Motor drive device, motor system, and motor drive method

Abstract

A motor drive device is a sensorless device that detects zero-crossing of a counter electromotive voltage generated in a winding of a motor (100) for rotation control of the motor (100), and comprises: a detection unit (10) that determines whether a phase of a winding current flowing through the winding of the motor (100) is ahead of a phase of the counter electromotive voltage; and a waveform setting unit (20) that receives an acceleration command for the motor (100) if determined that the phase of the winding current is ahead of the phase of the counter electromotive voltage, and does not receive the acceleration command for the motor if determined that the phase of the winding current is behind the phase of the counter electromotive voltage.

Description

Motor drive device, motor system, and motor drive method

[0001] The present disclosure relates to a motor drive device that controls a motor without a sensor, etc.

[0002] In a motor drive device that controls a motor without a sensor and without a position detection element, the rotor position or the rotation speed is detected by detecting the zero crossing of the back electromotive voltage, and the motor is driven and controlled. For example, the motor drive device disclosed in Patent Document 1 provides a non-energization period during which the motor winding is not energized, so that the winding current (hereinafter also referred to as the phase current) flowing through the winding to be detected becomes zero. Then, the motor drive device compares the drive voltage (hereinafter also referred to as the phase voltage) to the motor winding with the neutral point potential of the motor, and forms a position signal indicating the zero crossing of the back electromotive voltage by inverting the comparison signal. The energization timing of the winding can be determined based on this position signal.

[0003] Japanese Patent Application Laid-Open No. 2011-244617

[0004] When the motor is rotating at a constant speed, the energization timing of the winding is controlled at the time of detecting the zero crossing of the back electromotive voltage, so the phase of the phase current and the phase of the back electromotive voltage are substantially coincident while repeating delays or advances due to fluctuations in the motor load, etc. However, during the acceleration of the motor, control acts in the direction of increasing the amplitude of the phase current, and the phase of the phase current lags behind the back electromotive voltage that becomes higher in frequency as the acceleration progresses. When the phase lag of the phase current becomes large, the regeneration period from the start of the non-energization period until the phase current becomes zero becomes long, and the zero crossing of the back electromotive voltage is buried in the regeneration period, resulting in detection leakage and leading to out-of-synchronization.

[0005] Therefore, the present disclosure provides a motor drive device, etc. that can suppress the detection leakage of the zero crossing of the back electromotive voltage.

[0006] The motor drive device according to this disclosure is a sensorless motor drive device for detecting the zero-crossing of a back electromotive force generated in the windings of a motor for rotation control of the motor, and comprises: a detection unit that determines whether the phase of the winding current flowing through the windings of the motor is ahead of the phase of the back electromotive force; and a waveform setting unit that accepts an acceleration command to the motor if it is determined that the phase of the winding current is ahead of the phase of the back electromotive force, and does not accept an acceleration command to the motor if it is determined that the phase of the winding current is behind the phase of the back electromotive force.

[0007] The motor system relating to this disclosure comprises the motor drive device described above and the motor described above.

[0008] The motor driving method according to this disclosure is a motor driving method for a sensorless motor drive device that detects the zero-crossing of a back electromotive force generated in the windings of a motor for rotation control of the motor, and includes a detection step of determining whether the phase of the winding current flowing through the windings of the motor is ahead of the phase of the back electromotive force, and a waveform setting step of receiving an acceleration command to the motor if it is determined that the phase of the winding current is ahead of the phase of the back electromotive force, and not receiving an acceleration command to the motor if it is determined that the phase of the winding current is behind the phase of the back electromotive force.

[0009] These comprehensive or specific embodiments may be implemented as a system, method, integrated circuit, computer program, or recording medium such as a computer-readable CD-ROM, or as any combination of a system, method, integrated circuit, computer program, and recording medium.

[0010] According to this disclosure, it is possible to suppress the failure to detect the zero-crossing of the back electromotive force.

[0011] This is a circuit diagram showing an example of a motor drive device according to the first embodiment. This is a waveform diagram for detecting the zero-crossing of the back electromotive force from positive to negative when the phase current is leading. This is a waveform diagram for detecting the zero-crossing of the back electromotive force from positive to negative when the phase current is lagging. This is a waveform diagram for detecting the zero-crossing of the back electromotive force from positive to negative when detection is missed due to the phase lag of the phase current. This is a flowchart showing an example of torque command processing for the motor drive device according to the first embodiment. This is a flowchart showing an example of phase determination processing by phase voltage during the non-energized period of the motor drive device according to the first embodiment. This is a flowchart showing an example of phase determination processing by phase current during the non-energized period of the motor drive device according to the first embodiment. This is a flowchart showing an example of phase determination processing outside the non-energized period of the motor drive device according to the first embodiment. This is a flowchart showing another example of phase determination processing for the motor drive device according to the first embodiment. This is a waveform diagram for explaining the operation of the motor drive device according to the first embodiment. This is a waveform diagram for detecting the zero-crossing of the back electromotive force from negative to positive when the phase current is leading. This is a waveform diagram for detecting the zero-crossing of the back electromotive force from negative to positive when the phase current is lagging. This is a waveform diagram showing the detection of a zero-crossing of the back electromotive force from negative to positive when detection failure occurs due to a phase lag in the phase current. This is a circuit diagram showing an example of the detection unit and the non-energized period specification unit according to the second embodiment. This is a table showing an example of adjusting the non-energized period in the second embodiment. This is a waveform diagram for explaining the operation of the detection unit according to the second embodiment. This is a waveform diagram for explaining the operation of the non-energized period specification unit according to the second embodiment. This is a flowchart showing an example of a motor drive method according to another embodiment.

[0012] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, and their arrangement and connection configurations shown in the following embodiments are examples only and are not intended to limit this disclosure.

[0013] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In addition, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified.

[0014] (First Embodiment) Figure 1 is a circuit diagram showing an example of a motor drive device according to the first embodiment. The motor drive device according to this embodiment is a sensorless motor drive device that detects the zero-crossing of the back electromotive force generated in the windings of the motor 100 for rotation control of the motor 100. The motor 100 to be driven by the motor drive device according to this embodiment is, for example, a three-phase sensorless motor and has motor windings U, V, and W.

[0015] The detection unit 10 detects the phase currents Iu, Iv, and Iw, the phase voltages Vu, Vv, and Vw, and the neutral point potential Vc of the motor 100 for the motor windings U, V, and W. Signal processing is performed for each motor winding U, V, and W, but the following explanation will focus on motor winding U and describe the phase current Iu and phase voltage Vu. If the focus is on motor winding V, then in the following explanation, the terms motor winding U, phase current Iu, and phase voltage Vu can be replaced with motor winding V, phase current Iv, and phase voltage Vv. Similarly, if the focus is on motor winding W, then in the following explanation, the terms motor winding U, phase current Iu, and phase voltage Vu can be replaced with motor winding W, phase current Iw, and phase voltage Vw.

[0016] The detection unit 10 detects the zero-crossing of the back electromotive force Bemf by detecting the winding current of the motor winding U (hereinafter also referred to as the phase current Iu) and the drive voltage supplied to the motor winding U (hereinafter also referred to as the phase voltage Vu). Specifically, the detection unit 10 detects a reference potential corresponding to the neutral point potential Vc of the motor winding U, and detects the zero-crossing of the back electromotive force Bemf by comparing the phase voltage Vu and the neutral point potential Vc during the period when the phase current Iu is zero, as described later, in the non-energized period. More specifically, the detection unit 10 receives the non-energized period signal TP, described later, and detects the zero-crossing of the back electromotive force Bemf (= Vu - Vc) by comparing the phase voltage Vu and the neutral point potential Vc of the motor winding U when it is not energized, and outputs a position detection signal BEMF. The reason for de-energizing the motor winding U so that the phase current Iu is zero is that the back electromotive force Bemf cannot be correctly detected if the phase current Iu is flowing. Furthermore, the detection unit 10 outputs a phase signal PH by determining whether the phase of the phase current Iu flowing through the motor winding U leads the phase of the back electromotive force Bemf. In this embodiment, if the phase of the phase current Iu leads sufficiently more than the phase of the back electromotive force Bemf, PH = "H".

