JP7585772B2 - Vehicle control device and electric motor control method - Google Patents

Description

The present invention relates to a vehicle control device that controls an electric motor used as a drive source for a vehicle, and a method for controlling an electric motor.

In recent years, electric motors that generate torque using three-phase AC supplied from an inverter in which multiple switching elements are connected in a three-phase bridge have come to be widely used as a drive source for vehicles. Electric motors used as drive sources for vehicles generate drive force by powering when starting or accelerating, and generate regenerative power when braking, which is stored in a DC power source consisting of a secondary battery such as a lithium-ion battery. A control device for controlling such an electric motor is described in Patent Document 1.

When it is determined that the power supply side is in an abnormal state in which regenerative power cannot be regenerated to the DC power supply, the electric motor control device described in Patent Document 1 generates a three-phase short circuit execution command based on the d-axis current detection value Id, the q-axis current detection value Iq, and the electrical angle θe, and executes three-phase short circuit processing. Here, the three-phase short circuit processing is a control that turns on all of the upper-stage switching elements of the inverter or all of the lower-stage switching elements. In addition, the electrical angle θe is the rotor rotation angle θm (mechanical angle), which is the detection value of a rotation angle sensor such as a resolver or encoder that detects the rotation angle of the rotor relative to the stator of the electric motor, converted into an electrical angle based on the number of pole pairs of the permanent magnet of the electric motor, and is used to obtain the d-axis current detection value Id and the q-axis current detection value Iq by coordinate conversion of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw.

In addition, the electric motor control device described in Patent Document 1 is configured to start three-phase short-circuit processing at the timing when the maximum absolute value of the phase current after the three-phase short-circuit processing is minimized, in consideration of the problem that the phase current after the three-phase short-circuit processing is the sum of the current flowing before the three-phase short-circuit and the short-circuit current flowing due to the induced voltage of the electric motor after the three-phase short-circuit processing, which may destroy the switching elements of the inverter and the electric motor. Specifically, the rotation angle at which the maximum absolute value of the phase current is minimized is set based on the d-axis current and q-axis current on the d-q axis coordinate system, and the three-phase short-circuit processing is started when the electrical angle θe based on the detection value of the rotation angle sensor matches this rotation angle.

JP 2017-184448 A (see claims 1 to 5, paragraphs [0017], [0037], [0053]-[0057], and [0065] of the specification)

However, various types of failures can occur in on-board devices of a vehicle due to vibrations while the vehicle is traveling, etc. One such failure is a failure of a rotation angle detector that detects the rotation angle of an electric motor used as a drive source. When a failure occurs in the rotation angle detector, the electric motor cannot be controlled normally, so it is considered to execute the above-mentioned three-phase short circuit processing.

However, the electric motor control device described in Patent Document 1 is configured to start the three-phase short-circuit process at the timing when the maximum absolute value of the phase current after the three-phase short-circuit process is minimized, based on the electrical angle calculated from the detected value of the rotation angle. This creates a problem in that if the detected value of the rotation angle cannot be obtained correctly, the three-phase short-circuit process cannot be started at such a timing.

The present invention aims to provide a vehicle control device and an electric motor control method that can start three-phase short-circuit control at a timing that suppresses the maximum value of the phase current immediately after the start of three-phase short-circuit control, even if an abnormality occurs that prevents normal acquisition of the detection results of the rotation angle of an electric motor used as a drive source for a vehicle.

In order to achieve the above object, the present invention provides a vehicle control device that includes a stator having a three-phase winding consisting of U-phase, V-phase, and W-phase wound around an iron core, a rotor having a plurality of permanent magnets facing the iron core, and a rotation angle detector that detects a rotation angle of the rotor relative to the stator, and controls an electric motor that drives wheels of the vehicle by rotation of the rotor, the vehicle control device including an inverter having U-phase, V-phase, and W-phase arms each formed by connecting an upper-stage switching element and a lower-stage switching element in series, and having free wheel diodes connected in parallel to each of the upper-stage switching elements and the lower-stage switching elements, and supplies a three-phase AC current to the electric motor, and a control unit that outputs an on/off signal for turning on or off each of the plurality of switching elements, the control unit detecting the rotation angle detected by the rotation angle detector, and three-phase short-circuit control means for executing three-phase short-circuit control for turning on all switching elements on one of the upper and lower sides of each of the U-phase, V-phase, and W-phase arms and turning off all switching elements on the other side when an abnormality occurs that prevents the rotation angle detection result from being normally acquired by the rotation angle acquisition means, wherein the three-phase short-circuit control means starts the three-phase short-circuit control at a timing at which a maximum value of a current flowing through each of the three phase windings is suppressed immediately after start of the three-phase short-circuit control, based on an estimated value of the rotation angle and a rotation speed of the rotor when the detection result was normally acquired by the rotation angle acquisition means, and the timing at which the three-phase short-circuit control means starts the three-phase short-circuit control is a timing that avoids each of the peak values of (1) to (3) below . (1) The peak value of the induced current when the direction of the transient current flowing in the U-phase winding due to the magnetic flux generated in the U-phase winding is equal to the direction of the induced current induced in the U-phase winding due to the rotation of the rotor. (2) The peak value of the induced current when the direction of the transient current flowing in the V-phase winding due to the magnetic flux generated in the V-phase winding is equal to the direction of the induced current induced in the V-phase winding due to the rotation of the rotor. (3) The peak value of the induced current when the direction of the transient current flowing in the W-phase winding due to the magnetic flux generated in the W-phase winding is equal to the direction of the induced current induced in the W-phase winding due to the rotation of the rotor.

