Power Conversion Device

Abstract

To provide a power converter capable of shifting to two-phase control that outputs stable torque when one phase open failure of a three-phase motor occurs.SOLUTION: The power converter includes; a three-phase inverter circuit; a switching unit that connects the three-phase inverter wiring to either the three-phase motor wiring or the neutral point of the three-phase motor, respectively; and a control unit that controls the three-phase inverter circuit and the switching unit. The control unit is configured so as to, when one phase of the three-phase motor fails, control the switching unit to cut off the inverter wiring corresponding to the one phase that has failed and the motor wiring of the same phase, and to switch to the connection between the inverter wiring and the neutral point of the motor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] The safety of the operation of a three-phase electric motor connected to an on-board inverter is important to ensure the reliability of the vehicle. For example, if an open circuit fault occurs in one of the phases of this three-phase motor while driving, it is necessary to control the vehicle so that it can move to a safe location or a workshop where repairs can be made.

[0003] The following Patent Document 1 discloses a configuration of an electric vehicle that can deal with a failure by making it possible to disconnect a faulty phase of the motor from the inverter when the vehicle collides. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5692018 Publication Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, there is a possibility that torque ripple will occur when the inverter and motor are disconnected in the event of a fault, or that the motor will be unable to rotate if the vehicle stops at a specific phase angle. In view of this, an object of the present invention is to provide a power conversion device that can transition to two-phase control that outputs stable torque in the event of a one-phase open fault in a three-phase motor. [Means for solving the problem]

[0006] The power conversion device includes a three-phase inverter circuit that outputs AC power converted from DC power to drive a three-phase motor, a switching unit that connects three-phase inverter wirings drawn out from the three-phase inverter circuit to either three-phase motor wirings drawn out from the three-phase motor or the neutral point of the three-phase motor, and a control unit that controls the three-phase inverter circuit and the switching unit, and when one phase of the three-phase motor fails, the control unit controls the switching unit to cut off the inverter wiring corresponding to the failed phase and the motor wiring of the same phase, and switch the connection between the inverter wiring and the neutral point of the motor. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a power conversion device that can transition to two-phase control for outputting stable torque when one phase of a three-phase motor has an open circuit fault. [Brief explanation of the drawings]

[0008] [Figure 1] An explanatory diagram of a control unit that controls a power conversion device and a motor. [Figure 2] 1 is an explanatory diagram of a power conversion device according to an embodiment of the present invention; [Figure 3] An explanatory diagram of a conventional current path and a current path of the present invention when a one-phase open fault occurs. [Figure 4] An example in which the switching section and neutral connection section of Figure 2 are incorporated into an electronic switch [Figure 5] Control flow of a power conversion device according to an embodiment of the present invention [Figure 6] An example in which the electronic switch shown in Figure 4 is incorporated into each phase of the power conversion circuit [Figure 7] First and second modified examples [Figure 8] Third Modification [Figure 9] Fourth Modification

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0010] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0011] (One embodiment of the present invention and overall configuration of the device) (Figure 1) In a power conversion device (hereinafter referred to as inverter) mounted on a vehicle, a power conversion circuit 3 converts DC current input from a DC power supply 5 into AC current by switching power semiconductors, and drives a motor 1 with the converted AC current. When the power conversion circuit 3 is three-phase, a total of six power semiconductors, consisting of upper and lower arms for the three phases, exist within the power conversion circuit 3. The following explanation will be given using a three-phase inverter as an example.

[0012] The inverter control unit 10 receives a target torque commanded from the vehicle's upper controller, and a duty calculation unit calculates the duty ratio for each of the U, V, and W phases. Next, a PWM (Pulse Width Modulation) signal generation unit generates a PWM signal based on the calculated duty ratio and inputs the PWM signal to a driver circuit. The driver circuit generates a drive signal based on the input PWM signal and inputs the drive signal to a power conversion circuit 3. The power conversion circuit 3 operates based on the input drive signal. The power conversion circuit 3 includes a power semiconductor, such as an IGBT (Insulated Gate Bipolar Transistor), and converts DC power from a DC power source 5 into three-phase AC power by switching the power semiconductor. If the power conversion circuit 3 includes a relay circuit, the relay circuit is controlled by a relay circuit control unit 6 of the control unit 10.

