Motor control device and electric pump device

Abstract

To provide a motor control device and an electric pump device capable of performing sensorless control of a motor with stability even in a case where the motor is rotated at a rotation number close to a limit minimum rotation number under a low-temperature environment.SOLUTION: A motor control device 10 that controls a three-phase motor 20, comprises: a drive circuit 11 that converts a DC power supply voltage VM into a three-phase AC voltage and supplies the three-phase AC voltage to the three-phase motor; a current detection unit 12 that detects a power supply current flowing in the drive circuit; a voltage detection unit 13 that detects terminal voltages of three phases of the three-phase motor; and a control unit 14 that detects as a zero-cross point a point where an induction voltage appearing in each terminal voltage of the three phases crosses a predetermined zero-cross determination level, and controls the drive circuit on the basis of the detection results of the zero-cross point. The control unit changes a value of the zero-cross determination level on the basis of a power supply current value detected by the current detection unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor control device and an electric pump device. [Background technology]

[0002] A known control method for sensorless motors is to detect the zero-cross points where the induced voltages appearing in the terminal voltages of the three phases of the motor intersect with the neutral point potential, and to control the energization of the motor based on the results of the detection of the zero-cross points. Patent Document 1 listed below discloses a technology for stably driving a sensorless motor in the low rotation range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-273502 Summary of the Invention [Problem to be solved by the invention]

[0004] In a low-temperature environment, when a sensorless motor is controlled at a rotation speed close to the minimum limit rotation speed required to generate an induced voltage at which the zero-crossing point can be detected, the waveform of the induced voltage is distorted depending on the power supply current, which can cause the timing of detecting the zero-crossing point to deviate from the ideal timing, making it difficult to stably perform sensorless control of the motor. The technology in Patent Document 1 cannot solve this technical problem. [Means for solving the problem]

[0005] One aspect of the motor control device of the present invention is a motor control device for controlling a three-phase motor, comprising: a drive circuit that converts a DC power supply voltage into a three-phase AC voltage and supplies the voltage to the three-phase motor; a current detection unit that detects the power supply current flowing through the drive circuit; a voltage detection unit that detects the terminal voltages of the three phases of the three-phase motor; and a control unit that detects points where induced voltages appearing in the terminal voltages of the three phases cross predetermined zero-crossing determination levels as zero-crossing points and controls the drive circuit based on the detection results of the zero-crossing points, wherein the control unit changes the value of the zero-crossing determination level based on the power supply current value detected by the current detection unit.

[0006] One aspect of the electric pump device of the present invention comprises a three-phase motor having a shaft, a pump located on one axial side of the shaft and driven by the three-phase motor via the shaft, and a motor control device of the above aspect that controls the three-phase motor. [Effects of the Invention]

[0007] According to the above aspects of the present invention, a motor control device and an electric pump device are provided that are capable of stably performing sensorless control of a motor even when the motor is rotated at a rotation speed close to the minimum limit rotation speed in a low-temperature environment. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram that schematically shows an electric pump device 100 that includes a motor control device 10 according to this embodiment. [Figure 2] FIG. 2 is a diagram showing an example of an energization pattern and a phase pattern used in the sensorless 120° energization method in this embodiment. [Figure 3] FIG. 3 is a timing chart showing the basic principle of the sensorless 120° energization method in this embodiment. [Figure 4] FIG. 4 is a first diagram schematically showing the waveform of the induced voltage exposed to the U-phase terminal 22u during the current-carrying period P3 shown in FIG. [Figure 5] FIG. 5 is a second diagram schematically showing the waveform of the induced voltage exposed to the U-phase terminal 22u during the current-carrying period P3 shown in FIG. [Figure 6] FIG. 6 is a flowchart showing the processes included in the extremely low speed rotation control of the three-phase motor 20 executed by the control unit 14 in a low temperature environment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram that schematically shows an electric pump device 100 that includes a motor control device 10 according to this embodiment. As shown in Fig. 1, the electric pump device 100 includes the motor control device 10 and an electric pump 40. The electric pump 40 includes a three-phase motor 20 and a pump 30. The electric pump device 100 is a device that supplies cooling oil F to a drive motor mounted on, for example, a hybrid vehicle.

[0010] The motor control device 10 is a device that controls the three-phase motor 20 of the electric oil pump 40 without using a position sensor such as a Hall sensor. Specifically, the motor control device 10 detects the points where the induced voltage appearing in each of the three-phase terminal voltages of the three-phase motor 20 crosses a predetermined zero-cross determination level as zero-cross points, and controls the energization of the three-phase motor 20 based on the detection results of the zero-cross points. Details of the motor control device 10 will be described later.

[0011] Three-phase motor 20 is, for example, an inner rotor type three-phase brushless DC motor, and is a sensorless motor that does not have a position sensor such as a Hall sensor. Three-phase motor 20 has a shaft 21, a U-phase terminal 22u, a V-phase terminal 22v, a W-phase terminal 22w, a U-phase coil 23u, a V-phase coil 23v, and a W-phase coil 23w.

[0012] Although not shown in Figure 1, the three-phase motor 20 includes a motor housing and a rotor and stator housed in the motor housing. The rotor is a rotating body rotatably supported by bearing components inside the motor housing. The stator is fixed inside the motor housing while surrounding the outer circumferential surface of the rotor, and generates the electromagnetic force required to rotate the rotor.

[0013] The shaft 21 is an axial body that penetrates the radially inner side of the rotor in the axial direction and is coaxially joined to the rotor. The U-phase terminal 22u, the V-phase terminal 22v, and the W-phase terminal 22w are metal terminals that are exposed on the surface of the motor housing. As will be described in detail later, the U-phase terminal 22u, the V-phase terminal 22v, and the W-phase terminal 22w are each electrically connected to the drive circuit 11 of the motor control device 10. The U-phase coil 23u, the V-phase coil 23v, and the W-phase coil 23w are each excitation coils provided in the stator. The U-phase coil 23u, the V-phase coil 23v, and the W-phase coil 23w are star-connected inside the three-phase motor 20.

[0014] The U-phase coil 23u is electrically connected between the U-phase terminal 22u and the neutral point N. The V-phase coil 23v is electrically connected between the V-phase terminal 22v and the neutral point N. The W-phase coil 23w is electrically connected between the W-phase terminal 22w and the neutral point N. The energized states of the U-phase coil 23u, the V-phase coil 23v, and the W-phase coil 23w are controlled by the motor control device 10, thereby generating an electromagnetic force required to rotate the rotor. As the rotor rotates, the shaft 21 also rotates in synchronization with the rotor.

