JPH0947076A - Control method of brushless motor - Google Patents

Abstract

(57) [Summary] (Correction) [Problem] To reliably detect the position of the rotor of a brushless motor to prevent step-out and stop. SOLUTION: A terminal voltage of an armature winding of a brushless motor 14 is compared with a reference voltage by a position detection section 15, and a position detection signal which changes at an intersection of the comparison results is input to a control circuit 16. The control circuit 16 detects an intersection of the induced voltage generated in the armature winding by the input position detection signal and the reference voltage as a position detection point of the rotor of the brushless motor 14, and with the position detection point as a reference, the brushless motor 14 The drive signal for switching the energization state of the armature winding current of is output. At this time, the control circuit 16 detects the first edge and the next edge of the position detection signal after switching the energization, predicts the time of the position detection point based on the time between the position detection points, and reverses the predicted time. The generation time of the electromotive voltage is subtracted, the energization state of the armature winding current is switched at the time obtained by this subtraction, and the end of the counter electromotive voltage is always before the position detection point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation control technique of a brushless motor used for a motor of an air conditioner,
More particularly, it relates to a brushless motor control method for surely detecting the position of a rotor and controlling the rotation of the brushless motor.

[0002]

2. Description of the Related Art In recent years, brushless motors of this type have come to be used, for example, in fan motors and compressor motors of air conditioners, and sensorless control for controlling rotation of brushless motors without using sensors such as Hall elements. Various methods have been proposed.

In order to control the rotation of the brushless motor by this sensorless control method, for example, the control device shown in FIG. 3 is required. In this figure, this control device is
The DC power supply Vdc is switched by the inverter unit 1 to be converted into three-phase AC, and the converted three-phase AC voltage is applied to the three-phase armature winding of the brushless motor 2.

The position detecting section 3 is a brushless motor 2
Of the armature winding terminal voltages R, S, T and the reference voltage k (for example, Vdc / 2) from the reference voltage generation circuit 3a are compared by the comparison circuits 3b, 3c, 3d, and these comparison results (change at the intersection) Output signal) to the control circuit 4 as a position detection signal. The reference voltage generating circuit 3a divides the power supply Vdc to generate the reference voltage k.

The control circuit 4 switches the energization state of the armature winding current to a predetermined value based on the input position signal.
Transistors U, V, W, X, Y, Z of the inverter unit 1
Control.

The operation of the control device having the above structure will be described with reference to the time chart of FIG. 4. First, when the brushless motor 2 is in operation, the control circuit 4 obtains a position detection point based on the input position detection signal. .

For example, for the armature winding R, the comparison circuit 3b compares the terminal voltage of the armature winding R with the reference voltage k as shown in FIG. The position detection signal shown in b) is output to the control circuit 4.

In this case, when the energization is switched at the point a of FIG. 4A and the energization of the armature winding R is turned off, the armature winding R has a back electromotive force from point a to point b in FIG. A voltage pulse is generated. At this time, since the pulse intersects with the reference voltage k, a pulse that changes at the intersecting points a and c is generated in the position detection signal output from the comparison circuit 3b, but the control circuit 4 internally The pulse of the position detection signal is removed or the pulse is ignored.

Further, since the armature winding R is not energized from point a to point c (at the time of next energization switching) shown in FIG. 4A, an induced voltage is generated in the armature winding R. To do. Since this induced voltage and the reference voltage k intersect at point d shown in FIG. 4A, the comparison circuit 3b outputs a position detection signal that changes at that intersection. The control circuit 4, which has received the position detection signal, detects the edge of the intersection (point d in the figure) to detect the position of the rotor 2a. This intersection d point corresponds to an electrical angle of 30 degrees from point a in the figure.

The position detection point of the rotor 2a (d in FIG. 4)
(Point) as a reference, the time corresponding to an electrical angle of 30 degrees is measured, and as shown in FIG. 4 (c), the output drive signal is set to H to turn on the transistor U at the time elapsed point (point c).
The level is set and the armature winding R is energized. In addition, electrical angle 3
The time corresponding to 0 degree is calculated, for example, by measuring the time between the position detection points (electrical angle of 60 degrees) and based on the measured time.

