Power conversion device

In the present invention, a power conversion device is provided with an inverter for converting power output from a power source; a first power supply bus, connected to the positive electrode side of the inverter and the power source; a second power supply bus, connected to the negative electrode sides of the inverter and the power source; a first conductor that forms, along with the first power supply bus, a capacitor; a second conductor that forms, along with the second power supply bus, a capacitor; and a connection circuit, comprising a resistor, that electrically connects the first conductor and the second conductor.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese Patent Application No. 2011-186995, filed Aug. 30, 2011, incorporated herein in its entirety.

TECHNICAL FIELD

The present invention relates to a power conversion device.

BACKGROUND ART

There has been known a noise reduction device for reducing noise generated in a power conversion device that includes: a converter connected to an AC power supply; an inverter connected to a DC output side of the converter; and a DC smoothing capacitor connected to a DC intermediate circuit (see Japanese Patent Application Publication No. 2002-252985). The noise reduction device is a device configured to reduce a noise current which flows on the power conversion device in response to the turning on and off of semiconductor switching elements that constitute the inverter. The noise reduction device includes: a noise current detection unit configured to detect the noise current; and a noise compensation current supply unit configured to generate a noise compensation current for reducing the detected noise current, and to supply the noise compensation current to the power conversion device. The noise compensation current supply unit is an element whose output current is controlled according to a detection signal from the noise current detection unit. The noise compensation current supply unit includes a series circuit including transistors each having a breakdown voltage smaller than a voltage of the DC intermediate circuit; and Zener diodes.

However, there is a problem that the transistors and the Zener diodes cannot perform high-speed operations against high-frequency switching noise, thereby failing to suppress the noise.

BRIEF SUMMARY

An object of the present invention is to provide a power conversion device which is capable of suppressing noise caused by the switching of an inverter.

A power conversion device according to an aspect of the present invention includes: a first power supply bus being a power supply bus on a positive electrode side and a second power supply bus being a power supply bus on a negative electrode side, the power supply buses being connected to an inverter; a first conductive body and a second conductive body forming capacitors in conjunction with the first power supply bus and the second power supply bus, respectively; and a connection circuit provided with a resistor and configured to electrically connect the first conductive body and the second conductive body together.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below on the basis of the drawings.

First Embodiment

A drive system for an electric vehicle including a power conversion device according to an embodiment of the present invention will be described with reference toFIG. 1andFIG. 2. Although detailed illustration is omitted therein, an electric vehicle of this embodiment is a vehicle which runs on an electric motor300, such as a three-phase AC electric motor, as a running drive source. The electric motor300is joined to an axle of the electric vehicle. Although the following description will be provided by using the electric vehicle as an example, the present invention is also applicable to a hybrid electric vehicle (HEV), and to a power conversion device to be installed in equipment other than vehicles.

The drive system having the power conversion device of this embodiment includes a power conversion device100, a DC power supply200, the electric motor300, and shielded wires7and8. The DC power supply200is formed from multiple batteries and is connected to the power conversion device100through the shielded wires7. The DC power supply200serves as a power source for the vehicle and supplies DC power to the power conversion device100. The power conversion device100is connected between the DC power supply200and the electric motor300, and is configured to change the DC power supplied from the DC power supply200into AC power and to supply the AC power to the electric motor300. The shielded wires7and8are electric wires formed by covering metal wires with a resin. The shielded wires7include a pair of shielded wires. One of the shielded wires7connects a positive electrode terminal of the DC power supply200to a power supply bus11, and the other shielded wire7connects a negative electrode terminal of the DC power supply200to a power supply bus21. The shielded wires8include three shielded wires. The three shielded wires8correspond to U phase, V phase, and W phase of the electric motor300, and connect bus bars6to the electric motor300.

The power conversion device100includes the power supply buses11and21, dielectric bodies12and22, conductive bodies13and23, a connection circuit30, a smoothing capacitor4, a power module5, and the bus bars6. The power supply bus11is a power supply line formed from a conductive body in a plate shape such as a flat plate shape, and configured to supply electric power outputted from the positive electrode of the DC power supply200to the power module5. The power supply bus11corresponds to a P-side power supply line of an inverter circuit that constitutes the power conversion device100. The power supply bus21is a power supply line formed from a conductive body in a plate shape such as a flat plate shape, and is configured to supply electric power outputted from the negative electrode side of the DC power supply200to the power module5. The power supply bus21corresponds to an N-side power supply line of the inverter circuit that constitutes the power conversion device100. Of the two side surfaces of the power supply bus11, an inner side surface of the power supply bus11, which does not face the dielectric body12, is opposed to an inner side surface of the power supply bus21. Similarly, of the two side surfaces of the power supply bus21, the inner side surface of the power supply bus21, which does not face the dielectric body22, is opposed to the inner side surface of the power supply bus11. Parts of the power supply buses11and21, or tip end portions of the power supply buses11and21, serve as terminals (tabs) of the power conversion device100and are connected to tip ends of the shielded wires7.