[0015] The pump 30 is located on one axial side of the shaft 21 of the three-phase motor 20, and is driven by the three-phase motor 20 via the shaft 21. When the pump 30 is driven by the three-phase motor 20, the pump 30 discharges cooling oil F. The pump 30 has an oil suction port 31 and an oil discharge port 32. The cooling oil F is drawn into the pump 30 through the oil suction port 31, and then discharged from the oil discharge port 32 to the outside of the pump 30. In this way, the pump 30 and the three-phase motor 20 are connected adjacent to each other in the axial direction of the shaft 21, thereby forming an electric pump 40.

[0016] Motor control device 10 is a device that controls three-phase motor 20 without a position sensor based on a rotation speed command signal CS output from a higher-level control device (not shown). As an example, the higher-level control device is an on-board ECU (Electronic Control Unit) installed in a hybrid vehicle. Motor control device 10 includes a drive circuit 11, a shunt resistor 12 (current detection unit), a voltage detection circuit 13 (voltage detection unit), a control unit 14, and a memory unit 15.

[0017] The drive circuit 11 is driven by a DC power supply voltage V M The drive circuit 11 converts the DC power supply voltage V supplied from the DC power supply 200 into a three-phase AC voltage and supplies it to the three-phase motor 20. M is converted into a three-phase AC voltage and output to the three-phase motor 20. As an example, the DC power supply 200 is one of a plurality of batteries mounted on a hybrid vehicle, and outputs a 12V DC power supply voltage V M supply.

[0018] The drive circuit 11 is connected to the U-phase upper arm switch Q UH and V-phase upper arm switch Q VH and W-phase upper arm switch Q WH and U-phase lower arm switch Q UL and V-phase lower arm switch Q VL and W-phase lower arm switch Q WLIn this embodiment, each arm switch is, for example, an N-channel MOS-FET.

[0019] U-phase upper arm switch Q UH Drain terminal of V-phase upper arm switch Q VH The drain terminal of the W-phase upper arm switch Q WH The drain terminals of the U-phase lower arm switch Q are electrically connected to the positive terminals of the DC power supply 200. UL Source terminal of V-phase lower arm switch Q VL The source terminal of the W-phase lower arm switch Q WL The source terminals of the DC power supply 200 are electrically connected to the negative terminal of the DC power supply 200 via the shunt resistor 12. The negative terminal of the DC power supply 200 is electrically connected to the vehicle interior ground.

[0020] U-phase upper arm switch Q UH The source terminal of the U-phase terminal 22u of the three-phase motor 20 and the U-phase lower arm switch Q UL The drain terminals of the V-phase upper arm switch Q VH The source terminal of the V-phase terminal 22v of the three-phase motor 20 and the V-phase lower arm switch Q VL The drain terminals of the W-phase upper arm switch Q are electrically connected to the drain terminals of the W-phase upper arm switch Q. WH The source terminal of the three-phase motor 20 is connected to the W-phase terminal 22w of the W-phase lower arm switch Q. WL and the drain terminals of the transistors.

[0021] U-phase upper arm switch Q UH Gate terminal of V-phase upper arm switch Q VH The gate terminal of the W-phase upper arm switch Q WH The gate terminals of the U-phase lower arm switch Q are electrically connected to the control unit 14. UL Gate terminal of V-phase lower arm switch Q VL The gate terminal of the W-phase lower arm switch Q WLThe gate terminals of the transistors 11 and 12 are also electrically connected to the control unit 14.

[0022] As described above, the drive circuit 11 is configured as a three-phase full-bridge circuit having three upper arm switches and three lower arm switches. The drive circuit 11 configured in this manner is configured to convert the DC power supply voltage V supplied from the DC power supply 200 into a voltage V by controlling the switching of each arm switch by the control unit 14. M is converted into a three-phase AC voltage and output to a three-phase motor 20.

[0023] In this embodiment, a case where a sensorless 120° conduction method is used as the conduction method for the three-phase motor 20 is illustrated. For convenience of explanation, the basic principle of the sensorless 120° conduction method will be explained below, followed by explanations of the shunt resistor 12, voltage detection circuit 13, control unit 14, and storage unit 15. Note that the basic principle of the sensorless 120° conduction method explained below is merely an example, and the present invention is not limited to this.

[0024] When the sensorless 120° energization method is used, the switching of each arm switch is controlled based on the energization pattern shown in FIG. 2. As shown in FIG. 2, the energization pattern of the 120° energization method includes six energization patterns PA1, PA2, PA3, PA4, PA5, and PA6. In FIG. 2, "Q UH " to "Q WL Of the "1" and "0" in the column up to "," a "1" means that the corresponding arm switch is controlled to be on, and a "0" means that the corresponding arm switch is controlled to be off.

[0025] 3, a conduction period P1 from time t10 to time t11 indicates a period during which each arm switch is switched based on a conduction pattern PA1. In this conduction period P1, the U-phase upper arm switch Q UH and W-phase lower arm switch Q WL During the conduction period P1, the U-phase upper arm switch Q UHOnly the U-phase coil 23u and the W-phase coil 23w are switched at a predetermined duty ratio. During the current-carrying period P1, a drive current (power supply current) flows from the U-phase terminal 22u to the W-phase terminal 22w through the U-phase coil 23u and the W-phase coil 23w. That is, the current-carrying phases during the current-carrying period P1 are the U-phase and the W-phase.

[0026] 3, a conduction period P2 from time t11 to time t12 indicates a period during which each arm switch is switched based on the conduction pattern PA2. In this conduction period P2, the U-phase upper arm switch Q UH and V-phase lower arm switch Q VL During the conduction period P2, the U-phase upper arm switch Q UH Only the U-phase coil 23u and the V-phase coil 23v are switched at a predetermined duty ratio. During the current conduction period P2, a drive current flows from the U-phase terminal 22u to the V-phase terminal 22v, through the U-phase coil 23u and the V-phase coil 23v. That is, the current conduction phases during the current conduction period P2 are the U-phase and the V-phase.

[0027] 3, a current conduction period P3 from time t12 to time t13 indicates a period during which each arm switch is switched based on a current conduction pattern PA3. In this current conduction period P3, the W-phase upper arm switch Q WH and V-phase lower arm switch Q VL During the conduction period P3, the W-phase upper arm switch Q WH Only the W-phase coils 23w and 23v are switched at a predetermined duty ratio. During the current conduction period P3, a drive current flows from the W-phase terminal 22w to the V-phase terminal 22v, through the W-phase coil 23w and the V-phase coil 23v. That is, the current conduction phases during the current conduction period P3 are the W-phase and the V-phase.

[0028] 3, a current conduction period P4 from time t13 to time t14 indicates a period during which each arm switch is switched based on a current conduction pattern PA4. WH and U-phase lower arm switch Q ULDuring the conduction period P4, the W-phase upper arm switch Q WH Only the W-phase coil 23w and the U-phase coil 23u are switched at a predetermined duty ratio. During current conduction period P4, a drive current flows from the W-phase terminal 22w to the U-phase terminal 22u, to the W-phase coil 23w and the U-phase coil 23u. That is, the current conduction phases during current conduction period P4 are the W phase and the U phase.