Similarly, from the point e to the point f shown in FIG. 4A, after the energization of the armature winding R is turned off at the point e in the figure, the position detection point of the rotor 2a (see the figure). g point) is detected, the time corresponding to an electrical angle of 30 degrees is measured with this position detection point as a reference, and the transistor X is on-controlled at the time elapsed point (f point) as shown in FIG. Therefore, the output drive signal is set to H level, and the armature winding R is energized.

As for the OFF control of the transistors U, X and the ON / OFF control of the transistors V, W, Y, Z, the position of the rotor 2a is detected by the position detection signals from the comparison circuits 3c, 3d as described above. Then, the energization switching time is obtained with reference to this position detection point.

In this way, by switching the energization of the armature winding current of the brushless motor 2, it is possible to control the rotation of the brushless motor 2 in a predetermined manner.

[0014]

However, in the above brushless motor control method, the generation time (width) of the counter electromotive voltage generated in the armature winding of the brushless motor 2 at the time of switching energization varies depending on the load, and the counter electromotive voltage is changed. Since the generation time of the motor becomes shorter or the time becomes longer, the position detection of the rotor 2a may be hindered, the rotation of the brushless motor 2 may be stopped, and the control parts may be damaged. It could not be applied to equipment with large fluctuation range.

For example, when the load is light, the armature winding current becomes small as shown in FIG. 5 (a), so that the back electromotive force is generated at the point h at the time of switching the energization up to the point i. It is small, and its back electromotive voltage does not apply to the position detection point j which is the intersection of the terminal voltage (induced voltage) of the winding R and the reference voltage k. Therefore, as shown in FIG.
The position detection signal that is the output of the comparison circuit 3b changes at the j point where the electrical angle is 30 degrees from the point, and this edge is detected to detect the electrical angle 3
The energization can be switched at the l point after 0 degree.

However, when the load is heavy, the armature winding current increases and becomes large. Therefore, as shown in FIG.
The back electromotive voltage generated at the m point at the time of switching the energization may exceed the position detection point n at an electrical angle of 30 degrees from the m point and reach the o point.

Then, as shown in FIG. 6A, the winding R
Since the terminal voltage (induced voltage) and the reference voltage k do not intersect at the original position detection point n, the position detection signal output from the comparison circuit 3b is output at the n point as shown in FIG. Since there is no edge, that is, the original position detection point n cannot be obtained, energization of the armature winding current from the n point to the electrical angle 30
It will not be possible to switch at point P later.

In such a state, not only the brushless motor 2 is out of step and stopped, but also a large current flows through the brushless motor 2, so that the control parts may be broken or damaged. Further, even if the control components are protected by the overcurrent protection, the stop of the brushless motor 2 cannot be avoided.

Therefore, the conventional method can be applied only to a device having a constant load or a small load variation range. For example, load variation of a motor or the like for driving a compressor of a variable capacity air conditioner. It was difficult to apply to equipment with a large range.

The present invention has been made in view of the above problems, and an object thereof is to maintain the position of the rotor even if the time (width) of the back electromotive force generated when the energization of the armature winding current is switched is increased. It is possible to detect with certainty. Therefore, it is possible to prevent out-of-step and stop of the brushless motor, prevent failure and damage of control parts, and apply to equipment with a wide load fluctuation range. It is to provide a method of controlling a motor.

[0021]

In order to achieve the above object, the present invention compares an induced voltage generated at an armature winding terminal of a brushless motor with a reference voltage, and changes the position at an intersection of the comparison results. A detection signal is obtained, the intersection of the induced voltage generated in the armature winding by the change of the position detection signal and the reference voltage is detected as the position detection point of the rotor of the brushless motor, and the position detection point is used as a reference. A method of controlling a brushless motor for switching the energization state of the armature winding current of the brushless motor, wherein the generation time of the counter electromotive voltage generated when the energization of the armature winding is switched based on the position detection signal. (Width) is detected, and the energization switching time of the armature winding is changed according to the generation time of the counter electromotive voltage,
It is characterized in that the energization state of the armature winding current is switched so that the generation of the back electromotive force ends at least before the position detection point.

