Method for detecting excitation position of motor

Abstract

The invention provides an excitation position detection method for a motor, which can reliably detect the excitation position of the motor during operation and operate the motor even if the duty ratio of the driving voltage is changed when a three-phase brushless motor is operated in a sensorless driving mode through PWM control of 120-degree energization. When the MPU (51) is operated by changing the duty ratio applied to the three-phase coil drive voltage by the inverter circuit (52), the MPU (51) selects an optimal duty ratio that is most suitable for sensing the non-energized phase coil voltage at a predetermined drive voltage, and when driving is performed at the optimal duty ratio in the energization section of one cycle, the MPU (51) operates at a predetermined drive voltage. When a driving voltage is applied that exceeds a duty ratio based on the optimal duty ratio, the driving voltage is applied by dividing the on-duty ratio section of one cycle into a plurality of on-duty ratio sections including the optimal duty ratio, and when a driving voltage is applied that exceeds a duty ratio based on the optimal duty ratio, the driving voltage is applied by dividing the on-duty ratio section of one cycle into a plurality of on-duty ratio sections including the optimal duty ratio.

Description

Technical Field

[0001] The present invention relates to a method for detecting the excitation position of a motor when the motor is running at a low speed in a sensorless driving manner. Background Art

[0002] Conventionally, small DC motors have used brushed DC motors, but due to problems such as brush noise, electrical noise, and durability, brushless DC motors have emerged. In addition, recently, from the viewpoints of miniaturization, light weight, firmness, and low cost, sensorless motors without position sensors have attracted attention and have first been adopted in hard disk drives and the like in the information device field. With the development of vector control technology, they have also begun to be adopted in the home appliance and vehicle fields.

[0003] In the sensorless driving method, the rotor position is detected based on the induced voltage. However, since no induced voltage is generated at rest, the rotor position cannot be grasped, and thus the motor cannot be started. In order to detect the rotor position at rest, there is a method of providing a coil current sensor and a current detection circuit, flowing a sinusoidal coil current through the coil by PWM driving using an inverter, and estimating the position based on the current response. In addition, the rotor position at rest can be detected based on the inductance deviation using the above typical method. Alternatively, the position can be determined by forcibly rotating the rotor through forced commutation without performing position sensing.

[0004] However, once starting begins, power is applied for rotation, so the method of applying a sensing pulse and detecting the rotor position based on the inductance deviation becomes difficult. For example, it can be considered to superimpose a high-frequency current on the excitation current to detect the inductance deviation, but both the scale of the hardware and software will increase. In addition, the influence of magnetic saturation or induced voltage must be considered, and there are also difficult-to-estimate factors such as the inherent errors of the motor and the drive circuit. Therefore, after forcibly positioning the rotor by fixed excitation without performing position detection, the ramp start method of gradually increasing the rotational speed while maintaining synchronization is widely adopted. However, this method has the problems that the positioning of the rotor takes a long time and further reverse rotation is required. In addition, since synchronization is achieved by open-loop control, there are also disadvantages that acceleration also takes time and it is easy to get out of synchronization due to load changes. To avoid this situation, starting with a large current results in reduced efficiency and the DC power supply also becomes large. Since misalignment occurs during load changes, the applications are limited and it cannot be used in reciprocating motion mechanisms, applications that rotate using external force, viscous loads, or applications with load changes.

[0005] Therefore, as a method for detecting the excitation position that can achieve cost reduction by using simple hardware and software, and can detect the rotor position in units of 120° energization intervals without generating sensing noise during startup, the following method has been proposed: Utilize the fact that in the 120-degree energization drive of a three-phase brushless motor, if a voltage is applied to the motor, the induced voltage generated in the non-energized phase changes according to the position of the permanent magnet excitation (rotor) to detect the position of the rotor (Patent Document 1: Japanese Patent Laid-Open No. 2019-17235). Prior Art Documents Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2019-17235 Summary of the Invention Technical Problems to be Solved by the Invention

[0007] However, when the motor is energized in a 120° energization manner, the induced voltage generated in the non-energized phase changes according to the magnitude of the drive voltage applied to the motor. Especially in the case of PWM drive, it changes according to the magnitude of the duty ratio (energization time) of the applied voltage. Figure 12 It is a graph showing the change in the induced voltage generated in the non-energized phase of a certain motor according to the rotational position of the rotor for each duty ratio. From this graph, it can be seen that the magnitude of the generated induced voltage changes greatly with the magnitude of the duty ratio. In addition, Figure 13 is an example of the drive voltage waveform diagram when the duty ratio changes in PWM drive. In the case of the motor shown in Figure 12 , when the duty ratio is 20%, the changes in the positive and negative induced voltages generated in the non-energized phase are significant and easy to measure. However, at other duty ratios, the level of the induced voltage decreases, so the voltage change is slow and the measurement becomes difficult.