[0029] 3, a conduction period P5 from time t14 to time t15 indicates a period during which each arm switch is switched based on a conduction pattern PA5. In this conduction period P5, the V-phase upper arm switch Q VH and U-phase lower arm switch Q UL In the conduction period P5, the V-phase upper arm switch Q VH Only the V-phase coil 23v and the U-phase coil 23u are switched at a predetermined duty ratio. During the current-carrying period P5, a power supply current flows from the V-phase terminal 22v to the U-phase terminal 22u, through the V-phase coil 23v and the U-phase coil 23u. That is, the current-carrying phases during the current-carrying period P5 are the V-phase and the U-phase.

[0030] 3, a current conduction period P6 from time t15 to time t16 indicates a period during which each arm switch is switched based on a current conduction pattern PA6. VH and W-phase lower arm switch Q WL During the conduction period P6, the V-phase upper arm switch Q VH Only the V-phase coils 23v and 23w are switched at a predetermined duty ratio. During the current conduction period P6, a power supply current flows from the V-phase terminal 22v to the W-phase terminal 22w, through the V-phase coil 23v and the W-phase coil 23w. That is, the current conduction phases during the current conduction period P6 are the V-phase and the W-phase.

[0031] By controlling the switching of each arm switch according to the six current-carrying patterns described above, a rotating magnetic field is generated that rotates shaft 21 of three-phase motor 20 360° in a fixed direction. As a result, shaft 21 of three-phase motor 20 rotates 360° in a fixed direction during the period from time t10 to time t16. In other words, shaft 21 of three-phase motor 20 rotates 60° in a fixed direction during each of current-carrying periods P1 to P6.

[0032] The speed at which the current conduction pattern switches, i.e., the speed at which the current conduction phase switches, is called the commutation frequency Fs. The unit of the commutation frequency Fs is "Hz." If the period during which switching control is performed with one current conduction pattern is P (seconds), the commutation frequency Fs can be expressed as "Fs = 1 / P."

[0033] Figure 3 shows the waveforms of the voltages appearing at the U-phase terminal 22u, V-phase terminal 22v, and W-phase terminal 22w of the three-phase motor 20. In Figure 3, "Vu" is the U-phase terminal voltage appearing at the U-phase terminal 22u. "Vv" is the V-phase terminal voltage appearing at the V-phase terminal 22v. "Vw" is the W-phase terminal voltage appearing at the W-phase terminal 22w. Note that the actual waveforms of the U-phase terminal voltage Vu, V-phase terminal voltage Vv, and W-phase terminal voltage Vw have duty ratios that are the same as the switching duty ratio, but for convenience, Figure 3 shows only the envelopes of the voltage waveforms.

[0034] The U-phase terminal voltage Vu has an effective voltage value determined by the switching duty ratio during conduction periods P1 and P2, and is at ground level, i.e., 0 V, during conduction periods P4 and P5. The V-phase terminal voltage Vv has an effective voltage value determined by the switching duty ratio during conduction periods P5 and P6, and is 0 V during conduction periods P2 and P3. The W-phase terminal voltage Vw has an effective voltage value determined by the switching duty ratio during conduction periods P3 and P4, and is 0 V during conduction periods P1 and P6. In this way, in the sensorless 120° conduction method, the phase to which the drive voltage required to drive the three-phase motor 20 is applied switches every 120°.

[0035] During the energization period P3, no drive current flows through the U-phase coil 23u, but the energy stored in the U-phase coil 23u drives the U-phase lower arm switch Q UL A return current flows through the U-phase coil 23u for a fixed time via the body diode of the U-phase coil 23u. As a result, a ringing phenomenon occurs in which the U-phase terminal voltage Vu becomes 0V for a fixed time from the start of the period P3. After that, the U-phase terminal voltage Vu matches the induced voltage generated in the U-phase coil 23u. During the current conduction period P3, the induced voltage reaches the neutral point voltage V N It crosses from the high pressure side to the low pressure side.

[0036] Similarly, during the energization period P6, no drive current flows through the U-phase coil 23u, but the U-phase upper arm switch Q UH As a result, the U-phase terminal voltage Vu is equal to the DC power supply voltage V for a certain period of time from the start of the current-carrying period P6. M After that, the U-phase terminal voltage Vu coincides with the induced voltage generated in the U-phase coil 23u. During the conduction period P6, the induced voltage reaches the neutral point voltage V N It crosses from the low pressure side to the high pressure side.

[0037] As described above, while the three-phase motor 20 rotates 360°, an induced voltage is exposed at the U-phase terminal 22u only during the energization periods P3 and P6. By the same principle, while the three-phase motor 20 rotates 360°, an induced voltage is exposed at the V-phase terminal 22v only during the energization periods P1 and P4, and an induced voltage is exposed at the W-phase terminal 22w only during the energization periods P2 and P5. In the sensorless 120° energization method, in order to detect the phase of the three-phase motor 20, the neutral point voltage V N It is necessary to detect the zero crossing point, which is the point where the voltage and the induced voltage cross each other.

[0038] In FIG. 3, "Zu" indicates that the induced voltage exposed to the U-phase terminal 22u is equal to the neutral point voltage V N The induced voltage exposed at the U-phase terminal 22u becomes low when the neutral point voltage V N The U-phase zero-crossing point detection signal goes high when the induced voltage exposed to the V-phase terminal 22v reaches the neutral point voltage V N The voltage becomes low when the voltage drops below the neutral voltage V N The V-phase zero-crossing point detection signal goes high when the induced voltage exposed to the W-phase terminal 22w reaches the neutral point voltage V N The induced voltage exposed at the W-phase terminal 22w becomes low when the neutral point voltage V N This is a W-phase zero-crossing point detection signal that goes high when the output voltage Vout becomes higher.

[0039] In Fig. 3, "Hu" is a U-phase phase detection signal that has a phase delay of 30° with respect to the U-phase zero-cross point detection signal Zu. "Hv" is a V-phase phase detection signal that has a phase delay of 30° with respect to the V-phase zero-cross point detection signal Zv. "Hw" is a W-phase phase detection signal that has a phase delay of 30° with respect to the W-phase zero-cross point detection signal Zw.

[0040] Note that the three-phase motor 20 rotates 60° during the time between two adjacent zero-crossing points on the time axis. Therefore, by measuring the time between two adjacent zero-crossing points on the time axis and delaying the U-phase zero-crossing point detection signal Zu by half the time of the measurement result, it is possible to generate a U-phase phase detection signal Hu that has a phase delay of 30° relative to the U-phase zero-crossing point detection signal Zu. The V-phase phase detection signal Hv and W-phase phase detection signal Hw can also be generated in a similar manner.

