JP2020198754A - Control method and controller for brushless dc motor - Google Patents

Abstract

To provide a sensorless brushless DC motor, which has no sensor for detecting a position of a rotor, exactly detecting a zero cross point even during low-speed rotation and completely shifting forced commutation to control commutation without causing power swing or the like.SOLUTION: The control method, starting a motor which is a brushless DC motor, obtains an average value of measurements of terminal voltages of coils of each phase of the motor when a speed of a rotor is at most a threshold value to use the average value as a midpoint voltage for detecting a zero cross point at a counter electromotive voltage of each phase for detecting the position of the rotor.SELECTED DRAWING: Figure 2

Description

The present invention relates to the control of a brushless DC (direct current) motor, and more particularly to a control method and a control device for controlling the start of a sensorless brushless DC motor not provided with a sensor for detecting the position of a rotor.

The brushless DC motor is driven by passing an electric current through the armature winding of the motor by an inverter according to the position of the rotor. For example, in a three-phase brushless DC motor including U-phase, V-phase, and W-phase armature windings, a current flows from the W-phase to the U-phase at a certain timing, and a current flows from the V-phase to the U-phase at the next timing. Further, at the next timing, a rotating magnetic field is formed in the motor by passing a current from the V phase to the W phase. This rotating magnetic field causes the rotor to rotate. Changing the set of windings through which current flows is called commutation. When driving a brushless DC motor, it is necessary to perform commutation based on the position of the rotor.

As a method of determining the position of the rotor of the brushless DC motor, there is also a method of using a sensor such as a Hall element, but from the counter electromotive force (speed electromotive force) generated in the winding of each phase as the rotor rotates. There is also a method of estimating the position of the rotor. When driving a sensorless brushless DC motor that does not have a sensor that detects the position of the rotor, a sensorless drive that estimates the position of the rotor from the counter electromotive voltage generated in the winding of each phase and commutates is adopted. Has been done. When the motor is driven by using the sensorless drive, the motor is controlled based on the estimation of the position of the rotor, so that the closed loop control is performed. Since the counter electromotive voltage of each phase is an AC voltage having a frequency proportional to the rotation speed of the rotor, when the counter electromotive voltage crosses the mid point voltage by comparing the mid point voltage and the counter electromotive voltage. Can be detected as a zero cross point. The position of the rotor can be estimated by detecting the zero cross point for each phase, and the rotation speed of the motor can be calculated from the time interval between the zero cross points. The midpoint voltage is the voltage that becomes the midpoint in the back electromotive voltage waveform. Patent Document 1 discloses that, as a basic principle, the midpoint voltage is half of the power supply voltage V _dc supplied to the inverter driving the brushless DC motor, that is, V _dc / 2. Further, Patent Document 1 states that the midpoint voltage does not strictly become V _dc / 2 due to various conditions such as variations in resistance and inductance in the winding, variations in magnetization in the rotor, and the like. It also discloses that the voltage is adjusted.

Since the magnitude of the counter electromotive voltage generated in the armature winding is proportional to the rotation speed of the motor, sufficient voltage is not generated when the rotation speed is low, such as immediately after the motor starts, and the position of the rotor can be estimated. Can not. Therefore, in a sensorless brushless DC motor, at the time of its start, the windings of each phase of the motor are driven at a low commutation frequency that can be started stably to generate a rotating magnetic field, and the rotor is forced by this rotating magnetic field. It is common to perform forced commutation to rotate. When the rotor starts to rotate due to forced commutation and a sufficient counter electromotive voltage is generated in the winding, the control of the motor is switched to sensorless drive. Furthermore, the counter electromotive voltage is not detected during forced commutation, and the commutation frequency at the forced current is gradually increased to forcibly switch to sensorless drive when the compulsory commutation frequency is reached. There is. When the sensorless brushless DC motor is started by the forced current, the motor is controlled by the open loop control because the control is not performed based on the position of the rotor.

