Power conversion system

Abstract

The present application relates to a power conversion system. A control circuit alternately switches between full-phase upper conduction control, which makes all of the three-phase power modules enter an upper conduction state, and full-phase lower conduction control, which makes all of the three-phase power modules enter a lower conduction state, periodically, in discharging electric power of a smoothing capacitor disposed between a battery and a converter having the three-phase power modules. When a power module in which current flows from a motor to the converter is set as a negative current module and a power module in which current flows from the converter to the motor is set as a positive current module, the control circuit performs discharge processing, in which the negative current module is made to enter a lower conduction state while the positive current module is made to enter an upper conduction state, at a predetermined time during switching between the full-phase lower conduction control and the full-phase upper conduction control.

Description

Technical Field

[0001] This disclosure relates to a technique for discharging electrical energy stored in a smoothing capacitor disposed in a power conversion system. Background Technology

[0002] Typically, a power conversion system installed in an electric vehicle includes a converter that converts power between a battery and a motor, and a smoothing capacitor that smooths out voltage fluctuations between the converter and the battery. In such a power conversion system, it is desirable to discharge the power stored in the smoothing capacitor in advance when the vehicle stops or in the event of an accident.

[0003] An example of a method for discharging a smoothing capacitor is disclosed in Japanese Patent Application Publication No. 2016-123202. The power conversion system disclosed in Japanese Patent Application Publication No. 2016-123202 includes a converter for converting power between a battery and a motor, a smoothing capacitor disposed between the converter and the battery, and a control circuit for controlling the converter. The converter has three-phase power modules. Each of the three-phase power modules has an upper switching element and a lower switching element, and two diodes connected in reverse parallel with the upper and lower switching elements, respectively. When discharging the power in the smoothing capacitor, the control circuit consumes the power stored in the smoothing capacitor by periodically switching between a full-phase upper conduction control that puts all power modules in an upper conduction state (the upper switching element is on and the lower switching element is off) and a full-phase lower conduction control that puts all power modules in a lower conduction state (the upper switching element is off and the lower switching element is on). In addition, during the switching between full-phase up-conduction control and full-phase down-conduction control, the control circuit is configured with a full cut-off period that makes the upper and lower switching elements of all power modules cut off. Summary of the Invention

[0004] The control circuit disclosed in Japanese Patent Application Publication No. 2016-123202 has a full-off period during the switching between full-phase upper conduction control and full-phase lower conduction control. However, during the full-off period, if the motor is rotating using the vehicle's driving energy, the motor's regenerative power will charge the smoothing capacitor via the converter. Due to this effect, it may be impossible to discharge the power of the smoothing capacitor in advance.

[0005] This disclosure was made to solve the above-mentioned problems, and its purpose is to enable the smoothing capacitor to discharge prematurely without setting up a dedicated discharge circuit.

[0006] The power conversion system based on this disclosure includes: a converter for power conversion between a battery and a motor having three-phase stator windings; positive and negative lines connecting the battery and the converter; a smoothing capacitor disposed between the positive and negative lines; and a control circuit for controlling the converter. The converter includes a three-phase switching section consisting of an upper switching element and a lower switching element connected in parallel between the positive and negative lines and respectively connected to the three-phase stator windings. Each phase of the switching section includes: an upper switching element and a lower switching element connected in series from the positive to the negative line; and an upper diode and a lower diode connected in anti-parallel to the upper and lower switching elements, respectively. The control circuit, while discharging the charge of the smoothing capacitor, periodically switches between full-phase upper conduction control (where all three phases of the switching section are in a state where the upper switching elements are on and the lower switching elements are off) and full-phase lower conduction control (where all three phases of the switching section are in a state where the upper switching elements are off and the lower switching elements are on). During the switching period between full-phase up-conduction control and full-phase down-conduction control, the control circuit controls the on / off states of the upper and lower switching elements of each phase in a manner different from that of full-phase up-conduction control and full-phase down-conduction control. The control is such that: at the beginning and end of the switching period, in any phase, both the upper and lower switching elements are in the off state; between the beginning and end of the period, in each phase, it is either an up-conduction state where the upper switching element is on and the lower switching element is off, or a down-conduction state where the upper switching element is off and the lower switching element is on.

[0007] Based on the above configuration, during the discharge of the smoothing capacitor, all-phase up-conduction control and all-phase down-conduction control are alternately and periodically switched. Furthermore, between the beginning and end of the switching period between all-phase down-conduction control and all-phase up-conduction control, the control ensures that in each phase, either the upper and lower switching elements are in an up-conduction state (on and off respectively) or the upper and lower switching elements are in a down-conduction state (off and on respectively). Through this control, the smoothing capacitor is discharged even when the motor is rotating using the vehicle's driving energy. As a result, the smoothing capacitor can be discharged prematurely without a dedicated discharge circuit.

[0008] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description relating to the invention, which is understood in conjunction with the accompanying drawings. Attached Figure Description

[0009] Figure 1 It is a diagram that roughly shows the overall structure of the power conversion system.

[0010] Figure 2It shows the waveforms of phase currents Iu, Iv, and Iw, and the switching action between full-phase up-conduction control and full-phase down-conduction control.

[0011] Figure 3 This is a diagram showing the drive signals of the switching elements in pattern 1.

[0012] Figure 4 It is a diagram schematically showing the flow of current in mode A of pattern 1.

[0013] Figure 5 This is a diagram schematically illustrating the flow of current in pattern B of template 1.

[0014] Figure 6 This is a diagram schematically illustrating the flow of current in pattern C of design 1.

[0015] Figure 7 This is a diagram showing the drive signals of the switching element in Template 2.

[0016] Figure 8 This is a diagram schematically illustrating the flow of current in pattern A of template 2.

[0017] Figure 9 This is a diagram schematically illustrating the flow of current in pattern B of design 2.

[0018] Figure 10 This is a diagram schematically illustrating the flow of current in pattern C of design 2.

[0019] Figure 11 This is a diagram showing the drive signals of the switching element in Template 3.

[0020] Figure 12 This is a diagram schematically illustrating the flow of current in pattern A of template 3.

[0021] Figure 13 This is a diagram schematically illustrating the flow of current in pattern B of template 3.

[0022] Figure 14 This is a diagram schematically illustrating the flow of current in pattern C of template 3.

[0023] Figure 15 This is a diagram showing the drive signals of the switching element in Template 4.

[0024] Figure 16 This is a diagram schematically illustrating the flow of current in pattern A of template 4.

[0025] Figure 17 This is a diagram schematically illustrating the flow of current in pattern B of template 4.

[0026] Figure 18 This is a diagram schematically illustrating the flow of current in pattern C of formula 4.

[0027] Figure 19 This is a diagram showing the drive signals of the switching element in Template 5.

[0028] Figure 20 This is a diagram schematically illustrating the flow of current in pattern A of template 5.

[0029] Figure 21 This is a diagram schematically illustrating the flow of current in pattern B of template 5.

[0030] Figure 22 This is a diagram schematically illustrating the flow of current in pattern C of template 5.