[0017] As mentioned above, the phase voltage Vu is a signal representing the drive voltage to the motor winding U, but the actual phase voltage Vu is assumed to have undergone voltage division by a resistor or further conversion to a digital value. Similarly, the phase current Iu is a signal representing the drive current to the motor winding U, but the actual phase current Iu is assumed to have undergone processing to detect it as a voltage value by a resistor or further conversion to a digital value. The same applies to the signals representing other phase voltages and phase currents.

[0018] Furthermore, the neutral point potential Vc may be determined not only by directly detecting the connection point potential of the motor windings U, V, and W, but also by indirectly detecting it. Indirect methods for detecting the neutral point potential include using half the power supply voltage or using the average value of each phase voltage, but the method of detecting the neutral point potential is not limited.

[0019] The waveform setting unit 20 sets the energizing timing of the motor winding U based on the zero-crossing of the back electromotive force Bemf and sets an internal torque command based on an external torque command. Specifically, the waveform setting unit 20 sets an internal torque command Vsp, which corresponds to the internal torque command of the phase current Iu, based on the torque command signal TQ and the phase signal PH. The waveform setting unit 20 also outputs a non-energized period signal TP that rises at a predetermined start timing tp and falls based on the position detection signal BEMF. The start timing tp is set based on the time information of the previous cycle of the back electromotive force Bemf. As will be described in more detail later, the waveform setting unit 20 accepts an acceleration command to the motor 100 if it determines that the phase of the phase current Iu is ahead of the phase of the back electromotive force Bemf, and does not accept an acceleration command to the motor 100 if it determines that the phase of the phase current Iu is behind the phase of the back electromotive force Bemf. Specifically, if the waveform setting unit 20 determines that the phase of the phase current Iu is ahead of the phase of the back electromotive force Bemf, it increases the internal torque command according to the acceleration command among the torque commands that requires acceleration.

[0020] The energization control unit 30 generates a control signal for controlling the energization of the motor winding U by performing modulation such as PWM (Pulse Width Modulation) by comparing an internal sawtooth wave (not shown) with an internal torque command Vsp. The control signal includes a non-energization period indicated by the non-energization period signal TP and sets the energization timing of the motor winding U of the motor 100 based on the position detection signal BEMF.

[0021] The drive unit 40 has multiple pairs of switch elements, each consisting of an upper switch element and a lower switch element. The energization control unit 30 supplies control signals to each of the multiple pairs of switch elements in the drive unit 40 based on the energization timing and internal torque command set by the waveform setting unit 20. As a result, the drive unit 40 supplies winding current and drive voltage to each motor winding according to the control signals from the energization control unit 30. The following explanation will focus on the pair of upper switch elements 41 and lower switch elements 42 that correspond to the motor winding U. The pair of switch elements consisting of the upper switch element 41 and the lower switch element 42 supplies phase current Iu to the motor winding U by switching alternately at several tens of kHz according to the control signals from the energization control unit 30. The waveform setting unit 20 sets a non-energized period in which both the pair of switch elements (upper switch element 41 and lower switch element 42) are in the off state, and during the non-energized period, both the upper switch element 41 and the lower switch element 42 are in the off state. Here, the upper switching element 41 and the lower switching element 42 are represented as field-effect transistors having body diodes, but the switching elements of a motor drive device are not limited to field-effect transistors. The switching elements of a motor drive device may structurally have antiparallel diodes such as body diodes, or they may be connected separately.

[0022] Figures 2A and 2C show the operating waveforms for zero-cross detection of the back electromotive force Bemf, and from top to bottom, they show the back electromotive force Bemf, the non-energized period signal TP, the phase voltage Vu and neutral point potential Vc, the phase current Iu, and the position detection signal BEMF.

[0023] Figure 2A is a waveform diagram when detecting the zero-crossing of the positive-to-negative back electromotive force Bemf when the phase of the phase current Iu is leading. Figure 2B is a waveform diagram when detecting the zero-crossing of the positive-to-negative back electromotive force Bemf when the phase of the phase current Iu is lagging. Figure 2C is a waveform diagram when detecting the zero-crossing of the positive-to-negative back electromotive force Bemf when detection is missed due to the phase lag of the phase current Iu. Here, the phase voltage Vu is a high-frequency rectangular wave due to the switching operation of the upper switch element 41 and the lower switch element 42, except during periods when no power is supplied.

[0024] In Figure 2A, during the period from time tp until the pulse input of the position detection signal BEMF, when the non-energized period signal TP is at a high level, both the upper switch element 41 and the lower switch element 42 are in the off state. The phase current Iu is ahead, and immediately before time tp, current flows from the motor winding U to the lower switch element 42. At time tp, the phase voltage Vu rises due to the turn-off of the lower switch element 42, and the body diode of the upper switch element 41 conducts, allowing regenerative current to flow to the power supply. During the period when this regenerative current is flowing, the phase voltage Vu is higher than the power supply potential Vdd by the forward voltage of the body diode of the upper switch element 41.

[0025] When the phase current Iu becomes zero at time t1, the phase voltage Vu decreases, and a back electromotive force Bemf is generated superimposed on the neutral point potential Vc. At time t2, when the phase voltage Vu falls below the neutral point potential Vc, that is, when a zero-cross from positive to negative of the back electromotive force Bemf is detected, a one-shot pulse position detection signal BEMF is output. As the position detection signal BEMF rises, the de-energized period signal TP becomes L level, and the de-energized period ends. With the end of the de-energized period, the upper switch element 41 and the lower switch element 42 of the drive unit 40 resume switching operation according to the target current waveform and begin supplying current to the motor winding U.

[0026] Thus, if the phase of the phase current Iu leads the phase of the back electromotive force Bemf to some extent, the phase voltage Vu will be at a higher potential than the neutral point potential Vc at the end of the regenerative operation during the non-energized period. Therefore, even if the back electromotive force Bemf crosses zero during the regenerative operation, the phase voltage Vu will decrease and will always fall below the neutral point potential Vc. In other words, even if there is an error in the detection timing, the position detection signal BEMF will always rise after the back electromotive force Bemf crosses zero.

[0027] As mentioned above, if the phase of the phase current Iu is leading, the phase of the phase current Iu will initially coincide with the phase of the phase voltage Vu at the energization timing of time t2. However, at time t3, when the back electromotive force Bemf crosses zero from negative to positive half a cycle after time t2, the phase of the phase current Iu will lead again.

[0028] On the other hand, in Figure 2B, if the phase of the phase current Iu is lagging, then immediately before time tp, current flows from the upper switch element 41 into the motor winding U. At time tp, the upper switch element 41 turns off, causing the phase voltage Vu to decrease, and the body diode of the lower switch element 42 conducts, allowing regenerative current to flow. During the period when regenerative current is flowing, the phase voltage Vu is lower than the ground potential GND by the forward voltage of the body diode of the lower switch element 42.

[0029] When the phase current Iu becomes zero at time t1, the phase voltage Vu rises, and a back electromotive force Bemf is generated superimposed on the neutral point potential Vc. When the phase voltage Vu falls below the neutral point potential Vc at time t2, that is, when the back electromotive force Bemf crosses zero from positive to negative, the de-energized period signal TP becomes L level in accordance with the rising edge of the one-shot pulse position detection signal BEMF, and the de-energized period ends. With the end of the de-energized period, the upper switch element 41 and the lower switch element 42 of the drive unit 40 resume switching operation according to the target current waveform and begin supplying current to the motor winding U.