JP-A-2007-28886

As described above, the countercurrent voltage induced in the winding is proportional to the rotation speed of the rotor, that is, the rotation speed of the motor, so it is a very small value at low speed rotation immediately after the start of the motor, and it causes a large noise and Contains ripple. Therefore, there arises a problem that the zero cross point may not be detected accurately by comparing the midpoint voltage calculated as 1/2 of the power supply voltage V _dc and the counter electromotive voltage immediately after startup. With the aim of improving the accuracy on the midpoint voltage side, one end of three resistors with the same resistance value is connected to the terminals of the windings of each phase of the motor, and the other ends of these resistors are commonly connected. There is a midpoint that is used by measuring the voltage at this midpoint. In this case, an extra analog-to-digital (A / D) conversion must be performed to measure the voltage at the midpoint of the resistor, which increases the processing load on the controller for controlling the motor. .. In particular, when the control device is configured by using a microprocessor (MPU; Micro Processor Unit), the processing load of the microprocessor increases due to the extra A / D conversion, and the motor rotates at high speed by that amount. You will not be able to let it. Further, if the resistance value of the resistor for generating the midpoint voltage varies, the midpoint voltage cannot be obtained accurately, and an error occurs in the measurement of the zero cross point especially at low speed rotation. If the zero cross point cannot be detected accurately in the sensorless brushless DC motor, the motor cannot be controlled accurately, especially at low speed rotation. For example, the timing of commutation with respect to the rotor position shifts when shifting from forced commutation to sensorless drive. Therefore, a phenomenon called step-out may occur in which the rotation speed of the motor does not increase.

An object of the present invention is that a sensorless brushless DC motor can accurately detect a zero crossing point even at low speed rotation, and can reliably shift from forced commutation to controlled commutation without causing step-out or the like. An object of the present invention is to provide a control method and a control device for a DC motor.

The control method of the brushless DC motor of the present invention is a control method for starting a motor which is a brushless DC motor not provided with a sensor for detecting the position of the rotor, and for detecting the position of the rotor, each phase of the motor As the midpoint voltage for detecting the zero crossing point in the countercurrent voltage of that phase, when the rotor speed is below the threshold value, find the average of the measured values of the terminal voltage of the winding of each phase. use.

In the control method of the present invention, when the rotation speed of the motor is relatively slow when the rotor speed is equal to or less than the threshold value, for example, immediately after the motor is started, the average value of the measured values of the terminal voltages of the windings of each phase ( For a three-phase brushless DC motor, use {V _u + V _v + V _w } / 3), which is the average of the terminal voltages V _u , V _v , and V _w of the U phase, V phase, and W phase, as the midpoint voltage. As a result, the effects of noise and ripple are reduced by averaging, so the zero cross point can be detected more appropriately, and the occurrence of step-out during the transition from forced commutation to sensorless drive can be prevented. Will be able to.

In the control method of the present invention, it is preferable to detect the time point at which the sign changes as a result of subtracting the midpoint voltage from the counter electromotive voltage of each phase as the zero cross point in that phase. According to this, since the zero cross point is detected by the change of the sign, the detection of the zero cross point becomes easy.

In the control method of the present invention, when the speed of the rotor of the motor exceeds the threshold value, it is preferable to use half of the power supply voltage used to drive the motor as the midpoint voltage. By using the midpoint voltage for half of the power supply voltage, the amount of processing for calculating the midpoint voltage is reduced, and the motor can be rotated at a higher speed.

In the control method of the present invention, when the speed is equal to or less than the threshold value, the terminal voltage of the winding of each phase is processed by the low-pass filter, and the counter electromotive voltage and the medium based on the terminal voltage after being processed by the low-pass filter are used. A point voltage may be used. By processing the terminal voltage of each phase with a low-pass filter, it becomes less susceptible to noise, ripple, etc., and the accuracy of detecting the zero cross point is improved in a region where the rotation speed is particularly low.

In the control method of the present invention, a three-phase brushless DC motor can be used as the brushless DC motor. In this case, it is preferable to perform commutation with respect to the motor at a timing shifted by 30 degrees in electrical angle from the detection of the zero cross point. .. According to the present invention, the zero cross point can be accurately obtained even at low speed rotation. Therefore, in the case of a three-phase brushless DC motor, commutation is performed at a timing that is 30 degrees out of phase with the electric angle from the detection of the zero cross point. By doing so, the motor can be rotated with high efficiency.

