Power Conversion Systems

Abstract

To discharge a smoothing capacitor at an earlier stage without providing a dedicated discharge circuit.SOLUTION: When discharging power in a smoothing capacitor that is disposed between a battery and an inverter having three-phase power modules, a control circuit periodically and alternately performs all-phase upper on control of controlling all the three-phase power modules into an upper on state, and all-phase lower on control of controlling all the three-phase power modules into a lower on state. When a power module, of the three-phase power modules, in which current flows in a direction from a motor to the inverter is defined as a negative current module and a power module, of the three-phase power modules, in which current flows in a direction from the inverter to the motor is defined as a positive current module, the control circuit performs a discharge process of controlling the negative current module in the lower on state while controlling the positive current module in the upper on state for a prescribed time during a period in which switching between the all-phase lower on control and the all-phase upper on control is performed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a technique for discharging power stored in a smoothing capacitor provided in a power conversion system. [Background technology]

[0002] In general, a power conversion system installed in an electric vehicle includes an inverter that performs power conversion between a battery and a motor, and a smoothing capacitor that smoothes voltage fluctuations between the inverter and the battery. In such a power conversion system, it is desirable to quickly discharge the power stored in the smoothing capacitor when the vehicle stops operating or an accident occurs.

[0003] An example of a method for discharging a smoothing capacitor is disclosed in, for example, Japanese Patent Application Laid-Open No. 2016-123202 (Patent Document 1). The power conversion system disclosed in Japanese Patent Application Laid-Open No. 2016-123202 includes an inverter that performs power conversion between a battery and a motor, a smoothing capacitor disposed between the inverter and the battery, and a control circuit that controls the inverter. The inverter includes a three-phase power module. Each of the three-phase power modules has an upper switching element and a lower switching element, and two diodes that are connected in anti-parallel to the upper switching element and the lower switching element, respectively. When discharging power from the smoothing capacitor, the control circuit consumes the power stored in the smoothing capacitor by periodically switching between an all-phase upper-on control that sets all the power modules in an upper-on state (a state in which the upper-side switching elements are on and the lower-side switching elements are off) and an all-phase lower-on control that sets all the power modules in a lower-on state (a state in which the upper-side switching elements are off and the lower-side switching elements are on). Furthermore, the control circuit sets an all-off period in which the upper and lower switching elements of all power modules are turned off during a period in which the all-phase-upper-phase-on control and the all-phase-lower-phase-on control are switched over. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-123202 A Summary of the Invention [Problem to be solved by the invention]

[0005] The control circuit disclosed in JP 2016-123202 A sets an all-off period in a period in which all-phase-up-on control and all-phase-down-on control are switched. However, if the motor is rotated by the vehicle's running energy during the all-off period, the regenerative power of the motor is charged to the smoothing capacitor via the inverter, and there is a concern that this will make it difficult to quickly discharge the power of the smoothing capacitor.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its object is to quickly discharge a smoothing capacitor without providing a dedicated discharge circuit. [Means for solving the problem]

[0007] (1) A power conversion system according to the present disclosure includes an inverter that performs power conversion between a battery and a motor having a three-phase stator coil, positive and negative pole lines that connect the battery and the inverter, a smoothing capacitor disposed between the positive and negative pole lines, and a control circuit that controls the inverter. The inverter includes three-phase switching units that are connected in parallel to each other between the positive and negative pole lines and connected to the three-phase stator coils, respectively. Each phase of the switching unit includes an upper switching element and a lower switching element that are connected in series in this order from the positive pole line to the negative pole line, and an upper diode and a lower diode that are connected in inverse parallel to the upper switching element and the lower switching element, respectively. When discharging the charge of the smoothing capacitor, the control circuit alternately and periodically switches between an all-phase upper-side on control that keeps all three phases of the switching unit in a state in which the upper switching elements are on and the lower switching elements are off, and an all-phase lower-side on control that keeps all three phases of the switching unit in a state in which the upper switching elements are off and the lower switching elements are on. During a period when switching from one of the all-phase top-on control and the all-phase bottom-on control to the other, the control circuit controls the on / off states of the upper and lower switching elements of each phase to be different from the all-phase top-on control and the all-phase bottom-on control, so that at the beginning and end of the switching period, both the upper and lower switching elements are in the off state in either phase, and between the beginning and end, in either phase, the upper switching element is in the on state, where the lower switching element is in the off state, or the lower switching element is in the on state, where the upper switching element is in the off state, where the lower switching element is in the on state.

[0008] According to the above configuration (1), when the smoothing capacitor is discharged, all-phase-up-on control and all-phase-down-on control are alternately and periodically switched. Then, between the beginning and end of the period in which the all-phase-down-on control and all-phase-up-on control are switched, the upper and lower switching elements are controlled to be in an upper-on state in which they are on and off, respectively, or in a lower-on state in which they are off and on, respectively, in all phases. This control allows the smoothing capacitor to be discharged even when the motor is rotated by the traveling energy of the vehicle, etc. As a result, the smoothing capacitor can be discharged early without providing a dedicated discharge circuit.

[0009] (2) In one aspect, when the phase of the three phases of the switching unit through which current flows in the direction from the motor to the inverter is defined as a negative current phase and the phase through which current flows in the direction from the inverter to the motor is defined as a positive current phase, the control circuit executes a discharge process for a predetermined time during a period when switching from one of the all-phase bottom-on control and the all-phase top-on control to the other, in which the negative current phase is in the bottom on state and the positive current phase is in the top on state.

[0010] According to the above configuration (2), a discharge process is executed for a predetermined time between the beginning and end of the period in which the all-phase-lower-ON control and the all-phase-higher-ON control are switched, in which the negative current phase is in the lower-ON state and the positive current phase is in the upper-ON state. During the discharge process, the smoothing capacitor is discharged even if the motor generator is rotated by the traveling energy of the vehicle or the like. As a result, the smoothing capacitor can be discharged early without providing a dedicated discharge circuit.

[0011] (3) In one aspect, when switching from all-phase-lower-on control to all-phase-upper-on control, the control circuit executes a first dead-time process in which both the upper and lower switching elements of the positive current phase are turned off while maintaining the negative current phase in a lower-on state, executes a discharge process for a predetermined period of time after executing the first dead-time process, executes a second dead-time process in which both the upper and lower switching elements of the negative current phase are turned off while maintaining the positive current phase in an upper-on state, and executes all-phase-upper-on control by switching the negative current phase to an upper-on state while maintaining the positive current phase in an upper-on state after executing the second dead-time process.

