Three-phase inverter device and current detection method

Abstract

To provide a three-phase inverter device which can be incorporated into a space with strict layout restrictions, such as a motor housing.SOLUTION: The present invention provides a three-phase inverter device for motor driving, in which an upper arm U1UP and a lower arm U1LW of each phase are configured on separate substrates 10 and 20. Switching elements 11 and 21, diodes 12 and 22, and shunt resistors 13 and 23 are mounted on the substrates 10 and 20. Output wires 6 for each phase are connected to connection points 7 between the upper arms U1UP, V1UP, W1UP and the lower arms U1LW, V1LW, W1LW. Each phase includes a current detection circuit 2 that detects a composite current formed from the output currents of the upper arms V1UP and W1UP and the lower arms V1LW and W1LW.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a three-phase inverter device for driving a motor and a current detection method for detecting phase output currents of the device. [Background technology]

[0002] Patent Document 1 discloses a configuration for miniaturizing a device for monitoring the output current of an inverter device, reducing the space required for wiring, and saving space in a device that the inverter device is built into. Specifically, in a semiconductor device in which a power semiconductor, a drive circuit, and a protection circuit are built into the same package, a shunt resistor is installed on an insulating substrate on which the power semiconductor is mounted so as to be in series with the output line of the power semiconductor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3548024 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the semiconductor device in the above document has a configuration in which, in addition to the power semiconductor, the drive circuit, and the protection circuit, a shunt resistor is also incorporated into the same package, which makes the semiconductor device large and makes it difficult to incorporate it into a space with strict layout constraints.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide an inverter device that can be installed in a space with strict layout constraints. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a three-phase inverter device for driving a motor, in which an upper arm and a lower arm of each phase are formed on a separate board, switching elements, diodes, and shunt resistors are mounted on the board, an output line of each phase is connected to a connection point between the upper arm and the lower arm of each phase, and each phase is provided with a current detection circuit that detects a combined current of an output current of the upper arm and an output current of the lower arm. Effect of the Invention

[0007] According to the above aspect, an inverter device is provided that can be installed in a space with strict layout constraints. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic configuration diagram of a three-phase inverter device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of an example of a motor unit using a three-phase inverter device, where (A) is a cross-sectional view showing a cross section perpendicular to the rotor shaft, and (B) is a side view of the motor unit. [Diagram 3] FIG. 3 is a diagram illustrating the definition of the currents flowing through the upper arm and the lower arm, and the directions of the phase currents. [Figure 4] FIG. 4 is a table showing combination patterns of arm commands and resistance potential directions. [Diagram 5] FIG. 5 is a diagram showing a command pre-arm state and a command post-arm state of the first pattern. [Figure 6] FIG. 6 is a diagram showing a command pre-arm state and a command post-arm state of the second pattern. [Figure 7] FIG. 7 is a diagram showing a command pre-arm state and a command post-arm state of the third pattern. [Figure 8] FIG. 8 is a diagram showing a command pre-arm state and a command post-arm state of the fourth pattern. [Figure 9] FIG. 9 is a diagram showing a command pre-arm state and a command post-arm state of the fifth pattern. [Figure 10]FIG. 10 is a diagram showing a command pre-arm state and a command post-arm state of the sixth pattern. [Figure 11] FIG. 11 is a diagram of an H-bridge circuit including upper and lower arms according to the first embodiment. [Figure 12] FIG. 12 is a time chart when a switching operation is performed in the circuit of FIG. [Figure 13] FIG. 13 is a schematic configuration diagram of a three-phase inverter device according to the second embodiment. [Figure 14] FIG. 14 is a table summarizing the relationship between the directions of the arm currents and phase currents, the potential difference between the upper and lower shunt resistors, and the phase current output. [Figure 15] FIG. 15 is a circuit diagram of an H-bridge including upper and lower arms according to the second embodiment. [Figure 16] FIG. 16 is a time chart when a switching operation is performed in the circuit of FIG. [Figure 17] FIG. 17 is a time chart showing a transition of the arm current after an OFF command is issued. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [First embodiment] 1 is a configuration diagram of a U-phase arm U1 and a current detection circuit 2 of a three-phase inverter device according to this embodiment. Here, the U-phase arm U1 will be described, but the other V-phase arm V1 and W-phase arm W1 have the same configuration. The three-phase inverter device according to this embodiment is used to drive an electric motor used in, for example, an electric vehicle.