The control device for a brushless DC motor of the present invention is a control device for starting a motor that is a brushless DC motor that does not have a sensor for detecting the position of a rotor, and is a countercurrent voltage induced in at least the winding of each phase. The zero cross point in the countercurrent voltage of each phase of the motor is detected based on the digital value obtained by the A / D converter arranged so that The control means is provided with a control means for performing a control operation on the motor and outputting a command value to an inverter for driving the motor. The average of the measured values of the electromotive voltage is calculated and used as the midpoint voltage for detecting the zero crossing point.

In the control device of the present invention, when the rotation speed of the motor is relatively slow, for example, immediately after the motor is started, the average value of the measured values of the counter electromotive force of each phase is used as the midpoint voltage by averaging. Since the effects of noise and ripple are reduced, it becomes possible to detect the zero crossing point more appropriately, and it becomes possible to prevent the occurrence of step-out during the transition from forced commutation to sensorless drive. .. The control means is usually composed of a microprocessor or the like, but in the present invention, the counter electromotive voltage for each phase is measured when the rotation speed of the motor is relatively slow, so that the counter electromotive voltage of a plurality of phases is measured. Even if the measurement is performed, the increase in the processing load in the control means can be ignored.

In the control device of the present invention, the control means preferably detects the time point at which the sign changes as a result of subtracting the midpoint voltage from the counter electromotive voltage of each phase as the zero cross point in that phase. According to this, since it is detected by the change of the sign, it becomes easy to detect the zero crossing point.

In the control device of the present invention, it is preferable that the control means uses half of the power supply voltage supplied to the inverter as the midpoint voltage when the speed of the rotor of the motor exceeds the threshold value. By doing so, in order to detect the midpoint voltage in the control device, it is sufficient to perform two A / D conversions of the non-selective phase terminal voltage and the power supply voltage. Therefore, the A / D converter or The processing load on the control means is reduced, and the control means can handle the control of the motor at a higher rotation speed.

The control device of the present invention further includes a low-pass filter connected to each phase winding of the motor so that the output of the low-pass filter is also input to the A / D converter, and then the speed of the rotor of the motor. When is less than or equal to the threshold value, the control means may use the countercurrent voltage and the midpoint voltage based on the terminal voltage of the winding of each phase detected by the A / D converter through the low-pass filter. .. By processing the counter electromotive voltage induced in the winding of each phase with a low-pass filter, it becomes less susceptible to noise and ripple, and the accuracy of detecting the zero cross point is improved especially in the region where the rotation speed is low. ..

In the control device of the present invention, a three-phase brushless DC motor can be used as the brushless DC motor. In this case, the control means performs commutation with respect to the motor at a timing shifted by 30 degrees in electrical angle from the detection of the zero cross point. It is preferable to do so. According to the present invention, the zero cross point can be accurately obtained even at low speed rotation. Therefore, in the case of a three-phase brushless DC motor, commutation is performed at a timing that is 30 degrees out of phase with the electric angle from the detection of the zero cross point. By doing so, the motor can be rotated with high efficiency.

According to the present invention, when the zero cross point is detected, the average terminal voltage of each winding is used as the midpoint voltage when rotating at a relatively low speed, so that the sensorless brushless DC motor can be rotated at a low speed. The zero cross point can be detected accurately, and the transition from forced commutation to controlled commutation can be reliably performed without causing step-out.

It is a block diagram which shows the structure of the control device of one Embodiment of this invention. It is a state transition diagram explaining the operation at the time of starting a motor. It is a graph explaining the detection of the zero crossing point when a rotation speed is relatively low. It is a graph explaining the detection of the zero cross point when the rotation speed is relatively low in the prior art. It is a graph explaining the detection of a zero crossing point when a rotation speed is relatively high. It is a block diagram which shows the structure of the control device of another embodiment of this invention. It is a state transition diagram explaining the operation at the time of starting a motor. It is a graph explaining the detection of the zero crossing point when a rotation speed is relatively low.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a control device according to an embodiment of the present invention. The control device 30 drives the motor 10, which is a three-phase brushless DC motor, via the inverter 50. The motor 10 is a sensorless type that does not have a sensor for detecting the position of the rotor. A DC power supply 21 is connected to the inverter 50 as a drive power source for the motor 10. The DC power supply 21 generates a power supply voltage V _dc from one end thereof, and the other end is connected to the grounding point GND. A smoothing capacitor 21 is provided in parallel with the DC power supply 21. As the inverter 50, one generally used for driving a three-phase brushless DC motor by a rectangular wave is used. Further, in the motor 10, the windings of three phases (U phase, V phase and W phase) are connected by Y connection (star connection). A shunt resistor R _s is inserted in the wiring connected from the inverter 50 to the grounding point side of the DC power supply 21, and a current detection that detects the drive current I of the motor 10 by detecting the voltage across the shunt resistor R _s. The circuit 41 is provided.