[0013] The three-phase AC current value output from the power conversion circuit 3 is acquired by a current sensor 12 (hereinafter referred to as sensor 12) and is used for calculation in the duty calculation unit by feedback. When the motor 1 fails, the failure detection unit of the control unit 10 acquires the three-phase AC current value from the sensor 12 and feeds back failure information about the motor 1 to the PWM signal generation unit and a higher-level controller based on the acquired current value.

[0014] Motor 1 is a three-phase motor with three internal windings, and is driven by AC power output from power conversion circuit 3. Motor 1 may be, for example, a synchronous motor using permanent magnets, or an induction motor without permanent magnets. The power conversion device also has the function of converting the power of motor 1 into DC power and charging DC power supply 5.

[0015] (Figure 2) The power conversion circuit 3 has six power semiconductors for U, V, and W phases. The smoothing capacitor 4 smooths the current generated by the on / off switching of the power semiconductors and suppresses ripples in the DC current supplied from the DC power supply 5 to the power conversion circuit 3. For example, an electrolytic capacitor or a film capacitor is used as the smoothing capacitor 4. The DC power supply 5 is a power source that supplies power to drive the motor 1, and is, for example, a battery. The power conversion circuit 3 converts the DC power input from the DC power supply 5 into AC power to drive the motor 1 by switching the internal power semiconductors on / off according to a drive signal input from a driver circuit. The power semiconductor is not limited to an IGBT, but may also be, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0016] The power semiconductors are divided into two pairs, one above the other, for each phase, with the three upper power semiconductors forming the upper arm and the three lower power semiconductors forming the lower arm. Wiring (inverter wiring) drawn from the power conversion circuit 3 is connected to the windings of each phase of the motor 1 via the motor wiring. Sensor 12 measures the AC current flowing through each phase (U phase, V phase, W phase) of the motor 1. Sensor 12 outputs the measured AC current of each phase to control unit 10 as an AC current value.

[0017] Between the power conversion circuit 3 and the motor 1, there is provided a switching unit 8 that connects the three-phase inverter wiring drawn from the power conversion circuit 3 to either the three-phase motor wiring drawn from the motor 1 or the midpoint of the motor 1. The neutral point of the motor 1 and the switching unit 8 are also connected via a neutral point connecting unit 9.

[0018] The switching unit 8 is composed of three three-point relay circuits. The neutral point connection unit 9 is composed of one two-point relay circuit. The relay circuits of the switching unit 8 and the neutral point connection unit 9 are controlled by the relay circuit control unit 6 included in the control unit 10 described above. The relay circuit control unit 6 can be realized as one function of a microcomputer.

[0019] A control unit 10 that controls the power conversion circuit 3 and the switching unit 8 controls the switching unit 8 so that, when one phase of the motor 1 fails, the inverter wiring corresponding to the failed phase is disconnected from the motor wiring of the same phase, and the inverter wiring is switched to a connection with the neutral point of the three-phase motor 1.

[0020] (Figure 3) The effect of the configuration of the present invention illustrated in FIG. 2 will be explained using FIG. 3(a), which shows the flow of three-phase AC current when an open-circuit fault occurs in a three-phase motor using the conventional technology, and FIG. 3(b), which shows the flow of three-phase AC current when an open-circuit fault occurs in a three-phase motor using the present invention. When an open-circuit fault occurs in one of the three phases of motor 1, the fault detection unit illustrated in FIG. 1 compares the three-phase AC current values ​​acquired from sensor 12 with the operation of the driver circuit to detect the fault in motor 1 and the faulty phase. In the conventional motor 1 illustrated in FIG. 3(a), when an open-circuit fault occurs in one of the three phases, the remaining two phases form current path 11a only at a 180° phase in the AC return path (the same applies to flow in the opposite direction). This causes fluctuations in the magnitude of the torque output. If the vehicle stops at the electrical angle where the minimum torque is achieved, it may not be possible to obtain sufficient torque to move the vehicle again.

