Power conversion device and switching characteristic adjustment method

Abstract

A power conversion device according to an embodiment comprises a pressure-contact type semiconductor switching element, a drive circuit, and a connection cable. The drive circuit supplies a control signal for the semiconductor switching element. The connection cable connects the drive circuit and a control signal terminal of the semiconductor switching element and supplies the control signal to the control signal terminal of the semiconductor switching element. In the connection cable, a substantially half-rotation twist about the extension direction of the connection cable is provided at a predetermined distance away from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable.

Description

Power conversion device and switching characteristic adjustment method

[0001] FIELD An embodiment of the present invention relates to a power conversion device and a method for adjusting switching characteristics.

[0002] The switching characteristics of a pressure-welded type semiconductor switching element used in a power converter may be affected by the switching current of the element itself or an adjacent element, which may affect the reliability of the power converter.

[0003] Japanese Patent Application Laid-Open No. 2017-118608

[0004] An object of the present invention is to provide a power conversion device and a switching characteristic adjustment method that prevent the switching characteristics of a pressure-welded semiconductor switching element from being affected by the switching current of the element itself or an adjacent element, thereby affecting the reliability of the power conversion device.

[0005] According to an embodiment, a power conversion device includes a pressure-displacement semiconductor switching element, a drive circuit, and a connection cable. The drive circuit supplies a control signal to the semiconductor switching element. The connection cable connects the drive circuit to a control signal terminal of the semiconductor switching element and supplies the control signal to the control signal terminal of the semiconductor switching element. The connection cable has a twist of approximately half a turn about an axis in the extension direction of the connection cable, at a position spaced a predetermined distance from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable.

[0006] 1 is a configuration diagram of a power conversion system to which the state estimation system for a semiconductor device for power conversion of the present embodiment is applied. FIG. 1 is a configuration diagram of an inverter of the present embodiment. FIG. 2 is a current path diagram within the inverter of the present embodiment. FIG. 3 is an explanatory diagram of the operation of a leg within the inverter of the present embodiment. FIG. 4 is a configuration diagram of the interior of a leg of the present embodiment. FIG. 5 is a configuration diagram of the interior of a leg of the present embodiment. FIG. 6 is a diagram of an element layout within a leg of the present embodiment. FIG. 7 is a stack configuration diagram of semiconductor switching element units within a leg of the present embodiment. FIG. 8 is a stack configuration diagram of diode units within a leg of the present embodiment. FIG. 9 is an overhead view of a semiconductor switching element unit within a leg of the present embodiment. FIG. 10 is an overhead view of a semiconductor switching element unit within a leg of the present embodiment. FIG. 11 is a diagram for explaining a method of leading out a gate lead of a semiconductor switching element within a leg of the present embodiment. FIG. 12 is a diagram for explaining a method of leading out a gate lead of a semiconductor switching element within a leg of the present embodiment. FIG. 13 is a diagram for explaining a method of leading out a gate lead of the present embodiment. FIG. 14 is a diagram for explaining a method of leading out a gate lead of the present embodiment. FIG. 15 is a diagram for explaining a method of leading out a gate lead of the present embodiment.

[0007] Hereinafter, a power conversion device and a switching characteristic adjustment method according to an embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted. Electrical connection may also be simply referred to as "connected." The "connection cable" in the embodiment may also be called a gate lead or a gate line.

[0008] Fig. 1A is a configuration diagram of a power conversion system to which the state estimation system for a power conversion semiconductor device of this embodiment is applied. Fig. 1B is a configuration diagram of an inverter of this embodiment. Fig. 1C is a current path diagram in the inverter of this embodiment. Fig. 1D is an explanatory diagram of the operation of a leg in the inverter of this embodiment.

[0009] 1A includes an inverter 3 that supplies AC power to a three-phase AC motor 2. The inverter 3 includes legs 3U, 3V, and 3W that correspond to the U, V, and W phases, respectively. For example, each leg is configured as a three-level type as shown in FIG. 1B.

[0010] For example, as shown in FIG. 1B, leg 3U includes four semiconductor switching elements (Q1 to Q4), four freewheeling diodes (D1 to D4), and two diodes (D5 and D6).