[0012] (4) In one aspect, when switching from all-phase-top-on control to all-phase-bottom-on control, the control circuit executes a second dead time processing, executes a discharge processing for a predetermined period of time after executing the second dead time processing, executes a first dead time processing after executing the discharge processing, and after executing the first dead time processing, switches the positive current phase to the bottom on state while maintaining the negative current phase in the bottom on state, thereby executing all-phase-bottom-on control.

[0013] According to the above configurations (3) and (4), in the period in which the all-lower-phase-on control and the all-uper-phase-on control are switched, the first dead-time process, the discharge process period, and the second dead-time process are set in this order or in the reverse order. During any of the first dead-time process, the discharge process, and the second dead-time process, the regenerative power of the motor is not charged to the smoothing capacitor. Furthermore, during the discharge process, the smoothing capacitor is discharged even if the motor is rotating. As a result, the smoothing capacitor can be discharged early.

[0014] (5) In one embodiment, the predetermined time is adjusted in advance to a time when, while the motor is rotating, the output torque of the motor becomes negative and the power of the smoothing capacitor is discharged.

[0015] According to the above configuration (5), the predetermined time (the execution time of the discharge process) is adjusted in advance to the time when the output torque of the motor becomes negative torque and the power of the smoothing capacitor is discharged while the motor is rotating. Therefore, during the execution of the discharge process, the power of the smoothing capacitor can be discharged without generating a positive torque in the motor.

[0016] (6) In one aspect, when discharging power from the smoothing capacitor, the control circuit lengthens the switching period between the all-low-phase-on control and the all-up-phase-on control as the current flowing through the motor increases.

[0017] According to the configuration of (6) above, in consideration of the possibility that the motor may generate positive torque when the current flowing through the motor is large during discharge of the smoothing capacitor (i.e., when the rotation speed of the motor is high), the switching period between the all phases on-low control and the all phases on-low control is made longer as the current flowing through the motor increases. As a result, when the rotation speed of the motor is high, the frequency of switching between the all phases on-low control and the all phases on-low control is reduced, and the frequency of discharge of the smoothing capacitor due to the discharge process is reduced accordingly. Therefore, even when the current flowing through the motor is large (when the rotation speed of the motor is high), it is possible to easily suppress the motor from generating positive torque.

[0018] Furthermore, according to the configuration of (6) above, when the current flowing through the motor is small when discharging the smoothing capacitor (i.e., when the rotation speed of the motor is low), the smoothing capacitor cannot be expected to be discharged by the current flowing through the motor, so the smaller the current flowing through the motor, the shorter the switching period between the all-low-phase-on control and the all-high-phase-on control is made. As a result, when the current flowing through the motor is small (when the rotation speed of the motor is low), the power of the smoothing capacitor can be consumed by the switching loss of the inverter.

[0019] (7) In one aspect, when discharging power from the smoothing capacitor, the control circuit sets a switching period between the all phases low-side on control and the all phases high-side on control to a first period when the current flowing through the motor is between a first threshold and a second threshold lower than the first threshold. The control circuit sets a switching period between the all phases low-side on control and the all phases high-side on control to a second period longer than the first period when the current flowing through the motor is higher than the first threshold. The control circuit sets a switching period between the all phases low-side on control and the all phases high-side on control to a third period shorter than the first period when the current flowing through the motor is lower than the second threshold.

[0020] According to the configuration of (7) above, when the current flowing through the motor when the smoothing capacitor is discharged is greater than the first threshold (i.e., when the motor rotation speed is high), the switching period between the all phases on-low control and the all phases on-low control is set to a second period longer than the first period. As a result, when the motor rotation speed is high, the frequency of switching between the all phases on-low control and the all phases on-low control is reduced, and the frequency of discharge of the smoothing capacitor due to the discharge process is reduced accordingly. This makes it easier to suppress the motor from generating positive torque.

[0021] Furthermore, according to the configuration of (7) above, when the current flowing through the motor during discharge of the smoothing capacitor is smaller than the second threshold (i.e., when the rotation speed of the motor is low), the switching period between the all-low-phase-on control and the all-up-phase-on control is set to a third period shorter than the first period. This allows the power of the smoothing capacitor to be consumed by the switching loss of the inverter even when the current flowing through the motor is small (when the rotation speed of the motor is low). Effect of the Invention

[0022] According to the present disclosure, the smoothing capacitor can be discharged quickly without providing a dedicated discharge circuit. [Brief description of the drawings]

[0023] [Figure 1] 1 is a diagram illustrating an overall configuration of a power conversion system. [Diagram 2] 11A to 11C are diagrams illustrating waveforms of phase currents Iu, Iv, and Iw, and a switching operation between all-phase-on control and all-phase-on control. [Diagram 3] FIG. 13 is a diagram showing drive signals for switching elements in pattern 1. [Figure 4] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode A of pattern 1. [Diagram 5] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode B of pattern 1. [Figure 6] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode C of pattern 1. [Figure 7] FIG. 13 is a diagram showing drive signals for switching elements in pattern 2. [Figure 8] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode A of pattern 2. [Figure 9] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode B of pattern 2. [Figure 10] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode C of pattern 2. [Figure 11] FIG. 13 is a diagram showing driving signals for switching elements in Pattern 3. [Figure 12] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode A of pattern 3. [Figure 13] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode B of pattern 3. [Figure 14] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode C of pattern 3. [Figure 15] FIG. 13 is a diagram showing driving signals for switching elements in pattern 4. [Figure 16] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode A of pattern 4. [Figure 17] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode B of pattern 4. [Figure 18] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode C of pattern 4. [Figure 19] FIG. 13 is a diagram showing drive signals for switching elements in pattern 5. [Figure 20] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode A of pattern 5. [Figure 21] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode B of pattern 5. [Figure 22] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode C of pattern 5. [Diagram 23] FIG. 13 is a diagram showing drive signals for switching elements in pattern 6. [Figure 24] FIG. 13 is a diagram showing a schematic diagram of a current flow in mode A of pattern 6. [Diagram 25] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in mode B of pattern 6. [Figure 26] FIG. 13 is a diagram illustrating a schematic diagram of a current flow in Mode C of Pattern 6. [Figure 27] FIG. 11 is a diagram showing an example of a correspondence relationship between a discharge processing time and an M torque. [Figure 28] FIG. 2 is a functional block diagram of a control circuit. [Figure 29] 1 is a flowchart (part 1) of a control circuit. [Diagram 30] 10 is a timing chart showing an example of a change in the switching cycle between the all-top-phase-ON control period and the all-bottom-phase-ON control period. [Diagram 31] 2 is a flowchart (part 2) of the control circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and the description thereof will not be repeated.

[0025] <System configuration> 1 is a diagram showing a schematic overall configuration of a power conversion system 1 according to the present embodiment. The power conversion system 1 is mounted on, for example, a vehicle having a motor 3 as a driving force source.