Further, in the brushless motor control method of the present invention, the generation time (width) of the counter electromotive voltage generated when the energization of the armature winding is switched based on the position detection signal.
Is detected and the detection time of the position detection point is predicted based on the time between the position detection points, and at least the generation time of the counter electromotive voltage is subtracted from the predicted time to obtain the armature winding current. Is obtained, and the energization state of the armature winding current is switched so that the generation of the back electromotive force is completed before the position detection point.

When the position detection signal is obtained by comparing the terminal voltage of one armature winding with the reference voltage, the other energization switching times of the energization switching time are the generation times of the counter electromotive voltage. Should be taken into account when calculating.

Further, in the brushless motor control method of the present invention, the generation time (width) of the counter electromotive voltage generated at the time of switching the energization of the armature winding is detected based on the position detection signal to detect the position. While predicting the detection time of the position detection point based on the time between the detection points, the generation time of the back electromotive force and a predetermined time are subtracted from the prediction time to switch the energization of the armature winding current. Then, the energization state of the armature winding current is switched so that the generation of the counter electromotive voltage is completed before the position detection point.

When the position detection signal is obtained by comparing the terminal voltage of one armature winding with the reference voltage, the other energization switching times of the energization switching time are the generation times of the counter electromotive voltage. Also, it may be calculated in consideration of the predetermined time.

According to the above means, the induced voltage generated in the terminal voltage of the armature winding of the brushless motor is compared with the reference voltage, and the rotor is detected based on the position detection signal which changes at the intersection of the comparison results. Is detected, and the energization state of the armature winding current of the brushless motor is switched based on this position detection point.

At this time, a counter electromotive voltage is generated in the armature winding when the energization is switched, and an induced voltage is generated, and the position detection signal includes at least the intersection of the counter electromotive voltage and the reference voltage due to the energization switching and Information on the intersection of the induced voltage and the reference voltage is included.

After the energization is switched, the first edge (first edge) of the position detection signal is detected, and the generation time of the counter electromotive voltage is detected by this edge detection. Also,
The next edge (second edge) of the position detection signal is detected, the position of the rotor is detected by this edge detection, and the time of the position detection point is detected based on the time between the position detection points by this position detection point. Is predicted.

The generation time of the counter electromotive voltage is subtracted from this predicted time, and the time obtained by this subtraction is regarded as the energization switching time. Therefore, the end of the counter electromotive voltage is always before the position detection point, and the rotation is surely performed. The position of the child can be detected.

Depending on the application of the brushless motor, the rotational speed, the load, or the generation time of the counter electromotive voltage varies. Therefore, not only the generation time of the counter electromotive voltage is subtracted from the predicted time, but also the variation is taken into consideration. The predetermined time (for example, the time corresponding to an electrical angle of 10 degrees) is also subtracted.

Since the time obtained by this subtraction is the energization switching time, the end of the counter electromotive voltage is ahead of the position detection point with a margin, and even if there is the above fluctuation, the end of the counter electromotive voltage is detected by the position detection. The position of the rotor can be reliably detected without hitting any point.

On the other hand, when the position detection signal is obtained by comparing the terminal voltage of one armature winding with the reference voltage, the back electromotive voltage or the back electromotive voltage and the predetermined time are calculated when calculating the other energization switching times. Is added, the rotation control becomes smooth.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention compares an induced voltage generated in a terminal voltage of an armature winding of a brushless motor with a reference voltage, and based on a result of this comparison, based on a position detection signal which changes at an intersection. Focusing on the fact that the position detection method that detects the position of the rotor can detect the back electromotive force generation time by switching the energization, the energization switching time is determined according to the back electromotive voltage generation time (width). So that the back electromotive force does not reach the rotor position detection point.