The dielectric body12is formed in a plate shape such as a flat plate shape, and is made from a material such as a resin having a higher dielectric constant than the power supply bus11and the conductive body13. The two side surfaces of the dielectric body12are opposed to a principal surface of the power supply bus11and a principal surface of the conductive body13, respectively. The dielectric body12is provided between the power supply bus11and the conductive body13, and is sandwiched between the power supply bus11and the conductive body13. The dielectric body22is formed in a plate shape such as a flat plate shape, and is made from a material having a higher dielectric constant than the power supply bus21and the conductive body23. The two side surfaces of the dielectric body22are opposed to a principal surface of the power supply bus21and a principal surface of the conductive body23, respectively. The dielectric body22is provided between the power supply bus21and the conductive body23, and is sandwiched between the power supply bus21and the conductive body23.

The conductive body13is made from a conductive material in a plate shape, and is attached to the surface of the dielectric body12by attaching a metal tape to the dielectric body12, for example. The inner side surface of the conductive body13is located at a position opposed to the outer side surface of the dielectric body12. The conductive body23is made from a conductive material in a plate shape, and is attached to the surface of the dielectric body22by attaching a metal tape to the dielectric body22, for example. The inner side surface of the conductive body23is located at a position opposed to the outer side surface of the dielectric body22.

The power supply bus11, the dielectric body12, and the conductive body13include the dielectric material (an insulating material) and the two conductive plates sandwiched together with the dielectric material (the insulating material), thereby collectively forming a capacitor that accumulates electric charges. Similarly, the power supply bus21, the dielectric body22, and the conductive body23include the dielectric material (the insulating material) and the two conductive plates sandwiched together with the dielectric material (the insulating material), thereby collectively forming a capacitor that accumulates electric charges. In other words, a space between the power supply bus11and the conductive body13is insulated and provided with capacitance, while a space between the power supply bus21and the conductive body23is insulated and provided with capacitance.

The connection circuit30includes a resistor31, and lines32and33. The connection circuit30is a circuit configured to electrically connect the conductive body13and the conductive body23together. The resistor31is provided therein in order to impart a resistance component to the connection circuit30. A resistance value of the resistor31is set at least higher than resistance values of the conductive bodies13and23, and is made higher than resistance values of the line32and the line33. One end of the line32is connected to the conductive body13while the other end thereof is connected to the resistor31. One end of the line33is connected to the conductive body23while the other end thereof is connected to the resistor31. In other words, the connection circuit30includes the resistor31so as to establish electrical communication between the conductive body13and the conductive body23while preventing the occurrence of a short circuit between the conductive body13and the conductive body23.

Parts of the power supply buses11and21branch off, and the parts branching from the power supply bus11are connected to a positive terminal of the smoothing capacitor4and a positive terminal of the power module5, respectively, while the parts branching from the power supply bus21are connected to a negative terminal of the smoothing capacitor4and a negative terminal of the power module5, respectively. The smoothing capacitor4is connected between the power supply bus11and the power supply bus21, and is thereby connected between the DC power supply200and the power module5. The smoothing capacitor4is a capacitor configured to rectify the electric power to be inputted to and outputted from the DC power supply200.

The power module5is connected between the DC power supply200and the bus bars6through the power supply buses11and21. The power module5is provided with multiple semiconductor switching elements inclusive of IGBTs or MOSFETs which are placed on a board. Here, the power module5is an inverter configured to change the electric power from the DC power supply by turning the semiconductor switching elements on and off on the basis of control signals from a not-illustrated controller, and to output the electric power to the electric motor300through the bus bars6. The not-illustrated controller generates switching signals for the semiconductor switching elements by use of a torque command value corresponding to aperture of an accelerator of the vehicle, and outputs the switching signals to the power module5. The semiconductor switching elements are switched on and off on the basis of the switching signals, so that the power module5can output the AC power for allowing the electric motor300to gain desired output torque. The power module5is electrically connected to the three-phase electric motor300by means of U-phase, V-phase, and W-phase output lines corresponding to the respective phases of the electric motor300.

The bus bars6are formed from three conductive plates in a plate shape, which are made of a conductive material. The bus bars6connect the power module5to the shielded wires8. Tip end portions of the bus bars6serve as terminals (tabs) of the power conversion device100, and are connected to tip ends of the shielded wires8, respectively.

Next, operations of the power supply buses11and21, the dielectric bodies12and22, the conductive bodies13and23, and the connection circuit30of this embodiment will be described by usingFIG. 3. Note that illustration of part of the power conversion device100and the shielded wires7and8is omitted fromFIG. 3.

