POWER CONVERSION DEVICE AND MANUFACTURING METHOD THEREFOR

This power conversion device includes cast resin provided at least between an inner wall of a storage portion and a smoothing capacitor and between the inner wall of the storage portion and a resistor, so as to be formed integrally, and heat dissipation and vibration protection for the smoothing capacitor and the resistor can be made by the cast resin. Thus, a dedicated assembly process for a structure for heat dissipation and vibration protection for the resistor is not needed, so that the cost is reduced. In addition, reliability of heat dissipation and vibration protection for the discharge circuit is ensured more easily as compared to a conventional method of pressing only one surface of the resistor to the housing by means such as screw fastening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a power conversion device and a manufacturing method therefor.

2. Description of the Background Art

A power conversion device which is provided to an electric vehicle or the like and performs operations such as output adjustment and phase conversion for power, includes a power module having a plurality of power semiconductors in combination, a current detection circuit for detecting output current from the power module, a driving circuit for driving a power semiconductor, a control circuit for outputting a command to a driving circuit, a smoothing capacitor, a discharge circuit, and the like.

The discharge circuit has a resistor and consumes electric charge stored in the smoothing capacitor as heat by the resistor, thus implementing a discharge function. Such a function of the discharge circuit is not a main function of the power conversion device but is an auxiliary function which is only used in short-time operation at the time of stop of the vehicle, collision thereof, or the like. Therefore, for the discharge circuit, it is required that the configuration is simple, cost is low, and the discharge circuit has such high reliability as to assuredly operate when abnormality such as collision of the vehicle occurs.

In order to ensure reliability of a discharge circuit, a structure for appropriately dissipating heat generated in the resistor is needed. If heat dissipation of the resistor is insufficient, the resistor might be burned out during discharge, resulting in loss of the function of the discharge circuit. In addition, since the resistor has great rated power and is a component having comparatively large dimensions, a vibration protection structure is needed.

In a conventional power conversion device, the resistor is fastened to a housing by a screw, whereby functions for heat dissipation and vibration protection are implemented. As a method other than screw fastening, Patent Document 1 describes that a discharge resistor connected to a capacitor element via a wire is placed in a case together with the capacitor element and the case is filled with a potting material that is thermally conductive. In this conventional example, the discharge resistor is placed in contact with a side wall and a bottom wall of the case.Patent Document 1: Japanese Laid-Open Patent Publication No. 2020-58214

However, in the screw fastening method, a dedicated assembly process for fastening the screw is needed, so that the manufacturing cost for the power conversion device increases. In addition, since heat dissipation performance depends on the degree of close contact between a surface of the resistor and a housing, it is difficult to ensure reliability of heat dissipation performance. If fastening torque for the screw is increased for enhancing the degree of close contact between the resistor and the housing, a problem such as breakage of a screw thread occurs.

Although Patent Document 1 does not disclose a method for fixing the discharge resistor to the case, if the discharge resistor is fixed to the case by the potting material, the discharge resistor might move when the potting material is injected, so that the wire connecting the capacitor element and the discharge resistor might be disconnected. If the discharge resistor is fixed by another method, a dedicated process therefor is needed, so that the manufacturing cost increases. Further, the potting material is not present between the discharge resistor and the case, and heat dissipation performance depends on the degree of close contact between a side surface of the discharge resistor and the case. Therefore, it is difficult to ensure reliability of heat dissipation performance. In addition, vibration at the time of collision of a vehicle or the like is directly transmitted from the case to the discharge resistor. Therefore, a wire connected to the discharge resistor might be damaged.

SUMMARY OF THE INVENTION

The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide a power conversion device and a manufacturing method therefor that can implement the function of a discharge circuit for discharging electric charge stored in a smoothing capacitor, at low cost, while ensuring reliability of the discharge circuit.

