Field position detection method for motor

Abstract

To provide a field position detection method for a motor which can be operated while surely detecting a field position of the motor during the operation even if a duty ratio of a drive voltage is changed when operating a three-phase brushless motor with 120° electrification, under PWM control and in a sensor-less drive manner.SOLUTION: In the case of operation while changing a duty ratio of a drive voltage to be applied to a three-phase coil via an inverter circuit 52, an MPU 51 selects a duty ratio optimal for sensing a non-electrified phase coil voltage at a predetermined drive voltage. In the case of driving with the optimal duty ratio in an electrification phase of one cycle, the drive voltage is applied in an on-duty phase of the optimal duty ratio. When applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, the on-duty phase of one cycle is divided into a plurality of on-duty phases including the optimal duty ratio and the drive voltage is applied.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a method for detecting the field position of an electric motor when the electric motor is driven sensorlessly and operates at a low speed.

Background Art

[0002] Conventionally, brushed DC motors have been used for small DC motors. However, due to problems such as brush noise, electrical noise, and durability, brushless DC motors have emerged. More recently, sensorless motors without position sensors have attracted attention from the viewpoints of miniaturization, weight reduction, robustness, and low cost. First, they were adopted in hard disk drives and the like in the information device field, but with the development of vector control technology, they have begun to be adopted in the home appliance and in-vehicle fields as well.

[0003] In sensorless drive, the rotor position is detected from the induced voltage. However, since no induced voltage is generated at rest, the rotor position cannot be determined and the motor cannot be started. To detect the rotor position at rest, there is a method of providing a coil current sensor and a current detection circuit, and flowing a sine-wave-shaped coil current through the coil by PWM drive using an inverter to estimate the position from the current response. Also, the rotor position at rest can be detected from the inductance deviation using the method represented above. Alternatively, the rotor can be rotated by forced commutation without position sensing to determine the position.

[0004] However, once the startup begins, energization for rotation is performed, making it difficult to detect the rotor position from the inductance deviation by applying a sensing pulse. For example, it is conceivable to superimpose a high-frequency current on the exciting current to detect the inductance deviation, but this is a large-scale operation both in terms of hardware and software. Also, the effects of magnetic saturation and induced voltage must be considered, and furthermore, elements such as the inherent errors of the motor and drive circuit, which are difficult to estimate, are included. Therefore, the ramp start method, in which the rotor is forcibly positioned with fixed excitation without performing position detection and then the rotational speed is gradually increased while synchronizing, is widely used. However, this method requires a long time for rotor positioning and also has the problem of reverse rotation. In addition, since synchronization is achieved by open-loop control, it takes time to accelerate and is prone to losing synchronization due to load fluctuations. To avoid this, it starts with a large current, resulting in a decrease in efficiency and an increase in the size of the DC power supply. It cannot be used in applications where it goes out of tune during load fluctuations, such as reciprocating motion mechanisms or applications that rotate by external force, or applications with viscous loads or fluctuating loads.

[0005] Therefore, as a field excitation position detection method that achieves cost reduction with simple hardware and software and can detect the rotor position in units of excitation sections in 120° energization without generating a sensing sound during startup, in the 120-degree energization drive of a three-phase brushless motor, when a voltage is applied to the motor, a method has been proposed to detect the rotor position by utilizing the fact that the induced voltage generated in the non-energized phase changes depending on the position of the permanent magnet field excitation (rotor). (Patent Document 1; Japanese Unexamined Patent Application Publication No. 2019-17235)

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when the motor is energized with 120° conduction, the induced voltage generated in the non-energized phase varies depending on the magnitude of the drive voltage applied to the motor. Particularly in the case of PWM drive, it will vary depending on the magnitude (on-time) of the duty ratio of the applied voltage. FIG. 12 is a graph showing the change in the induced voltage generated in the non-energized phase for each duty ratio of a certain motor according to the rotational position of the rotor. From this graph, it can be seen that the magnitude of the induced voltage generated varies significantly depending on the magnitude of the duty ratio. FIG. 13 is an example of a drive voltage waveform diagram when changing the duty ratio in PWM drive. In the case of the motor shown in FIG. 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, for other duty ratios, since the level of the induced voltage decreases, the voltage change is slow and measurement becomes difficult.

