Power conversion device and drive device

Abstract

To provide a power conversion device and a drive device capable of suppressing processing load and torque fluctuation during discharge.SOLUTION: A power conversion device 50 includes a capacitor (smoothing capacitor 31), a three phase bridge circuit connected in parallel to the capacitor and composed of a plurality of switching elements (power semiconductors 32), and a discharge control unit 16 for discharging electric charges accumulated in the capacitor to a motor 60 connected to the three phase bridge circuit. When the target angle indicating the sum of the electrical angle of the motor 60 and the phase angle (reference angle) passes through any axis line of the three phase stationary coordinate system, the discharge control unit 16 switches each switching element to the switching state for generating the composite voltage vector Vo in the direction of the axis line through which the target angle passes.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A capacitor is installed in the power conversion device and the drive device to stabilize the power supply when the device is operating. To prevent electric shock, a technique for discharging the charge of the capacitor installed in the power conversion device is known.

[0003] Patent Document 1 describes an invention relating to a main circuit power supply discharging method in which a current is passed through a motor to discharge a capacitor.

[0004] Patent Document 2 describes an invention for a motor control device and vehicle system that causes the charge stored in a capacitor placed between a power supply and ground to be consumed by the motor coil by turning on a combination of upper and lower transistors placed in different arms. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-89264 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-220286 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 uses conventional motor drive control to perform discharge, but current feedback is required to accurately perform motor drive control, which poses a problem of a large processing load for control.

[0007] Although Patent Document 2 lists combinations of upper and lower transistors that are turned on during discharge, it does not specifically specify which combination should be used to control discharge. Discharge itself can be achieved using any combination, but there is a risk of large torque fluctuations occurring during discharge.

[0008] An object of the present invention is to provide a power conversion device and a drive device that can suppress processing load and torque fluctuations during discharge. [Means for solving the problem]

[0009] In order to achieve the above object, one example of a power conversion device of the present invention includes a capacitor, a three-phase bridge circuit connected in parallel to the capacitor and consisting of a plurality of switching elements, and a discharge control unit that discharges the charge stored in the capacitor to a motor connected to the three-phase bridge circuit, and when a target angle indicating the sum of the electrical angle and phase angle of the motor passes through any of the axes of a three-phase stationary coordinate system, the discharge control unit switches each of the switching elements to a switching state that generates a resultant voltage vector in the direction of the axis through which the target angle passes. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the processing load and torque fluctuation during discharge. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a drive device for driving a vehicle. [Figure 2] 1 is a diagram illustrating an example of the configuration of a power conversion device and a driving device according to a first embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a power conversion circuit and a motor. [Figure 4] 4 is an example of a process flowchart of discharge control in the first embodiment. [Figure 5]3 is a diagram illustrating an example of a motor electrical angle and a switching state in the first embodiment. FIG. [Figure 6A] FIG. 1 is a diagram showing voltage vectors in a three-phase stationary coordinate system at an electrical angle of 0 degrees. [Figure 6B] FIG. 1 is a diagram showing voltage vectors in a rotating coordinate system (dq axes) at an electrical angle of 0 degrees. [Figure 7A] This is a diagram showing voltage vectors in a three-phase stationary coordinate system at an electrical angle of 60 degrees. [Figure 7B] FIG. 1 is a diagram showing voltage vectors in a rotating coordinate system (dq axes) at an electrical angle of 60 degrees. [Figure 8] FIG. 3 is a diagram illustrating an example of discharge control in the first embodiment. [Figure 9] FIG. 10 is a diagram showing an example of an electrical angle determination range α in the second embodiment. [Figure 10] This is a diagram showing the relationship between Vd and Vq to make Iq=0[A]. [Figure 11] 10 is a diagram illustrating an example of a motor electrical angle and a switching state in the third embodiment. FIG. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a power conversion device and a driving device according to a fourth embodiment. [Figure 13] 10 is an example of a process flowchart of discharge control in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Background of the Example) Examples 1 to 4 described below relate to discharge control using a motor in an on-board inverter (power conversion circuit), for example. In the event of a vehicle collision, etc., it is necessary to discharge the charge accumulated in the capacitor in the inverter to prevent electric shock. Because this discharge is related to safety, the processing must be implemented at ASIL (Automotive Safety Integrity Level). Conventional current feedback control allows discharge while controlling torque, but there is a problem in that the amount of processing required is large for execution by an ASIL-compliant microcomputer core (processor core). Discharge is also necessary when battery power is lost, but current feedback control requires many sensors, which creates the problem of high costs for backup power sources when battery power is lost.

[0013] (Basic principle of the embodiment) Setting the q-axis current to 0 can suppress torque fluctuations during discharge, and when the motor rotation speed is low, controlling the q-axis voltage to 0 can make the q-axis current = 0. In order to make the q-axis voltage = 0, the motor is operated using a switching pattern that is predetermined for each electrical angle of the motor.

[0014] (Example of basic configuration of embodiment) The discharge control unit controls the inverter (power conversion circuit) based on a switching pattern determined for each electrical angle of the motor, and discharges the charge in the capacitor within the inverter.

[0015] (Examples of Effects of the Examples) This technology allows control using only the motor angle sensor value, reducing the amount of control processing compared to conventional current feedback control. It also keeps torque fluctuations during discharge below the required value.

[0016] Example 1 In this embodiment, an example of a power conversion device and a drive device that can reduce the processing load of discharge control and also suppress torque fluctuations during discharge is shown.