[0008] In Patent Document 1, in order to eliminate this phenomenon, a method of multiplying the duty ratio by a correction coefficient was proposed. However, depending on the motor, even if the induced voltage is multiplied by the correction coefficient, position detection is difficult at low duty ratios above a certain level or high duty ratios above a certain level. Therefore, only a limited range of duty ratios can be utilized. This results in a limited control range of the motor torque, and thus the target speed and torque of the motor cannot be achieved. Technical Means for Solving the Technical Problems

[0009] The present invention is proposed to solve these problems, and its purpose is to provide a method for detecting the excitation position of a motor. When a three-phase brushless motor operates at a low speed in a sensorless driving mode by performing PWM control with 120-degree power-on, even if the duty ratio of the driving voltage is changed, the excitation position of the motor can be reliably detected and the motor can operate at a low speed.

[0010] A method for detecting the excitation position of a motor, the motor used includes: a rotor with permanent magnet excitation; a stator with three-phase coils; an output unit that supplies power to the three-phase coils bidirectionally via a half-bridge inverter circuit; a control unit that performs PWM control on the coil output according to an instruction from an upper controller, stores power-on angle information and power-on mode information in units of 60° power-on intervals capable of continuous rotation, and performs switching control on the output unit based on this information to switch the power-on state; and a measurement unit that performs A / D conversion on the three-phase coil voltage and sends it to the control unit. The control unit periodically performs 120-degree power-on including a cut-off cycle in a power-on mode in which the position where self-excitation stops by two-phase fixed power-on coincides with the starting position of the 60° power-on interval via the output unit, measures the power-on phase voltage and the non-power-on phase voltage during the conduction cycle of PWM power-on through the measurement unit, and drives the motor in a sensorless manner while detecting the excitation position of the motor. The characteristic of this method for detecting the excitation position of the motor is that When the control unit operates by changing the duty ratio of a specified driving voltage applied to the three-phase coils through the output unit, in the conduction duty ratio interval, the optimal duty ratio most suitable for sensing the non-power-on phase coil voltage is selected, and in the power-on interval of one cycle, when driving with the optimal duty ratio, the driving voltage is applied in the conduction duty ratio interval of the optimal duty ratio. When applying a driving voltage based on a duty ratio exceeding the optimal duty ratio, the conduction duty ratio interval of one cycle is divided into multiple conduction duty ratio intervals including the optimal duty ratio, and the driving voltage is applied.

[0011] A method for detecting the excitation position of a motor, the motor used includes: a rotor with permanent magnet excitation; a stator with three-phase coils; an output unit that supplies power to the three-phase coils bidirectionally via a half-bridge inverter circuit; a control unit that performs PWM control on the coil output according to an instruction from an upper controller, stores power-on angle information and power-on mode information in units of 60° power-on intervals capable of continuous rotation, and performs switching control on the output unit based on this information to switch the power-on state; and a measurement unit that performs A / D conversion on the three-phase coil voltage and sends it to the control unit. The control unit periodically performs 120° power-on including a cut-off cycle in a power-on mode in which the position where self-excitation is stopped by two-phase fixed power-on coincides with the starting position of the 60° power-on interval via the output unit, measures the power-on phase voltage and the non-power-on phase voltage in the conduction cycle of PWM power-on by the measurement unit, and drives the motor without a sensor while detecting the excitation position of the motor. The method for detecting the excitation position of the motor is characterized in that When the control unit operates by changing the duty ratio of a specified drive voltage applied to the three-phase coil via the output unit, in the conduction duty ratio interval, the optimal duty ratio most suitable for sensing the non-power-on phase coil voltage is selected. In the power-on interval of one cycle, when driving at the optimal duty ratio, the drive voltage is applied in the conduction duty ratio interval of the optimal duty ratio. When applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, the time of one cycle is extended or the drive voltage including the optimal duty ratio is applied over multiple cycles.

[0012] In this way, when changing the duty ratio of the drive voltage for PWM power-on of the three-phase coil of a sensorless drive motor, in the power-on interval of one cycle, when driving at the optimal duty ratio, the drive voltage is applied in the conduction duty ratio interval of the optimal duty ratio. When applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, the conduction duty ratio interval of one cycle is divided into multiple conduction duty ratio intervals including the optimal duty ratio, and the drive voltage is applied. When applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, the time of one cycle is extended or the drive voltage including the optimal duty ratio is applied over multiple cycles. Thereby, when changing the duty ratio of the drive voltage for PWM power-on of the three-phase coil of a sensorless drive motor, even if any controllable duty ratio is selected, at least the excitation position of the motor during low-speed drive can be detected from the non-power-on phase coil voltage by applying the drive voltage based on the optimal duty ratio. Therefore, the motor can smoothly and continuously operate in the low-speed region. Advantages of the Invention

