Power converter and electrical discharge machining device

Abstract

This power converter converts power supplied from a power supply into power suitable for driving a load. The power converter comprises a power conversion substrate (13) and a control substrate. The power conversion substrate (13) includes an input unit (80) connected to the power supply and an output unit (81) connected to the load, and has mounted thereon a plurality of semiconductor switching elements (70) that perform power conversion between the input unit (80) and the output unit (81). The control substrate generates control signals for controlling on / off states of the plurality of semiconductor switching elements (70). The power converter further comprises a metal heat dissipator (77) that is fixed to the surface of the power conversion substrate (13) and dissipates heat generated by the plurality of semiconductor switching elements (70). In a plan view of the surface of the power conversion substrate (13), the heat dissipator (77) is disposed between the output unit (81) and the plurality of semiconductor switching elements (70).

Description

Power Converter and Electrical Discharge Machining Apparatus

[0001] The present disclosure relates to a power converter and an electrical discharge machining apparatus.

[0002] In recent years, miniaturization, high-frequency operation, and high-voltage operation of power electronics devices have been progressing. In a power converter among power electronics devices, the circuit voltage may reach several kV or more, and the switching frequency may reach the order of several tens of kHz. In order for a miniaturized power converter to perform high-frequency operation stably, a design with high noise resistance and no malfunction is required.

[0003] Also, under conditions of high voltage, large current, and high frequency, it is necessary to shorten the length of the wiring in order to suppress the influence of the impedance of the wiring connecting the power converter and the load and the radiation of noise from the wiring. Therefore, it is required to bring the distance between the power converter and the load as close as possible.

[0004] In order to achieve such requirements, it is desirable to arrange the power converter in a limited space near the load, and miniaturization and low-profile of the power converter are required. Also, the power converter is required to be resistant to noise from the load that becomes a noise source.

[0005] For example, in U.S. Patent No. 9,682,436 (Patent Document 1), in a power converter connected to an electrical discharge machining machine, a technique is shown in which a plurality of substrates on which semiconductor elements and the like are mounted are arranged near a discharge electrode serving as a load. In Patent Document 1, miniaturization and low-profile of the power converter are achieved by arranging a plurality of substrates side by side on the same plane.

[0006] U.S. Patent No. 9,682,436 Specification

[0007] However, in the technique described in Patent Document 1, since a plurality of substrates are arranged close to the discharge electrode, noise generated by the discharge electrode during discharge may enter the plurality of substrates, which may cause the power converter to malfunction. Note that Patent Document 1 does not mention noise countermeasures.

[0008] Therefore, the primary objective of this disclosure is to provide a power converter that is miniaturized and low-profile while being highly resistant to noise entering from the load.

[0009] A power converter according to one aspect of this disclosure converts power supplied from a power source into power suitable for driving a load. The power converter comprises a power conversion board and a control board. The power conversion board includes an input section connected to a power source and an output section connected to a load, and a plurality of semiconductor switching elements that perform power conversion between the input section and the output section are mounted on it. The control board generates control signals for controlling the on / off state of the plurality of semiconductor switching elements. The power converter further comprises a metal heat sink fixed to the surface of the power conversion board and for dissipating the heat generated by the plurality of semiconductor switching elements. In a plan view of the surface of the power conversion board, the heat sink is positioned between the output section and the plurality of semiconductor switching elements.

[0010] According to this disclosure, it is possible to provide a power converter that is highly resistant to noise entering from the load.

[0011] This is a schematic block diagram showing the configuration of an electrical discharge machining apparatus to which a power converter according to Embodiment 1 is applied. This is a circuit diagram showing an example of the configuration of the power converter shown in Figure 1. This is a schematic cross-sectional view showing the configuration of an electrical discharge machining apparatus according to Embodiment 1. This is a schematic plan view showing a power conversion board. This is a view of the power conversion board from the direction of arrow A in Figure 4. This is a view of the power conversion board from the direction of arrow B in Figure 5. This is a schematic plan view showing a power conversion board in a power converter according to Embodiment 2. This is a view of the power conversion board from the direction of arrow C in Figure 7. This is a schematic block diagram showing the configuration of an electrical discharge machining apparatus according to Embodiment 3. This is a schematic plan view showing a power conversion board in a power converter according to Embodiment 3. This is a schematic diagram showing the current path formed in the power converter and the induced magnetic field generated by the current path. This is a schematic plan view showing a power conversion board in a power converter according to Embodiment 4. This is a schematic cross-sectional view showing the configuration of an electrical discharge machining apparatus to which a power converter according to Embodiment 4 is applied. This is a block diagram showing the configuration of a power conversion system to which a power converter according to Embodiment 5 is applied.

[0012] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated in principle.

[0013] Embodiment 1. <Configuration of the electrical discharge machining apparatus> Figure 1 is a schematic block diagram showing the configuration of an electrical discharge machining apparatus to which the power converter according to Embodiment 1 is applied. As shown in Figure 1, the electrical discharge machining apparatus 100 according to Embodiment 1 is an apparatus for performing electrical discharge machining on a workpiece 42 made of metal material, which is supplied with power from a grid power supply 10. The electrical discharge machining apparatus 100 comprises a DC power supply 11, a power converter 12, and an electrical discharge machining machine 40.

[0014] The DC power supply 11 is connected to the grid power supply 10 and receives AC power at the grid frequency from the grid power supply 10. The DC power supply 11 converts the AC power to DC power and outputs it to the power converter 12. The DC power supply 11 is composed of an AC / DC converter. The AC / DC converter generates a machining voltage that matches the machining conditions of the workpiece 42 and applies it to the power converter 12.

[0015] The power converter 12 converts the DC power supplied from the DC power supply 11 into power suitable for driving the load. In Embodiment 1, the load is the discharge electrode 41 included in the electrical discharge machining machine 40. However, the load is not limited to this.

[0016] The power converter 12 includes a power conversion board 13 that performs power conversion between a DC power supply 11 and a discharge electrode 41 which is a load, and a control board 14 that controls the power conversion on the power conversion board 13. The input section 80 of the power conversion board 13 is connected to the DC power supply 11, and its output section 81 is connected to the discharge electrode 41 via a connecting conductor 79. The power converter 12 will be described in detail later.