[0021] Therefore, in the present invention, as shown in Fig. 3(b), a switching unit 8 of a three-point relay circuit is provided between the motor 1 and each of the power semiconductors of the U-phase, V-phase, and W-phase of the power conversion circuit 3. In addition, a neutral point connection unit 9 of a two-point relay circuit is provided between the switching unit 8 and the neutral point of the motor 1. The relay circuit of the switching unit 8 switches the circuit in response to a command from the relay circuit control unit 6 (Fig. 1) so as to connect either between the power semiconductor and the motor 1 or between the neutral point connection unit 9 and the motor 1.

[0022] The two-point relay circuit of the neutral point connection unit 9 is installed between one of the three-point relay circuits of the switching unit 8 and the neutral point of the motor 1. Like the relay circuit of the switching unit 8, the neutral point connection unit 9 performs an on / off switching operation in response to a command from the relay circuit control unit 6. As a result, the induced voltage on the motor 1 side is completely cut off from the power conversion circuit 3.

[0023] In the present invention, when an open-circuit fault occurs in one of the three phases, the switching unit 8 switches the three-way relay circuit to connect the relay circuit corresponding to the failed phase to the neutral point of the motor 1. At this time, the neutral point connection unit 9 also switches the relay circuit of the switching unit 8 corresponding to the failed phase to the neutral point of the motor 1, thereby connecting the leg of the power conversion circuit 3 corresponding to the open-circuit faulted phase of the motor 1 to the neutral point of the motor 1. This disconnects the failed phase of the motor 1 with the power conversion circuit 3, creating a state similar to an open phase, and controls the driver circuits of the remaining two phases so that the current phase difference between the remaining two phases is 60 degrees. This ensures a current return path 11b for two-phase control from the neutral point of the motor 1 to the inverter, enabling torque control with reduced torque ripple. In other words, stable torque can be output in a vehicle even when a winding fault occurs in the motor 1.

[0024] (Figure 4) This shows an embodiment in which switching of the relay circuit of the present invention is configured using FETs (Field Effect Transistors). Three pairs of two FETs are connected back-to-back to form a switch circuit between each leg of the power conversion circuit 3 and the input to each phase of the motor 1. In addition, three pairs of two FETs are connected back-to-back to form a switch circuit between each leg of the power conversion circuit 3 and the neutral point of the motor 1. In this way, the switching unit 8 and the neutral point connecting unit 9 are each configured with an electronic switch 7, which is a semiconductor switching circuit. The on / off of these FETs is controlled by signals from the relay circuit control unit 6 included in the control unit 10.

[0025] In this configuration, during normal operation, the FETs between all phases and the motor 1 are ON, and all FETs between the motor 1 and the neutral point are OFF. Furthermore, in the event of an open-circuit fault in one of the motor 1 phases, the circuit between the leg of one of the phases and the motor 1 winding is turned OFF, electrically disconnecting the faulted winding from the power conversion circuit 3, while the FET connecting the leg of one of the phases corresponding to the fault and the neutral point of the motor 1 is turned ON. This allows for a connection of the motor 1 windings that enables two-phase control, even when the electronic switch 7 is configured using a relay circuit. Therefore, it can be realized with six semiconductor switches. Furthermore, by using the semiconductor switch 7 to implement the switching unit 8 and the neutral point connection unit 9 in this way, the system can be made smaller and lighter, and the response speed to commands from the relay circuit control unit 6 can be increased.

[0026] (Figure 5) The control flowchart of the control unit 10 will be described. In step S1, the HVAC current and IGBT operation are compared to detect an open circuit fault in the motor 1. In step S1, for example, the upper and lower arms are checked to see if no current flows even though the IGBT is turned on. If an open circuit fault in the motor 1 cannot be detected in step S1, the flow ends. In step S2, after detecting a fault in the motor 1, all IGBTs are turned off to enter a zero-torque state in order to transition to a safe state. In step S3, the three-point relay circuit connected to one of the phases of the motor 1 for which a fault has been identified is switched to a connection between each leg of the power conversion circuit 3 and a two-point relay circuit. Note that the three-point relay circuit connected to the normal phase in step S3 maintains the same connection as in normal operation. In step S4, the two-point relay circuit connecting the three-point relay circuit and the neutral point of the three-phase motor 1 is turned on. In step S5, the operation of the remaining two phases, which are operating normally, is confirmed. In step S5, for example, if the motor 1 is rotating due to inertia, and the current due to the generated induced voltage is detected by the current sensors 12 for the remaining two phases, it can be determined that the two phases of the motor 1 are valid. If it is determined in step S5 that the remaining two phases are normal, the power conversion circuit 3 is switched to two-phase control in step S6, and the flow ends. If it is not determined in step S5 that the remaining two phases are normal, the process returns to step S1, and a fault diagnosis of the motor 1 is performed.