A power conversion device according to the present disclosure includes: a power module including a power device; a smoothing capacitor for smoothing input voltage to the power module; a discharge circuit including a resistor for discharging electric charge stored in the smoothing capacitor; a wiring plate connected to the power module and the smoothing capacitor; a housing storing the power module, the smoothing capacitor, the discharge circuit, and the wiring plate; and cast resin included inside the housing. The housing has a storage portion storing the smoothing capacitor and the resistor. The cast resin is provided at least between an inner wall of the storage portion and the smoothing capacitor and between the inner wall of the storage portion and the resistor, so as to be formed integrally.

A manufacturing method for a power conversion device according to the present disclosure includes the steps of: preparing a power module including a power device, a smoothing capacitor, a discharge circuit including a resistor, a wiring plate connected to the power module and the smoothing capacitor, a housing having a storage portion, and cast resin that has not been cured; fixing the wiring plate to the housing so as to cover an opening of the storage portion in a state in which the smoothing capacitor and the resistor are placed inside the storage portion; and injecting the cast resin into the storage portion from one or more through holes provided in the wiring plate fixed to the housing, so that the cast resin is provided at least between an inner wall of the storage portion and the smoothing capacitor and between the inner wall of the storage portion and the resistor, so as to be formed integrally.

In the power conversion device according to the present disclosure, heat dissipation and vibration protection for the smoothing capacitor and the resistor are made by the cast resin provided in the storage portion so as to be formed integrally. Thus, a dedicated assembly process for a structure for heat dissipation and vibration protection for the resistor is not needed, so that the cost is reduced. In addition, since heat dissipation and vibration protection for the resistor are made by the cast resin, reliability of heat dissipation and vibration protection for the discharge circuit is ensured more easily as compared to a conventional method of pressing only one surface of the resistor to the housing by means such as screw fastening.

In the manufacturing method for the power conversion device according to the present disclosure, the step of injecting the cast resin into the storage portion from the through hole provided in the wiring plate is performed after the step of fixing the wiring plate to the housing. Therefore, such an adverse effect that the cast resin that has not been cured adheres to a wiring plate fixation part provided to the housing, does not occur. Thus, workability is improved and cost reduction is achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, a power conversion device according to the first embodiment of the present disclosure will be described with reference to the drawings.FIG.1is a plan view schematically showing the configuration of the power conversion device according to the first embodiment, andFIG.2is a sectional view along line A-A inFIG.1. In the drawings, the same or corresponding parts are denoted by the same reference characters.

A power conversion device1according to the first embodiment is provided between a battery and a motor, as a power conversion device for driving a vehicle such as an electric vehicle or a hybrid vehicle, for example, and performs operations such as output adjustment and phase conversion for power.

As shown inFIG.1, the power conversion device1includes a housing11, a power module12, a circuit board13, a current detection circuit16, a wiring plate17, a smoothing capacitor18, a discharge circuit19, cast resin21, and the like.

The housing11forms an outer case of the power conversion device1and stores the power module12, the circuit board13, the current detection circuit16, the wiring plate17, the smoothing capacitor18, the discharge circuit19, and the like. The housing11has a storage portion11astoring the smoothing capacitor18and the resistor20.

The power module12includes a power device (not shown) such as power MOSFET or IGBT. The circuit board13includes a driving circuit14for driving the power device, and a control circuit15for controlling the driving circuit14. The current detection circuit16includes a Hall element, a magneto resistive element, etc., and detects output current from the power module12.

The wiring plate17is a printed board and is connected to the power module12and the smoothing capacitor18. The smoothing capacitor18smooths input voltage to the power module12. The discharge circuit19includes a resistor20for discharging electric charge stored in the smoothing capacitor18. The cast resin21is included inside the housing11.

InFIG.1, the storage portion11a, the smoothing capacitor18, the resistor20, and the cast resin21are present under the wiring plate17and therefore cannot be seen in a top view, but they are shown by dotted lines, for convenience. InFIG.1, the storage portion11aand the wiring plate17have rectangular shapes in a top view, but their shapes are not particularly limited. The wiring plate17often has a complicated shape corresponding to the internal configuration of the power conversion device1. Therefore, the wiring plate17is desirably made of a material having a high degree of freedom in shape, and is preferably a printed board.