[0017] The electrical discharge machining (EDM) machine 40 is used to perform electrical discharge machining on a workpiece 42, and includes an electrical discharge electrode 41 and a machining tank 44. The machining tank 44 is configured to hold a machining fluid 45 in which the workpiece 42 is immersed. Two types of machining fluids 45 are mainly used: water and oil. The machining tank 44 is grounded. The workpiece 42 is also grounded by being connected to the machining tank 44 via a connecting wire 50.

[0018] The discharge electrode 41 is used for electrical discharge machining of a metal material to which the processing fluid 45 is supplied. The discharge electrode 41 is a shaped electrode, a wire electrode, or a rod electrode. The shape of the discharge electrode 41 is selected according to the target metal material and the processing shape, etc.

[0019] The electrical discharge machining machine 40 receives power from the power converter 12 to generate a discharge phenomenon between the discharge electrode 41 and the workpiece 42, and processes the workpiece 42 by removing a portion of its surface with the heat of the discharge. Noise is generated during the discharge phenomenon that occurs between the discharge electrode 41 and the workpiece 42. This noise can enter the power converter 12 from the discharge electrode 41 via the connecting conductor 79, potentially causing malfunctions in the power converter 12. This embodiment provides a novel configuration for the power converter 12 that can resolve these concerns.

[0020] <Configuration of the Power Converter> Figure 2 is a circuit diagram showing an example configuration of the power converter 12 shown in Figure 1. As shown in Figure 2, the power converter 12 is composed of a power conversion board 13 and a control board 14.

[0021] The power conversion board 13 includes an input section 80, an output section 81, a capacitor 72, a plurality of semiconductor switching elements 70a, 70b, a plurality of diodes 71a to 71e, and a gate circuit 15. Hereinafter, the semiconductor switching elements 70a, 70b will be collectively referred to as "semiconductor switching elements 70," and the diodes 71a to 71e will be collectively referred to as "diodes 71."

[0022] The semiconductor switching element 70 is a self-extinguishing semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Field Effect Transistor). The semiconductor switching element 70 is mainly formed from a wide-bandgap semiconductor material such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or diamond.

[0023] A Schottky diode or a fast recovery diode is used as the diode 71. The diode 71 is mainly made of Si or a wide-bandgap semiconductor material.

[0024] The input unit 80 has a positive input terminal 80p connected to the positive terminal of the DC power supply 11 and a negative input terminal 80n connected to the negative terminal of the DC power supply 11. The input unit 80 receives a DC voltage from the DC power supply 11.

[0025] The output unit 81 has output terminals 81a and 81b. Output terminal 81a is connected to the first terminal of the discharge electrode 41 via a connecting conductor 79. Output terminal 81b is connected to the second terminal of the discharge electrode 41 via a connecting conductor 79.

[0026] Capacitor 72 is connected between the positive input terminal 80p and the negative input terminal 80n, and smooths and stabilizes the DC voltage between the positive input terminal 80p and the negative input terminal 80n.

[0027] The semiconductor switching element 70a and the diode 71c are connected in series between the positive input terminal 80p and the negative input terminal 80n. The diode 71a is connected in antiparallel to the semiconductor switching element 70a. The connection point between the semiconductor switching element 70a and the diode 71a is connected to the output terminal 81b.

[0028] Diode 71d and semiconductor switching element 70b are connected in series between the positive input terminal 80p and the negative input terminal 80n. Diode 71b is connected in antiparallel to semiconductor switching element 70b. The connection point between diode 71d and semiconductor switching element 70b is connected to the cathode of diode 71e. The anode of diode 71e is connected to output terminal 81a.

[0029] The gate circuit 15 is connected to the control board 14 via a gate input connector 83. The gate circuit 15 drives the semiconductor switching elements 70a and 70b according to the control signal provided by the control board 14. By switching the semiconductor switching elements 70a and 70b on and off, the gate circuit 15 can switch the voltage applied to the discharge electrode 41 on and off. Although not shown in the diagram, it is also possible to change the polarity of the voltage applied to the discharge electrode 41 by connecting multiple semiconductor switching elements 70 in a full bridge configuration.

[0030] The control board 14 generates control signals to control the on / off state of the semiconductor switching elements 70a and 70b, and outputs the generated control signals to the gate circuit 15. The control board 14 generates control signals based on processing conditions input from the outside and various conditions set based on the processing conditions. These conditions include the processing time of the workpiece 42, the processing current, the timing for turning on the semiconductor switching elements 70a and 70b, and the on / off ratio of the semiconductor switching elements 70a and 70b (the ratio of off time to on time).

[0031] In the power conversion board 13, the heat generated in the semiconductor switching element 70 and the diode 71 is determined by the voltage applied to the semiconductor switching element 70 and the diode 71, and the losses due to the current flowing through the semiconductor switching element 70 and the diode 71. To reduce these losses, each of the semiconductor switching elements 70a and 70b in Figure 2 may be configured by combining multiple semiconductor switching elements in series and / or in parallel. Similarly, each of the diodes 71a to 71e may be configured by combining multiple diodes in series and / or in parallel.

[0032] <Configuration of the electrical discharge machining machine> Figure 3 is a schematic cross-sectional view showing the configuration of an electrical discharge machining apparatus 100 according to Embodiment 1.

[0033] As shown in Figure 3, the discharge electrode 41 and the workpiece 42 are arranged in a processing tank 44 that stores processing fluid 45. The workpiece 42 is placed on a sample stand 49 installed in the processing tank 44. The sample stand 49 is connected to the processing tank 44 by a connecting wire 50. The processing tank 44 is grounded.

[0034] The power converter 12 further includes a housing 16 that houses a power conversion board 13 and a control board 14. The housing 16 is attached to the side of the processing tank 44. The housing 16 has a substantially rectangular parallelepiped shape.