[0031] Figure 23 This is a diagram showing the drive signals of the switching element in Template 6.

[0032] Figure 24 This is a diagram schematically illustrating the flow of current in pattern A of template 6.

[0033] Figure 25 This is a diagram schematically illustrating the flow of current in pattern B of template 6.

[0034] Figure 26 This is a diagram schematically illustrating the flow of current in pattern C of template 6.

[0035] Figure 27 This is a diagram illustrating an example of the relationship between discharge processing time and M torque.

[0036] Figure 28 This is a functional block diagram of the control circuit.

[0037] Figure 29 This is a flowchart of the control circuit (Part 1).

[0038] Figure 30 This is a time diagram illustrating an example of the changing pattern of the switching cycle during full-phase up-conduction control and full-phase down-conduction control.

[0039] Figure 31 This is the flowchart of the control circuit (Part Two). Detailed Implementation

[0040] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0041] <System Composition>

[0042] Figure 1 This diagram schematically illustrates the overall configuration of the power conversion system 1 according to this embodiment. The power conversion system 1 is, for example, mounted on a vehicle that uses a motor 3 as its driving force source.

[0043] The power conversion system 1 includes a motor 3, a battery 11, a system main relay SMR, a positive line PL, a negative line NL, a smoothing capacitor C0, a converter 20, current sensors 31-33, and a control circuit 100.

[0044] Battery 11 is a battery pack comprising multiple individual cells. Each individual cell is a secondary battery such as a lithium-ion battery or a nickel-metal hydride battery. The output voltage of battery 11 is, for example, a high value of several hundred volts.

[0045] The positive line PL connects the positive terminal of battery 11 to converter 20. The negative line NL connects the negative terminal of battery 11 to converter 20.

[0046] The system main relay SMR is electrically connected between the battery 11 and the converter 20. The system main relay SMR closes according to the command from the control circuit 100. The closing of the system main relay SMR enables power transfer between the battery 11 and the converter 20.

[0047] A smoothing capacitor C0 is connected between the positive line PL and the negative line NL. The smoothing capacitor C0 smooths the AC component of the voltage fluctuation between the positive line PL and the negative line NL, supplying the smoothed DC voltage to the converter 20. The voltage VL between the positive line PL and the negative line NL is the same as the voltage across the smoothing capacitor C0. When the system main relay SMR is closed, charge flows from the battery 11 into the smoothing capacitor C0, and the voltage across the smoothing capacitor C0 (voltage VL) becomes the output voltage of the battery 11.

[0048] The converter 20 includes three power modules 21, 22, and 23 corresponding to the U-phase, V-phase, and W-phase, respectively. Power modules 21, 22, and 23 are connected in parallel between the positive line PL and the negative line NL. Each power module 21, 22, and 23 includes an upper and a lower switching element connected in series between the positive line PL and the negative line NL, and two diodes connected in reverse parallel to the upper and lower switching elements, respectively. Specifically, the U-phase power module 21 includes an upper switching element Q1, a lower switching element Q2, and diodes D1 and D2. The V-phase power module 22 includes an upper switching element Q3, a lower switching element Q4, and diodes D3 and D4. The W-phase power module 23 includes an upper switching element Q5, a lower switching element Q6, and diodes D5 and D6.

[0049] Switching elements Q1 to Q6 perform switching operations (on / off operations) according to the drive signals from the control circuit 100. Switching elements Q1 to Q6 can be IGBTs (Insulated Gate Bipolar Transistors), MOS (Metal Oxide Semiconductor) transistors for power applications, or bipolar transistors for power applications.

[0050] The switching elements Q1 and Q2 of phase U are controlled in a complementary and alternating manner. The switching elements Q3 and Q4 of phase V are controlled in a complementary and alternating manner. The switching elements Q5 and Q6 of phase W are controlled in a complementary and alternating manner.

[0051] The converter 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 converter 20 converts the DC power from the battery 11 into AC power and supplies it to the motor 3. Thus, the motor 3 is driven. 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 converter 20 converts the AC power generated by the motor 3 into DC power and supplies this DC power to the battery 11.

[0052] Motor 3 is a three-phase permanent magnet synchronous motor with three stator coils: U-phase, V-phase, and W-phase. One end of each of the U-phase, V-phase, and W-phase stator coils is connected to the neutral point. The other ends of each stator coil are connected to the midpoints of power modules 21, 22, and 23 of converter 20, respectively. The output torque of motor 3 is transmitted to the drive wheels (not shown) via power transmission gears, causing vehicle 10 to move. Furthermore, motor 3 generates electricity using the rotational force of the drive wheels during regenerative braking of vehicle 10 (regenerative power generation).

[0053] Current sensor 31 detects the U-phase current Iu flowing from the U-phase power module 21 of converter 20 to the motor 3. Current sensor 32 detects the V-phase current Iv flowing from the V-phase power module 22 of converter 20 to the motor 3. Current sensor 33 detects the W-phase current Iw flowing from the W-phase power module 23 of converter 20 to the motor 3. Each current sensor 31 to 33 sends the detection result to the control circuit 100.

[0054] The U-phase current Iu, V-phase current Iv, and W-phase current Iw are detected as positive (+) when flowing in the positive direction and negative (-) when flowing in the negative direction, with the direction from the converter 20 to the motor 3 defined as the positive direction and the direction from the motor 3 to the converter 20 defined as the negative direction. Furthermore, the sum of the U-phase current Iu, V-phase current Iv, and W-phase current Iw is 0, so if any two values ​​are determined, the remaining value is also determined. Therefore, any one of the current sensors 31, 32, and 33 can be omitted.

[0055] The control circuit 100 includes a processor such as a CPU (Central Processing Unit), a memory such as ROM (Read Only Memory) and RAM (Random Access Memory), and ports for inputting and outputting various signals (not shown). Based on the program and mapping stored in the memory, and signals received from various sensors, the control circuit 100 controls the system main relay SMR and the control converter 20.

[0056] The control circuit 100 controls the driving state of the motor 3 and the charging and discharging of the battery 11 by periodically switching between the upper conduction state (the upper switching element is on and the lower switching element is off) and the lower conduction state (the upper switching element is off and the lower switching element is on) in each phase of the converter 20.

[0057] The control circuit 100 controls the switching operation of each phase of the converter 20 through pulse width modulation (PWM). In PWM control, the switching period of each phase (the sum of the duration of one on-state and one off-state) is determined according to the frequency of the carrier signal (carrier frequency fc). By adjusting the duty cycle command value in PWM control, the control circuit 100 can adjust the ratio of the on-state duration to one switching cycle (duty cycle).

[0058] <Discharge control of smoothing capacitor C0>

[0059] When the vehicle equipped with the power conversion system 1 stops operating or in the event of an accident, it is desirable to discharge the electrical energy (charge) stored in the smoothing capacitor C0 in advance.