In order to achieve the above object, the present invention provides a control method for an electric motor that includes a stator having three-phase windings wound around an iron core to which a three-phase AC current of U-phase, V-phase, and W-phase is supplied from an inverter, a rotor having a plurality of permanent magnets facing the iron core, and a rotation angle detector that detects a rotation angle of the rotor relative to the stator, and drives wheels of a vehicle by rotation of the rotor, wherein the inverter has U-phase, V-phase, and W-phase arms each formed by connecting an upper-stage switching element and a lower-stage switching element in series, and has free wheel diodes connected in parallel to each of the upper-stage switching elements and the lower-stage switching elements, Provided is a control method for an electric motor, in which when an abnormality occurs that prevents the detection result of the rotation angle by a detector from being normally acquired, three-phase short-circuit control is performed in which all switching elements on one of the upper and lower sides of each of the U-phase, V-phase, and W-phase arms are turned on and all switching elements on the other side are turned off, the three-phase short-circuit control is started at a timing at which the maximum value of current flowing through each of the three-phase windings immediately after start of the three-phase short-circuit control is suppressed based on estimated values of the rotation angle and the rotational speed of the rotor when the detection result could be normally acquired , and the timing at which the three-phase short-circuit control is started is a timing that avoids each of the peak values of (1) to (3) below . (1) The peak value of the induced current when the direction of the transient current flowing in the U-phase winding due to the magnetic flux generated in the U-phase winding is equal to the direction of the induced current induced in the U-phase winding due to the rotation of the rotor. (2) The peak value of the induced current when the direction of the transient current flowing in the V-phase winding due to the magnetic flux generated in the V-phase winding is equal to the direction of the induced current induced in the V-phase winding due to the rotation of the rotor. (3) The peak value of the induced current when the direction of the transient current flowing in the W-phase winding due to the magnetic flux generated in the W-phase winding is equal to the direction of the induced current induced in the W-phase winding due to the rotation of the rotor.

The vehicle control device and electric motor control method of the present invention make it possible to start three-phase short-circuit control at a timing that suppresses the maximum value of the phase current immediately after the start of three-phase short-circuit control, even if an abnormality occurs that prevents the detection result of the rotation angle of the electric motor used as the drive source of the vehicle from being obtained normally.

1 is a schematic diagram showing an example of the configuration of a four-wheel drive vehicle equipped with a vehicle control device according to an embodiment of the present invention; FIG. 2 is a cross-sectional view of an electric motor. FIG. 2 is a schematic diagram showing a configuration example of a motor controller. 4A is a graph showing an example of a change over time in a transient current flowing through a U-phase winding when three-phase short-circuit control is executed, FIG. 4B is a graph showing an example of a change over time in an induced current flowing through a U-phase winding when three-phase short-circuit control is started in a steady state with no fluctuation in the motor rotation speed, and FIG. 4C is a graph showing an example of a change over time in a U-phase current that is the sum of the transient current and the induced current. 11 is a diagram showing the relative positional relationship between the stator and the rotor when the electrical angle θ is 0°, 90°, 180°, and 270°. FIG. 1A is a graph showing an example of a change over time in an induced current induced in a U-phase winding when three-phase short-circuit control is started in a steady state with no fluctuation in the motor rotation speed when the electrical angle θ is 0°, 90°, 180°, and 270°, and FIG. 1B is a graph showing an example of a change over time in a U-phase current obtained by adding a transient current to the induced current. 10 is a flowchart illustrating an example of a process executed by a control unit.

[Embodiment]
An embodiment of the present invention will be described with reference to Figures 1 to 7. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

Figure 1 is a schematic diagram showing an example of the configuration of a four-wheel drive vehicle equipped with a vehicle control device according to an embodiment of the present invention. In this four-wheel drive vehicle 1, the left and right front wheels 111, 112 are driven by an engine 12 as a main drive source, and the left and right rear wheels 113, 114 are driven by an electric motor 2 as an auxiliary drive source.

The driving force of the engine 12 is changed in the transmission 13 and transmitted to a differential case 141 of the front differential 14. The front differential 14 has a differential case 141, a pinion shaft 142 whose both ends are supported by the differential case 141, a pair of pinion gears 143, 143 journaled on the pinion shaft 142, and left and right side gears 144, 145 that mesh with the pair of pinion gears 143, 143 with their gear axes perpendicular to each other. A drive shaft 151 that transmits driving force to the left front wheel 111 is connected to the left side gear 144 so as not to rotate relative to the left side gear 144, and a drive shaft 152 that transmits driving force to the right front wheel 112 is connected to the right side gear 145 so as not to rotate relative to the right side gear 145.