[0035] The power conversion board 13 is fixed to a substrate fixing surface 17 provided on the inner surface of the housing 16. In Figure 3, the substrate fixing surface 17 is located only on the side opposite the electrical discharge machining machine 40, but it may also be located on both the side facing the electrical discharge machining machine 40 and the side opposite the electrical discharge machining machine 40. Similarly, the power conversion board 13 may be attached not only to the substrate fixing surface 17 located on the side facing the electrical discharge machining machine 40, but also to the substrate fixing surface 17 located on the side facing the electrical discharge machining machine 40. The power conversion board 13 is positioned so that its surface faces the machining chamber 44. The control board 14 is attached to the surface of the power conversion board 13.

[0036] The discharge electrode 41 in the processing tank 44 and the power conversion board 13 in the housing 16 are connected by a connecting conductor 79. A voltage is applied to the discharge electrode 41 from the power conversion board 13. When at least one of the workpiece 42 and the discharge electrode 41 moves and the workpiece 42 approaches the discharge electrode 41, a discharge occurs between the discharge electrode 41 and the workpiece 42. The heat from this discharge melts a portion of the surface of the workpiece 42. By repeating the discharge, the workpiece 42 can be processed into the desired shape. However, noise is generated during the discharge.

[0037] In the electrical discharge machining apparatus 100, with the increasing demand for higher voltage, higher current, and higher frequency power converters 12, there are concerns that the impedance influence of the wiring between the power conversion board 13 and the discharge electrodes 41, as well as the influence of noise emitted from the wiring, will increase. To suppress these effects, it is necessary to shorten the length of the wiring as much as possible.

[0038] In Embodiment 1, the power converter 12 is placed on the side of the processing tank 44 as shown in Figure 3. This brings the power conversion board 13 closer to the discharge electrode 41, and shortens the length of the connecting conductor 79 that connects the power conversion board 13 and the discharge electrode 41. Although the output section 81 (output terminals 81a, 81b) of the power conversion board 13 is not shown in Figure 3, it is not limited to either output terminal 81a or 81b.

[0039] On the other hand, by positioning the power conversion board 13 close to the discharge electrode 41, which is a source of noise, a drawback arises: noise can easily penetrate from the discharge electrode 41 into the power conversion board 13 via the connecting conductor 79. Noise that penetrates into the power conversion board 13 can propagate through the space inside the housing 16 and potentially cause the semiconductor switching elements 70 mounted on the power conversion board 13 to malfunction. Therefore, in Embodiment 1, as described below, a shield is placed on the power conversion board 13 to block noise that propagates through space to the semiconductor switching elements 70.

[0040] <Configuration of Power Conversion Board 13> Figure 4 is a schematic plan view of the power conversion board 13. Figure 4 is a plan view of the surface of the power conversion board 13. Although a control board 14 is fixed to the surface of the power conversion board 13, the control board 14 is not shown in Figure 4.

[0041] As shown in Figure 4, the power conversion board 13 has a substantially rectangular shape. The power conversion board 13 has a pair of long sides 13a and 13b along a first direction (corresponding to the horizontal direction of the paper) and a pair of short sides 13c and 13d along a second direction (corresponding to the vertical direction of the paper).

[0042] The input unit 80 and the output unit 81 are arranged side by side along the long side 13a on the surface of the power conversion substrate 13. The input unit 80 includes a positive input terminal 80p and a negative input terminal 80n (FIG. 2). The output unit 81 includes output terminals 81a and 81b (FIG. 2).

[0043] The capacitor 72 is composed of a plurality of capacitive elements electrically connected in parallel. The plurality of capacitive elements are arranged side by side on the surface of the power conversion substrate 13. In order to reduce the wiring impedance between the input unit 80 and the capacitor 72, it is preferable to arrange the plurality of capacitive elements close to the input unit 80. Specifically, the capacitor 72 is arranged between the input unit 80 and the output unit 81 and the plurality of semiconductor switching elements 70.

[0044] The connector 83 for gate input includes a plurality of connector terminals. The plurality of connector terminals are arranged side by side along the long side 13b on the surface of the power conversion substrate 13. The gate circuit 15 is arranged close to the connector 83 on the surface of the power conversion substrate 13.

[0045] A plurality of heat sinks 77 are arranged between the capacitor 72 and the gate circuit 15. The plurality of heat sinks 77 are arranged side by side along the long sides 13a and 13b of the power conversion substrate 13. The plurality of heat sinks 77 are for releasing the heat generated by the plurality of semiconductor switching elements 70 and the plurality of diodes 71. Each heat sink 77 is formed of a metal material such as aluminum or an aluminum alloy. The number of heat sinks 77 may be single or plural.

[0046] In the example of FIG. 4, the plurality of heat sinks 77 are air-cooled heat sinks configured to cool the plurality of semiconductor switching elements 70 and the plurality of diodes 71 by performing heat exchange between air and the plurality of semiconductor switching elements 70 and the plurality of diodes 71.

[0047] Each of the plurality of heat sinks 77 is formed in a substantially rectangular parallelepiped shape that is long in the first direction. Each heat sink 77 has a first surface 77a on the output unit 81 side and a second surface 77b on the side opposite to the first surface 77a.

[0048] At least one diode 71 is attached to the first surface 77a of each radiator 77. At least one semiconductor switching element 70 is attached to the second surface 77b of each radiator 77. In the example of FIG. 4, two semiconductor switching elements 70 and two diodes 71 are attached to each radiator 77, but the number of each of the semiconductor switching elements 70 and diodes 71 attached to each radiator 77 is not limited thereto.

[0049] Inside each radiator 77, an air flow path is formed so that the direction of the air flow is parallel to the first surface 77a and the second surface 77b. In FIG. 4, the direction in which air flows inside each radiator 77 is indicated by a broken-line arrow.

[0050] A fan 82 is arranged on the air flow path. In the example of FIG. 4, the fan 82 is arranged at the most upstream in the air flow direction. The fan 82 may be arranged at the most downstream in the air flow direction.