[0030] As described above, if the phase of the phase current Iu is lagging, the phase of the phase current Iu will initially coincide with the phase of the phase voltage Vu at the energization timing at time t2. However, at time t3, when the back electromotive force Bemf crosses zero from negative to positive half a cycle after time t2, the phase of the phase current Iu will lag again.

[0031] Furthermore, Figure 2C shows the waveform when the zero-crossing of the back electromotive force Bemf cannot be detected due to a phase lag in the phase current Iu. During the regeneration period from time tp to time t1, the phase voltage Vu falls below the neutral point potential Vc, and the position detection signal BEMF is not generated. As a result, the switching operation of the upper switch element 41 and the lower switch element 42 cannot be resumed. The example shown in Figure 2C is an extreme example of a zero-crossing detection failure, but as shown in Figure 2B, even when the timing of the end of the regeneration period and the timing of the zero-crossing of the back electromotive force Bemf are close, the zero-crossing of the back electromotive force Bemf may occur before the phase voltage Vu, which rises with the end of the regeneration period, exceeds the neutral point potential Vc, and the position detection signal BEMF may not be generated.

[0032] Therefore, in the motor drive device of this embodiment, the detection unit 10 generates a phase signal PH indicating whether the phase of the phase current Iu is leading the phase of the back electromotive force Bemf. If the phase signal PH from the detection unit 10 indicates a phase lag of the phase current Iu with respect to the back electromotive force Bemf, the waveform setting unit 20 does not comply with the torque command requesting acceleration until the phase of the phase current Iu advances. In other words, the waveform setting unit 20 controls the acceleration of the motor 100 to wait for the phase of the phase current Iu to advance.

[0033] Figure 3 is a flowchart showing an example of torque command processing for a motor drive device according to the first embodiment. In torque command processing, an internal torque command Vsp is set for the torque command TQ. The waveform setting unit 20 performs torque determination (step S101).

[0034] In the torque determination, the waveform setting unit 20 determines that the internal torque command Vsp is greater than the torque command TQ (Vsp > TQ). Since the torque command requests deceleration, the unit performs a deceleration process (torque reduction process) to decrease the internal torque command Vsp (Vsp → Vsp - ΔVsp) (step S102).

[0035] If the waveform setting unit 20 determines that the internal torque command Vsp is equal to the torque command TQ (Vsp = TQ), the internal torque command Vsp performs a process to maintain its value (Vsp → Vsp) because the torque command requests that the current value be maintained (step S103).

[0036] If the waveform setting unit 20 determines that the internal torque command Vsp is smaller than the torque command TQ (Vsp < TQ), the torque command requests acceleration, but the detection unit 10 checks the phase of the phase current Iu and the phase of the back electromotive force Bemf (step S104). If it is determined that the phase of the phase current Iu is leading the phase of the back electromotive force Bemf (PH = "H"), the waveform setting unit 20 performs an acceleration process (torque increase process) to increase the internal torque command Vsp (Vsp → Vsp + ΔVsp) (step S105). However, if it is determined that the phase of the phase current Iu is lagging behind the phase of the back electromotive force Bemf (PH = "L"), the internal torque command Vsp maintains its value (step S103). In other words, if the phase of the phase current Iu is lagging behind the phase of the back electromotive force Bemf, the waveform setting unit 20 does not comply with the torque command requesting acceleration.

[0037] Furthermore, if the waveform setting unit 20 determines that the phase of the phase current Iu and the phase of the back electromotive force Bemf are the same, it may or may not accept an acceleration command to the motor 100.

[0038] Here, the range of change ΔVsp of the internal torque command Vsp can be set arbitrarily. If rapid acceleration or deceleration is required, the range of change ΔVsp should be increased, and if gradual acceleration or deceleration is required to reduce stress on the motor 100, the range of change ΔVsp should be decreased. Furthermore, setting upper or lower limits on the internal torque command Vsp to protect the motor 100 is a design consideration.

[0039] Figures 4A and 4B are flowcharts of phase determination during the non-energized period. Figure 4A is a flowchart of an example of phase determination processing by phase voltage during the non-energized period of the motor drive device according to the first embodiment. Figure 4B is a flowchart of an example of phase determination processing by phase current during the non-energized period of the motor drive device according to the first embodiment. Any of the phase determination processes may be performed if there is sufficient time to perform signal processing during the non-energized period.

[0040] In Figure 4A, when the non-energized period begins due to the rising edge of the non-energized period signal TP (TP = "L" → "H") (step S201), the detection unit 10 performs a phase determination (step S202). The detection unit 10 determines that the phase of the phase current Iu is leading when the phase voltage Vu rises and becomes higher than the neutral point potential Vc (Vu > Vc) (PH = "H": step S203), and determines that the phase of the phase current Iu is lagging when the phase voltage Vu falls below the neutral point potential Vc (Vu ≤ Vc) (PH = "L": step S204).

[0041] Thus, the detection unit 10 may generate a phase signal PH according to the level of the phase voltage Vu during the period when the phase current Iu is flowing during the non-energized period. The phase voltage Vu during the period when the phase current Iu is flowing during the non-energized period will have a predetermined magnitude that differs depending on whether the phase of the phase current Iu is leading or lagging the phase of the back electromotive force Bemf.

[0042] Specifically, as shown in Figures 2A to 2C, when detecting the zero-crossing of the back electromotive force Bemf from positive to negative, the phase voltage Vu during the period when the phase current Iu is flowing in the non-energized period will be greater than the neutral point potential Vc when the phase of the phase current Iu is leading the phase of the back electromotive force Bemf, and less than or equal to the neutral point potential Vc when the phase of the phase current Iu is lagging behind the phase of the back electromotive force Bemf. Furthermore, as shown in Figures 8A to 8C described later, when detecting the zero-crossing of the back electromotive force Bemf from negative to positive, the phase voltage Vu during the period when the phase current Iu is flowing in the non-energized period will be greater than or equal to the neutral point potential Vc when the phase of the phase current Iu is lagging behind the phase of the back electromotive force Bemf, and less than the neutral point potential Vc when the phase of the phase current Iu is leading the phase of the back electromotive force Bemf.

[0043] Therefore, during the period when the phase current Iu is flowing in the non-energized period, it is possible to determine whether the phase of the phase current Iu leads the phase of the back electromotive force Bemf, depending on the level of the phase voltage Vu, and consequently, to generate a phase signal PH.

[0044] In FIG. 4A, an example of comparing the phase voltage Vu with the neutral point voltage Vc at the start of the non-conduction period in the phase determination of the phase current Iu is shown, but the present invention is not limited to this. If a faster advance angle condition is desired, the voltage to be compared with the phase voltage Vu may be a voltage higher than the neutral point voltage Vc (for example, the power supply voltage Vdd), or if it is sufficient to advance the angle even slightly, the voltage to be compared with the phase voltage Vu may be a voltage lower than the neutral point voltage Vc (for example, the ground voltage GND). That is, the reference voltage corresponding to the neutral point voltage Vc to be compared with the phase voltage Vu may be the neutral point voltage Vc, or may be the power supply voltage Vdd or the ground voltage GND.

[0045] In FIG. 4B, when the non-conduction period is started by the rising edge of the non-conduction period signal TP (TP = "L" → "H") (step S301), the detection unit 10 performs phase determination (step S302). When the detection unit 10 determines that the phase current Iu is in the direction flowing out from the motor winding U to the drive unit 40 (Iu < 0), it determines that the phase of the phase current Iu is advanced (PH = "H": step S303), and when the phase current Iu is in the direction flowing into the motor winding U from the drive unit , it determines that the phase of the phase current Iu is delayed (PH = "L": step S304).