[0011] The semiconductor switching elements Q1-Q4 of leg 3U are configured in a four-stage cascode connection. The freewheeling diodes D1-D4 are configured in a four-stage cascode connection. Diodes D5 and D6 are connected in series with each other. The cathode of diode D5 is connected to the junction of semiconductor switching elements Q1-Q2. The anode of diode D6 is connected to the junction of semiconductor switching elements Q3-Q4. The junction of diodes D5 and D6 is connected to electrode CP, which serves as the neutral point.

[0012] Furthermore, it is preferable that a snubber capacitor (C1-C4) is provided for each pair of the semiconductor switching element Q and the freewheeling diode D.

[0013] The semiconductor switching elements Q1-Q4, freewheeling diodes D1-D4, and snubber capacitors C1-C4 are configured in parallel with each other in each pair. Similarly, the diodes D5 and D6 are configured in parallel with the snubber capacitors C5 and C6.

[0014] The operation of the legs will be described with reference to FIGS. 1C and 1D. FIG. 1C is a current path diagram within the inverter of this embodiment. Capacitors C1-C6 are omitted from FIGS. 1C and 1D. FIG. 1C shows a specific leg (3U) and its surrounding circuit (DC power supply and load). The solid and dashed arrows indicate the paths of current flow when semiconductor switching elements Q2 and Q3 are turned ON and semiconductor switching elements Q1 and Q4 are turned OFF. Arrows IQ1 and IQ2 indicate the current flowing through semiconductor switching elements Q1 and Q2. As described above, because semiconductor switching elements Q2 and Q3 are turned ON and semiconductor switching elements Q1 and Q4 are turned OFF, no current flows through the dashed-dotted line path (arrow IQ1). The current passing through the semiconductor switching elements becomes the current through the solid-line path (arrow IQ2) passing through semiconductor switching element Q2.

[0015] Although the semiconductor switching element Q3 is in the ON state, no current flows through the semiconductor switching element Q3 due to the voltage relationship, and current flows through the freewheeling diodes D3-D4 along the broken line path.

[0016] In this way, a load current IL according to the current state flows through the AC output terminal of a particular leg (3U).

[0017] The timing chart shown in Figure 1D shows an example of a sequence including the states shown in Figure 1C. From the top to bottom, Figure 1D shows the conduction states (logic states) of the semiconductor switching elements Q1-Q4, the load current IL, and the magnitude of the current (IQ2) of the semiconductor switching element Q2. Note that the state shown in Figure 1C is one example of several states that are used when the inverter 3 is functioning.

[0018] In the initial state shown in this timing chart, the semiconductor switching elements Q1 to Q4 are in the OFF state, and neither the load current IL nor the current (IQ2) of the semiconductor switching element Q2 flows.

[0019] At time t1, semiconductor switching elements Q1 and Q4 are maintained in the OFF state, while semiconductor switching elements Q2 and Q3 are transitioned to the ON state. Accordingly, the load current IL and the current (IQ2) of semiconductor switching element Q2 gradually increase. This state continues until time t2. This state corresponds to the state shown in FIG. 1C.

[0020] At time t2, semiconductor switching element Q2 is switched to the OFF state and semiconductor switching element Q4 is switched to the ON state while semiconductor switching element Q1 is kept in the OFF state and semiconductor switching element Q3 is kept in the ON state. As a result, the current (IQ2) through semiconductor switching element Q2 stops, but current flows through freewheeling diodes D3 and D4, so the load current IL continues to flow.

[0021] At time t3, semiconductor switching element Q1 is kept in the OFF state, semiconductor switching element Q3 is kept in the ON state, and semiconductor switching element Q2 is switched to the ON state and semiconductor switching element Q4 is switched to the OFF state. Accordingly, the load current IL and the current (IQ2) of semiconductor switching element Q2 begin to increase again. This state continues until time t4.

[0022] At time t4, the states of the semiconductor switching elements Q2 and Q4 are reversed, as was the case at time t2. Accordingly, the current (IQ2) through the semiconductor switching element Q2 stops, and the load current IL continues to flow. This timing chart includes times t2, t3, and t4, when the current (IQ2) through the semiconductor switching element Q2 suddenly rises or suddenly stops. These times also coincide with the sudden change in the level of the gate signal to the semiconductor switching element Q2.