[0051] Air flows sequentially through the interiors of the plurality of radiators 77. At that time, heat exchange is performed between the air and the semiconductor switching element 70 and the diode 71, whereby the semiconductor switching element 70 and the diode 71 are cooled.

[0052] FIG. 5 is a view of the power conversion substrate 13 as seen from the direction of arrow A in FIG. 4. As shown in FIG. 5, the power conversion substrate 13 is fixed to a substrate fixing surface 17 provided on the inner surface of the housing 16 via a spacer 74. A control substrate 14 is fixed to the surface of the power conversion substrate 13 via a spacer 74. The spacer 74 is formed of a resin material or a metal material.

[0053] Multiple semiconductor switching elements 70 are mounted on the surface of the power conversion board 13. Each semiconductor switching element 70 is composed of a semiconductor module in which the semiconductor switching element 70 is sealed with a sealing resin. The semiconductor module is provided with external terminals 70p for electrical connection to the power conversion board 13. The external terminals 70p of each semiconductor switching element 70 are connected to the power conversion board 13 by solder or the like. Each semiconductor switching element 70 is further attached to the second surface 77b of the corresponding heat sink 77 by screws or adhesive.

[0054] Figure 6 is a view of the power conversion board 13 from the direction of arrow B in Figure 5. Figure 6 shows an excerpt of a portion of the power conversion board 13, including the heat sink 77. As shown in Figure 6, the heat sink 77 is fixed to the power conversion board 13 via a spacer 75. The heat sink 77 is provided with a plurality of fins 77f. The plurality of fins 77f are arranged parallel to each other with a gap between them.

[0055] Multiple diodes 71 are further mounted on the surface of the power conversion board 13. Each diode 71 is composed of a diode module in which the diode 71 is sealed with a sealing resin. The diode module is provided with an external terminal 71p for electrical connection to the power conversion board 13. The external terminal 71p of each diode 71 is connected to the power conversion board 13 by solder or the like. Each diode 71 is further attached to the first surface 77a of the corresponding heat sink 77 by screws or adhesive.

[0056] It is preferable that the height h1 of the upper end of the heat sink 77 from the surface of the power conversion substrate 13 is higher than the height h2 of the upper end of the semiconductor switching element 70 from the surface of the power conversion substrate 13. The upper end of the heat sink 77 is the end opposite to the end facing the power conversion substrate 13. The upper end of the semiconductor switching element 70 is the end opposite to the end connected to the power conversion substrate 13.

[0057] As described above, noise generated during the discharge of the electrical discharge machine 40 enters the output section 81 of the power conversion board 13 via the discharge electrode 41 and the connecting conductor 79. The invading noise may propagate through space and cause malfunctions in multiple semiconductor switching elements 70. Therefore, it is necessary to block the spatial propagation of noise.

[0058] Here, we will explain the effect of shielding to block the spatial propagation of noise. It is known that the shielding effect when noise propagates as radio waves can be expressed as the sum of three items. The first item is the loss (reflection loss) of radio waves that strike the first surface of the shield and are reflected by the first surface. The second item is the loss (attenuation loss) of radio waves that enter from the first surface of the shield and are attenuated inside the shield. The third item is the effect of multiple reflections of radio waves between the first and second surfaces of the shield (multiple reflection effect).

[0059] Furthermore, it is known that when magnetic flux due to noise is incident on the first surface of the shield, eddy currents are induced in the shield, thereby blocking the magnetic flux that penetrates the shield and forming part of the shielding effect. However, in the case of shields that utilize induced current, the flow of induced current through the shield causes inductive heating. Since the shield generates heat due to this inductive heating, it is necessary to appropriately adjust the shielding effect and the heat generated by the shield.

[0060] In Embodiment 1, in a plan view of the surface of the power conversion substrate 13 (see Figure 4), the multiple heat sinks 77 are arranged between the output section 81 and the multiple semiconductor switching elements 70. The multiple heat sinks 77 are made of a metallic material and function as shields to block noise that has entered the output section 81 of the power conversion substrate 13 from the discharge electrode 41 via the connecting conductor 79 from spatially propagating to the multiple semiconductor switching elements 70.

[0061] Specifically, noise radiated from the output section 81 of the power conversion board 13 propagates through space and hits the first surface 77a of the heat sink 77. At this time, due to the shielding effect described above, the noise leaking to the second surface 77b of the heat sink 77 is attenuated more than the noise hitting the first surface 77a of the heat sink 77. In addition, the magnetic flux caused by the noise induces eddy currents in the heat sink 77, blocking the noise that penetrates the heat sink 77. In this way, the multiple heat sinks 77 placed between the output section 81 and the multiple semiconductor switching elements 70 act as a shield to block the spatial propagation of noise, thereby suppressing malfunctions of the multiple semiconductor switching elements 70.

[0062] Furthermore, the multiple heat sinks 77 can release the heat generated by the multiple semiconductor switching elements 70 and the multiple diodes 71, while simultaneously releasing the heat generated by induction heating. Therefore, the temperature rise of the multiple heat sinks 77 due to the shielding effect can be suppressed.

[0063] Furthermore, as shown in Figure 6, by making the height h1 from the surface of the power conversion substrate 13 at the upper end of each heat sink 77 higher than the height h2 from the surface of the power conversion substrate 13 at the upper end of the semiconductor switching element 70, the shielding effect of the heat sink 77 can be further enhanced.

[0064] Furthermore, while Embodiment 1 described a configuration in which multiple heat sinks 77 function as a shield, a configuration in which an integrated heat sink 77 functions as a shield is also possible. However, one advantage of configuring the heat sink for dissipating the heat generated by multiple semiconductor switching elements 70 and multiple diodes 71 with multiple heat sinks 77 is that, when the amount of heat generated differs for each heat-generating element, including the semiconductor switching elements 70 and diodes 71, an appropriate heat sink 77 can be selected according to the amount of heat generated by the corresponding heat-generating element. In addition, it becomes possible to improve handling during the assembly of the power conversion board 13, as well as to miniaturize the heat sink manufacturing equipment and reduce manufacturing costs.