[0041] As shown in FIG. 3, it can be seen that the levels of the U-phase phase detection signal Hu, the V-phase phase detection signal Hv, and the W-phase phase detection signal Hw change regularly depending on six current conduction patterns. Hereinafter, the patterns in which the levels of the U-phase phase detection signal Hu, the V-phase phase detection signal Hv, and the W-phase phase detection signal Hw change depending on the current conduction pattern will be referred to as phase patterns. As shown in FIG. 2, the phase patterns of the sensorless 120° current conduction method include six phase patterns PB1, PB2, PB3, PB4, PB5, and PB6. In FIG. 2, "H U ","H V " and "H W Of the "1" and "0" in the " " column, "1" means that the corresponding phase detection signal is at a high level, and "0" means that the corresponding phase detection signal is at a low level.

[0042] In the sensorless 120° energization method, the phase pattern is recognized for each energization period based on the three phase detection signals Hu, Hv, and Hw, and the energization pattern to be used in the next energization period is determined based on the phase pattern recognition result.The energization pattern is then switched to the next energization pattern when the phase pattern changes.

[0043] 3, for example, during energization period P1, the phase pattern for energization period P1 is recognized as phase pattern PB1 from the phase detection signals Hu, Hv, and Hw. Because the phase pattern for energization period P1 is phase pattern PB1, energization pattern PA2 is determined as the energization pattern to be used in the next energization period P2. Then, when the phase pattern PB1 changes, that is, when a falling edge occurs in the V-phase phase detection signal Hv, the energization pattern is switched from energization pattern PA1 to energization pattern PA2.

[0044] In the sensorless 120° energization method, the above-described energization pattern switching is performed at 60° intervals in synchronization with the phase detection signals Hu, Hv, and Hw generated using the induced voltage generated in the three-phase motor 20, thereby enabling rotation control of the three-phase motor 20 without a position sensor such as a Hall sensor. Hereinafter, controlling the energization of the three-phase motor 20 in synchronization with the phase detection signals Hu, Hv, and Hw generated using the induced voltage generated in the three-phase motor 20 will be referred to as "sensorless synchronous control."

[0045] The above is the basic principle of the sensorless 120° conduction method. In order to generate the phase detection signals Hu, Hv, and Hw in the sensorless 120° conduction method, the neutral point voltage V N It is necessary to detect the zero-crossing points, which are the points where the induced voltage intersects with the zero-crossing points, but unless the rotation speed of the three-phase motor 20 is equal to or greater than a predetermined rotation speed, an induced voltage at which the zero-crossing points can be detected will not be generated. In the following explanation, the minimum rotation speed required to generate an induced voltage at which the zero-crossing points can be detected will be referred to as the minimum limit rotation speed.

[0046] For example, when the electric pump device 100 is used in a low-temperature environment, the load on the three-phase motor 20 increases due to the increased viscosity of the cooling oil F, and therefore the three-phase motor 20 needs to be rotated at a relatively low rotation speed. In such a low-temperature environment, the three-phase motor 20 may be rotated at a rotation speed close to the minimum limit rotation speed. In this case, the neutral point voltage V N (=V M / 2) is set as the zero-cross determination level, and the point where the zero-cross determination level and the induced voltage intersect is detected as the zero-cross point. However, the inventors' research has revealed that, for reasons explained below, it may be difficult to stably perform sensorless synchronous control of three-phase motor 20.

[0047] FIG. 4 is a diagram schematically showing the waveform of the induced voltage exposed to the U-phase terminal 22u during the current-carrying period P3 shown in FIG. 3, that is, the induced voltage appearing in the U-phase terminal voltage Vu. 4, waveform W0 is the waveform of the induced voltage that appears in the U-phase terminal voltage Vu when three-phase motor 20 is rotated at a rotation speed that generates an induced voltage sufficient to detect the zero-crossing point. Hereinafter, waveform W0 will be referred to as the ideal induced voltage waveform. In Figure 4, LV0 is the neutral point voltage V N (=V M / 2). Hereinafter, LV0 will be referred to as the ideal zero-crossing detection level. 4, Pz0 is the zero-cross point where the ideal zero-cross determination level LV0 intersects with the ideal induced voltage waveform W0. Hereinafter, Pz0 will be referred to as the ideal zero-cross point. 4, tz0 is the timing at which the ideal zero-cross point Pz0 is detected. Hereinafter, tz0 will be referred to as the ideal zero-cross detection timing.

[0048] As a result of research by the inventors of the present application, it was found that when extremely low-speed rotation control is performed in which the three-phase motor 20 rotates at a speed close to the minimum limit rotation speed in a low-temperature environment, the waveform of the induced voltage is distorted depending on the magnitude of the power supply current flowing through the drive circuit 11 (the drive current flowing through the three-phase motor 20). 4, waveform W1 is the waveform of the induced voltage that appears in the U-phase terminal voltage Vu when a power supply current of 30 (A) flows during extremely low-speed rotation control of three-phase motor 20. Hereinafter, waveform W1 will be referred to as the first induced voltage waveform. 4, waveform W2 is the waveform of the induced voltage that appears in the U-phase terminal voltage Vu when a power supply current of 20 (A) flows during extremely low-speed rotation control of three-phase motor 20. Hereinafter, waveform W2 will be referred to as the second induced voltage waveform. 4, waveform W3 is the waveform of the induced voltage that appears in the U-phase terminal voltage Vu when a power supply current of 10 (A) flows during extremely low-speed rotation control of three-phase motor 20. Hereinafter, waveform W3 will be referred to as the third induced voltage waveform. As shown in FIG. 4, when the three-phase motor 20 is subjected to extremely low-speed rotation control, the smaller the power supply current flowing through the drive circuit 11, the more the waveform of the induced voltage appearing in the U-phase terminal voltage Vu becomes distorted compared to the ideal induced voltage waveform W0.

[0049] 4, Pz1 is the zero-cross point where the ideal zero-cross determination level LV0 intersects with the first induced voltage waveform W1. Hereinafter, Pz1 will be referred to as the first zero-cross point. 4, tz1 is the timing at which the first zero-cross point Pz1 is detected. Hereinafter, tz1 will be referred to as the first zero-cross detection timing. As shown in Figure 4, due to distortion of the first induced voltage waveform W1 compared to the ideal induced voltage waveform W0, the first zero crossing point Pz1 shifts to the left of the ideal zero crossing point Pz0, and as a result, the first zero crossing detection timing tz1 shifts to the left of the ideal zero crossing detection timing tz0.

[0050] 4, Pz2 is the zero-cross point where the ideal zero-cross determination level LV0 intersects with the second induced voltage waveform W2. Hereinafter, Pz2 will be referred to as the second zero-cross point. 4, tz2 is the timing at which the second zero-cross point Pz2 is detected. Hereinafter, tz2 will be referred to as the second zero-cross detection timing. As shown in Figure 4, because the second induced voltage waveform W2 is distorted more than the first induced voltage waveform W1, the second zero cross point Pz2 shifts to the left of the first zero cross point Pz1, and the second zero cross detection timing tz2 shifts to the left of the first zero cross detection timing tz1.