[0060] When the smoothing capacitor C0 is discharged, and the battery 11 is disconnected from the converter 20 by disconnecting the system main relay SMR, the control circuit 100 alternately switches periodically between "all-phase up conduction control" which puts all-phase power modules 21, 22, and 23 of the converter 20 into the up conduction state and "all-phase down conduction control" which puts all-phase power modules 21, 22, and 23 into the down conduction state.

[0061] Figure 2 This diagram shows the waveforms of the phase currents Iu, Iv, and Iw when the power of the smoothing capacitor C0 is discharged, and the switching action between full-phase up-conduction control and full-phase down-conduction control.

[0062] like Figure 2 As shown, the control circuit 100 periodically switches between full-phase up-conduction control and full-phase down-conduction control while discharging the power of the smoothing capacitor C0. At this time, the duty cycle command value of each phase of the converter 20 is set to 50%, so that the period of full-phase up-conduction control relative to the switching cycle 1 in each phase is approximately 50%. By setting the duty cycle command value of each phase to 50% in this way, the voltage applied to the motor 3 can be made approximately 0 volts, so that current does not flow from the converter 20 to the motor 3 (i.e., so that the motor 3 does not output the positive torque required to drive the vehicle).

[0063] Furthermore, during the switching between all-phase up-conductance control and all-phase down-conductance control, the control circuit 100 performs feedforward control for discharging the power of the smoothing capacitor C0. Specifically, when setting the power modules with negative current flow in the three-phase power modules 21, 22, and 23 as negative current modules and the power modules with positive current flow as positive current modules, the control circuit 100 performs a "discharge process" for a predetermined time during the switching from one of all-phase down-conductance control and all-phase up-conductance control to the other, which simultaneously sets the negative current module to the down-conducting state and the positive current module to the up-conducting state.

[0064] When the control circuit 100 switches from full-phase down-conduction control to full-phase up-conduction control, it determines whether each power module 21, 22, and 23 is a negative current module or a positive current module, and then controls it in the order of mode A, mode B, and mode C.

[0065] First, in mode A, the control circuit 100 performs the first dead time processing of maintaining the negative current module in the lower conduction state while setting the first dead time DT1 to make both the upper and lower switching elements of the positive current module in the off state.

[0066] After the execution of the first dead-time processing, the control circuit 100 switches the control mode from mode A to mode B. In mode B, the control circuit 100 executes the aforementioned "discharge processing" for a predetermined time. Furthermore, the execution time (discharge processing time) of the discharge processing based on mode B is determined by [the following description]. Figure 27 The method described in the text is preset.

[0067] 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: while maintaining the positive current module in the upper conducting state, it sets a second dead time DT2 to make both the upper and lower switching elements of the negative current module in the off state.

[0068] Then, after the second dead time processing is completed, the control circuit 100 maintains the positive current module in the on state while switching the negative current module to the on state, and performs full-phase on-state control.

[0069] When the control circuit 100 switches from full-phase up-conduction control to full-phase down-conduction control, it performs control in the reverse order of switching from full-phase down-conduction control to full-phase up-conduction control, that is, in the order of mode C, mode B, and mode A.

[0070] Specifically, firstly, in mode C, the control circuit 100 performs the second dead time processing of setting the second dead time DT2 to make both the upper and lower switching elements of the negative current module turn off while maintaining the positive current module in the upper conducting state.

[0071] After the second dead-time processing is completed, the control circuit 100 switches the control mode from mode C to mode B. In mode B, the control circuit 100 performs the aforementioned "discharge processing" for a predetermined time.

[0072] 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 the following: while maintaining the negative current module in the lower conduction state, the first dead time DT1 is set to make both the upper and lower switching elements of the positive current module in the off state.

[0073] Then, after the execution of the first dead time processing, the control circuit 100 maintains the negative current module in the lower conduction state while switching the positive current module to the lower conduction state, and performs full-phase lower conduction control.

[0074] As a combination of positive and negative phase currents Iu, Iv, Iw (Iu, Iv, Iw), such as Figure 2 As shown, consider the following patterns 1 to 6.

[0075] Formula 1: (Iu, Iv, Iw) = (+, -, +)

[0076] Formula 2: (Iu, Iv, Iw) = (+, -, -)

[0077] Formula 3: (Iu, Iv, Iw) = (+, +, -)

[0078] Formula 4: (Iu, Iv, Iw) = (-, +, -)

[0079] Formula 5: (Iu, Iv, Iw) = (-, +, +)

[0080] Pattern 6: (Iu, Iv, Iw) = (-, -, +)

[0081] The following describes in detail the switching operations of switching elements Q1 to Q6 in the discharge control of smoothing capacitor C0, according to each of the patterns 1 to 6 of the positive and negative combinations of phase currents Iu, Iv, and Iw.

[0082] Figure 3 This is a diagram showing the drive signals of switching elements Q1 to Q6 in Formula 1: (Iu, Iv, Iw) = (+, -, +). In Formula 1, the power modules 21 and 23 of phase U and phase W are "positive current modules", and the power module 21 of phase V is a "negative current module".

[0083] When switching from full-phase down-conduction control to full-phase up-conduction control, control is performed in the order of Mode A, Mode B, and Mode C as described above.

[0084] First, in Mode A, the lower switching elements Q2 and Q6 of the power modules 21 and 23 (positive current modules) of phase U and phase W are turned off. Thus, while maintaining the negative current module in a lower conducting state, the first dead time DT1 of the positive current module is set. The first dead time DT1 lasts for a predetermined period.

[0085] Figure 4 This diagram schematically illustrates the current flow in Mode A (first dead time DT1) of Sample 1. In Mode A of Sample 1, a current circulation path is formed between the motor 3 and the converter 20. That is, the current from the motor 3 returns to the motor 3 through the lower switching element Q4 and the lower diodes D2 and D6. Therefore, the discharge current Idc of the smoothing capacitor C0 is 0. That is, in Mode A, even when the motor 3 is rotating (regenerative state), the smoothing capacitor C0 is not charged or discharged.

[0086] return Figure 3After the first dead time DT1, the system switches from mode A to mode B. In mode B, the upper switching elements Q1 and Q5 of the power modules 21 and 23 (positive current modules) of phase U and phase W are turned on. Thus, the negative current module becomes the lower conducting state, and the positive current module becomes the upper conducting state. This mode B is the aforementioned "discharge process." The discharge process is performed for a predetermined time.

[0087] Figure 5 This diagram schematically illustrates the current flow in Mode B (discharge process) of Sample 1. In Mode B of Sample 1, a discharge path is formed for the smoothing capacitor C0. That is, a current path is formed from the smoothing capacitor C0 through the upper switching elements Q1 and Q5, the motor 3, and the lower switching element Q4 back to the smoothing capacitor C0. In this case, the discharge current Idc of the smoothing capacitor C0 becomes |Iv|. That is, in Mode B, even when the motor 3 is rotating (regeneration state), the smoothing capacitor C0 is discharged.

[0088] return Figure 3 After performing the discharge process for a predetermined time, the system switches from mode B to mode C. In mode C, the lower switching element Q4 of the V-phase power module 22, which is the negative current module, is turned off. Thus, while maintaining the positive current module in the on-state, the second dead time DT2 of the negative current module is set. The second dead time DT2 lasts for a predetermined period.

