JPH07123773A - Driving method of brushless DC motor - Google Patents

Abstract

(57) [Abstract] [Purpose] Detects induced voltage information without using a filter, estimates the rotor position from the amount of change in voltage over time, and drives a DC brushless motor. [Configuration] As effective induced voltage information of the stator winding,
The terminal voltage of each winding in the period Ts shown in (b) is detected, and these are interpolated to obtain a processed waveform as shown in (c). The terminal voltage of each winding in the detected period Ts is discrete due to chopping and freewheeling of the inverter circuit that controls the motor, and the voltage of the undetected portion is interpolated from the change amount of the voltage with time. Is obtained by performing. Then, the time indicating the maximum value and the minimum value of the voltage value of this processed waveform is the commutation timing with respect to the rotor, and is the rotor position to be detected
Controls motor drive. [Effect] The position of the rotor can be accurately estimated irrespective of the change in the duty ratio of the inverter, and good speed control of the DC brushless motor can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a brushless DC motor, and more particularly to a so-called sensorless brushless DC motor which can detect the position of a rotor without using magnetic detection means such as a Hall element. It relates to a driving method.

[0002]

2. Description of the Related Art Generally, drive control of a brushless DC motor must be performed by closely associating a magnetic pole position of a rotor with a position of a winding to be passed. The output torque of the motor is generated by the interaction between the magnetic flux of the magnetic pole of the rotor and the current flowing through the winding of the stator. Therefore, when driving a brushless DC motor, the maximum torque is generated by rotating the motor by passing a current through the winding of the phase existing in the vicinity of the maximum magnetic flux generated from the magnetic poles of the rotor. is necessary.

Further, the drive control of the brushless DC motor is performed by momentarily switching the phase through which the current should flow according to the rotation of the magnetic pole position of the rotor.
When the timing of commutation, which is the switching of this phase, deviates significantly from the maximum magnetic pole position, the torque generated thereby decreases, and in the worst case, the motor loses step and stops.

Therefore, the drive control of the brushless motor is
It is necessary to detect the magnetic pole position of the rotor by some means and control it accordingly.

As a conventional technique relating to a rotor magnetic pole position detecting circuit of this type of sensorless brushless motor, for example, a technique described in Japanese Patent Publication No. 58-25038 is known.

In this prior art, the induced voltage in the winding of the brushless motor is delayed by using a bandpass filter, and the phase delay waveform of the filter is compared with the neutral point of three phases of the filter output voltage to compare with the brushless motor. The commutation timing of the motor is created and the inverter circuit that drives the motor is controlled based on this timing to perform commutation.

[0007]

In the prior art, a filter is used to create a phase delay waveform of the induced voltage of the brushless motor. However, in this conventional technique, when rotation pulsation occurs in the rotor due to load fluctuations or the like, the phase delay of the filter becomes inaccurate, and when the motor return current flows under conditions where the motor load is large, There is a problem that the time when the terminal voltage of the stator becomes equal to the DC voltage of the inverter increases, waveform distortion occurs in the filter output voltage after filtering the induced voltage of the motor, and accurate commutation timing cannot be obtained. is doing.

Further, in the above-mentioned prior art, when the load torque fluctuates repeatedly during one rotation of the motor, the speed of the rotation of the motor fluctuates when the motor output torque is controlled to be constant. There is a problem in that vibration causes vibrations to make the motor unstable, and in the worst case, the motor stops.

In order to solve the above-mentioned problems, an inverter circuit is used, and a pulse width is changed to control the output AC voltage variably, that is, so-called Pulse Width Modulation (hereinafter referred to as PWM) control, so that the current flows to each phase. A drive method that changes the flow rate for each period to match the motor torque and the load torque is conceivable, but in this case as well, the commutation timing is determined by using the conventional technology that uses a filter. If this is done, the difference in the conduction ratio during each conduction period will be reflected in the output voltage of the filter, and the phase delay will be inaccurate, which will make the motor drive unstable as in the case described above, and in the worst case. However, there is a problem that the motor stops.

That is, the conventional technique for determining the commutation timing using a filter cannot detect the correct rotor position, and the commutation timing cannot be matched with the magnetic pole position and speed. However, there is a problem in that the torque generated by the motor is reduced and the motor may be out of step.

Therefore, in the above-mentioned prior art, the commutation timing caused by the inaccuracy of the phase delay of the filter output is introduced by some method such as introducing another parameter such as a direct current value in addition to the induced voltage of the stator winding. It is necessary to correct the error and determine the commutation timing so that the current flows through the winding of the phase existing near the maximum of the magnetic flux generated by the rotor magnetic field. This creates the problem of complexity.