[0011] [Arm configuration] The arm U1 is composed of an upper arm U1UP and a lower arm U1LW. The upper arm U1UP and the lower arm U1LW are independent of each other, with the upper arm U1UP having an upper insulating substrate 10 and the lower arm U1LW having a lower insulating substrate 20. The output terminal of the upper arm U1UP and the output terminal of the lower arm U1LW are connected at a connection point 7, and a phase output line 6 is connected to the connection point 7.

[0012] The upper arm U1UP has a configuration in which an upper switching element 11, an upper diode 12, and an upper shunt resistor 13 are mounted on an upper insulating substrate 10. The upper switching element 11 and a lower switching element 21, which will be described later, are so-called power semiconductors, and in this embodiment, an IGBT is used, but the present invention is not limited to this and may be, for example, a MOSFET.

[0013] The upper switching element 11 and the upper diode 12 are connected in parallel, and the cathode of the upper diode 12 faces the power supply side. The upper shunt resistor 13 is disposed between the anode of the upper diode 12 and the connection point 7.

[0014] Similarly, the lower arm U1LW has a configuration in which a lower switching element 21, a lower diode 12, and a lower shunt resistor 23 are mounted on a lower insulating substrate 20.

[0015] The lower switching element 21 and the lower diode 22 are connected in parallel, and the anode of the lower diode 22 faces the GND side. The lower shunt resistor 23 is disposed between the cathode of the lower diode 12 and the connection point 7.

[0016] The current detection circuit 2 detects a phase current based on a potential difference between the power supply side of the upper shunt resistor 13 and the GND side of the lower shunt resistor 23, and includes an operational amplifier (hereinafter also referred to as an op-amp) 3 that detects the potential difference, amplifies it, and outputs it, and a detector 4 that calculates a current value based on the output. The current value calculated by the detector 4 is read into a controller 5. With this configuration, it becomes possible to detect a composite current of a current flowing through the upper arm U1UP and a current flowing through the lower arm U1LW as a phase current. The controller 5 also reads current values ​​of the V phase and W phase (not shown).

[0017] The controller 5 not only reads the current value but also switches the upper switching element 11 and the lower switching element 21 ON and OFF. The controller 5 is composed of a microcomputer equipped with a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM) and an input / output interface (I / O interface). The controller 5 can also be composed of multiple microcomputers.

[0018] As described above, the upper shunt resistor 13 is disposed between the anode of the upper diode 12 and the output terminal (i.e., the connection point 7), and the lower shunt resistor 23 is disposed between the cathode of the lower diode 22 and the connection point 7, which are positions with the lowest impedance in the arm circuits. Therefore, it is possible to detect the phase current, which is the combined output current from the upper and lower arms U1UP and U1LW, without adding any configuration for ensuring insulation.

[0019] 2 is a schematic diagram of an example of a motor unit 30 using the three-phase inverter device configured as above, where (A) is a cross-sectional view showing a cross section perpendicular to the rotor shaft 31, and (B) is a side view of the motor unit. Note that in Fig. 2, the diodes 13 and 23 of each arm, the output line 6, and the current detection circuit 2 are omitted.

[0020] The motor unit 30 is housed in a hollow hexagonal prism motor housing 34, which includes a motor section 32 that houses an electric motor, and an inverter section 33 that houses a three-phase inverter device. Note that in this embodiment, the motor section 32 and the inverter section 33 are provided inside the motor housing 34, but this is not limited to this, and for example, a housing including the inverter section 33 may be connected to the axial end of the motor housing 34.