[0017] FIG. 1 shows a drive system 100 for driving a vehicle.

[0018] This drive unit 100 is connected to the axle and contains a power converter, a motor, and a reducer. In response to the driver's operation of the accelerator pedal, the drive unit controls the power converter and the motor to generate driving force, which is then transmitted to the axle via the reducer.

[0019] 1, the drive unit 100 is installed on the axle of the front wheels of the vehicle, but it may also be installed on the axle of the rear wheels. Also, the drive unit 100 may be installed on each of the front and rear axles, or independent drive units 100 may be installed on each of the left and right wheels instead of on the axles.

[0020] Furthermore, a drive unit using a drive source other than the drive unit 100 shown in FIG. 1, for example, a drive unit using an engine, may be installed in parallel with the axle.

[0021] FIG. 2 is a diagram illustrating an example of the configuration of the power conversion device 50 and the driving device 100 according to the first embodiment.

[0022] The driving device 100 is surrounded by a control device 1, a DC power supply 2, and a switch 3. The control device 1 transmits information such as a target torque, an operation mode, and a discharge command to the driving device 100. In this embodiment, only one control device 1 is described, but multiple control devices may transmit and receive information.

[0023] The DC power supply 2 is a power supply for driving the motor 60 in the drive device 100, and is, for example, a battery.

[0024] The switch 3 controls the connection between the DC power supply 2 and the drive device 100. When the control device 1 outputs a discharge command, the switch 3 is in a non-connected state, and the connection between the DC power supply 2 and the drive device 100 is cut off. When the control device 1 does not output a discharge command, the switch 3 is in a connected state.

[0025] The driving device 100 includes a power converter 50, a motor 60, and a reducer (not shown). The reducer may be omitted.

[0026] The reducer serves to amplify the driving force of the motor 60 and transmit it to the axle or wheel. Motor 60 is a three-phase electric motor with three internal windings, and may be, for example, a synchronous motor using permanent magnets or an induction motor without permanent magnets. Motor 60 is equipped with a motor angle sensor 61 for measuring the angle of motor 60. Motor angle sensor 61 outputs the measured angle to power conversion device 50 as a motor angle sensor value.

[0027] The power conversion device 50 converts DC power obtained from the DC power supply 2 into AC power to drive the motor 60. The power conversion device 50 also has a function of converting the power of the motor 60 into DC power to charge the DC power supply 2. The power conversion device 50 has a control circuit 10, a driver circuit 20, a power conversion circuit 30, a DC voltage sensor 51, and an AC current sensor 52 inside.

[0028] The power conversion circuit 30 receives a drive signal from the driver circuit 20 to drive an internal power semiconductor and control the current flowing through the motor 60. The internal configuration of the power conversion circuit 30 will be described with reference to FIG.

[0029] 3 is a diagram showing an example of the configuration of the power conversion circuit 30 and the motor 60. The power conversion circuit 30 has a smoothing capacitor 31 and six power semiconductors 32 inside.

[0030] The power semiconductor 32 switches on / off in response to a drive signal input from the driver circuit 20, and converts DC power to AC power. Examples of the power semiconductor 32 include a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor).

[0031] The smoothing capacitor 31 is a capacitor that smoothes the current generated by turning on / off the power semiconductor 32 and suppresses ripples in the DC current supplied from the DC power supply 2 to the power conversion circuit 30. For example, an electrolytic capacitor or a film capacitor is used as this smoothing capacitor 31.

[0032] In this embodiment, the motor neutral point is floating, but it may be connected to the ground (not shown). Methods for connecting the motor neutral point to the ground include direct grounding, resistance grounding, compensation reactor grounding, and arc suppression reactor grounding.

[0033] The DC voltage sensor 51 shown in FIG. 2 is a sensor that measures the output voltage of the DC power supply 2, and outputs the measured voltage value to the control circuit 10 as a DC voltage sensor value.

[0034] The AC current sensors 52 are sensors that measure the AC current flowing through each phase (U phase, V phase, W phase) of the motor 60, and output the measured AC current of each phase as an AC current sensor value to the control circuit 10. In this embodiment, three AC current sensors 52 are provided, one for each phase, but AC current sensors 52 may be provided for only two phases. Because the relationship U phase current + V phase current + W phase current = 0 holds, when AC current sensors 52 are provided for only two phases, the control circuit 10 calculates the AC current sensor value for the remaining phase.

[0035] The driver circuit 20 receives a PWM (Pulse Width Modulation) signal output by the control circuit 10 and outputs a drive signal for switching the power semiconductor 32 on and off.

[0036] The control circuit 10 communicates with an external control device 1 and receives an operation mode, a target torque, and a discharge command from the control device 1. Based on the operation mode and target torque, the control circuit 10 controls the PWM signal so as to control the current of each phase output from the power conversion device 50 to a predetermined value, and drives the power conversion circuit 30 via the driver circuit 20. Based on the discharge command, the control circuit 10 also controls the PWM signal so as to discharge the charge accumulated in the smoothing capacitor 31 in the power conversion circuit 30 within a certain time period, and drives the power conversion circuit 30 via the driver circuit 20.

[0037] The control circuit 10 includes a processor such as a CPU (Central Processing Unit), storage devices such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and a communication circuit (not shown). The ROM may be an electrically erasable programmable ROM (EEPROM) or a flash ROM.

