Power converter

Abstract

This suppresses surge voltage during switching when switching a toggle switch from the ON state to the OFF state. [Solution] The power conversion device comprises a first inverter connected to a power line connected to an energy storage device and connected to each phase of an open-winding motor, a second inverter connected to a power line and connected to each phase of an open-winding motor, and a line connection switching element attached to the positive electrode side line of the power line between the first inverter and the second inverter. The line connection switching element is made of a semiconductor switching element having a larger parasitic capacitance than the switching elements of the first and second inverters.

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, and more particularly to a power conversion device having two inverters for driving an open-winding motor.

Background Art

[0002] Conventionally, as this type of power conversion device, there has been proposed one including a first inverter connected to a power line connected to a battery and connected to each phase of an open-winding motor, a second inverter connected to the power line and connected to each phase of the open-winding motor, and a switching switch attached to the positive electrode side of the power line between the first inverter and the second inverter (see, for example, Patent Document 1). This power conversion device switches between Y-connection driving with the switching switch in an off state and Δ-connection driving with the switching switch in an on state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above-described power conversion device, when the switching switch is switched from an on state to an off state, there is a concern that a switching surge may occur due to wiring inductance and interrupting current. If the surge voltage is large, the elements constituting the switching switch may be damaged.

[0005] The main object of the power conversion device of the present disclosure is to suppress the surge voltage in the switching surge when the switching switch is switched from an on state to an off state.

Means for Solving the Problems

[0006] The power conversion device of this disclosure employs the following means to achieve the main objective described above.

[0007] The power conversion device of this disclosure, A power conversion device connected to an energy storage device and a three-phase open-wound motor, A first inverter is connected to the power line connected to the energy storage device and to each phase of the open-winding motor, A second inverter connected to the aforementioned power line and connected to each phase of the open-winding motor, A line connection switching element attached to the positive terminal side line of the power line between the first inverter and the second inverter, Equipped with, The line connection switching element is composed of a semiconductor switching element having a larger parasitic capacitance compared to the switching elements of the first inverter and the second inverter. It is characterized by the following:

[0008] The power conversion device of this disclosure comprises a first inverter connected to a power line connected to an energy storage device and connected to each phase of an open-winding motor, a second inverter connected to a power line and connected to each phase of an open-winding motor, and a line connection switching element attached to the positive electrode side line of the power line between the first inverter and the second inverter. The line connection switching element is composed of a semiconductor switching element having a larger parasitic capacitance than the switching elements of the first and second inverters. The surge voltage in a switching surge of the line connection switching element is larger as the interruption current increases and is smaller as the parasitic capacitance of the line connection switching element increases. Therefore, by composing the line connection switching element with a semiconductor switching element having a large parasitic capacitance, the surge voltage in a switching surge of the line connection switching element can be kept low.

[0009] In the power conversion device of this disclosure, the line connection switching element may be a Si-IGBT (Si-Insulated Gate Bipolar Transistor) or a Si-MOSFET (Si-Metal Oxide Semiconductor Field Effect Transistor), and the switching elements of the first inverter and the second inverter may be a SiC-MOSFET (SiC-Metal Oxide Semiconductor Field Effect Transistor).

[0010] In the power conversion device of this disclosure, a control device is provided to control the on / off state of the line connection switching element, and when the control device switches the line connection switching element from on to off, it may turn off the line connection switching element at the timing when the current of any of the three phases of the open winding motor becomes zero. As described above, the surge voltage in the switching surge of the line connection switching element increases as the interruption current increases, so it is preferable to turn off the line connection switching element at the timing when the current flowing through the line connection switching element decreases. The current flowing through this line connection switching element is the sum of the three phases of the open winding motor, and the timing when the sum of the three phases of the open winding motor decreases is the timing when the current of any of the three phases of the open winding motor becomes zero. For this reason, by turning off the line connection switching element at the timing when the current of any of the three phases of the open winding motor becomes zero, the surge voltage in the switching surge can be reduced.