[0013] The present invention provides a method for detecting the excitation position of a motor. When the motor performs PWM control by 120-degree power-on and operates at low speed in a sensorless manner, even if the duty ratio is changed for power-on, the excitation position of the motor can be reliably detected and the motor can operate at low speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a waveform diagram of the inductance and the non-power-on phase coil voltage during U-V excitation. Figure 2It is the waveform diagram of the inductance and the voltage of the non-energized phase coil during U-W excitation. Figure 3 It is the waveform diagram of the inductance and the voltage of the non-energized phase coil during V-W excitation. Figure 4 It is the waveform diagram of the inductance and the voltage of the non-energized phase coil during V-U excitation. Figure 5 It is the waveform diagram of the inductance and the voltage of the non-energized phase coil during W-U excitation. Figure 6 It is the waveform diagram of the inductance and the voltage of the non-energized phase coil during W-V excitation. Figure 7 is the measured waveform diagram of the voltage of the non-energized phase coil. Figure 8 It is the structural block diagram of the drive circuit of the three-phase DC brushless motor. Figure 9 It is the structural diagram of the star-connected three-phase brushless DC motor. Figure 10 is the waveform diagram of the drive voltage of each duty ratio in the energization intervals of two cycles in the 120° energization timing diagram. Figure 11 is the waveform diagram of the drive voltage of each duty ratio in the energization intervals of two cycles in the 120° energization timing diagram. Figure 12 It is the waveform diagram of the induced voltage caused by the voltage of the non-energized phase coil when changing the duty ratio in PWM drive. Figure 13 It is the waveform diagram of the drive voltage when changing the duty ratio in PWM drive. Detailed implementation mode

[0015] Hereinafter, an implementation mode of the excitation position detection method of the motor of the present invention will be described with reference to the drawings. In the present application invention, a sensorless motor having a permanent magnet excitation on the rotor, windings arranged with a 120° phase difference on the stator and star-connected, and the phase ends connected to the motor output unit is used as an example of the motor for description.

[0016] Hereinafter, as an example, a method for detecting the permanent magnet excitation position of a sensorless motor for driving a three-phase DC brushless motor will be described together with the structure of a sensorless motor drive device. Refer to Figure 9 It shows an embodiment of the three-phase brushless DC motor related to the present invention. As an example, a three-phase brushless DC motor having a 2-pole permanent magnet rotor and a stator 4 provided with 3 slots is illustrated. The motor can be an inner rotor type or an outer rotor type. In addition, as the permanent magnet type excitation, it can be any one of a permanent magnet embedded type (IPM type) motor and a surface permanent magnet type (SPM type) motor.

[0017] In Figure 9In this case, a rotor 2 is integrally provided on a rotor shaft 1, and a two-pole permanent magnet 3 is provided as an excitation source. On a stator 4, pole teeth U, V, and W are disposed opposite to the permanent magnet 3 with a 120° phase difference. Windings u, v, and w are provided on respective pole teeth U, V, and W of the stator 4, and are star-connected at a common point C between phases, forming a three-phase brushless DC motor that is wired to a motor drive device described later. In addition, since a common line is not required, it is omitted.

[0018] Next, Figure 8 FIG. 1 shows an example of a drive circuit for a three-phase DC brushless motor. As a drive method during startup, 120°-electrification bipolar rectangular wave excitation is assumed. MOTOR is a three-phase sensorless motor. MPU51 is a microcontroller (control unit). MPU51 stores excitation position information, and performs switching control of an output unit based on a rotation command RUN from an upper controller 50, arbitrarily switching the excitation state. The excitation position information specifies six energization patterns for the three-phase coils (U, V, W) and excitation switching intervals (intervals 1 to 6) for 120° energization corresponding to each energization pattern.

[0019] An inverter circuit 52 (INV: output unit) energizes the three-phase coils and performs switching operations such as excitation phase switching or PWM control to control the motor torque. The inverter circuit 52 includes diodes reversely connected in parallel with switching elements, and a half-bridge type switching circuit capable of arbitrarily connecting to a positive power supply line and a ground power supply line is provided for each of the three phases. An A / D conversion circuit 53 (ADC: measurement unit) is connected to coil output terminals U, V, and W, simultaneously samples the coil voltages of the three phases using a conversion start signal from MPU51, sequentially performs analog-digital conversion, and sends the conversion results to MPU51. Usually, ADC53 is built into MPU51. In the case of using the built-in ADC53, since the maximum input voltage is low, it is preferable to provide a resistance-based voltage dividing circuit. Thus, according to this solution, the drive circuit can be configured very simply.

[0020] It is known that the inductance change (spatial high-order harmonics) caused by the rotor angle θ can be approximated as ΔL = -cos(2θ), and there are two periods for each electrical angle. On the other hand, it is known that when two-phase energization is performed on the three-phase coils by rectangular wave PWM energization, two periodic voltage fluctuations are observed in the non-energized phase centered on the neutral point potential according to θ.

[0021] Figure 1It represents the theoretical value waveforms of the voltage change waveform ΔVw of the non-energized phase, the inductance changes (ΔLu, ΔLv) of the U-phase and V-phase, and the combined inductance change ΔLu-v of the two phases when rotating one electrical angle while exciting U-V by PWM energization. The voltage change waveform is obtained by inverting the polarity of the combined inductance change waveform and oscillates positively and negatively centered on the neutral point potential that is 1 / 2 of the coil applied voltage.