An object of the present invention is to solve the above-mentioned problems of the prior art and to perform control for changing the flow rate for each flow period in order to change the motor torque in accordance with the change in the load on the motor. Even when performing, the magnetic pole position of the rotor is correctly estimated, the commutation is performed at an appropriate timing without stopping the motor, the speed fluctuation during one rotation of the motor is reduced, and vibration and vibration caused by the speed fluctuation are reduced. It is an object of the present invention to provide a method for driving a brushless DC motor capable of suppressing noise.

[0013]

SUMMARY OF THE INVENTION According to the present invention, the above object is to provide an A / D converter which directly detects a motor terminal voltage of a non-energized phase of a motor without using a filter, and an A / D converter which detects the sampling value. The rate of change of the detected voltage with respect to time is obtained, and the extrapolated interpolation is used to obtain the induced voltage information, and the rotor position is estimated based on this induced voltage information. And a controller for driving the brushless DC motor so as to carry out commutation at an appropriate time.

[0014]

The A / D converter samples and detects the motor terminal voltage in the non-energized phase of the motor.
The induced voltage information is calculated by extrapolating the detected voltage value based on the rate of change of the voltage value discretely taken in by the D converter with respect to time, and the commutation timing is calculated from this information. Then, the driver of the inverter that drives the motor is driven, and the motor is finally rotated. Further, the control unit has a memory function of storing the captured detected voltage value and time, and a function of calculating commutation timing and the like from the information and the rate of change of the voltage value with time.

As described above, according to the present invention, it is possible to perform good drive control of a DC brushless motor using an inverter circuit.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for driving a brushless DC motor according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the system configuration of a brushless DC motor to which the driving method according to the present invention is applied, and FIG. 2 is a diagram showing the flow control of the motor at an ideal commutation timing so that the motor has a constant speed. Showing schematically the waveforms of the induced voltage, detection terminal voltage, and processing voltage of the motor in the state where the motor rotates, FIG. 3 is an enlarged view of the detection terminal voltage waveform, and FIG. 4 is the phase advance / delay of commutation timing. It is a figure which shows the process voltage waveform explaining. In FIG. 1, 1 is a DC power supply, 2 is an inverter circuit, 3 is a selector, and 4 is A /
D converter, 5 is a control unit, 6 is a driver circuit unit, 7 is a stator, 8 is a rotor, and 9 is a load.

As shown in FIG. 1, a brushless DC motor system to which the present invention is applied includes a DC power source 1, an inverter circuit 2, and a selector 3 for selecting one non-energized phase among three-phase windings. Converts the analog value of the terminal voltage of the selected terminal into a digital value so that it can be calculated by an electronic computer A
/ D converter 4, a control unit 5 that determines the rate of change and commutation time from the detected voltage and outputs a signal to a driver that controls the inverter circuit 2, a driver circuit unit 6, U, V of the inverter circuit 2. , A W-phase winding is connected at one end to a stator 7 of a three-phase DC brushless motor, a rotor 8 having magnetic poles using permanent magnets, and a load 9 coupled to the motor.

In the following description, the motor driving method according to the embodiment of the present invention is the 120-degree conduction type driving capable of obtaining a high output torque, and the motor controlling method is the DC voltage from the DC power source 1. Is applied to the motor through the inverter circuit 2 to control the direct current flow rate of the motor, and the switching element for chopping is connected to the positive voltage side of the DC power supply 1. .

A switching element for chopping may be connected to the negative voltage side of the DC power source 1, and the inverter circuit 2 corresponds to the winding of each phase, although not shown in the figure. Therefore, it is configured to include three sets of switching elements.

In general, in a DC motor which is full-wave driven by the inverter circuit 2, the effective induced voltage information from the winding is obtained from the winding of one phase which is not always energized among the windings of three phases. Only the voltage, and the induced voltage information during the period when the chopping by the inverter circuit is not performed is effective. For this reason, the selector 3 has a switching function for switching the terminals of the detected phases in accordance with the current flow mode.
The / D converter 4 is a so-called A / D converter that converts an analog voltage value into a digital value in synchronization with a PWM control signal.
It has a conversion function.