[0023] Next, an example of the leg configuration will be described with reference to FIGS. 2, 3A, 3B, 4A, 4B, 5A, and 5B. FIG. 2 is a diagram showing the configuration inside a leg of this embodiment. FIG. 3A is a diagram showing the configuration inside a leg of this embodiment. FIG. 3B is a diagram showing the arrangement of elements inside a leg of this embodiment. FIG. 4A is a diagram showing the stack configuration of semiconductor switching element units inside a leg of this embodiment. FIG. 4B is a diagram showing the stack configuration of diode units inside a leg of this embodiment. FIGS. 5A and 5B are overhead views of the semiconductor switching element units inside a leg of this embodiment. The semiconductor switching element units shown in these overhead views are obtained by looking down from directions that show the front and back of the semiconductor switching element units. The semiconductor switching element units have a surface on which connection terminals FINQT for connecting freewheeling diodes D1-D4 are provided (see FIG. 5B) and a surface on which the connection terminals FINQT are not provided (see FIG. 5A).

[0024] In this embodiment, leg 3U is configured as two stacks as shown in FIG. 2. Note that leg 3V and leg 3W may be configured in the same manner as leg 3U. The first stack including semiconductor switching elements Q1-Q4 is called stack STACKA (FIGS. 4A, 5A, and 5B). The semiconductor switching elements Q1-Q4 in stack STACKA are configured in a four-stage cascode connection.

[0025] The second stack including the freewheeling diodes D1-D4 is called stack STACKB (FIG. 4B). The freewheeling diodes D1-D4 are configured in a four-stage cascode connection.

[0026] 3A and 3B, heat dissipation fins FINQ1-FINQ5 are provided between each of the cascode-connected semiconductor switching elements Q1-Q4 and at both ends of the cascode connection. These fins FINQ1-FINQ5 also serve as connection terminals for the reflux diodes D1-D4. The fins FINQ1-FINQ5 shown here are an example of a water-cooled type.

[0027] A more specific example of the configuration of stack STACKA is shown below. For example, a fin FINQ1 is connected to the drain of a semiconductor switching element Q1 provided on the positive electrode side of stack STACKA, and a fin FINQ2 is connected to the source of semiconductor switching element Q1. Fin FINQ2 is connected to the drain of semiconductor switching element Q2 in the next stage. This also applies to the following stages.

[0028] As shown in Figure 3A, heat dissipation fins FIND1-FIND5 are provided between and at both ends of the reflux diodes D1-D4. These fins FIND1-FIND5 also serve as connection terminals for the semiconductor switching elements Q1-Q4. The fins FIND1-FIND5 shown here are an example of a water-cooled type.

[0029] A more specific example of the configuration of stack STACKB is shown below. For example, fin FIND1 is connected to the cathode of freewheeling diode D1 provided on the positive electrode side of stack STACKB, and fin FIND2 is connected to the anode of freewheeling diode D1. Fin FIND2 is connected to the cathode of freewheeling diode D2 in the next stage. This also applies to the following stages.

[0030] A pair of stack STACKA and stack STACKB is formed as a leg by electrically connecting fins corresponding to the same stage in each stack.

[0031] Incidentally, while repeatedly evaluating the inverter 3 configured as described above, it was confirmed that differences in the method of drawing out the gate leads of the semiconductor switching elements could cause phenomena that affect the switching characteristics, etc.

[0032] The effects of different methods of drawing out the gate leads of semiconductor switching elements will be described with reference to Figures 6A, 6B, 7A, 7B, 7C, 8A, 8B, etc. Figures 6A and 6B are diagrams for explaining the method of drawing out the gate leads of semiconductor switching elements in a leg according to this embodiment. Figures 7A, 7B, and 7C are diagrams for explaining the method of drawing out the gate leads according to this embodiment. Figures 8A and 8B are diagrams for explaining the current generated in the gate leads according to this embodiment.