As described previously, the conductive body13and the conductive body23are respectively located opposed to the power supply bus11and the power supply bus21while interposing the dielectric body12and the dielectric body22in between. Hence, the conductive bodies13and23, the dielectric bodies12and22, and the power supply buses11and21are represented as two capacitors as shown inFIG. 3. Moreover, the space between the power supply bus11and the power supply bus21is represented by an equivalent circuit designed to connect the capacitors and the resistor31.

In the meantime, switching noise is generated when the switching elements included in the power module5are subjected to the switching operations. The switching noise grows to noise containing various frequencies that correspond to timings to switch the switching elements, and further to a generation source of noise in each power supply bus11or21, which has a peak value at a specific frequency. For this reason, the switching noise is likely to leak from the power conversion device100to the outside. Moreover, if the frequency of the noise interferes with a frequency band of a car radio that is installed in the vehicle equipped with the power conversion device100, the noise is also likely to render radio broadcast inaudible or to bring about jarring sounds to a user. Furthermore, the noise is also likely to adversely affect other electronic devices installed in the vehicle.

In this embodiment, the conductive body13and the conductive body23form the capacitors in conjunction with the power supply bus11and the power supply bus21, respectively. Accordingly, if the switching noise from the power module5generates the noise in any of the power supply buses11and21, the noise is used for induction by any of the capacitors. Then, a noise current thus induced by the capacitor on the basis of the noise is used by the resistor31for generating heat. Thus, this embodiment suppresses the noise and avoids the leakage of the noise from the power conversion device100to the outside.

Moreover, in this embodiment, a resistance value of the resistor31and capacitances of the capacitors formed from the power supply buses11and21, the dielectric bodies12and22, and the conductive bodies13and23are set in accordance with the frequency of the switching noise, and the switching-based noise is thus suppressed. Specifically, the switching noise contains multiple frequencies and the noise generated in the power supply bus11has the specific frequency attributed to the shape of the power supply bus11. For this reason, it is possible to control a peak of the noise by setting the resistance value of the resistor31and the capacitance of the corresponding capacitor in accordance with a noise component so as to control a peak value of the noise having the specific frequency.

As described above, the power conversion device of this embodiment includes: the power supply bus11and the power supply bus21which are connected to the power module5; the conductive body13and the conductive body23which form the capacitors in conjunction with the power supply bus11and the power supply bus21, respectively; and the connection circuit30which includes the resistor and establishes electrical communication between the conductive body13and the conductive body23. Thereby, the noise currents attributed to the noise generated in the power supply buses11and21by the switching of the power module5can be conducted to the capacitors. Thus, it is possible to accumulate electric charges in the capacitors and to use the electric charges with the resistor31for generating the heat. In other words, the noise can be used for induction and thus absorbed by the resistor31. As a consequence, it is possible to suppress the noise and to avoid the leakage of the noise from the power conversion device100to the outside.

In this embodiment, the resistance value of the resistor31is set higher than the resistance value of the conductive body13or the conductive body23. Thus, when the connection circuit30connects the conductive body13and the conductive body23together, it is possible to prevent a short circuit between the conductive bodies13and23and to suppress the noise.

The power conversion device100of this embodiment includes the dielectric body12provided between the power supply bus11and the conductive body13, and the dielectric body22provided between the power supply bus21and the conductive body23. This configuration increases each electrostatic capacitances between the power supply buses11and21and the conductive bodies13and23, respectively, and can thus enhance a noise suppression effect. Moreover, in this embodiment, the conductive bodies13and23are located in the vicinities of the power supply buses11and21via the dielectric bodies12and22, respectively. Thus, it is possible to increase the electrostatic capacitances between the power supply buses11and21and the conductive bodies13and23, respectively, and thus to enhance the noise suppression effect.

In addition, each of the conductive bodies13and23is made from the metal tape. Thus, the conductive bodies13and23can be formed easily.

In this embodiment, the resistance value of the resistor31or the capacitances of the capacitors are set in accordance with the frequency of the noise generated in the power supply bus11and21by the switching operation of the power module5. Thus, the capacitors and the resistor31can absorb the noise in accordance with the peak of the noise generated by the switching operation, and thereby suppressing the noise.

In this embodiment, the dielectric bodies12and22are sandwiched between the power supply bus11and the conductive body13as well as between the power supply bus21and the conductive body23, respectively. However, as shown inFIG. 4, the dielectric bodies12and22are not indispensable. Note that illustration of part of the power conversion device100and the shielded wires7and8is omitted fromFIG. 4.