Therefore, the controller of the brushless motor of the present invention has the configuration shown in FIG. This control device is applied to a compressor of an air conditioner.

In FIG. 1, this control device inputs an AC power supply 10 to a converter section 12 via a reactor 11 for power factor improvement and converts it into a direct current, and this DC-converted power supply Vdc is converted by an inverter section 13. The voltage is switched and converted into a three-phase alternating current, and the voltage converted into the three-phase alternating current is applied to the three-phase armature winding of the brushless motor 14.

The converter section 12 is composed of a rectifying circuit composed of a diode bridge, a voltage doubling capacitor circuit, and a smoothing capacitor. The inverter unit 13 corresponds to the inverter unit 1 shown in FIG. 3, and the brushless motor 14 is shown in FIG.
2 corresponds to the brushless motor 2 and the rotor 14a corresponds to the rotor 2a shown in FIG.

Further, this controller is a brushless motor 1
Among the four armature windings, for example, the terminal voltage of the armature winding R is input to the position detection unit 15, and the position detection unit 15
Is a terminal voltage of the armature winding R and a reference voltage generating circuit 15
The comparison circuit 15b compares the reference voltage k from a (for example, Vdc / 2), and outputs a position detection signal that changes at the intersection of the comparison results to the control circuit (microcomputer) 16. The reference voltage generation circuit 15a divides the voltage Vdc to generate the reference voltage k.

The control circuit 16 detects the position of the rotor on the basis of the input position detection signal, and also detects the time (width) of the back electromotive force due to the switching of energization. Brushless motor 1 based on the detection point
In order to switch the energization of the armature winding current to a predetermined value so that 4 rotates, the transistors U, V,
The drive signals for W, X, Y, and Z are output to the drive circuit 17, while the rotation speed of the brushless motor 14 is controlled. Therefore, the drive signal is chopped at a predetermined on / off ratio and applied to the brushless motor 14. And outputs a PWM signal for changing the value to the drive circuit 17.

As shown in FIGS. 2 (c) to 2 (h), a part of the on-drive portion of the signal for driving each transistor of the inverter section 13 is chopped so that one transistor of the upper arm or the lower arm is turned on. In order to perform PWM control, the control circuit 16 outputs the chopping upper / lower arm switching signal to the drive circuit 17. The control circuit 16 also has the function of the control circuit 4 shown in FIG. Drive circuit 1
Reference numeral 7 indicates a transistor U, which combines the drive signal and the PWM signal in accordance with the upper and lower arm switching signals, and forms the upper arm of the inverter unit 13 based on the combined signal.
V, W and transistors X, Y,
Drive Z.

Next, the operation of the above control device will be described in detail with reference to the time chart of FIG. When the brushless motor 14 is used as a motor for a compressor of an air conditioner, for example, the rotation speed and the load do not change abruptly and change relatively slowly. Even if the position of the rotor is not detected every 60 degrees, sufficient control can be performed if the position of the rotor is detected every 180 degrees of the electrical angle by the position detection signal for one phase. Therefore, the case where the method of controlling by the position detection signal for one phase is applied will be described below as an example.

First, the position detector 15 compares the terminal voltage (see FIG. 2A) of the armature winding R with the reference voltage k, and changes the position at the intersection of the comparison results to detect an edge position. A signal (see FIG. 2B) is input to the control circuit 16.

The control circuit 16 detects the position of the rotor 14a based on the input position detection signal, and switches the energization of the armature winding current based on this position detection, while PWM
The on / off ratio (duty ratio) of the signal is changed to control the brushless motor 14 at a predetermined rotation speed. At this time, for example, when the load becomes heavier, the armature winding current increases and increases, so that the counter electromotive voltage generation times Ts and Tss due to the energization switching shown in FIG. 2A increase.