The driving force of the electric motor 2 is transmitted to the left and right rear wheels 113, 114 via the reduction mechanism 16, the rear differential 17, and the left and right drive shafts 153, 154. The reduction mechanism 16 has a pinion gear 161 fixed to the motor shaft 20, which is the output rotating shaft of the electric motor 2, a large diameter gear 162 meshing with the pinion gear 161, a small diameter gear 164 connected to the large diameter gear 162 by a connecting shaft 163, and a ring gear 165 fixed to the differential case 171 of the rear differential 17. The small diameter gear 164 has a smaller pitch circle diameter than the large diameter gear 162 and the ring gear 165, and is connected to the large diameter gear 162 by the connecting shaft 163 so as not to rotate relative to it.

The rear differential 17 has a differential case 171, a pinion shaft 172 whose both ends are supported by the differential case 171, a pair of pinion gears 173, 173 journaled on the pinion shaft 172, and left and right side gears 174, 175 that mesh with the pair of pinion gears 173, 173 with their gear axes perpendicular to each other. The left side gear 174 is non-rotatably connected to the drive shaft 153 that transmits driving force to the left rear wheel 113, and the right side gear 175 is non-rotatably connected to the drive shaft 154 that transmits driving force to the right rear wheel 114.

Wheel speed sensors 181-184 for detecting the wheel speed are attached to the left and right front wheels 111, 112 and the left and right rear wheels 113, 114. The wheel speed sensors 181-184 output pulse signals with pulse widths corresponding to the rotational speeds of the left and right front wheels 111, 112 and the left and right rear wheels 113, 114, for example.

Furthermore, the four-wheel drive vehicle 1 is equipped with an overall controller 101, an engine controller 102 that controls the engine 12, a transmission controller 103 that controls the transmission 13, a motor controller 3 that controls the electric motor 2, and a battery 19 that is used as a power source for the electric motor 2 and the like. The battery 19 is a secondary battery, such as a lithium-ion battery, and is capable of being charged and discharged. The motor controller 3 is one aspect of the vehicle control device of the present invention.

The overall controller 101 can acquire various vehicle information such as the wheel speed of each wheel (left and right front wheels 111, 112 and left and right rear wheels 113, 114), the steering wheel angle, and the amount of depression of the accelerator pedal and brake pedal, and controls the engine controller 102, transmission controller 103, and motor controller 3 in an overall manner based on this vehicle information.

The overall controller 101 also determines the vehicle speed of the four-wheel drive vehicle 1 based on the wheel speeds of each wheel detected by the wheel speed sensors 181-184, and transmits the vehicle speed information to the engine controller 102, the transmission controller 103, and the motor controller 3. The vehicle speed can be determined, for example, based on the wheel speed of the wheel with the slowest rotation speed among the wheels. The vehicle speed may also be determined taking into account the steering angle, yaw rate, and longitudinal acceleration, etc.

The motor controller 3 includes an inverter 4 in which multiple switching elements are connected in a three-phase bridge, a control unit 5 that outputs an on/off signal to turn on or off each of the multiple switching elements of the inverter 4, and a drive circuit 6 that amplifies the on/off signal output by the control unit 5 and outputs it to the multiple switching elements of the inverter 4. The inverter 4 switches the DC voltage of the battery 19 and supplies three-phase AC current consisting of U-phase, V-phase, and W-phase to the electric motor 2. As a result, the left and right rear wheels 113, 114 are driven by the electric motor 2, and the four-wheel drive vehicle 1 is in a four-wheel drive state. In addition, when the four-wheel drive vehicle 1 is decelerating, the electric motor 2 generates regenerative power by the rotation of the left and right rear wheels 113, 114, and the battery 19 is charged. At this time, the inverter 4 functions as a converter.

Figure 2 is a cross-sectional view of the electric motor 2. The electric motor 2 has a motor shaft 20, a rotor 21 that rotates integrally with the motor shaft 20, and a stator 22 arranged to surround the rotor 21. The stator 22 has an iron core 221 with multiple teeth 220, and a U-phase winding 222, a V-phase winding 223, and a W-phase winding 224 wound around each of the multiple teeth 220, and generates a rotating magnetic field when a sinusoidal three-phase AC current is supplied from the inverter 4.

The rotor 21 has a rotor core 211 through the center of which the motor shaft 20 is inserted, and a plurality of permanent magnets 212 fixed to the outer periphery of the rotor core 211 and facing the plurality of teeth 220 of the iron core 221. The plurality of permanent magnets 212 are arranged alternately in the circumferential direction of the rotor 21, with N-pole magnets 212N with their N poles arranged on the outer periphery and S-pole magnets 212S with their S poles arranged on the outer periphery. The electric motor 2 drives the left and right rear wheels 113, 114 by rotating the rotor 21 together with the motor shaft 20 due to the rotating magnetic field generated in the stator 22.