[0027] (Figure 6) The power conversion circuit 3 provided in the inverter is configured by bundling together structures called power cards or power modules, which are single modules that combine the IGBTs for the upper and lower arms of one phase, their peripheral circuits, and a heat dissipation mechanism, for the U, V, and W phases. Therefore, relay circuits for the switching unit 8 and neutral point connection unit 9, configured as semiconductor switches 7, are incorporated into this power conversion circuit 3. With this configuration, the cooling of the semiconductors that correspond to the heat generated by the relay circuits can be shared with power semiconductors such as IGBTs, simplifying the heat dissipation structure and minimizing changes to the layout of the cooling structure.

[0028] (Figure 7) (First modified example, second modified example) As shown in a first modified example in Fig. 7(a), the inverter 3a may be configured to include a switching unit 8 and a neutral point connection unit 9 in addition to the power conversion circuit 3. This allows the faulty phase of the motor 1 to be separated from the inverter 3a, and a return path for current for two-phase control to be secured from the neutral point to the inverter 3a. Similar effects can also be achieved with a configuration having multiple three-phase inverter circuits 3.

[0029] Alternatively, as shown in a second modified example in FIG. 7(b), the switching unit 8 and neutral point connection unit 9 may be provided on the motor housing 1a side. By arranging the switching unit 8 and neutral point connection unit 9 inside the housing of the motor 1a, the switching unit 8 can be switched to the neutral point connection unit 9 side for all three phases while simultaneously turning off the neutral point connection unit 9. This allows the motor 1 and the faulty phase to be electrically isolated from the inverter 3a in preparation for the possibility of a high-voltage cable break in the event of significant damage to the vehicle, such as in a collision accident. This also ensures a current return path for two-phase control from the neutral point to the inverter 3a. Furthermore, by turning off the relay inside the motor housing 1a, electric shock due to induced voltage caused by a cable break is prevented, stable operation is achieved even in the event of an open circuit fault in the motor winding, and safety against high-voltage electric shock is improved.

[0030] (Figure 8) (Third Modification) The inverter 3a and the motor 1a may be connected by four cables. Of the four cables connecting the power conversion circuit 3 provided in the inverter 3a and the motor 1 (motor housing 1a), three cables connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining cable connects the switching unit 8 and the neutral point of the motor 1. This improves the flexibility of mounting the inverter 3a and the motor housing 1a in the vehicle.

[0031] (Figure 9) (Fourth Modification) The present invention may be an integrated configuration in which the power conversion circuit 3 included in the inverter 3a and the motor 1 are directly connected by four bus bars 14. In this case, three of the four bus bars connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining bus bar connects the switching unit 8 and the neutral point of the motor 1. With this configuration, the effects of cost and weight can be minimized compared to a configuration in which the inverter 3a and the motor 1a are separated, which requires the connection of a high-voltage cable.

[0032] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0033] (1) The power conversion device includes a three-phase inverter circuit 3 that outputs AC power converted from DC power to drive a three-phase motor 1, a switching unit 8 that connects three-phase inverter wirings drawn from the three-phase inverter circuit 3 to either three-phase motor wirings drawn from the three-phase motor 1 or the neutral point of the three-phase motor 1, and a control unit 10 that controls the three-phase inverter circuit 3 and the switching unit 8. When one phase of the three-phase motor 1 fails, the control unit 10 controls the switching unit 8 to cut off the inverter wiring corresponding to the failed phase and the motor wiring of the same phase, and to switch the connection between the inverter wiring and the neutral point of the three-phase motor 1. In this way, a power conversion device can be provided that can transition to two-phase control that outputs stable torque when one phase of the three-phase motor 1 experiences an open-circuit fault.

[0034] (2) The neutral point of the three-phase motor 1 and the switching unit 8 are connected via the neutral point connection unit 9. This allows the faulty phase of the motor 1 to be separated from the power conversion circuit 3, and a return path for the current for two-phase control can be secured from the neutral point to the power conversion circuit 3.