[0008] In Patent Document 1, in order to solve this phenomenon, a method of multiplying by a correction coefficient according to the duty ratio has been proposed. However, depending on the motor, even if a correction coefficient is multiplied by the induced voltage, position detection becomes difficult at duty ratios below a certain level or above a certain level. Therefore, only a limited range of duty ratios can be used. This results in a limitation of the control range of the motor torque, and thus the target rotational speed and torque of the motor cannot be achieved.

Means for Solving the Problems

[0009] The present invention has been made to solve these problems, and an object thereof is to provide a method for detecting the field position of an electric motor that can reliably detect the field position of the electric motor and perform low-speed operation even when changing the duty ratio of the drive voltage when a three-phase brushless motor is driven sensorlessly at low speed by PWM control with 120° conduction.

[0010] A rotor having a permanent magnet field, a stator having a three-phase coil, an output means for bidirectionally energizing the three-phase coil via a half-bridge type inverter circuit, PWM controlling the coil output according to a command from a host controller, storing energization angle information and energization pattern information in units of 60° energization intervals enabling continuous rotation, and switching the energization state by performing switching control on the output means based on these, a measuring means for A / D converting the three-phase coil voltage and sending it to the control means, using an electric motor equipped with these, the control means periodically performs 120° energization including an off cycle in an energization pattern where the position of self-excitation stop by two-phase fixed energization through the output means coincides with the start position of the 60° energization interval, and while detecting the field position of the motor by measuring the energized phase voltage and the non-energized phase voltage at the on cycle of PWM energization by the measuring means, it is a method for detecting the field position of a sensorless drive motor, when the control means operates by changing the duty ratio of a predetermined drive voltage applied to the three-phase coil through the output means, it selects the duty ratio optimal for sensing the non-energized phase coil voltage for the on duty interval, in one cycle of the energization interval, when driving at the optimal duty ratio, it applies the drive voltage during the on duty interval of the optimal duty ratio, when applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, it divides the on duty interval of one cycle into a plurality of on duty intervals including the optimal duty ratio and applies the drive voltage.

[0011] A rotor having a permanent magnet field, a stator having a three-phase coil, an output means for applying bidirectional power to the three-phase coil via a half-bridge type inverter circuit, and PWM controlling the coil output according to a command from a higher controller, storing energization angle information and energization pattern information in units of 60° energization sections enabling continuous rotation, and switching the energization state by controlling the switching of the output means based on these, and a measuring means for A / D converting the three-phase coil voltage and sending it to the control means. Using the motor provided with these, the control means performs 120° energization including an off cycle periodically in an energization pattern where the position of self-excitation stop by two-phase fixed energization through the output means coincides with the starting position of the 60° energization section, and while detecting the field position of the motor by measuring the energized phase voltage and the non-energized phase voltage at the on cycle of PWM energization by the measuring means, a method for detecting the field position of a sensorless drive motor, wherein when the control means operates by changing the duty ratio of a predetermined drive voltage applied to the three-phase coil through the output means, it selects the duty ratio optimal for sensing the non-energized phase coil voltage for the on duty section, and in one cycle of the energization section, when driving at the optimal duty ratio, applies the drive voltage in the on duty section of the optimal duty ratio, and when applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, extends the time of one cycle or applies a drive voltage including the optimal duty ratio in a plurality of cycles.

[0012] Thus, when changing the duty ratio of the drive voltage for PWM energizing the three-phase coil of a sensorless drive motor, in one cycle of the energization section, when driving at the optimal duty ratio, apply the drive voltage in the on duty section of the optimal duty ratio, and when applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, divide the on duty section of one cycle into a plurality of on duty sections including the optimal duty ratio and apply the drive voltage, and when applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, extend the time of one cycle or apply a drive voltage including the optimal duty ratio in a plurality of cycles. Accordingly, when changing the duty ratio of the drive voltage for PWM energization of the three-phase coils of a sensorless-driven motor, no matter which controllable duty ratio is selected, the detection of the field position of the motor during the low-speed driving period from the non-energized phase coil voltage is possible by applying the drive voltage based on at least the optimal duty ratio. Therefore, smooth continuous operation of the motor in the low-speed range is possible.

Advantages of the Invention

[0013] It is possible to provide a method for detecting the field position of a motor that can surely detect the field position of the motor and perform low-speed operation even when changing the duty ratio during sensorless low-speed operation of the motor by PWM control with 120-degree energization.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

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Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the field magnetic position detection method for an electric motor according to the present invention will be described with reference to the accompanying drawings. As an example of the present invention, a sensorless motor having a permanent magnet field on the rotor, with windings arranged on the stator at a 120° phase difference and star-connected, and the phase terminals connected to the motor output means will be used for explanation.