[0022] Figure 7A It represents the measured waveform of the voltage of the non-energized phase coil of an inner-rotor type motor. The theoretical value of the voltage waveform of the non-energized phase reflects the inductance and becomes anti-polar, but the waveforms are approximately the same, indicating that the assumption is correct. In addition, in the case of rectangular wave energization, ringing occurs in the induced voltage. However, as a result of the measurement, the ringing time is very short and converges within the range of measurement error in the order of several μs to several tens of μs in various motors. Even for the rectangular wave PWM energization pulse for motor drive, the induced voltage can be detected with high precision.

[0023] If a large current flows through the three-phase coil, magnetic saturation will occur and the inductance will not change, which is particularly significant in small outer-rotor type motors. When magnetic saturation occurs, among the two periodic inductance change waveforms, the peaks and valleys adjacent to the excitation (Setup) position where self-excitation is stopped by fixed two-phase energization are retained, but the other peaks and valleys disappear, becoming one periodicity. Figure 7B It represents an example of the inductance waveform that becomes one periodicity due to magnetic saturation. The motor used in the measurement is a small outer-rotor type motor, which is different from the motor used in Figure 7A . The excitation position during U-V energization is 150°. In the ΔVw waveform, only the peaks and valleys adjacent to the excitation position are clearly observed.

[0024] The excitation position where self-excitation is stopped by fixed two-phase energization is the zero-crossing point of the inductance and also the zero-crossing point of the induced voltage. The excitation point and the adjacent peaks and valleys are also stable with respect to magnetic saturation. As can be seen from Figure 7A and Figure 7B , the voltage variation of the non-energized phase reflects the rotor angle θ and monotonicity is ensured within the interval. Therefore, even when no induced voltage is generated at rest, the rotor position can be estimated by flowing the excitation current. The voltage variation amplitude is more than 10% of the coil applied voltage and is also in the order of several volts. Considering that the induced voltage in the order of millivolts is detected during startup in the existing method, it has an overwhelming advantage.

[0025] As described above, by using rectangular wave PWM control for motor drive to detect the inductance change of the non-energized phase coil voltage, and only using the inductance change near the excitation position, stable position detection can be performed from the stationary state to the low-speed rotation region. Thereby, the sensing step is simplified, power is not required during sensing, efficiency is improved, and no sensing noise is generated, achieving silence.

[0026] The angles and energization patterns of each energization interval of 120° energization are summarized in the following table. CW energization in the table is the energization pattern that rotates in the direction of increasing angle, and CCW energization is the energization pattern that rotates in the direction of decreasing angle. The excitation energization is the energization pattern that stops self-excitation at the angle described in the () within the frame in the table, and both the starting point and the ending point are recorded for each interval. In each energization pattern, the phase connected to the + power supply side is recorded first, and the phase connected to the GND side is recorded after the hyphen.

[0027]

Table 1

[0028] The rotation direction in which the interval number in Table 1 increases is set as CW, and the rotation direction in which it decreases is set as CCW. The ending position of the interval when rotating in the CW direction is the adjacent + side interval, and the ending position of the interval when rotating in the CCW direction is the boundary point with the - side interval. For example, in the case of interval 1, the ending position of the interval when rotating in the CW direction is the boundary point 90° with interval 2, and the ending position of the interval when rotating in the CCW direction is the boundary point 30° with interval 6.

[0029] In Figure 1 when U-V excitation is performed, the starting point of the energization interval when rotating in the CW direction is point A, and the ending point of the energization interval is point B. The excitation point is point C, and the phase of the trough part where point B is located is stable and can be used for position detection. Therefore, positive and negative threshold values Vth with a specified potential difference relative to the neutral point potential are preset, and the non-energized phase coil voltage ΔV w is compared with the threshold value Vth in each measurement. If it exceeds the threshold value, it can be detected that the interval end point has been exceeded. When rotating in the CCW direction, V-U energization is performed, so refer to Figure 4 . The rotor rotates from the 90° electrical angle side to the 30° electrical angle side. Therefore, the interval end point is the 30° electrical angle. Since the excitation point is the 330° electrical angle, the trough part on the 30° electrical angle side has a stable phase and can be used for position detection. Therefore, similar to the CW case, by comparing the voltage of the non-energized phase W with the threshold value Vth, the interval end point can be detected.

[0030] In interval 2 where the electrical angle is from 90° to 150°, U-W excitation is selected. Figure 2 Indicates the inductance change during U-W excitation and the change in the voltage of the non-energized phase coil. The waveform is obtained by shifting the waveform of Figure 1 by 60° and reversing the polarity. The non-energized phase is the V phase, and the excitation starting position C is at an electrical angle of 210°. When located in interval 2 and rotating in the CW direction, the voltage of the non-energized phase coil must pass through point B. Therefore, the rotor position at this moment is at an electrical angle of 150°. If it switches to interval 3 after detecting point B, continuous rotation can be achieved.