[0065] As described above, in Embodiment 1, a heat sink 77 made of a metal material is placed between the output unit 81 and the plurality of semiconductor switching elements 70 in the power conversion board 13, and this is used as a shield to block the spatial propagation of noise radiated from the output unit 81. This makes it possible to miniaturize and reduce the height of the power converter 12 while suppressing malfunctions of the plurality of semiconductor switching elements 70 and improving the noise immunity of the power converter 12.

[0066] Embodiment 2. Figure 7 is a schematic plan view showing the power conversion board 13 in the power converter 12 according to Embodiment 2. The basic configuration of the power converter 12 according to Embodiment 2 is the same as that of the power converter 12 according to Embodiment 1. The power converter 12 according to Embodiment 2 can also be applied to the electrical discharge machining apparatus 100 shown in Figure 1.

[0067] The power converter 12 according to Embodiment 2 differs from the power converter 12 according to Embodiment 1 in that it includes multiple heat sinks 76 and multiple cooling pipes 78 instead of multiple heat sinks 77.

[0068] As shown in Figure 7, multiple heat sinks 76 are arranged between the capacitor 72 and the gate circuit 15, along the long sides 13a and 13b of the power conversion board 13. Each heat sink 76 is made of a metallic material such as aluminum or an aluminum alloy. The number of heat sinks 76 may be one or more.

[0069] The multiple heat sinks 76 are liquid-cooled heat sinks configured to cool the multiple semiconductor switching elements 70 and the multiple diodes 71 by exchanging heat between the coolant and the multiple semiconductor switching elements 70 and the multiple diodes 71. For example, water is used as the coolant.

[0070] Each of the multiple heat sinks 76 is formed in a roughly rectangular parallelepiped shape that is elongated in the first direction. Multiple cooling pipes 78 are used to connect adjacent heat sinks 76 to each other, or to connect the external flow path of the power conversion board 13 to the heat sinks 76. Multiple cooling pipes 78 serve as flow paths for the coolant.

[0071] Each heat sink 76 has a first surface 76a on the output section 81 side and a second surface 76b on the opposite side of the first surface 76a. At least one diode 71 is mounted on the first surface 76a of each heat sink 76. At least one semiconductor switching element 70 is mounted on the second surface 76b of each heat sink 76. In the example in Figure 7, each heat sink 76 has two semiconductor switching elements 70 and two diodes 71 mounted on it, but the number of semiconductor switching elements 70 and diodes 71 mounted on each heat sink 76 is not limited to this.

[0072] Multiple heat sinks 76 and multiple cooling pipes 78 form a flow path for the coolant so that the direction of the coolant flow is parallel to the first surface 76a and the second surface 76b. In Figure 7, the direction of coolant flow inside the multiple heat sinks 76 and multiple cooling pipes 78 is indicated by dashed arrows. The coolant flows sequentially through the inside of the multiple heat sinks 77. During this process, heat exchange occurs between the coolant and the semiconductor switching elements 70 and diodes 71, thereby cooling the multiple semiconductor switching elements 70 and multiple diodes 71.

[0073] Figure 8 is a view of the power conversion board 13 from the direction of arrow C in Figure 7. Figure 8 shows an excerpt of a portion of the power conversion board 13, including the heat sink 76. As shown in Figure 8, the heat sink 76 is fixed to the power conversion board 13 via a spacer 75. Cooling pipes 78 are connected to the heat sink 76.

[0074] The external terminals 71p of each diode 71 are connected to the power conversion board 13 by solder or the like. Each diode 71 is further attached to the first surface 77a of the corresponding heat sink 77 by screws or adhesive.

[0075] The external terminals 70p of each semiconductor switching element 70 are connected to the power conversion board 13 by solder or the like. Each semiconductor switching element 70 is further attached to the second surface 76b of the corresponding heat sink 76 by screws or adhesive.

[0076] The height h3 from the surface of the power conversion substrate 13 at the upper end of the heat sink 76 is preferably higher than the height h2 from the surface of the power conversion substrate 13 at the upper end of the semiconductor switching element 70. The upper end of the heat sink 76 is the end opposite to the end facing the power conversion substrate 13. This enhances the shielding effect of the heat sink 76.

[0077] In Embodiment 2, in a plan view of the surface of the power conversion substrate 13 (see Figure 7), the multiple heat sinks 76 are arranged between the output section 81 and the multiple semiconductor switching elements 70. Similar to the multiple heat sinks 77 in Embodiment 1, the multiple heat sinks 76 function as shields to block noise that has entered the output section 81 of the power conversion substrate 13 via the discharge electrode 41 and connecting conductor 79 from spatially propagating to the multiple semiconductor switching elements 70. Therefore, it is possible to achieve miniaturization and a low profile of the power converter 12 while suppressing malfunctions of the multiple semiconductor switching elements 70.

[0078] In Embodiment 2, the heat generated by the semiconductor switching element 70 and the diode 71 is released by the heat sink 76 via the coolant, which differs from Embodiment 1, where the heat sink 77 releases the heat via air. Focusing on the cooling performance of the heat sinks 76 and 77, the cooling performance of the heat sink 77, which uses air as a coolant, depends on the ambient temperature, while the cooling performance of the heat sink 76, which uses a coolant, depends on the temperature of the coolant. Since the coolant temperature is less affected by the operating environment temperature of the electrical discharge machining apparatus 100, the heat sink 76 can more easily maintain its cooling performance compared to the heat sink 77. This is also advantageous in shielding using induced current, as it suppresses heating of the heat sink due to induction heating.

[0079] Embodiment 3. Figure 9 is a schematic block diagram showing the configuration of an electrical discharge machining apparatus according to Embodiment 3. The electrical discharge machining apparatus 110 according to Embodiment 3 differs from the electrical discharge machining apparatus 100 shown in Figure 1 in that it includes a contaminated liquid tank 51, a clean liquid tank 52, pumps 53 and 54, a filter 55, a cooler 56, and flow paths 58 to 61. The remaining configuration, including the electrical discharge machining machine 40, is the same as that of the electrical discharge machining apparatus 100 shown in Figure 1.