[0038] The control circuit 10 also includes a state control unit 11 , a target current calculation unit 12 , a current control unit 13 , a PWM signal generation unit 14 , a motor speed calculation unit 15 , and a discharge control unit 16 .

[0039] The motor speed calculation unit 15 calculates the motor rotation speed from the change in the motor angle sensor value, and outputs the calculated motor speed value to the target current calculation unit 12 .

[0040] The state control unit 11 transitions the operation state of the power conversion device 50 using the operation mode and the discharge command, and outputs the current operation state to the PWM signal generation unit 14. Examples of the operation state include a PWM state, a three-phase short-circuit state, a three-phase open state, and a discharge state.

[0041] Using the target torque, the DC voltage sensor value, and the motor speed value, the target current calculation unit 12 calculates the current value that should be passed through the motor 60 so that the motor outputs the same torque as the target torque, and outputs this current value as the target current value to the current control unit 13. This target current value is expressed, for example, in the form of a d-axis target current value and a q-axis target current value.

[0042] The current control unit 13 performs feedback control using the target current value, AC current sensor value, motor angle sensor value, and DC voltage sensor value so that the AC current flowing through the motor 60 follows the target current value, and calculates duty values ​​for three phases. Then, the current control unit 13 outputs the duty values ​​to the PWM signal generation unit 14.

[0043] The PWM signal generating unit 14 switches the signal to be output to the driver circuit 20 depending on the operating state output from the state control unit 11. The PWM signal generating unit 14 has an internal timer (not shown), and when the operating state is the PWM state, generates a PWM signal using this timer value and the duty of each phase output by the current control unit 13.

[0044] When the operating state is a three-phase open state, the PWM signal generating unit 14 generates a PWM signal that turns off all six power semiconductors 32 in the power conversion circuit 30.

[0045] When the operating state is a three-phase short-circuit state, the PWM signal generating unit 14 generates a PWM signal that turns off all of the upper arms and turns on all of the lower arms of the six power semiconductors 32 in the power conversion circuit 30, or a PWM signal that turns on all of the upper arms and turns off all of the lower arms.

[0046] When the operating state is the discharging state, the PWM signal generating unit 14 generates a PWM signal using the timer value and the duty of each phase output by the discharge control unit 16. Then, the PWM signal generating unit 14 outputs the generated PWM signal to the driver circuit 20. The discharge control unit 16 receives a discharge command and performs discharge control.

[0047] 4 is an example of a processing flowchart of discharge control in Example 1. This processing is performed at regular time intervals after the discharge control unit 16 receives a discharge command.

[0048] The discharge control unit 16 determines whether the value of the DC voltage sensor 51 is greater than the threshold value Th1 (S41). If the value of the DC voltage sensor 51 is greater than the threshold value Th1 (S41: Yes), the discharge control unit 16 determines that discharge is necessary and proceeds to angle determination processing (S42). If the value of the DC voltage sensor 51 is less than the threshold value Th1 (S41: No), the discharge control unit 16 determines that discharge is not necessary and outputs a duty of each phase so that the power conversion circuit 30 is in a three-phase short-circuit state (S45).

[0049] The discharge control unit 16 calculates the electrical angle of the motor 60 from the motor angle sensor value and the number of motor pole pairs, and determines whether the calculated motor electrical angle is within a predetermined range (S42). If the motor electrical angle is within the predetermined range (S42: Yes), the discharge control unit 16 outputs a duty for each phase so that the power conversion circuit 30 is in a switching state set for each electrical angle, in order to perform discharge (S43). If the motor electrical angle is outside the predetermined range (S42: No), the discharge control unit 16 outputs a duty for each phase so that the power conversion circuit 30 is in a three-phase short-circuit state (S44).

[0050] Fig. 5 is a diagram showing an example of the motor electrical angle and switching state in the first embodiment. In the example of Fig. 5, the electrical angle is divided into 60-degree intervals, and the switching state corresponding to each electrical angle is defined. In Fig. 5, α indicates the determination range of the electrical angle, and is set taking into consideration the error of the motor angle sensor 61 and the execution cycle of the discharge control.

[0051] The switching states in Figure 5 are set for the purpose of stabilizing torque during discharge. The output torque T of the synchronous motor is expressed by equation (1), where Pp is the number of pole pairs of motor 60, Φ is the magnetic flux of motor 60, Ld is the d-axis inductance of motor 60, Lq is the q-axis inductance of motor 60, Id is the d-axis current flowing through motor 60, and Iq is the q-axis current flowing through motor 60. From equation (1), if Iq = 0 [A] and |Id| > 0 [A], current flows through motor 60 while keeping the motor output torque at 0 [Nm], and discharge is possible.

[0052] The relationship between the voltage and current of the motor 60 is expressed by equation (2), where R is the winding resistance, ω is the electrical angular velocity of the motor 60, and P is the differential coefficient. By eliminating the differential term and solving equation (2) for a steady state, equation (3) can be derived. Assuming that the rotational speed of the motor 60 is small and ω is close to 0, equation (3) can be simplified to equation (4). From equation (4), if Vq = 0 [V] and |Vd| > 0 [V], then Iq = 0 [A] and |Id| > 0 [A] can be achieved.

[0053]

number

[0054]

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[0055]

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[0056]

number

[0057] The switching control of Fig. 5 will be explained using voltage vector diagrams. Figs. 6A and 6B are diagrams showing voltage vectors at an electrical angle of 0 degrees. Fig. 6A is a vector diagram in a three-phase stationary coordinate system, and Fig. 6B is a vector diagram in a rotating coordinate system (dq axes). When the electrical angle is 0 degrees, the state overlaps with the axis of the U phase, and at this time, the control of Fig. 5 turns on the power semiconductors 32 on the lower side of the U phase, the upper side of the V phase, and the upper side of the W phase.