[0031] In interval 3 from an electrical angle of 150° to an electrical angle of 210°, V-W excitation is selected. Figure 3 Indicates the inductance change during V-W excitation and the change in the voltage of the non-energized phase coil. The waveform is obtained by shifting the waveform of Figure 2 by 60° and reversing the polarity. The non-energized phase is the U phase, and the excitation starting position C is at an electrical angle of 270°. When located in interval 3 and rotating in the CW direction, the voltage of the non-energized phase coil must pass through point B. Therefore, the rotor position at this moment is at an electrical angle of 210°. If it switches to interval 4 after detecting point B, continuous rotation can be achieved.

[0032] In interval 4 from an electrical angle of 210° to an electrical angle of 270°, V-U excitation is selected. Figure 4 Indicates the inductance change during V-U excitation and the change in the voltage of the non-energized phase coil. The waveform is obtained by shifting the waveform of Figure 3 by 60° and reversing the polarity. The non-energized phase is the W phase, and the excitation starting position C is at an electrical angle of 330°. When located in interval 4 and rotating in the CW direction, the voltage of the non-energized phase coil must pass through point B. Therefore, the rotor position at this moment is at an electrical angle of 270°. If it switches to interval 5 after detecting point B, continuous rotation can be achieved.

[0033] In interval 5 from an electrical angle of 270° to an electrical angle of 330°, W-U excitation is selected. Figure 5 Indicates the inductance change during W-U excitation and the change in the voltage of the non-energized phase coil. The waveform is obtained by shifting the waveform of Figure 4 by 60° and reversing the polarity. The non-energized phase is the V phase, and the excitation starting position C is at an electrical angle of 30°. When located in interval 5 and rotating in the CW direction, the voltage of the non-energized phase coil must pass through point B. Therefore, the rotor position at this moment is at an electrical angle of 330°. If it switches to interval 6 after detecting point B, continuous rotation can be achieved.

[0034] In section 6 where the electrical angle ranges from 330° to 30°, W-V excitation is selected. Figure 6 It shows the inductance change and the change in the voltage of the non-energized phase coil during W-V excitation. The waveform is obtained by shifting the waveform of Figure 5 by 60° and reversing the polarity. The non-energized phase is phase U, and the excitation start position C is at an electrical angle of 90°. When rotating in the CW direction within section 6, the voltage of the non-energized phase coil must pass through point B. Therefore, the rotor position at this moment is at an electrical angle of 30°. If it switches to section 1 after detecting point B, continuous rotation can be achieved.

[0035] In this way, the end points of the sections located at the peak or trough adjacent to the excitation start position can be detected by a preset threshold. Then, if the section number after the voltage of the non-energized phase coil exceeds the threshold is +1 during CW rotation and -1 during CCW rotation, continuous rotation can be achieved.

[0036] Similar to the above, the rotation direction in which the section number increases is set as CW, and the one in which it decreases is set as CCW. The start position of the section during CW is the adjacent -(negative) side section, and the start position of the section during CCW is the boundary point with the +(positive) side section. For example, in the case of energized section 1, the start position of the section during CW is the boundary point of 30° with energized section 6, and the start position of the section during CCW is the boundary point of 90° between energized section 1 and section 2.

[0037] Figure 1 In , the start position of the section during CW rotation when U-V is energized is represented by point A. During normal operation, since it rotates in the desired rotation direction, detection of the start position of the section is not required. However, when rotating at a low speed in the direction opposite to the desired rotation direction using an external force, start position detection is required for accurate excitation switching. Braking and deceleration are required during high-speed rotation, and start position detection is only considered during low-speed rotation. When rotating in the opposite direction, the induced voltage becomes a problem. In Figure 1 , the induced voltage of the non-energized phase W is at the zero-crossing point at the electrical angle of 60° in the middle of the section. When rotating in the forward rotation direction, the gradient caused by the inductance change is consistent with the gradient of the induced voltage, and the end point of the section can be reliably detected. However, when rotating in the reverse direction, the gradients of the two are opposite, and the waveform caused by the inductance change is cancelled out, making it difficult to detect the start position of the section. In addition, in the case of a motor with one cycle due to magnetic saturation, it is almost impossible to detect the start position of the section.

[0038] Therefore, if we focus on Figure 5For the excitation starting position C of W-U excitation, since point C passes through an electrical angle of 30°, the neutral point potential and the non-energized phase V phase voltage ΔVv are compared in magnitude. If ΔVv is less than the neutral point potential, it is possible to detect the situation of rotation towards section 6 beyond the electrical angle of 30°. Therefore, when performing U-V excitation in section 1, if it is instantaneously switched to W-U excitation and the non-energized phase V phase voltage is measured, it is possible to determine whether it is before or after the electrical angle of 30°. If it is periodically measured repeatedly before passing through the electrical angle of 30°, the starting point of the section, i.e., the excitation switching position, can be detected.

