Motor drive circuits, motor systems, and electrical equipment

Abstract

To provide a motor drive circuit capable of improving rotation accuracy of a motor.SOLUTION: A motor drive circuit (100) includes: a PWM signal generation part (10) configured to generate a PWM signal on the basis of a count value of a counter (11); a detection part (20) configured to detect a zero crossing of a counter electromotive voltage generated in a coil of a motor (200); a prediction part (30) configured to predict an arrival timing of the zero crossing of the counter electromotive voltage; a stop part (40) configured to stop a counting operation of the counter after a first time point going back from the arrival timing predicted by the prediction part; and a reset part (50) configured to reset the count value at a timing at which the detection part detects the zero crossing of the counter electromotive voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The invention disclosed in this specification relates to a motor drive circuit, a motor system, and an electrical device.

Background Art

[0002] Sensorless motor drive circuits that drive a three-phase brushless motor without using sensors such as Hall elements have been variously developed (see, for example, Patent Document 1). The sensorless motor drive circuit monitors the back electromotive voltage generated in the coils of the three-phase brushless motor and obtains the rotational position information of the rotor by detecting the zero crossing of the back electromotive voltage where the back electromotive voltage becomes equal to the midpoint voltage of the motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the performances of the motor drive circuit is rotational accuracy. If the actual rotational speed of the motor varies with respect to the target rotational speed of the motor, the rotational accuracy deteriorates. In conventional motor drive circuits, the rotational accuracy may deteriorate depending on the waveform of the drive voltage supplied to the three-phase brushless motor.

Means for Solving the Problems

[0005] A motor drive circuit disclosed herein includes: a PWM signal generation unit configured to generate a PWM signal based on the count value of a counter; a detection unit configured to detect the zero-crossing of the back electromotive force generated in the motor coil; a prediction unit configured to predict the timing at which the zero-crossing of the back electromotive force occurs; a stop unit configured to stop the counting operation of the counter after a first time point in time preceding the timing at which the arrival predicted by the prediction unit occurs; and a reset unit configured to reset the count value at the timing when the zero-crossing of the back electromotive force is detected by the detection unit.

[0006] A motor system disclosed herein comprises a motor and a motor drive circuit configured to drive the motor.

[0007] The electrical equipment disclosed herein comprises a motor system having the above configuration. [Effects of the Invention]

[0008] According to the motor drive circuits, motor systems, and electrical equipment disclosed herein, the rotational accuracy of the motor can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram showing the schematic configuration of a motor system according to an embodiment. [Figure 2] Figure 2 shows the waveforms of the output signal and U-phase drive voltage of the detection unit. [Figure 3] Figure 3 shows an example configuration of a PWM signal generation unit. [Figure 4] Figure 4 shows the waveform of a PWM signal. [Figure 5] Figure 5 shows a schematic configuration of a hard disk drive. [Modes for carrying out the invention]

[0010] Figure 1 is a diagram showing the schematic configuration of a motor system according to an embodiment. The motor system 300 according to the embodiment comprises a motor drive circuit 100 and a three-phase brushless motor 200.

[0011] The motor drive circuit 100 is configured to drive a three-phase brushless motor 200. The motor drive circuit 100 includes a PWM (Pulse Width Modulation) signal generation unit 10, a detection unit 20, a prediction unit 30, a stop unit 40, a reset unit 50, a window setting unit 60, a drive signal generation unit 70, a U-phase switching circuit 80u, a V-phase switching circuit 80v, and a W-phase switching circuit 80w.

[0012] The three-phase brushless motor 200 comprises a U-phase coil Lu, a V-phase coil Lv, and a W-phase coil L80w. The motor drive circuit 100 supplies a U-phase drive voltage Vu to the first end of the U-phase coil Lu. The motor drive circuit 100 supplies a V-phase drive voltage Vv to the first end of the V-phase coil Lv. The motor drive circuit 100 supplies a W-phase drive voltage Vw to the first end of the W-phase coil Lw. The second ends of the U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw are connected in common. A midpoint voltage Vcom is generated at the midpoint of the three-phase brushless motor 200, i.e., at the second ends of the U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw. Alternatively, a virtual midpoint voltage generated at a virtual midpoint inside the motor drive circuit 100 may be used instead of the midpoint voltage Vcom generated at the midpoint of the three-phase brushless motor 200. The virtual midpoint inside the motor drive circuit 100 is formed by connecting three resistors of the same resistance value in a star configuration.