[0089] Figure 6 This diagram schematically illustrates the current flow in Mode C (second dead time DT2) of Sample 1. In Mode C of Sample 1, a current circulation path is formed between the motor 3 and the converter 20. That is, the current from the motor 3 returns to the motor 3 through the upper diode D3, upper switching elements Q1 and Q5 of the converter 20. Therefore, the discharge current Idc of the smoothing capacitor C0 is 0. That is, in Mode C, even when the motor 3 is rotating (regenerative state), the regenerative power of the motor 3 does not charge the smoothing capacitor C0.

[0090] return Figure 3 After the execution of the second dead time DT2, while maintaining the U-phase and W-phase power modules 21 and 23 (positive current modules) in the on-state, the upper switching element Q1 of the V-phase power module 22 (negative current module) is switched to the on-state. Thus, the switching to full-phase on-state control is completed.

[0091] When switching from full-phase on-off control to full-phase off-off control, control is performed in the order of Mode C, Mode B, and Mode A as described above. Furthermore, the current flow in Modes A, B, and C of Scheme 1 is as described above. Figure 4 , Figure 5 , Figure 6As shown. Therefore, when switching from full-phase up-conduction control to full-phase down-conduction control, the smoothing capacitor C0 is not charged or discharged in modes A and C, while the smoothing capacitor C0 is discharged in mode B.

[0092] also, Figure 3 The drive signals shown in dashed lines are comparative examples relative to this disclosure, where only modes A and C are performed without mode B (discharge processing). In this case, the smoothing capacitor C0 in mode B (discharge processing) is not discharged.

[0093] In contrast, in this disclosure, a mode B (discharge process) is provided between mode A (first dead time DT1) and mode C (second dead time DT2). Therefore, in this disclosure, compared with the comparative example, the discharge of the smoothing capacitor C0 is promoted, and the smoothing capacitor C0 can be discharged further earlier.

[0094] Figure 7 This diagram illustrates the drive signals for switching elements Q1 to Q6 in Formula 2: (Iu, Iv, Iw) = (+, -, -). In Formula 2, the power module 21 of phase U is a "positive current module," and the power modules 22 and 23 of phases V and W are "negative current modules." Similar to Formula 1, in Formula 2, when switching from full-phase down-conduction control to full-phase up-conduction control, the first dead time DT1 of the positive current module is set in Mode A, the discharge process is performed for a predetermined time in subsequent Mode B, and the second dead time DT2 of the negative current module is set in subsequent Mode C. Similarly, when switching from full-phase up-conduction control to full-phase down-conduction control, the second dead time DT2 of the negative current module is set in Mode C, the discharge process is performed for a predetermined time in subsequent Mode B, and the first dead time DT1 of the positive current module is set in subsequent Mode A.

[0095] Figure 8 This is a diagram schematically illustrating the current flow in Mode A (first dead time DT1) of Pattern 2. Figure 9 This is a diagram schematically illustrating the flow of current in Mode B (discharge process) of Sample 2. Figure 10 This is a schematic diagram illustrating the current flow in mode C (second dead time DT2) of pattern 2. (See diagram below.) Figures 8-10 As shown, in Pattern 2, similar to Pattern 1, the smoothing capacitor C0 is not charged or discharged in Modes A and C, while in Mode B, the smoothing capacitor C0 is discharged.

[0096] Figure 11This diagram illustrates the drive signals for switching elements Q1 to Q6 in Formula 3: (Iu, Iv, Iw) = (+, +, -). In Formula 3, power modules 21 and 22 of phases U and V are "positive current modules," and power modules 22 and 23 of phase W are "negative current modules." Figure 11 As shown, in Sample 3, similar to Sample 1, when switching from full-phase down-conduction control to full-phase up-conduction control, control is performed in the order of modes A, B, and C; when switching from full-phase up-conduction control to full-phase down-conduction control, control is performed in the order of modes C, B, and A.

[0097] Figure 12 This is a diagram schematically illustrating the current flow in Mode A (first dead time DT1) of Pattern 3. Figure 13 This is a diagram schematically illustrating the flow of current in Mode B (discharge process) of Pattern 3. Figure 14 This is a schematic diagram illustrating the current flow in mode C (second dead time DT2) of pattern 3. (See diagram below.) Figures 12-14 As shown, in Pattern 3, similar to Pattern 1, the smoothing capacitor C0 is not charged or discharged in Modes A and C, while in Mode B, the smoothing capacitor C0 is discharged.

[0098] Figure 15 This is a diagram showing the drive signals of switching elements Q1 to Q6 in Formula 4: (Iu, Iv, Iw) = (-, +, -). In Formula 4, the power module 22 of phase V is a "positive current module", and the power modules 21 and 23 of phase U and phase W are "negative current modules".

[0099] like Figure 15 As shown, in Sample 4, similar to Sample 1, when switching from full-phase down-conduction control to full-phase up-conduction control, control is performed in the order of modes A, B, and C; when switching from full-phase up-conduction control to full-phase down-conduction control, control is performed in the order of modes C, B, and A.

[0100] Figure 16 This is a diagram schematically illustrating the current flow in Mode A (first dead time DT1) of Pattern 4. Figure 17 This is a diagram schematically illustrating the flow of current in Mode B (discharge process) of Pattern 4. Figure 18 This is a schematic diagram illustrating the current flow in mode C (second dead time DT2) of pattern 4. (See diagram below.) Figures 16-18 As shown, in Pattern 4, similar to Pattern 1, the smoothing capacitor C0 is not charged or discharged in Patterns A and C, while in Pattern B, the smoothing capacitor C0 is discharged.

[0101] Figure 19This diagram illustrates the drive signals for switching elements Q1 to Q6 in Formula 5: (Iu, Iv, Iw) = (-, +, +). In Formula 5, power modules 22 and 23 for phases V and W are "positive current modules," and power module 21 for phase U is a "negative current module." Figure 19 As shown, in Model 5, similar to Model 1, when switching from full-phase down-conduction control to full-phase up-conduction control, control is performed in the order of Mode A, B, C; when switching from full-phase up-conduction control to full-phase down-conduction control, control is performed in the order of Mode C, B, A.

[0102] Figure 20 This is a diagram schematically illustrating the current flow in Mode A (first dead time DT1) of Pattern 5. Figure 21 This is a diagram schematically illustrating the flow of current in Mode B (discharge process) of Pattern 5. Figure 22 This is a schematic diagram illustrating the current flow in mode C (second dead time DT2) of pattern 5. (See diagram below.) Figures 20-22 As shown, in Pattern 5, similar to Pattern 1, the smoothing capacitor C0 is not charged or discharged in Modes A and C, while in Mode B, the smoothing capacitor C0 is discharged.