[0046] As described above, the detection unit 10 may generate the phase signal PH according to the direction in which the phase current Iu flows during the non-conduction period. The direction in which the phase current Iu flows during the non-conduction period is a predetermined direction that is different when the phase of the phase current Iu is advanced and delayed compared to the phase of the back electromotive force Bemf, respectively.

[0047] Specifically, as shown in FIGS. 2A to 2C, when detecting the zero crossing of the reverse electromotive force Bemf from positive to negative, the direction in which the phase current Iu flows during the non-conduction period is such that when the phase of the phase current Iu is ahead of the phase of the reverse electromotive force Bemf, it flows from the motor winding U to the drive unit 40, and when the phase of the phase current Iu is behind the phase of the reverse electromotive force Bemf, it flows from the drive unit 40 into the motor winding U. As shown in FIGS. 8A to 8C described later, when detecting the zero crossing of the reverse electromotive force Bemf from negative to positive, the direction in which the phase current Iu flows during the non-conduction period is such that when the phase of the phase current Iu is behind the phase of the reverse electromotive force Bemf, it flows from the motor winding U to the drive unit 40, and when the phase of the phase current Iu is ahead of the phase of the reverse electromotive force Bemf, it flows from the drive unit 40 into the motor winding U.

[0048] Therefore, it is possible to determine whether the phase of the phase current Iu is ahead of the phase of the reverse electromotive force Bemf according to the direction in which the phase current Iu flows during the non-conduction period, and thus a phase signal PH can be generated.

[0049] Figure 5 is a flowchart showing an example of phase determination processing outside of the non-energized period of the motor drive device according to the first embodiment. Specifically, it is a flowchart of phase determination processing when there is no time to perform signal processing during the non-energized period. The detection unit 10 starts timing from the detection of the zero-crossing of the back electromotive force Bemf (BEMF = "H") (t = 0: step S401), and performs a time determination to determine whether half a period has elapsed since the detection of the zero-crossing of the back electromotive force Bemf (step S402). If the detection unit 10 determines that half a period has not elapsed since the detection of the zero-crossing of the back electromotive force Bemf (t < T / 2), it waits until it has elapsed, and performs a phase determination half a period after the detection of the zero-crossing of the back electromotive force Bemf (t ≥ T / 2, time t3 in Figures 2A and 2B) (step S403). In addition, the period T of the back electromotive force Bemf is measured by timing separately from the previous zero-crossing point, and half a period T / 2 is calculated. If the detection unit 10 determines that the phase current Iu is flowing from the drive unit 40 to the motor winding U (Iu > 0), it determines that the phase of the phase current Iu is leading (PH = "H": step S404), and if it determines that the phase current Iu is flowing out of the motor winding U to the drive unit 40 (Iu ≤ 0), it determines that the phase of the phase current Iu is lagging (PH = "L": step S405).

[0050] Thus, the detection unit 10 may calculate the half-period of the back electromotive force Bemf by storing the past zero-crossing points of the back electromotive force Bemf, and generate a phase signal PH according to the direction in which the phase current Iu flows half a period after the detected zero-crossing point of the back electromotive force Bemf. The direction in which the phase current Iu flows half a period after the zero-crossing point of the back electromotive force Bemf is a predetermined direction that differs depending on whether the phase of the phase current Iu is leading or lagging the phase of the back electromotive force Bemf.

[0051] Specifically, as shown in Figures 2A to 2C, when detecting the zero-crossing of the back electromotive force Bemf from positive to negative, the direction in which the phase current Iu flows half a cycle after the zero-crossing of the back electromotive force Bemf is such that when the phase of the phase current Iu leads the phase of the back electromotive force Bemf, it flows from the drive unit 40 to the motor winding U, and when the phase of the phase current Iu lags behind the phase of the back electromotive force Bemf, it flows out from the motor winding U to the drive unit 40. Furthermore, as shown in Figures 8A to 8C described later, when detecting the zero-crossing of the back electromotive force Bemf from negative to positive, the direction in which the phase current Iu flows during the non-energized period is such that when the phase of the phase current Iu lags behind the phase of the back electromotive force Bemf, it flows from the drive unit 40 to the motor winding U, and when the phase of the phase current Iu leads the phase of the back electromotive force Bemf, it flows out from the motor winding U to the drive unit 40.

[0052] Therefore, it is possible to determine whether the phase of the phase current Iu is leading the phase of the back electromotive force Bemf, depending on the direction in which the phase current Iu flows half a cycle after the zero-crossing point, and consequently, generate the phase signal PH. For this reason, phase determination can be performed even if there is no time to process the signal during the non-energized period.

[0053] Figure 6 is a flowchart showing another example of the phase determination process of the motor drive device according to the first embodiment. The difference from the flowchart shown in Figure 4A is that the phase is determined to be advanced when a phase lead of the phase current Iu relative to the back electromotive force Bemf is detected multiple times in a row. The phase determination process of the flowchart in Figure 6 will be described below.

[0054] As the non-energized period begins (TP = "L" → "H": step S501), the switching operation stops and the detection unit 10 performs a phase determination (step S502). When the phase voltage Vu decreases (Vu ≤ Vc), the detection unit 10 determines that the phase of the phase current Iu is lagging and resets the lead count N to zero (N = 0: step S503), and sets the phase signal PH to L level (PH = "L": step S504). Conversely, when the phase voltage Vu increases and exceeds the neutral point potential Vc (Vu > Vc), the detection unit 10 determines that the phase of the phase current Iu is leading and increments the lead count N (N + 1: step S505), and determines whether the value of N is 2 or greater (step S506). If the value of N is 2 or greater (Yes in step S506), the detection unit 10 sets the phase signal PH to the H level (PH = "H": step S507), and if the value of N is less than 2 (No in step S506), it leaves the phase signal PH at the L level (PH = "L": step S504).

[0055] Thus, if the detection unit 10 detects multiple consecutive times that the phase of the phase current Iu is leading the phase of the back electromotive force Bemf, it may generate a phase signal PH indicating that the phase of the phase current Iu is leading the phase of the back electromotive force Bemf. In other words, if the detection unit 10 detects multiple consecutive times that the phase of the phase current Iu is leading the phase of the back electromotive force Bemf, it determines that the phase is leading, sets the phase signal PH to an H level (PH = "H"), and allows the motor 100 to accelerate. This makes the phase determination, which prevents false detections, more robust. For example, it can prevent the motor 100 from accelerating incorrectly even though the phase of the phase current Iu is lagging behind the phase of the back electromotive force Bemf.

[0056] In this embodiment, the number of advances N is set to 2 or more, but this is just an example and not limited to this. To determine phase advance more reliably, the number of advances N (i.e., the condition for allowing acceleration) may be set to 3 or more.

[0057] Furthermore, although illustrations and detailed explanations are omitted, the phase determination step (step S502) shown in the flowchart of Figure 6 is not limited to the comparison between the phase voltage Vu and the neutral point potential Vc as in Figure 4A. For example, the determination in the phase determination step of the flowchart of Figure 6 may be changed to a determination based on the direction of the phase current Iu as explained in Figure 4B, or a determination based on the direction of the phase current Iu after half a cycle as explained in Figure 5.

[0058] Figure 7 is a waveform diagram illustrating the operation of the motor drive device according to the first embodiment, and shows the operation waveforms of the main parts of the motor drive device according to this embodiment. From top to bottom in Figure 7, the torque command TQ, phase signal PH, internal torque command Vsp, target current waveform Ui, and non-energized period signal TP are shown, and the changes in each signal due to the torque command TQ are represented. Note that Figure 7 does not show the change in period due to acceleration and deceleration.