[0051] 4, Pz3 is the zero-cross point where the ideal zero-cross determination level LV0 intersects with the third induced voltage waveform W3. Hereinafter, Pz3 will be referred to as the third zero-cross point. 4, tz3 is the timing at which the third zero-cross point Pz3 is detected. Hereinafter, tz3 will be referred to as the third zero-cross detection timing. As shown in Figure 4, because the third induced voltage waveform W3 is distorted more than the second induced voltage waveform W2, the third zero cross point Pz3 shifts to the left of the second zero cross point Pz2, and the third zero cross detection timing tz3 shifts to the left of the second zero cross detection timing tz2.

[0052] As described above, when very low speed rotation control is performed, the smaller the power supply current flowing through the drive circuit 11, the more the waveform of the induced voltage appearing in the U-phase terminal voltage Vu is distorted, causing the zero-cross detection timing to shift to the left of the ideal zero-cross detection timing tz0. The zero-cross detection timing based on the induced voltage appearing in the V-phase terminal voltage Vv and the zero-cross detection timing based on the induced voltage appearing in the W-phase terminal voltage Vw also shift depending on the power supply current. As a result, the timing of the rising and falling edges of the phase detection signals Hu, Hv, and Hw deviates from the ideal timing, making it impossible to switch the current conduction pattern accurately at 60° intervals. This is why, when very low speed rotation control is performed on the three-phase motor 20, the neutral point voltage V N (=V M This is because if the point where the induced voltage crosses the zero-cross determination level set to (1 / 2) is detected as the zero-cross point, it becomes difficult to stably perform sensorless synchronous control of the three-phase motor 20.

[0053] In order to solve the above technical problem, in this embodiment, the value of the zero-crossing determination level is changed according to the power supply current flowing through the drive circuit 11. Hereinafter, with reference to Fig. 5, the reason why it is possible to stably perform sensorless synchronous control of the three-phase motor 20 by changing the value of the zero-crossing determination level according to the power supply current will be described.

[0054] For example, in FIG. 5, LV1 is a zero-crossing detection level that is lower than the ideal zero-crossing detection level LV0. Hereinafter, LV1 will be referred to as the first zero-crossing detection level. Pz1' is a zero-crossing point where the first zero-crossing detection level LV1 intersects with the first induced voltage waveform W1. Hereinafter, Pz1' will be referred to as the first offset zero-crossing point. As shown in FIG. 5, the timing at which the first offset zero-crossing point Pz1' is detected coincides with the ideal zero-crossing detection timing tz0.

[0055] In FIG. 5, LV2 is a zero-crossing detection level lower than the first zero-crossing detection level LV1. Hereinafter, LV2 will be referred to as the second zero-crossing detection level. Pz2' is a zero-crossing point where the second zero-crossing detection level LV2 intersects with the second induced voltage waveform W2. Hereinafter, Pz2' will be referred to as the second offset zero-crossing point. As shown in FIG. 5, the timing at which the second offset zero-crossing point Pz2' is detected coincides with the ideal zero-crossing detection timing tz0.

[0056] In FIG. 5, LV3 is a zero-crossing detection level lower than the second zero-crossing detection level LV2. Hereinafter, LV3 will be referred to as the third zero-crossing detection level. Pz3' is a zero-crossing point where the third zero-crossing detection level LV3 intersects with the third induced voltage waveform W3. Hereinafter, Pz3' will be referred to as the third offset zero-crossing point. As shown in FIG. 5, the timing at which the third offset zero-crossing point Pz3' is detected coincides with the ideal zero-crossing detection timing tz0.

[0057] As shown in Figure 5, for example, when the power supply current value is 30 (A), by offsetting (changing) the value of the zero-crossing determination level from LV0 to LV1, the detection timing of the zero-crossing point where the induced voltage corresponding to the power supply current value of 30 (A) intersects with the zero-crossing determination level can be made to coincide with the ideal zero-crossing detection timing tz0. Furthermore, for example, if the power supply current value is 20 (A), by offsetting (changing) the value of the zero-crossing determination level from LV0 to LV2, the detection timing of the zero-crossing point where the induced voltage corresponding to the power supply current value of 20 (A) intersects with the zero-crossing determination level can be made to coincide with the ideal zero-crossing detection timing tz0. Furthermore, for example, if the power supply current value is 10 (A), by offsetting (changing) the value of the zero-crossing determination level from LV0 to LV3, the detection timing of the zero-crossing point where the induced voltage corresponding to the power supply current value of 10 (A) intersects with the zero-crossing determination level can be made to coincide with the ideal zero-crossing detection timing tz0.

[0058] As described above, by changing the value of the zero-crossing determination level in response to the power supply current flowing through the drive circuit 11, even if the waveform of the induced voltage appearing in each of the three-phase terminal voltages is distorted depending on the power supply current when performing extremely low-speed rotation control of the three-phase motor 20, the zero-crossing detection timing can be made to approximately coincide with the ideal zero-crossing detection timing tz0. As a result, the occurrence timing of the rising and falling edges of the phase detection signals Hu, Hv, and Hw can be made to approximately coincide with the ideal timing, enabling precise switching of the current conduction pattern at 60° intervals. This enables stable sensorless synchronous control of the three-phase motor 20 when performing extremely low-speed rotation control of the three-phase motor 20.

[0059] Below, we will explain the shunt resistor 12, voltage detection circuit 13, control unit 14, and memory unit 15 provided in the motor control device 10 of this embodiment, based on the explanation of the basic principle of the above-mentioned sensorless 120° current supply method and the explanation of the technical effect obtained by changing the value of the zero-crossing judgment level according to the power supply current.

[0060] The shunt resistor 12 detects the power supply current flowing through the drive circuit 11. One end of the shunt resistor 12 is connected to the U-phase lower arm switch Q UL , V-phase lower arm switch Q VL , and W-phase lower arm switch Q WLThe shunt resistor 12 is electrically connected to the source terminals of the DC power supply 200 and the output terminals of the shunt resistor 12. The other end of the shunt resistor 12 is electrically connected to the negative terminal of the DC power supply 200. Furthermore, one end of the shunt resistor 12 is electrically connected to the control unit 14. The power supply current flowing through the drive circuit 11 flows into the vehicle ground via the shunt resistor 12. Therefore, a voltage proportional to the power supply current appears between the terminals of the shunt resistor 12. This voltage between the terminals of the shunt resistor 12 is supplied to the control unit 14 as a power supply current value indicating the detection result of the power supply current. Note that a resistive voltage divider circuit may be provided between the one end of the shunt resistor 12 and the control unit 14, if necessary.