[0103] Figure 23 This diagram illustrates the drive signals for switching elements Q1 to Q6 in Formula 6: (Iu, Iv, Iw) = (-, -, +). In Formula 6, the power module 23 of phase W is a "positive current module," and the power modules 21 and 22 of phases U and V are "negative current modules." Figure 23 As shown, in Sample 6, similar to Sample 1, when switching from full-phase down-conduction control to full-phase up-conduction control, control is performed in the order of modes A, B, and C; when switching from full-phase up-conduction control to full-phase down-conduction control, control is performed in the order of modes C, B, and A.

[0104] Figure 24 This is a diagram schematically illustrating the current flow in Mode A (first dead time DT1) of Pattern 6. Figure 25 This is a diagram schematically illustrating the flow of current in Mode B (discharge process) of Pattern 6. Figure 26 This is a schematic diagram illustrating the current flow in mode C (second dead time DT2) of pattern 6. (See diagram below.) Figures 24-26 As shown, in Pattern 6, similar to Pattern 1, the smoothing capacitor C0 is not charged or discharged in Modes A and C, while in Mode B, the smoothing capacitor C0 is discharged.

[0105] <Setting the discharge processing time>

[0106] In Mode B described above, the control circuit 100 performs the "discharge process" for a predetermined time. Furthermore, the execution time (discharge process time) of the discharge process based on Mode B is preset such that the output torque of the motor 3 becomes a negative torque and the power of the smoothing capacitor C0 is discharged.

[0107] Figure 27 This is a diagram illustrating an example of the relationship between the discharge processing time based on mode B, the discharge current Idc of the smoothing capacitor C0, and the output torque (hereinafter also referred to as "M torque") of the motor 3 when the motor speed is 100 rpm, 1000 rpm, 2000 rpm, and 3000 rpm.

[0108] exist Figure 27 The upper section shows the relationship between discharge processing time (horizontal axis) and discharge current Idc (vertical axis) for each rotational speed of motor 3. Figure 27 The lower section shows the relationship between discharge processing time (horizontal axis) and M torque (vertical axis) for each speed of motor 3. Figure 27 The correspondence shown can be obtained, for example, through simulation or experimentation.

[0109] In addition, Figure 27 In the above, a positive discharge current Idc indicates that the smoothing capacitor C0 is being discharged, while a negative discharge current Idc indicates that the smoothing capacitor C0 is being charged. Additionally, in... Figure 27 In the diagram, a positive value for the torque M indicates that motor 3 is in power operation mode, while a negative value for the torque M indicates that motor 3 is in regenerative mode.

[0110] In obtaining such Figure 27 In the case shown, 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 positive and the smoothing capacitor C0 is discharged, and the torque M becomes negative and the motor 3 generates negative torque.

[0111] In view of this, in this embodiment, the discharge processing time (the execution time of mode B) is set to include the following time periods ( Figure 27 In the "discharge negative torque region" shown, during this time period, the motor 3 is at a speed less than a predetermined speed (the predetermined speed is, for example, at...). Figure 27 In the example shown (at 2000 rpm), the output torque of motor 3 becomes negative, and the power of smoothing capacitor C0 is discharged. Therefore, even when motor 3 is rotating, during the discharge process (in execution of mode B), it is possible to discharge smoothing capacitor C0 while generating negative torque in motor 3, thereby causing the vehicle to stop.

[0112] <Function Block>

[0113] Figure 28 This is a functional block diagram of the control circuit 100 when it controls the discharge of the smoothing capacitor C0. The control circuit 100 includes an instruction generation unit 110, a current prediction unit 120, a mode setting unit, a correction unit 140, and a PWM control unit 150.

[0114] When the vehicle stops or an accident occurs, a command (hereinafter also referred to as a "discharge command") for discharging the smoothing capacitor C0 is input to the command generation unit 110 and the current prediction unit 120.

[0115] When the command generation unit 110 receives a discharge command, it generates U-phase duty cycle command values ​​Duc, V-phase duty cycle command value Dvc, and W-phase duty cycle command value Dwc for periodically switching between all-phase up-conduction control and all-phase down-conduction control. Each duty cycle command value (Duc, Dvc, Dwc) is in phase with the others and is set to 50%. The command generation unit 110 outputs the generated duty cycle command values ​​Duc, Dvc, and Dwc to the correction unit 140.

[0116] When the current prediction unit 120 receives a discharge command, it predicts the phase currents Iu, Iv, and Iw in the next operation cycle of PWM control based on the historical records of the phase currents Iu, Iv, and Iw detected by the current sensors 31 to 33, and outputs the prediction result together with the detection results of the current sensors 31 to 33 to the mode setting unit 130.

[0117] Based on the prediction results of phase currents Iu, Iv, and Iw, the mode setting unit 130 determines patterns 1 to 6 of positive and negative combinations of phase currents Iu, Iv, and Iw, and sets the processing order and processing content of the aforementioned modes A, B, and C based on the determined patterns. Furthermore, the method for setting the processing order and processing content of modes A, B, and C is as already explained.

[0118] The correction unit 140 corrects the 50% duty cycle command values ​​Duc, Dvc, and Dwc obtained from the command generation unit 110 based on the processing order and processing content of modes A, B, and C obtained from the mode setting unit 130. The correction unit 140 outputs the corrected duty cycle command values ​​Du, Dv, and Dw to the PWM control unit 150.

[0119] The PWM control unit 150 controls the switching elements Q1 to Q6 of the converter 20 based on the corrected duty cycle command values ​​Du, Dv, and Dw obtained from the correction unit 140. Thus, the aforementioned... Figures 3 to 26 As explained in the control, the smoothing capacitor C0 is discharged.

[0120] <Flowchart>

[0121] Figure 29 This is a flowchart illustrating an example of the processing steps in which the control circuit 100 controls the discharge of the smoothing capacitor C0. Figure 29 The flowchart shown is executed repeatedly at predetermined operation cycles when the system's main relay SMR is disconnected.

[0122] The control circuit 100 acquires the phase currents Iu, Iv, and Iw detected by the current sensors 31 to 33 (step S10).

[0123] Next, the control circuit 100 predicts the phase currents Iu, Iv, and Iw in the next operation cycle of PWM control based on the historical records of the phase currents Iu, Iv, and Iw detected by the current sensors 31-33 (step S20).

[0124] Next, the control circuit 100 determines which of the above-described patterns 1 to 6 the positive and negative combinations (Iu, Iv, Iw) of the phase currents Iu, Iv, and Iw predicted in step S02 conforms to (steps S21 to S26). Then, the control circuit 100 performs the above-described steps based on the determined positive and negative combinations of the phase currents Iu, Iv, and Iw. Figures 3 to 26 The mode settings described in the previous section (steps S31 to S36).

[0125] For example, when the combination of positive and negative phase currents Iu, Iv, and Iw (Iu, Iv, Iw) is (+, -, +) ("Yes" in step S21), the control circuit 100 performs the above-described... Figures 3-6 The discharge control of the smoothing capacitor C0 is performed using the mode setting shown in Pattern 1 (step S31). When the combination of positive and negative phase currents Iu, Iv, and Iw (Iu, Iv, Iw) is (+, -, -) ("Yes" in step S22), the control circuit 100 performs the above-described... Figures 7-10 The discharge control of the smoothing capacitor C0 is performed using the mode setting shown in Pattern 2 (step S32). The same applies to other combinations.