The electric motor 2 also has a rotation angle detector 23 (shown in FIG. 1) that detects the rotation angle of the rotor 21 relative to the stator 22. The rotation angle detector 23 is, for example, a resolver or an encoder, and outputs a detection signal of the rotation angle to the control unit 5 of the motor controller 3.

Figure 3 is a schematic diagram showing an example of the configuration of the motor controller 3 together with a schematic diagram of the electric motor 2. The rotor 21 of the electric motor 2 has multiple magnetic poles as shown in Figure 2 (six in the illustrated example of Figure 2), but Figure 3 shows a pair of magnetic poles (one north pole magnet 212N and one south pole magnet 212S). The rotation angle detector 23 detects the mechanical angle of the rotor 21. When the number of magnetic poles of the rotor 21 is P, the electrical angle of the rotor 21 can be obtained by multiplying the mechanical angle detected by the rotation angle detector 23 by P/2.

The inverter 4 has first to sixth switching elements 41 to 46 connected in a three-phase bridge configuration between an upper bus 401 connected to the positive pole of the battery 19 and a lower bus 402 electrically grounded, and six free wheel diodes 40 connected in parallel to each of the first to sixth switching elements 41 to 46. Of the first to sixth switching elements 41 to 46, the first to third switching elements 41 to 43 are upper-stage switching elements connected to the upper bus 401, and the fourth to sixth switching elements 44 to 46 are lower-stage switching elements connected to the lower bus 402.

The first to sixth switching elements 41 to 46 are, for example, N-channel IGBTs (Insulated Gate Bipolar Transistors) in which a current flows from the collector to the emitter when the gate is turned on (a positive voltage is applied). Note that the first to sixth switching elements 41 to 46 are not limited to IGBTs, and may be, for example, MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors).

The first switching element 41 and the fourth switching element 44 are connected in series to form a U-phase arm 47, and a U-phase current is supplied to the electric motor 2 from a node 471 between the first switching element 41 and the fourth switching element 44. The second switching element 42 and the fifth switching element 45 are connected in series to form a V-phase arm 48, and a V-phase current is supplied to the electric motor 2 from a node 481 between the second switching element 42 and the fifth switching element 45. The third switching element 43 and the sixth switching element 46 are connected in series to form a W-phase arm 49, and a W-phase current is supplied to the electric motor 2 from a node 491 between the third switching element 43 and the sixth switching element 46.

The motor controller 3 also has first to third current sensors 71 to 73 that detect the U-phase current, V-phase current, and W-phase current, respectively. The first to third current sensors 71 to 73 are, for example, Hall type sensors having Hall elements, but may also be shunt type sensors having shunt resistors. In addition, considering that the sum of the U-phase current, V-phase current, and W-phase current is zero, any of the first to third current sensors 71 to 73 may be omitted, and the phase current of the one phase for which the current sensor is omitted may be found by calculation.

The control unit 5 is composed of a CPU (Central Processing Unit), a storage unit consisting of ROM and RAM for storing programs executed by the CPU and various data, and peripheral circuits of the CPU such as a gate IC, an AD converter, and a transmission/reception IC. The control unit 5 also has, as its functional components, a normal control means 51, a three-phase short circuit control means 52, a rotation angle acquisition means 53, a phase current acquisition means 54, and a vehicle speed information acquisition means 55.

The normal control means 51 and the three-phase short circuit control means 52 are realized, for example, by a CPU executing a program. The rotation angle acquisition means 53 acquires the detection result of the rotation angle of the rotor 21 from the rotation angle detector 23 of the electric motor 2. The phase current acquisition means 54 receives detection signals from the first to third current sensors 71 to 73 and acquires the current values of the U-phase current, V-phase current, and W-phase current. The vehicle speed information acquisition means 55 acquires information regarding the vehicle speed of the four-wheel drive vehicle 1, for example, by communicating with the general controller 101.

The normal control means 51 sets command values for the U-phase current, V-phase current, and W-phase current based on the rotation angle of the rotor 21 so as to rotate the electric motor 2 with a torque commanded by the general controller 101, for example, and performs current feedback control based on the deviation from the actual values of the U-phase current, V-phase current, and W-phase current acquired by the phase current acquisition means 54. The normal control means 51 also outputs on/off signals that turn on or off each of the first to sixth switching elements 41 to 46.

This on/off signal is a PWM signal according to the duty in each control period, is amplified by the drive element 61 of the drive circuit 6, and is applied to the gates of the first to sixth switching elements 41 to 46 as a gate voltage that turns on the first to sixth switching elements 41 to 46. In addition, the drive circuit 6 cuts off the output of the gate voltage to protect the first to sixth switching elements 41 to 46 when the phase current of any of the U phase, V phase, and W phase exceeds a threshold value according to the detection signals of the first to third current sensors 71 to 73.

When an abnormality occurs in which the rotation angle acquisition means 53 cannot normally acquire the detection result of the rotation angle of the rotor 21 (hereinafter, this abnormality is referred to as a "rotation angle detection abnormality"), the three-phase short circuit control means 52 executes three-phase short circuit control to turn on all of the upper switching elements (first to third switching elements 41 to 43) and lower switching elements (fourth to sixth switching elements 44 to 46) of each of the U-phase, V-phase, and W-phase arms 47, 48, 49 on one side and turn off all of the switching elements on the other side. For example, when turning on the upper switching elements, an on/off signal is output to turn on all of the first to third switching elements 41 to 43 and turn off all of the fourth to sixth switching elements 44 to 46.