[0061] The voltage detection circuit 13 is a circuit that detects the three-phase terminal voltages of the three-phase motor 20. The voltage detection circuit 13 is electrically connected to each of the U-phase terminal 22u, V-phase terminal 22v, and W-phase terminal 22w of the three-phase motor 20. The voltage detection circuit 13 detects a U-phase terminal voltage Vu, which is the voltage at the U-phase terminal 22u, and supplies the detected value to the control unit 14. The voltage detection circuit 13 detects a V-phase terminal voltage Vv, which is the voltage at the V-phase terminal 22v, and supplies the detected value to the control unit 14. The voltage detection circuit 13 detects a W-phase terminal voltage Vw, which is the voltage at the W-phase terminal 22w, and supplies the detected value to the control unit 14. As an example, the voltage detection circuit 13 is configured by a resistive voltage divider circuit.

[0062] The control unit 14 is, for example, a microprocessor such as an MCU (Microcontroller Unit). A rotation speed command signal CS output from a higher-level control device (not shown) is input to the control unit 14. The rotation speed command signal CS is a signal that indicates a target rotation speed of the three-phase motor 20. The control unit 14 is communicably connected to the storage unit 15 via a communication bus (not shown). As will be described in detail later, the control unit 14 executes a process of rotating the three-phase motor 20 at the target rotation speed indicated by the rotation speed command signal CS in accordance with a program stored in advance in the storage unit 15.

[0063] The control unit 14 obtains the power supply current value as digital data by A / D converting the inter-terminal voltage of the shunt resistor 12. The control unit 14 obtains the U-phase terminal voltage Vu, the V-phase terminal voltage Vv, and the W-phase terminal voltage Vw as digital data by A / D converting the output voltage of the voltage detection circuit 13. The control unit 14 detects the points where the induced voltage appearing in each of the three-phase terminal voltages crosses a predetermined zero-cross determination level as zero-cross points, and controls the drive circuit 11 based on the zero-cross point detection results.

[0064] Specifically, the control unit 14 generates a U-phase zero-cross point detection signal Zu based on the detection result of the zero-cross point where the induced voltage appearing in the U-phase terminal voltage Vu crosses the zero-cross determination level, and generates a U-phase phase detection signal Hu that has a phase delay of 30° with respect to the U-phase zero-cross point detection signal Zu. Furthermore, the control unit 14 generates a V-phase zero-cross point detection signal Zv based on the detection result of the zero-cross point where the induced voltage appearing in the V-phase terminal voltage Vv crosses the zero-cross determination level, and generates a V-phase phase detection signal Hv having a phase delay of 30° with respect to the V-phase zero-cross point detection signal Zv. Furthermore, the control unit 14 generates a W-phase zero-cross point detection signal Zw based on the detection result of the zero-cross point where the induced voltage appearing in the W-phase terminal voltage Vw crosses the zero-cross determination level, and generates a W-phase phase detection signal Hw having a phase delay of 30° with respect to the W-phase zero-cross point detection signal Zw.

[0065] The control unit 14 switches the energization pattern based on the phase detection signals Hu, Hv, and Hw, determines a switching duty ratio required to make the actual rotation speed of the three-phase motor 20 match the target rotation speed, and controls the switching of each arm switch using the determined switching duty ratio. As a result, a three-phase AC voltage that matches the actual rotation speed of the motor 20 to the target rotation speed is supplied from the drive circuit 11 to the three-phase motor 20.

[0066] The control unit 14 changes the value of the zero-crossing determination level based on the power supply current value detected by the shunt resistor 12. Specifically, the control unit 14 calculates an offset value based on the power supply current value detected by the shunt resistor 12, and changes the value of the zero-crossing determination level to a value obtained by offsetting the reference zero-crossing determination value with the offset value. The reference zero-crossing determination value is a reference value for the zero-crossing determination level. As an example, the reference zero-crossing determination value in this embodiment is M That is, in this embodiment, the reference zero-crossing determination value is set to the same value as the ideal zero-crossing determination level LV0.

[0067] Referring to FIG. 5, for example, when the power supply current value is 30 (A), the control unit 14 calculates an offset value required to change the value of the zero-crossing determination level from the reference zero-crossing determination value (LV0) to LV1. Furthermore, for example, when the power supply current value is 20 (A), the control unit 14 calculates an offset value required to change the value of the zero-crossing determination level from the reference zero-crossing determination value (LV0) to LV2. Furthermore, for example, when the power supply current value is 10 (A), the control unit 14 calculates an offset value required to change the value of the zero-crossing determination level from the reference zero-crossing determination value (LV0) to LV3. The arithmetic equation used to calculate the offset value is prepared in advance through experiments, simulations, or the like, and is stored in advance in the storage unit 15. Hereinafter, the arithmetic equation used to calculate the offset value will be referred to as the offset arithmetic equation.

[0068] The storage unit 15 includes a nonvolatile memory that stores programs and various setting data required for the control unit 14 to execute various processes, and a volatile memory that is used as a temporary storage destination for data when the control unit 14 executes various processes. The nonvolatile memory is, for example, an EEPROM (Electrically Erasable Programmable Read-Only Memory) or a flash memory. The volatile memory is, for example, a RAM (Random Access Memory).

[0069] The storage unit 15 stores various data necessary for controlling the three-phase motor 20 using the sensorless 120° energization method. For example, the storage unit 15 stores in advance the energization pattern and phase pattern shown in FIG. 2. The storage unit 15 also stores in advance a reference zero-crossing determination value, which is a reference value for the zero-crossing determination level, and an offset calculation formula used to calculate the offset value. As shown in FIG. 1, the storage unit 15 may be provided outside the control unit 14, or may be built into the control unit 14.

[0070] Next, with reference to FIG. 6, the extremely low speed rotation control of the three-phase motor 20 executed by the control unit 14 in a low-temperature environment will be described in detail. FIG. 6 is a flowchart showing the processes included in the extremely low speed rotation control. The control unit 14 starts the extremely low speed rotation control of the three-phase motor 20 when the target rotation speed indicated by the rotation speed command signal CS is close to the minimum limit rotation speed. As an example, the rotation speed close to the minimum limit rotation speed is 300 rpm to 600 rpm. Note that the three-phase motor 20 is in a stopped state when the extremely low speed rotation control starts.

[0071] As shown in FIG. 6, when the control unit 14 starts the extremely low speed rotation control, it first aligns the rotor of the three-phase motor 20 (step S1), and after rotor alignment is completed, starts the forced commutation control of the three-phase motor 20 (step S2).

[0072] When starting three-phase motor 20 using the sensorless 120° conduction method, phase detection signals Hu, Hv, and Hw cannot be generated until the rotation speed of three-phase motor 20 reaches the minimum limit rotation speed at which an induced voltage that allows zero-crossing points to be detected is generated, and therefore sensorless synchronous control of three-phase motor 20 cannot be performed. Therefore, when starting three-phase motor 20 using the sensorless 120° conduction method, it is necessary to control the conduction of three-phase motor 20 in accordance with a predetermined start-up sequence until the rotation speed of three-phase motor 20 reaches the minimum limit rotation speed.