[0011] In the power conversion device of this disclosure, a capacitor connected in parallel with the line connection switching element may be provided. As described above, the surge voltage in the switching surge of the line connection switching element decreases as the parasitic capacitance of the line connection switching element increases. Therefore, if a capacitor is connected in parallel with the line connection switching element, the capacitance of the capacitor is added to the parasitic capacitance of the line connection switching element, and thus the surge voltage in the switching surge of the line connection switching element decreases. [Brief explanation of the drawing]

[0012] [Figure 1] This diagram shows a schematic configuration of a drive unit 20 including a power converter 30 as one embodiment of the present disclosure. [Figure 2] This is an explanatory diagram illustrating an example of how the parasitic capacitance of the connection switch 36 and the voltage between the drain and source (DS) change over time when the connection switch 36 is switched from on to off. [Figure 3] This is an explanatory diagram showing an example of the time variation of the three-phase currents of an open-winding motor 40 and the current flowing through the connecting switch 36. [Figure 4] This is a flowchart of an example of a switch-off process performed by the electronic control unit 38. [Figure 5] This is a schematic diagram showing the configuration of the drive unit 20B, including the modified power converter 30B. [Modes for carrying out the invention]

[0013] Next, embodiments for implementing this disclosure will be described. Figure 1 is a schematic diagram showing the configuration of a drive unit 20 including a power converter 30 as one embodiment of this disclosure. The drive unit 20 comprises a battery 22, a power converter 30, and an open-wound motor 40.

[0014] The battery 22 is configured as, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery, and its positive and negative terminals are connected to the positive power line 24p and the negative power line 24n. A smoothing capacitor 26 is attached to the positive power line 24p and the negative power line 24n.

[0015] The power converter 30 comprises a first inverter 32, a second inverter 34, a connection switch 36, and an electronic control unit 38.

[0016] The first inverter 32 is connected to the positive power line 24p and the negative power line 24n to which the battery 22 is connected, and has six switching elements, transistors T11 to T16, and six diodes D11 to D16 connected in parallel to each of the six transistors T11 to T16. Transistors T11 to T16 are all made of SiC-MOSFETs (SiC - Metal Oxide Semiconductor Field Effect Transistors). Two pairs of transistors from T11 to T16 (transistor T11 and transistor T14, transistor T12 and transistor T15, transistor T13 and transistor T16) are arranged so as to be the source and sink sides with respect to the positive power line 24p and the negative power line 24n. In addition, each connection point of two pairs of transistors T11 to T16 is connected to one end of the three-phase coil (u-phase, v-phase, and w-phase coils) of the open-winding motor 40.

[0017] The second inverter 34 is connected to the positive power line 24p and the negative power line 24n to which the battery 22 is connected so as to sandwich the first inverter 32 with the battery 22, and has six transistors T21 to T26 as switching elements and six diodes D21 to D26 connected in parallel to each of the six transistors T21 to T26. All of the transistors T21 to T26 are composed of SiC-MOSFET (SiC - Metal Oxide Semiconductor Field Effect Transistor). Two transistors each paired among the transistors T21 to T26 (transistor T21 and transitor T24, transitor T22 and transitor T25, transitor T23 and transitor T26) are arranged to be on the source side and the sink side with respect to the positive power line 24p and the negative power line 24n. Further, each of the connection points of the two paired transistors of the transistors T21 to T26 is connected to the other end side of the three-phase coils (coils of the u-phase, v-phase, and w-phase) of the open-winding motor 40.

[0018] The connection switch 36 is attached between the first inverter 32 and the second inverter 34 on the positive power line 24p. The connection switch 36 is composed of a Si-IGBT (Si - Insulated Gate Bipolar Transistor) having a larger parasitic capacitance than the transistors T11 to T16 of the first inverter 32 and the transistors T21 to T26 of the second inverter 34.

[0019] The electronic control unit 38 is configured as a microcomputer centered on a CPU. The electronic control unit 38 also functions as a control device for the drive device 20, calculates a torque command for the open-winding motor 40 based on a drive command (not shown), and performs switching control on the six transistors T11 to T16 of the first inverter 32 and the six transistors T21 to T26 of the second inverter 34, or controls the on / off of the connection switch 36.