Current paths and operation of the power conversion device1configured as described above will be described with reference toFIG.1. Power conversion device input current P1inputted to the smoothing capacitor18from a power supply (not shown) such as a battery is smoothed by the smoothing capacitor18, to become power module input current P2. By the circuit board13and the power module12, the power module input current P2becomes desired power conversion device output current P3which then passes through the current detection circuit16and is supplied to the motor (not shown).

The control circuit15collects information such as output current information S4obtained from the current detection circuit16and an external signal (not shown), and calculates a difference between the present motor operation state and a desired motor operation state. On the basis of the calculation result, the control circuit15generates a command signal S1for the driving circuit14so as to achieve the desired motor operation state.

The driving circuit14generates a command signal S2for the power module12on the basis of the command signal S1from the control circuit15. The driving circuit14switches a conduction state and a non-conduction state of the power module12by the command signal S2, to control the power conversion device output current P3so as to achieve the desired motor operation state.

At the time of stop of the vehicle, collision thereof, or the like, the discharge circuit19consumes electric charge stored in the smoothing capacitor18as smoothing capacitor discharge current P4by the resistor20, on the basis of the command signal S3from the control circuit15. In the first embodiment, the discharge circuit19is placed at the wiring plate17, and the command signal S3from the control circuit15is inputted to the discharge circuit19via a signal cable24.

Connection between the wiring plate17and the power module12affects the power module input current P2, and therefore it is desirable that they are directly connected without using a cable, a busbar, or the like. If the wiring plate17is formed by a printed board, direct connection with the power module12can be easily made.

For the purpose of simplifying the system, electric charge stored in the smoothing capacitor18may be always consumed by the resistor20without providing the command signal S3from the control circuit15to the discharge circuit19. A plurality of resistors20may be provided so that the speed of consumption of electric charge stored in the smoothing capacitor18may be switched in accordance with the operation state of the motor.

The power conversion device1includes the smoothing capacitor18having a comparatively large capacitance in order to smooth ripple current occurring at a timing of switching the conduction state and the non-conduction state of the power module12. The discharge circuit19is electrically connected to the smoothing capacitor18, and electric charge stored in the smoothing capacitor18is discharged by being consumed as heat by the resistor20. The resistor20is a component having great rated power and comparatively large dimensions, and a structure for heat dissipation and vibration protection for the resistor20is needed in order to ensure reliability of the discharge circuit19.

The structure for heat dissipation and vibration protection for the resistor20in the power conversion device1will be described.

As shown inFIG.2, a terminal181of the smoothing capacitor18and a terminal201of the resistor20are connected to the wiring plate17, and the smoothing capacitor18and the resistor20are fixed to one main surface of the wiring plate17. The storage portion11ahas an opening11c, and the wiring plate17is fixed to the housing11so as to cover at least a part of the opening11cin a state in which the smoothing capacitor18and the resistor20are placed inside the storage portion11a. In the first embodiment, as shown inFIG.1, the wiring plate17covers the entire opening11cof the storage portion11a.

The wiring plate17is fixed to the housing11by fixation members22a,22b(collectively referred to as fixation members22) such as screws or rivets, for example. In the first embodiment, the fixation members22are provided at two locations, but may be provided at one location or three or more locations. A method for fixing the wiring plate17to the housing11is not particularly limited and an adhesive or the like may be used.

The cast resin21is included inside the storage portion11a. As the cast resin21, for example, epoxy-based resin may be used. When the cast resin21is not cured, the cast resin21is in a liquid state having appropriate fluidity, and after being injected, the cast resin21is cured by being heated in a heating furnace or the like, or the cast resin21is formed by mixing a main agent and a curing agent, for example. The cast resin21needs to be resin having high thermal conductivity, and specifically, it is desirable that the thermal conductivity is 0.2 W/m·K or higher.