[0073] A commonly known example of a startup sequence is one in which the rotor is aligned to a specific position (a position corresponding to one of the motor control states) by applying DC excitation to the three-phase motor 20 for a predetermined time, and then a forced commutation control is performed to forcibly switch the current-carrying phases (current-carrying patterns) at a predetermined forced commutation frequency while applying a predetermined drive voltage to the current-carrying phases. The processes of steps S1 and S2 are included in the known startup sequence as described above, and therefore a detailed description thereof will be omitted.

[0074] When forced commutation control is started, the rotation speed of three-phase motor 20 gradually increases toward the rotation speed corresponding to the forced commutation frequency. When forced commutation control is started, control unit 14 acquires a power supply current value (step S3) and changes the value of the zero-crossing determination level based on the acquired power supply current value (step S4). Specifically, in step S4, control unit 14 reads an offset calculation formula from storage unit 15 and calculates an offset value by substituting the acquired power supply current value into the offset calculation formula. Then, in step S4, control unit 14 reads a reference zero-crossing determination value from storage unit 15 and changes the value of the zero-crossing determination level to a value obtained by offsetting the reference zero-crossing determination value with the offset value.

[0075] 5, for example, when the power supply current value is 30 (A), the control unit 14 calculates an offset value required to change the value of the zero-crossing determination level from the reference zero-crossing determination value (LV0) to LV1. Then, the control unit 14 changes the value of the zero-crossing determination level to a value (LV1) obtained by offsetting the reference zero-crossing determination value (LV0) with the offset value.

[0076] After changing the value of the zero-crossing determination level as described above, the control unit 14 starts a process of detecting points where the induced voltages appearing in the terminal voltages Vu, Vv, and Vw of each phase cross the zero-crossing determination level as zero-crossing points, and determines whether zero-crossing points have been detected n times consecutively (step S5), where n is an integer equal to or greater than 2. The control unit 14 starts a process of generating zero-cross point detection signals Zu, Zv, and Zw for each phase based on the detection results of the zero-cross points for each phase, and a process of generating phase detection signals Hu, Hv, and Hw for each phase based on the zero-cross point detection signals Zu, Zv, and Zw for each phase.

[0077] After the start of forced commutation control, when the rotation speed of three-phase motor 20 reaches the minimum limit rotation speed, a relatively large induced voltage begins to appear in the terminal voltages Vu, Vv, and Vw of each phase, and zero-crossing points begin to be detected. If it is determined in step S5 that zero-crossing points have been detected n times in succession, it is estimated that three-phase motor 20 has begun to rotate stably at a rotation speed equal to or higher than the minimum limit rotation speed.

[0078] If the answer to step S5 is "No," that is, if the number of consecutive zero-crossing points detected is less than n, it is estimated that the three-phase motor 20 has not yet started to rotate stably at a rotation speed equal to or greater than the minimum limit rotation speed. In this case, the control unit 14 returns to the process of step S3.

[0079] On the other hand, if the answer to step S5 is "Yes," i.e., if the number of consecutive zero-crossing points detected reaches n, it is estimated that the three-phase motor 20 has begun to rotate stably at a rotation speed equal to or greater than the minimum limit rotation speed. In this case, the control unit 14 recognizes the phase pattern of the current current-carrying period based on the phase detection signals Hu, Hv, and Hw, and determines the current-carrying pattern to be used in the next current-carrying period based on the phase pattern recognition result (step S6).

[0080] For example, as shown in Figure 3, when a zero-cross point is detected during the conduction period P1, where the induced voltage appearing in the V-phase terminal voltage Vv intersects with the zero-cross determination level, it is assumed that the number of consecutive zero-cross point detections reaches n. In Figure 3, the zero-cross determination level is the neutral point potential V N (=V M / 2), but the value of the zero-crossing determination level is changed to a value based on the power supply current value by the processes in steps S3 and S4.

[0081] When the number of consecutive zero-crossing points detected during the current conduction period P1 reaches n in this manner, the control unit 14 recognizes the phase pattern of the current current conduction period P1 based on the phase detection signals Hu, Hv, and Hw. During the current conduction period P1, the phase detection signals Hu and Hv are each at a high level ("1"), and the phase detection signal Hw is at a low level ("0"). In this case, the control unit 14 recognizes that the phase pattern of the current current conduction period P1 is PB1 by referring to the phase patterns stored in the memory unit 15 (see FIG. 2).

[0082] Then, control unit 14 determines the energization pattern to be used in the next energization period based on the phase pattern recognition result. For example, as described above, when control unit 14 recognizes that the phase pattern of the current energization period P1 is PB1, control unit 14 determines energization pattern PA2 as the energization pattern to be used in the next energization period by referring to the energization patterns stored in memory unit 15 (see FIG. 2).

[0083] After determining the current conduction pattern to be used in the next current conduction period, the control unit 14 switches the current conduction pattern to the current conduction pattern determined in step S6 when the level of any of the phase detection signals Hu, Hv, and Hw changes (step S7). For example, if the number of consecutive zero-crossing points detected in current conduction period P1 reaches n as described above, the level of the phase detection signal Hv changes from high to low when the three-phase motor 20 rotates 30° from the time of the zero-crossing point detection based on the induced voltage appearing in the V-phase terminal voltage Vv (see time t11 in FIG. 3). Therefore, in this case, the control unit 14 switches the current conduction pattern to the current conduction pattern PA2 determined in step S6 when a falling edge occurs in the phase detection signal Hv (time t11).

[0084] In addition to switching the energization pattern, the control unit 14 determines a switching duty ratio required to make the actual rotation speed of the three-phase motor 20 coincide with the target rotation speed, and performs switching control of each arm switch at the determined switching duty ratio. For example, when the energization pattern is switched to the energization pattern PA2 as described above, the control unit 14 controls the U-phase upper arm switch Q UH and V-phase lower arm switch Q VL In the case of the energization pattern PA2, the control unit 14 controls the U-phase upper arm switch Q to be on and controls the remaining arm switches to be off (see FIG. 2). UH Only then, switching is controlled at the determined switching duty ratio (see FIG. 3). As a result, a three-phase AC voltage that causes the actual rotation speed of the three-phase motor 20 to coincide with the target rotation speed is supplied from the drive circuit 11 to the three-phase motor 20.

[0085] Thereafter, the control unit 14 switches the current conduction pattern at 60° intervals and controls the switching of each arm switch in synchronization with the phase detection signals Hu, Hv, and Hw, thereby rotating the three-phase motor 20 at the target rotation speed. In this way, from step S6 onwards, the control unit 14 starts sensorless synchronous control for controlling the three-phase motor 20 in synchronization with the phase detection signals Hu, Hv, and Hw.