[0021] In the inverter section 33, when viewed in the axial direction about the rotation axis of the rotor shaft 31, the U-phase, V-phase, and W-phase arms are arranged in an annular shape on the inner wall of the motor housing 34. The U-phase upper arm U1UP and lower arm U1LW have their surfaces opposite to the surfaces on which the switching elements 11, 21, etc. of each of the insulating substrates 10, 20 are mounted fixed to the inner wall of the motor housing 34, while maintaining the positional relationship in which the upper shunt resistor 13 and the lower shunt resistor 23 are adjacent to each other as shown in Fig. 1. The same is true for the V-phase and W-phase arms.

[0022] By arranging as described above, the shunt resistor of the upper arm and the shunt resistor of the lower arm, which are in phase, are arranged close to each other, and the impedance of the connection point 7 can be made low.

[0023] The shape of the inner diameter side of the motor housing 34 is not limited to a hexagon. As long as the upper and lower arms of each phase can be arranged as described above, it may be another polygon or a circle.

[0024] [Phase current detection] Incidentally, in the above circuit configuration, the magnitude of the phase current can be detected, but the direction in which it flows (hereinafter also referred to as the phase current direction) cannot be identified. For example, when a current flows from the upper arm U1UP to the output line 6, the shunt resistor has a positive potential, and when a current flows from the lower arm U1LW to the output line 6, the shunt resistor has a negative potential. However, the phase current direction is the same in either case. In other words, even if the phase current direction is the same, the potential of the shunt resistor can be in two states, positive and negative, depending on the state of the upper and lower arms. Therefore, the current detection circuit 2, which detects the current value based on the potential difference of the shunt resistor, cannot identify the phase current direction.

[0025] Therefore, in this embodiment, the phase current direction is identified by the method described below.

[0026] 3 is a diagram showing the definitions of the currents flowing through the upper arm U1UP and the lower arm U1LW, and the phase current directions. An arrow IU indicates the direction of the current IU flowing through the upper arm U1UP, and the direction of the arrow, i.e., the direction from the power supply through the upper shunt resistor 13, is considered positive. An arrow IL indicates the direction of the current IL flowing through the lower arm U1LW, and the direction of the arrow, i.e., the direction flowing from the lower shunt resistor 23 to GND, is considered positive. An arrow IP indicates the phase current direction, and the direction of the arrow, i.e., the direction flowing from the connection point 7 to a load (not shown) is considered positive.

[0027] Furthermore, the resistance value of the upper shunt resistor 13 is RU, the resistance value of the lower shunt resistor 23 is RL, the voltage on the power supply side is HV+, and the voltage on the GND side is HV-.

[0028] The ON / OFF of the upper switching element 11 and the lower switching element 21 is controlled by a command (hereinafter also referred to as an arm command) from the controller 5. Therefore, the controller 5 can obtain the direction of current flow in the upper arm U1UP and the lower arm U1LW based on the states of the upper switching element 11 and the lower switching element 21. The controller 5 can also obtain the potential difference between both ends of the upper shunt resistor 13 and the lower shunt resistor 23, in other words, the potential difference between the anode of the upper diode 12 and the anode of the lower diode 22, from the current detection circuit 2. Hereinafter, regarding this potential difference, when the upper arm U1UP side is at a high potential, the resistance potential direction is defined as positive, and when the lower arm U1LW side is at a high potential, the resistance potential direction is defined as negative.

[0029] The controller 5 determines the phase current direction based on the arm command and the resistance potential direction as described below.