The power module5corresponds to an “inverter” according to the present invention. The power supply bus11corresponds to a “first power supply bus” of the present invention. The power supply bus21corresponds to a “second power supply bus” of the present invention. The conductive body13corresponds to a “first conductive body” of the present invention. The conductive body23corresponds to a “second conductive body” of the present invention. The dielectric body12corresponds to a “first dielectric body” of the present invention. The dielectric body22corresponds to a “second dielectric body” of the present invention.

Second Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 5andFIG. 6. This embodiment includes a dielectric body having a different configuration from the configuration of the dielectric bodies in the above-described first embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions of the first embodiment will be incorporated herein as appropriate.

A dielectric body14is made from a resin provided between the power supply bus11and the conductive body13as well as between the power supply bus21and the conductive body23while covering surfaces of the power supply bus11and the power supply bus21. The dielectric body14is held between the conductive body13and the conductive body23. In other words, part of the outer periphery of the power supply bus11is covered with the dielectric body14, part of the outer periphery of the power supply bus21is covered with the dielectric body14, and the dielectric body14is also held between the power supply bus11and the power supply bus21. Thus, the conductive body13and the power supply bus11collectively form a capacitor while the conductive body23and the power supply bus21collectively form a capacitor.

Here, a method of setting the resistance value of the resistor31of this embodiment will be described by usingFIG. 7toFIG. 9. InFIG. 7, the length of the power supply buses11and21is denoted by I, their width is denoted by w, their height is denoted by H, and a distance between the power supply bus11and the power supply bus21is denoted by d.

If an inductance component between the power supply bus11and the power supply bus21is Lpn and a capacitance component therebetween is Cpn, then as shown in following formula (1), a resistance value (Rpn) of the power supply buses11and21is approximated to a value which is proportional to a square root of the inductance component (Lpn) and inversely proportional to a square root of the capacitance component (Cpn).

Meanwhile, a self-inductance (Lo) and a mutual inductance (Mo) between the power supply bus11and the power supply bus21are expressed by the formula 2 and the formula 3 shown below.

When the length (I) is sufficiently longer than the distance (d), the capacitance component (Cpn) between the power supply bus11and the power supply bus21becomes dominant as compared to the inductance component (Lpn=2(Lo−Mo)) between the power supply bus11and the power supply bus21in the formula (1).

If a relative permittivity between the power supply bus11and the power supply bus21is denoted by ∈r, a dielectric constant of the vacuum therebetween is denoted by ∈0, and the area of each of the surfaces of the power supply bus11and the power supply bus21facing each other is denoted by S, then the capacitance component (Cpn) is approximated by the following formula (4).

Then, the following formula (5) is derived by assigning the formula (4) to the formula (1).

Specifically, the resistance value (Rpn) of the power supply buses11and21is approximated to a value which is proportional to a square root of the distance (d) and inversely proportional to a square root of the area (S).

In order to make the connection circuit30exert a noise reduction effect, it is preferable to adjust the resistance value of the resistor31on the basis of the resistance value of the power supply buses11and21.FIG. 8shows a noise characteristic when the resistance value of the resistor31is changed with a central focus on the resistance value (Rpn) of the power supply buses11and21. InFIG. 8, the horizontal axis indicates the resistance value of the resistor31and the vertical axis indicates the intensity of the noise. The noise is reduced most in the case where the resistance value of the resistor31is set equal to the resistance value (Rpn) of the power supply buses11and21. Here, the noise can be reduced at least by setting the resistance value of the resistor31in a range from a resistance value (Rpn/10) to a resistance value (10Rpn).

Next, with reference toFIG. 9, a description will be given of impedance characteristics with respect to the frequency of the switching noise generated by the switching operations of the switching elements included in the power module5. Here, the impedance of the capacitors and the connection circuit30from the viewpoint of the power supply buses11and21is denoted by Zo. A solid line AL ofFIG. 9indicates an impedance characteristic when the resistance value (R) of the resistor31is adjusted on the basis of the resistance value (Rpn) of the power supply buses11and21(R≈Rpn). A dashed line BL ofFIG. 9indicates an impedance characteristic either when the resistance value of the resistor31is sufficiently greater than the resistance value (Rpn) of the power supply buses11and21(R>>Rpn) or when the resistance value of the resistor31is sufficiently smaller than the resistance value (Rpn) of the power supply buses11and21(R<<Rpn).