[0016] Hereinafter, as an example, a method for detecting the permanent magnet field position of a sensorless motor that sensorlessly drives a three-phase DC brushless motor will be described together with the configuration of a sensorless motor drive device. FIG. 9 shows an embodiment of a three-phase brushless DC motor according to the present invention. As an example, a three-phase brushless DC motor provided with a 2-pole permanent magnet rotor and a stator 4 provided with 3 slots is illustrated. The motor may be either an inner rotor type or an outer rotor type. Also, as the permanent magnet type field, either an interior permanent magnet type (IPM type) motor or a surface permanent magnet type (SPM type) motor may be used.

[0017] In FIG. 9, a rotor 2 is integrally provided on a rotor shaft 1, and a 2-pole permanent magnet 3 is provided as the field. On the stator 4, pole teeth U, V, and W are arranged opposite to the permanent magnet 3 at a 120° phase difference. Windings u, v, and w are provided on each of the pole teeth U, V, and W of the stator 4, and the phases are star-connected with a common C and wired to a motor drive device described later to form a three-phase brushless DC motor. Note that the common line is omitted because it is unnecessary.

[0018] Next, an example of a drive circuit for a three-phase DC brushless motor is shown in FIG. 8. As a drive method at startup, 120° conduction bipolar rectangular wave excitation is assumed. MOTOR is a three-phase sensorless motor. MPU51 is a microcontroller (control means). MPU51 stores field position information that designates six conduction patterns for the three-phase coils (U, V, W) and the excitation switching intervals (intervals 1 to 6) of 120° conduction corresponding to each conduction pattern, and switches the output means by switching control in response to a rotation command RUN from the upper controller 50 to arbitrarily switch the excitation state.

[0019] The inverter circuit 52 (INV: output means) supplies power to 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 connected in anti-parallel to the switching elements, and three half-bridge type switching circuits that can be arbitrarily connected to the positive power supply line and the ground power supply line are provided. The A / D conversion circuit 53 (ADC: measurement means) has the coil output terminals U, V, W connected, simultaneously samples the coil voltages of each of the three phases according to a conversion start signal from MPU51, sequentially performs analog-to-digital conversion, and sends the conversion result to MPU51. Usually, ADC53 is built into MPU51. When using the built-in ADC53, since the maximum input voltage is low, it is desirable to provide a voltage dividing circuit using resistors. Thus, according to this case, the drive circuit can be configured very simply.

[0020] The change in inductance (spatial harmonic) due to the rotor angle θ is approximated as ΔL = -cos(2θ) and is known to have a two-periodicity per electrical angle. On the other hand, when two-phase conduction is performed on the three-phase coils with rectangular wave PWM conduction, it is known that voltage fluctuations with a two-periodicity centered on the neutral point potential are observed in the non-conducting phase according to θ.

[0021] Fig. 1 shows the theoretical value waveforms of the voltage change waveform ΔVw of the non-energized phase, the inductance changes (ΔLu, ΔLv) of the U and V phases, and the synthetic inductance change ΔLu-v of the two phases when rotating by one electrical angle while exciting U-V with PWM energization. Note that the voltage change waveform is obtained by inverting the polarity of the synthetic inductance change waveform and is assumed to oscillate between positive and negative with the neutral point voltage, which is half of the coil applied voltage, as the center.

[0022] Fig. 7A shows the measured waveform of the non-energized phase coil voltage using an inner rotor type motor. The theoretical value of the voltage waveform of the non-energized phase is assumed to be of reverse polarity reflecting the inductance, and the waveforms are approximately similar, indicating that the assumption is correct. Also, in the case of rectangular wave energization, ringing occurs in the induced voltage. However, as a result of measurement, the ringing time is very short and converges within the range of measurement error in various motors, from several μs to several tens of μs, and the induced voltage can be accurately detected even with the rectangular wave PWM energization pulse for motor drive.

[0023] When a large current flows through the three-phase coil, magnetic saturation occurs and the inductance no longer changes, which is particularly significant in a small outer rotor type motor. When magnetic saturation occurs, the two-periodic inductance change waveform has peaks and bottoms adjacent to the setup position where self-excitation stops due to two-phase fixed energization remaining, while the other peaks and bottoms disappear and become one-periodic. Fig. 7B shows an example of the inductance waveform that becomes one-periodic due to magnetic saturation. The motor used for measurement is a small outer rotor type motor, different from the motor used in Fig. 7A. The setup position during U-V energization is 150°, and in the ΔVw waveform, only the peaks and bottoms adjacent to the setup position are clearly observed.