[0013] Now, let's explain the various parts of the motor drive circuit 100.

[0014] The PWM signal generation unit 10 is configured to generate a PWM signal based on the count value of the counter 11 (see Figure 3). The duty cycle of the PWM signal is set according to the target rotational speed and target torque of the three-phase brushless motor 200 so that the U-phase drive voltage Vu, V-phase drive voltage Vv, and W-phase drive voltage Vw each form a sinusoidal voltage with one period of electrical angle 360°.

[0015] The detection unit 20 is configured to detect the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200. More specifically, the detection unit 20 is configured to detect the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 at every 360° of the mechanical angle of the three-phase brushless motor 200.

[0016] Unlike this embodiment, the detection unit 20 can also detect, for example, the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 at every 360° of the electrical angle of the three-phase brushless motor 200. However, by detecting the zero-crossing of the back electromotive force at every 360° of the mechanical angle of the three-phase brushless motor 200, it is possible to prevent the detection results of the detection unit 20 from being affected by variations in the magnetization position of the rotor of the three-phase brushless motor 200.

[0017] The output signal Sbemf of the detection unit 20 transitions from a HIGH level to a LOW level when it detects the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 (see Figure 2). Furthermore, the output signal Sbemf of the detection unit 20 transitions from a LOW level to a HIGH level at the timing when it is estimated that the rotor of the three-phase brushless motor 200 has rotated 180° in mechanical angle from the time it detects the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 (see Figure 2).

[0018] The prediction unit 30 is configured to predict the timing at which the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 will occur.

[0019] Specifically, the prediction unit 30 is configured to predict the above arrival timing from the past detection results of the detection unit 20. For example, the prediction unit 30 measures the interval between the (n-1)th detection timing by the detection unit 20 and the nth detection timing by the detection unit 20, and can set the timing when the above interval has elapsed from the nth detection timing as the above arrival timing. Also, for example, the prediction unit 30 measures the first interval between the (n-3)th detection timing by the detection unit 20 and the (n-2)th detection timing by the detection unit 20, the second interval between the (n-2)th detection timing by the detection unit 20 and the (n-1)th detection timing by the detection unit 20, and the third interval between the (n-1)th detection timing by the detection unit 20 and the nth detection timing by the detection unit 20, and can set the timing when the average value of the above first to third intervals has elapsed from the nth detection timing as the above arrival timing.

[0020] The stop unit 40 is configured to stop the counting operation of the counter 11 (see FIG. 3) after the first time point counted back from the above arrival timing predicted by the prediction unit 30.

[0021] Since the stop unit 40 is used to improve the rotation accuracy of the three-phase brushless motor 200, when the motor drive circuit 100 drives the three-phase brushless motor 200 at a constant target rotation speed, the stop unit 40 operates. Thereby, the rotation accuracy of the motor can be improved when the motor drive circuit 100 drives the three-phase brushless motor 200 at a constant target rotation speed. Conversely, when the motor drive circuit 100 accelerates or decelerates the rotation of the three-phase brushless motor 200, the stop unit 40 may be made inoperative.

[0022] The reset unit 50 is configured to reset the count value of the counter 11 (see FIG. 3) at the timing when the zero cross of the back electromotive voltage generated in the U-phase coil Lu of the three-phase brushless motor 200 is detected by the detection unit 20.

[0023] The reset unit 50 is used to improve the rotational accuracy of the three-phase brushless motor 200. Therefore, the reset unit 50 operates when the motor drive circuit 100 drives the three-phase brushless motor 200 at a constant target rotational speed. This improves the rotational accuracy of the motor when the motor drive circuit 100 drives the three-phase brushless motor 200 at a constant target rotational speed.

[0024] The window setting unit 60 sets a window (see Figure 2) to stop the switching of the U-phase switching circuit 80u that outputs the U-phase drive voltage Vu, so that the U-phase drive voltage Vu does not interfere with monitoring the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200. In other words, the U-phase is not driven during the window period.