As indicated with the dashed line BL, a sharp resonance is observed when the resistance value of the resistor31is either sufficiently greater or sufficiently smaller than the resistance value (Rpn) of the power supply buses11and21. Here, an amount of change in impedance becomes large at each resonance point. On the other hand, as indicated with the solid line AL, the resonance becomes dull when the resistance value (R) of the resistor31is approximate to the resistance value (Rpn) of the power supply buses11and21(R≈Rpn). Here, the amount of change in impedance becomes small at each resonance point. Thus, the noise at the frequency corresponding to the resonance point is suppressed. Accordingly, the noise can be suppressed by setting the resistance value (R) of the resistor31on the basis of the resistance value (Rpn) of the power supply buses11and21. Meanwhile, even when a frequency band such as a radio broadcast frequency that should be prevented from interference is allocated near the resonance point, the amount of change in the impedance (Zo) at the resonance frequency can be suppressed by adjusting the resistance value (R) of the resistor31on the basis of the resistance value (Rpn) of the power supply buses11and21. As a consequence, the noise in the frequency band can be suppressed.

As described above, this embodiment includes the dielectric body14made from the resin, which is provided between the power supply bus11and the conductive body13as well as between the power supply bus21and the conductive body23while partially covering the surfaces of the power supply bus11and the power supply bus21. Accordingly, the surfaces of the power supply bus11and the power supply bus21are partially molded with the resin. When the conductive bodies13and23are positioned such that the conductive bodies13and23and the power supply buses11and21form the capacitors, the conductive bodies13and23only need to be disposed on surfaces of the dielectric body14. Thus, it is possible to facilitate the positioning of the conductive bodies13and23with respect to the power supply buses11and21, and consequently to suppress the noise generated in the power supply buses11and21.

In addition, the resistance value of the resistor31is set at the value which is proportional to the square root of the inductance component between the power supply bus11and the power supply bus21and inversely proportional to the square root of the capacitance component between the power supply bus11and the power supply bus21. Thus, it is possible to suppress the noise generated in the power supply buses11and21, and to avoid the leakage of the noise from the power conversion device100to the outside.

Moreover, in this embodiment, the resistance value of the resistor31is set at the value which is proportional to the square root of the distance between the power supply bus11and the power supply bus21and inversely proportional to the square root of either the area of the opposed surface of the power supply bus11facing the power supply bus21or the area of the opposed surface of the power supply bus21facing the power supply bus11. Thus, it is possible to suppress the noise generated in the power supply buses11and21, and to avoid the leakage of the noise from the power conversion device100to the outside.

In this embodiment, the dielectric body14is integrated and thus configured to cover the power supply bus11and the power supply bus21. Instead, a configuration may be adopted in which: the dielectric body14is divided into pieces; and the divided pieces of the dielectric bodies14covers part of the power supply bus11and part of the power supply bus21, respectively.

The above-described dielectric body14corresponds to the “first dielectric body” and the “second dielectric body” of the present invention.

Third Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 10andFIG. 11. In this embodiment, a configuration of a connecting portion between the power supply buses11and21and the lines32and33, respectively, is different from that of the above-described first embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions of the first embodiment or the second embodiment will be incorporated herein as appropriate.

Of the end portions of the power supply buses11and21, cylindrical cable units81and82, which have the power supply buses11and21as their central lines, are respectively formed in the end portions opposite the DC power supply200. Capacitors are formed in the cable units81and82.

The cable unit81includes the power supply bus11, the dielectric body12, the conductive body13, and an insulating portion15. The power supply bus11, the dielectric body12, the conductive body13, and the insulating portion15are each formed in a cylindrical shape and concentrically arranged around the center of an axis on a cross section taken in a perpendicular direction. The power supply bus11serves as the center of the axis of the cable unit81. The dielectric body12is formed coaxially with the power supply bus11to cover the outer periphery of the power supply bus11. The conductive body13is formed coaxially with the power supply bus11to cover the outer periphery of the dielectric body12. The insulating portion15is formed coaxially with the power supply bus11to cover the outer periphery of the conductive body13. Thereby, the dielectric body12is sandwiched between the power supply bus11and the conductive body13. Thus, the conductive body13and the power supply bus11collectively form a capacitor.

The cable unit82includes the power supply bus21, the dielectric body22, the conductive body23, and an insulating portion25. The power supply bus21, the dielectric body22, the conductive body23, and the insulating portion25are each formed in a cylindrical shape and coaxially arranged. The power supply bus21serves as the center of an axis of the cable unit82. The dielectric body22is formed coaxially with the power supply bus21to cover the outer periphery of the power supply bus21. The conductive body23is formed coaxially with the power supply bus21to cover the outer periphery of the dielectric body22. The insulating portion25is formed coaxially with the power supply bus21to cover the outer periphery of the conductive body23. Thereby, the dielectric body22is sandwiched between the power supply bus21and the conductive body23. Thus, the conductive body23and the power supply bus21collectively form a capacitor.

The line32is connected to the conductive body13while the line33is connected to the conductive body23.