The control unit 5 receives the detected value of the induced voltage described above as an input, and calculates the rate of change of the voltage with time, that is, the slope of the voltage based on the detected value, and the time from the slope to the target voltage value. And a function of outputting a signal that controls the driver circuit 6 that controls the switching element of the inverter circuit 2, and a function of storing the above-mentioned detected value and inclination.

Further, the driver circuit section 6 has a function of driving a switching element forming the inverter circuit 2 in response to a signal from the control section 5.

In the above-described embodiment of the present invention, the control section 5 and the driver circuit section 6 of the switching element of the inverter circuit 2 are constituted by different circuits, but these functions are summarized as one. A microcomputer may be used as the control unit.

The stator 7 which constitutes the motor has three-phase windings of windings U, V and W which are poled by passing an electric current, and one ends of these windings are connected to each other. ing. The rotor 8 is a permanent magnet having a magnetic pole, and rotates in accordance with the change in the proper magnetic pole position of the stator described above.

Next, in the brushless DC motor configured as described above, the respective windings of the stator 7 are controlled to flow at an ideal commutation timing, and the motor is assumed to be rotating at a constant speed. The state will be described with reference to FIG.

FIG. 2 (a) shows the induced voltage waveform of each phase which occurs as a physical phenomenon in this state, and FIG. 2 (b) shows the terminal voltage waveform of the winding of each phase detected in full-wave drive. Two
In the present invention, (c) is a signal waveform that can be obtained by detecting the terminal voltage waveform in synchronization with the PWM signal and extrapolating and interpolating the undetectable point from the change amount of the detected value with respect to time.

As shown in FIG. 2, when the motor commutates at an ideal commutation timing and rotates at a constant speed, as shown in FIG. 2 (a) so as to prevent rotation as a physical phenomenon. Reverse voltage is induced. This induced voltage is induced by the magnetic pole of the rotor, and its Peak
The to Peak value is proportional to the rotation speed of the motor, and the transient value is determined in correlation with the magnetic pole position of the rotor. Usually, the commutation timing of the motor can be determined based on this induced voltage information.

That is, the ideal commutation timing (maximum output can be obtained) of the motor is represented by the points tp1 and tp shown in the drawing where the induced voltages of the adjacent phases intersect.
In the embodiment of the present invention, the voltage at this time is the maximum value e (tp1) of the voltage which is the upward convex inflection point, and the minimum value e of the voltage which is the downward convex inflection point. It is obtained as (tp2).
When the motor is rotating at a constant speed, the maximum value and the minimum value of the voltage at that time are substantially equal in any adjacent phases.

On the other hand, what can be detected as an actual system is the terminal voltage of the stator winding of the motor, which has a waveform as shown in FIG. 2 (b). This detected waveform shows the voltage between the midpoint potential at which each phase winding is coupled and the terminal of each phase winding, which is obtained by calculation, and the drive voltage applied to rotate the motor. It is a mixture of induced voltage.
Then, in the 120-degree energization type drive of the motor, the effective induced voltage information is the period Ts shown in FIG. 2B, and only one of the three phases is always present.

Further, even during the effective induced voltage information period Ts, the potential is fixed to the positive or negative value of the DC voltage in the section in which the current flows through the freewheeling diode during commutation, and the inverter is used. When the circuit is performing PWM control, chopping is performed, so that the circuit does not become continuous as shown in FIG. Therefore, it is necessary to detect the induced voltage information by some method and determine the commutation timing by performing arithmetic processing based on the information.

Therefore, in one embodiment of the present invention, the effective induced voltage information is such that, in the 120-degree conduction type drive as described above, only one of the three phases is always in the period Ts shown in FIG. Selector 3 because it can only be obtained from
In this way, one of the three phase windings of the motor, which is not energized, is switched and selected according to the conduction mode, and as shown in the enlarged view of the detected waveform shown in FIG. Current is not flowing in the freewheeling diode at, and the terminal voltages e (t1) and e (t2) when chopping off
However, the induced voltage information is directly picked up from the terminal voltage, though it is discrete, by sampling etc.

Further, in one embodiment of the present invention, the control unit 5
Then, the change rate Δv / Δt of the voltage with respect to time is calculated from the induced voltage information obtained discretely, and the induced voltage between discrete values (the broken line portion in the figure) is calculated by extrapolation. By continuously connecting, a processed waveform having a triangular wave signal waveform as shown in FIG. 2C is obtained.