[0080] The wastewater tank 51 is connected to the processing tank 44 via a flow path 61. Processing fluid discharged from the processing tank 44 is introduced into the wastewater tank 51. The wastewater tank 51 stores the processing fluid 45 that has been contaminated by electrical discharge machining.

[0081] The clean liquid tank 52 is connected to the clean liquid tank 52 via a flow path 57, a pump 53, and a filter 55. By driving the pump 53, the processing fluid 45 is drawn from the contaminated liquid tank 51 into the clean liquid tank 52. At this time, impurities contained in the processing fluid 45 (such as processing debris from the workpiece 42) are filtered out by the filter 55 provided in the flow path 57. The clean liquid tank 52 stores the processing fluid 45 from which impurities have been removed.

[0082] The clean water tank 52 is connected to the machining tank 44 via a pump 54 and a flow path 58. By driving the pump 54, machining fluid 45 is drawn from the clean water tank 52 into the machining tank 44. At this time, the machining fluid 45 passes through a cooler 56 provided in the flow path 58, so that cooled machining fluid 45 is drawn into the machining tank 44. The machining fluid 45 supplied to the machining tank 44 is cooled in order to cool the discharge electrode 41 and the workpiece 42 during discharge. Also, by keeping the temperature of the machining fluid 45 constant, variations in machining accuracy are suppressed.

[0083] The flow path 59 branches off from the flow path 58 at branching point 58a and is connected to the upstream end of the heat sink 76, which is located on the power conversion board 13. The branching point 58a is located downstream of the cooler 56. In other words, the flow path 59 supplies the processing fluid 45, which has been cooled by the cooler 56, to the heat sink 76 by branching off from the flow path 58.

[0084] The flow path 60 is connected to the downstream end of the heat sink 76. The downstream end of the flow path 60 is connected to the flow path 61 at the confluence point 61a. The processing fluid 45 output from the heat sink 76 passes through the flow path 60 and merges with the flow path 61 at the confluence point 61a.

[0085] In the electrical discharge machining apparatus 110 according to Embodiment 3, a circulation circuit for circulating the machining fluid 45 is formed by the flow paths 57, 58, 61 and the pumps 53, 54. The heat sink 76 is positioned between a branching point 58a located upstream of the machining tank 44 on the circulation circuit and a confluence point 61a located downstream of the machining tank 44 on the circulation circuit. A portion of the machining fluid 45 flowing through the circulation circuit is used as a coolant to cool the multiple semiconductor switching elements 70 and multiple diodes 71 on the power conversion board 13.

[0086] Figure 10 is a schematic plan view showing the power conversion board 13 in the power converter 12 according to Embodiment 3. The basic configuration of the power converter 12 according to Embodiment 3 is the same as that of the power converter 12 according to Embodiment 2. The power converter 12 according to Embodiment 3 differs from the power converter 12 according to Embodiment 2 in that the multiple cooling pipes 78 are eliminated and the multiple heat sinks 76 are integrated.

[0087] In Embodiment 3, as well as in a plan view of the surface of the power conversion substrate 13, the heat sink 76 is positioned between the output section 81 and the plurality of semiconductor switching elements 70. Therefore, the heat sink 76 functions as a shield to block noise that has entered the output section 81 of the power conversion substrate 13 via the discharge electrode 41 and connecting conductor 79 from spatially propagating to the plurality of semiconductor switching elements 70, similar to the plurality of heat sinks 76 in Embodiment 2.

[0088] Furthermore, in Embodiment 3, by integrating multiple heat sinks 76, it is possible to suppress noise from entering through the gaps between adjacent heat sinks 76 and propagating to multiple semiconductor switching elements 70. Embodiment 3 is effective in improving the shielding effect in a configuration where the variation in the amount of heat generated by the heating elements in the power conversion substrate 13 is small.

[0089] Embodiment 4. In Embodiment 1, as shown in Figure 3, the power conversion board 13 is fixed to a substrate fixing surface 17 provided on the inner surface of a housing 16 attached to the side of the processing tank 44. As described above, the power conversion board 13 can be fixed to at least one of the substrate fixing surface 17 on the opposite side of the electrical discharge machining machine 40 and the substrate fixing surface 17 on the side of the electrical discharge machining machine 40.

[0090] In this configuration, depending on the orientation in which the power conversion board 13 is mounted, the current flowing between the power conversion board 13 and the discharge electrode 41 via the output unit 81 generates an induced magnetic field around the current path. This induced magnetic field links with the board fixing surface 17 or the processing bath 44, which causes the housing 16 or the processing bath 44 to heat up.

[0091] Figure 11 is a schematic diagram showing the current path formed in the circuit configuration of the power converter 12 shown in Figure 2, and the induced magnetic field generated by the current path. Figure 11 shows a plan view of the power conversion board 13 according to Embodiment 2. The output section 81 (output terminals 81a, 81b) of the power conversion board 13 is connected to the discharge electrode 41 via a connecting conductor 79.

[0092] In the example shown in Figure 11, a current path 1, indicated by an arrow in the figure, is formed between the power conversion substrate 13 and the discharge electrode 41. This current path 1 generates an induced magnetic field that extends in the direction normal to the surface of the power conversion substrate 13 (perpendicular to the plane of the paper).

[0093] Here, if the main surface on which the capacitor 72, semiconductor switching element 70, and diode 71 are mounted is designated as the first main surface of the power conversion substrate 13, and the main surface opposite to the first main surface is designated as the second main surface, then an induced magnetic field is generated around the current path 1 in the direction from the second main surface toward the first main surface. This induced magnetic field links with the substrate fixing surface 17 and the processing bath 44, causing the housing 16 and the processing bath 44 to heat up due to induction heating.

[0094] To solve the above problems, Embodiment 4 is configured to form multiple current paths between the power conversion substrate 13 and the discharge electrode 41. In this configuration, the induced magnetic field generated by one of the multiple current paths and the induced magnetic field generated by another current path are directed in opposite directions. In this way, it is possible to cancel out the two induced magnetic fields.