The control device 30 drives the inverter 50 by driving a command value from the microprocessor 31 between the microprocessor 31 and the inverter 50 and a microprocessor 31 that performs a control operation on the motor 10 by software processing and generates a command value for the inverter 50. It includes a predriver 32 that converts a signal and an A / D (analog-digital) converter 33. The command value from the microprocessor 31 is represented by, for example, the voltage applied to the armature winding of each phase of the motor 10, but the predriver 32 sets the command value in PWM (Pulse Width Modulation) drive. The drive signal is output to the inverter 50 after being converted into an on / off duty ratio. In the A / D converter 33, the power supply voltage V _dc , the drive current I of the motor 10, and the terminal voltages V _u , V _v , V _w of the windings of the U, V, and W phases of the motor 10 are input. , Analog-to-digital conversion of these inputs, which are analog quantities, is performed, and the digital value obtained by the conversion is output to the microprocessor 31. The microprocessor 31 operates the A / D converter 33 at a predetermined carrier frequency (for example, 20 kHz) to perform A / D conversion, and as a result, the motor 10 is based on each digital value input from the A / D converter 33. To perform control of.

For convenience of explanation, the A / D converter 33 is drawn separately from the microprocessor 31 in FIG. 1, but the A / D converter 33 may be built in the microprocessor 31. The power supply voltage V _dc , drive current I, terminal voltage V _u , V _v , and V _w are input, and the A / D converter 33 is configured to be capable of analog-digital conversion of all of these inputs in parallel at the same time. Do not mean. The A / D converter 33 typically includes one or two A / D conversion circuits, and converts a plurality of input analog values into digital values with a time lag by switching inputs. Therefore, when the number of inputs to be A / D converted increases, the time required to sequentially perform A / D conversion for a plurality of input values by one A / D conversion circuit and the A / D conversion result can be determined. The processing time in the microprocessor 31 puts pressure on the entire processing time, and as a result, it becomes difficult to drive and control the motor 10 at high speed rotation.

Next, the process when the motor 10 is started by using the control device 30 of the present embodiment will be described. In this embodiment as well, as in the case of starting a general sensorless brushless DC motor, the microprocessor 31 determines an excitation vector fixed to the wiring of each phase of the motor 10 in order to determine the initial position of the rotor of the motor 10. The rotor is positioned by passing the current of. After that, the motor 10 is driven by setting the operation mode of the motor 10 to forced commutation, which is open loop control. In forced commutation, the microprocessor 31 selectively switches the armature winding through which current flows to rotate the excitation vector in the motor 10, starting commutation with a very low cycle at first, and then gradually commutating cycle. Synchronized operation of the motor 10 is performed while accelerating. After that, when the speed of the rotor reaches a certain value, the microprocessor 31 switches the operation mode of the motor 10 to the sensorless drive. Switching from forced commutation to sensorless drive is performed by determining the rotation speed of the motor 10 from the interval of zero cross points in the counter electromotive voltage generated in the armature winding of the motor 10 and checking whether the rotation speed exceeds a predetermined value. It may be performed depending on whether or not the commutation cycle in forced commutation is shorter than a certain period.