[0025] The drive signal generation unit 70 generates a U-phase drive signal based on the PWM signal Spwm and the window, and outputs the U-phase drive signal to the U-phase switching circuit 80u. The U-phase switching circuit 80u turns on the high-side switch and off the low-side switch when the PWM signal Spwm is at a HIGH level, in response to the U-phase drive signal. Also, the U-phase switching circuit 80u turns off the high-side switch and on the low-side switch when the PWM signal Spwm is at a LOW level, in response to the U-phase drive signal. However, during the window period, the drive signal generation unit 70 turns off both the high-side switch and the low-side switch in response to the U-phase drive signal, regardless of the level of the PWM signal Spwm.

[0026] The drive signal generation unit 70 generates a V-phase drive signal based on the PWM signal Spwm and outputs the V-phase drive signal to the V-phase switching circuit 80v. The V-phase drive voltage Vv output from the V-phase switching circuit 80v is shifted by 120° in electrical angle from the U-phase drive voltage Vu, and is a voltage that does not have the window that exists in the U-phase drive voltage Vu.

[0027] The drive signal generation unit 70 generates a W-phase drive signal based on the PWM signal Spwm and outputs the W-phase drive signal to the W-phase switching circuit 80v. The W-phase drive voltage Vw output from the W-phase switching circuit 80w is shifted by 240° in electrical angle from the U-phase drive voltage Vu, and is a voltage that does not have the window that exists in the U-phase drive voltage Vu.

[0028] Figure 3 shows an example configuration of the PWM signal generation unit 10. In the example configuration shown in Figure 3, the PWM signal generation unit 10 includes a counter 11, a reference value generation unit 12, and a comparison unit 13.

[0029] In its countdown operation, the counter 11 decreases the count value CNT by one each clock cycle. When the count value CNT reaches 0, or when reset by the reset unit 50, the counter 11 returns the count value CNT to its initial value in the next clock cycle.

[0030] The reference value generation unit 12 generates a reference value REF. The reference value REF is set according to the target rotational speed and target torque of the three-phase brushless motor 200 so that the U-phase drive voltage Vu, V-phase drive voltage Vv, and W-phase drive voltage Vw each form a sinusoidal voltage with one cycle at an electrical angle of 360°.

[0031] The comparison unit 13 compares the count value CNT with the reference value REF. When the count value CNT exceeds the reference value REF, the comparison unit 13 sets the PWM signal Spwm to a LOW level. On the other hand, when the count value CNT does not exceed the reference value REF, the comparison unit 13 sets the PWM signal Spwm to a HIGH level.

[0032] Figure 4 is a diagram showing the waveform of the PWM signal Spwm. More specifically, Figure 4 shows the waveform of the PWM signal Spwm when the motor drive circuit 100 is driving the three-phase brushless motor 200 at a constant target rotational speed, and also shows the waveform of the PWM signal Spwm before and after the arrival timing when the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200, as predicted by the prediction unit 30, occurs.

[0033] Note that in Figure 4, the count value CNT is shown as an analog value for convenience, but it is actually a digital value.

[0034] The prediction unit 30 predicts the arrival timing TM1 at which the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200 occurs for each rotation of the rotor of the three-phase brushless motor 200.

[0035] The stop unit 40 sets the timing pulse signal Detect Range to a HIGH level at a first time point t1, which is a predetermined time A1 [μsec] before the arrival timing TM1. The timing pulse signal Detect Range is a signal used by the stop unit 40. When the timing pulse signal Detect Range is at a HIGH level, the PWM signal Spwm is also forcibly set to a HIGH level.

[0036] The stopping unit 40 stops the counting operation of the counter 11 at point t2 when the timing pulse signal Detect Range is at a HIGH level and the count value CNT reaches a predetermined value (0 < predetermined value < initial value).

[0037] The reset unit 50 then resets the count value of the counter 11 at the timing TM2 when the detection unit 20 detects the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200.

[0038] By resetting the count value in the reset unit 50, the rotational drive of each phase of the rotor of the three-phase brushless motor 200, which starts from the timing TM2 when the detection unit 20 detects the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200, can be started using the same waveform of each phase drive voltage.