[0024] The setup position where self-excitation stops due to two-phase fixed energization is both the inductance zero crossing point and the induced voltage zero crossing point, and the setup point and the adjacent peaks and bottoms are stable against magnetic saturation. As can be seen from FIGS. 7A and 7B, the voltage fluctuation of the non-energized phase reflects the rotor angle θ and monotonicity is ensured within the interval. Therefore, even when the induced voltage at rest is not generated, the rotor position can be estimated by flowing the exciting current. The voltage fluctuation amplitude is more than 10% of the coil allowable voltage and reaches the order of several volts. Considering that the conventional method detects the induced voltage on the order of millivolts at startup, this is overwhelmingly advantageous.

[0025] As described above, by detecting the inductance change of the non-energized phase coil using the rectangular wave PWM control for motor drive and using only the inductance change near the setup position, stable position detection is enabled from the stationary state to the low-speed rotation range. This simplifies the sensing procedure, improves efficiency without requiring power for sensing, and eliminates the sensing noise for quiet operation.

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

[0027] ((Margin below))

Table 1

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

[0029] In Fig. 1, the starting point of the energization section during CW rotation with U-V excitation is shown as point A, and the ending point of the energization section is shown as point B. The setup point is point C, and the bottom part where point B is located has a stable phase and can be used for position detection. Therefore, positive and negative threshold values Vth with a predetermined potential difference with respect to the neutral point potential are set in advance, and for each measurement, the non-energized phase coil voltage ΔVw and the threshold value Vth are compared in magnitude. If the threshold value is exceeded, it can be detected that the end point of the section has been exceeded. During CCW rotation, since V-U energization is performed, refer to Fig. 4. The rotor rotates from the electrical angle 90° side toward the electrical angle 30° side. Therefore, the end point of the section is the electrical angle 30°. Since the setup point is the electrical angle 330°, the bottom part on the electrical angle 30° side has a stable phase and can be used for position detection. Therefore, similar to the CW case, the end point of the section can be detected by comparing the voltage of the non-energized phase W and the threshold value Vth in magnitude.

[0030] In section 2 from the electrical angle 90° to the electrical angle 150°, U-W excitation is selected. Fig. 2 shows the inductance change and the change in the non-energized phase coil voltage during U-W excitation. The waveform is obtained by shifting the waveform in Fig. 1 by 60° and inverting the polarity. The non-energized phase is the V phase, and the setup position C point is the electrical angle 210°. When located in section 2 and rotating in the CW direction, since the non-energized phase coil voltage always passes through point B, at that time, the rotor position is the electrical angle 150°. If point B is detected and switched to section 3, continuous rotation can be achieved.

[0031] In section 3 from the electrical angle 150° to the electrical angle 210°, V-W excitation is selected. Fig. 3 shows the inductance change and the change in the non-energized phase coil voltage during V-W excitation. The waveform is obtained by shifting the waveform in Fig. 2 by 60° and inverting the polarity. The non-energized phase is the U phase, and the setup position C point is the electrical angle 270°. When located in section 3 and rotating in the CW direction, since the non-energized phase coil voltage always passes through point B, at that time, the rotor position is the electrical angle 210°. If point B is detected and switched to section 4, continuous rotation can be achieved.

[0032] In section 4 from electrical angle 210° to electrical angle 270°, V-U excitation is selected. Fig. 4 shows the inductance change and the non-energized phase coil voltage change during V-U excitation. The waveform is obtained by shifting the waveform in Fig. 3 by 60° and reversing the polarity. The non-energized phase is the W phase, and the setup position C point is at electrical angle 330°. When located in section 4 and rotating in the CW direction, since the non-energized phase coil voltage always passes through point B, the rotor position at that time is electrical angle 270°. If point B is detected and switched to section 5, continuous rotation can be achieved.

[0033] In section 5 from electrical angle 270° to electrical angle 330°, W-U excitation is selected. Fig. 5 shows the inductance change and the non-energized phase coil voltage change during W-U excitation. The waveform is obtained by shifting the waveform in Fig. 4 by 60° and reversing the polarity. The non-energized phase is the V phase, and the setup position C point is at electrical angle 30°. When located in section 5 and rotating in the CW direction, since the non-energized phase coil voltage always passes through point B, the rotor position at that time is electrical angle 330°. If point B is detected and switched to section 6, continuous rotation can be achieved.