In sensorless drive, of the three phase armature windings, the countercurrent voltage induced by the change in magnetic flux due to the magnetizing pattern of the rotor magnet in the winding of the phase that is not used for excitation at that time is applied. The measurement is performed, the position of the magnetic pole of the rotor is estimated from the measurement result of the countercurrent voltage, and the commutation is executed accordingly. Since the motor 10 is driven by PWM drive using a square wave, there is a timing when the current does not flow even in the winding of the phase where the current is supposed to flow due to commutation, and the counter electromotive voltage should be measured at that timing. Can be done. By performing commutation based on the counter electromotive voltage, a rotating magnetic field corresponding to the position of the magnetic pole of the rotor is generated, and the rotor rotates. However, since the amplitude of the counter electromotive voltage, which is an AC waveform, is proportional to the rotation speed, it is not realistic to execute commutation based on an arbitrary instantaneous value of the counter electromotive voltage, and the zero cross point at the counter electromotive voltage is detected. Will perform commutation.

In order to detect the zero cross point in the counter electromotive force, the midpoint voltage V _center corresponding to the midpoint in the AC waveform is required. In Patent Document 1, 1/2 of the power supply voltage V _dc is set as the midpoint voltage V _center , but in the present embodiment, the motor 10 includes the case of determining whether to shift from forced commutation to sensorless drive. When the rotation speed N of the rotor is equal to or less than the threshold value N _th , the armature voltage of each phase measured by the A / D converter 33, that is, the terminal voltage of the winding of each phase V _u , V _v , V. Let the average of _{w be} the midpoint voltage V _center . That is,
V _center = {V _u + V _v + V _w } / 3
And. Then, the counter electromotive voltage V _bemf is _set to V _bemf = Vi-V _center (however, i = u, v, w).
The point at which the sign of the counter electromotive voltage V _bemf changes is _defined as the zero crossing point. The microprocessor 31 calculates such a midpoint voltage V _center and a counter electromotive voltage V _bemf based on the detection result of the A / D converter 33, and detects the zero crossing point. Then, in order to drive the motor 10 with high efficiency, the microprocessor 31 performs commutation at a time when the phase is shifted by 30 degrees by the electric angle from the detected zero cross point. A sensorless drive in which the average of the terminal voltages V _u , V _v , and V _w of the windings of each phase is set as the midpoint voltage V _center is called a mode 1 sensorless drive. In the sensorless drive of mode 1, the A / D converter 33 needs to perform A / D conversion of the terminal voltages V _u , V _v , and V _w of the three windings, and further, the power supply voltage for controlling the motor 10. Since it is necessary to perform A / D conversion for V _dc and the drive current I, A / D conversion is performed for a total of five input values.

When the sensorless drive in mode 1 is performed and the rotation speed of the motor 10 is increased, the rotation speed N of the rotor exceeds the threshold value N _th . When the rotation speed N exceeds the threshold value N _th , the microprocessor 21 in turn sets the midpoint voltage V _center used for calculating the counter electromotive voltage V _bemf to 1/2 of the power supply voltage V _dc , that is, V _dc / 2. Switch. The sensorless drive performed by using V _dc / 2 as the midpoint voltage V _center is called the mode 2 sensorless drive. In the sensorless drive of mode 2, the A / D converter 33 has A / D of a total of three input values of one of the terminal voltages V _u , V _v , and V _w of the winding, the power supply voltage V _dc, and the drive current I. Since the conversion may be performed, the processing load on the control device 30 is smaller than that in the mode 2, and the motor 10 can be rotated at a higher speed by that amount. The power supply voltage V _dc and the drive current I need to be A / D converted at all times according to the carrier frequency described above for monitoring.

FIG. 2 is a state transition diagram illustrating the operation of the control device 30 described here. After the initialization of the control device 30, the control device 30 is in the standby state, and when the motor 10 is instructed to start from the outside, forced commutation and then the sensorless drive in mode 1 are executed, and the speed N of the rotor is increased. When the threshold value N _th is exceeded, mode 1 sensorless drive is executed. When the stop of the motor is commanded, the control device 30 returns to the standby state. The threshold value N _th is determined based on the model of the motor and the power supply voltage V _dc used as the rotation speed at which the zero crossing point can be accurately determined even if 1/2 of the power supply voltage is set as the midpoint voltage. Is stored in advance in.