[0030] FIG. 4 is a table showing combination patterns of arm commands and resistance potential directions. In the table, "upper" of the arm commands refers to the upper switching element 11, and "lower" refers to the lower switching element 21. "Pre-command arm state" refers to the conduction state of the upper and lower arms before switching operation is performed according to the arm command. "Post-command arm state" refers to the conduction state of the upper and lower arms after switching operation is performed according to the arm command. "Phase current output" is the detection value by detector 4. "Inversion" means a reversal of the phase current direction, and the circles in the table indicate that the phase current direction in the post-command arm state is reversed relative to the phase current direction in the pre-command arm state.

[0031] Lower arm Di return is a state in which a current flows through the lower diode 22. Upper arm DI return is a state in which a current flows through the upper diode 12. Lower arm IGBT conduction is a state in which a current flows through the lower switching element 21. Upper arm IGBT conduction is a state in which a current flows through the upper switching element 11.

[0032] As mentioned above, the phase current direction cannot be specified by the resistance potential direction alone. However, as shown in the table of Fig. 4, the phase current direction can be specified by combining it with an arm command. Below, each pattern in the table of Fig. 4 will be explained with reference to Figs. 5 to 10. In Figs. 5 to 10, the left diagram shows the arm state before the command, the right diagram shows the arm state after the command, and the thick arrows show the current flow.

[0033] FIG. 5 shows the pre-command arm state and post-command arm state of the first pattern. In the first pattern, the arm command is up ON, down OFF, and the resistor potential direction is positive. In this case, it is considered that the upper arm IGBT conduction state is entered when the upper switching element 11 is turned ON from the lower arm Di freewheel state. That is, in the post-command arm state, the current IU is positive, and the cathode voltage of the lower diode 22 is almost HV+, so that the current IL is zero, and it can be determined that IP is in the positive direction. Therefore, the phase current direction is the same as in the pre-command arm state, and the phase current output is +IP×RU. Note that the pre-command arm state when the arm command is up ON, down OFF, and the resistor potential direction is positive may be 0 [A] as in the seventh pattern, but even in this case, the post-command arm state is the same as the first pattern, so the calculation of the phase current output is also the same as the first pattern.

[0034] FIG. 6 shows the pre-command arm state and post-command arm state of the second pattern. In the second pattern, the arm command is up ON, down OFF, and the resistor potential direction is negative. In this case, the upper switching element 11 turns ON from the upper arm Di return state, and it is considered that the upper arm Di return state continues. That is, in the post-command arm state, the current IU is negative and the current IL is zero, so it can be determined that IP is negative. Therefore, the phase current direction is the same as in the pre-command arm state, and the phase current output is -IP×RU. Note that the pre-command arm state when the arm command is up ON, down OFF, and the resistor potential direction is negative may be 0 [A] as in the eighth pattern, but even in this case, the post-command arm state is the same as in the second pattern, so the calculation of the phase current output is also the same as in the second pattern.

[0035] FIG. 7 shows the pre-command arm state and post-command arm state of the third pattern. In the third pattern, the arm command value is upper OFF, lower ON, and the resistive battery direction is positive. In this case, it is considered that the upper arm Di reflux state is changed to the lower arm IGBT conduction state by the lower switching element 21 being turned ON. That is, in the post-command arm state, the anode voltage of the upper diode 12 is almost HV-, so that the current IU is zero and the current IL is positive, and therefore it can be determined that IP is negative. Therefore, the phase current direction is reversed from the pre-command arm state, and the phase current output is -IP×RU.

[0036] FIG. 8 shows the pre-command arm state and post-command arm state of the fourth pattern. In the fourth pattern, the arm command value is up OFF, down ON, and the resistive battery direction is negative. In this case, it is considered that the lower arm Di return state continues as the lower switching element 21 turns ON from the lower arm Di return state. That is, in the post-command arm state, it can be determined that the current IU is zero and the current IL is negative, so that IP is positive. Therefore, the phase current direction is reversed from the pre-command arm state, and the phase current output becomes +IP×RU.