[0020] The open-winding motor 40 is a generator motor in which both ends of each of the three-phase windings of the u-phase, v-phase, and w-phase are configured as connection terminals. At one end side of each of the three-phase windings of the u-phase, v-phase, and w-phase, three connection points of two transistors that form a pair with the first inverter 32 are connected. At the other end side of each of the three-phase windings of the u-phase, v-phase, and w-phase, three connection points of two transistors that form a pair with the second inverter 34 are connected.

[0021] In the power conversion device 30 of the embodiment, the open-winding motor 40 can be driven in a Y-connection by performing switching control on the transistors T11 to T16 of the first inverter 32 with the connection switch 36 turned off, and with the transistors T21 to T23 of the upper arm of the second inverter 34 turned on and the transistors T24 to T26 of the lower arm turned off. That is, by turning off the connection switch 36 and turning on the transistors T21 to T23 of the upper arm of the second inverter 34, the u-phase, v-phase, and w-phase of the open-winding motor 40 are made into a neutral point by the transistors T21 to T23 that are turned on, and the open-winding motor 40 is driven by the first inverter 32 as a Y-connected motor. Further, in the power conversion device 30 of the embodiment, the open-winding motor 40 can be driven in a Δ-connection by performing switching control on the transistors T11 to T16 of the first inverter 32 and performing switching control on the transistors T21 to T26 of the second inverter 34 with the connection switch 36 turned on.

[0022] In the power converter 30 of this embodiment, the surge voltage during switching surges when transitioning from a delta-connected drive state (by turning on the connection switch 36) to a wy-connected drive state (by turning off the connection switch 36) is suppressed by configuring the connection switch 36 with an element (Si-IGBT) that has a larger parasitic capacitance than transistors T11-T16 of the first inverter 32 and transistors T21-T26 of the second inverter 34. Figure 2 shows an example of the time change of the parasitic capacitance of the connection switch 36 and the voltage between the drain and source (DS) when the connection switch 36 is turned off. In the figure, the solid line shows the DS voltage when an element with a small parasitic capacitance is used as the connection switch 36, the dashed line shows the DS voltage when an element with a medium parasitic capacitance is used as the connection switch 36, and the dashed line shows the DS voltage when an element with a large parasitic capacitance is used as the connection switch 36. As shown in the figure, the larger the parasitic capacitance of the connection switch 36, the smaller the surge voltage during switching surges can be. Therefore, in the power conversion device 30 of this embodiment, the connection switch 36 is made of an element with a large parasitic capacitance (Si-IGBT).

[0023] The surge voltage in the switching surge of the connection switch 36 decreases as the interruption current decreases. Therefore, in the power converter 30 of this embodiment, the connection switch 36 is turned off at the timing when the current flowing through it decreases. The current flowing through this connection switch 36 is the sum of the three phases (u phase, v phase, w phase) of the open-winding motor 40, and the timing when the sum of the three phases of the open-winding motor 40 decreases corresponds to the timing when the current of any of the three phases of the open-winding motor 40 becomes zero. Therefore, the connection switch 36 is turned off at the timing when the current of any of the three phases of the open-winding motor 40 becomes zero. Figure 3 shows an example of the time variation of the three phase currents of the open-winding motor 40 and the current flowing through the connection switch 36. As shown in the figure, the current flowing through the connection switch 36 is minimized at the timing when the current of any of the three phases of the open-winding motor 40 becomes zero. In other words, in Figure 3, the connection switch 36 should be turned off at any of the timings T0 to T6. Figure 4 shows a flowchart of an example of the switch-off process executed by the electronic control unit 38 when the connection switch 36 is turned off.

[0024] When the switch-off process is executed, the electronic control unit 38 first determines whether the connection switch 36 is in the ON state (step S100). If it determines that the connection switch 36 is not in the ON state (is in the OFF state), it determines that this process is unnecessary and terminates the process. On the other hand, if it determines that the connection switch 36 is in the ON state, it determines whether a command to turn off the connection switch 36 has been issued (step S110). If it determines that a command to turn off the connection switch 36 has not been issued, it determines that this process is unnecessary and terminates the process. On the other hand, if it determines that a command to turn off the connection switch 36 has been issued, it waits for the timing when one of the three phase currents of the open-winding motor 40 becomes 0 (step S120), turns off the connection switch 36 (step S130), and terminates the process.