The rotation angle detection abnormality may occur, for example, due to a failure of the rotation angle detector 23 or a break in the signal line between the rotation angle detector 23 and the motor controller 3. When a rotation angle detection abnormality occurs, control of the electric motor 2 by the normal control means 51 cannot be continued, so control by the normal control means 51 is switched to control by the three-phase short-circuit control means 52. By executing the three-phase short-circuit control, it is possible to suppress overcharging of the battery 19 and a sudden increase in the braking force of the left and right rear wheels 113, 114 due to regenerative braking generated in the electric motor 2, compared to when all of the first to sixth switching elements 41 to 46 are turned off.

However, when the three-phase short circuit control is started, the phase current of each phase may increase instantaneously because the current equivalent to the sum of the transient current due to the residual magnetic flux of the U-phase winding 222, the V-phase winding 223, and the W-phase winding 224 and the induced current induced in the U-phase winding 222, the V-phase winding 223, and the W-phase winding 224 by the rotation of the rotor 21 accompanying the rotation of the left and right rear wheels 113, 114 flows as the phase current of each phase. Therefore, if an overcurrent abnormality is detected in the drive circuit 6 in which the phase current exceeds the threshold value, and all of the first to sixth switching elements 41 to 46 are turned off, or if the drive circuit 6 does not have an overcurrent detection function, the current flowing through any of the first to sixth switching elements 41 to 46 or the current flowing through the freewheel diode 40 may become excessive.

Here, the transient current due to the residual magnetic flux reaches a maximum immediately after the start of the three-phase short circuit control, but then gradually decreases with a predetermined time constant. Therefore, if the three-phase short circuit control is started while avoiding the peak time when the transient current and the induced current overlap, it is possible to prevent an overcurrent abnormality from being detected in the drive circuit 6, or the current flowing through any of the first to sixth switching elements 41 to 46 or the freewheeling diode 40 from becoming excessive.

For this reason, in this embodiment, the three-phase short circuit control means 52 starts three-phase short circuit control at a timing when the maximum value of the current flowing through each of the U-phase winding 222, V-phase winding 223, and W-phase winding 224 is suppressed immediately after the start of three-phase short circuit control, based on the rotation angle when the detection result of the rotation angle detector 23 was normally acquired by the rotation angle acquisition means 53 and the estimated value of the rotation speed of the rotor 21.

In addition, in this embodiment, an estimate of the rotation speed of the rotor 21 is obtained based on information related to the vehicle speed obtained by the vehicle speed information obtaining means 55. More specifically, based on the estimate of the rotation speed of the rotor 21 obtained by converting the vehicle speed obtained by the vehicle speed information obtaining means 55 into the rotation angular velocity of the rotor 21, the three-phase short-circuit control is started at a timing when the maximum values of the currents flowing through the U-phase winding 222, the V-phase winding 223, and the W-phase winding 224 are suppressed immediately after the start of the three-phase short-circuit control. Since the vehicle speed and the rotation speed of the rotor 21 are proportional to each other, it is possible to obtain an estimate of the rotation speed of the rotor 21 from the vehicle speed.

In addition, the vehicle speed information obtained by the general controller 101 may be used as is as the information on the vehicle speed, but the rotation speeds of the left and right rear wheels 113, 114 may also be used as the information on the vehicle speed. In this case, the average rotation speed of the left and right rear wheels 113, 114 may be multiplied by the inverse of the reduction ratio of the reduction mechanism 16 to obtain an estimate of the rotation speed of the rotor 21. In addition, considering that the rate of change per unit time when the rotation speed of the rotor 21 changes is extremely small compared to the rate of change per unit time of the current induced by the rotation of the rotor 21, the rotation speed of the rotor 21 when the detection result of the rotation angle detector 23 was normally obtained may be used as an estimate of the rotation speed of the rotor 21 after the occurrence of a rotation angle detection abnormality.

In this embodiment, the timing at which the three-phase short circuit control means 52 starts the three-phase short circuit control when a rotation angle detection abnormality occurs is a timing that avoids each of the peak values (1) to (3) below.
(1) The peak value of the U-phase induced current when the direction of the transient current flowing in the U-phase winding 222 due to the magnetic flux generated in the U-phase winding 222 is equal to the direction of the induced current induced in the U-phase winding 222 due to the rotation of the rotor 21. (2) The peak value of the V-phase induced current when the direction of the transient current flowing in the V-phase winding 223 due to the magnetic flux generated in the V-phase winding 223 is equal to the direction of the induced current induced in the V-phase winding 223 due to the rotation of the rotor 21. (3) The peak value of the W-phase induced current when the direction of the transient current flowing in the W-phase winding 224 due to the magnetic flux generated in the W-phase winding 224 is equal to the direction of the induced current induced in the W-phase winding 224 due to the rotation of the rotor 21.