[0058] When the upper power semiconductor 32 is turned on, a voltage vector is generated in the positive direction, and when the lower power semiconductor 32 is turned on, a voltage vector is generated in the negative direction. If the three-phase switching state is described in a three-phase stationary coordinate system, the three-phase composite voltage vector Vo is generated on the negative side of the U-phase axis. If this is converted to a rotating coordinate system of the dq axes, Vd<0 [V] and Vq=0 [V], and therefore, from the above explanation, Id<0 [A] and Iq=0 [A].

[0059] 7A and 7B are diagrams showing voltage vectors at an electrical angle of 60 degrees. FIG. 7A is a vector diagram in a three-phase stationary coordinate system, and FIG. 7B is a vector diagram in a rotating coordinate system (dq axes). When the electrical angle is 60 degrees, the voltage vectors overlap with the W-phase axis. At this time, the control in FIG. 5 turns on the power semiconductors 32 on the lower side of the U-phase, the lower side of the V-phase, and the upper side of the W-phase. When this three-phase switching state is depicted in a three-phase stationary coordinate system, the three-phase composite voltage vector Vo is generated on the positive side of the W-phase axis. When this is converted to a rotating coordinate system with dq axes, Vd<0 [V] and Vq=0 [V], just as when the electrical angle is 0 degrees.

[0060] In this way, in the discharge control of this embodiment, when the motor electrical angle overlaps with the axis of any of the phases in the three-phase stationary coordinate system, the switching state of the power semiconductor 32 is controlled to generate a voltage vector of the overlapping phase, and discharge is performed. Then, when the electrical angle deviates from the axis of any of the phases in the three-phase stationary coordinate system by a certain amount or more, a transition to a three-phase short-circuit state occurs, and discharge is stopped.

[0061] By doing this, when the motor rotation speed is low, |Id|>0 [A] and Iq≈0 [A] can be maintained during discharge, and discharge can be performed while maintaining the motor output torque between the torque when three phases are shorted and 0 [Nm]. Furthermore, in the discharge control of this embodiment, switching control is performed using only the motor angle, and no current feedback is performed, so the processing load of the discharge control can be reduced compared to when discharge is performed using conventional current feedback control.

[0062] 5 in this embodiment, control is performed so that Vd<0 [V] and Vq=0 [V] in order to suppress torque fluctuations during discharge, but control may also be performed so that Vd>0 [V] and Vq=0 [V]. However, when switching between the discharge state and the three-phase short-circuit state based on the electrical angle, as in the present invention, discharge can be completed in a shorter time by controlling so that Vd<0 [V].

[0063] In a three-phase short-circuit state, Id<0[A] and Iq<0[A], but if control is performed from this state so that Vd>0[V], Id changes from negative to positive. Therefore, immediately after switching from a three-phase short-circuit state to discharge control, the absolute value of Id decreases and the amount of discharge also decreases. If control is performed so that Vd<0[V], Id remains negative, so a large amount of discharge can be maintained even immediately after switching from a three-phase short-circuit state to a discharge state.

[0064] Furthermore, in the example of FIG. 5, the switching state does not need to be maintained constantly when the electrical angle is within a specific range, but may be switched to a three-phase short-circuit state at regular intervals. For example, instead of always having the U-phase lower side on, the V-phase upper side on, and the W-phase upper side on when the motor electrical angle is 0 degrees, the U-phase lower side, the V-phase upper side, and the W-phase upper side may be on for half the time of the discharge control period, and the three-phase short-circuit state may be maintained for the other half. When the motor rotation speed is high, the method of this embodiment increases torque fluctuations as the discharge time increases. Therefore, by dividing the discharge time into shorter periods, torque fluctuations during discharge can be suppressed.

[0065] Fig. 8 is a diagram showing an example of discharge control in the first embodiment. The upper graph in Fig. 8 shows the output torque of the motor 60, the middle graph shows Vd input to the motor 60, and the lower graph shows Vq input to the motor 60. In the upper graph in Fig. 8, the solid line shows the motor output torque, and the dashed line shows the three-phase short-circuit torque. The three-phase short-circuit torque is the torque generated by the motor when only three-phase short-circuiting is performed without performing discharge.

[0066] In the figure, the time periods when Vd and Vq are other than 0 [V] are the time periods when discharging is actually occurring, and the time periods when Vd = 0 [V] and Vq = 0 [V] are the time periods when discharging is not occurring in a three-phase short circuit state. In this example, there are moments when regenerative torque greater than the three-phase short circuit torque is temporarily generated during discharging, but when discharging transitions to a three-phase short circuit, the regenerative torque weakens compared to the three-phase short circuit torque, and for most of the time when discharging and three-phase short circuiting are repeated, a regenerative torque smaller than the regenerative torque generated by the three-phase short circuit is generated. By weakening the regenerative torque through discharging in this way, it is possible to avoid situations where the vehicle decelerates significantly due to discharging.

[0067] The main features of the first embodiment can be summarized as follows.