[0026] The power conversion system 1 includes a motor 3, a battery 11, a system main relay SMR, a positive electrode line PL, a negative electrode line NL, a smoothing capacitor C0, an inverter 20, current sensors 31 to 33, and a control circuit 100.

[0027] The battery 11 is a battery pack including a plurality of cells. Each cell is a secondary battery such as a lithium ion battery or a nickel metal hydride battery. The output voltage of the battery 11 is a high value, for example, on the order of several hundred volts.

[0028] The positive electrode line PL electrically connects the positive electrode of the battery 11 and the inverter 20. The negative electrode line NL electrically connects the negative electrode of the battery 11 and the inverter 20.

[0029] The system main relay SMR is electrically connected between the battery 11 and the inverter 20. The system main relay SMR is closed in accordance with a command from the control circuit 100. When the system main relay SMR is closed, power transmission between the battery 11 and the inverter 20 becomes possible.

[0030] The smoothing capacitor C0 is connected between the positive electrode line PL and the negative electrode line NL. The smoothing capacitor C0 smoothes the AC component of the voltage fluctuation between the positive electrode line PL and the negative electrode line NL, and supplies the smoothed DC voltage to the inverter 20. The voltage VL between the positive electrode line PL and the negative electrode line NL matches the voltage across the smoothing capacitor C0. When the system main relay SMR is closed, charge flows from the battery 11 to the smoothing capacitor C0, and the voltage across the smoothing capacitor C0 (voltage VL) becomes the output voltage of the battery 11.

[0031] The inverter 20 includes three power modules 21, 22, and 23 corresponding to the U, V, and W phases, respectively. The power modules 21, 22, and 23 are connected in parallel to each other between the positive electrode line PL and the negative electrode line NL. Each of the power modules 21, 22, and 23 includes an upper switching element and a lower switching element connected in series in this order between the positive electrode line PL and the negative electrode line NL, and two diodes connected in anti-parallel to the upper switching element and the lower switching element, respectively. Specifically, the U-phase power module 21 includes an upper switching element Q1 and a lower switching element Q2, and diodes D1 and D2. The V-phase power module 22 includes an upper switching element Q3 and a lower switching element Q4, and diodes D3 and D4. The W-phase power module 23 includes an upper switching element Q5 and a lower switching element Q6, and diodes D5 and D6.

[0032] The switching elements Q1 to Q6 each perform a switching operation (ON / OFF operation) in accordance with a drive signal from the control circuit 100. As the switching elements Q1 to Q6, an IGBT (Insulated Gate Bipolar Transistor), a power MOS (Metal Oxide Semiconductor) transistor, a power bipolar transistor, or the like can be used.

[0033] The U-phase switching elements Q1 and Q2 are controlled to perform switching operations in a complementary and alternating manner. The V-phase switching elements Q3 and Q4 are controlled to perform switching operations in a complementary and alternating manner. The W-phase switching elements Q5 and Q6 are controlled to perform switching operations in a complementary and alternating manner.

[0034] The inverter 20 performs power conversion between the battery 11 and the motor 3 by switching the switching elements Q1 to Q6. When the torque command value of the motor 3 is positive, the inverter 20 converts the DC power from the battery 11 into AC power and supplies it to the motor 3. This drives the motor 3. On the other hand, during regenerative braking of the vehicle 10, the torque command value of the motor 3 is set to negative. In this case, the inverter 20 converts the AC power generated by the motor 3 into DC power and supplies the DC power to the battery 11.

[0035] The motor 3 is a three-phase permanent magnet type synchronous motor having three stator coils of U-phase, V-phase, and W-phase. One end of the U-phase, V-phase, and W-phase stator coils is commonly connected to a neutral point. The other ends of the U-phase, V-phase, and W-phase stator coils are respectively connected to intermediate points of power modules 21, 22, and 23 of the inverter 20. The output torque of the motor 3 is transmitted to drive wheels (none of which are shown) through a power transmission gear, causing the vehicle 10 to travel. In addition, the motor 3 generates electricity using the rotational force of the drive wheels during regenerative braking of the vehicle 10 (regenerative power generation).

[0036] The current sensor 31 detects a U-phase current Iu flowing from the U-phase power module 21 of the inverter 20 to the motor 3. The current sensor 32 detects a V-phase current Iv flowing from the V-phase power module 22 of the inverter 20 to the motor 3. The current sensor 33 detects a W-phase current Iw flowing from the W-phase power module 23 of the inverter 20 to the motor 3. Each of the current sensors 31 to 33 transmits the detection result to the control circuit 100.

[0037] The U-phase current Iu, V-phase current Iv, and W-phase current Iw are detected as positive values ​​(+) when flowing in a positive direction and negative values ​​(-) when flowing in a negative direction, where the direction from inverter 20 toward motor 3 is the positive direction and the direction from motor 3 toward inverter 20 is the negative direction. Since the sum of U-phase current Iu, V-phase current Iv, and W-phase current Iw is zero, the U-phase current Iu, V-phase current Iv, and W-phase current Iw are in such a relationship that if any two values ​​are determined, the remaining one value is also determined. Therefore, any one of current sensors 31, 32, and 33 may be omitted.

[0038] The control circuit 100 includes a processor such as a CPU (Central Processing Unit), memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and ports for inputting and outputting various signals (none of which are shown). The control circuit 100 controls the system main relay SMR and the inverter 20 based on programs and maps stored in the memory, as well as signals received from each sensor.

[0039] The control circuit 100 periodically switches between an upper on state (where the upper switching element is on and the lower switching element is off) and a lower on state (where the upper switching element is off and the lower switching element is on) in each phase of the inverter 20, thereby controlling the driving state of the motor 3 and controlling the charging and discharging of the battery 11.

[0040] The control circuit 100 controls the switching operation of each phase of the inverter 20 by pulse width modulation (PWM) control. In PWM control, the switching period (the sum of one upper on-state period and one lower on-state period) in each phase is determined by the frequency of a carrier signal (carrier frequency fc). The control circuit 100 can adjust the ratio of the upper on-state period to one switching period (duty ratio) by adjusting the duty command value in PWM control.

[0041] <Discharge control of smoothing capacitor C0> When the vehicle in which the power conversion system 1 is mounted stops operating or an accident occurs, it is desirable to quickly discharge the power (charge) stored in the smoothing capacitor C0.

[0042] When discharging power from the smoothing capacitor C0, the control circuit 100 opens the system main relay SMR to disconnect the battery 11 from the inverter 20, and periodically switches between an "all-phase up-on control" in which the power modules 21, 22, 23 of all phases of the inverter 20 are in the up-on state, and an "all-phase down-on control" in which the power modules 21, 22, 23 of all phases are in the down-on state.