[0095] Figure 12 is a schematic plan view showing the power conversion board in a power converter according to Embodiment 4. The basic configuration of the power converter 12 according to Embodiment 4 is the same as that of the power converter 12 according to Embodiment 1. The power converter 12 according to Embodiment 4 can also be applied to the electrical discharge machining apparatus 100 shown in Figure 1.

[0096] As shown in Figure 12, the power converter 12 according to Embodiment 4 includes a plurality (for example, two) of power conversion boards 13A and 13B. Figure 12 is a plan view of the surface (first main surface) of the power conversion boards 13A and 13B. In Figure 12, the control board 14 is not shown.

[0097] Each of the power conversion boards 13A and 13B can be fitted with the power conversion board 13 according to Embodiments 1 and 2. In the example shown in Figure 12, each of the power conversion boards 13A and 13B has the same configuration as the power conversion board 13 according to Embodiment 3 (Figure 10).

[0098] The input section 80A of the power conversion board 13A and the input section 80B of the power conversion board 13B are both connected to a DC power supply 11 (not shown). The output section 81A of the power conversion board 13A is connected to the discharge electrode 41 via a connecting conductor 79A. The output terminals 81a and 81b of the output section 81A correspond to one embodiment of the "first output terminal pair". The plurality of semiconductor switching elements 70A mounted on the power conversion board 13A correspond to one embodiment of the "first semiconductor switching element" that performs power conversion between the input section 80A and the output section 81A.

[0099] The output section 81B of the power conversion board 13B is connected to the discharge electrode 41 via a connecting conductor 79B. The output terminals 81a and 81b of the output section 81B correspond to one embodiment of the "second output terminal pair". The plurality of semiconductor switching elements 70B mounted on the power conversion board 13B correspond to one embodiment of the "second semiconductor switching elements" that perform power conversion between the input section 80B and the output section 81B.

[0100] Note that although Figure 12 shows two discharge electrodes 41 for simplicity, in reality, the output units 81A and 81B are commonly connected to a single discharge electrode 41.

[0101] By switching multiple semiconductor switching elements 70A on and off, a current path 1A, indicated by an arrow in the figure, is formed between the power conversion substrate 13A and the discharge electrode 41. This current path 1A generates an induced magnetic field in the direction from the second main surface to the first main surface of the power conversion substrate 13A.

[0102] By switching multiple semiconductor switching elements 70B on and off, a current path 1B, indicated by an arrow in the figure, is formed between the power conversion substrate 13B and the discharge electrode 41. This current path 1B generates an induced magnetic field in the direction from the first main surface to the second main surface of the power conversion substrate 13A.

[0103] Here, the current paths 1A and 1B have opposite directions of current flow. This can be achieved, for example, by reversing the connections between the output terminals 81a and 81b of output unit 81A and output terminals 81a and 81b of output unit 81B to the first and second terminals of the discharge electrode 41.

[0104] Since the induced magnetic field generated by current path 1A and the induced magnetic field generated by current path 1B are in opposite directions, these two induced magnetic fields cancel each other out and disappear. This makes it possible to suppress the heating of the housing 16 and the processing tank 44 due to induction heating.

[0105] In Figure 12, an example configuration for forming multiple current paths 1A and 1B using multiple power conversion boards 13A and 13B is described. However, it is also possible to form multiple current paths 1A and 1B using a single power conversion board 13 formed by combining multiple power conversion boards 13A and 13B. Alternatively, even if three or more power conversion boards 13 are used to form three or more current paths 1, a similar effect can be obtained by configuring the system so that three or more induced magnetic fields cancel each other out.

[0106] The power converter 12 according to Embodiment 4 can be applied, for example, to an electrical discharge machining machine 40 that receives power from a plurality of output units 81 of a power conversion board 13, as shown in Figure 13. In the example of Figure 13, the power conversion board 13 has two output units 81A and 81B (see Figure 12), where output unit 81A is connected to the discharge electrode 41 via a connecting conductor 79A, and output unit 81B is connected to the discharge electrode 41 via a connecting conductor 79B.

[0107] Embodiment 5. Embodiments 1 to 4 described above describe a configuration in which the power converter 12 according to the present disclosure is applied to an electrical discharge machining apparatus. Embodiment 5 describes how the power converter 12 according to the present disclosure is applied to a power converter. The following describes the case in which the power converter 12 according to the present disclosure is applied to a three-phase inverter.

[0108] Figure 14 is a block diagram showing the configuration of a power conversion system to which a power converter according to Embodiment 5 is applied.

[0109] As shown in Figure 14, the power conversion system comprises a power supply 1000, a power conversion device 2000, and a load 3000. The power supply 1000 is a DC power supply and supplies DC power to the power conversion device 2000. The power supply 1000 can be made up of various materials, for example, a DC grid, a solar cell, or a storage battery. Alternatively, the power supply 1000 may be made up of a rectifier circuit or AC / DC converter connected to an AC grid. Furthermore, the power supply 1000 may be made up of a DC / DC converter that converts DC power supplied from a DC grid into power usable by the load 3000.

[0110] The power converter 2000 is a three-phase inverter connected between the power supply 1000 and the load 3000, and converts the DC power supplied from the power supply 1000 into three-phase AC power and supplies it to the load 3000. The power converter 2000 has a power converter 12. The power converter 12 includes a power conversion board 13 on which a plurality of semiconductor switching elements and a plurality of diodes are mounted, and a control board 14. The power conversion board 13 is a power conversion board 13 according to the embodiments 1 to 4 described above.

[0111] Load 3000 is a three-phase motor driven by AC power supplied from power converter 2000, and is used, for example, as a motor for hybrid vehicles, electric vehicles, railway vehicles, elevators, or air conditioners.

[0112] In the power conversion device according to Embodiment 5, since the power converter 12 is the power converter according to Embodiments 1 to 4, spatial propagation of noise that has entered the inside of the power conversion board 13 from the load 3000 can be blocked, similar to Embodiments 1 to 4. This makes it possible to suppress malfunctions of the power converter 12.