The timing to avoid these peak values is specifically the timing to avoid, for example, 90% or more or 95% or more (absolute value) of the maximum value of the induced current that changes in a sinusoidal manner. The magnitude and phase of the induced current can be obtained based on the rotation angle of the rotor 21 before the rotation angle detection abnormality occurs and the estimated value of the rotation speed of the rotor 21 after the rotation angle detection abnormality occurs. In other words, by integrating the estimated value of the rotation speed of the rotor 21 after the rotation angle detection abnormality occurs, the amount of rotation (estimated value) of the rotor 21 after the rotation angle detection abnormality occurs can be obtained. Therefore, by adding this amount of rotation to the rotation angle of the rotor 21 before the rotation angle detection abnormality occurs, the rotation angle of the rotor 21 at each time point can be estimated, and the magnitude of the induced current of each phase can be obtained based on this.

If a rotation angle detection abnormality is detected and the time when the three-phase short circuit control means 52 attempts to start three-phase short circuit control is a timing that can avoid the peak values of (1) to (3) above, the three-phase short circuit control means 52 immediately starts three-phase short circuit control. Also, if the time when the three-phase short circuit control means 52 attempts to start three-phase short circuit control overlaps with any of the peak values of (1) to (3) above, the three-phase short circuit control means 52 starts three-phase short circuit control when the time period of that peak value has passed.

In this way, the three-phase short circuit control means 52 calculates an estimated value of the rotation angle based on the time that has elapsed since the occurrence of the rotation angle detection abnormality and the estimated value of the rotation speed of the rotor 21 during this elapsed time, and from this estimated value, determines the occurrence times of each of the peak values (1) to (3) above, and starts three-phase short circuit control while avoiding these occurrence times.

Figure 4(a) is a graph showing an example of the change over time of the transient current flowing through the U-phase winding 222 when three-phase short circuit control is executed. Figure 4(b) is a graph showing an example of the change over time of the induced current flowing through the U-phase winding 222 when three-phase short circuit control is started in a steady state with no fluctuation in the motor rotation speed. Figure 4(c) is a graph showing an example of the change over time of the U-phase current obtained by adding the transient current shown in Figure 4(a) and the induced current shown in Figure 4(b). The vertical and horizontal axes of each graph shown in Figures 4(a) to (c) are on a common scale. Note that while Figure 4(b) shows an example of the case where the transient current is positive, the transient current may be negative depending on the timing of starting the three-phase short circuit control.

As shown in FIG. 4(a), the transient current decreases exponentially over time. The time constant of the change in the transient current is determined by the inductance and DC resistance of the U-phase winding 222. Also, as shown in FIG. 4(b), the induced current generated by the rotation of the rotor 21 changes in a sinusoidal manner. Therefore, after the start of three-phase short-circuit control, the phase current obtained by adding up the transient current and the induced current has an absolute value larger than the amplitude of the induced current when the transient current and the induced current are both positive or negative.

Figure 5 shows the relative positional relationship between the U-phase winding 222, the V-phase winding 223, and the W-phase winding 224 and the N-pole magnet 212N and S-pole magnet 212S of the rotor 21 when the electrical angle θ is 0°, 90°, 180°, and 270°. Here, the electrical angle θ is set to 0° when the S-pole magnet 212S faces the U-phase winding 222.

Figure 6(a) is a graph showing an example of the change over time of the induced current induced in the U-phase winding 222 by the rotation of the rotor 21 in a steady state with no fluctuation in the motor rotation speed. Figure 6(b) is a graph showing an example of the change over time of the U-phase current obtained by adding the transient current shown in Figure 4(a) to the induced current induced in the U-phase winding 222 by the rotation of the rotor 21. Figures 6(a) and (b) show the changes in the U-phase induced current and the U-phase current when the electrical angle θ at the time corresponding to the left end of the time axis of the graph is 0°, 90°, 180°, and 270°, respectively.

As shown in FIG. 6B, when the three-phase short circuit control is started when the induced current induced in the U-phase winding 222 reaches a positive peak value (when the electrical angle θ = 0°), the induced current of the U-phase and the transient current are added together, and the absolute value of the U-phase current becomes large. If the U-phase current at this time exceeds the current threshold value in the drive circuit 6, the first to sixth switching elements 41 to 46 are all turned off, and the three-phase short circuit control is no longer performed. However, if the electrical angle θ at the time when the three-phase short circuit control is started is shifted, that is, if the time when the three-phase short circuit control is started is shifted from the time when the induced current of the U-phase reaches its peak value, the maximum value of the U-phase current immediately after the three-phase short circuit control is started can be suppressed.

The same is true for the V-phase current and W-phase current, which are out of phase with the U-phase current by ±120°. Therefore, by adjusting the start time of the three-phase short-circuit control according to the electrical angle calculated from the estimated value of the rotation angle of the rotor 21 when a rotation angle detection abnormality occurs, and starting the three-phase short-circuit control at a timing that suppresses the maximum values of the U-phase current, V-phase current, and W-phase current immediately after the start of the three-phase short-circuit control, it is possible to prevent the phase current of each phase from exceeding the current threshold value in the drive circuit 6, or to prevent the first to sixth switching elements 41 to 46 or the freewheel diode 40 from being damaged by an overcurrent.