[0034] In section 6 from electrical angle 330° to electrical angle 30°, W-V excitation is selected. Fig. 6 shows the inductance change and the non-energized phase coil voltage change during W-V excitation. The waveform is obtained by shifting the waveform in Fig. 5 by 60° and reversing the polarity. The non-energized phase is the U phase, and the setup position C point is at electrical angle 90°. When located in section 6 and rotating in the CW direction, since the non-energized phase coil voltage always passes through point B, the rotor position at that time is electrical angle 30°. If point B is detected and switched to section 1, continuous rotation can be achieved.

[0035] The end points of the intervals located at the peak or bottom adjacent to the setup position can be detected using a preset threshold value in this way. When the non-energized phase coil voltage exceeds the threshold value, the interval number can be incremented by +1 for CW rotation and decremented by -1 for CCW rotation, enabling continuous rotation.

[0036] Similar to the above, the rotation direction in which the interval number increases is defined as CW, and the rotation direction in which it decreases is defined as CCW. The starting position of the interval is the boundary point with the adjacent -(minus) side interval for CW rotation and the +(plus) side interval for CCW rotation. For example, in the case of energized interval 1, it is the boundary point of 30° with energized interval 6 for CW rotation and the boundary point of 90° with energized interval 2 for CCW rotation.

[0037] In FIG. 1, the starting point of the interval during CW rotation with U-V energization is illustrated as point A. During normal operation, detection of the starting point of the interval is not necessary for rotation in the desired direction. However, when rotated at a low speed in the opposite direction to the desired rotation direction by an external force, starting point detection is required for correct excitation switching. During high-speed rotation, it is necessary to apply a brake to decelerate, and the detection of the starting position is considered to be only during low-speed rotation. When rotating in the opposite direction, the induced voltage becomes a problem. In FIG. 1, the induced voltage of the non-energized phase W has a zero-crossing point at the electrical angle 60° position in the center of the interval. When rotating in the forward rotation direction, the gradient due to the inductance change and the gradient of the induced voltage match, and the end point of the interval can be reliably detected. However, when rotating in the reverse direction, the gradients of both become opposite, and the waveform due to the inductance change is canceled out, making it difficult to detect the starting point of the interval. Furthermore, in the case of a motor with a 1-periodicity due to magnetic saturation, it is almost impossible to detect the starting point of the interval.

[0038] Therefore, focusing on point C of the W-U excitation setup position in FIG. 5, since point C passes through an electrical angle of 30°, by comparing the neutral point potential with the non-energized phase V phase voltage ΔVv, when ΔVv becomes smaller than the neutral point potential, it can be detected that the rotation has passed the electrical angle of 30° and moved to the interval 6 side. Therefore, when exciting in the U-V direction in interval 1, if the excitation is switched to the W-U direction for an instant and the non-energized phase V-phase voltage is measured, it can be determined whether it is before or after the electrical angle of 30°. By repeating the measurement periodically until the electrical angle of 30° is passed, the interval start point, i.e., the excitation switching position, can be detected.

[0039] Regarding the detection of the electrical angle of 90° at the start point during counterclockwise rotation, similar to the case of clockwise rotation, by referring to FIG. 6, performing W-V excitation and measuring the non-energized phase U-phase voltage, the position of the electrical angle of 90° can be detected. Around the electrical angle of 30° or the electrical angle of 90°, which is the setup position, the voltage change gradient is steep, the positive and negative determination is easy, and the phase shift is small, so the position can be detected reliably. Although a small amount of power is consumed for sensing, it is desirable to increase the sensing period.

[0040] Regarding the energization intervals 2 to 6 as well, by selecting the energization pattern that becomes the setup point in the same way and detecting the inductance zero-crossing point periodically, the interval start point can be detected. If the start point is detected, since it means that the rotation is in the reverse direction, the interval number can be reversed to enable continuous rotation.

