.sub.1 is a combined capacity of the line-to-ground bypass capacitor, and t.sub.r is a rise time of a voltage across a switch of the semiconductor switch.

2. The power conversion device according to claim 1, wherein the filter circuit and the two reactors are connected to an input side of the switching circuit.

3. The power conversion device according to claim 1, wherein the filter circuit and the two reactors are connected to an output side of the switching circuit.

4. The power conversion device according to claim 1, wherein the filter circuit and the two reactors are connected to an input side and an output side of the switching circuit.

5. The power conversion device according to claim 1, wherein the line-to-ground bypass capacitor is formed between a wiring pattern of the pair of lines and the ground.

6. A power conversion device comprising: a filter circuit having a line-to-ground bypass capacitor connected between a pair of lines and a ground; a switching circuit having a semiconductor switch; and reactors connected between the filter circuit and the switching circuit, wherein the reactors are two reactors provided in both of the pair of lines, the two reactors sharing a core, and a common-mode inductance value L.sub.2 of the two reactors is set such that a relationship L.sub.2<1/{(1010.sup.6).sup.2C.sub.2} is satisfied, C.sub.2 being a combined capacity of the line-to-ground bypass capacitor.

7. The power conversion device according to claim 6, wherein the filter circuit and the two reactors are connected to an input side of the switching circuit.

8. The power conversion device according to claim 6, wherein the filter circuit and the two reactors are connected to an output side of the switching circuit.

9. The power conversion device according to claim 6, wherein the filter circuit and the two reactors are connected to an input side and an output side of the switching circuit.

10. The power conversion device according to claim 6, wherein the line-to-ground bypass capacitor is a formed between a wiring pattern of the pair of lines and the ground.

11. A power conversion device comprising: a filter circuit having a line-to-ground bypass capacitor connected between a pair of lines and a ground; a switching circuit having a semiconductor switch; and reactors connected between the filter circuit and the switching circuit, wherein the reactors are two reactors provided in both of the pair of lines, the two reactors sharing a core, and if a common-mode inductance value L.sub.3 of the two reactors is set such that a relationship L.sub.3<1/{(1010.sup.5).sup.2C.sub.3} is satisfied, C.sub.3 being a combined capacity of the line-to-ground bypass capacitor.

12. The power conversion device according to claim 11, wherein the filter circuit and the two reactors are connected to an output side of the switching circuit.

13. The power conversion device according to claim 11, wherein the filter circuit and the two reactors are connected to an input side of the switching circuit.

14. The power conversion device according to claim 11, wherein the filter circuit and the two reactors are connected to an input side and an output side of the switching circuit.

15. The power conversion device according to claim 11, wherein the line-to-ground bypass capacitor is a formed between a wiring pattern of the pair of lines and the ground.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram depicting the configuration of a power conversion device according to Embodiment 1 of this invention.

(2) FIG. 2 is a diagram explaining an example of the operation of the power conversion device according to Embodiment 1 of this invention.

(3) FIG. 3 is a diagram explaining another example of the operation of the power conversion device according to Embodiment 1 of this invention.

(4) FIG. 4 is a diagram depicting an equivalent circuit model in which a common-mode noise resonance path of the power conversion device according to Embodiment 1 of this invention is simplified.

(5) FIG. 5 is a diagram depicting the Fourier spectral envelope of a pulse at the time of switching operation.

(6) FIG. 6 is a diagram depicting a limit value defined in International Standard IEC61000-6-3 (second edition; 2006).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Hereinafter, preferred embodiments of a power conversion device according to this invention will be described with reference to the drawings.

(8) Embodiment 1.

(9) FIG. 1 is a schematic configuration diagram of a power conversion device according to Embodiment 1 of this invention. As depicted in FIG. 1, the power conversion device according to Embodiment 1 is formed of component elements from a component element that is connected to a commercial alternating-current input 1 as an alternating-current input power-supply to a component element that supplies power to a load 13. The commercial alternating-current input 1 is connected to a first noise filter 5 formed of a first inter-line bypass capacitor 2, a first common-mode choke 3, and a first line-to-ground bypass capacitor 4, and first reactors 6a and 6b sharing a core are connected to a pair of lines of an output of the first noise filter 5.