As described with reference to FIG. 2, in a state where the flow of current to the windings of each phase is controlled at the ideal commutation timing and the motor is rotating at a constant speed, as shown in FIG. 2 (c). In each adjacent phase, the voltage at the point where the induced voltages of the adjacent phases intersect (the maximum value of the voltage that is the upward convex inflection point, the minimum value that is the downward convex inflection point) is Also becomes almost constant, and emax and emin of the processed waveform can be obtained from the voltage value at each inflection point of this signal at this time. From this, to find the optimum commutation timing, the induced voltage in each phase is detected, and the induced voltage obtained from the rate of change with respect to time at that time is emax and
All we have to do is find the time that becomes emin.

When the phase of the commutation timing is delayed or advanced, as shown in FIGS. 4 (b) and 4 (c), the voltage at the previous rotational flow point depending on the current rate of change of the induced voltage. Value e (t'41) and e (t'42) and voltage value at the time of pre-rotation flow
Take the difference between e (t41) and e (t42), and estimate and compare the optimum value of the voltage value e (tpb) at the last commutation time t41 and t42 based on the current or previous induced voltage change rate information. Therefore, the delay of the previous commutation time and the advance time Δtbd are estimated,
Correction is performed at the next commutation point without accumulating commutation time error.

In one embodiment of the present invention, the commutation timing can be finally brought close to the optimum commutation time by repeating the above-mentioned correction. In addition, since the induced voltage information depends on the rotational speed and the magnetic pole position of the rotor, one embodiment of the present invention, even if rotational pulsation occurs in the motor due to the above-mentioned correction, Since the induced voltage also changes, an appropriate commutation timing can always be estimated.

The above-mentioned processing for obtaining the commutation time will be described in more detail below.

Now, it is assumed that the load 9 on the motor is a constant load having no periodic load fluctuation, and the motor is rotated at a constant speed. In this case, as the induced voltage,
A voltage waveform as shown in FIG. 3 is detected. Sampling for obtaining the induced voltage information from this voltage waveform validates the data only during the period when the PWM output of the inverter circuit 2 is ON and the current does not flow through the freewheeling diode during commutation. Done.

The data of the invalid period is calculated from the detected voltage value and time by extrapolation using the change rate Δv / Δt. In this way, by obtaining the voltage value in the ineffective period by extrapolation interpolation, it is possible to continuously estimate the rotor position for each conduction period from the time or voltage obtained as a result.

Further, the commutation time is estimated from the maximum value or lower value which is the upwardly convex inflection point previously obtained at one revolution from the rate of change Δv / Δt of the induced voltage obtained based on the current time. The time to reach the minimum voltage, which is a convex inflection point, is calculated as the reference time tbm, and the commutation phase advance and delay time tbd are estimated based on the information of the previous rotation flow point. The reference time tbm of is the advance of the previous commutation time, the delay is the time tbd
It is performed by the method of correcting with.

In practice, the voltage value in the detectable region is treated as being represented by an approximate expression of a linear function with respect to time, and the rate of change K = Δv / Δt with respect to time is the sampled voltage as shown in FIG. Formula (1) from the values e (t1) and e (t2)
Ask by.

K = Δv / Δt = {e (t2) -e (t1)} / (t2-t1) ………… (1) Next, based on the current time tn, it was obtained at the previous one rotation. Based on the rate of change K and the voltage value e (tn) at the current time, the next rotation flow reference time tbm, which is the time until the maximum value of the voltage that is an upwardly convex inflection point, is calculated by the formula (2 ). At this time, it is desirable that e (tn) be a voltage value at a position of 1/5 to 4/5 where the most linear approximation is effective in the time width from emax to emin.

In the formula (2), the case of the maximum value is described, but the same applies to the case of the minimum value. Then, as shown in FIG. 4A, the phase of the commutation timing advances, and if there is no delay, the voltage values of the adjacent phases match at the commutation time, and the rotor position is continuously determined based on the change rate K described above. And the commutation timing can be determined.

Tbm = {emax-e (tn)} / K (2) Further, as shown in FIGS. 4B and 4C, the commutation phase generated at the previous commutation If there is a delay or advance, the correction time tbd is the time at which the voltage value at the previous rotation flow point is estimated from the current change rate K and the change rate Kb obtained from the previous rotation flow time, and the voltage value is the same. And That is, first, the voltage e (t'41) at the previous commutation time, during which the current is flowing through the freewheeling diode, is estimated by the equation (3).