The cast resin21is provided at least between an inner wall11bof the storage portion11aand the smoothing capacitor18and between the inner wall11bof the storage portion11aand the resistor20, and is formed integrally. In other words, the cast resin21provided between the inner wall11bof the storage portion11aand the smoothing capacitor18, and the cast resin21provided between the inner wall11bof the storage portion11aand the resistor20, are at least partially contiguous to each other. The cast resin21is provided with a gap from the wiring plate17.

The cast resin21transmits heat generated from the smoothing capacitor18and the resistor20during operation of the power conversion device1, to the housing11, thereby dissipating heat, so as to protect the smoothing capacitor18and the resistor20from reaching temperatures greater than their respective guaranteed temperatures. In addition, the cast resin21provides protection so as not to cause such a trouble that, when the power conversion device1is subjected to vibration due to collision of a vehicle or the like, the smoothing capacitor18and the resistor20excessively vibrate and connection parts with the wiring plate17, etc., are damaged. That is, the cast resin21serves for heat dissipation and vibration protection for the smoothing capacitor18and the resistor20.

These functions are mainly imparted by the cast resin21provided between the housing11and the smoothing capacitor18and between the housing11and the resistor20. In addition, as shown inFIG.2, the cast resin21closely contacts with all side surfaces of the smoothing capacitor18other than a side surface from which the terminal181protrudes, and with all side surfaces of the resistor20other than a side surface from which the terminal201protrudes. Thus, since the cast resin21closely contacts with the side surfaces of the smoothing capacitor18and the resistor20so as to surround the side surfaces, reliability of heat dissipation and vibration protection can be ensured, whereby high reliability is obtained.

The wiring plate17has one or more through holes23a,23b(collectively referred to as through holes23) at locations opposed to the cast resin21. In the first embodiment, the wiring plate17has the through hole23aat a location corresponding to a part between the housing11and the smoothing capacitor18, and has the through hole23bat a location corresponding to a part between the housing11and the resistor20.

If the injection amount of the cast resin21is excessive, the cast resin21might flow out from a predetermined design range, leading to an adverse effect on operation of the power conversion device1. Therefore, the injection amount of the cast resin21is set so that the cast resin21does not come into contact with the wiring plate17. Since the wiring plate17has a plurality of through holes23, it is possible to inject the cast resin21from one through hole23and confirm the injection amount from another through hole23. If three or more through holes23are provided, the cast resin21can be injected from a plurality of through holes23simultaneously.

A flow of a manufacturing process for the power conversion device1will be described with reference to a flowchart inFIG.3.

First, in step S1, the power module12including the power device, the smoothing capacitor18, the discharge circuit19including the resistor20, the wiring plate17connected to the power module12and the smoothing capacitor18, the housing11having the storage portion11a, and the cast resin21that has not been cured, are prepared. In the first embodiment, the discharge circuit19is provided at the wiring plate17, and the smoothing capacitor18and the resistor20are fixed to one main surface of the wiring plate17.

Next, in step S2, the wiring plate17is fixed to the housing11so as to cover the opening11cof the storage portion11ain a state in which the smoothing capacitor18and the resistor20are placed inside the storage portion11a. At this time, neither the smoothing capacitor18nor the resistor20contacts with the inner wall11bof the storage portion11a, and there are gaps therebetween.

Subsequently, in step S3, the cast resin21is injected into the storage portion11afrom one or more through holes23provided in the wiring plate17fixed to the housing11, so that the cast resin21is provided at least between the inner wall11bof the storage portion11aand the smoothing capacitor18and between the inner wall11bof the storage portion11aand the resistor20, so as to be formed integrally. Since the cast resin21is formed integrally, this operation is completed in one step without the need of performing a plurality of casting steps.

As described above, since the wiring plate17has the through holes23, the casting step in step S3can be performed after the wiring plate17is fixed to the housing11in step S2. If the cast resin21is injected into the storage portion11afrom the opening11cbefore the wiring plate17is fixed to the housing11, structural parts (e.g., screw holes) of the housing11provided for the fixation member22might be damaged by scattering of the cast resin21that has not been cured.