[0068] The power conversion device 50 includes a capacitor (smoothing capacitor 31), a three-phase bridge circuit connected in parallel to the capacitor and composed of multiple switching elements (power semiconductors 32), and a discharge control unit 16 that discharges the charge stored in the capacitor to a motor 60 connected to the three-phase bridge circuit (FIGS. 2 and 3). When a target angle indicating the sum of the electrical angle and phase angle (reference angle) of the motor 60 passes through any axis of a three-phase stationary coordinate system, the discharge control unit 16 switches each switching element to a switching state that generates a resultant voltage vector Vo in the direction of the axis through which the target angle passes (FIGS. 6A, 6B, etc.).

[0069] When the rotational speed of the motor 60 is low (ω≈0, phase angle (reference angle) = 0 degrees), in a switching state that generates a resultant voltage vector Vo in the direction of the axis through which the target angle (electrical angle) passes, Vq = 0 [V] (see, e.g., FIGS. 6B and 7B) and Iq = 0 [A]. By setting Iq = 0 [A], torque fluctuations during discharge are suppressed. Furthermore, by using only the motor angle sensor value as input, the processing load of discharge control can be reduced compared to current feedback control. Note that, although the phase angle (reference angle) is 0 degrees in the first embodiment, it may be an angle in the range of 0 to 90 electrical degrees that is set according to the rotational speed (electrical angular velocity ω) of the motor 60 (see, e.g., the third embodiment described below).

[0070] Specifically, as shown in FIG. 6A, the resultant voltage vector Vo is synthesized from voltage vectors (Vu, Vv, Vw) in the directions of the respective axes of the three-phase stationary coordinate system. In the switching state, when the direction of the voltage vector (e.g., Vv, Vw, FIG. 6A) is positive, the switching elements (power semiconductors 32) of the upper arms of the three-phase bridge circuit for the phase (e.g., V phase, W phase) corresponding to the voltage vector are turned on (upper on, FIG. 5), and the switching elements of the lower arms of the three-phase bridge circuit for the phase (e.g., V phase, W phase) corresponding to the voltage vector are turned off. In addition, in the switching state, when the direction of the voltage vector (e.g., Vu, FIG. 6A) is negative, the switching elements of the lower arms of the three-phase bridge circuit for the phase (e.g., U phase) corresponding to the voltage vector are turned on (lower on, FIG. 5), and the switching elements of the upper arms of the three-phase bridge circuit for the phase (e.g., U phase) corresponding to the voltage vector are turned off.

[0071] As a result, Vq becomes 0 [V] (FIGS. 6B, 7B, etc.) and Iq becomes 0 [A]. By making Iq = 0 [A], torque fluctuations during discharge are suppressed.

[0072] During a period when the target angle is away from any axis of the three-phase stationary coordinate system by a predetermined electrical angle (α, FIG. 5) or more (S42: No, FIG. 4), the discharge control unit 16 executes a three-phase short circuit by simultaneously turning on the switching elements (power semiconductors 32) of either the upper arm or the lower arm of the three-phase bridge circuit (S44, FIG. 4), thereby intermittently stopping the discharge of the capacitor (smoothing capacitor 31).

[0073] If discharge occurs during a period when the target angle is more than a certain electrical angle (α, Figure 5) away from one of the axes in the three-phase stationary coordinate system, Vq ≠ 0 [V], and torque fluctuations become large. Torque fluctuations can be suppressed by stopping discharge during this period.

[0074] 8, the torque generated by the motor 60 during a predetermined period up to the timing when the three-phase short circuit is executed during the period when the capacitor (smoothing capacitor 31) is discharged is equal to or less than the three-phase short circuit torque that indicates the torque generated by the motor 60 when only the three-phase short circuit is executed. This makes it possible to suppress torque fluctuations.

[0075] 2, the driving device 100 includes a power conversion device 50 and a motor 60. This makes it possible to drive the motor 60 using the power conversion device 50, which can suppress processing load and torque fluctuations during discharge.

[0076] Example 2 In this embodiment, an example of a power conversion device 50 and a driving device 100 that are capable of discharging even when the motor is stopped is shown.

[0077] In the first embodiment, discharge is performed when the motor electrical angle falls within a predetermined range, and when the motor electrical angle deviates from the predetermined range, the system transitions to a three-phase short-circuit state and stops discharging. However, when the motor 60 is stopped, the motor electrical angle does not change, which creates a problem in that discharge is not possible if the motor is stopped with the motor electrical angle deviating from the predetermined range. Furthermore, when the motor rotation speed is extremely slow, it takes a long time for the motor electrical angle to fall within the predetermined range, and there is a possibility that discharging may not be completed within the certain time.

[0078] To solve the above problem, in this embodiment, the electrical angle determination range α is changed depending on the motor rotation speed. Fig. 9 is a diagram showing an example of the electrical angle determination range α in the second embodiment. When the motor rotation speed is less than a threshold value Th2, α is set to 30 degrees, and when the motor rotation speed is equal to or greater than the threshold value Th2, α is set to 5 degrees. In the example of Fig. 5, when α is set to 30 degrees, the motor electrical angle always falls within one of the electrical angle ranges regardless of its value, so that discharge is possible even when the motor 60 is stopped.

[0079] On the other hand, if the electrical angle judgment range α is increased, discharge will be performed even in a range where Vq cannot be set to 0 V, and torque fluctuations will increase during discharge. Therefore, when the motor rotation speed is above a certain level, it is desirable to reduce the electrical angle judgment range α and discharge only at electrical angles where Vq can be controlled to 0 V.

[0080] The main features of the second embodiment can be summarized as follows.