In this position detection, the control circuit 16 detects the first and second edges of the position detection signal after switching the energization (see the arrow in FIG. 2B), but the first and second edges are not detected. It can be easily distinguished from other edges generated by chopping by the PWM signal.

For example, when the first edge corresponds to t4 and the second edge corresponds to t5 (see FIG. 2A), the control circuit 16 detects the first edge and switches the energization switching time (t).
The time from 3) to the first edge time (t4) is calculated, and the generation time Ts of the counter electromotive voltage due to the energization switching is detected. Thereafter, every time the second edge is detected (position detection), the time T360a from the second edge detection time (t1) two times before last to the second edge time (t5) this time is calculated.

In this case, since the control circuit 16 turns off the transistor X at time t3, a back electromotive voltage is generated in the armature winding R from time t3, and this back electromotive voltage ends at time t4. The position detection signal from the detection unit 15 becomes the falling edge. This falling edge is the first edge, and the control circuit 16 detects the falling edge to detect time t4, and also calculates t4-t3 = Ts to detect the counter electromotive voltage generation time Ts. To do.

Next, based on the measured time T360a, a time corresponding to an electrical angle of 180 degrees (T360a
/ 2) is calculated and the calculated time (T360a / 2) is added to the second edge time t5 to predict the position detection point time t10 (= t5 + T360a / 2) 180 degrees after the electrical angle.

Here, in the motor for driving the compressor of the air conditioner, the number of revolutions and the load fluctuate to some extent, and the generation time of the back electromotive voltage also fluctuates to some extent.
And an actual time of the intersection (position detection point), an error occurs, and also an error occurs in the generation time of the counter electromotive voltage.

Therefore, in consideration of the above error, for example, a time α (= 10/360 × T360) corresponding to an electrical angle of 10 degrees.
a) is subtracted from the predicted time t10 together with the counter electromotive voltage generation time Ts to obtain the energization switching time t8.
That is, t8 = t10− (Ts + α), and this time t
If the transistor U is turned off at 8, the counter electromotive voltage becomes t
It ends at time t9 before 10.

For example, even if the load becomes heavier and the armature winding current increases and increases accordingly, and the counter electromotive voltage generation time increases, the previous counter electromotive voltage generation time is taken into consideration. Since the energization switching time of the armature winding current is obtained, that is, the energization switching time can be advanced according to the generation time of the counter electromotive voltage. Therefore, the counter electromotive voltage does not reach the second edge (position detection point), and the position of the rotor 14a can be reliably detected.

At other energization switching times t6 and t7, t6 = t8-120 / 360 × T360a,
It is calculated using the formula of t7 = t8-60 / 360 × T360a. That is, in order to smoothly control the rotation of the brushless motor 14, it is sufficient to switch the energization state of the armature winding current for each 60 electrical degrees.

When the calculation result of the other energization switching time t6 is t6 ≦ t5, the energization switching time has passed and the energization switching is immediately performed (the transistor U is turned on and the transistor W is turned on). Turn off).
This is because the generation time of the back electromotive voltage becomes extremely long,
This is because there is a possibility that it will occur if the arithmetic processing such as the energization switching time is delayed due to the influence of multiple interrupts or the like. However, the probability that such a situation will occur is extremely low, and it is a measure for the sake of completeness.

The following process will be briefly described. The first edge time t9 is detected, and the time from the energization switching times t8 to t9 (the time when the counter electromotive voltage is generated due to the energization switching) Tss is calculated. Further, the second edge time t10 is detected and the energization switching time t2
The time T360b of the electrical angle 360 from to 10 is calculated, and the electrical angle 180 is calculated based on the calculated time T360b.
Position detection point time t14 (= t10 + T360b /
Predict 2).

Subsequently, in the same manner as described above, the energization switching times t13, t12, t11 are sequentially calculated, and a predetermined transistor of the inverter section 13 is driven at this calculated time to switch the energization state of the armature winding current.