The maximum values (absolute values) of the U-phase current, V-phase current, and W-phase current at the start of three-phase short circuit control are not necessarily larger when the rotation speed of the rotor 21 is high. When the rotation speed of the rotor 21 is low, the maximum value of each phase current may be larger than when the rotation speed is high. When the rotation speed of the rotor 21 is low, the induced voltage that induces the phase current is low, but due to the relationship Z = jωL (Z is impedance, j is the imaginary unit, ω is angular frequency, and L is inductance), the impedance due to the inductance of the U-phase winding 222, V-phase winding 223, and W-phase winding 224 is also low.

Figure 7 is a flowchart showing an example of the process executed by the control unit 5. The control unit 5 executes the process shown in this flowchart at a predetermined control period (e.g., 5 ms).

In the process shown in this flowchart, the control unit 5 first acquires the detection result of the rotation angle of the rotor 21 by the rotation angle acquisition means 53 (step S1), and determines whether the detection result of the rotation angle has been acquired normally (step S2). If the detection result of the rotation angle has been acquired normally (S2: Yes), the information of the rotation angle acquired in step S1 is stored in the storage unit (step S3), and the electric motor 2 is controlled by the normal control means 51. That is, an on/off signal is output to the drive circuit 6 based on the rotation angle of the rotor 21 and the phase current acquired by the phase current acquisition means 54 so that the electric motor 2 is rotated with the torque commanded by the overall controller 101.

On the other hand, if the rotation angle detection result could not be obtained normally (S2: No), the rotation angle information stored in step S3 in the previous control cycle is read from the memory unit (step S5). In addition, information about the vehicle speed is obtained by the vehicle speed information acquisition means 55 (step S6), and an estimate of the rotation speed of the rotor 21 is calculated from the obtained information about the vehicle speed (step S7). Then, the occurrence time of the peak values of the U-phase current, the V-phase current, and the W-phase current is calculated from the information obtained in steps S5 and S7 (step S8). If the current time is the occurrence time of the peak value of any of the U-phase current, the V-phase current, and the W-phase current, the occurrence time of the peak value is waited for to pass (step S9), and three-phase short-circuit control is executed (step S10). The three-phase short-circuit control continues until the start switch (ignition switch) of the four-wheel drive vehicle 1 is turned off, and the four-wheel drive vehicle 1 runs in two-wheel drive state by the driving force of the engine 12 only.

If the rotation angle detection result cannot be obtained normally, a signal to notify the driver of the occurrence of an abnormality may be sent to the general controller 101. The occurrence of this abnormality is notified to the driver, for example, by a lamp display on the instrument panel in the driver's seat, a message display, or a voice, and the driver is prompted to have the repairs performed.

According to the embodiment of the present invention described above, even if an abnormality occurs in which the control unit 5 cannot normally obtain the detection result of the rotation angle of the electric motor, the three-phase short-circuit control can be started at a timing that suppresses the maximum value of the phase current immediately after the start of the three-phase short-circuit control, and it is possible to prevent the phase current from exceeding the current threshold value in the drive circuit 6, causing all of the first to sixth switching elements 41 to 46 to be turned off, or to prevent the first to sixth switching elements 41 to 46 or the freewheeling diode 40 from being damaged by an overcurrent.

(Additional Note)
The present invention has been described above based on the embodiments, but the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention. The present invention can be modified as appropriate by omitting some components or adding or replacing components without departing from the spirit of the invention.

In the above embodiment, as an example, the present invention has been described as being applied to a motor controller 3 that controls an electric motor 2 of a four-wheel drive vehicle in which the left and right front wheels 111, 112 are driven by an engine 12 as a main drive source, and the left and right rear wheels 113, 114 are driven by an electric motor 2 as an auxiliary drive source. However, the configuration of the vehicle to which the control device and control method of the present invention are applied is not limited to this, and the present invention may be applied to, for example, an electric vehicle or hybrid vehicle in which one or both of the left and right front wheels and the left and right rear wheels are driven by an electric motor, or the present invention may be applied to a so-called in-wheel motor that drives one wheel.

In the above embodiment, the reduction ratio of the reduction mechanism 16 is fixed, but this is not limiting and a transmission may be disposed between the electric motor 2 and the rear differential 17. In this case, the estimated rotational speed of the rotor 21 is calculated from information related to the vehicle speed, taking into account the gear ratio of the transmission.