[0081] The discharge control unit 16 switches each switching element (power semiconductor 32) to a switching state that generates a composite voltage vector Vo in the direction of the axis through which the target angle passes, during a period when the target angle (electrical angle + phase angle (reference angle)) is within a range of a predetermined electrical angle (α, FIG. 9) that is set according to the rotational speed of the motor 60 from any axis of the three-phase stationary coordinate system.

[0082] This allows discharge to occur regardless of the electrical angle at which the motor 60 stops. In the second embodiment, the phase angle (reference angle) is 0 degrees, but it may be an angle in the range of electrical angles 0 to 90 degrees that is set according to the rotation speed (electrical angular velocity ω) of the motor 60 (Example 3, described later).

[0083] Specifically, the predetermined electrical angle (α, FIG. 9) is 30 degrees when the rotation speed of the motor 60 is lower than the threshold value Th2, and is an angle smaller than 30 degrees (for example, 5 degrees) when the rotation speed of the motor 60 is equal to or higher than the threshold value Th2.

[0084] By setting the predetermined electrical angle (α, Figure 9) to 30 degrees, the target angle is always within the range of the predetermined electrical angle (α = 30 degrees) from one of the axes in the three-phase stationary coordinate system. As a result, discharge can be carried out reliably. On the other hand, by setting the predetermined electrical angle (α, Figure 9) to an angle smaller than 30 degrees (for example, 5 degrees), torque fluctuations during discharge can be suppressed.

[0085] Example 3 In this embodiment, an example of a power converter 50 and a drive device 100 that can discharge while suppressing torque fluctuations more effectively than in the first embodiment is shown.

[0086] 10 is a diagram showing the relationship between Vd and Vq for achieving Iq=0 [A]. In the first embodiment, equation (3) was transformed using the assumption that ω≒0, but the condition for achieving Iq=0 [A] can be derived from equation (3) to obtain equation (5). Therefore, if the switching state of the power semiconductor 32 is controlled to conform to the relational expression of equation (5), discharge can be performed while suppressing torque fluctuations even when ω is large.

[0087]

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[0088] Figure 10 shows this equation (5) for Vd and Vq. If the angle that the resultant vector of Vd and Vq makes with the Vd axis is taken as the reference angle, then when ω is 0, the reference angle is 0 degrees, but as ω increases, the reference angle also increases, reaching a maximum of 90 degrees.

[0089] Fig. 11 is a diagram showing an example of the motor electrical angle and the switching state in embodiment 3. In the example of Fig. 11, by controlling the motor electrical angle by shifting it by the reference angle compared to the example of Fig. 5, it is possible to control the switching state of the power semiconductor 32 so as to generate a voltage vector that matches the relationship between Vd and Vq described in Fig. 10.

[0090] The main features of the third embodiment can be summarized as follows.

[0091] When the target angle, which indicates the sum of the electrical angle and phase angle (reference angle) of the motor 60, passes through any of the axes of the three-phase stationary coordinate system (FIG. 11), the discharge control unit 16 switches each switching element to a switching state that generates a composite voltage vector Vo in the direction of the axis through which the target angle passes.

[0092] The phase angle is a reference angle (FIG. 10) that indicates an angle in the range of electrical angles from 0 to 90 degrees and is set according to the rotational speed (electrical angular velocity ω) of motor 60, with reference to the d-axis direction of the rotating coordinate system of the rotor of motor 60. The reference angle increases as the rotational speed of motor 60 increases. This suppresses torque fluctuations during discharge even if the rotational speed (electrical angular velocity ω) of motor 60 is high.

[0093] Example 4 In this embodiment, an example of a power converter 50 and a drive device 100 that can discharge while suppressing torque fluctuations more effectively than in the first embodiment is shown.

[0094] 12 is a diagram showing an example of the configuration of a power conversion device 50 and a drive device 100 according to a fourth embodiment. The power conversion device 50 and the drive device 100 according to the fourth embodiment have a discharge abnormality determination unit 17 in addition to the components of the power conversion device 50 and the drive device 100 according to the first embodiment. In addition, a discharge command output from the control device 1 is also input to a target current calculation unit 12.

[0095] In the fourth embodiment, the target current calculation unit 12 outputs a target current for discharge when a discharge command is input. Examples of the target current for discharge include a q-axis current of 0 [A] and a d-axis current of −100 [A].

[0096] The discharge abnormality determination unit 17 determines whether an abnormality has occurred during discharge and outputs the determination result to the state control unit 11. For example, if the target current for discharge output by the target current calculation unit 12 does not match the current flowing through the motor 60, or if an abnormality is found when diagnosing the AC current sensor 52 using the AC current sensor value, it outputs an abnormality, indicating that proper discharge may not be possible.

[0097] The state control unit 11 switches the state to the discharge state when a discharge command is input, but in the fourth embodiment, there are two types of discharge state: a discharge state by current control and a discharge state by the discharge control unit 16, and so these two states are switched by the abnormality signal output by the discharge abnormality determination unit 17. When a discharge command is input and the determination result output by the discharge abnormality determination unit 17 is normal, the state switches to the discharge state by current control. When a discharge command is input and the determination result output by the discharge abnormality determination unit 17 is abnormal, the state switches to the discharge state by the discharge control unit 16.