[0025] In the power conversion device 30 of the embodiment described above, by configuring the connection switch 36 with an element (Si-IGBT) that has a larger parasitic capacitance than the transistors T11 to T16 of the first inverter 32 and the transistors T21 to T26 of the second inverter 34, it is possible to suppress the surge voltage in the switching surge when transitioning from the delta-connection drive state by turning on the connection switch 36 to the w-connection drive state by turning off the connection switch 36.

[0026] Furthermore, in the power conversion device 30 of this embodiment, the connecting switch 36 is turned off at the timing when the current of any of the three phases of the open-winding motor 40 becomes zero. This makes it possible to reduce the surge voltage in the switching surge when the connecting switch 36 is turned from on to off.

[0027] In the power converter 30 of this embodiment, the connection switch 36 is made of Si-IGBTs. However, the connection switch 36 only needs to have a parasitic capacitance greater than the transistors T11 to T16 of the first inverter 32 and the transistors T21 to T26 of the second inverter 34, so it may also be made of Si-MOSFETs.

[0028] In the power converter 30 of this embodiment, the connection switch 36 is made of a Si-IGBT with a large parasitic capacitance. However, since the effective parasitic capacitance of the connection switch 36 is sufficient, it is also possible to include a capacitor 37 connected in parallel with the connection switch 36, as shown in the power converter 30B of the modified drive device 20B in Figure 5. This increases the number of elements constituting the power converter, but it dramatically reduces the surge voltage in the switching surge when the connection switch 36 is turned from on to off.

[0029] The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be explained. In the embodiment, the battery 22 corresponds to the "energy storage device", the open winding motor 40 corresponds to the "open winding motor", the first inverter 32 corresponds to the "first inverter", the second inverter 34 corresponds to the "second inverter", and the connecting switch 36 corresponds to the "line connection switching element".

[0030] Furthermore, the correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem is merely an example to specifically explain the form in which the embodiment implements the invention described in the section on means for solving the problem, and does not limit the elements of the invention described in the section on means for solving the problem. In other words, the interpretation of the invention described in the section on means for solving the problem should be based on the description in that section, and the embodiment is merely one specific example of the invention described in the section on means for solving the problem.

[0031] Although the present disclosure has been described above using embodiments, the present disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of the present disclosure. [Industrial applicability]

[0032] This disclosure can be used in industries such as the manufacturing of power conversion equipment. [Explanation of Symbols]

[0033] 20, 20B drive unit, 22 battery, 24p positive power line, 24n negative power line, 26 capacitor, 30, 30B power converter, 32 first inverter, 34 second inverter, 36 connection switch, 37 capacitor, 38 electronic control unit, 40 open winding motor, T11~T16, T21~T26 transistors, D11~D16, D21~D26 diodes.

Claims

1. A power conversion device connected to an energy storage device and a three-phase open-wound motor, A first inverter is connected to the power line connected to the energy storage device and to each phase of the open-winding motor, A second inverter connected to the aforementioned power line and connected to each phase of the open-winding motor, A line connection switching element attached to the positive terminal side line of the power line between the first inverter and the second inverter, Equipped with, The line connection switching element is composed of a semiconductor switching element having a larger parasitic capacitance compared to the switching elements of the first inverter and the second inverter. A power conversion device characterized by the following features.

2. A power conversion device according to claim 1, The line connection switching element is a Si-IGBT or a Si-MOSFET. The switching elements of the first inverter and the second inverter are SiC-MOSFETs. Power converter.

3. A power conversion device according to claim 1 or 2, The system includes a control device that controls the on / off switching of the line connection switching element, When the control device switches the line connection switching element from on to off, it turns off the line connection switching element at the timing when the current of any of the three phases of the open-winding motor becomes zero. Power converter.

4. A power conversion device according to claim 1, A capacitor connected in parallel with the aforementioned line connection switching element, A power conversion device equipped with the following features.

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