[0059] In Figure 7, prior to time t1, the torque command TQ and the internal torque command Vsp are equal, and the phase current Iu is in a phase-lag state (PH = "L"). At time t1, when the de-energization period signal TP rises after the torque command TQ has decreased due to deceleration, the internal torque command Vsp also decreases in accordance with the decrease in torque command TQ. Since the phase current Iu is PWM controlled according to the control signal from the energization control unit 30, its amplitude decreases in accordance with the internal torque command Vsp. The motor 100 decelerates as the current amplitude of the phase current Iu decreases. As the motor 100 decelerates, the phase of the phase current Iu advances, and the phase signal PH eventually becomes "H".

[0060] Next, as the torque command TQ increases for acceleration, the phase signal PH = "H" at times t2 and t3, so the internal torque command Vsp also increases in accordance with the increase in the torque command TQ. As the current amplitude increases, the motor 100 accelerates, and the phase of the phase current Iu lags behind, so the phase signal PH becomes "L" at time t4. Since the phase signal PH = "L", the subsequent increase in the torque command TQ is ignored, and the internal torque command Vsp is maintained. As the current amplitude is maintained, the phase is adjusted each time the position detection signal BEMF is set, so the phase current Iu becomes almost in phase with the back electromotive force Bemf, and the phase repeatedly lags and leads. At times t5 and t6, after the phase has advanced and the phase signal PH = "H", the internal torque command Vsp also increases to follow the increased torque command TQ, and the motor 100 accelerates due to the increase in the current amplitude. From this point onward, the torque command TQ maintains high-speed rotation, but the phase of the phase current Iu becomes almost in phase with the back electromotive force Bemf, and the phase repeatedly lags and leads.

[0061] As described above, during acceleration, the motor 100's acceleration response will be delayed because it will wait until the phase advances before following the torque command TQ. However, this does not exacerbate the phase lag of the phase current Iu associated with acceleration, and the zero-crossing of the back electromotive force Bemf can be reliably detected, preventing loss of synchronism.

[0062] In the above description of this embodiment, an example of detecting a zero-cross from a positive voltage to a negative voltage of the back electromotive force Bemf was shown, but it is also acceptable to detect a zero-cross from a negative voltage to a positive voltage. Figures 8A to 8C show the waveforms of the operation of detecting a zero-cross from a negative voltage to a positive voltage of the back electromotive force Bemf. From top to bottom, the waveforms are: back electromotive force Bemf, non-energized period signal TP, phase voltage Vu and neutral point potential Vc, current Iu, and position detection signal BEMF. Figure 8A is a waveform diagram when detecting a zero-cross from a negative to a positive back electromotive force Bemf when the phase of the phase current Iu is leading. Figure 8B is a waveform diagram when detecting a zero-cross from a negative to a positive back electromotive force Bemf when the phase of the phase current Iu is lagging. Figure 8C is a waveform diagram when detecting a zero-cross from a negative to a positive back electromotive force Bemf when detection is missed due to the phase lag of the phase current Iu. As in Figures 2A to 2C, a phase lag in the phase current Iu increases the risk of missing the zero-crossing detection of the back electromotive force Bemf, but the phase determination differs from that in Figures 2A to 2C.

[0063] Although not shown in the diagram, as shown in Figure 4A, when comparing the phase voltage Vu and the neutral point potential Vc during a non-energized period, the detection unit 10 determines that the phase of the phase current Iu is lagging and sets the phase signal PH to L level if the phase voltage Vu rises to be equal to or greater than the neutral point potential Vc (Vu ≥ Vc), and determines that the phase of the phase current Iu is not lagging and sets the phase signal PH to H level if the phase voltage Vu falls below the neutral point potential Vc (Vu < Vc). Furthermore, although not shown in the figures, when determining the phase based on the direction of the phase current Iu during the non-energized period, as shown in Figure 4B, the detection unit 10 determines that the phase is leading if the phase current Iu flows into the motor winding U in the positive direction (Iu > 0) and sets the phase signal PH to the H level (PH = "H"), and determines that the phase is lagging if the phase current Iu flows out of the motor winding U in the negative direction (Iu ≤ 0) and sets the phase signal PH to the L level (PH = "L"). In addition, although not shown in the figures, when determining the phase based on the direction of the phase current Iu after half a cycle, as shown in Figure 5, the detection unit 10 determines that the phase is lagging if the phase current Iu flows into the motor winding U in the positive direction (Iu ≥ 0) and sets the phase signal PH to the L level (PH = "L"), and determines that the phase is leading if the phase current Iu flows out of the motor winding U in the negative direction (Iu < 0) and sets the phase signal PH to the H level (PH = "H").

[0064] Furthermore, there is a control method called advance angle control, which actively aligns the phase of the phase current Iu with the back electromotive force Bemf, or advances the phase of the phase current Iu, which tends to lag, by a predetermined angle. By performing advance angle control, the phase of the phase current Iu that has lagged for any reason is controlled to immediately lead the back electromotive force Bemf. Therefore, by combining this with the technology of this disclosure, it is possible to avoid zero-crossing detection failures during acceleration and mitigate the deterioration of the acceleration response.

[0065] Furthermore, at least the detection unit 10 and the waveform setting unit 20 may be integrated, and the power supply control unit 30 may also be integrated. This makes it possible to miniaturize the motor drive device.

[0066] As explained above, even if an acceleration command is received from an external source for the motor 100, if the phase of the phase current Iu lags behind the phase of the back electromotive force Bemf, the acceleration command is not accepted. Only after it is confirmed that the phase of the phase current Iu is ahead of the phase of the back electromotive force Bemf is the acceleration command accepted and the motor 100 accelerates. In other words, the motor 100 accelerates only when the phase of the phase current Iu is ahead of the phase of the back electromotive force Bemf. This suppresses the phase of the phase current Iu lagging behind the phase of the back electromotive force Bemf, and thus suppresses the failure to detect the zero-crossing of the back electromotive force Bemf. Therefore, it is possible to prevent step loss due to the failure to detect the zero-crossing.

[0067] (Second Embodiment) Prior to this disclosure, the inventors filed an application for an invention that suppresses waveform distortion of the phase current Iu by shortening the zero-cross detection period (i.e., the non-energized period) (Japanese Patent Application No. 2024-55688). The technology described in Japanese Patent Application No. 2024-55688 can be combined with the technology of this disclosure. The technology described in Japanese Patent Application No. 2024-55688, which can be combined with the technology of this disclosure, will be described below as a second embodiment.

[0068] Figure 9A is a circuit diagram showing an example of the detection unit 10 and the non-energized period specification unit 21 according to the second embodiment. For example, the waveform setting unit 20 may have the non-energized period specification unit 21 shown in Figure 9A. In addition, the detection unit 10 may have the functions shown in Figure 9A in addition to the functions described in the first embodiment.

[0069] As shown in Figure 9A, the detection unit 10 includes, for example, a comparator 11 and a one-shot pulse circuit 12. The comparator 11 is activated by the non-energized period signal TP. For example, if the non-energized period signal TP is at an L level, the comparator 11 also outputs an L level. The comparator 11 also compares the drive voltage (phase voltage Vu) of the motor winding U with the neutral point potential Vc of the motor 100. The one-shot pulse circuit 12 outputs a one-shot pulse by detecting the falling edge of the output signal CMP of the comparator 11. The output of this one-shot pulse circuit 12 is the position detection signal BEMF.

[0070] The non-energized period designation unit 21 includes a timing circuit 210, a comparison circuit 211, a non-energized timing setting circuit 212, and a latch circuit 213.