[0041] When the rotor reverses at an extremely low speed in the opposite direction to the desired rotation direction due to an external force, etc., it is necessary to detect the interval start point and switch the excitation to return to the forward rotation. The interval start point can be detected by setting a start point threshold. For example, in FIG. 1, when located in interval 1, the potential at point A can be set as the start point threshold. Similarly, for intervals 2 to 6 in FIGS. 2 to 6, the potential at point A in each interval can be set as the start point threshold. Therefore, a start point threshold Vth2 having a predetermined potential difference with respect to the neutral point potential is set in advance, and for each measurement, the non-energized phase coil voltage ΔV and the start point threshold Vth2 are compared in magnitude. When the start point threshold is exceeded, it can be detected that the interval start point has been exceeded. Also, the gradient of the non-energized phase coil voltage ΔV can be determined, and if the gradient is opposite to that during forward rotation, it can be detected that it is in the reverse rotation state.

[0042] Therefore, if the rotor detects the starting point in the reverse rotation state, the excitation section can be returned by one section and excitation can be performed to generate a forward torque, that is, to apply a brake to suppress reverse rotation and return to forward rotation. However, since the polarity of the induced voltage during reverse rotation is opposite to that during forward rotation, the non-energized phase coil voltage ΔV at the section starting point becomes smaller than that during forward rotation and does not exceed the starting point threshold Vth2. In that case, it is also possible to estimate the induced voltage by calculation and correct the starting point threshold Vth2. Alternatively, the starting point detection may be limited only to the extremely low speed rotation at which the error due to the induced voltage can be ignored.

[0043] According to this method, the starting point can be detected in the drive excitation state without performing special field position detection excitation. Therefore, the energization efficiency is not reduced and no electromagnetic noise is generated due to sensing energization. Further, by detecting the starting point, a brake can be applied from the reverse rotation state and the motor can return to forward rotation.

[0044] The change in the non-energized phase coil voltage is due to inductance when stationary, but when the rotor rotates, an induced voltage is superimposed. In the case of PWM control, the induced voltage changes greatly by changing the duty ratio, and it is assumed that it is difficult to detect the field position within the measurement section. Therefore, the following field position detection method for the motor is adopted.

[0045] When accelerating and operating the rotation of the rotor 2 by changing the duty ratio of the predetermined drive voltage applied to the three-phase coil, the duty ratio optimal for sensing the non-energized phase coil voltage is selected for the on-duty section, and the drive voltage is applied by dividing the on-duty section in one cycle of the energization section into a plurality of on-duty sections including the optimal duty ratio.

[0046] Figures 10 and 11 are drive voltage waveform diagrams for each duty ratio in the energization intervals for two cycles in the timing chart of 120° energization. As shown in FIG. 10, the MPU 51 selects, through the inverter circuit 52, a duty ratio (optimal duty ratio; for example, 20%) suitable for sensing that can detect the non-energized phase coil voltage in the energization interval of one cycle. When applying a drive voltage based on a duty ratio exceeding this optimal duty ratio, the drive voltage is applied by dividing the on-duty interval of one cycle into a plurality of energization intervals including the optimal duty ratio. Also, when applying a drive voltage based on a duty ratio not exceeding the optimal duty ratio, the time of one cycle is extended or a drive voltage including the optimal duty ratio is applied over a plurality of cycles.

[0047] Regarding a specific example, in FIG. 10, the predetermined drive voltage with a duty ratio of 20% shown in FIG. 10B is set as the optimal duty ratio suitable for sensing that can detect the non-energized phase coil voltage. For example, if one cycle of PWM control is 25 μsec, the on-duty interval with an optimal duty ratio of 20% is 5 μsec. This on-duty interval of 5 μsec will hereinafter be referred to as the optimal on-duty interval. By applying a predetermined drive voltage at other duty ratios to this optimal on-duty interval, it becomes easier to measure the changes in the positive and negative induced voltages generated in the non-energized phase coil even at duty ratios other than the optimal duty ratio.

[0048] First, an example of driving the motor at a duty ratio of 10% that does not exceed the optimal duty ratio of 20% will be illustrated. As described above, when the optimal duty ratio is 20% and the optimal on-duty interval is 5 μsec, if the duty ratio is 10% and one cycle is also 25 μsec, the on-duty interval will be 2.5 μsec. Then, it is not possible to apply the driving voltage for the optimal on-duty interval of 5 μsec. Therefore, as shown in FIG. 10A, for example, the time of one cycle is extended from 25 μsec to twice, i.e., 50 μsec, and a driving voltage including the optimal on-duty interval of 5 μsec at the optimal duty ratio of 20% is applied to achieve a duty ratio of 10%. In FIG. 10A, an example of extending the time of one cycle is shown, but it may also be achieved by applying a driving voltage including the optimal on-duty interval of 5 μsec at the optimal duty ratio of 20% over a plurality of cycles. For example, if it is to be achieved in two cycles, a control operation of applying the driving voltage at a duty ratio of 20% for the optimal on-duty interval of 5 μsec in the first cycle and then setting the driving voltage to zero in the second cycle may be repeated.