2... Electric motor 21... Rotor 22... Stator 222... U-phase winding 223... V-phase winding 224... W-phase winding 23... Rotation angle detector 3... Motor controller (control device)
4... inverter 40... freewheeling diodes 41 to 43... first to third switching elements (upper stage switching elements)
44 to 46: Fourth to sixth switching elements (lower stage switching elements)
47, 48, 49...U-phase, V-phase, and W-phase arms 5...Control unit 52...Three-phase short-circuit control means 53...Rotation angle acquisition means

Claims (4)

A vehicle control device comprising: a stator having a three-phase winding consisting of U-phase, V-phase, and W-phase wound around an iron core; a rotor having a plurality of permanent magnets facing the iron core; and a rotation angle detector for detecting a rotation angle of the rotor relative to the stator, the vehicle control device controlling an electric motor that drives wheels of the vehicle by rotation of the rotor,
an inverter having U-phase, V-phase, and W-phase arms each formed by connecting upper-stage switching elements and lower-stage switching elements in series, and having free wheel diodes connected in parallel to the upper-stage switching elements and the lower-stage switching elements, and supplying a three-phase AC current to the electric motor;
a control unit that outputs an on/off signal that turns on or off each of the plurality of switching elements,
the control unit includes a rotation angle acquisition means for acquiring a detection result of the rotation angle by the rotation angle detector, and a three-phase short circuit control means for executing a three-phase short circuit control in which, when an abnormality occurs that prevents the detection result of the rotation angle from being normally acquired by the rotation angle acquisition means, all switching elements on one side of the upper stage and the lower stage of each of the U-phase, V-phase, and W-phase arms are turned on and all switching elements on the other side are turned off,
the three-phase short circuit control means starts the three-phase short circuit control at a timing at which a maximum value of a current flowing through each of the windings of the three phases is suppressed immediately after the start of the three-phase short circuit control , based on an estimated value of the rotation angle and a rotation speed of the rotor when the detection result was normally acquired by the rotation angle acquisition means;
The timing at which the three-phase short circuit control means starts the three-phase short circuit control is a timing at which each of the peak values (1) to (3) below is avoided.
Vehicle control device.
(1) The peak value of the induced current when the direction of the transient current flowing in the U-phase winding due to the magnetic flux generated in the U-phase winding is equal to the direction of the induced current induced in the U-phase winding due to the rotation of the rotor.
(2) The peak value of the induced current when the direction of the transient current flowing in the V-phase winding due to the magnetic flux generated in the V-phase winding is equal to the direction of the induced current induced in the V-phase winding due to the rotation of the rotor.
(3) A peak value of the induced current when the direction of a transient current flowing in the W-phase winding due to a magnetic flux generated in the W-phase winding is equal to the direction of an induced current induced in the W-phase winding due to the rotation of the rotor. The control unit further includes a vehicle speed information acquisition unit for acquiring information regarding a vehicle speed,
the three-phase short circuit control means starts the three-phase short circuit control at a timing at which a maximum value of a current flowing through each of the three phase windings is suppressed immediately after the start of the three-phase short circuit control, based on the rotation angle when the detection result was normally acquired by the rotation angle acquisition means and an estimated value of the rotation speed of the rotor obtained by converting the vehicle speed acquired by the vehicle speed information acquisition means into a rotation angular speed of the rotor.
The vehicle control device according to claim 1 . the three-phase short circuit control means calculates an estimated value of the rotation angle based on the elapsed time after the occurrence of the abnormality and an estimated value of the rotation speed of the rotor during the elapsed time, determines the occurrence times of the peak values from the estimated values, and starts the three-phase short circuit control while avoiding the occurrence times.
The vehicle control device according to claim 1 . A method for controlling an electric motor that includes a stator having a three-phase winding wound around an iron core to which a three-phase AC current of U-phase, V-phase, and W-phase is supplied from an inverter, a rotor having a plurality of permanent magnets facing the iron core, and a rotation angle detector that detects a rotation angle of the rotor relative to the stator, the method comprising the steps of:
the inverter has U-phase, V-phase, and W-phase arms, each of which is formed by connecting an upper-stage switching element and a lower-stage switching element in series, and has free wheel diodes connected in parallel to the upper-stage switching element and the lower-stage switching element,
when an abnormality occurs that prevents the detection result of the rotation angle by the rotation angle detector from being normally acquired, a three-phase short-circuit control is executed in which all switching elements on one side of the upper stage and the lower stage of each of the U-phase, V-phase, and W-phase arms are turned on and all switching elements on the other side are turned off, the three-phase short-circuit control is started at a timing at which a maximum value of a current flowing through each of the three-phase windings is suppressed immediately after the start of the three-phase short-circuit control , based on an estimated value of the rotation angle and a rotation speed of the rotor when the detection result could be normally acquired;
The timing to start the three-phase short circuit control is a timing to avoid each of the peak values (1) to (3) below.
A method for controlling an electric motor.
(1) The peak value of the induced current when the direction of the transient current flowing in the U-phase winding due to the magnetic flux generated in the U-phase winding is equal to the direction of the induced current induced in the U-phase winding due to the rotation of the rotor.
(2) The peak value of the induced current when the direction of the transient current flowing in the V-phase winding due to the magnetic flux generated in the V-phase winding is equal to the direction of the induced current induced in the V-phase winding due to the rotation of the rotor.
(3) A peak value of the induced current when the direction of a transient current flowing in the W-phase winding due to a magnetic flux generated in the W-phase winding is equal to the direction of an induced current induced in the W-phase winding due to the rotation of the rotor.

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