[0126] As described above, the control circuit 100 of this embodiment periodically switches between full-phase up-conduction control and full-phase down-conduction control while discharging the power of the smoothing capacitor C0. At this time, the control circuit 100 sets the duty cycle command value of each phase of the converter 20 to 50%, so that the period of full-phase up-conduction control is approximately 50% relative to the switching cycle 1 (the sum of one full-phase up-conduction control period and the full-phase down-conduction control period). This allows the voltage applied to the motor 3 to be approximately 0 volts, preventing the power of the smoothing capacitor C0 from being supplied to the motor 3.

[0127] Furthermore, in this embodiment, the control circuit 100, during the switching between full-phase up-conduction control and full-phase down-conduction control, sets the first dead time DT1 (mode A), the discharge processing time (mode B), and the second dead time DT2 (mode C) in either this order or the reverse order, as described above. Therefore, compared to the case where a full-phase cutoff period is set during the switching between full-phase up-conduction control and full-phase down-conduction control, the smoothing capacitor C0 can be discharged even earlier and more reliably.

[0128] That is, assuming a full off period is set during the switching between full-phase upper conduction control and full-phase lower conduction control, when the motor 3 is rotating using the vehicle's driving energy, the regenerative power of the motor 3 will charge the smoothing capacitor C0 through the converter 20 during the full off period. Due to this effect, it may be impossible to discharge the power of the smoothing capacitor C0 in advance.

[0129] In contrast, the control circuit 100 of this embodiment does not set a full-off period during the switching between full-phase up-conduction control and full-phase down-conduction control. Instead, as described above, the first dead time DT1, the discharge processing period, and the second dead time DT2 are set in either this order or the reverse order. During any of these periods, as described above, the regenerative power of the motor 3 does not charge the smoothing capacitor C0. Furthermore, during the discharge processing period (mode B), the smoothing capacitor C0 is discharged even when the motor 3 is in regenerative mode. As a result, without providing a dedicated discharge circuit, the smoothing capacitor C0 can be discharged earlier and more reliably.

[0130] Furthermore, in this embodiment, the aforementioned discharge processing time (execution time of mode B) is pre-adjusted to the time during which the output torque of motor 3 becomes negative while motor 3 is rotating, and the power of smoothing capacitor C0 is discharged (refer to the above). Figure 27 Therefore, during the discharge process (in the execution of mode B), the motor 3 will not generate positive torque, allowing the smoothing capacitor C0 to discharge more effectively.

[0131] Furthermore, in the discharge control of the smoothing capacitor C0 in this embodiment, the detection signal of the resolver (not shown) that detects the rotation angle of the motor 3 is not used. Therefore, even if the control circuit 100 cannot grasp the rotation angle of the motor 3 due to a break in the signal line connecting the resolver to the control circuit 100, the smoothing capacitor C0 can still be discharged.

[0132] [Variation Example]

[0133] In the above-described embodiment, the switching period between the full-phase up-conduction control period and the full-phase down-conduction control period is set to a certain (fixed). In contrast, in this modified example, the switching period between the full-phase up-conduction control period and the full-phase down-conduction control period is varied according to the magnitude of the current flowing in the motor 3.

[0134] Figure 30 This is a time diagram illustrating an example of the changing pattern of the switching cycle during the full-phase up-conduction control period and the full-phase down-conduction control period, based on this variation. Figure 30 The upper section shows the duty cycle command values ​​for each phase of converter 20. Figure 30 The lower section shows the maximum values ​​(maximum current values) of the phase currents Iu, Iv, and Iw, representing the current flowing in motor 3.

[0135] At the moment t1 when the control circuit 100 receives the discharge command, the maximum current value is greater than the first threshold th1. In this state, the motor 3 rotates at a high speed, and the motor 3 may generate positive torque.

[0136] Therefore, when the maximum current value is greater than the first threshold th1, the control circuit 100 sets the switching frequency mode to Lo mode. In Lo mode, the switching frequency between the full-phase up-conduction control period and the full-phase down-conduction control period is set to a frequency f0 lower than the carrier frequency fc. That is, in Lo mode, the period when the duty command value is fixed at 100% (full-phase up-conduction control period) and the period when the duty command value is fixed at 0% (full-phase down-conduction control period) are switched with a period longer than the period determined by the carrier frequency fc (=1 / fc).

[0137] Therefore, when the maximum current value is greater than the first threshold th1 (when the motor 3 rotates at a high speed), the switching frequency between the full-phase up-conduction control period and the full-phase down-conduction control period is reduced. Correspondingly, the discharge frequency of the smoothing capacitor C0 based on the discharge process is reduced. As a result, it is easy to suppress the generation of positive torque by the motor 3.

[0138] Furthermore, the discharge amount of the smoothing capacitor C0 based on a single discharge process depends on the maximum current. Therefore, in Lo mode, although the frequency of discharge processes is low, the discharge amount of the smoothing capacitor C0 based on a single discharge process is large, so the overall discharge amount of the smoothing capacitor C0 will not decrease excessively.

[0139] Thereafter, when the rotational speed of the motor 3 decreases and the maximum current value decreases, the possibility that the motor 3 generates a positive torque becomes low. Therefore, when the maximum current value becomes less than the first threshold 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 full-phase upper conduction control period and the full-phase lower conduction control period is set to a frequency f1 higher than the frequency f0 in the Lo mode. Specifically, in the Mid mode, based on the state where the switching frequency between the full-phase upper conduction control period and the full-phase lower conduction control period is made to coincide with the carrier frequency fc, the carrier frequency fc is set to the frequency f1.

[0140] Thus, in a state where the maximum current value is less than the first threshold th1, compared with the case where the maximum current value is greater than or equal to the first threshold th1, the switching frequency between the full-phase upper conduction control period and the full-phase lower conduction control period increases. Therefore, correspondingly, the discharge frequency of the smoothing capacitor C0 based on the discharge process increases. Thus, although the discharge amount of the smoothing capacitor C0 based on one discharge process is small, the overall discharge amount of the smoothing capacitor C0 is ensured.

[0141] Thereafter, when the rotational speed of the motor 3 further decreases and the maximum current value further decreases, it is impossible to expect the discharge of the smoothing capacitor C0 achieved by the current flowing in the motor 3. Therefore, when the maximum current value becomes less than the second threshold 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 full-phase upper conduction control period and the full-phase lower conduction control period is set to a frequency f2 higher than the frequency f1 in the Mid mode. Specifically, in the Hi mode, based on the state where the switching frequency between the full-phase upper conduction control period and the full-phase lower conduction control period is made to coincide with the carrier frequency fc, the carrier frequency fc is set to the frequency f2. Thus, in a state where the maximum current value is less than the second threshold th2, the power of the smoothing capacitor C0 can be consumed through the switching loss of the converter 20.