In this case, the energization switching time t13,
In calculating t12 and t11, the counter electromotive voltage generation time Ts
Since s is taken into consideration, the position detection point at time t14 can be reliably detected, and the rotation control can be smoothly performed.

The above operation will be described generally. After the time t3 when the transistor X of the inverter unit 13 is turned off and the transistor Y of the inverter unit 13 is turned on, the end edge of the counter electromotive voltage, that is, the first position detection signal after the energization is switched. The falling edge time t4 is detected and the counter electromotive voltage generation time Ts is calculated.

Then, the first rising edge time t5 of the position detection signal after switching the energization is detected (the position detection point is detected), and the time T360a corresponding to the electrical angle of 360 degrees (time between position detections) is calculated. To do. The energization switching times t8, t7, t6 are sequentially calculated using the time T360a thus calculated and the time Ts and α (for example, 10/360 × T360a) of occurrence of the counter electromotive voltage, and the calculated time is set in the timer. To do.

When the set time is detected by the timer, the transistor W of the inverter unit 13 is turned off and the transistor U is turned on at time t6. At time t7, the transistor Y is turned off and the transistor Z is turned on. At time t8, the transistor U is turned off and the transistor V is turned on.

After the transistor U is turned off and the transistor V is turned on, the first rising edge time t9 of the position detection signal is detected (the end time of the back electromotive force is detected), and the back electromotive force is detected. The voltage generation time Tss is calculated.

Subsequently, the first falling edge time t10 of the position detection signal after switching the energization is detected (the position detection point is detected), and the time corresponding to the electrical angle of 360 degrees (time between position detections) T360b is detected. calculate. The energization switching times t13, t12, t11 are calculated using the time T360b thus calculated, the counter electromotive voltage generation time Tss and α (in this case; 10/360 × T360b),
This calculated time is set in the timer.

When the set time is detected by the timer, the transistor Z is turned off and the transistor X is turned on at time t11. At time t12, the transistor V is turned off and the transistor W is turned on. At time t13, the transistor X is turned off and the transistor Y is turned on.

By repeating the above-described processing, the load becomes heavy, the armature winding current increases and increases, and the generation times Ts and Tss of the counter electromotive voltage shown in FIG. According to the rotation control, the generation time T
Even when s and Tss become longer than the time corresponding to the electrical angle of 30 degrees and reach the position detection point, the energization switching time can be advanced according to the counter electromotive voltage generation times Ts and Tss. In other words, the end of the back electromotive force is surely before the position detection point, and the position of the rotor 14a can be reliably detected.

When the counter electromotive force generation times Ts and Tss are shorter than the time corresponding to the electrical angle of 30 degrees, the above-mentioned processing need not be executed.
It may be properly used depending on the values of s and Tss. in this case,
Times T360a and T360b corresponding to an electrical angle of 360 degrees
The energization switching time is calculated based only on this, and the energization state of the armature winding current is switched at this calculated time.

When calculating the energization switching time,
Times T360a and T360b corresponding to an electrical angle of 360 degrees
However, a time corresponding to an electrical angle of 180 degrees may be used.

Further, in the above embodiment, the energization switching timing is obtained based on the one-phase position detection signal obtained from the one-phase winding terminal voltage and the reference voltage. Also applicable to the method to obtain the energization switching timing based on the two-phase position detection signal obtained from the reference voltage and the three-phase position detection signal obtained from the three-phase winding terminal voltage and the reference voltage. You can

[0065]

As described above, according to the present invention, the terminal voltage of the armature winding of the brushless motor is compared with the reference voltage, and based on the comparison result, the position detection signal inverted at the intersection is used as the basis. The position of the rotor is detected by using this position, and when the energization state of the armature winding current is switched based on this position detection point, the counter electromotive voltage generation time due to the energization switching is detected, and the detected counter electromotive voltage is generated. Since the energization switching time is changed according to the time, the load becomes heavy and the armature winding current increases and becomes large. Even if (width) becomes large and it reaches the position detection point, the back electromotive force can be ended before the position detection point,
That is, it is possible to reliably detect the position of the rotor, and thus to prevent step-out and stop of the brushless motor, prevent failure and damage of control parts, and eventually improve reliability. Further, there is a useful effect that it can be applied to a device having a large load variation range.