E (t'41) = e (tn) − (tn-t41) · K (3) Furthermore, the change rate Kb used in the previous commutation time calculation was obtained in advance, The difference from the estimated voltage e (t41) at the time of the previous rotation is taken, and the half point is assumed to be the voltage value when the commutation is optimally performed, and from that voltage value and the current rate of change K At the time obtained from the obtained voltage e (t'41), the previous phase time t
Next rotation flow correction time tbd (n) is calculated by adding bd (n-1) as in Expression (4), and the result is set as the phase delay time at the previous rotation flow point. The voltage value assumed at this time is reflected at the time of the next rotation flow as the maximum voltage value at the ideal commutation timing.

Tbd (n) = [{e (t'41) -e (tpb)} / K] + tbd (n-1) (4) And finally, up to the next rotational flow time The time tb is the time when the next rotational flow reference time tbm is corrected by the phase delay time tbd by the equation (5).

Tb = tbm + tbd (n) (5) Although the above description is for the case of commutation phase delay shown in FIG. 4B, the phase lead shown in FIG. The same applies when the rate of change is negative.

In the above description, the commutation time is obtained from the detected change rate of the induced voltage of the motor, and the commutation is performed by managing the time at that time. However, the change rate of the induced voltage of the motor is Since it has voltage and time information, it compares the detected voltage or extrapolated voltage with the voltage value estimated to be the commutation timing, and when it matches or exceeds that voltage. It is also effective to control the drive of the motor by controlling with a voltage that causes commutation.

That is, the rate of change Δv of voltage with time
Since / Δt has both voltage and time information, the rotor position and commutation timing can be controlled by both voltage and time.

Next, the characteristics when the motor is driven according to the above-described embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows a motor output having a position detection sensor attached so that the rotational position of the rotor can be known, which is estimated as a sensor output when the motor is rotated at a constant load of 2000 rpm by the method according to the embodiment of the present invention. It is the figure which converted and showed the time difference with the flow time to the angle difference. A three-winding DC motor has one
Since there are 12 commutation points in rotation, the number of measurement points shown in FIG. 5 is 12 during one rotation, and the figure shows the measurement results for several rotations.

According to FIG. 5, the time difference between the sensor output and the commutation time according to the embodiment of the present invention is 1 in terms of angle.
Since the position detection accuracy of the Hall element that is generally used is about ± 6 degrees, the driving method according to the embodiment of the present invention is capable of performing good motor position detection. It turns out that this is a good driving method.

FIG. 6 is a diagram showing a case where driving is performed under the same conditions as in the case of FIG. 5 described above so that the load is changed cyclically, and FIG. 7 shows the speed fluctuation of the motor in this case. It is a figure.

As can be seen from FIG. 6 showing the result, in the embodiment of the present invention, even when the load of the motor fluctuates greatly, as in the case of FIG. The detection can be performed, and the speed fluctuation can be reduced as shown in FIG. 7.

FIG. 8 shows continuous learning control in which a load having the same fluctuations as in the case of FIG. 6 is connected to the motor, the deviation of the commutation phase is calculated for each rotation, and the result is reflected after one rotation. By differentiating the flowing time in the flowing period twice to obtain the acceleration, decreasing the flowing ratio during the accelerating period and increasing the flowing ratio during the decelerating period,
A diagram showing the results when control is performed by changing the flow rate for each flow period by reflecting the acceleration as a parameter in the flow rate, and outputting the motor torque so that it matches the load torque. FIG. 9 is a diagram showing the speed variation of the motor in this case.

As can be seen from the results shown in FIGS. 8 and 9, when the drive method according to the embodiment of the present invention is used, the rotor position can be accurately measured even when the flow rate is changed for each flow period. Therefore, even when the learning torque is used to control the motor torque to approach the load torque, it is possible to reduce the speed fluctuation during one rotation of the motor. Vibration and noise due to fluctuation can be suppressed.

Further, in this case, since the rate of change of the induced voltage of the motor with respect to time is the speed information, it is possible to use a method of controlling the rate of flow based on the average rate of change for each current flow period. Is.

The present invention is not limited to the method of the above-described embodiment, but since the variation amount of the induced voltage and the maximum value of the intersection thereof are proportional to the speed, the maximum value and the minimum value of the induced voltage are adjacent to each other. It is also possible to control the motor to rotate at a constant speed by controlling the same in the matched phases.

FIG. 10 is a diagram for explaining a motor driving method in this case.