[0033] 6A and 6B show schematic plan views of a semiconductor switching element Q. The symbol FINQ shown in these figures is an example of a heat dissipation fin in the stack STACKA. An electrical connection terminal FINQT facing a specific direction is arranged at an asymmetrical position. The magnetic field around the electrical connection terminal FINQT changes depending on the current flowing through the electrical connection terminal FINQT.

[0034] There is a method for reducing the influence of the above-mentioned magnetic field by adjusting the direction in which the gate lead connected to the semiconductor switching element Q is drawn out from the semiconductor switching element Q (see, for example, Japanese Patent Laid-Open Publication No. 2017-118608). An angle difference of approximately 45 degrees is set between the drawing direction shown in FIG. 6A and the drawing direction shown in FIG. 6B. The magnitude of this angle difference may be adjusted as appropriate. As described above, the degree of influence of the current flowing through the semiconductor switching element Q can be changed depending on the position at which the gate lead is connected.

[0035] As shown in Figures 8A and 8B, the position where the gate lead is connected generates a magnetic flux that is affected by changes in the main current. The direction of the magnetic flux determines the direction of the current induced in the gate lead. The amount of current induced in this way varies depending on the relationship between the area of ​​the gap between the two wires of the gate lead and the magnitude of the magnetic flux in that vicinity. The magnitude of the magnetic flux is related to the amount of change in current per unit time.

[0036] For example, the fins used to cool a pressure-welded semiconductor switching element Q do not have the same external shape as the element itself. The fins are provided with terminals (fin terminals) for electrical connection to an external conductor. For example, the main current of the semiconductor switching element Q flows from the semiconductor switching element Q to the fin terminals, but the gate lead is affected by the magnetic field of the main current, causing the gate current to increase in either the negative or positive direction. If the gate current increases in the positive direction, the turn-off di / dt decreases, and if the gate current increases in the negative direction, the turn-off di / dt increases.

[0037] As shown in Figures 7B and 7C, the gate lead of this embodiment has a twist at a predetermined position, rotated around the extension direction of the gate lead. The difference between Figures 7B and 7C is the difference in the distance (x1, x2) from the peripheral edge of the semiconductor switching element Q to the twisted position of the two wires of the gate lead. The longer this distance, the greater the difference in the area between the two wires of the gate lead from the peripheral edge of the semiconductor switching element Q to the twisted position, and the area between the two wires of the gate lead from the twisted position to the driver circuit. This twist cancels out the magnetic flux penetrating the area of ​​the gap between the two wires of the gate lead on either side of the twisted position, achieving the same effect as reducing the magnetic flux compared to using a gate lead without a twist, as shown in Figure 7A.

[0038] As described above, the power conversion device of the embodiment includes a pressure-contact semiconductor switching element, a drive circuit, and a connection cable. The drive circuit supplies a control signal to the semiconductor switching element. The connection cable connects the drive circuit to a control signal terminal of the semiconductor switching element and supplies a control signal to the control signal terminal of the semiconductor switching element. The connection cable has a twist of approximately half a turn about an axis in the extension direction of the connection cable, located a predetermined distance from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable. This reduces the influence of the environment during use on the switching characteristics of the pressure-contact semiconductor switching element. This reduces the influence on the reliability of the power conversion device.

[0039] Preferably, the rate of change of the current induced in the connection cable when the semiconductor switching element is switched can be adjusted by changing the twist position of the connection cable in the extension direction of the connection cable.

[0040] A plurality of substantially circular pressure-contact semiconductor switching elements are stacked with their axes aligned. In this case, a conductor (fin) is provided between one semiconductor switching element (Q) and the semiconductor switching element (Q') adjacent to that semiconductor switching element (Q). This conductor (fin) preferably has a terminal portion protruding in a specific radial direction of the substantially circular shape. Furthermore, the direction in which the connection cable is drawn out may be a direction spaced a predetermined angle around the axis from that specific direction.

[0041] The inverter 3 (power conversion device) includes pressure-contact freewheel diodes D connected in anti-parallel to pressure-contact semiconductor switching elements Q. The pressure-contact semiconductor switching elements Q are arranged in stack STACKA (first stack row). The pressure-contact freewheel diodes D may be provided in stack STACKB (second stack row).