(10) In a subsequent stage of the first reactors 6a and 6b, a switching circuit 7 having a semiconductor switch is connected, and second reactors 8a and 8b sharing a core are connected to a pair of lines of an output of the switching circuit 7. In a subsequent stage of the second reactors 8a and 8b, a second noise filter 12 formed of a second line-to-ground bypass capacitor 9, a second common-mode choke 10, and a second inter-line bypass capacitor 11 is connected, and the direct-current load 13 is connected to an output of the second noise filter 12.

(11) An example of the operation of the switching circuit including the first reactors 6a and 6b and the second reactors 8a and 8b of the power conversion device connected in the above-described manner will be described with reference to FIGS. 2 and 3.

(12) First, the operation of the switching circuit including the first reactors 6a and 6b of FIG. 1 will be described. FIG. 2 is a schematic configuration diagram depicting a state in which the first reactors 6a and 6b are applied to an AC/DC converter. Incidentally, the commercial alternating-current input 1, the first noise filter 5, the first inter-line bypass capacitor 2, the first common-mode choke 3, the first line-to-ground bypass capacitor 4, and the first reactors 6a and 6b are similar to those depicted in FIG. 1.

(13) As depicted in FIG. 2, the first reactors 6a and 6b sharing a core are connected to a pair of lines of the output of the first noise filter 5, and a diode bridge 14 is connected to an output of the first reactors 6a and 6b. A switching element 15 and a diode 16 are connected in a subsequent stage of the diode bridge 14, and the cathode side of the diode 16 is connected to a positive electrode of a smoothing capacitor 17 in an output stage. To the other end of the switching element 15, the first reactor 6b and a negative electrode of the smoothing capacitor 17 are connected.

(14) First, when the switching element 15 is turned on, a current flows through the first reactors 6a and 6b and energy is accumulated therein. Next, when the switching element 15 is turned off, the accumulated energy is transferred to a load 18 by a counter-electromotive force generated in the first reactors 6a and 6b. At this time, it is possible to control a power factor by controlling the pulse width of ON/OFF of the switching element 15 such that an input current waveform takes the form of a sinusoidal wave.

(15) The switching circuit including the first reactors 6a and 6b is not limited to the circuit configuration of FIG. 2 and may be formed of another AC/DC converter circuit that performs power conversion by switching of an interleaved switching element, for example.

(16) Next, the operation of the switching circuit including the second reactors 8a and 8b of FIG. 1 will be described. FIG. 3 is a schematic circuit diagram depicting a state in which the second reactors 8a and 8b are applied to a full-bridge DC/DC converter. Incidentally, the second reactors 8a and 8b, the second noise filter 12, the second line-to-ground bypass capacitor 9, the second common-mode choke 10, and the second inter-line bypass capacitor 11 are similar to those depicted in FIG. 1.

(17) As depicted in FIG. 3, a direct-current power-supply input 19 is connected to a bridge circuit 20 formed of four switching elements 20a, 20b, 20c, and 20d, and the primary side of an isolating transformer 21 is connected to an output of the bridge circuit 20. A diode bridge 22 is connected to the secondary side of the isolating transformer 21, and the second reactors 8a and 8b sharing a core are connected to a pair of lines of an output of the diode bridge 22. In a subsequent stage of the second reactors 8a and 8b, the second noise filter 12 formed of the second line-to-ground bypass capacitor 9, the second common-mode choke 10, and the second inter-line bypass capacitor 11 is connected, and a direct-current load 23 connected to the output of the second noise filter 12.

(18) A direct current of an input is converted into a high-frequency alternating current by alternately turning ON/OFF the four switching elements 20a, 20b, 20c, and 20d, a voltage is generated between the secondary-side terminals of the isolating transformer 21, and rectification is performed by the diode bridge 22. When a voltage is generated to the secondary side of the isolating transformer 21, energy is accumulated in the second reactors 8a and 8b; in other periods, the accumulated energy is transferred to the load 23 by a counter-electromotive force generated in the second reactors 8a and 8b. At this time, it is possible to control an output current by controlling the pulse width of ON/OFF of the switching elements 20a, 20b, 20c, and 20d.

(19) The switching circuit including the second reactors 8a and 8b is not limited to the circuit configuration of FIG. 3 and may be formed of another DC/DC converter circuit that performs power conversion by switching of a half-bridge or flyback switching element, for example.