[0043] FIG. 2 is a diagram showing waveforms of phase currents Iu, Iv, Iw and a switching operation between the all-phase-on control and the all-phase-on control when power is discharged from the smoothing capacitor C0.

[0044] As shown in Fig. 2, when discharging power from the smoothing capacitor C0, the control circuit 100 alternates between all-phase-on control and all-phase-off control in a cyclical manner. At this time, the duty command value of each phase of the inverter 20 is set to 50% so that the period of the all-phase-on control relative to one switching cycle in each phase is approximately 50%. By setting the duty command value of each phase to 50% in this manner, the voltage applied to the motor 3 can be set to approximately 0 volts, and no current can be passed from the inverter 20 to the motor 3 (i.e., the motor 3 is prevented from outputting a positive torque for driving the vehicle).

[0045] Furthermore, the control circuit 100 performs feedforward control to discharge the power of the smoothing capacitor C0 during a period when the all-phase-up-on control and the all-phase-down-on control are switched. Specifically, when the power module through which a negative current flows among the three-phase power modules 21, 22, and 23 is the negative current module and the power module through which a positive current flows is the positive current module, the control circuit 100 performs a "discharge process" for a predetermined time during a period when the all-phase-down-on control and the all-phase-up-on control are switched from one to the other, to set the negative current module to the down-on state and the positive current module to the up-on state.

[0046] When switching from all-lower-phase-on control to all-uper-phase-on control, the control circuit 100 identifies whether each of the power modules 21, 22, and 23 is a negative current module or a positive current module, and then performs control in the order of mode A, mode B, and mode C.

[0047] First, in mode A, the control circuit 100 executes a first dead time process that sets a first dead time DT1 that turns both the upper switching element and the lower switching element of the positive current module into the off state while maintaining the negative current module in the lower on state.

[0048] After the first dead time process is performed, the control circuit 100 switches the control mode from mode A to mode B. In mode B, the control circuit 100 performs the above-mentioned "discharge process" for a predetermined time. Note that the execution time of the discharge process in mode B (discharge process time) is set in advance by a method described later in FIG. 27.

[0049] After performing the discharge process for a predetermined time, the control circuit 100 switches the control mode from mode B to mode C. In mode C, the control circuit 100 performs a second dead time process that sets a second dead time DT2 that turns both the upper switching element and the lower switching element of the negative current module into the OFF state while maintaining the positive current module in the upper ON state.

[0050] After the second dead time process is performed, the control circuit 100 switches the negative current module to the high-side on state while maintaining the positive current module in the high-side on state, thereby performing all-phase high-side on control.

[0051] When switching from all-top-on control to all-bottom-on control, the control circuit 100 performs control in the reverse order to when switching from all-bottom-on control to all-top-on control, that is, in the order of mode C, mode B, and mode A.

[0052] Specifically, first, in mode C, the control circuit 100 executes a second dead time process that sets a second dead time DT2 that turns both the upper switching element and the lower switching element of the negative current module into the off state while maintaining the positive current module in the upper on state.

[0053] After the second dead time process is performed, the control circuit 100 switches the control mode from mode C to mode B. In mode B, the control circuit 100 performs the above-mentioned "discharging process" for a predetermined time.

[0054] After performing the discharge process for a predetermined time, the control circuit 100 switches the control mode from mode B to mode A. In mode A, the control circuit 100 performs a first dead time process to set a first dead time DT1 that turns both the upper switching element and the lower switching element of the positive current module into the OFF state while maintaining the negative current module in the ON state.

[0055] After the first dead time process is executed, the control circuit 100 switches the positive current module to the low-side on state while maintaining the negative current module in the low-side on state, thereby executing the all-phase low-side on control.

[0056] As shown in FIG. 2, the following patterns 1 to 6 are assumed as combinations of positive and negative phase currents Iu, Iv, Iw (Iu, Iv, Iw).

[0057] Pattern 1: (Iu, Iv, Iw) = (+, -, +) Pattern 2: (Iu, Iv, Iw) = (+, -, -) Pattern 3: (Iu, Iv, Iw)=(+,+,-) Pattern 4: (Iu, Iv, Iw)=(-,+,-) Pattern 5: (Iu, Iv, Iw)=(-,+,+) Pattern 6: (Iu, Iv, Iw)=(-,-,+) Hereinafter, the switching operations of the switching elements Q1 to Q6 in the discharge control of the smoothing capacitor C0 will be specifically described for each of patterns 1 to 6 of the positive and negative combinations of the phase currents Iu, Iv, Iw.

[0058] 3 is a diagram showing drive signals of switching elements Q1 to Q6 in pattern 1: (Iu, Iv, Iw)=(+, -, +). In pattern 1, the U-phase and W-phase power modules 21, 23 are "positive current modules", and the V-phase power module 21 is a "negative current module".

[0059] When switching from the all-lower-phase-on control to the all-uper-phase-on control, the control is performed in the above-mentioned order of mode A, mode B, and mode C.

[0060] First, in mode A, the lower switching elements Q2, Q6 of the U-phase and W-phase power modules 21, 23 (positive current modules) are turned off. This maintains the negative current module in the lower on state, and sets the first dead time DT1 of the positive current module. The first dead time DT1 continues for a predetermined time.

[0061] 4 is a diagram showing a schematic diagram of a current flow during mode A (first dead time DT1) of pattern 1. During mode A of pattern 1, a path is formed through which a current circulates between the motor 3 and the inverter 20. That is, a current from the motor 3 passes through the lower switching element Q4 and the lower diodes D2 and D6, and is returned to the motor 3. Therefore, the discharge current Idc of the smoothing capacitor C0 is 0. That is, during mode A, the smoothing capacitor C0 is not charged or discharged even when the motor 3 is rotating (regenerative state).

[0062] Returning to FIG. 3, after the first dead time DT1, mode A is switched to mode B. In mode B, the upper switching elements Q1, Q5 of the U-phase and W-phase power modules 21, 23 (positive current modules) are turned on. This causes the negative current module to be in the lower on state and the positive current module to be in the upper on state. This mode B is the "discharge process" described above. The discharge process is executed for a predetermined time.

[0063] FIG. 5 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 1. In mode B of pattern 1, a discharge path for smoothing capacitor C0 is formed. That is, a current path is formed that runs from smoothing capacitor C0 through upper switching elements Q1 and Q5, motor 3, and lower switching element Q4, and returns to smoothing capacitor C0. In this case, the discharge current Idc of smoothing capacitor C0 is |Iv|. That is, in mode B, smoothing capacitor C0 is discharged even when motor 3 is rotating (regenerative state).