[0042] The inverter 3 includes output electrodes for outputting AC from legs of a three-level circuit formed as a stack STACKA (first stack row). The connection cables are twisted at predetermined positions so as to pass a current that is smaller than the current corresponding to the magnitude of the magnetic flux generated by the current flowing through the output electrodes. The current flowing through the output electrodes is, for example, a current induced in the connection cables provided near the output electrodes by magnetic flux generated near the output electrodes when a current is passed through the output electrodes.

[0043] A current corresponding to the magnitude of the magnetic flux caused by the current flowing through the output electrode flows through the connection cable, and a signal generated by receiving the magnetic flux is superimposed on the control signal for the semiconductor switching element Q.

[0044] Second Embodiment A second embodiment will be described. In the first embodiment described above, it was explained that the switching characteristics of a pressure-contact type semiconductor switching element are affected by the switching of the element itself or an adjacent element. In this embodiment, however, a method for suppressing the induction of resonance in a circuit including a pressure-contact type semiconductor switching element will be described.

[0045] For example, the inverter 3 of this embodiment includes capacitors C1 to C6. These capacitors C1 to C6 are an example of a "snubber capacitor." A "snubber capacitor" is sometimes used in parallel with a semiconductor switching element that switches a relatively large current, in order to reduce the parasitic inductance of electrical wiring, etc.

[0046] In the comparative example, the combination of a snubber capacitor and a parasitic inductance can cause the circuit to become unstable. Furthermore, if the current change rate (turn-off di / dt) when turning off a semiconductor switching element becomes high, a steep current change occurs in the unstable circuit due to the high turn-off di / dt, which can induce circuit resonance. The occurrence of such resonance can affect the reliability of each product.

[0047] Therefore, in this embodiment, in addition to adjusting the position of the gate lead (connection position, lead-out position) and the direction of the main current flowing through the semiconductor switching element Q, we propose twisting the gate lead to set the di / dt characteristic (turn-off di / dt) when turning off the semiconductor switching element Q to an appropriate value. The turn-off di / dt can be set to any value suited to the purpose. This can minimize any impact on the reliability of the power conversion device.

[0048] Third Embodiment A third embodiment will be described. In this embodiment, a case where the turn-off di / dt is set to a value lower than an arbitrary value according to the purpose will be described.

[0049] Generally, when the turn-off di / dt becomes high, the loss during switching of the semiconductor switching element Q exceeds an allowable value, and the semiconductor switching element Q is more likely to be damaged.

[0050] In this embodiment, in addition to adjusting the position of the gate lead (connection position, lead-out position) and the direction of the main current flowing through the semiconductor switching element Q, we propose providing a twist in the gate lead. This makes it possible to arbitrarily set the di / dt characteristic (turn-off di / dt) when turning off the semiconductor switching element Q, and the turn-off di / dt can be set to a value lower than an arbitrary value suited to the purpose.

[0051] The main current flows from the semiconductor switching element Q toward the fin terminal, but the gate lead is affected by the magnetic field of the main current, causing the gate current of the semiconductor switching element Q to increase in either the negative or positive direction. For example, if the gate current increases in the positive direction, the turn-off di / dt decreases, and if the gate current increases in the negative direction, the turn-off di / dt increases. This makes it possible to suppress any impact on the reliability of the power conversion device.

[0052] According to at least one embodiment described above, a power conversion device includes a pressure-displacement semiconductor switching element, a drive circuit, and a connection cable. The drive circuit supplies a control signal to the semiconductor switching element. The connection cable connects the drive circuit to a control signal terminal of the semiconductor switching element and supplies the control signal to the control signal terminal of the semiconductor switching element. The connection cable has a twist of approximately half a turn about an axis in the extension direction of the connection cable, at a position a predetermined distance from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable. This can suppress any impact on the reliability of the power conversion device.