FIG. 3 shows the relationship between the counter electromotive voltage of each phase and the detection of the zero cross point when the rotor velocity N is sufficiently smaller than the threshold value N _th in the present embodiment, that is, when the motor 10 is rotating at a low speed. Is shown. On the other hand, FIG. 4 shows the relationship between the counter electromotive voltage of each phase and the detection of the zero cross point when the midpoint voltage V _center is fixed to 1/2 of the power supply voltage V _dc even at a low speed as a conventional example. Shown. In either case, noise and ripple are superimposed on the counter electromotive voltage. Further, the rising and falling edges of the rectangular wave expressed as the zero cross point correspond to the detected zero cross point. Here, for the sake of explanation, it is assumed that the same noise and ripple are superimposed on the counter electromotive voltage in FIGS. 3 and 4. When V _center = {V _u + V _v + V _w } / 3 based on this embodiment, as shown in FIG. 3, zero cross points can be detected at approximately equal intervals even if noise and ripple are superimposed. From now on, it is predicted that the forced commutation can be reliably shifted to the controlled commutation without causing step-out. On the other hand, when V _center = V _dc / 2, as shown in FIG. 4, zero cross points are detected at uneven intervals due to the superposition of noise and ripple. If the intervals between the zero cross points are not uniform in this way, step-out may occur when the sensorless drive is performed based on the zero cross points.

FIG. 5 shows the relationship between the counter electromotive voltage of each phase and the detection of the zero cross point when the rotor speed N exceeds the threshold value N _th in the present embodiment, that is, when the motor 10 is rotating at high speed. Shown. In this state, noise and ripple are negligible compared to the amplitude of the counter electromotive voltage, and the zero cross point can be detected accurately even if V _center = V _dc / 2.

According to the present embodiment described above, the midpoint voltage V _center for detecting the zero cross point is set to V _center = {V _u + V _v + V _w when the rotation speed N of the rotor is equal to or less than the threshold value N _th. } / 3, and if the rotation speed N exceeds the threshold value N _th , V _center = V _dc / 2, which enables the motor 10 to rotate at high speed and at the zero cross point even at low speed rotation. Can be accurately detected, and the motor 10 can be reliably shifted from forced commutation to controlled commutation without causing step-out or the like.

Next, the control device of another embodiment of the present invention will be described. FIG. 6 shows a control device 30 of another embodiment. The illustrated control device 30 is a low-pass filter (LPF) 34 _u , 34 _v , 34 _{w in which} the terminal voltages V _u , V _v , and V _w of the windings of each phase are input to the control device shown in FIG. Is provided, and the outputs of the low-pass filters 34 _u , 34 _v , and 34 _w are also input to the A / D converter 33. One of the causes of noise and ripple superimposed on the counter electromotive voltage is that the motor 10 is driven by a PWM square wave having a predetermined carrier frequency. Therefore, in the present embodiment, in order to remove the component of the PWM carrier frequency. The low-pass filters 34 _u , 34 _v , and 34 _w are provided in. As the low-pass filter (LPF) 34 _u , 34 _v , 34 _w , for example, a general one consisting of a combination of a resistor (R) and a capacitor (C) can be used. Terminal voltage V _u, V _v, the voltage obtained by treated by V _w the low pass filter _{34 u, 34 v, 34 w} , respectively, V _uf, V _vf, and V _wf. And when performing the sensorless drive mode 1, the microprocessor 31, a low pass filter 34 _u, 34 _v, 34 _w terminal voltage V _u passing through the, V _v, V _w, that is, the voltage V _uf, V _vf, V _wf Use to set the midpoint voltage V _center to V _center = {V _uf + V _vf + V _wf } / 3
And. The microprocessor 31, the voltage V _uf also when calculating the back electromotive force, V _vf, using a V _wf. In mode 2, V _dc / 2 is used as V _center as described above. The cutoff frequency of the low-pass filters 34 _u , 34 _v , and 34 _w is set so that the carrier frequency component used for the PWM drive of the motor 10 can be sufficiently removed. If the carrier frequency of the PWM drive is 20 kHz, a sufficient effect can be obtained by using 1 kHz as the cutoff frequency.