[0071] The timing circuit 210 timings the period of no power supply and outputs a time signal Tp indicating the length of the period of no power supply. The time signal Tp may be, for example, an analog value indicating the voltage of a capacitor due to constant current charging, or a digital value indicating the count of a predetermined clock by a counter. The timing time indicated by the time signal Tp corresponds to the period of no power supply, so hereafter the period of no power supply will also be referred to as the period of no power supply Tp.

[0072] The comparison circuit 211 compares the non-energized period Tp with a predetermined value to determine the level, and the non-energized timing setting circuit 212 adjusts the start timing tp of the non-energized period Tp based on the output of the comparison circuit 211.

[0073] Figure 9B is a table showing an example of adjusting the non-energized period Tp in the second embodiment.

[0074] In this embodiment, the comparison circuit 211 sets a predetermined value T1 and a predetermined value T2 that is greater than the predetermined value T1 as predetermined values ​​to be compared with the non-energized period Tp. The predetermined value T1 is an example of a first predetermined value, and the predetermined value T2 is an example of a second predetermined value.

[0075] As shown in Figure 9B, when the non-energized period Tp is less than or equal to a predetermined value T1 (Tp ≤ T1), both the comparison result a1 with the predetermined value T1 and the comparison result a2 with the predetermined value T2 are at the H level. Therefore, the non-energized timing setting circuit 212 determines that the non-energized period Tp is too short and advances the start timing tp of the non-energized period Tp (for example, advancing the start timing tp by a change of ΔT: tp → tp - ΔT). As shown in Figure 9B, when the non-energized period Tp is longer than the predetermined value T1 and less than or equal to a predetermined value T2 (T1 < Tp ≤ T2), the comparison result a1 with the predetermined value T1 is at the L level and the comparison result a2 with the predetermined value T2 is at the H level. Therefore, the non-energized timing setting circuit 212 determines that the non-energized period Tp is appropriate and maintains the start timing tp of the non-energized period Tp (tp → tp). As shown in Figure 9B, if the non-energized period Tp is longer than a predetermined value T2 (Tp > T2), both the comparison result a1 with the predetermined value T1 and the comparison result a2 with the predetermined value T2 are at the L level. Therefore, the non-energized timing setting circuit 212 determines that there is too much margin in the non-energized period Tp and delays the start timing tp of the non-energized period Tp (for example, delaying the start timing tp by a change of ΔT: tp → tp + ΔT).

[0076] In this way, the waveform setting unit 20 adjusts the start timing tp of the non-energized period Tp based on the non-energized period Tp. This allows the start timing tp of the non-energized period Tp to be adjusted to shorten the non-energized period Tp if the non-energized period Tp is too long, and to lengthen the non-energized period Tp if it is too short. For example, instead of selecting the start timing tp of the non-energized period Tp from a predetermined list of candidates, the start timing tp of the non-energized period Tp can be flexibly adjusted by feedback control of the non-energized period Tp. Therefore, optimization of the non-energized period Tp becomes possible. For example, since the non-energized period Tp can be shortened while setting the non-energized period Tp necessary for rotor position detection, vibration, noise, or malfunctions can be suppressed.

[0077] For example, if the waveform setting unit 20 detects that the non-energized period Tp is shorter than a predetermined value T1, it advances the start timing tp of the non-energized period Tp. If the non-energized period Tp is too short, the start timing tp of the non-energized period Tp is advanced to make the non-energized period Tp longer, thereby optimizing the non-energized period Tp.

[0078] For example, if the waveform setting unit 20 detects that the non-energized period Tp is longer than a predetermined value T2, it delays the start timing tp of the non-energized period Tp. If the non-energized period Tp is too long, the start timing tp of the non-energized period Tp is delayed so that the non-energized period Tp becomes shorter, thereby optimizing the non-energized period Tp.

[0079] The latch circuit 213 latches an H-level signal in synchronization with the output of the non-energized timing setting circuit 212 and is reset by the position detection signal BEMF via the inverter 214. The Q output of the latch circuit 213 becomes the non-energized period signal TP.

[0080] The operation of the motor drive device according to this embodiment, having the above configuration, will be explained using the waveform diagrams in Figures 10 and 11. First, the operation of the detection unit 10 will be explained using Figure 10.

[0081] Figure 10 is a waveform diagram illustrating the operation of the detection unit 10 according to the second embodiment. From top to bottom, Figure 10 shows the back electromotive force Bemf, the non-energized period signal TP, the phase voltage Vu and neutral point potential Vc, the current Iu, the output CMP of the comparator 11, and the position detection signal BEMF. Here, the phase voltage Vu is a high-frequency rectangular wave due to the switching operation of the upper switch element 41 and the lower switch element 42, except during the non-energized period Tp, but in Figure 10 it is shown as a smoothed waveform. That is, if the duty cycle of the upper switch element 41 during switching operation (the ratio of the on time to one switching period) is δ and the power supply potential is Vdd, then Vu = δ × Vdd. Similarly, in the following waveform diagrams, the phase voltage Vu is also shown as a smoothed waveform.

[0082] The non-energized period designation unit 21 sets the non-energized period signal TP to a high level from time tp until the next pulse input of the position detection signal BEMF. As a result, the waveform setting unit 20 generates a current waveform that is zero level during the period when the non-energized period signal TP is at a high level. According to this current waveform, the power control unit 30 outputs a control signal that turns off both the upper switch element 41 and the lower switch element 42 during the period when the non-energized period signal TP is at a high level. Due to the turn-off of the upper switch element 41, which was supplying current to the motor winding U, the phase voltage Vu drops sharply, the body diode of the lower switch element 42 conducts, and a regenerative current flows as current Iu. The regenerative current is a decreasing current, and during the period when the regenerative current is flowing, the phase voltage Vu is lower than the ground potential by the forward voltage of the body diode of the lower switch element 42. Comparator 11 is active during the period when the non-energized signal TP is at a high level, but since the phase voltage Vu is lower than the neutral point potential Vc, the output CMP is at a low level.

[0083] When the regenerated current Iu at time t1 becomes zero, the phase voltage Vu rises and becomes higher than the neutral point potential Vc, and the output CMP of comparator 11 becomes high. At this time, since no current Iu flows, a back electromotive force Bemf is generated in the phase voltage Vu, superimposed on the neutral point potential Vc.

[0084] When the phase voltage Vu falls below the neutral point potential Vc at time t2, that is, when the back electromotive force Bemf crosses zero, the output CMP of the comparator 11 falls to an L level. The one-shot pulse circuit 12 outputs a position detection signal BEMF by detecting this falling edge. As the position detection signal BEMF rises, the latch circuit 213 of the non-energized period specification unit 21 is reset, the non-energized period signal TP becomes L level, and the non-energized period Tp ends. With the end of the non-energized period Tp, the upper switch element 41 and the lower switch element 42 of the drive unit 40 resume switching operation according to the current waveform generated by the waveform setting unit 20, and begin supplying current to the motor winding U.

[0085] Next, using Figure 11, an example of the operation of the motor drive device of this embodiment will be explained, showing how the long period of no power supply Tp reaches an appropriate value.

[0086] Figure 11 is a waveform diagram illustrating the operation of the non-energized period designation unit 21 according to the second embodiment. From top to bottom, Figure 11 shows the back electromotive force Bemf, the non-energized period signal TP, the phase voltage Vu and neutral point potential Vc, and the position detection signal BEMF. Time 0 on the horizontal axis in the figure indicates the timing when the position detection signal BEMF rises, and the rising edge of the position detection signal BEMF resets the time information for timing the non-energized period Tp to zero.