(20) As described above, since the switching element forming the switching circuit 7 performs switching control at a high-frequency switching frequency which is assumed to be 20 kHz or higher, high switching noise caused by the switching frequency is generated. As the noise, there are two types of noise: common-mode noise and normal-mode noise. The common-mode noise is noise that is generally generated by a potential difference with a ground, and the normal-mode noise is noise that is generated by a potential difference between lines.

(21) At this time, by inserting the first reactors 6a and 6b and the second reactors 8a and 8b having the same impedance into both lines, it is possible to reduce the common-mode noise as compared to a case in which insertion into only one line is performed.

(22) The first reactors 6a and 6b will be taken up as an example; if the first reactors 6a and 6b are concentrated on only one line, there is the impedance of the first reactors 6a and 6b on the side of the line into which the first reactors 6a and 6b are inserted and there is no impedance by the reactors on the side of the line into which the reactors are not inserted.

(23) As a result, on the side of the line into which the reactors are not inserted, noise directly flows into the ground via the line-to-ground bypass capacitor, but, on the side of the line into which the first reactors 6a and 6b are inserted, noise can be attenuated by the impedance of the first reactors 6a and 6b before the noise flows into the ground. As described above, as a result of an imbalance between the impedances of both lines, common-mode noise generated. Thus, by inserting the first reactors 6a and 6b having the same impedance into both lines, the impedances are equilibrated with each other, which makes it possible to reduce the common-mode noise.

(24) Furthermore, by making the first reactors 6a and 6b, which are inserted into both lines, share a core, the magnetic fluxes generated in the first reactors 6a and 6b are added to each other in the direction in which a coil is wound, whereby it is possible to increase the total normal-mode inductance and make the first reactors 6a and 6b smaller.

(25) In the above description, the first reactors 6a and 6b have been described; likewise, by making the second reactors 8a and 8b share a core, it is possible to make the second reactors 8a and 8b smaller.

(26) Next, a method of shifting the common-mode noise resonance frequency, which is the feature of this embodiment, will be described. In FIG. 4, an equivalent circuit model in which a common-mode noise resonance path formed of the first reactors 6a and 6b, the second reactors 8a and 8b, the first line-to-ground bypass capacitor 4, and the second line-to-ground bypass capacitor 9 of FIG. 1 is simplified is depicted.

(27) As depicted in FIG. 4, the common-mode inductance value of the first reactors 6a and 6b is assumed to be L.sub.common6, the common-mode inductance value of the second reactors 8a and 8b is assumed to be L.sub.common8 the capacity of the first line-to-ground bypass capacitor 4 is assumed to be C.sub.4, and the capacity of the second line-to-ground bypass capacitor 9 is assumed to be C.sub.9.

(28) A resonance frequency f.sub.r1 formed in the resonance path depicted in FIG. 4 is expressed by Equation (4).
f.sub.r1={(L.sub.common6+L.sub.common8)(C.sub.4+C.sub.9)}(4)

(29) By making settings such that f.sub.r1 of Equation (4) and f.sub.2 of Equation (3) satisfy f.sub.r1f.sub.2, it is possible to shift the common-mode noise resonance frequency to a band in which the attenuation of a harmonic component of a fundamental of a switching frequency is great and suppress common-mode noise in a resonance band.

(30) By making smaller the common-mode inductance values L.sub.common6 and L.sub.common8 and the capacities C.sub.4 and C.sub.9 of the first and second line-to-ground bypass capacitors 4 and 9, it is possible to make settings such that f.sub.r1f.sub.2 holds; however, if the capacities C.sub.4 and C.sub.9 of the first and second line-to-ground bypass capacitors 4 and 9 are made smaller, the common-mode noise reduction effect is reduced. On the other hand, as for the first reactors 6a and 6b and the second reactors 8a and 8b, by making the first reactors 6a and 6b share one core and the second reactors 8a and 8b share one core, since it is possible to make the magnetic fluxes in the core cancel each other out for a common-mode current, it is possible to reduce a common-mode inductance value while maintaining the common-mode noise reduction effect.

(31) Therefore, the values of L.sub.common6 and L.sub.common8 are set as in Equation (5) such that f.sub.r1f.sub.2 holds.
L.sub.common6+L.sub.common8<t.sub.r.sup.2/4(C.sub.4+C.sub.9)(5)

(32) According to this embodiment, by inserting the reactors having the same inductance value into both of a pair of lines, since it is possible not only to reduce common-mode noise, but also to shift, b by setting the values of L.sub.common6 and L.sub.common8 as in Equation (5), the resonance frequency f.sub.r1 of the capacity of the line-to-ground bypass capacitor and the reactors which are inserted into both lines to a band in which the attenuation of a harmonic component of a fundamental of a switching frequency is great, there no need to provide a countermeasures part such as a common-mode choke separately for reduction in noise which is increased in a resonance frequency band, which makes it possible to achieve a reduction in the size of a noise filter and a reduction in cost and effectively suppress common-mode noise.