As described above, in this embodiment, each of the cable units81and82is provided at one end of the corresponding power supply bus11or21. Then, the power supply buses11and21are used as the centers of the axes of the cable units81and82while the conductive bodies13and23are used as the conductive bodies located outside the centers of the axes of the corresponding cable units81and82, respectively. Thereby, the capacitors are formed in the cable units81and82. Thus, it is possible to prevent parasitic capacitances from affecting the noise in conduction paths from the power supply buses11and21to the lines32and33, respectively, and to suppress the noise generated in the power supply buses11and21, as well as to avoid the leakage of the noise from the power conversion device100to the outside.

Fourth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 12andFIG. 13. In this embodiment, configurations of the power supply buses11and21and the conductive bodies13and23are different from those of the above-described first embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions of the first embodiment or the second embodiment will be incorporated herein as appropriate.

Each of the power supply buses11and21is formed in a cylindrical line shape. One end of each power supply bus11or21is connected to the DC power supply200and the other end thereof is left open. Each of the conductive bodies13and23is formed in such a manner as to cover the power supply bus11or21while retaining a predetermined distance from the power supply bus11or21. Each of the conductive bodies13and23has a columnar shape made by bending a plate-shaped conductive body, and is formed coaxially with the power supply bus11or21and in such a manner as to form an arc shape around an axis on a cross section taken in a perpendicular direction. Since a gap is formed between each power supply bus11or21and each conductive body13or23, each conductive body13or23and each power supply bus11or21collectively form a capacitor.

As described above, in this embodiment, each power supply bus11or21is formed in the cylindrical line shape, and each conductive body13or23is formed in the columnar shape by bending the flat plate in such a manner as to cover a side surface of the power supply bus11or21. Thereby, part of the side surface of the power supply bus11or21is covered with the conductive body13or23, whereby each conductive body13or23acts to shield the noise. Thus, the leakage of the noise generated in the power supply buses11and21can be avoided. As a consequence, it is possible to suppress the noise generated in the power supply buses11and21and to avoid the leakage of the noise from the power conversion device100to the outside.

Fifth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 14andFIG. 15. This embodiment is different from the above-described fourth embodiment in that conductive bodies16and26are further provided in this embodiment. Since the configurations other than the above are the same as those of the above-described fourth embodiment, the descriptions of the fourth embodiment will be incorporated herein as appropriate.

The columnar-shaped conductive bodies16and26are further provided outside the conductive bodies13and23. Each of the conductive bodies16and26is formed in the columnar shape by bending a flat plate in such a manner as to cover the side surfaces of the power supply buses11and21. Moreover, the conductive bodies16and26are disposed in such a manner as to cover gaps between the conductive body13and the conductive body23. The conductive bodies16and26are connected to the lines32and33, respectively. Thus, each conductive body16or26and each power supply bus11or21collectively form a capacitor.

As described above, in addition to the conductive bodies13and23, this embodiment includes the conductive bodies16and26which form the capacitors in conjunction with the power supply buses11and21, and the conductive bodies16and26are disposed in such a manner as to cover the gaps between the conductive body13and the conductive body23. Thereby, the conductive bodies16and26act to shield the noise. Thus, the leakage of the noise generated in the power supply buses11and21can be avoided. In addition, since the conductive bodies16and26and the power supply buses11and21form the capacitors, it is possible to suppress the noise generated in the power supply buses11and21.

Sixth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 16andFIG. 17. This embodiment is different from the above-described fourth embodiment in that conductive bodies12and22are provided in this embodiment. Since the configurations other than the above are the same as those of the above-described fourth embodiment, the descriptions of the fourth embodiment will be incorporated herein as appropriate.

The cylindrical dielectric bodies12and22are formed in such a manner as to cover the side surfaces of the outer peripheries of the power supply buses11and21each formed in the cylindrical line shape, and the conductive bodies13and23are formed in such a manner as to cover parts of side surfaces of the outer peripheries of the dielectric bodies12and22. Thereby, each dielectric body12or22is sandwiched between each power supply bus11or21and each conductive body13or23. Thus, each conductive body13or23and each power supply bus11or21collectively form a capacitor.

As described above, this embodiment includes the cylindrical dielectric bodies12and22, which are located between the power supply buses11and21and the conductive bodies13and23, respectively, and configured to cover the side surfaces of the outer peripheries of the power supply buses11and21. Moreover, the conductive bodies13and23are disposed in such a manner as to cover the parts of the side surfaces of the outer peripheries of the dielectric bodies12and22. Thereby, parts of the side surfaces of the power supply buses11and21are covered with the conductive bodies13and23while interposing the dielectric bodies12and22in between, and the conductive bodies13and23thereby act to shield the noise. Thus, the leakage of the noise can be avoided. As a consequence, it is possible to suppress the noise generated in the power supply buses11and21and to avoid the leakage of the noise from the power conversion device100to the outside.