[0064] Returning to FIG. 3, after the discharge process is performed for a predetermined time, the mode is switched from mode B to mode C. In mode C, the lower switching element Q4 of the V-phase power module 22, which is a negative current module, is turned off. This causes the positive current module to be maintained in the upper on state, and sets a second dead time DT2 for the negative current module. The second dead time DT2 continues for a predetermined time.

[0065] 6 is a diagram showing a schematic diagram of a current flow during mode C (second dead time DT2) of pattern 1. During mode C of pattern 1, a path is formed through which a current circulates between the motor 3 and the inverter 20. That is, the current from the motor 3 passes through the upper diode D3 and upper switching elements Q1 and Q5 of the inverter 20 and is returned to the motor 3. Therefore, the discharge current Idc of the smoothing capacitor C0 is 0. That is, during mode C, even if the motor 3 is rotating (regenerative state), the regenerative power of the motor 3 is not charged to the smoothing capacitor C0.

[0066] 3, after the second dead time DT2 is executed, the upper switching element Q1 of the V-phase power module 22 (negative current module) is switched to the upper on state while the U-phase and W-phase power modules 21, 23 (positive current modules) are maintained in the upper on state. This completes the switching to the all-phase upper on control.

[0067] When switching from all-phase-on control to all-phase-on control, the control is performed in the order of mode C, mode B, and mode A described above. The current flows in modes A, B, and C in pattern 1 are as shown in Figures 4, 5, and 6 above. Therefore, even when switching from all-phase-on control to all-phase-on control, the smoothing capacitor C0 is not charged or discharged in modes A and C, but is discharged in mode B.

[0068] 3 is a drive signal in a comparative example of the present disclosure in which mode B (discharging process) is not performed and only modes A and C are performed. In this case, the smoothing capacitor C0 is not discharged in mode B (discharging process).

[0069] In contrast, in the present disclosure, mode B (discharging process) is set between mode A (first dead time DT1) and mode C (second dead time DT2). Therefore, in the present disclosure, the discharge of the smoothing capacitor C0 is promoted more than in the comparative example, and the smoothing capacitor C0 can be discharged earlier.

[0070] FIG. 7 is a diagram showing the drive signals of the switching elements Q1 to Q6 in pattern 2: (Iu, Iv, Iw)=(+, -, -). In pattern 2, the U-phase power module 21 is the "positive current module", and the V-phase and W-phase power modules 22, 23 are the "negative current modules". In pattern 2, similarly to pattern 1, when switching from all-phase-low-ON control to all-phase-high-ON control, the first dead time DT1 of the positive current module is set in mode A, a discharge process is executed for a predetermined time in mode B thereafter, and a second dead time DT2 of the negative current module is set in mode C thereafter. When switching from all-phase-high-ON control to all-phase-low-ON control, the second dead time DT2 of the negative current module is set in mode C, a discharge process is executed for a predetermined time in mode B thereafter, and a first dead time DT1 of the positive current module is set in mode A thereafter.

[0071] FIG. 8 is a diagram showing a schematic diagram of a current flow in mode A (first dead time DT1) of pattern 2. FIG. 9 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 2. FIG. 10 is a diagram showing a schematic diagram of a current flow in mode C (second dead time DT2) of pattern 2. As shown in FIG. 8 to FIG. 10, in pattern 2 as in pattern 1, charging and discharging of smoothing capacitor C0 are not performed in modes A and C, and smoothing capacitor C0 is discharged in mode B.

[0072] 11 is a diagram showing drive signals of switching elements Q1 to Q6 in pattern 3: (Iu, Iv, Iw)=(+, +, -). In pattern 3, the U-phase and V-phase power modules 21, 22 are "positive current modules", and the W-phase power modules 22, 23 are "negative current modules". As shown in FIG. 11, in pattern 3 as well, as in pattern 1, when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes A, B, C, and when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes C, B, A.

[0073] Fig. 12 is a diagram showing a schematic diagram of a current flow in mode A (first dead time DT1) of pattern 3. Fig. 13 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 3. Fig. 14 is a diagram showing a schematic diagram of a current flow in mode C (second dead time DT2) of pattern 3. As shown in Figs. 12 to 14, in pattern 3 as well, similar to pattern 1, charging and discharging of smoothing capacitor C0 are not performed in modes A and C, and smoothing capacitor C0 is discharged in mode B.

[0074] 15 is a diagram illustrating drive signals of switching elements Q1 to Q6 in pattern 4: (Iu, Iv, Iw)=(-, +, -). In pattern 4, the V-phase power module 22 is a "positive current module", and the U-phase and W-phase power modules 21, 23 are "negative current modules".

[0075] As shown in Figure 15, in pattern 4, as in pattern 1, when switching from all-phase-on control to all-phase-on control, control is performed in the order of modes A, B, C, and when switching from all-phase-on control to all-phase-on control, control is performed in the order of modes C, B, A.

[0076] FIG. 16 is a diagram showing a schematic diagram of a current flow in mode A (first dead time DT1) of pattern 4. FIG. 17 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 4. FIG. 18 is a diagram showing a schematic diagram of a current flow in mode C (second dead time DT2) of pattern 4. As shown in FIGS. 16 to 18, in pattern 4 as well, similar to pattern 1, charging and discharging of smoothing capacitor C0 are not performed in modes A and C, and smoothing capacitor C0 is discharged in mode B.

[0077] 19 is a diagram showing drive signals of switching elements Q1 to Q6 in pattern 5: (Iu, Iv, Iw)=(-, +, +). In pattern 5, the V-phase and W-phase power modules 22, 23 are "positive current modules", and the U-phase power module 21 is a "negative current module". As shown in FIG. 19, in pattern 5, similarly to pattern 1, when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes A, B, C, and when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes C, B, A.

[0078] FIG. 20 is a diagram showing a schematic diagram of a current flow in mode A (first dead time DT1) of pattern 5. FIG. 21 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 5. FIG. 22 is a diagram showing a schematic diagram of a current flow in mode C (second dead time DT2) of pattern 5. As shown in FIG. 20 to FIG. 22, in pattern 5 as in pattern 1, charging and discharging of smoothing capacitor C0 are not performed in modes A and C, and smoothing capacitor C0 is discharged in mode B.

[0079] 23 is a diagram showing drive signals of switching elements Q1 to Q6 in pattern 6: (Iu, Iv, Iw)=(-, -, +). In pattern 6, the W-phase power module 23 is a "positive current module", and the U-phase and V-phase power modules 21, 22 are "negative current modules". As shown in FIG. 23, in pattern 6 as well, similar to pattern 1, when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes A, B, C, and when switching from all-phase-on-control to all-phase-on-control, control is performed in the order of modes C, B, A.