FIG. 7 is a state transition diagram showing the operation of the control device 30 shown in FIG. 6, and the difference between this state transition diagram and the state transition diagram shown in FIG. 2 is that the midpoint voltage V _{center in} mode 1 is V _center. = {V _uf + V _vf + V _wf } / 3 is used. FIG. 8 shows the relationship between the counter electromotive voltage of each phase and the detection of the zero cross point when the rotor velocity N in the present embodiment is sufficiently smaller than the threshold value N _th , that is, when the motor 10 is rotating at a low speed. Is shown. Counter electromotive voltage shown here, the low pass filter 34 _u, 34 _v, 34 voltage V _uf passed through the _w, V _vf, a V _wf, in which noise and ripple has been removed. In the one shown in FIG. 8, since the zero crossing points are detected based on the counter electromotive voltage from which noise and ripple are removed, the intervals between the zero crossing points are more even than those shown in FIG. ..

In the embodiments shown in FIGS. 6 to 8, the zero-cross points at low speed rotation can be obtained more accurately by using the low-pass filters 34 _u , 34 _v , and 34 _w .

Although the preferred embodiment of the present invention has been described above, the sensorless brushless DC motor which is the target of the control method and the control device based on the present invention is not limited to the three-phase one, and the present invention is more polyphase. It can also be applied to sensorless brushless DC motors.

10 ... motor; 21 ... DC power supply; 22 ... smoothing capacitor; 30 ... controller; 31 ... microprocessor (MPU); 32 ... predriver; 33 ... A / D (analog-to-digital) converter; 34 _u , 34 _v , 34 _w ... Low-pass filter (LPF); 41 ... Voltage detection circuit; 50 ... Inverter.

Claims (10)

A control method for starting a motor, which is a brushless DC motor that does not have a sensor that detects the position of the rotor.
When the speed of the rotor is equal to or less than the threshold value as the midpoint voltage for detecting the zero crossing point in the counter electromotive voltage of the phase for each phase of the motor for detecting the position of the rotor. A control method used to find and use the average of the measured terminal voltages of the windings of each phase. The control method according to claim 1, wherein the time point at which the sign changes as a result of subtracting the midpoint voltage from the counter electromotive voltage of each phase is detected as the zero cross point in the phase. The control method according to claim 1 or 2, wherein when the speed exceeds the threshold value, half of the power supply voltage used to drive the motor is used as the midpoint voltage. When the speed is equal to or lower than the threshold value, the terminal voltage of the winding of each phase is processed by the low-pass filter, and the counter electromotive voltage based on the terminal voltage after being processed by the low-pass filter and the above-mentioned medium. The control method according to any one of claims 1 to 3, which uses a point voltage. The method according to any one of claims 1 to 4, wherein the brushless DC motor is a three-phase brushless DC motor, and commutates the motor at a timing that is 30 degrees out of phase with the electric angle from the detection of the zero cross point. Control method. A control device that starts a motor that is a brushless DC motor that does not have a sensor that detects the position of the rotor.
With an A / D converter arranged so that at least the terminal voltage of the winding of each phase can be detected,
Based on the digital value obtained by the A / D converter, the zero cross point in the counter electromotive voltage of the phase is detected for each phase of the motor, and the control operation for the motor is performed based on the detected zero cross point, and the motor is operated. A control means that outputs a command value to the inverter that drives the
With
The control means calculates the average of the measured values of the terminal voltages of the windings of the respective phases when the speed of the rotor is equal to or less than the threshold value, and detects the zero cross point. The control device. The control device according to claim 6, wherein the control means detects a time point at which the sign changes as a result of subtracting the midpoint voltage from the counter electromotive voltage of each phase as the zero cross point in the phase. The control device according to claim 6 or 7, wherein the control means uses half of the power supply voltage supplied to the inverter as the midpoint voltage when the speed exceeds the threshold value. A low-pass filter is provided for connecting to each of the windings of the respective phases of the motor.
The output of the low-pass filter is also input to the A / D converter,
The control means has the counter electromotive voltage based on the terminal voltage of the winding of each phase detected by the A / D converter via the low-pass filter when the speed is equal to or lower than the threshold value, and the inside of the control means. The control device according to any one of claims 6 to 8, which uses a point voltage. The brushless DC motor is a three-phase brushless DC motor, and the control means executes commutation with respect to the motor at a timing shifted by 30 degrees in electrical angle from the detection of the zero cross point. The control device according to any one item.

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