[0039] Furthermore, the PWM signal Spwm can be fixed at a HIGH level from the time t2 when the count value CNT reaches a predetermined value until the timing TM2 when the detection unit 20 detects the zero-crossing of the back electromotive force generated in the U-phase coil Lu of the three-phase brushless motor 200. By resetting the count value in the reset unit 50 as described above and fixing the PWM signal Spwm at a HIGH level as described above, the reproducibility of the waveform of the drive voltage of each phase between rotational drives of the rotor of the three-phase brushless motor 200 can be improved.

[0040] This improves the rotational accuracy of the three-phase brushless motor 200.

[0041] Furthermore, in this embodiment, the counting operation of the counter 11 is stopped at point t2 when the count value CNT reaches a predetermined value (0 < predetermined value < initial value), thus preventing unintended level transitions of the PWM signal Spwm. This ensures a reliable improvement in the rotational accuracy of the three-phase brushless motor 200.

[0042] Furthermore, it is desirable that the predetermined time A1 [μsec] be longer than the period of the PWM signal Spwm. This allows the PWM signal Spwm to be fixed at a HIGH level for a relatively long period immediately before the detection unit 20 detects the zero-crossing of the back electromotive force. This further improves the rotational accuracy of the three-phase brushless motor 200.

[0043] The motor system 300 according to this embodiment (hereinafter abbreviated as "motor system 300") is mounted, for example, on a hard disk drive 400 shown in Figure 5. The hard disk drive 400 shown in Figure 5 comprises the motor system 300, a voice coil motor 310, a magnetic disk 320, a swing arm 330, a magnetic head 340, and a housing 350. The motor system 300, the voice coil motor 310, the magnetic disk 320, the swing arm 330, and the magnetic head 340 are housed inside the housing 350. The motor system 300 is used as a spindle motor.

[0044] The magnetic disk 320 is a hard disk with a magnetic material on its surface. The magnetic disk 320 may be a single or multiple disks. The motor system 300 rotates the magnetic disk 320 at high speed. The magnetic head 340 reads and writes data to the magnetic disk 320 by generating a magnetic field. The magnetic head 340 is attached to the tip of the swing arm 330.

[0045] The swing arm 330 oscillates around its axis relative to the rotating magnetic disk 320. The voice coil motor 310 is an actuator that drives the swing arm 330. The voice coil motor 310 is driven by the magnetic field effect between a coil through which current flows and a magnet. Naturally, the motor system 300 may also be mounted on electrical equipment other than the hard disk drive 400, such as a fan or printer.

[0046] The configuration of the present invention can be modified in various ways, in addition to the embodiments described above, without departing from the spirit of the invention. The embodiments described above should be considered in all respects to be illustrative and not restrictive, and the technical scope of the present invention is indicated by the claims, not by the description of the embodiments described above, and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0047] For example, in the embodiment described above, zero-crossing of the back electromotive force was detected only in the U phase, but zero-crossing of the back electromotive force may be detected in each of the U, V, and W phases.

[0048] Furthermore, for example, in the embodiment described above, the counter performed a countdown operation, but the counter may also perform a count-up operation, or the counter may perform both countdown and count-up operations in sequence.

[0049] Furthermore, in the embodiment described above, a window was set because the current was supplied at a so-called 180° angle, but if the current is supplied at a so-called 120° angle, a window does not need to be set.

[0050] The motor drive circuit (100) described above comprises a PWM signal generation unit (10) configured to generate a PWM signal based on the count value of a counter (11), a detection unit (20) configured to detect the zero-crossing of the back electromotive force generated in the coil of the motor (200), a prediction unit (30) configured to predict the timing at which the zero-crossing of the back electromotive force occurs, a stop unit (40) configured to stop the counting operation of the counter after a first time point preceding the timing of arrival predicted by the prediction unit, and a reset unit (50) configured to reset the count value at the timing when the zero-crossing of the back electromotive force is detected by the detection unit (first configuration).

[0051] The motor drive circuit, which is the first configuration described above, can improve the rotational accuracy of the motor.

[0052] In the motor drive circuit having the first configuration described above, the stopping unit may be configured to stop the counting operation at a second time when the count value reaches a predetermined value (second configuration).

[0053] The motor drive circuit, which is the second configuration described above, can prevent unintended level transitions of the PWM signal. This reliably improves the rotational accuracy of the motor.