[0087] If the start timing tp of the non-energized period Tp is time tp1, the measurement of the non-energized period Tp is started by the timing circuit 210 from time tp1, and the comparison circuit 211 determines that Tp > T2. In this case, the non-energized timing setting circuit 212 delays the start timing tp of the next non-energized period Tp by a change of ΔT from time tp1, and sets it to time tp2 (tp2 = tp1 + ΔT). If the comparison circuit 211 also determines that Tp > T2 for the non-energized period Tp measured from time tp2 of the next cycle, the non-energized timing setting circuit 212 delays the start timing tp of the next non-energized period Tp by a change of ΔT from time tp2, similar to the previous cycle. Then, if the non-energized period Tp measured from time tp3 (= tp2 + ΔT) of the next cycle is determined to be T1 < Tp ≤ T2. In this case, the non-energized timing setting circuit 212 maintains the start timing tp of the next non-energized period Tp at time tp3. As a result, the non-energized period Tp is maintained between a predetermined value T1 and a predetermined value T2 thereafter.

[0088] As described above, according to this embodiment, the non-energized period Tp can be shortened so that the zero-cross detection period (non-energized period Tp) in sensorless motor drive approaches the target value. This enables low-vibration and low-noise driving.

[0089] In this way, by shortening the zero-crossing detection period (i.e., the non-energized period), waveform distortion of the phase current Iu is suppressed, and by accepting an acceleration command to the motor 100 only when it is determined that the phase of the phase current Iu is ahead of the phase of the back electromotive force Bemf, it is possible to suppress the failure to detect the zero-crossing of the back electromotive force Bemf. Shortening the zero-crossing detection period may exacerbate the failure to detect the zero-crossing due to the phase lag of the phase current Iu, so by combining the technology of the first embodiment and the technology of the second embodiment, this problem can be overcome and an even greater effect can be achieved. In this case, since it is difficult to determine the phase during a short non-energized period, it is preferable to determine the phase in the direction of the phase current Iu after half a cycle, as shown in Figure 5.

[0090] In the second embodiment, the predetermined values ​​T1, T2, and the change range ΔT are arbitrarily set during the design process. For example, the change range ΔT may be different depending on whether the start timing tp is delayed or advanced. Furthermore, the above values ​​do not have to be fixed and may be changed as appropriate.

[0091] Furthermore, a change in the start timing of the non-energized period Tp does not have to be determined solely by comparing a single non-energized period Tp with a predetermined value; it may also be determined by the fact that the comparison results are the same for a predetermined number of consecutive times, or by the average value of a predetermined number of comparison results.

[0092] For example, if the start timing tp of the non-energized period Tp is advanced each time it is detected that the non-energized period Tp is shorter than a predetermined value T1, the non-energized period Tp will be changed frequently. Therefore, the waveform setting unit 20 may advance the start timing tp of the non-energized period Tp when it has detected that the non-energized period Tp is shorter than the predetermined value T1 a predetermined number of times. This makes it possible to suppress vibration, noise, or malfunctions associated with frequent changes in the non-energized period Tp.

[0093] For example, if the start timing tp of the non-energized period Tp is delayed each time it is detected that the non-energized period Tp is longer than a predetermined value T2, the non-energized period Tp will be changed frequently. Therefore, the waveform setting unit 20 may delay the start timing tp of the non-energized period Tp when it has detected that the non-energized period Tp is longer than a predetermined value T2 a predetermined number of times. This makes it possible to suppress vibration, noise, or malfunctions associated with frequent changes in the non-energized period Tp.

[0094] (Other Embodiments) Embodiments have been described above as examples of the technology relating to this disclosure. However, the technology relating to this disclosure is not limited thereto and can be applied to embodiments that have been modified, replaced, added, or omitted as appropriate. For example, the following modified examples are also included as embodiments of this disclosure.

[0095] For example, this disclosure can be implemented not only as a motor drive device, but also as a motor drive method that includes steps (processes) performed by the components constituting the motor drive device.

[0096] Figure 12 is a flowchart showing an example of a motor drive method according to another embodiment.

[0097] The motor driving method is a motor driving method for a sensorless motor drive device that detects the zero-crossing of the back electromotive force generated in the motor windings for motor rotation control, and includes, as shown in Figure 12, a detection step (step S11) that determines whether the phase of the winding current flowing through the motor windings leads the phase of the back electromotive force, and a waveform setting step (steps S12 and S13) that accepts an acceleration command to the motor if it is determined that the phase of the winding current leads the phase of the back electromotive force (Yes in step S11), and does not accept an acceleration command to the motor if it is determined that the phase of the winding current lags behind the phase of the back electromotive force (No in step S11).

[0098] For example, this disclosure can be implemented as a program that causes a computer (processor) to execute steps included in a motor drive method. Furthermore, this disclosure can be implemented as a non-temporary computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0099] For example, if this disclosure is implemented in a program (software), each step is executed by the program using hardware resources such as the computer's CPU, memory, and input / output circuits. In other words, each step is executed by the CPU obtaining data from memory or input / output circuits, performing calculations, and outputting the calculation results to memory or input / output circuits.

[0100] In the above embodiment, each component included in the motor drive device may be implemented by dedicated hardware or by executing a software program suitable for each component. Each component may also be implemented by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0101] Some or all of the functions of the motor drive device according to the above embodiment are typically implemented as an LSI, which is an integrated circuit. These may be individually integrated onto a single chip, or some or all of them may be integrated onto a single chip. Furthermore, the implementation is not limited to an LSI, but may also be implemented using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells inside the LSI may also be used.

[0102] Furthermore, if advances in semiconductor technology or other derived technologies lead to the emergence of integrated circuit technologies that can replace LSIs, then naturally, those technologies may be used to integrate each component included in the motor drive device into an integrated circuit.

[0103] Furthermore, this disclosure also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of this disclosure.

[0104] (Note) The above description of embodiments discloses the following technology.

[0105] (Technology 1) A sensorless motor drive device for detecting the zero-crossing of the back electromotive force generated in the windings of a motor for rotation control of the motor, comprising: a detection unit that determines whether the phase of the winding current flowing through the motor windings leads the phase of the back electromotive force; and a waveform setting unit that accepts an acceleration command to the motor when it is determined that the phase of the winding current leads the phase of the back electromotive force, and does not accept an acceleration command to the motor when it is determined that the phase of the winding current lags behind the phase of the back electromotive force.

[0106] According to this, even if an acceleration command is received from an external source, if the phase of the winding current lags behind the phase of the back EMF, the acceleration command will not be accepted. The motor will only accelerate after it is confirmed that the phase of the winding current is ahead of the phase of the back EMF. In other words, the motor will only accelerate if the phase of the winding current is ahead of the phase of the back EMF, thus suppressing the lag of the winding current phase behind the phase of the back EMF and preventing missed detection of the back EMF zero crossing. Therefore, it is possible to prevent step loss due to missed detection of the zero crossing.

[0107] (Technology 2) The motor drive device further comprises a drive unit and an energization control unit, wherein the drive unit has a plurality of switch element pairs consisting of an upper switch element and a lower switch element, and supplies the winding current and drive voltage to the winding of the motor, the detection unit detects the zero-crossing of the back electromotive force by detecting the winding current and the drive voltage, the waveform setting unit sets the energization timing of the winding based on the zero-crossing of the back electromotive force and sets an internal torque command based on an external torque command, the energization control unit supplies a control signal to each of the plurality of switch element pairs based on the energization timing and the internal torque command, and the waveform setting unit increases the internal torque command according to the acceleration command among the torque commands that requests acceleration when it is determined that the phase of the winding current is ahead of the phase of the back electromotive force.

[0108] Thus, when the phase of the winding current leads the phase of the back electromotive force, the motor can be accelerated by increasing the internal torque command in accordance with the torque command indicating an external acceleration command.