In the power conversion device1according to the first embodiment, heat dissipation and vibration protection for the smoothing capacitor18and the resistor20are made by the cast resin21provided in the storage portion11aso as to be formed integrally. Thus, a dedicated assembly process for the structure for heat dissipation and vibration protection for the resistor20is not needed. That is, the structure for heat dissipation and vibration protection for the smoothing capacitor18and the resistor20can be manufactured at one time in the same process. Thus, the number of components and the number of assembly steps can be decreased and the cost can be reduced, as compared to a case where structures for heat dissipation and vibration protection are manufactured in separate processes.

Since heat dissipation and vibration protection for the resistor20are made by the cast resin21, reliability of heat dissipation and vibration protection for the discharge circuit19is ensured more easily as compared to a conventional method of pressing only one surface of the resistor20to the housing11by means such as screw fastening. Further, since the cast resin21closely contacts with side surfaces of the smoothing capacitor18and the resistor20so as to surround the side surfaces, high reliability is obtained.

In the manufacturing method for the power conversion device1according to the first embodiment, the step of injecting the cast resin21into the storage portion11afrom the through hole23provided in the wiring plate17is performed after the step of fixing the wiring plate17to the housing11. Therefore, such an adverse effect that the cast resin21that has not been cured adheres to a wiring plate fixation part provided to the housing11, does not occur. Thus, workability is improved and cost reduction is achieved.

Since the wiring plate17has a plurality of through holes23, it becomes possible to confirm the injection amount of the cast resin21and inject the cast resin21from a plurality of through holes23simultaneously, in the casting step. Thus, work accuracy is improved and work time is shortened, so that workability is further improved.

As described above, according to the first embodiment, it is possible to provide the power conversion device1and the manufacturing method therefor that can implement the function of the discharge circuit19for discharging electric charge stored in the smoothing capacitor18, at low cost, while ensuring reliability of the discharge circuit19.

Second Embodiment

FIG.4is a plan view schematically showing the configuration of a power conversion device according to the second embodiment of the present disclosure, andFIG.5is a sectional view along line B-B inFIG.4. In a power conversion device1A according to the second embodiment, the smoothing capacitor includes a plurality of capacitors. The other configurations in the power conversion device1A are the same as those in the power conversion device1according to the first embodiment, and therefore only difference will be described here.

As shown inFIG.4, power conversion device input currents P1split from the power supply (not shown) are respectively inputted to smoothing capacitors18a,18b, and are smoothed by the smoothing capacitors18a,18b. Then, the resultant currents merge as power module input current P2. The discharge circuit19is electrically connected to the smoothing capacitors18a,18b. At the time of stop of a vehicle, collision thereof, or the like, the discharge circuit19consumes electric charge stored in each smoothing capacitor18a,18bas smoothing capacitor discharge current P4by the resistor20, on the basis of the command signal S3from the control circuit15.

The cast resin21is provided at least between the inner wall11bof the storage portion11aand the smoothing capacitors18a,18band between the inner wall11bof the storage portion11aand the resistor20. In the second embodiment, the cast resin21is also provided between the smoothing capacitor18aand the smoothing capacitor18band between the smoothing capacitor18band the resistor20, so as to be formed integrally. As in the first embodiment, since the cast resin21closely contacts with the side surfaces of the smoothing capacitors18a,18band the resistor20so as to surround the side surfaces, reliability of heat dissipation and vibration protection can be ensured, whereby high reliability is obtained.

As described above, also in the case of having a plurality of smoothing capacitors18a,18b, since the cast resin21is formed integrally, the cast resin21can be provided in one casting step without the need of performing a plurality of casting steps in assembling the power conversion device1A. That is, even if the smoothing capacitor18is divided into a plurality of smoothing capacitors, the number of assembly steps does not increase.