[0039] For the detection of the starting electrical angle of 90° in the CCW rotation direction, similar to the CW rotation direction, refer to Figure 6 Perform W-V excitation, and by measuring the non-energized phase U phase voltage, the position of the electrical angle of 90° can be detected. Before and after the excitation starting position, i.e., the electrical angle of 30° or the electrical angle of 90°, the voltage change gradient is sharp, making it easy to determine positive and negative, and the phase shift is also small. Therefore, the position can be detected reliably. Although the sensing consumes power, albeit rarely, it is desirable to extend the sensing period.

[0040] The same applies to the energized sections 2 - 6. If the energization mode that becomes the excitation point is selected to periodically detect the inductor zero crossing point, the starting point of the section can be detected. In the case of detecting the starting point, since it is rotating in the reverse direction, as long as the section number is reversed backward, continuous rotation can be achieved.

[0041] In the case where the rotor reverses at an extremely low speed in the direction opposite to the desired rotation direction due to external force, etc., in order to resume forward rotation, it is necessary to detect the starting point of the section and perform excitation switching. The starting point of the section can be detected by setting a starting threshold. For example, in Figure 1 when in section 1, setting the potential of point A as the starting threshold is sufficient. Figures 2 - 6 The same applies to sections 2 - 6 of

[0042] Just set the potential of point A in each section as the starting threshold. Therefore, a starting threshold Vth2 with a specified potential difference relative to the neutral point potential is preset. Each time the measurement is made, the non-energized phase coil voltage ΔV and the starting threshold Vth2 are compared in magnitude. If it exceeds the starting threshold, it is possible to detect exceeding the starting point of the section. Additionally, it is also possible to determine the gradient of the non-energized phase coil voltage ΔV. If the gradient is opposite to that in the forward rotation, it can be detected as a reverse rotation state. However, since the polarity of the induced voltage during reverse rotation is opposite to that during forward rotation, the voltage ΔV of the non-energized phase coil at the start of the interval is smaller than that during forward rotation and does not exceed the start threshold Vth2. In this case, the induced voltage can be estimated by calculation and the start threshold Vth2 can be corrected. Alternatively, the start detection can also be limited to a very low speed rotation where the error caused by the induced voltage can be ignored.

[0043] According to this method, without performing special excitation position detection and excitation, the start can be detected in the driving excitation state. Thus, the power-on efficiency is not reduced, and the electromagnetic noise caused by sensing the power-on is not generated. In addition, by detecting the start, braking can be performed from the reverse state and restored to forward rotation.

[0044] Suppose the following situation: the change in the voltage of the non-energized phase coil is caused by inductance when stationary, and an induced voltage is superimposed when the rotor rotates. In the case of PWM control, changing the duty ratio will cause a large change in the induced voltage, making it difficult to detect the excitation position within the measurement interval. Therefore, the following motor excitation position detection method is adopted.

[0045] When operating by changing the duty ratio of the specified drive voltage applied to the three-phase coil to accelerate the rotation of the rotor 2, the optimal duty ratio for sensing the voltage of the non-energized phase coil is selected within the on-duty ratio interval, and the on-duty ratio interval in one cycle of the power-on interval is divided into multiple on-duty ratio intervals including the optimal duty ratio, and the drive voltage is applied.

[0046] FIG. 10 and FIG. 11 are waveform diagrams of the drive voltage for each duty ratio in two cycles of the power-on interval in the 120° power-on timing diagram. As shown in FIG. 10, the MPU 51 selects, through the inverter circuit 52, the duty ratio (optimal duty ratio: for example, 20%) suitable for sensing the voltage of the non-energized phase coil that can be detected within the on-duty ratio interval in one cycle of the power-on interval. When applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, the on-duty ratio interval in one cycle is divided into multiple power-on intervals including the above optimal duty ratio, and the drive voltage is applied. In addition, when applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, the time of one cycle is extended or the drive voltage including the above optimal duty ratio is applied through multiple cycles.

[0047] A specific example will be described. In FIG. 10, Figure 10BThe specified drive voltage with a duty ratio of 20% shown is the optimal duty ratio suitable for performing sensing capable of detecting the voltage of the non-energized phase coil. For example, if one cycle of PWM control is 25 μsec, the conduction duty ratio interval with an optimal duty ratio of 20% is 5 μsec. The interval after this conduction duty ratio interval of 5 μsec is called the optimal conduction duty ratio interval. In this optimal conduction duty ratio interval, a specified drive voltage is also applied for other duty ratios, so that even for duty ratios other than the optimal duty ratio, it is easy to measure the changes in the positive and negative induced voltages generated in the non-energized phase coil.