[0037] FIG. 9 shows the pre-command arm state and post-command arm state of the fifth pattern. In the fifth pattern, the arm command value is up OFF, down OFF, and the resistive battery direction is negative. In this case, if the pre-command arm state is the lower arm IGBT conductive state, it is considered that the upper arm Di reflux state is entered by the upper switching element 11 and the lower switching element 21 being turned off. That is, in the post-command arm state, it can be determined that the current IU is negative and the current IL is zero, so that IP is negative. Therefore, the phase current direction is the same as in the pre-command arm state, and the phase current output is -IP×RU.

[0038] FIG. 10 shows the pre-command arm state and post-command arm state of the sixth pattern. In the sixth pattern, the arm command value is up OFF, down OFF, and the resistive battery direction is positive. In this case, if the pre-command arm state is the upper arm IGBT conductive state, it is considered that the upper switching element 11 and the lower switching element 21 are turned off, resulting in the lower arm Di freewheel state. That is, in the post-command arm state, the current IU is zero and the current IL is negative, so it can be determined that IP is positive. Therefore, the phase current direction is reversed from the pre-command arm state, and the phase current output is +IP×RU.

[0039] As described above, when the arm command to the lower arm U1LW is ON (third, fourth, eighth patterns), or when the arm command is upper OFF or lower OFF (sixth pattern), the phase current direction is reversed.

[0040] Next, as an application example of the above-mentioned phase current detection method, a case where a switching operation is performed in an H-bridge circuit including the above-mentioned arm U1 will be described with reference to FIGS.

[0041] Fig. 11 shows an H-bridge circuit, and Fig. 12 shows a time chart when switching is performed in the same circuit. The solid line in Fig. 12 shows the gate voltage of the lower switching element 21, and the dashed line shows the gate voltage of the upper switching element 11. Also, Vshunt is the potential difference between the cathode of the upper shunt resistor 13 and the anode of the lower shunt resistor 23, as shown in Fig. 11.

[0042] In the time chart of FIG. 12, the arm command value changes from upper OFF, lower ON to upper ON, lower OFF to upper OFF, lower ON to upper ON, lower OFF. Since a dead time is provided when switching in response to the arm command, the arm state changes from lower IGBT conduction state to upper Di reflux state to upper IGBT conduction state to lower Di reflux state to lower IGBT conduction state to upper Di reflux state to upper IGBT conduction state. At this time, the phase current direction cannot be specified by the detection signal from the current detection circuit 2 alone, but in this embodiment, as described above, the phase current direction is reversed when the arm command to the lower arm U1LW becomes ON. This makes it possible to grasp the current phase current direction. In addition, if the absolute value of the sum of the current IU and the current IL is greater than the absolute value of the current value assumed during normal control, it can be determined that a short circuit has occurred.

[0043] As described above, in this embodiment, a three-phase inverter device for driving a motor is provided. In this device, the upper arm U1UP and the lower arm U1LW of each phase are formed on separate substrates 10 and 20, and switching elements 11 and 21, diodes 12 and 22, and shunt resistors 13 and 23 are mounted on the substrates 10 and 20. An output line 6 is connected to a connection point 7 between the upper arm U1UP and the lower arm U1LW of each phase, and a current detection circuit 2 is provided for detecting a composite current of the output current of the upper arm U1UP and the output current of the lower arm U1LW of each phase. By making the substrates of the upper and lower arms different members in this way, it is possible to incorporate the device in a space with strict layout constraints. In addition, it is possible to measure the output current of each bridge. In addition, by dividing the shunt resistors 13 and 23, the loss is also divided, so that a shunt resistor that has a smaller allowable loss and is smaller and less expensive than a case in which one shunt resistor is disposed for the upper and lower arms can be used. Furthermore, while a magnetic field detection type current sensor is generally used to detect the current in an inverter device for a drive motor, the use of a shunt resistor makes mounting easier and also contributes to miniaturization.