(33) Incidentally, in the above description, a case in which the reactors are connected to the input side and the output side of the switching circuit 7 has been described; however, even in a case in which the reactors are provided only on the input side of the switching circuit 7, by setting the common-mode inductance value of the reactors on the input side such that f.sub.r1f.sub.2 holds, it is possible to suppress common-mode noise effectively. Moreover, even in a case in which the reactors are provided only on the output side of the switching circuit 7, by setting the common-mode inductance value of the reactors on the output side such that f.sub.r1f.sub.2 holds, it is possible to suppress common-mode noise effectively.

(34) Moreover, in FIG. 2, a configuration in which the first reactors 6a and 6b are connected in front of the diode bridge 14 is depicted, but a configuration in which the diode bridge 14 is connected in front of the first reactors 6a and 6b also makes it possible to obtain the effect similar to that of this embodiment.

(35) The line-to-ground capacity of this embodiment has been described by using the first and second line-to-ground bypass capacitors 4 and 9, but a line-to-ground capacity formed by a wiring pattern of a pair of lines and the ground may be used.

(36) Embodiment 2.

(37) Next, a power conversion device according to Embodiment 2 of this invention will be described.

(38) In Embodiment 1, the values of the common-mode inductances L.sub.common6 and L.sub.common8 of the first reactors 6a and 6b and the second reactors 8a and 8b are set such that the common-mode noise resonance frequency f.sub.r1 formed in the first reactors 6a and 6b, the second reactors 8a and 8b, the first line-to-ground bypass capacitor 4 and the second line-to-ground bypass capacitor 9 satisfies f.sub.r1f.sub.2; in Embodiment 2, the values of the common-mode inductances L.sub.common6 and L.sub.common8 of the first reactors 6a and 6b and the second reactors 8a and 8b are set such that the common-mode noise resonance frequency f.sub.r1 becomes f.sub.4=5 MHz or higher, f.sub.4 at which a conduction noise limit value defined in International Standard IEC61000-6-3 (second edition; 2006) depicted in FIG. 6 is switched and increases.

(39) In FIG. 6, a conduction noise limit value defined in International Standard IEC61000-6-3 (second edition; 2006) is depicted. In this type of power conversion device, it is necessary to keep conduction noise to a limit value depicted in FIG. 6 or less so as not to cause harm such as a malfunction or a shutdown of other electronic devices. As depicted in FIG. 6, the limit value gradually decreases until 500 kHz, the limit value becomes constant at 500 kHz or higher, and the limit value increases at 5 MHz or higher. Even when common-mode noise resonance occurs at 5 MHz or higher, since the limit value is high, it is possible to keep conduction noise to the limit value or less easily without providing a countermeasures part.

(40) Therefore, the values of L.sub.common6 and L.sub.common8 are set as in Equation (6) such that f.sub.r1f.sub.4 holds.
L.sub.common6+L.sub.common8<1/{(1010.sup.6).sup.2(C.sub.4+C.sub.9)}(6)

(41) According to this embodiment, by inserting the reactors having the same inductance value, into both of a pair of lines, since it is possible not only to reduce common-mode noise, but also to shift, by setting the values of L.sub.common6 and L.sub.common8 as in Equation (6), the resonance frequency f.sub.r1 of the capacity of the line-to-ground bypass capacitor and the reactors which are inserted into both lines to 5 MHz or higher at which the conduction noise limit value increases, there is no need to provide a countermeasures part such as a common-mode choke separately for reduction in noise which is increased in a resonance frequency band, which makes it possible to keep conduction noise to a limit value or less while achieving a reduction in the size of a noise filter and a reduction in cost.

(42) In the above description, a case in which the reactors are connected to the input side and the output side of the switching circuit 7 has been described; however, even in a case in which the reactors are provided only on the input side of the switching circuit 7, by setting the common-mode inductance value of the reactors on the input side such that f.sub.r1f.sub.4 holds, it is possible to suppress common-mode noise effectively. Moreover, even in a case in which the reactors are provided only on the output side of the switching circuit 7, by setting the common-mode inductance value of the reactors on the output side such that f.sub.r1f.sub.4 holds, it is possible to suppress common-mode noise effectively.