[0035] (3) The switching unit 8 and the neutral point connection unit 9 are each configured with an electronic switch 7. This configuration allows for a smaller and lighter unit, and also allows for a faster response to commands from the relay circuit control unit 6.

[0036] (4) The electronic switch 7 is provided inside the three-phase inverter circuit 3. This simplifies the heat dissipation structure and minimizes changes to the layout.

[0037] (5) The three-phase inverter circuit 3 and the three-phase motor 1 are connected by four cables 13, three of which connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining cable connects the switching unit 8 and the neutral point of the three-phase motor 1. This increases the flexibility of mounting the inverter 3a and the motor 1a in the vehicle.

[0038] (6) The three-phase inverter circuit 3 and the three-phase motor 1 are connected by four bus bars 14, three of which connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining bus bar connects the switching unit 8 and the neutral point of the three-phase motor 1. This arrangement minimizes the impact of cost and weight.

[0039] (7) The three-phase motor has a plurality of three-phase inverter circuits 3. This allows the motor to switch to two-phase control, which can output stable torque, even if the output is increased, when one phase of the three-phase motor 1 experiences an open circuit failure.

[0040] (8) The switching unit 8 and neutral point connection unit 9 are located inside the three-phase motor housing 1a. This prevents electric shock due to induced voltage caused by a cable break, ensures stable operation even in the event of an open circuit fault in the motor winding, and improves safety against high-voltage electric shock.

[0041] The present invention is not limited to the above-described embodiments, and various modifications and combinations of other configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to those having all of the configurations described in the above-described embodiments, and includes those in which some of the configurations are omitted. [Explanation of symbols]

[0042] 1 Three-phase motor 1a Motor housing 2 Relay Circuit 3 Power Conversion Circuit 3a Power conversion device (inverter) 4 smoothing capacitors 5 DC power supply 6 Relay circuit control section 7. Solid-state switches 8 Switching unit (3-point relay circuit) 9 Neutral point connection (two-point relay circuit) 10 Control Unit 11 Current Flow 11a Current path during conventional one-phase fault 11b Current path when one phase of the present invention is faulty 12 Current Sensor 13 4 cables 14 4-bar

Claims

1. a three-phase inverter circuit that converts DC power into AC power and outputs the AC power to drive a three-phase motor; a switching unit that connects three-phase inverter wirings respectively drawn from the three-phase inverter circuit to either three-phase motor wirings respectively drawn from the three-phase motor or a neutral point of the three-phase motor; a control unit that controls the three-phase inverter circuit and the switching unit, When one phase of the three-phase motor fails, the control unit controls the switching unit to cut off the inverter wiring corresponding to the failed phase and the motor wiring of the same phase, and to switch the connection between the inverter wiring and a neutral point of the motor, and also controls the three-phase inverter circuit connected to the remaining two unfailed phases of the three-phase motor so that a current phase difference between the two phases in the AC power is 60 degrees. Power conversion device.

2. The power conversion device according to claim 1, The neutral point of the three-phase motor and the switching unit are connected via a neutral point connection unit. Power conversion device.

3. The power conversion device according to claim 2, The switching unit and the neutral point connection unit are each composed of an electronic switch. Power conversion device.

4. The power conversion device according to claim 3, The electronic switch is provided in the three-phase inverter circuit. Power conversion device.

5. The power conversion device according to claim 1, the three-phase inverter circuit and the three-phase motor are connected by four cables; Of the four cables, three cables connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining cable connects the switching unit and the neutral point of the three-phase motor. Power conversion device.

6. The power conversion device according to claim 1, The three-phase inverter circuit and the three-phase motor are connected by four bus bars, Of the four bus bars, three bus bars connect the three-phase inverter wiring and the three-phase motor wiring, and the remaining bus bar connects the switching unit and the neutral point of the three-phase motor. Power conversion device.

7. The power conversion device according to claim 1, The three-phase inverter circuit includes a plurality of the three-phase inverter circuits. Power conversion device.

8. The power conversion device according to claim 2, The switching unit and the neutral point connection unit are disposed within the housing of the three-phase motor. Power conversion device.

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