[0044] In this embodiment, the shunt resistors 13, 23 are provided in the upper arm U1UP between the anode of the upper diode 12 and the phase output terminal, and in the lower arm U1LW between the cathode of the lower diode 22 and the phase output terminal. That is, the shunt resistors 13, 23 are arranged at positions where the impedance is low, so that the phase current, which is the combined output current of the upper and lower arms U1UP, U1LW, can be detected without adding any new insulation function. That is, the noise resistance performance can also be improved.

[0045] In this embodiment, three-phase arms are arranged in a ring shape with the upper shunt resistor 13 and the lower shunt resistor 23 of the same phase adjacent to each other, and the substrates 10, 20 of each arm are fixed to the inner wall of the motor housing 34 or the inverter housing connected to the axial end of the motor housing 34. This results in the upper shunt resistor 13 and the lower shunt resistor 23 of the same phase being arranged adjacent to each other, thereby maintaining the effect of arranging them at a position that provides low impedance as described above. Furthermore, by arranging the inverter device inside the motor housing 34, etc., the unit consisting of the drive motor and the inverter device can be made smaller.

[0046] In this embodiment, the controller 5 acquires the states of the upper switching element 11 and the lower switching element 21, and identifies the direction of the phase current flow based on the states and the direction of the voltage acquired from the current detection circuit 2. This makes it possible to identify the direction of the phase current flow without adding an ammeter. It is also possible to detect whether or not a short circuit has occurred in the upper and lower arms U1UP and U1LW.

[0047] [Second embodiment] 13 is a configuration diagram of a U-phase arm U1 and a current detection circuit 2 of a three-phase inverter device according to a second embodiment of the present invention. The difference from the first embodiment is that while the first embodiment has one operational amplifier 3, this embodiment has three operational amplifiers. The following description will focus on this difference.

[0048] As shown in Figure 13, the current detection circuit 2 includes a first operational amplifier 31 that detects and amplifies the potential difference across the upper shunt resistor 13, a second operational amplifier 32 that detects and amplifies the potential difference across the lower shunt resistor 23, and a third operational amplifier 33 that amplifies the input signals from the first operational amplifier 31 and the second operational amplifier 32.

[0049] As in the first embodiment, the current detection circuit 2 can detect the phase current but cannot specify the phase current direction. In this embodiment, the phase current output and the phase current direction are specified using the potential difference between both ends of the upper shunt resistor 13 and the potential difference between both ends of the lower shunt resistor 23, and the phase current output is calculated.

[0050] FIG. 14 is a table summarizing the relationship between the directions of the current IU flowing through the upper arm U1UP, the current IL flowing through the lower arm U1LW, and the current (phase current) IP flowing through the output line 6, the potential difference between the upper shunt resistor 13 and the lower shunt resistor 23, and the phase current output. The positive and negative signs of the currents IU, IL, and IP are the same as in FIG. 3. The shunt resistor potential difference VRU is the potential difference across the upper shunt resistor 13, and VRL is the potential difference across the lower shunt resistor 23. When control is performed correctly (hereinafter also referred to as normal control), either the current IU or the current IL becomes zero. In other words, when neither the current IU nor the current IL is zero, a short circuit has occurred in the upper or lower arms.

[0051] Pattern 1 is the case where the potential difference VRU is zero and the potential difference VRL is positive. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is negative. Also, since no current flows in the upper arm U1UP and a current flows in the positive direction in the lower arm U1LW, the phase current direction is negative. In other words, the current IU is zero, the current IL is positive, and the phase current IP is negative. The phase current output is then -IL×RL.

[0052] Pattern 2 is when the potential difference VRU is zero and the potential difference VRL is negative. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is positive. Also, since no current flows in the upper arm U1UP and a current flows in the negative direction in the lower arm U1LW, the phase current direction is positive. In other words, the current IU is zero, the current IL is negative, and the phase current IP is positive. The phase current output is then +IL×RL.