In the power conversion device1A according to the second embodiment, the same effects as in the power conversion device1according to the first embodiment are provided, and in addition, since the smoothing capacitor18which is a comparatively large component is divided into a plurality of smoothing capacitors, the degree of freedom in layout in the housing11is improved.

Third Embodiment

FIG.6is a plan view schematically showing the configuration of a power conversion device according to the third embodiment of the present disclosure, andFIG.7is a sectional view along line C-C inFIG.6. In a power conversion device1B according to the third embodiment, the discharge circuit19is provided at the circuit board13. The other configurations in the power conversion device1B are the same as those in the power conversion device1A according to the second embodiment, and therefore only difference will be described.

In the first and second embodiments, the discharge circuit19is provided at the wiring plate17, and the command signal S3from the control circuit15provided at the circuit board13to the discharge circuit19is inputted via the signal cable24(seeFIG.1andFIG.4). In general, a signal cable often has a smaller copper-wire diameter than a power cable, and the risk of disconnection thereof due to vibration at the time of collision of a vehicle or the like is higher than in a case of a power cable. Therefore, in order to improve reliability of operation of the discharge circuit19, it is preferable that the circuit board13and the wiring plate17are connected via a power cable.

In the third embodiment, since the discharge circuit19is provided at the circuit board13, input of the command signal S3to the discharge circuit19is completed only inside the circuit board13, so that the signal cable24for inputting the command signal S3from the control circuit15to the discharge circuit19is not needed. The circuit board13and the wiring plate17are connected via a power cable25for inputting smoothing capacitor discharge currents P4from the smoothing capacitors18a,18bto the discharge circuit19.

The circuit board13is fixed to the housing11so as to cover a part of the opening11cof the storage portion11a, and the cast resin21is provided with a gap from the circuit board13. The wiring plate17has one through hole23and is fixed to the housing11by the fixation member22provided at one location. The fixation members22and the through holes23may be provided at a plurality of locations of the wiring plate17.

A flow of a manufacturing process for the power conversion device1B will be described with reference to the flowchart inFIG.3again. In step S1, the power module12including the power device, the circuit board13, the smoothing capacitors18a,18b, the discharge circuit19including the resistor20, the wiring plate17connected to the power module12and the smoothing capacitors18a,18b, the housing11having the storage portion11a, and the cast resin21that has not been cured, are prepared. In the third embodiment, the discharge circuit19is provided at the circuit board13, and the smoothing capacitors18a,18band the resistor20are respectively fixed to one main surface of the wiring plate17and one main surface of the circuit board13.

Next, in step S2, the wiring plate17and the circuit board13are fixed to the housing11so as to cover the opening11cof the storage portion11ain a state in which the smoothing capacitors18a,18band the resistor20are placed inside the storage portion11a. For fixation of the circuit board13to the housing11, a screw, a rivet, an adhesive, or the like may be used.

Subsequently, in step S3, the cast resin21is injected into the storage portion11afrom the through hole23provided in the wiring plate17fixed to the housing11, so that the cast resin21is provided at least between the inner wall11bof the storage portion11aand the smoothing capacitors18a,18band between the inner wall11bof the storage portion11aand the resistor20, so as to be formed integrally.

In the power conversion device1B according to the third embodiment, the same effects as in the power conversion devices1,1A according to the first and second embodiments are provided, and in addition, since the discharge circuit19is provided at the circuit board13, reliability of the discharge function for consuming electric charge stored in each smoothing capacitor18a,18bas smoothing capacitor discharge current P4by the resistor20is improved.

Fourth Embodiment

FIG.8is a plan view schematically showing the configuration of a power conversion device according to the fourth embodiment of the present disclosure, andFIG.9is a sectional view along line D-D inFIG.8. In a power conversion device1C according to the fourth embodiment, the cast resin21is not provided at a part that less contributes to heat dissipation and vibration protection for the smoothing capacitors18a,18band the resistor20, and thus the volume of the cast resin21is reduced. Specifically, a small-thickness area21ais provided at a part, of the cast resin21, that does not contribute to or less contributes to heat dissipation and vibration protection.