[0142] In addition, in the Hi mode, since the power of the smoothing capacitor C0 is consumed through the switching loss of the converter 20 as described above, even when the cable connecting the converter 20 and the motor 3 is disconnected, the smoothing capacitor C0 can be discharged.

[0143] Figure 31 It is a flowchart showing an example of the processing steps performed by the control circuit 100 when setting the switching frequency mode in the discharge control of the smoothing capacitor C0. Figure 31 The shown flowchart is repeatedly executed at a predetermined operation cycle in the discharge control of the smoothing capacitor C0.

[0144] The control circuit 100 acquires the phase currents Iu, Iv, and Iw detected by the current sensors 31-33 (step S60). Next, the control circuit 100 determines the relationship between the maximum value (= maximum current value) of the phase currents Iu, Iv, and Iw detected by the current sensors 31-33 and the aforementioned first threshold th1 and second threshold th2 (steps S61-S63).

[0145] Then, the control circuit 100 determines the result based on the relationship between the maximum current value and the first threshold th1 and the second threshold th2, as described above. Figure 30 As explained earlier, the switching frequency mode is set (steps S71 to S73). Specifically, when the maximum current value is greater than the first threshold th1 ("Yes" in step S61), the control circuit 100 sets the switching frequency mode to the Lo mode described above (step S71). When the maximum current value is less than the first threshold th1 but greater than the second threshold th2 ("Yes" in step S62), the control circuit 100 sets the switching frequency mode to the Mid mode described above (step S72). When the maximum current value is less than the second threshold th2 ("Yes" in step S63), the control circuit 100 sets the switching frequency mode to the Hi mode described above (step S73).

[0146] As described above, the switching cycle between the full-phase upper conduction control period and the full-phase lower conduction control period can also be changed according to the magnitude of the current flowing in the motor 3.

[0147] Power modules 21, 22, and 23 can also be a single module, rather than separate modules.

[0148] Switching elements Q1 to Q6 can also be MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). In this case, diodes D1 to D6 can also be body diodes.

[0149] Embodiments of the present invention have been described, but should be considered illustrative rather than limiting in all respects. The scope of the invention is set forth in the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0150] The exemplary implementation methods and their variations described above are specific examples of the following solutions.

[0151] (1) The power conversion system based on this disclosure includes: a converter for converting power between a battery and a motor having three-phase stator coils; positive and negative lines connecting the battery and the converter; a smoothing capacitor disposed between the positive and negative lines; and a control circuit for controlling the converter. The converter includes a three-phase switching section connected in parallel between the positive and negative lines and respectively connected to the three-phase stator coils. Each phase of the switching section includes: an upper switching element and a lower switching element connected in series from the positive line to the negative line; and an upper diode and a lower diode connected in reverse parallel with the upper and lower switching elements, respectively. When the charge of the smoothing capacitor is discharged, the control circuit alternately switches periodically between full-phase upper conduction control (where all three phases of the switching section are in a state where the upper switching elements are turned on and the lower switching elements are turned off) and full-phase lower conduction control (where all three phases of the switching section are in a state where the upper switching elements are turned off and the lower switching elements are turned on). During the switching period between full-phase up-conduction control and full-phase down-conduction control, the control circuit controls the on / off states of the upper and lower switching elements of each phase in a manner different from that of full-phase up-conduction control and full-phase down-conduction control. The control is such that: at the beginning and end of the switching period, both the upper and lower switching elements in any phase are in the off state; between the beginning and end of the period, in each phase, it is either an up-conduction state where the upper switching element is on and the lower switching element is off, or a down-conduction state where the upper switching element is off and the lower switching element is on.

[0152] According to the configuration described in (1) above, during the discharge of the smoothing capacitor, the all-phase up-conduction control and the all-phase down-conduction control are alternately and periodically switched. Furthermore, between the beginning and end of the switching period between the all-phase down-conduction control and the all-phase up-conduction control, control is performed such that in each phase, the upper and lower switching elements are either in an up-conduction state (on and off respectively) or in a down-conduction state (off and on respectively). Through this control, even when the motor is rotating using the vehicle's driving energy, the smoothing capacitor is discharged. As a result, the smoothing capacitor can be discharged prematurely without a dedicated discharge circuit.

[0153] (2) In a certain scheme, when the phase in the three phases of the switch section in which the current flows from the motor to the converter is set as the negative current phase and the phase in which the current flows from the converter to the motor is set as the positive current phase, the control circuit performs a discharge process for a predetermined time during the period when switching from one of the full-phase lower conduction control and the full-phase upper conduction control to the other, which simultaneously makes the negative current phase become the lower conduction state and the positive current phase become the upper conduction state.

[0154] According to the configuration described in (2) above, during the initial and final stages of switching between all-phase down-conduction control and all-phase up-conduction control, a discharge process is performed at a predetermined time to simultaneously make the negative current phase become the down-conduction state and the positive current phase become the up-conduction state. During the execution of the discharge process, even when the electric generator is rotating using the vehicle's driving energy, the smoothing capacitor is in a discharged state. As a result, the smoothing capacitor can be discharged in advance without the need for a dedicated discharge circuit.

[0155] (3) In a certain scheme, when the control circuit switches from full-phase down-conduction control to full-phase up-conduction control, it performs a first dead-time process that keeps the negative current phase in the down-conduction state while making both the upper and lower switching elements of the positive current phase in the off state. After the execution of the first dead-time process, a discharge process is performed for a predetermined time. After the execution of the discharge process, a second dead-time process is performed that keeps the positive current phase in the up-conduction state while making both the upper and lower switching elements of the negative current phase in the off state. After the execution of the second dead-time process, the negative current phase is switched to the up-conduction state while keeping the positive current phase in the up-conduction state, and full-phase up-conduction control is performed.

[0156] (4) In a certain scheme, when the control circuit switches from full-phase on-conductance control to full-phase off-conductance control, it performs the second dead time processing. After the execution of the second dead time processing, it performs the discharge processing for a predetermined time. After the execution of the discharge processing, it performs the first dead time processing. After the execution of the first dead time processing, it switches the positive current phase to the off-conductance state while maintaining the negative current phase in the off-conductance state, and performs full-phase off-conductance control.

[0157] Based on the configurations in (3) and (4) above, during the switching between full-phase down-conduction control and full-phase up-conduction control, the first dead-time processing, the discharge processing period, and the second dead-time processing are set in this order or the reverse order. During the execution of any of these processes—the first dead-time processing, the discharge processing, and the second dead-time processing—the motor's regenerative power is not supplied to the smoothing capacitor. Furthermore, during the discharge processing, the smoothing capacitor is discharged even when the motor is rotating. As a result, the smoothing capacitor can be discharged earlier.

[0158] (5) In a certain scheme, the predetermined time is pre-adjusted to be the time when the output torque of the motor becomes negative while the motor is rotating and the power of the smoothing capacitor is discharged.

[0159] According to the configuration described in (5) above, the predetermined time (execution time of the discharge process) is pre-adjusted to be the time when the output torque of the motor becomes negative while the motor is rotating and the power of the smoothing capacitor is discharged. Therefore, during the execution of the discharge process, the motor will not generate positive torque, and the power of the smoothing capacitor can be discharged.