[0080] FIG. 24 is a diagram showing a schematic diagram of a current flow in mode A (first dead time DT1) of pattern 6. FIG. 25 is a diagram showing a schematic diagram of a current flow in mode B (discharging process) of pattern 6. FIG. 26 is a diagram showing a schematic diagram of a current flow in mode C (second dead time DT2) of pattern 6. As shown in FIG. 24 to FIG. 26, in pattern 6 as in pattern 1, charging and discharging of smoothing capacitor C0 are not performed in modes A and C, and smoothing capacitor C0 is discharged in mode B.

[0081] <Discharge processing time setting> In the above-mentioned mode B, the control circuit 100 executes the above-mentioned "discharge process" for a predetermined time. Note that the execution time of the discharge process in mode B (discharge process time) is preset so that the output torque of the motor 3 becomes negative torque and the power of the smoothing capacitor C0 is discharged.

[0082] FIG. 27 is a diagram showing an example of the correspondence between the discharge processing time in mode B, the discharge current Idc of the smoothing capacitor C0, and the output torque of the motor 3 (hereinafter also referred to as "M torque") when the rotation speed of the motor 3 is 100 rpm, 1000 rpm, 2000 rpm, and 3000 rpm.

[0083] The upper part of Fig. 27 shows the correspondence relationship between the discharge processing time (horizontal axis) and the discharge current Idc (vertical axis) for each rotation speed of the motor 3. The lower part of Fig. 27 shows the correspondence relationship between the discharge processing time (horizontal axis) and the M torque (vertical axis) for each rotation speed of the motor 3. The correspondence relationship shown in Fig. 27 can be obtained, for example, by simulation or experiment.

[0084] In addition, in Fig. 27, when the discharge current Idc is a positive value, it means that the smoothing capacitor C0 is discharged, and when the discharge current Idc is a negative value, it means that the smoothing capacitor C0 is charged. In addition, in Fig. 27, when the M torque is a positive value, it means that the motor 3 is in a powering state, and when the M torque is a negative value, it means that the motor 3 is in a regenerative state.

[0085] When the correspondence relationship shown in FIG. 27 is obtained, when the motor 3 is rotating at less than 2000 rpm and the discharge processing time is 18 to 28 μs, the discharge current Idc becomes approximately a positive value, the smoothing capacitor C0 is discharged, and the M torque becomes a negative value, causing the motor 3 to generate negative torque.

[0086] In view of this, in this embodiment, the discharge processing time (execution time of mode B) is set so as to be included in a time period ("discharge / negative torque region" shown in FIG. 27) in which the output torque of motor 3 becomes negative torque and the power of smoothing capacitor C0 is discharged when motor 3 is rotating less than a predetermined rotation speed (for example, 2000 rpm in the example shown in FIG. 27). Therefore, even when motor 3 is rotating, during the discharge processing (execution of mode B), negative torque can be generated in motor 3 while discharging smoothing capacitor C0, thereby facilitating the stopping of the vehicle.

[0087] <Function block> 28 is a functional block diagram of the control circuit 100 when the control circuit 100 controls the discharge of the smoothing capacitor C0. The control circuit 100 includes a command generating unit 110, a current predicting unit 120, a mode setting unit, a correcting unit 140, and a PWM control unit 150.

[0088] A command to discharge the smoothing capacitor C0 (hereinafter also referred to as a "discharge command") is input to the command generating unit 110 and the current predicting unit 120 when the vehicle stops driving, an accident occurs, or the like.

[0089] When the command generating unit 110 receives a discharge command, it generates a U-phase duty command value Duc, a V-phase duty command value Dvc, and a W-phase duty command value Dwc for periodically switching between the all-phase-on control and the all-phase-on control. The duty command values ​​Duc, Dvc, and Dwc are in phase with each other and are all set to 50%. The command generating unit 110 outputs the generated duty command values ​​Duc, Dvc, and Dwc to the correcting unit 140.

[0090] When the current prediction unit 120 receives a discharge command, it predicts the phase currents Iu, Iv, Iw in the next calculation cycle of PWM control based on the history of the phase currents Iu, Iv, Iw detected by the current sensors 31-33, and outputs the prediction result to the mode setting unit 130 together with the detection results of the current sensors 31-33.

[0091] Based on the prediction results of the phase currents Iu, Iv, Iw, the mode setting unit 130 specifies patterns 1 to 6 of combinations of positive and negative values ​​of the phase currents Iu, Iv, Iw, and based on the specified patterns, sets the processing order and processing contents of the above-mentioned modes A, B, and C. The method of setting the processing order and processing contents of the modes A, B, and C has already been described.

[0092] The correction unit 140 corrects the in-phase 50% duty command values ​​Duc, Dvc, and Dwc acquired from the command generation unit 110, based on the processing order and processing contents of the modes A, B, and C acquired from the mode setting unit 130. The correction unit 140 outputs the corrected duty command values ​​Du, Dv, and Dw to the PWM control unit 150.

[0093] The PWM control unit 150 controls the switching elements Q1 to Q6 of the inverter 20 based on the corrected duty command values ​​Du, Dv, and Dw acquired from the correction unit 140. As a result, the control described with reference to Figs. 3 to 26 above is performed, and the smoothing capacitor C0 is discharged.

[0094] <Flowchart> Fig. 29 is a flowchart showing an example of a processing procedure when the control circuit 100 controls the discharge of the smoothing capacitor C0. The flowchart shown in Fig. 29 is repeatedly executed at a predetermined calculation period with the system main relay SMR in an open state.

[0095] The control circuit 100 acquires the phase currents Iu, Iv, and Iw detected by the current sensors 31 to 33 (step S10).

[0096] Next, the control circuit 100 predicts the phase currents Iu, Iv, Iw in the next calculation cycle of the PWM control based on the history of the phase currents Iu, Iv, Iw detected by the current sensors 31 to 33 (step S20).

[0097] Next, the control circuit 100 determines which of the above-mentioned patterns 1 to 6 the positive / negative combination (Iu, Iv, Iw) of the phase currents Iu, Iv, Iw predicted in step S02 corresponds to (steps S21 to S26). Then, the control circuit 100 performs mode setting as described above with reference to Figs. 3 to 26 according to the determined positive / negative combination of the phase currents Iu, Iv, Iw (steps S31 to S36).

[0098] For example, when the positive / negative combination (Iu, Iv, Iw) of the phase currents Iu, Iv, Iw is (+, -, +) (YES in step S21), the control circuit 100 performs the mode setting of the pattern 1 shown in the above-mentioned Figs. 3 to 6 to control the discharge of the smoothing capacitor C0 (step S31). When the positive / negative combination (Iu, Iv, Iw) of the phase currents Iu, Iv, Iw is (+, -, -) (YES in step S22), the control circuit 100 performs the mode setting of the pattern 2 shown in the above-mentioned Figs. 7 to 10 to control the discharge of the smoothing capacitor C0 (step S32). The same applies to other combinations.