The cast resin21may have the small-thickness area21awhere the resin thickness in a direction perpendicular to a direction from the smoothing capacitor18btoward the resistor20and a depth direction of the opening11cis smaller than the resin thickness in the other area. In this case, the storage portion11ahas, between the smoothing capacitor18band the resistor20, a partition wall11eextending toward the opening11cfrom a bottom11dlocated in the depth direction of the storage portion11a, and a groove11fextending in a direction from the smoothing capacitor18btoward the resistor20is provided at an opening-side end of the partition wall11e. The small-thickness area21ais provided at the groove11f.

The cast resin21may have, between the smoothing capacitor18band the resistor20, the small-thickness area21awhere the resin thickness in the depth direction of the opening11cis smaller than the resin thickness in the other area. In this case, the storage portion11ahas, between the smoothing capacitor18band the resistor20, the partition wall11eextending toward the opening11cfrom the bottom11dlocated in the depth direction of the storage portion11a, and the small-thickness area21ais provided on the opening11cside of the partition wall11e.

The small-thickness area21aof the cast resin21in the power conversion device1C will be described with reference toFIG.8andFIG.9. InFIG.8andFIG.9, the direction from the smoothing capacitor18btoward the resistor20is defined as an X direction, the depth direction of the opening11cis defined as a Z direction, and a direction perpendicular to the X direction and the Z direction is defined as a Y direction. As shown inFIG.8, a resin thickness T1in the Y direction in the small-thickness area21ais smaller than a resin thickness T2in the Y direction in the other area. In addition, as shown inFIG.9, a resin thickness T3in the Z direction in the small-thickness area21ais smaller than a resin thickness T4in the Z direction in the other area. Specifically, the resin thicknesses T1, T3in the Y direction and the Z direction in the small-thickness area21aare smaller than the maximum thicknesses of the smoothing capacitors18a,18b.

As described above, in the power conversion device1C, the cast resin21has the small-thickness area21awhere the resin thicknesses in the Y direction and the Z direction are respectively smaller than the resin thicknesses in the Y direction and the Z direction in the other area. The dimension in the Z direction of the partition wall11eis set to be greater than the resin thickness T4in the other area of the cast resin21, except for the groove11fpart provided at the opening-side end of the partition wall11e.

The small-thickness area21amay be an area where the resin thickness in one of the Y direction and the Z direction is smaller. In a case where the small-thickness area21ais an area where the resin thickness T3in the Z direction is smaller than the resin thickness T4in the Z direction in the other area, the dimension in the Z direction of the partition wall11emay be set to be equal to a difference between T4and T3and the small-thickness area21amay be provided on the opening11cside of the partition wall11e. In this case, the groove11fneed not be provided at the opening-side end of the partition wall11e.

The other configurations of the power conversion device1C and the manufacturing method therefor are the same as in the power conversion device1B according to the third embodiment, and therefore the description thereof is omitted here. Although the divided smoothing capacitors18a,18bare provided in the power conversion device1C, one smoothing capacitor18may be used as in the first embodiment.

In the power conversion device1C according to the fourth embodiment, the same effects as in the power conversion devices1,1A,1B according to the first to third embodiments are provided, and in addition, an unnecessary part of the cast resin21is removed so that the volume thereof is optimized. Thus, the material cost for the cast resin21can be reduced, whereby further cost reduction is achieved. In addition, since the smoothing capacitors18a,18band the resistor20can be placed at locations separate from each other, the degree of freedom in layout is improved.

In the above embodiments, the power conversion devices for driving a single motor has been described. However, the present disclosure is applicable also to a power conversion device for driving a plurality of motors. In this case, a plurality of each component such as the power module may be provided for each motor to be driven, or some components may be shared. In addition, application of the present disclosure is not limited to a power conversion device used for driving a vehicle that travels on a land, and the present disclosure is applicable also to a power conversion device used for driving a ship that travels on water, etc.