[0086] As described above, the motor control device 10 in this embodiment detects the points where the induced voltage appearing in each of the three-phase terminal voltages crosses a predetermined zero-cross determination level as zero-cross points, and includes a control unit 14 that controls the drive circuit 11 based on the zero-cross point detection results, and the control unit 14 changes the value of the zero-cross determination level based on the power supply current value detected by the shunt resistor 12. According to this embodiment, when the three-phase motor 20 is rotated at a speed close to the minimum limit speed in a low-temperature environment, even if the waveform of the induced voltage appearing in each of the three-phase terminal voltages is distorted depending on the power supply current, the zero-crossing detection timing can be made to approximately coincide with the ideal zero-crossing detection timing tz0. As a result, the occurrence timing of the rising and falling edges of the phase detection signals Hu, Hv, and Hw can be made to approximately coincide with the ideal timing, enabling precise switching of the energization pattern at 60° intervals. This allows stable sensorless synchronous control of the three-phase motor 20, even when the three-phase motor 20 is rotated at a speed close to the minimum limit speed in a low-temperature environment.

[0087] In addition, the motor control device 10 in this embodiment further includes a memory unit 15 that stores a reference zero-cross judgment value, which is a reference value of the zero-cross judgment level, and the control unit 14 calculates an offset value based on the power supply current value detected by the shunt resistor 12, and changes the value of the zero-cross judgment level to a value obtained by offsetting the reference zero-cross judgment value with the offset value. This allows the value of the zero-crossing determination level to be changed through simple calculations, thereby reducing the processing load on the control unit 14. Furthermore, because the value of the zero-crossing determination level can be changed based on the power supply current value, the zero-crossing detection timing can be made to approximately coincide with the ideal zero-crossing detection timing tz0 even if the waveform of the induced voltage appearing in each of the three-phase terminal voltages is distorted depending on the power supply current. As a result, the current conduction pattern can be switched at precise intervals, and sensorless synchronous control of the three-phase motor 20 can be stably performed even when the three-phase motor 20 is rotated at a rotation speed close to the minimum limit rotation speed in a low-temperature environment.

[0088] In this embodiment, the reference zero-crossing determination value is the DC power supply voltage V M It is half the value of. As a result, even if the waveform of the induced voltage appearing in each of the three-phase terminal voltages is distorted depending on the power supply current, the zero-cross detection timing can be made to approximately coincide with the detection timing of the zero-cross point where the neutral point potential and the induced voltage intersect (ideal zero-cross detection timing tz0), making it possible to switch the current flow pattern at 60° intervals with greater precision.

[0089] [Modification] The present invention is not limited to the above-described embodiment, and the configurations described in this specification can be combined as appropriate within a range that does not contradict each other. In the above embodiment, an example was given in which the control unit 14 calculates an offset value based on the power supply current value and changes the value of the zero-crossing determination level to a value obtained by offsetting the reference zero-crossing determination value with the offset value, but the method of changing the value of the zero-crossing determination level is not limited to this.

[0090] For example, the storage unit 15 may store in advance the correspondence relationship between candidate values of the zero-crossing determination level and the power supply current value, and the control unit 14 may read from the storage unit 15 a candidate value corresponding to the power supply current value detected by the shunt resistor 12, and change the value of the zero-crossing determination level to the read candidate value. The storage unit 15 may store the correspondence relationship between candidate values of the zero-crossing determination level and the power supply current value in the form of table data or in the form of a mathematical formula. The correspondence relationship between candidate values of the zero-crossing determination level and the power supply current value is prepared in advance through experiments, simulations, or the like, and stored in the storage unit 15 in advance. This allows the value of the zero-crossing determination level to be changed by simple processing, thereby reducing the processing load on the control unit 14.

[0091] Referring to Figure 5, for example, if the correspondence between the candidate values for the zero-cross determination level and the power supply current value is in the form of table data, LV1 is linked to a power supply current value of 30 (A) as the candidate value for the zero-cross determination level, LV2 is linked to a power supply current value of 20 (A) as the candidate value for the zero-cross determination level, and LV3 is linked to a power supply current value of 10 (A) as the candidate value for the zero-cross determination level.

[0092] In the above embodiment, the electric pump device of the present invention is exemplified as the electric pump device 100 that supplies cooling oil F to a drive motor mounted on a hybrid vehicle, but the electric pump device of the present invention is not limited to this and can also be applied to, for example, an electric pump device that supplies oil to a transmission. Furthermore, the fluid discharged from the electric pump is not limited to oil such as cooling oil. [Explanation of symbols]

[0093] 10...motor control device, 11...drive circuit, 12...shunt resistor (current detection unit), 13...voltage detection circuit (voltage detection unit), 14...control unit, 15...storage unit, 20...three-phase motor, 30...pump, 40...electric pump, 100...electric pump device, 200...DC power supply, F...cooling oil

Claims

1. A motor control device for controlling a three-phase motor, a drive circuit that converts a DC power supply voltage into a three-phase AC voltage and supplies the three-phase AC voltage to the three-phase motor; a current detection unit that detects a power supply current flowing through the drive circuit; a voltage detection unit that detects three-phase terminal voltages of the three-phase motor; a control unit that detects points where induced voltages appearing in the three-phase terminal voltages cross a predetermined zero-cross determination level as zero-cross points, and controls the drive circuit based on the detection results of the zero-cross points; Equipped with the control unit changes a value of the zero-crossing determination level based on the power supply current value detected by the current detection unit so that a detection timing of a zero-crossing point at which the induced voltage appearing in each of the three-phase terminal voltages crosses the zero-crossing determination level coincides with an ideal zero-crossing detection timing; the ideal zero-cross detection timing is a timing at which the induced voltage appearing in each of the three-phase terminal voltages crosses an ideal zero-cross determination level having a value half the DC power supply voltage when the three-phase motor is rotated at a minimum rotation speed required to generate an induced voltage at which the zero-cross point can be detected; Motor control device.

2. Further comprising a memory unit that stores a reference zero-crossing determination value that is 1 / 2 of the DC power supply voltage, the control unit calculates an offset value based on the power supply current value detected by the current detection unit, and changes the value of the zero-crossing determination level to a value obtained by offsetting the reference zero-crossing determination value with the offset value. The motor control device according to claim 1 .

3. a storage unit that stores a correspondence relationship between the candidate values of the zero-crossing determination level and the power supply current value, the control unit reads out from the storage unit the candidate value corresponding to the power supply current value detected by the current detection unit, and changes the value of the zero-crossing determination level to the read candidate value. The motor control device according to claim 1 .

4. a three-phase motor having a shaft; a pump located on one axial side of the shaft and driven by the three-phase motor via the shaft; The motor control device according to any one of claims 1 to 3, which controls the three-phase motor; An electric pump device comprising:

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