[0048] First, an example of driving the motor with a duty ratio of 10% that does not exceed the optimal duty ratio of 20% is illustrated. As described above, when the optimal duty ratio is 20% and the optimal conduction duty ratio interval is 5 μsec, for a duty ratio of 10%, if one cycle is also 25 μsec, the conduction duty ratio interval is 2.5 μsec. Thus, the drive voltage cannot be applied within the optimal conduction duty ratio interval of 5 μsec. Therefore, as Figure 10A shown, for example, the time of one cycle is extended to twice, set to 50 μsec, and a duty ratio of 10% is achieved by applying a drive voltage including the optimal conduction duty ratio interval of 5 μsec when the optimal duty ratio is 20%. In Figure 10A an example of extending the time of one cycle is shown, but it can also be achieved by applying a drive voltage including the optimal conduction duty ratio interval of 5 μsec when the optimal duty ratio is 20% over multiple cycles. For example, if it is achieved in two cycles, the drive voltage with a duty ratio of 20% can be applied in the optimal conduction duty ratio interval of 5 μsec in the first cycle, and the drive voltage can be set to zero in the second cycle, and such control actions can be repeated.

[0049] Next, the case where the motor is driven with a duty cycle of 5 μsec, which is an optimal on-duty cycle interval when the optimal duty cycle of 20% is sensed, is exemplified. In this case, the on-duty cycle interval of one cycle is composed of a driving voltage of 5 μsec, which includes the optimal duty cycle of 20%, and a driving voltage of the on-duty cycle interval based on the duty cycle exceeding the optimal duty cycle of 20%, and the on-duty cycle interval is divided into a plurality of sections to apply the driving voltage. For example, when the duty cycle of the motor is increased from the optimal duty cycle of 20% to 30% for driving, in the power-on interval of one cycle, after the driving voltage is applied in the optimal duty cycle interval of 5 μsec, which includes the optimal duty cycle of 20%, the driving voltage is applied in the on-duty cycle interval of 2.5 μsec, which is the duty cycle of 10% exceeding the optimal duty cycle of 20%, after passing through the off-duty cycle interval. That is, the on-duty interval consisting of the optimum on-duty interval 5 μsec and the on-duty interval exceeding the optimum on-duty interval 5 μsec, i.e., 2.5 μsec, is 7.5 μsec. Since one cycle is 25 μsec, the total on-duty interval 7.5 μsec is 30% duty.

[0050] In addition, when the duty ratio is increased to 50% to drive and control the motor, after applying the driving voltage for 5 μsec in the optimal on-duty ratio interval including the optimal duty ratio of 20% in the conduction interval of one cycle, the driving voltage is applied for 7.5 μsec in the conduction duty ratio interval of 30% after the off-duty ratio interval. In addition, in the conduction interval of one cycle, the divided conduction duty ratio intervals may be two or more.

[0051] At the end of one cycle of PWM drive, the cut-off duty cycle interval must be set. For example, when driving control is performed with the above-mentioned duty cycle of 50%, after the optimal on-duty cycle interval of 5μsec, the cut-off duty cycle interval, the on-duty cycle interval of 7.5μsec, and the cut-off duty cycle interval, the next cycle will come. This is to clarify the range of one cycle and facilitate control.

[0052] In this way, when the duty cycle of the driving voltage for PWM energization of the three-phase coil of the sensorless driven motor changes, any duty cycle that can be controlled is selected, and at least the excitation position of the motor during low-speed driving can be detected from the non-energized phase coil voltage in the energization interval of the conduction duty cycle interval (for example, 5μsec) based on the optimal duty cycle (for example, 20%), thereby enabling the motor to operate smoothly and continuously in the low-speed area.

[0053] in addition, Figure 10B and Figure 11BIn the drive voltage waveform diagram, during the energization interval of one cycle, the application timing of the drive voltage in the remaining conduction duty ratio interval applied after the drive voltage based on the optimal conduction duty ratio (e.g., 20%) capable of detecting the non-energized phase coil voltage is different. Figure 10B This is an example of a case where the length of the cut-off duty ratio interval is adjusted after applying the drive voltage in the optimal conduction duty ratio interval (e.g., 5 μsec) based on the optimal conduction duty ratio (e.g., 20%), and then the drive voltage in the conduction duty ratio interval exceeding the above optimal conduction duty ratio interval is applied. Figure 11B This is an example of a case where the drive voltage in the optimal conduction duty ratio interval (e.g., 5 μsec) based on the optimal conduction duty ratio (e.g., 20%) is applied, and the cut-off duty ratio intervals before and after applying the drive voltage in the conduction duty ratio interval exceeding the above optimal conduction duty ratio interval are made equal.

[0054] In addition, the drive voltage applied to the three-phase coil preferably varies the duty ratio between 10% and 80% to detect the excitation position of the motor. This is because when the duty ratio is less than 10% or exceeds 80%, in the energization interval of one cycle, the cut-off duty ratio interval becomes short, it is difficult to capture the change in the induced voltage, and it is difficult to detect the excitation position of the motor. Thus, even if the duty ratio of the drive voltage applied to the coil of the motor changes significantly, it is possible to perform low-speed operation while detecting the excitation position of the motor, improving the controllability of the motor.