[0054] In the motor drive circuit having the first or second configuration described above, the prediction unit may be configured to predict the arrival timing from the past detection results of the detection unit (third configuration).

[0055] In the motor drive circuit, which is the third configuration described above, the prediction unit can easily predict the arrival timing.

[0056] In a motor drive circuit having any of the first to third configurations described above, the detection unit may be configured to detect the zero-crossing of the back electromotive force at every 360° mechanical angle of the motor (fourth configuration).

[0057] In the motor drive circuit, which is the fourth configuration described above, it is possible to prevent the detection result of the detection unit from being affected by variations in the magnetization position of the motor rotor. This makes it possible to further improve the rotational accuracy of the motor.

[0058] In a motor drive circuit having any of the above configurations 1 to 4, the stop unit and the reset unit may operate when the motor is driven at a certain target rotational speed (a fifth configuration).

[0059] In the motor drive circuit, which is the fifth configuration described above, the rotational accuracy of the motor can be improved when driving the motor at a constant target rotational speed.

[0060] In a motor drive circuit having any of the above configurations 1 to 5, the length of time tracing back from the arrival timing to the first time point may be longer than the period of the PWM signal (sixth configuration).

[0061] In the motor drive circuit with the sixth configuration described above, the level of the PWM signal can be fixed for a relatively long period of time immediately before the detection unit detects the zero-crossing of the back electromotive force. This further improves the rotational accuracy of the motor.

[0062] The motor system (300) described above comprises the motor (200) and a motor drive circuit which is one of the first to sixth configurations described above and is configured to drive the motor (seventh configuration).

[0063] The motor system, which is the seventh configuration described above, can improve the rotational accuracy of the motor.

[0064] The electrical equipment (400) described above has a configuration that includes a motor system, which is the seventh configuration described above (the eighth configuration).

[0065] The eighth component described above, an electrical device, can improve the rotational accuracy of the motor. [Explanation of Symbols]

[0066] 10 PWM signal generation section 20 Detection unit 30 Prediction Section 40 Stop part 50 Reset section 60 Window Settings Section 70 Drive signal generation unit 80uU U-phase switching circuit 80V V-phase switching circuit 80W W-phase switching circuit 100 Motor drive circuit 200 Three-phase brushless motor 300 Motor system according to an embodiment 310 Voice Coil Motor 320 magnetic disks 330 Swingarm 340 Magnetic Heads 350 cabinets 400 hard disk drives Lu, Lv, Lw: U-phase coil, V-phase coil, W-phase coil

Claims

1. A PWM signal generation unit configured to generate a PWM signal, A detection unit configured to detect the zero-crossing of the back electromotive force generated in the motor coil, A prediction unit configured to predict the timing at which the zero-crossing of the back electromotive force occurs, A stop unit is configured to stop the counting operation of the counter at a second time point, after a first time point preceding the predicted arrival timing, when the counter's count value reaches a predetermined value that is greater than the counter's minimum count value and less than the counter's maximum count value. A reset unit configured to reset the count value at the timing when the detection unit detects the zero-crossing of the back electromotive force, Equipped with, The PWM signal generation unit is, From the first time point until the detection unit detects the zero-crossing of the back electromotive force, the PWM signal is fixed at the first level. When the count value is reset by the reset unit, the PWM signal is transitioned from the first level to the second level based on the count value. A motor drive circuit configured to transition the PWM signal between a first level and a second level based on the count value until the next first time point is reached.

2. The motor drive circuit according to claim 1, wherein the prediction unit is configured to predict the arrival timing from the past detection results of the detection unit.

3. The motor drive circuit according to claim 1 or claim 2, wherein the detection unit is configured to detect the zero-crossing of the back electromotive force at every 360° mechanical angle of the motor.

4. The motor drive circuit according to any one of claims 1 to 3, wherein the stop unit and the reset unit operate when the motor is driven at a certain target rotational speed.

5. The motor drive circuit according to any one of claims 1 to 4, wherein the length of time retrospectively from the arrival timing to the first time point is longer than the period of the PWM signal.

6. The motor and, A motor system comprising a motor drive circuit according to any one of claims 1 to 5, configured to drive the motor.

7. An electrical device comprising the motor system described in claim 6.

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