[0099] As described above, when discharging power from the smoothing capacitor C0, the control circuit 100 according to this embodiment alternates between the all-phase-on control and the all-phase-on control periodically. At this time, the control circuit 100 sets the duty command value of each phase of the inverter 20 to 50% so that the period of the all-phase-on control is approximately 50% of one switching cycle (the sum of one all-phase-on control period and one all-phase-on control period). This makes it possible to make the voltage applied to the motor 3 approximately 0 volts, so that power from the smoothing capacitor C0 is not supplied to the motor 3.

[0100] In the control circuit 100 according to the present embodiment, the first dead time DT1 (mode A), the discharge processing time (mode B), and the second dead time DT2 (mode C) are set in this order or in the reverse order during the period when the all-phase-on control and the all-phase-on control are switched, as described above. Therefore, the smoothing capacitor C0 can be discharged earlier and more reliably than when an all-phase-off period is provided during the period when the all-phase-on control and the all-phase-on control are switched.

[0101] In other words, if an all-off period is set in the period during which all-phase-up on control and all-phase-down on control are switched over, when the motor 3 is rotated by the vehicle's running energy, the regenerative power of the motor 3 will be charged to the smoothing capacitor C0 via the inverter 20 during the all-off period, and as a result, there is a concern that the power of the smoothing capacitor C0 will not be able to be discharged quickly.

[0102] In contrast, the control circuit 100 according to the present embodiment does not set an all-off period in the period in which the all-phase-on control and the all-phase-on control are switched, but sets the first dead time DT1, the discharge processing period, and the second dead time DT2 in this order or in the reverse order, as described above. In any of the first dead time DT1, the discharge processing period, and the second dead time DT2, the regenerative power of the motor 3 is not charged to the smoothing capacitor C0, as described above. Furthermore, in the discharge processing period (mode B), the smoothing capacitor C0 is discharged even if the motor 3 is in a regenerative state. As a result, the smoothing capacitor C0 can be discharged earlier and more reliably without providing a dedicated discharge circuit.

[0103] Furthermore, in this embodiment, the above-mentioned discharge process time (execution time of mode B) is adjusted in advance to a time when the output torque of the motor 3 becomes negative torque and the power of the smoothing capacitor C0 is discharged while the motor 3 is rotating (see FIG. 27 above). Therefore, during the discharge process (execution of mode B), the smoothing capacitor C0 can be discharged more reliably without generating positive torque in the motor 3.

[0104] Furthermore, the discharge control of the smoothing capacitor C0 in this embodiment does not use a detection signal from a resolver (not shown) that detects the rotation angle of the motor 3. Therefore, even if the control circuit 100 cannot grasp the rotation angle of the motor 3 due to a break in a signal line connecting the resolver and the control circuit 100, for example, the smoothing capacitor C0 can be discharged.

[0105] [Variations] In the above embodiment, the switching cycle between the all-phase-on control period and the all-phase-on control period is constant (fixed). In contrast, in this modification, the switching cycle between the all-phase-on control period and the all-phase-on control period is changed according to the magnitude of the current flowing through the motor 3.

[0106] Fig. 30 is a timing chart showing an example of a change in the switching cycle between the all-top-phase-ON control period and the all-bottom-phase-ON control period according to this modification. The upper part of Fig. 30 shows the duty command value of each phase of the inverter 20. The lower part of Fig. 30 shows the maximum values ​​(maximum current values) of the phase currents Iu, Iv, and Iw as the current flowing through the motor 3.

[0107] At time t1 when the control circuit 100 receives the discharge command, the maximum current value is greater than the first threshold value th1. In this state, the rotation speed of the motor 3 is high, and there is a concern that the motor 3 may generate positive torque.

[0108] Therefore, when the maximum current value is greater than the first threshold value th1, the control circuit 100 sets the switching frequency mode to the Lo mode. In the Lo mode, the switching frequency between the all-phase-on control period and the all-phase-on control period is set to a frequency f0 lower than the carrier frequency fc. That is, in the Lo mode, the period in which the duty command value is fixed to 100% (all-phase-on control period) and the period in which the duty command value is fixed to 0% (all-phase-on control period) are switched at a period longer than the period (=1 / fc) determined by the carrier frequency fc.

[0109] As a result, when the maximum current value is greater than the first threshold th1 (when the rotation speed of the motor 3 is high), the frequency of switching between the all-phase-on control period and the all-phase-on control period is reduced, and the frequency of discharging the smoothing capacitor C0 by the discharging process is reduced accordingly. This makes it easier to suppress the motor 3 from generating positive torque.

[0110] The amount of discharge from the smoothing capacitor C0 in one discharge process depends on the maximum current value. Therefore, in the Lo mode, although the frequency of discharge processes is reduced, the amount of discharge from the smoothing capacitor C0 in one discharge process is large, so the total amount of discharge from the smoothing capacitor C0 does not decrease excessively.

[0111] Thereafter, when the rotation speed of the motor 3 decreases and the maximum current value decreases, the possibility that the motor 3 will generate positive torque becomes low. Therefore, when the maximum current value becomes less than the first threshold value th1 at time t2, the control circuit 100 switches the switching frequency mode to the Mid mode. In the Mid mode, the switching frequency between the all-phase-on control period and the all-phase-low on control period is set to a frequency f1 that is higher than the frequency f0 in the Lo mode. Specifically, in the Mid mode, the switching frequency between the all-phase-on control period and the all-phase-low on control period is set to a carrier frequency fc, and then the carrier frequency fc is set to the frequency f1.

[0112] As a result, when the maximum current value is less than the first threshold th1, the frequency of switching between the all-phase-up-ON control period and the all-phase-down-ON control period increases compared to when the maximum current value is equal to or greater than the first threshold th1, and the frequency of discharging the smoothing capacitor C0 by the discharging process increases accordingly. Therefore, although the amount of discharge of the smoothing capacitor C0 by one discharging process is small, the total amount of discharge of the smoothing capacitor C0 is ensured.

[0113] Thereafter, when the rotational speed of the motor 3 further decreases and the maximum current value further decreases, the discharge of the smoothing capacitor C0 by the current flowing through the motor 3 cannot be expected. Therefore, when the maximum current value becomes less than the second threshold value th2 (th2 < th1) at time t3, the control circuit 100 switches the switching frequency mode to the Hi mode. In the Hi mode, the switching frequency between the all-phase upper-on control period and the all-phase lower-on control period is set to a frequency f2 higher than the frequency f1 in the Mid mode. Specifically, in the Hi mode, after the switching frequency between the all-phase upper-on control period and the all-phase lower-on control period is made to coincide with the carrier frequency fc, the carrier frequency fc is set to the frequency f2. Thereby, in a state where the maximum current value is less than the second threshold value th2, the power of the smoothing capacitor C0 can be consumed by the switching loss of the inverter 20.