[0098] When the operating state output by the state control unit 11 is a discharge state by current control, the PWM signal generation unit 14 generates a PWM signal using the timer value and the duty of each phase output by the current control unit 13. When the operating state is a discharge state by the discharge control unit 16, the PWM signal generation unit 14 generates a PWM signal using the timer value and the duty of each phase output by the discharge control unit 16.

[0099] 13 is an example of a processing flowchart of discharge control in Example 4. This processing is performed at regular time intervals after the control circuit 10 receives a discharge command.

[0100] In the power conversion device 50 and the drive device 100 in the fourth embodiment, after receiving a discharge command, first, discharge is performed by current control (S131). Here, a target current for discharge is set in the target current calculation unit 12, and discharge is performed by current control so that a current equal to this target current for discharge flows through the motor 60.

[0101] If the discharge abnormality determination unit 17 detects an abnormality during discharge using current control (S132: Yes), the control state output by the state control unit 11 switches from a discharge state by current control to a discharge state by the discharge control unit 16. As a result, the PWM signal generation unit 14 generates a PWM signal based on the duty output by the discharge control unit 16, and the discharge is switched to a discharge by the discharge control unit 16 (S133).

[0102] If the discharge abnormality determination unit 17 does not detect an abnormality during the discharge using the current control (S132: No), the discharge using the current control continues as is.

[0103] In the fourth embodiment, discharge is first performed by current control, and if an abnormality occurs during this discharge, control is performed to switch to discharge by the discharge control unit 16. Discharge control by the discharge control unit 16 imposes a smaller processing load than discharge control by current control, but the accuracy of torque control may be inferior to discharge control by current control. Therefore, discharge is first performed by current control, and if a failure occurs in the sensors used during discharge or if discharge control cannot be performed correctly due to an excessive processing load, discharge is switched to discharge by the discharge control unit 16, thereby making it possible to perform discharge with torque fluctuations more suppressed than in the first embodiment.

[0104] The main features of the fourth embodiment can be summarized as follows.

[0105] 12, the power conversion device 50 includes an AC current sensor 52 that measures the current of the motor 60, a current control unit 13 that causes the current of the motor 60 to follow a target current, and a discharge abnormality determination unit 17 that determines whether or not an abnormality has occurred, indicating that the AC current sensor 52 is broken or that the current of the motor 60 does not follow the target current. If no abnormality has occurred, the current control unit 13 discharges the capacitor (smoothing capacitor 31) by causing the current of the motor 60 to follow a target current for discharge (e.g., q-axis current = 0 [A], d-axis current = -100 [A]). If the abnormality occurs during discharge by the current control unit 13, the discharge control unit 16 discharges the capacitor.

[0106] By having the current control unit 13 perform discharge when no abnormality has occurred, it is possible to suppress torque fluctuations with high precision in an operating range where the rotation speed of the motor 60 is high. By having the discharge control unit 16 perform discharge when an abnormality has occurred during discharge, it is possible to continue discharging while suppressing the processing load and torque fluctuations.

[0107] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0108] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0109] The embodiment of the present invention may be in the following form.

[0110] (C1) A power conversion device connected to a motor for converting DC voltage to AC voltage, comprising: a motor angle detection unit for detecting the electrical angle of the motor; and a discharge control unit for discharging the charge stored in a capacitor to which the DC voltage is applied by passing current through the motor. When a specific reference angle in the rotor of the motor becomes an electrical angle that overlaps with one of the axes in a three-phase stationary coordinate system whose axes are the center directions of each of the three-phase windings, the discharge control unit switches each switching element constituting a three-phase bridge circuit to a predetermined switching state corresponding to the axial voltage vector that overlaps with the reference angle (Figs. 4 and 5).

[0111] This reduces the amount of processing required for discharge control while suppressing torque fluctuations. To discharge while keeping the torque at 0 [Nm], it is necessary to set Iq = 0 [A] and |Id| > 0 [A]. When the rotation speed of the motor 60 is low (ω ≒ 0), setting Vq = 0 [V] makes it possible to set Iq = 0 [A]. Therefore, a voltage vector is generated so that Vq = 0 [V] when the voltage falls within a specific electrical angle range, and discharge is performed.

[0112] (C2) In the power conversion device described in (C1), the discharge control unit intermittently stops discharging the capacitor by providing a period in which a three-phase short circuit is performed by simultaneously turning on either the upper arm or the lower arm of the three-phase bridge circuit when the reference angle of the rotor is separated from either one of the axes of the three-phase stationary coordinate system by a predetermined electrical angle or more (Figures 4 and 5).

[0113] This allows discharge to be performed while suppressing torque fluctuations. If the electrical angle deviates from a specific range, discharging will result in Vq ≠ 0 [V], which will increase torque fluctuations. Therefore, the system transitions to a three-phase short-circuit state and stops discharging.

[0114] (C3) In the power conversion device described in (C1), the torque generated by the motor during discharge by the discharge control unit is equal to or less than the torque generated by the motor during the three-phase short circuit (FIG. 8).

[0115] This allows discharge while suppressing torque fluctuations.

[0116] (C4) In the power conversion device described in (C1), the reference angle is a phase angle advanced by a predetermined phase angle in the ±d-axis direction of the rotor of the motor, or in the range of electrical angles 0 to π / 2 based on the ±d-axis, depending on the rotational angular velocity of the motor (Figure 10).

[0117] This allows discharge while suppressing torque fluctuations. To make Iq = 0 [A], it is necessary to make Vq = (ωLd / R)Vd + ωΦ (Equation (5)). When ω is small, Vq = 0 [V] and the reference angle is 0 [deg], but as ω increases, the reference angle increases, reaching a maximum of 90 [deg].