[0109] (Technology 3) The motor drive device according to Technology 2, wherein the waveform setting unit sets a non-energized period in which both of the pair of switch elements are in the off state, the detection unit detects a reference potential corresponding to the neutral point potential of the motor winding, and detects the zero-crossing of the back electromotive force by comparing the drive voltage and the reference potential during the period in the non-energized period when the winding current is zero.

[0110] According to this method, since the back electromotive force cannot be correctly detected when winding current is flowing, the zero-crossing of the back electromotive force, which is the difference between the driving voltage and the reference potential, can be correctly detected by comparing the driving voltage and the reference potential during the period when the winding current is zero.

[0111] (Technical 4) The motor drive device according to Technical 3, wherein the detection unit generates a phase signal indicating whether the phase of the winding current leads the phase of the back electromotive force.

[0112] According to this, the waveform setting unit and other components can be controlled by a phase signal that indicates whether the phase of the winding current leads the phase of the back electromotive force.

[0113] (Technical 5) The motor drive device according to Technical 4, wherein the detection unit generates the phase signal according to the level of the drive voltage during the period when the winding current is flowing during the non-energized period.

[0114] During periods when winding current is flowing but the power supply is off, the drive voltage will have predetermined magnitudes that differ depending on whether the phase of the winding current is leading or lagging the phase of the back electromotive force. Therefore, it is possible to determine whether the phase of the winding current is leading the phase of the back electromotive force based on the level of the drive voltage during periods when winding current is flowing but the power supply is off, and consequently, to generate a phase signal.

[0115] (Technical 6) The motor drive device according to Technical 4, wherein the detection unit generates the phase signal according to the direction in which the winding current flows during the non-energized period.

[0116] During periods of no power supply, the direction in which the winding current flows is predetermined and differs depending on whether the phase of the winding current leads or lags the phase of the back electromotive force. Therefore, it is possible to determine whether the phase of the winding current leads the phase of the back electromotive force depending on the direction in which the winding current flows during periods of no power supply, and consequently, to generate a phase signal.

[0117] (Technical 7) The motor drive device according to Technical 4, wherein the detection unit calculates half a period of the back electromotive force by storing the past zero-crossing points of the back electromotive force, and generates the phase signal according to the direction in which the winding current is flowing half a period after the detected zero-crossing point of the back electromotive force.

[0118] The direction in which the winding current flows half a cycle after the zero-crossing point is a predetermined direction that differs depending on whether the phase of the winding current is leading or lagging the phase of the back EMF. Therefore, it is possible to determine whether the phase of the winding current is leading the phase of the back EMF based on the direction in which the winding current flows half a cycle after the zero-crossing point, and consequently, to generate a phase signal. Phase determination can be performed even if there is no time to process the signal during the non-energized period.

[0119] (Technical 8) A motor drive device according to any one of Technical 4 to 7, wherein the detection unit detects multiple times in a row that the phase of the winding current is leading the phase of the back electromotive force, and generates the phase signal indicating that the phase of the winding current is leading the phase of the back electromotive force.

[0120] According to this, it is possible to suppress the motor from accelerating incorrectly even though the phase of the winding current lags behind the phase of the back electromotive force.

[0121] (Technology 9) A motor drive device according to any one of the technologies 1 to 8, wherein at least the detection unit and the waveform setting unit are integrated.

[0122] Thus, the detection unit and the waveform setting unit may be integrated.

[0123] (Technical 10) A motor system comprising a motor drive device according to any one of Technical 1 to 9, and the motor.

[0124] This allows for the provision of a motor system that can suppress the failure to detect the zero-crossing of the back electromotive force.

[0125] (Technical 11) A motor driving method for a sensorless motor drive device that detects the zero-crossing of a back electromotive force generated in the windings of a motor for rotation control of the motor, comprising: a detection step of determining whether the phase of the winding current flowing through the windings of the motor is ahead of the phase of the back electromotive force; and a waveform setting step of accepting an acceleration command to the motor if it is determined that the phase of the winding current is ahead of the phase of the back electromotive force, and not accepting an acceleration command to the motor if it is determined that the phase of the winding current is behind the phase of the back electromotive force.

[0126] This provides a motor drive method that can suppress the failure to detect the zero-crossing of the back electromotive force.

[0127] The motor drive device described herein can be applied to spindle motors and the like of various disk devices that require driving sensorless motors with low vibration and low noise.

[0128] 10 Detection unit 11 Comparator 12 One-shot pulse circuit 20 Waveform setting unit 21 Non-energized period specification unit 210 Timing circuit 211 Comparison circuit 212 Non-energized timing setting circuit 213 Latch circuit 214 Inverter 30 Power control unit 40 Drive unit 41 Upper switch element 42 Lower switch element 100 Motor

Claims

1. A sensorless motor drive device for detecting the zero-crossing of the back electromotive force generated in the windings of a motor for rotation control of the motor, comprising: a detection unit that determines whether the phase of the winding current flowing through the motor windings leads the phase of the back electromotive force; and a waveform setting unit that accepts an acceleration command to the motor if it is determined that the phase of the winding current leads the phase of the back electromotive force, and does not accept an acceleration command to the motor if it is determined that the phase of the winding current lags behind the phase of the back electromotive force.

2. The motor drive device further comprises a drive unit and an energization control unit, wherein the drive unit has a plurality of switch element pairs consisting of an upper switch element and a lower switch element, and supplies the winding current and drive voltage to the motor winding, the detection unit detects the zero-crossing of the back electromotive force by detecting the winding current and the drive voltage, the waveform setting unit sets the energization timing of the winding based on the zero-crossing of the back electromotive force and sets an internal torque command based on an external torque command, the energization control unit supplies a control signal to each of the plurality of switch element pairs based on the energization timing and the internal torque command, and the waveform setting unit increases the internal torque command according to the acceleration command among the torque commands that requests acceleration when it is determined that the phase of the winding current is ahead of the phase of the back electromotive force.

3. The motor drive device according to claim 2, wherein the waveform setting unit sets a non-energized period in which both of the pair of switch elements are in the off state, the detection unit detects a reference potential corresponding to the neutral point potential of the motor winding, and detects the zero-crossing of the back electromotive force by comparing the drive voltage and the reference potential during the period in the non-energized period when the winding current is zero.

4. The motor drive device according to claim 3, wherein the detection unit generates a phase signal indicating whether the phase of the winding current leads the phase of the back electromotive force.

5. The motor drive device according to claim 4, wherein the detection unit generates the phase signal according to the level of the drive voltage during the period when the winding current is flowing in the non-energized period.

6. The motor drive device according to claim 4, wherein the detection unit generates the phase signal according to the direction in which the winding current flows during the non-energized period.

7. The motor drive device according to claim 4, wherein the detection unit calculates a half-period of the back electromotive force by storing the past zero-crossing points of the back electromotive force, and generates the phase signal according to the direction in which the winding current is flowing half a period after the detected zero-crossing point of the back electromotive force.

8. The motor drive device according to any one of claims 4 to 7, wherein the detection unit generates the phase signal indicating that the phase of the winding current is leading the phase of the back electromotive force when it detects multiple times in a row that the phase of the winding current is leading the phase of the back electromotive force.

9. A motor drive device according to any one of claims 1 to 8, wherein at least the detection unit and the waveform setting unit are integrated.

10. A motor system comprising a motor drive device according to any one of claims 1 to 9, and the motor.

11. A motor driving method for a sensorless motor drive device that detects the zero-crossing of a back electromotive force generated in the windings of a motor for rotation control of the motor, comprising: a detection step of determining whether the phase of the winding current flowing through the windings of the motor is ahead of the phase of the back electromotive force; and a waveform setting step of accepting an acceleration command to the motor if it is determined that the phase of the winding current is ahead of the phase of the back electromotive force, and not accepting an acceleration command to the motor if it is determined that the phase of the winding current is behind the phase of the back electromotive force.

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