[0055] Hereinafter, an example of the excitation position detection operation of the MPU 51 at startup will be described. First, the detection operation during forward rotation will be described. A threshold value Vth is appropriately set in advance. The initial speed and the rotation direction are measured. Usually, it is detected as stationary. If it is rotating, it transfers to the rotation operation. If it is stationary, the initial position is detected by any method. As a result, for example, it is assumed to be in interval 1. The excitation mode U-V energization suitable for CW rotation in energization interval 1 is selected.

[0056] In Figure 8 one pulse of U-V energization is provided from the inverter circuit 52 through PWM control, and the three-phase coil voltage is A / D converted by the ADC 53 during the conduction cycle. The MPU 51 calculates the neutral point potential by (U-phase voltage + V-phase voltage) / 2. Then, it is determined whether the non-energized phase W-phase voltage - neutral point potential exceeds Vth. If it does not exceed, it returns to PWM control and repeats energization and measurement. If it exceeds, it is the end point of the interval, so the interval number is incremented. After that, the excitation mode is selected in the same way as in energization interval 1, and energization is repeated by PWM control for continuous rotation.

[0057] When increasing the duty ratio of the drive voltage from the optimal duty ratio (e.g., 20%) most suitable for detecting the non-energized phase W-phase coil voltage in order to accelerate the motor, the energization interval of one cycle of PWM energization is divided into multiple on-duty ratio intervals including the optimal duty ratio (e.g., 20%), and the drive voltage is applied. For example, when performing drive control with a duty ratio of 50%, in the energization interval of one cycle, after applying the drive voltage with a duty ratio of 20%, after passing through the off-duty ratio interval, the drive voltage with a duty ratio of 30% is applied again.

[0058] In addition, the above-described embodiment has described the case where the motor starts accelerating from low-speed rotation, but the same applies to the case where the motor decelerates to low-speed rotation.

Claims

1. A method for detecting the excitation position of a motor, The motors used include: A rotor with permanent magnet excitation; a stator with three-phase coils; an output unit, which bidirectionally energizes the three-phase coil via a half-bridge inverter circuit; a control unit, which performs PWM control on the coil output according to an instruction from a host controller, stores energization angle information and energization mode information in units of 60° energization intervals that can be continuously rotated, and switches the output unit based on this information to switch the energization state; and a measuring unit, which performs A / D conversion on the three-phase coil voltage and sends it to the control unit, The control unit periodically performs 120° energization including a cutoff cycle in a energization mode in which the position where self-excitation is stopped by fixed energization of two phases coincides with the starting position of the 60° energization interval via the output unit, and measures the energized phase voltage and the non-energized phase voltage in the conduction cycle of PWM energization by the measuring unit, thereby performing sensorless driving while detecting the excitation position of the motor. The method for detecting the excitation position of the motor is characterized in that: When the control unit operates by changing the duty cycle of the prescribed driving voltage applied to the three-phase coil through the output unit, the control unit selects the optimal duty cycle that is most suitable for sensing the voltage of the non-energized phase coil in the on-duty cycle interval, and applies the driving voltage in the on-duty cycle interval of the optimal duty cycle when driven at the optimal duty cycle in the energization interval of one cycle, and divides the on-duty cycle interval of one cycle into a plurality of on-duty cycle intervals including the optimal duty cycle and applies the driving voltage when applying a driving voltage based on a duty cycle exceeding the optimal duty cycle.

2. A method for detecting the excitation position of a motor, The motors used include: A rotor with permanent magnet excitation; a stator with three-phase coils; an output unit, which bidirectionally energizes the three-phase coil via a half-bridge inverter circuit; a control unit, which performs PWM control on the coil output according to an instruction from a host controller, stores energization angle information and energization mode information in units of 60° energization intervals that can be continuously rotated, and switches the output unit based on this information to switch the energization state; and a measuring unit, which performs A / D conversion on the three-phase coil voltage and sends it to the control unit, The control unit periodically performs 120° energization including a cutoff cycle in a energization mode in which the position where self-excitation is stopped by fixed energization of two phases coincides with the starting position of the 60° energization interval via the output unit, and measures the energized phase voltage and the non-energized phase voltage in the conduction cycle of PWM energization by the measuring unit, thereby performing sensorless driving while detecting the excitation position of the motor. The method for detecting the excitation position of the motor is characterized in that: When the control unit operates by changing the duty cycle of the prescribed driving voltage applied to the three-phase coil through the output unit, the control unit selects the optimal duty cycle that is most suitable for sensing the voltage of the non-energized phase coil in the conduction duty cycle interval, and applies the driving voltage in the conduction duty cycle interval of the optimal duty cycle when driven at the optimal duty cycle in the conduction interval of one cycle, and extends the time of one cycle or applies the driving voltage including the optimal duty cycle through multiple cycles when applying a driving voltage based on a duty cycle that does not exceed the optimal duty cycle.

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