[0049] Next, an example is given of the case where the motor is driven at a duty ratio exceeding the optimum on-duty interval of 5 μsec at an optimum duty ratio of 20% that is optimal for sensing. In this case, the on-duty interval of one cycle is divided into a plurality of on-duty intervals, and a drive voltage is applied by using a drive voltage for an on-duty interval including the on-duty interval of 5 μsec at the optimum duty ratio of 20% and a drive voltage for an on-duty interval based on the duty ratio exceeding the optimum duty ratio of 20%. For example, when the duty ratio of the motor is increased from the optimum duty ratio of 20% to 30% for driving, after applying a drive voltage for the optimum on-duty interval of 5 μsec including the optimum duty ratio of 20% in the energization interval of one cycle, a drive voltage is applied for an on-duty interval of 2.5 μsec, which is the on-duty ratio of 10% exceeding the optimum duty ratio of 20%, via an off-duty interval. That is, the total on-duty interval of the optimum on-duty interval of 5 μsec and the on-duty interval of 2.5 μsec, which is the on-duty interval exceeding the optimum on-duty interval of 5 μsec, is 7.5 μsec. Since one cycle is 25 μsec, the total on-duty interval of 7.5 μsec results in a duty ratio of 30%.

[0050] Also, when the motor is driven with the drive control at a duty ratio of 50%, after applying a drive voltage for the optimum on-duty interval of 5 μsec including the optimum duty ratio of 20% in the energization interval of one cycle, a drive voltage is applied for an on-duty interval of 7.5 μsec with a duty ratio of 30% via an off-duty interval. Note that the number of on-duty intervals to be divided may be two or more in the energization interval of one cycle.

[0051] It is assumed that an off-duty interval is always provided at the end of one cycle of PWM drive. For example, when driving and controlling at the above duty ratio of 50%, the next cycle is reached after passing through the optimum on-duty interval of 5 μsec, the off-duty interval, the on-duty interval of 7.5 μsec, and the off-duty interval. This is for clarifying the range of one cycle and facilitating control.

[0052] Thus, when changing the duty ratio of the drive voltage for PWM energization of the three-phase coils of the sensorless-driven motor, no matter which controllable duty ratio is selected, detection of the field position of the motor in the low-speed driving period can be achieved from the non-energized phase coil voltage in the energization period based on at least the on-duty period (e.g., 5 μsec) of the optimal duty ratio (e.g., 20%). Therefore, smooth continuous operation of the motor in the low-speed range becomes possible.

[0053] Also, the drive voltage waveforms in FIGS. 10B and 11B have different application timings of the drive voltage in the remaining on-duty periods applied following the drive voltage based on the optimal on-duty ratio (e.g., 20%) at which the non-energized phase coil voltage can be detected in one cycle of the energization period. FIG. 10B is an example of the case where, from the application of the drive voltage based on the optimal on-duty period (e.g., 5 μsec) of the optimal on-duty ratio (e.g., 20%), the off-duty period is made longer, and the drive voltage in the on-duty period exceeding the optimal on-duty period is applied. FIG. 11B is an example of the case where the drive voltage based on the optimal on-duty period (e.g., 5 μsec) of the optimal on-duty ratio (e.g., 20%) is applied, and the off-duty periods before and after applying the drive voltage in the on-duty period exceeding the optimal on-duty period are made equal.

[0054] Also, it is preferable that the drive voltage applied to the three-phase coils changes the duty ratio between 10% and 80% to detect the field position of the motor. This is because when the duty ratio is less than 10% or exceeds 80%, in one cycle of the energization period, the off-duty period becomes short, the fluctuation of the induced voltage becomes difficult to capture, and it becomes difficult to detect the field position of the motor. Thereby, even when widely changing the duty ratio of the drive voltage applied to the motor coil, it is possible to perform low-speed operation while detecting the field position of the motor, and the controllability of the motor is improved.

[0055] The following describes an example of the field magnetic position detection operation at startup by the MPU51. First, the detection operation when rotating forward is described. Appropriately set the threshold value Vth in advance. Measure the initial speed and rotation direction. Usually, static is detected. If it is rotating, shift to the rotation operation. If it is static, detect the initial position by any method. As a result, for example, assume it is located in section 1. Select the excitation pattern U-V energization that matches the CW rotation in the energization section 1.