Seventh Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 18. In this embodiment, the shapes of the power supply buses11and21and the shapes of the conductive bodies13and23are different from those in the above-described first embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions of the first to sixth embodiments will be incorporated herein as appropriate.

As shown inFIG. 18, each of the power supply buses11and21is formed from a conductive plate in a plate shape. Each power supply bus11or21is bent at two positions each at a right angle. Each of the conductive bodies13and23is made from a metal tape, each bent at two positions at a right angle, and thus formed in the same shape as part of the power supply bus11or21. In other words, part of a flat surface of each power supply bus11or21, inclusive of an open end of the power supply bus11or21and the bent portions of the power supply bus11or21, is opposed to a flat surface portion of the corresponding conductive body13or23. Thus, each conductive body13or23inclusive of its bent portions and each power supply bus11or21inclusive of its bent portions collectively form a capacitor.

As described above, this embodiment includes: the power supply buses11and21each formed from the conductive plate in the bent plate shape; and the conductive bodies13and23formed in the same shape as part of the shapes of the power supply buses11and21and opposed to the flat surface portions of the power supply buses11and21. Thus, each capacitor is formed between the conductive body13or23and the power supply bus11or21. For this reason, it is possible to suppress the noise generated in the power supply buses11and21and to avoid the leakage of the noise from the power conversion device100to the outside.

In this embodiment, the dielectric bodies12and22may also be provided between the power supply bus11and the conductive body13as well as between the power supply bus21and the conductive body23.

Eighth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 19. This embodiment is different from the above-described first embodiment in that a connection circuit40is provided in this embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions of the first to seventh embodiments will be incorporated herein as appropriate.

The connection circuit40includes a resistor41, and lines42and43. As is the case with the connection circuit30, the connection40connects the conductive body13and the conductive body23together. The connection circuit30is connected to one end of the conductive body13and one end of the conductive body23, while the connection circuit40is connected to the other end of the conductive body13and the other end of the conductive body23. As is the case with the resistor31, a resistance value of the resistor41is set in accordance with the noise component of the noise generated in the power supply buses11and21, and is adjusted on the basis of the resistance value of the power supply buses11and21.

As described above, in the power conversion device of this embodiment, the connection circuits30and40respectively including the resistors31and41are connected between the conductive body13and the conductive body23. Accordingly, the two resistors31and41are connected between the conductive body13and the conductive body23. Thus, the noise current induced by any of the capacitors from the noise generated in the power supply buses11and12can be used by the two resistors for generating heat. Thus, it is possible to shorten the time needed for suppressing the noise. In addition, it is possible to disperse modes of the noise and thus to enhance the noise suppression effect.

In this embodiment, a connection circuit50including a resistor51and lines52and53may further be connected between the conductive body13and the conductive body23, as shown inFIG. 20. In addition, one or more resistors similar to the resistors31,41, and51may further be connected between the conductive body13and the conductive body23. The connection circuit50is a circuit similar to the connection circuits30and40.

In this embodiment, as shown inFIG. 21, the conductive body13may be formed from a conductive body13aand a conductive body13beach having a flat plate shape, and the conductive body23may be formed from a conductive body23aand a conductive body23beach having a flat plate shape. Then, the conductive body13aand the conductive body13bmay be connected to each other using a connection circuit40while the conductive body23aand the conductive body23bmay be connected to each other using another connection circuit40. Thereby, the noise current induced by the capacitors can be used by the multiple resistors for generating heat. Thus, it is possible to shorten the time needed for suppressing the noise. In addition, it is possible to disperse modes of the noise and thus to enhance the noise suppression effect.

Ninth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 22. This embodiment is different from the above-described first embodiment in that resistors60are provided in this embodiment. Since the configurations other than the above are the same as those of the above-described first embodiment, the descriptions thereof will be incorporated herein as appropriate.

The resistors60include resistors60ato60c. Each of the resistors60ato60cis formed in a plate shape. Moreover, the resistors60ato60care provided at given intervals on one of side surfaces of the conductive body23, which is the side surface not opposed to the dielectric body22. Here, the material of the resistors60ato60cis selected such that a resistance value per unit length of the resistors60ato60cbecomes greater than a resistance value per unit length of the conductive body23. Alternatively, the shapes of the resistors60ato60care designed to meet the aforementioned requirement.

A plate-shaped conductive body17is connected between a tip end of the conductive body13and a tip end of the conductive body23. The conductive body13and the conductive body23are electrically connected to each other through the conductive body17.

The resistance value of the resistors60ato60cis higher than the resistance value of the conductive bodies13,17, and23. The resistors60ato60care provided in order to increase the resistance of the conductive body23. When noise currents attributed to the noise generated in the power supply buses11and21flow on the conductive bodies13,17, and23, the noise currents are used by the resistors60ato60cwith the higher resistance value for generating heat. Thus, the resistors60ato60cabsorb the noise current with a high frequency.