[0118] (C5) In the power conversion device described in (C1), the discharge control unit has an angle margin when determining that a specific reference angle in the rotor of the motor is an electrical angle that overlaps with one of the axes in a three-phase stationary coordinate system whose axes are in the center directions of each of the three-phase windings, and the angle margin changes depending on the rotational speed of the motor (Figures 5 and 9).

[0119] This allows discharge even when the motor is stopped. Since the angle does not change when the motor is stopped, discharge is not possible even if you wait until a specific electrical angle is reached. Therefore, when the motor is stopped, the angle allowance range is widened so that discharge is possible at any electrical angle, and when the motor is rotating, the angle allowance is narrowed so that discharge is only possible at a specific electrical angle.

[0120] (C6). In the power conversion device described in (C1), the power conversion device has a function of controlling torque by flowing a specified target current to the motor, and the power conversion device first attempts discharge using the torque control function by setting the target current to a predetermined value, and if an abnormality occurs during discharge using the torque control function, discharge is performed by the discharge control unit (Figure 12).

[0121] This makes it possible to suppress torque fluctuations during discharge. Discharge using the torque control function is better at suppressing torque fluctuations at high motor revolutions, so discharge is first performed using the torque control function. If an abnormality occurs during discharge, such as a malfunction of the torque control function or the sensor being used, discharging can be switched to discharging by the discharge control unit, allowing discharge to continue even in the event of an abnormality. [Explanation of symbols]

[0122] 1...Control device 2…DC power supply 3...Switch 10...Control circuit 11...State control unit 12…Target current calculation section 13...Current control section 14...PWM signal generation section 15...Motor speed calculation section 16...Discharge control unit 17…Discharge abnormality determination section 20...Driver circuit 30...Power conversion circuit 31...Smoothing capacitor 32...Power semiconductors 50...Power conversion device 51...DC voltage sensor 52...AC current sensor 60...Motor 61...Motor angle sensor 100...Driver

Claims

1. A capacitor, a three-phase bridge circuit connected in parallel to the capacitor and configured with a plurality of switching elements; a discharge control unit that discharges the charge stored in the capacitor to a motor connected to the three-phase bridge circuit, The discharge control unit When a target angle indicating the sum of the electrical angle and phase angle of the motor passes through any axis of a three-phase stationary coordinate system, each of the switching elements is switched to a switching state that generates a composite voltage vector in the direction of the axis through which the target angle passes. A power conversion device characterized by:

2. The power conversion device according to claim 1, The discharge control unit During a period in which the target angle is separated from any axis of the three-phase stationary coordinate system by a predetermined electrical angle or more, a three-phase short circuit is executed in which the switching elements of either the upper arm or the lower arm of the three-phase bridge circuit are simultaneously turned on, thereby intermittently stopping the discharge of the capacitor. A power conversion device characterized by:

3. The power conversion device according to claim 2, The torque generated by the motor during a predetermined period until the timing of executing the three-phase short circuit during the period in which the capacitor is discharged is equal to or less than a three-phase short circuit torque that indicates the torque generated by the motor when only the three-phase short circuit is executed. A power conversion device characterized by:

4. The power conversion device according to claim 1, The phase angle is a reference angle that indicates an angle in the range of 0 to 90 electrical degrees that is set according to the rotation speed of the motor with reference to the d-axis direction of the rotating coordinate system of the rotor of the motor. A power conversion device characterized by:

5. The power conversion device according to claim 1, The discharge control unit Each of the switching elements is switched to the switching state during a period in which the target angle is within a range of a predetermined electrical angle set according to the rotational speed of the motor from any axis of the three-phase stationary coordinate system. A power conversion device characterized by:

6. The power conversion device according to claim 1, an AC current sensor for measuring the current of the motor; a current control unit that controls the current of the motor to follow a target current; a discharge abnormality determination unit that determines whether or not an abnormality has occurred, which indicates that the AC current sensor is broken or that the current of the motor does not follow the target current, When the abnormality does not occur, the current control unit discharges the capacitor by making the current of the motor follow a target current for discharge; When the abnormality occurs during discharge by the current control unit, the discharge control unit discharges the capacitor. A power conversion device characterized by:

7. The power conversion device according to claim 4, The reference angle increases as the rotation speed of the motor increases. A power conversion device characterized by:

8. The power conversion device according to claim 5, The predetermined electrical angle is When the rotation speed of the motor is less than the threshold value, the rotation speed is 30 degrees. When the rotation speed of the motor is equal to or greater than a threshold value, the angle is less than 30 degrees. A power conversion device characterized by:

9. The power conversion device according to claim 1, The resultant voltage vector is The voltage vectors are synthesized in the directions of the respective axes of the three-phase stationary coordinate system, In the switching state, When the direction of the voltage vector is positive, the switching elements of the upper arms of the three-phase bridge circuit in the phase corresponding to the voltage vector are turned on, and the switching elements of the lower arms of the three-phase bridge circuit in the phase corresponding to the voltage vector are turned off; When the direction of the voltage vector is negative, the switching elements of the lower arms of the three-phase bridge circuit of the phase corresponding to the voltage vector are turned on, and the switching elements of the upper arms of the three-phase bridge circuit of the phase corresponding to the voltage vector are turned off. A power conversion device characterized by:

10. A drive device comprising the power conversion device according to claim 1 and a motor.

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