[0056] In FIG. 8, from the inverter circuit 52, only U-V energization is performed with PWM control for 1 pulse, and during the on-cycle, the three-phase coil voltage is A / D converted by the ADC53. The MPU51 obtains the neutral point potential by (U-phase voltage + V-phase voltage) / 2. Next, it is determined whether the non-energized phase W-phase voltage - neutral point potential exceeds Vth. If it does not exceed, return to PWM control and repeat the energization and measurement. If it exceeds, since it is the end point of the section, step the section number. Thereafter, select the excitation pattern in the same manner as in the energization section 1 and repeat the energization with PWM control for continuous rotation.

[0057] When increasing the duty ratio of the drive voltage to accelerate the motor to a value higher than the optimal duty ratio (for example, 20%) for detecting the non-energized phase W-phase coil voltage, divide the energization section of one cycle of PWM energization into a plurality of on-duty sections including the optimal duty ratio (for example, 20%) and apply the drive voltage. For example, when performing drive control with a duty ratio of 50%, after applying a drive voltage with a duty ratio of 20% in the energization section of one cycle, apply a drive voltage with a duty ratio of 30% via the off-duty section.

[0058] In addition, although the above embodiment has described the case of accelerating the motor from low-speed rotation, the same applies to the case of decelerating the motor to low-speed rotation.

Description of Reference Numerals

[0059] 1 Rotor shaft 2 Rotor 3 Permanent magnet 4 Stator 50 Upper controller 51 MPU 52 Inverter circuit (INV) 53 A / D converter (ADC)

Claims

1. Using a motor comprising: a rotor having a permanent magnet field; a stator having a three-phase coil; output means for bidirectionally energizing the three-phase coil via a half-bridge type inverter circuit; control means for PWM controlling the coil output according to a command from a host controller, storing energization angle information and energization pattern information in units of 60° energization intervals enabling continuous rotation, and switching the energization state by performing switching control on the output means based on these; and measurement means for A / D converting the three-phase coil voltage and sending it to the control means, The control means performs 120° energization including an off-cycle in a energization pattern where the position for self-excitation stop by two-phase fixed energization through the output means coincides with the start position of a 60° energization interval, and detects the field position of the motor by measuring the energized phase voltage and the non-energized phase voltage at the on-cycle of PWM energization by the measurement means while performing sensorless drive. When the control means operates by changing the duty ratio of a predetermined drive voltage applied to the three-phase coil through the output means, it selects a duty ratio optimal for sensing the non-energized phase coil voltage for the on-duty interval, and in the energization interval of one cycle, when driving at the optimal duty ratio, applies the drive voltage in the on-duty interval of the optimal duty ratio, and when applying a drive voltage based on a duty ratio exceeding the optimal duty ratio, divides the on-duty interval of one cycle into a plurality of on-duty intervals including the optimal duty ratio and applies the drive voltage. A method for detecting the field position of an electric motor, characterized by this.

2. Using a motor comprising: a rotor having a permanent magnet field; a stator having a three-phase coil; output means for bidirectionally energizing the three-phase coil via a half-bridge type inverter circuit; control means for PWM controlling the coil output according to a command from a host controller, storing energization angle information and energization pattern information in units of 60° energization intervals enabling continuous rotation, and switching the energization state by performing switching control on the output means based on these; and measurement means for A / D converting the three-phase coil voltage and sending it to the control means, The control means performs 120° conduction including an off-cycle periodically in a conduction pattern in which the position of self-excited stop by two-phase fixed conduction through the output means coincides with the starting point position of a 60° conduction section, and detects the field position of the motor while sensorless driving by measuring the conduction phase voltage and the non-conduction phase voltage at the on-cycle of PWM conduction by the measuring means. In the method for detecting the field position of a motor, when the control means operates by changing the duty ratio of a predetermined driving voltage applied to the three-phase coil through the output means, the control means selects the duty ratio optimal for sensing the non-conduction phase coil voltage for the on-duty section, and in the conduction section of one cycle, when driving at the optimal duty ratio, applies the driving voltage in the on-duty section of the optimal duty ratio, and when applying a driving voltage based on a duty ratio not exceeding the optimal duty ratio, extends the time of one cycle or applies the driving voltage including the optimal duty ratio in a plurality of cycles.

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