[0053] Pattern 3 is the case where the potential difference VRU is positive and the potential difference VRL is zero. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is positive. Also, since a current flows in the positive direction in the upper arm U1UP and no current flows in the lower arm U1LW, the phase current direction is positive. In other words, the current IU is positive, the current IL is zero, and the phase current IP is positive. The phase current output is then +IU x RU.

[0054] Pattern 4 is the case where the potential difference VRU is negative and the potential difference VRL is zero. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is negative. Also, current flows in the negative direction in the upper arm U1UP and no current flows in the lower arm U1LW, so the phase current direction is negative. In other words, the current IU is negative, the current IL is zero, and the phase current IP is negative. The phase current output is then -IU x RU.

[0055] Pattern 5 is a case where both the potential difference VRU and the potential difference VRL are positive. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is zero. In addition, a current flows in the positive direction in both the upper arm U1UP and the lower arm U1LW. In other words, a short circuit occurs, and the phase current IP is zero, so the phase current output is also zero.

[0056] Pattern 6 is a case where both the potential difference VRU and the potential difference VRL are negative. In this case, the value obtained by subtracting the potential difference VRL from the potential difference VRU is zero. Also, current flows in the negative direction in both the upper arm U1UP and the lower arm U1LW. In other words, a short circuit occurs, and the phase current IP is zero, so the phase current output is also zero.

[0057] As described above, if the value obtained by subtracting the potential difference VRL from the potential difference VRU is positive, the phase current direction is also positive, if the subtracted value is negative, the phase current direction is also negative, and if the subtracted value is zero, it can be determined that no phase current is flowing. In other words, detecting the potential difference VRU across the upper shunt resistor 13 and the potential difference VRL across the lower shunt resistor 23 individually is equivalent to detecting the currents in the upper and lower arms individually. Therefore, the phase current direction can be identified without using the states of the upper and lower switching elements 11, 21.

[0058] In this embodiment, the phase current direction is determined using the value obtained by subtracting the potential difference VRL from the potential difference VRU, but the method of determination using the potential difference VRU and the potential difference VRL is not limited to this. For example, the determination can also be made using the result of adding the potential difference VRU and the potential difference VRL. If the addition result is positive, the phase current direction is negative if the potential difference VRU is zero, and the phase current direction is positive if the potential difference VRL is zero. If the addition result is negative, the phase current direction is positive if the potential difference VRU is zero, and the phase current direction is negative if the potential difference VRL is zero. In addition, if the absolute value of the potential difference VRU or the potential difference VRL is greater than the value assumed during normal control, it is determined that a short circuit has occurred.

[0059] Next, as an application example of the above-mentioned phase current detection method, a case where a switching operation is performed in an H-bridge circuit will be described with reference to FIGS.

[0060] Fig. 15 shows an H-bridge circuit, and Fig. 16 shows a time chart when switching is performed in the same circuit. The solid line in Fig. 15 shows the gate voltage and potential difference (Vlw) of the lower switching element 21, and the dashed line shows the gate voltage and potential difference (Vup) of the upper switching element 11. Furthermore, Vup is the potential difference across the upper shunt resistor 13 as shown in Fig. 15, and Vlw is the potential difference across the lower shunt resistor 23.

[0061] When the lower arm U1LW is ON, the potential difference Vlw is negative and the potential difference Vup is zero, so Vup+Vlw is negative. In contrast, when the upper arm U1UP is ON, the potential difference Vup is negative and the potential difference Vlw is zero, so Vup+Vlw is positive.

[0062] Although the phase current direction cannot be specified from the detection value of the current detection circuit 2, the phase current direction can be switched according to the calculation result using the potential difference Vup and the potential difference Vlw. Also, if the potential difference Vup and the potential difference Vlw become larger than the value expected during normal control, it can be determined that a short circuit has occurred (the dashed circle part in the figure).