[0113] Furthermore, the power conversion device to which this disclosure is applied is not limited to cases where the load is an electric motor, but can also be used, for example, as a power supply device for an electrical discharge machine, laser processing machine, induction heating cooker, or contactless power supply system, and can even be used as a power conditioner for a solar power generation system or energy storage system.

[0114] Furthermore, the power converters described in each embodiment can be combined in various ways as needed.

[0115] The embodiments disclosed herein are illustrative and not limiting. This disclosure is indicated by the claims, not the scope described above, and all modifications in the meaning and scope equivalent to the claims are intended.

[0116] 1, 1A, 1B Current path, 10 System power supply, 11 DC power supply, 12 Power converter, 13, 13A, 13B Power conversion board, 14 Control board, 15 Gate circuit, 16 Housing, 17 Board fixing surface, 40 EDM machine, 41 Discharge electrode, 42 Workpiece, 44 Processing tank, 45 Processing fluid, 49 Sample stage, 50 Connecting wire, 51 Contaminated liquid tank, 52 Clean liquid tank, 53, 54 Pump, 55 Filter, 56 Cooler, 57-61 Flow path, 70, 70a, 70b Semiconductor switching element, 71, 71a-71e Diode, 72 Capacitor, 74, 75 Spacer, 76, 77 Heat sink, 76a, 77a First surface, 76b, 77b Second surface, 77f Fin, 78 Cooling pipes, 79, 79A, 79B; connecting conductors, 80, 80A, 80B; input section, 80p; positive input terminal, 80n; negative input terminal, 81, 81A, 81B; output section, 81a, 81b; output terminal, 82; fan, 83; connector, 100, 110; electrical discharge machining equipment, 1000; power supply, 2000; power converter, 3000; load.

Claims

1. A power converter that converts power supplied from a power source into power suitable for driving a load, comprising: an input section connected to the power source and an output section connected to the load, a power conversion board on which a plurality of semiconductor switching elements that perform power conversion between the input section and the output section are mounted; a control board that generates control signals for controlling the on / off state of the plurality of semiconductor switching elements; and a metal heat sink fixed to the surface of the power conversion board for dissipating heat generated by the plurality of semiconductor switching elements, wherein in a plan view of the surface of the power conversion board, the heat sink is positioned between the output section and the plurality of semiconductor switching elements.

2. The power converter according to claim 1, wherein the heat sink has a first surface on the output side and a second surface opposite to the first surface, and the plurality of semiconductor switching elements are arranged on the second surface.

3. The power converter according to claim 1, wherein the height of the upper end of the heat sink from the surface is greater than the height of the upper ends of the plurality of semiconductor switching elements from the surface.

4. The power converter according to claim 1, wherein the power conversion board further includes a gate circuit that drives the plurality of semiconductor switching elements according to a control signal provided from the control board, and in a plan view of the surface of the power conversion board, the heat sink is disposed between the output unit and the gate circuit.

5. The power converter according to claim 2, wherein the heat sink is an air-cooled heat sink in which air passages are formed inside such that the direction of airflow is parallel to the first and second surfaces, and the air-cooled heat sink cools the plurality of semiconductor switching elements by performing heat exchange between the air flowing through the passages and the plurality of semiconductor switching elements.

6. The power converter according to claim 5, wherein the plurality of semiconductor switching elements are arranged on the second surface of the air-cooled heat sink in the direction of airflow.

7. The power converter according to claim 2, wherein the heat sink is a liquid-cooled heat sink in which a flow path for the coolant is formed inside such that the direction of the flow of the coolant is parallel to the first surface and the second surface, and the liquid-cooled heat sink cools the plurality of semiconductor switching elements by performing heat exchange between the coolant flowing through the flow path and the plurality of semiconductor switching elements.

8. The power converter according to claim 7, wherein the plurality of semiconductor switching elements are arranged in a line on the second surface of the liquid-cooled heat sink in the direction of flow of the cooling liquid.

9. The power converter according to claim 1, further comprising a housing that houses the power conversion board, the control board, and the heat sink, wherein the housing is attached to the load.

10. The power converter according to claim 9, wherein the output unit includes a first pair of output terminals connected to the load and a second pair of output terminals connected to the load, and the plurality of semiconductor switching elements include a first semiconductor switching element that performs power conversion between the input unit and the first pair of output terminals and a second semiconductor switching element that performs power conversion between the input unit and the second pair of output terminals, and the first induced magnetic field generated by a first current path formed between the first semiconductor switching element, the first pair of output terminals and the load and the second induced magnetic field generated by a second current path formed between the second semiconductor switching element, the second pair of output terminals and the load are in opposite directions.

11. An electrical discharge machining apparatus comprising a power converter according to any one of claims 1 to 8, and an electrical discharge machining machine for machining a workpiece by electrical discharge machining, wherein the electrical discharge machining machine includes a discharge electrode connected to the output section of the power converter board via a connecting conductor, and a machining tank for storing a machining fluid in which the discharge electrode and the workpiece are immersed, and further comprises a housing for housing the power converter board, the control board and the heat sink, the housing being attached to the side of the machining tank.

12. The electrical discharge machining apparatus according to claim 11, further comprising a circulation circuit for circulating the processing fluid between the processing tank and another tank, wherein the heat sink is positioned between a branching point provided on the upstream side of the processing tank on the circulation circuit and a confluence point provided on the downstream side of the processing tank on the circulation circuit, and the heat sink cools the plurality of semiconductor switching elements by performing heat exchange between the processing fluid and the plurality of semiconductor switching elements.

13. The electrical discharge machining apparatus according to claim 11, wherein the output unit includes a first pair of output terminals connected to the load and a second pair of output terminals connected to the load, the plurality of semiconductor switching elements include a first semiconductor switching element that performs power conversion between the input unit and the first pair of output terminals and a second semiconductor switching element that performs power conversion between the input unit and the second pair of output terminals, and the first induced magnetic field generated by a first current path formed between the first semiconductor switching element, the first pair of output terminals and the load and the second induced magnetic field generated by a second current path formed between the second semiconductor switching element, the second pair of output terminals and the load are in opposite directions.

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