[0114] Also, in the Hi mode, since the power of the smoothing capacitor C0 is consumed by the switching loss of the inverter 20 as described above, even when the cable connecting the inverter 20 and the motor 3 is disconnected, the smoothing capacitor C0 can be discharged.

[0115] Figure 31 is a flowchart showing an example of the processing procedure performed when the control circuit 100 sets the switching frequency mode during the discharge control of the smoothing capacitor C0. The flowchart shown in Figure 31 is repeatedly executed at a predetermined calculation cycle during the discharge control of the smoothing capacitor C0.

[0116] The control circuit 100 acquires the phase currents Iu, Iv, Iw detected by the current sensors 31 to 33 (step S60). Next, the control circuit 100 determines the magnitude relationship between the maximum value of the phase currents Iu, Iv, Iw detected by the current sensors 31 to 33 (= the maximum current value), the first threshold value th1, and the second threshold value th2 described above (steps S61 to S63).

[0117] Then, the control circuit 100 sets the switching frequency mode as described above in FIG. 30 according to the result of judging the magnitude relationship between the maximum current value and the first threshold value th1 and the second threshold value th2 (steps S71 to S73). That is, if the maximum current value is greater than the first threshold value th1 (YES in step S61), the control circuit 100 sets the switching frequency mode to the above-mentioned Lo mode (step S71). If the maximum current value is smaller than the first threshold value th1 and greater than the second threshold value th2 (YES in step S62), the control circuit 100 sets the switching frequency mode to the above-mentioned Mid mode (step S72). If the maximum current value is smaller than the second threshold value th2 (YES in step S63), the control circuit 100 sets the switching frequency mode to the above-mentioned Hi mode (step S73).

[0118] As described above, the switching cycle between the all-top-phase-ON control period and the all-bottom-phase-ON control period may be changed according to the magnitude of the current flowing through the motor 3.

[0119] The power modules 21, 22, and 23 do not have to be separate modules, but may be one module.

[0120] The switching elements Q1 to Q6 may be MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), in which case the diodes D1 to D6 may be body diodes.

[0121] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0122] 1 power conversion system, 3 motor, 10 vehicle, 11 battery, 20 inverter, 21, 22, 23 power module, 31, 32, 33 current sensor, 100 control circuit, 110 command generation unit, 120 current prediction unit, 130 mode setting unit, 140 correction unit, 150 PWM control unit, C0 smoothing capacitor, D1 to D6 diodes, NL negative pole line, PL positive pole line, Q1 to Q6 switching elements, SMR system main relay.

Claims

1. an inverter that performs power conversion between a battery and a motor having a three-phase stator coil; a positive line and a negative line connecting the battery and the inverter; A smoothing capacitor disposed between the positive electrode line and the negative electrode line; A control circuit for controlling the inverter, the inverter includes three-phase switching units connected in parallel to each other between the positive pole line and the negative pole line and connected to the three-phase stator coils, respectively; Each phase of the switching unit is an upper switching element and a lower switching element connected in series in this order between the positive electrode line and the negative electrode line; an upper diode and a lower diode connected in anti-parallel to the upper switching element and the lower switching element, respectively; When discharging the charge of the smoothing capacitor, the control circuit an all-phase upper-side switching control for turning on all three phases of the switching unit, the upper-side switching element being turned on and the lower-side switching element being turned off, and an all-phase lower-side switching control for turning off all three phases of the switching unit, the upper-side switching element being turned off and the lower-side switching element being turned on, a power conversion system in which, during a period in which the all-phase-upper-on control and the all-phase-lower-on control are switched from one to the other, the on / off states of the upper and lower switching elements of each phase are controlled to be different from the all-phase-upper-on control and the all-phase-lower-on control, and at the beginning and end of the switching period, both the upper and lower switching elements are in the off state in any phase, and between the beginning and end, in any phase, the upper switching element is in the on state and the lower switching element is in the off state, or the lower switching element is in the off state and the lower switching element is in the on state.

2. 2. The power conversion system according to claim 1, wherein, of the three phases of the switching unit, a phase through which current flows in a direction from the motor to the inverter is defined as a negative current phase, and a phase through which current flows in a direction from the inverter to the motor is defined as a positive current phase, and during a period in which the all-phase-lower-on control and the all-phase-uper-on control are switched from one to the other, the control circuit executes a discharge process for a predetermined time in which the negative current phase is in the lower-on state while the positive current phase is in the upper-on state.

3. When switching from the all-low-phase-on control to the all-up-phase-on control, the control circuit A first dead time process is executed to turn both the upper side switching element and the lower side switching element of the positive current phase into an OFF state while maintaining the negative current phase into the lower ON state; The discharge process is performed for the predetermined time after the first dead time process is performed; After the discharge process is performed, a second dead time process is performed in which both the upper and lower switching elements of the negative current phase are turned off while the positive current phase is maintained in the upper on state; The power conversion system according to claim 2 , wherein after the second dead time process is performed, the all-phase-up-on control is performed by switching the negative current phase to the up-on state while maintaining the positive current phase in the up-on state.

4. When switching from the all-phase-up-on control to the all-phase-down-on control, the control circuit Executing the second dead time process; The discharge process is performed for the predetermined time after the second dead time process is performed; performing the first dead time process after performing the discharge process; The power conversion system according to claim 3 , wherein after the first dead time process is performed, the all-phase low-on control is performed by switching the positive current phase to the low-on state while maintaining the negative current phase in the low-on state.

5. 3. The power conversion system according to claim 2, wherein the predetermined time is adjusted in advance to a time when, while the motor is rotating, an output torque of the motor becomes negative torque and power of the smoothing capacitor is discharged.

6. The power conversion system according to any one of claims 1 to 5, wherein the control circuit, when discharging power from the smoothing capacitor, lengthens the switching period between the all-phase-lower-on control and the all-phase-up-on control as the current flowing through the motor increases.

7. When discharging power from the smoothing capacitor, the control circuit when the current flowing through the motor is between a first threshold value and a second threshold value that is smaller than the first threshold value, a switching cycle between the all-low-phase-on control and the all-up-phase-on control is set to a first cycle; when the current flowing through the motor is greater than the first threshold value, a switching period between the all-low-phase-on control and the all-up-phase-on control is set to a second period longer than the first period; 7. The power conversion system according to claim 6, wherein when the current flowing through the motor is smaller than the second threshold, a switching period between the all-low-phase-on control and the all-up-phase-on control is set to a third period shorter than the first period.

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