[0053] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0054] 1 Power conversion system 2 Three-phase AC motor 3 Inverter 3U, 3V, 3W Leg C, C1-C6 Snubber capacitor D, D1-D4 Freewheeling diode D5, D6 Diode Q, 1-Q4 Semiconductor switching element

Claims

1. A power conversion device comprising: a pressure-displacement semiconductor switching element; and a connection cable that connects a drive circuit that supplies a control signal to the semiconductor switching element and a control signal terminal of the semiconductor switching element, and supplies the control signal to the control signal terminal of the semiconductor switching element, wherein the connection cable is twisted by approximately half a turn around an axis in the extension direction of the connection cable, at a predetermined distance from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable.

2. A power conversion device as described in claim 1, which is configured to be able to adjust the rate of change of the current induced in the connection cable when the semiconductor switching element is switched by changing the position of the twist in the connection cable in the extension direction of the connection cable.

3. A power conversion device according to claim 1, comprising a conductor in which a plurality of said pressure-contact type semiconductor switching elements having a substantially circular shape are stacked with their axes aligned, said conductor being provided between one semiconductor switching element and a semiconductor switching element adjacent to said one semiconductor switching element and having a terminal portion protruding in a specific radial direction of said substantially circular shape, and wherein the drawing direction of said connection cable is a direction spaced a predetermined angle around said axis from said specific direction.

4. The power conversion device according to claim 1, further comprising pressure-contact type freewheeling diodes connected in anti-parallel to the pressure-contact type semiconductor switching elements, wherein the pressure-contact type semiconductor switching elements are arranged in a row of a first stack, and the pressure-contact type freewheeling diodes are provided in a row of a second stack.

5. The power conversion device according to claim 4, further comprising output electrodes for outputting AC from the legs of the three-level circuit arranged in a row of the first stack, wherein the connection cable is twisted at a predetermined position so as to pass a current that is reduced in magnitude compared to a current corresponding to the magnitude of the magnetic flux generated by the current flowing through the output electrodes.

6. The power conversion device according to claim 5, wherein a current corresponding to the magnitude of magnetic flux caused by a current flowing through the output electrode flows through the connection cable, and a signal generated by receiving the magnetic flux is superimposed on the control signal.

7. A method for adjusting the switching characteristics of a pressure-displacement semiconductor switching element of a power conversion device comprising: a drive circuit that supplies a control signal to the semiconductor switching element; and a connection cable that connects the drive circuit and the control signal terminal of the semiconductor switching element to supply the control signal to the control signal terminal of the semiconductor switching element, the method comprising providing a twist of approximately half a turn in the connection cable, with the twist being centered on the extension direction of the connection cable, at a predetermined distance from the control signal terminal of the semiconductor switching element in the extension direction of the connection cable.

8. A characteristic adjustment method according to claim 7, wherein the magnitude of the rate of change of the current induced in the connection cable when the semiconductor switching element is switched can be adjusted by changing the position of the twist in the connection cable in the extension direction of the connection cable.

9. The characteristic adjustment method according to claim 7, wherein the power conversion device is configured by stacking a plurality of the pressure-displacement type semiconductor switching elements of approximately circular shape with their axes aligned, and is provided with a conductor provided between one semiconductor switching element and a semiconductor switching element adjacent to the one semiconductor switching element, the conductor having a terminal portion protruding in a specific radial direction of the approximately circular shape, and the drawing direction of the connection cable is a direction spaced a specific angle around the axis from the specific direction.

10. The characteristic adjustment method according to claim 7, wherein the power conversion device comprises pressure-contact type freewheeling diodes connected in anti-parallel to the pressure-contact type semiconductor switching elements, the pressure-contact type semiconductor switching elements are arranged in a row of a first stack, and the pressure-contact type freewheeling diodes are provided in a row of a second stack.

11. The characteristic adjustment method according to claim 10, wherein the power conversion device comprises output electrodes for outputting AC from the legs of the three-level circuit arranged in a row of the first stack, and the connection cable is twisted at a predetermined position so as to pass a current that is reduced compared to a current corresponding to the magnitude of the magnetic flux generated by the current flowing through the output electrodes.

12. The characteristic adjustment method according to claim 11, wherein a current corresponding to the magnitude of the magnetic flux caused by the current flowing through the output electrode flows through the connection cable, and a signal generated by receiving the magnetic flux is superimposed on the control signal.

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