As described above, in this embodiment, the resistors60having the resistance value higher than the resistance value of the conductive body13or the conductive body23are provided to the conductive body23, and the conductive body17electrically connects the conductive body13and the conductive body23together. Thereby, the noise currents attributed to the noise generated in the power supply buses11and21are used by the resistors60. Thus, it is possible to suppress the noise generated in the power supply buses11and21.

In this embodiment, as shown inFIG. 23, the conductive body13may be formed from a conductive body13a, a conductive body13b, and a conductive body13ceach having a flat plate shape, and the conductive body23may be formed from a conductive body23a, a conductive body23b, and a conductive body23ceach having a flat plate shape. Then, resistors60ato60dmay be provided at spaces between the conductive body13aand the conductive body13b, between the conductive body13band the conductive body13c, between the conductive body23aand the conductive body23b, and between the conductive body23band the conductive body23c. Note that the resistors60aand60bare hidden behind the conductive body13and the like, and are therefore not illustrated inFIG. 23.

Thus, when noise currents attributed to the switching noise are conducted between the conductive body13aand the conductive body13b, between the conductive body13band the conductive body13c, between the conductive body23aand the conductive body23b, and between the conductive body23band the conductive body23c, the noise currents flow on the added resistors60ato60dand are used by the resistors60ato60dfor generating heat. For this reason, it is possible to suppress the noise generated in the power supply buses11and21. In addition, each of the resistors60ato60dcan be reduced in size in comparison with each of the resistors60ato60cshown inFIG. 22.

Although the resistance is increased by providing the resistors60ato60din this embodiment, resistors60ato60dmay be formed by providing ferrite to at least portions of the conductive bodies13,17, and23, instead of the aforementioned resistors60ato60d. Thereby, a resistance value in each of the conductive bodies13,17and23is higher at the ferrite-containing portion than at the other portion containing no ferrite. Accordingly, each ferrite-containing portion can use a noise current, thereby suppressing the noise. Here, it is only necessary to spray ferrite onto parts of the conductive body23. Thus, the resistance components can easily be added to the conductive bodies13,17, and23.

Here, the resistors60may be provided to the conductive body17.

Note that the resistors60ato60dof this embodiment correspond to the “resistor” according to the present invention, and the conductive body17thereof corresponds to the “connection circuit” of the present invention.

Tenth Embodiment

A drive system for an electric vehicle including a power conversion device according to another embodiment of the present invention will be described with reference toFIG. 24. This embodiment is different from the above-described ninth embodiment in that the conductive body23is provided with slits70. Since the configurations other than the above are the same as those of the above-described ninth embodiment, the descriptions thereof will be incorporated herein as appropriate.

The slits70are provided on a side surface of the conductive body23. The slits70include three slits70ato70c. The slits70are formed in such a manner as to penetrate from one side surface to the other side surface of the conductive body23, which are opposite from each other. On a cross section of the conductive body23taken parallel to the slits70, the cross-sectional area of a portion provided with a slit70is smaller than the cross-sectional area of a portion not provided with a slit70. For this reason, a resistance value of the portion provided with the slit70becomes higher than a resistance value of the portion not provided with the slit70. Accordingly, when the switching noise is generated by the switching operation of the power module5and the noise current flows on the conductive body23, the noise current is used by the portions provided with the slits70for generating heat.

As described above, in this embodiment, the conductive body23is provided with the slits70, each of which is formed to make the cross-sectional area of the corresponding portion smaller than the cross-sectional area of the remaining portions. Thus, each slit70forms the portion where the resistance is increased. In this way, the resistance of the conductive body23is increased at each of the portions provided with the slits70. Thus, the noise currents generated in the power supply buses11and21can be used by these portions for generating heat, and the noise can be suppressed. In addition, the slits70can be formed by processing the corresponding parts of the conductive body23. Thus, the resistance components can be easily added to the conductive body23.

Although the three slits70are provided in this embodiment, two slits may be instead provided therein, or four or more slits70may be provided therein. Here, the slits70may be provided to the conductive body13or the conductive body17.

The entire contents of Japanese Patent Application No. 2011-186995 (filing date: Aug. 30, 2011) are incorporated herein.

Although the contents of the present invention have been described with reference to the embodiments, it is obvious to those skilled in the art that the present invention is not limited only to these descriptions but various modifications and improvements are possible.

According to the present invention, noise generated in a power supply bus due to the switching of an inverter is absorbed by a resistor included in a connection circuit, and the noise can thus be suppressed. The present invention is therefore industrially applicable.