[0160] (6) In a certain scheme, when the control circuit discharges the power of the smoothing capacitor, the larger the current flowing in the motor, the longer the switching cycle between the full-phase down conduction control and the full-phase up conduction control.

[0161] Based on the configuration described in (6) above, when the current flowing in the motor is large during the discharge of the smoothing capacitor (i.e., when the motor speed is high), the motor may generate positive torque. Therefore, the larger the current flowing in the motor, the longer the switching cycle between the full-phase down-conduction control and the full-phase up-conduction control. Consequently, when the motor speed is high, the switching frequency between the full-phase up-conduction control and the full-phase down-conduction control is reduced, and correspondingly, the discharge frequency of the smoothing capacitor based on the discharge process is reduced. Therefore, even when the current flowing in the motor is large (when the motor speed is high), it is easy to suppress the generation of positive torque in the motor.

[0162] Furthermore, according to the configuration described in (6) above, when the current flowing in the motor is small during the discharge of the smoothing capacitor (i.e., when the motor speed is low), it is impossible to expect the smoothing capacitor to discharge through the current flowing in the motor. Therefore, the smaller the current flowing in the motor, the shorter the switching cycle between all-phase down-conduction control and all-phase up-conduction control. Thus, when the current flowing in the motor is small (when the motor speed is low), the power of the smoothing capacitor can be consumed through the switching losses of the converter.

[0163] (7) In one embodiment, when the power of the smoothing capacitor is discharged, and the current flowing in the motor is between a first threshold and a second threshold smaller than the first threshold, the switching period between all-phase down-conduction control and all-phase up-conduction control is set to the first period. When the current flowing in the motor is greater than the first threshold, the switching period between all-phase down-conduction control and all-phase up-conduction control is set to the second period, which is longer than the first period. When the current flowing in the motor is less than the second threshold, the switching period between all-phase down-conduction control and all-phase up-conduction control is set to the third period, which is shorter than the first period.

[0164] Based on the configuration described in (7) above, when the current flowing in the motor during the discharge of the smoothing capacitor is greater than the first threshold (i.e., when the motor speed is high), the switching cycle between the full-phase down-conduction control and the full-phase up-conduction control is set to a second cycle that is longer than the first cycle. Therefore, when the motor speed is high, the switching frequency between the full-phase up-conduction control and the full-phase down-conduction control is reduced, and correspondingly, the discharge frequency of the smoothing capacitor based on the discharge process is reduced. Consequently, it is easier to suppress the generation of positive torque in the motor.

[0165] Furthermore, according to the configuration described in (7) above, when the current flowing in the motor during the discharge of the smoothing capacitor is smaller than the second threshold (i.e., when the motor speed is low), the switching cycle between the full-phase down-conduction control and the full-phase up-conduction control is set to a third cycle, which is shorter than the first cycle. Thus, even when the current flowing in the motor is small (when the motor speed is low), the power of the smoothing capacitor can be consumed through the switching losses of the converter.

Claims

1. A power conversion system, comprising: A converter that performs power conversion between a battery and a motor with three-phase stator coils; The positive and negative wires connect the battery to the converter. A smoothing capacitor is disposed between the positive electrode line and the negative electrode line; as well as The control circuit controls the converter. The converter includes a three-phase switching section, which is connected in parallel between the positive and negative lines and is respectively connected to the stator coils of the three phases. Each phase of the switching section includes: The upper and lower switching elements are connected in series from the positive line to the negative line. and The upper diode and the lower diode are connected in reverse parallel with the upper switching element and the lower switching element, respectively. When the control circuit discharges the charge of the smoothing capacitor, The system alternately switches between full-phase up-conduction control and full-phase down-conduction control periodically. Full-phase up-conduction control ensures that all three phases of the switching unit are in a state where the upper switching element is on and the lower switching element is off. Full-phase down-conduction control ensures that all three phases of the switching unit are in a state where the upper switching element is off and the lower switching element is on. During the switching from one of the full-phase up-conduction control and the full-phase down-conduction control to the other, the states of the upper and lower switching elements of each phase are controlled in a manner different from the full-phase up-conduction control and the full-phase down-conduction control, such that: at the beginning and end of the switching period, both the upper and lower switching elements in at least one phase are in a cut-off state; and between the beginning and the end, in each phase, either the upper switching element is in a conducting state and the lower switching element is in a cut-off state, or the upper switching element is in a cut-off state and the lower switching element is in a conducting state.

2. The power conversion system according to claim 1, When the phase in the three phases of the switching unit in which the current flows from the motor to the converter is designated as the negative current phase and the phase in which the current flows from the converter to the motor is designated as the positive current phase, the control circuit performs a discharge process for a predetermined time during the period when switching from one of the full-phase lower conduction control and the full-phase upper conduction control to the other. This process simultaneously makes the negative current phase become the lower conduction state and the positive current phase become the upper conduction state.

3. The power conversion system according to claim 2, When the control circuit switches from the full-phase lower conduction control to the full-phase upper conduction control... The process involves performing a first dead-time operation that simultaneously maintains the negative current phase in the lower on state while turning off both the upper and lower switching elements of the positive current phase. After the execution of the first dead-time processing, the discharge processing is performed at the predetermined time. After the discharge process is executed, a second dead-time process is performed that simultaneously maintains the positive current phase in the upper conducting state and makes both the upper and lower switching elements of the negative current phase in the off state. After the execution of the second dead time processing, while maintaining the positive current phase in the on-state, the negative current phase is switched to the on-state to perform the full-phase on-state control.

4. The power conversion system according to claim 3, When the control circuit switches from full-phase up-conduction control to full-phase down-conduction control... Perform the second dead time processing. After the execution of the second dead-time processing, the discharge processing is performed at the predetermined time. After the discharge process is executed, the first dead time process is executed. After the execution of the first dead time processing, while maintaining the negative current phase in the lower conduction state, the positive current phase is switched to the lower conduction state to execute the full-phase lower conduction control.

5. The power conversion system according to claim 2, The predetermined time is pre-adjusted to be the time during which the output torque of the motor becomes negative while the motor is rotating, and the charge of the smoothing capacitor is discharged.

6. The power conversion system according to any one of claims 1 to 5, When the control circuit discharges the charge of the smoothing capacitor, the greater the current flowing through the motor, the longer the switching cycle between the full-phase down-conduction control and the full-phase up-conduction control becomes.

7. The power conversion system according to claim 6, When the control circuit discharges the charge of the smoothing capacitor, If the current flowing through the motor is between a first threshold and a second threshold smaller than the first threshold, the switching period between the full-phase down-conduction control and the full-phase up-conduction control is set to the first period. If the current flowing through the motor is greater than the first threshold, the switching period between the full-phase down-conduction control and the full-phase up-conduction control is set to a second period that is longer than the first period. If the current flowing through the motor is less than the second threshold, the switching period between the full-phase down-conduction control and the full-phase up-conduction control is set to a third period, which is shorter than the first period.

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