[0063] Meanwhile, the controller 5 variably controls the switching dead time. The dead time is set so that a through current does not occur through the upper and lower arms. In this embodiment, the shunt resistors 13 and 23 are provided at the output parts of the upper arm U1UP and the lower arm U1LW, that is, at parts with low impedance, so that the through current can be detected with high accuracy. Therefore, the dead time is set as short as possible within a range in which a through current does not occur.

[0064] Fig. 17 is a diagram showing the change over time in the current (arm current) flowing through the arm after the arm command is turned OFF. The controller 5 detects the current value after the arm command is turned OFF, measures the time until the current value reaches the arm's allowable current value (0 [A] or more), and sets this as the dead time. In Fig. 17, Td is the dead time. Setting of this dead time is performed repeatedly while the system is operating.

[0065] As described above, this embodiment includes the controller 5 that variably controls the switching dead time of the switching elements 11 and 21, and the controller 5 detects the current value of the arm whose switching element is turned off, and sets the time required for the detected current value to decrease to the allowable current of the arm as the dead time. This makes it possible to set the dead time as short as possible within a range in which no through current occurs.

[0066] In this embodiment, the controller 5 acquires an upper side potential difference VRU, which is a potential difference across the upper side shunt resistor 13, and a lower side potential difference VRL, which is a potential difference across the lower side shunt resistor 23, from the current detection circuit 2, and specifies the direction of the phase current flow based on the result of adding or subtracting the upper side potential difference VRU and the lower side potential difference VRL. This makes it possible to specify the phase current direction without using the states of the switching elements 11, 21 of the upper and lower arms U1UP, U1LW. It is also possible to detect whether the upper and lower arms U1UP, U1LW are short-circuited.

[0067] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0068] U1 U-phase arm, 2 current detection circuit, 3 operational amplifier, 4 current detector, 6 output line, 10 upper insulating board, 11 upper switching element, 12 upper diode, 13 upper shunt resistor, 20 lower insulating board, 21 lower switching element, 22 lower diode, 23 lower shunt resistor, 30 motor unit, 34 motor housing

Claims

1. In a three-phase inverter device for driving a motor, The upper and lower arms of each phase are composed of separate boards. A switching element, a diode, and a shunt resistor are mounted on the substrate, an output line for each phase is connected to a connection point between the upper arm and the lower arm for each phase; A three-phase inverter device, comprising: a current detection circuit for detecting a combined current of an output current of the upper arm and an output current of the lower arm, in each phase.

2. 2. The three-phase inverter device according to claim 1, A three-phase inverter device, wherein the shunt resistor is provided between the anode of the diode and the phase output terminal in the upper arm, and is provided between the cathode of the diode and the phase output terminal in the lower arm.

3. 2. The three-phase inverter device according to claim 1, a controller for variably controlling a dead time of the switching element; The controller detects the current value of the arm whose switching element has been turned OFF, and sets the time required for the detected current value to decrease to the allowable current of the arm as the dead time.

4. 3. The three-phase inverter device according to claim 2, A three-phase inverter device, in which the upper arm and the lower arm of three phases are arranged in a ring so that the shunt resistor of the upper arm and the shunt resistor of the lower arm of the same phase are adjacent to each other, and the substrate of each arm is fixed to an inner wall of a motor housing or an inverter housing connected to an axial end of the motor housing.

5. 3. The current detection method for detecting phase output currents of a three-phase inverter device according to claim 2, The controller acquiring states of the switching elements of the upper arm and the lower arm; A current detection method comprising: determining a direction in which a phase current flows based on a state of the switching element and a direction of the voltage acquired from the current detection circuit.

6. 3. The current detection method for detecting phase output currents of a three-phase inverter device according to claim 2, The controller an upper potential difference, which is a potential difference between both ends of the shunt resistor placed on the upper arm, and a lower potential difference, which is a potential difference between both ends of the shunt resistor placed on the lower arm, are acquired from the current detection circuit; A current detection method for identifying a direction in which a phase current flows based on a result of adding or subtracting the upper potential difference and the lower potential difference.

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