In the method shown in FIG. 10, the average value (emax and emin) of the maximum voltage value and the minimum voltage value of the induced voltage in one rotation of the motor is calculated, and the ideal value estimated from the rate of change of the induced voltage is calculated. The difference (Δv1 and Δv2) between the voltage at the time of commutation and the calculated average value is used as a parameter of the current flow rate, and the ideal voltage at the time of commutation assumed from the rate of change of the induced voltage is the average. When it is lower than the value, the conduction ratio is increased, and when it is higher than the average value, the conduction ratio is decreased, etc., so that the maximum and minimum values of the induced voltage become the same in each adjacent phase during each conduction period. To control it. Also in this case, it is possible to perform the learning control similar to that described above.

In the above-described embodiment of the present invention, the stator winding of the motor is described as having three phases. However, the present invention can be applied to the case where the stator has more phases. In this case, the inverter circuit for driving is also configured in multiple phases according to the number of phases of the motor.

[0062]

As described above, according to the present invention, the position of the rotor can be accurately estimated even when the flow rate is different for each flow period, so that it is possible to prevent periodic load fluctuations. By changing the flow rate for each flow period, it is possible to perform control such that the motor torque matches the load torque, and it is possible to suppress the speed fluctuation of the motor and the accompanying vibration and noise.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a brushless DC motor to which a driving method according to the present invention is applied.

FIG. 2 schematically shows waveforms of an induced voltage, a detection terminal voltage, and a processing voltage of the motor in a state where the commutation is controlled at an ideal commutation timing with respect to the motor and the motor is rotating at a constant speed. It is a figure.

FIG. 3 is an enlarged view of a detection terminal voltage waveform.

FIG. 4 is a diagram showing processing voltage waveforms for explaining the advance and delay of the phase of commutation timing.

FIG. 5 is a commutation time estimated as a sensor output when a motor equipped with a position detection sensor so that the rotational position of the rotor is known can be driven and rotated at a constant load of 2000 rpm by a method according to an embodiment of the present invention. It is the figure which converted the time difference with and into an angle difference, and was shown.

FIG. 6 is a diagram showing a case where driving is performed under the same conditions as in FIG. 5 while periodically changing the load.

FIG. 7 is a diagram showing a speed variation of the motor shown in FIG.

FIG. 8 is a diagram illustrating a case where a load having the same fluctuations as in the case of FIG. 6 is connected to a motor and the acceleration is reflected as a parameter in the conduction ratio to change the conduction ratio for each conduction period to match the load torque. FIG. 6 is a diagram showing a result when a control for outputting a motor torque is performed as described above.

9 is a diagram showing a speed variation of the motor shown in FIG.

FIG. 10 is a diagram for explaining another example of the motor driving method according to the embodiment of the present invention.

[Explanation of symbols]

 1 DC power supply 2 Inverter circuit 3 Selector 4 A / D converter 5 Control part 6 Driver circuit part 7 Stator 8 Rotor 9 Load

Claims (8)

[Claims] 1. A method of driving a brushless DC motor, comprising a permanent magnet and an armature coil, wherein one end of each phase of the armature coil is commonly connected, wherein a non-energized phase of the brushless DC motor is A method for driving a brushless DC motor, which comprises detecting a terminal voltage and determining commutation timing based on a rate of change of the detected terminal voltage with respect to time. 2. The drive of the brushless DC motor is performed using an inverter circuit.
A method for driving the described brushless DC motor. 3. The detection of the terminal voltage is performed in synchronization with a PWM signal that controls an inverter circuit, and extrapolation interpolation is performed based on the rate of change of the detection voltage with respect to time, so that the rotor position when detection is impossible is continuously performed. 3. The method for driving a brushless DC motor according to claim 2, wherein the driving method is a method for estimating a brushless DC motor. 4. The method for driving a brushless DC motor according to claim 3, wherein the commutation timing is determined with a point at which the interpolated value with respect to the detected value of the terminal voltage of each adjacent phase intersects as commutation time. 5. The output torque of the motor is controlled so that the maximum value and the minimum value of the voltage value at the intersection of the voltage interpolation values of the adjacent phases calculated based on the rate of change of the terminal voltage with respect to time become constant. The method for driving a brushless DC motor according to claim 3 or 4, wherein. 6. The method of driving a brushless DC motor according to claim 3, wherein the drive rate of the motor is controlled by handling the rate of change of the interpolation value with respect to time as continuous motor speed change information. 7. The method for driving a brushless DC motor according to claim 4, wherein the voltage value at the commutation timing estimated based on the interpolation value is reflected in the next rotation. 8. The method for driving a brushless DC motor according to claim 3, wherein the extrapolation is performed based on a rate of change of a portion of the detected voltage having good linearity.