(43) Incidentally, the line-to-ground capacity of this embodiment has been described by using the first and second line-to-ground bypass capacitors 4 and 9, but a line-to-ground capacity formed by a wiring pattern of a pair of lines and the ground may be used.

(44) Moreover, in this embodiment, descriptions have been given by using the conduction noise limit value of IEC61000-6-3, but other standards, such as IEC61581-21, in which a conduction no limit value increases at 5 MHz may be used.

(45) Embodiment 3.

(46) Next, a power conversion device according to Embodiment 3 of this invention will be described.

(47) The values of the common-mode inductances L.sub.common6 and L.sub.common8 of the first reactors 6a and 6b and the second reactors 8a and 8b are set such that the common-mode noise resonance frequency f.sub.r1 formed in the first reactors 6a and 6b, the second reactors 8a and 8b, the first line-to-ground bypass capacitor 4, and the second line-to-ground bypass capacitor 9 satisfies f.sub.r1f.sub.2 in Embodiment 1 and f.sub.r1f.sub.4 in Embodiment 2; in Embodiment 3, the values of the common-mode inductances L.sub.common6 and L.sub.common8 of the first reactors 6a and 6b and the second reactors 8a and 8b are set such that the common-mode noise resonance frequency f.sub.r1 becomes f.sub.3=500 kHz or higher, f.sub.3 at which a conduction noise limit value defined in International Standard IEC61000-6-3 (second edition; 2006) shown in FIG. 6 is switched and becomes constant.

(48) As depicted in FIG. 5, the frequency of a harmonic component of a fundamental component f.sub.0 of a switching frequency attenuates at a slope of 20 dB/decade or 40 dB/decade. Moreover, as depicted in FIG. 6, the conduction noise limit value becomes constant at a frequency of 500 kHz or higher. Even when common-mode noise resonance occurs at 500 kHz or higher, since the harmonic component of f.sub.0 attenuates at a slope of 20 dB/decade or 40 dB/decade while the limit value is constant, it is possible to keep conduction noise to a limit value or less easily without providing a countermeasures part.

(49) Therefore, the values of L.sub.common6 and L.sub.common8 are set as in Equation (7) such that f.sub.r1f.sub.3 holds.
L.sub.common6+L.sub.common8<1/{(1010.sup.5).sup.2(C.sub.4+C.sub.9)}(7)

(50) According to this embodiment, by inserting the reactors having the same inductance value into both of a pair of lines, since it is possible not only to reduce common-mode noise, but also to shift, by setting the values of L.sub.common6 and L.sub.common8 as in Equation (7), the resonance frequency f.sub.r1 of the capacity of the line-to-ground bypass capacitor and the reactors which are inserted into both lines to 500 kHz or higher at which the conduction noise limit value becomes constant and a harmonic component of a fundamental component f.sub.0 of a switching frequency attenuates at a slope of 20 dB/decade or 40 dB/decade while the limit value is constant, there is no need to provide a countermeasures part such as a common-mode choke separately for reduction in noise which is increased in a resonance frequency band, which makes it possible to keep conduction noise to a limit value or less while achieving a reduction in the size of a noise filter and a reduction in cost.

(51) In the above description, a case in which the reactors are connected to the input side and the output side of the switching circuit 7 has been described; however, even in a case in which the reactors are provided only on the input side of the switching circuit 7 and resonate with the line-to-ground capacitor, it is possible to suppress common-mode noise effectively. Moreover, even in a case in which the reactors are provided only on the output side of the switching circuit 7 and resonate with the line-to-ground capacitor, it is possible to suppress common-mode noise effectively.

(52) The line-to-ground capacity of this embodiment has been described by using the first and second line-to-ground bypass capacitors 4 and 9, but a line-to-ground capacity formed by a wiring pattern of a pair of lines and the ground may be used.

(53) Moreover, in this embodiment, descriptions have been given by using the conduction noise limit value of IEC61000-6-3, but other standards, such as IEC61581-21, in which a conduction noise limit value becomes constant at 500 kHz may be used.

(54) While Embodiments 1 to 3 of this invention have been described, this invention allows the embodiments to be combined with each other or appropriately modified or omitted within the scope of the invention.