Further, according to the present invention, when the one-phase position detection signal obtained by comparing the one-phase winding terminal voltage and the reference voltage is used, the counter electromotive voltage is generated also in other energization switching. Since time is taken into consideration, smooth rotation control can be performed, step-out and stop of the brushless motor can be prevented, and failure and damage to control parts can be prevented. The effect of is obtained.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a control device to which an embodiment of the present invention is applied and to which a brushless motor control method is applied.

FIG. 2 is a schematic time chart diagram for explaining the operation of the controller for the brushless motor shown in FIG.

FIG. 3 is a schematic block diagram of a conventional control device for a brushless motor.

FIG. 4 is a schematic time chart diagram for explaining the operation of the brushless motor control device shown in FIG.

5 is a schematic time chart diagram for explaining the operation of the controller for the brushless motor shown in FIG.

FIG. 6 is a schematic time chart diagram for explaining the operation of the controller for the brushless motor shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 AC power supply 11 Reactor 12 Converter section 13 Inverter section 14 Brushless motor (sensorless DC brushless motor) 14a Rotor (of brushless motor 14) 15 Position detection section 16 Control circuit (microcomputer) 17 Drive circuit k Reference voltage (Vdc / 2) ) R armature winding (of brushless motor 14) U, V, W switching element (upper arm transistor) X, Y, Z switching element (lower arm transistor)

Claims (5)

[Claims] 1. An armature winding terminal of a brushless motor is compared with an induced voltage generated at a terminal and a reference voltage is obtained to obtain a position detection signal which changes at an intersection of the comparison results. The intersection of the induced voltage generated in the winding and the reference voltage is detected as the position detection point of the rotor of the brushless motor, and the energization state of the armature winding current of the brushless motor is switched based on the position detection point. A method of controlling a brushless motor, wherein a generation time (width) of a counter electromotive voltage generated at the time of switching the energization of the armature winding is detected based on the position detection signal, and the generation time of the counter electromotive voltage is detected. Accordingly, the energization switching time of the armature winding is changed, and the energization state of the armature winding current is switched so that the generation of the counter electromotive voltage ends at least before the position detection point. The method of a brushless motor according to claim. 2. An armature winding terminal of a brushless motor is compared with an induced voltage generated at a terminal, a position detection signal which changes at an intersection of the comparison results is obtained, and the armature is changed by the change of the position detection signal. The intersection of the induced voltage generated in the winding and the reference voltage is detected as the position detection point of the rotor of the brushless motor, and the energization state of the armature winding current of the brushless motor is switched based on the position detection point. A method for controlling a brushless motor, wherein a generation time (width) of a counter electromotive voltage generated when energization of the armature winding is switched is detected based on the position detection signal, and a time between the position detection points is calculated. Based on the prediction time of the position detection point, at least the generation time of the counter electromotive voltage is subtracted from the prediction time to obtain the energization switching time of the armature winding current to detect the position. The method of the brushless motor, characterized in that generation of the counter electromotive voltage is to switch the energization of the armature winding current so as to end before. 3. The position detection signal is obtained by comparing a terminal voltage of one of the armature windings of the brushless motor with a reference voltage, and other than the energization switching time. 3. The brushless motor control method according to claim 1, wherein the energization switching time is calculated in consideration of the generation time of the counter electromotive voltage. 4. An armature winding terminal of a brushless motor is compared with a reference voltage, a position detection signal which changes at an intersection of the comparison results is obtained, and the armature is changed by the change of the position detection signal. The intersection of the induced voltage generated in the winding and the reference voltage is detected as the position detection point of the rotor of the brushless motor, and the energization state of the armature winding current of the brushless motor is switched based on the position detection point. A method for controlling a brushless motor, wherein a generation time (width) of a counter electromotive voltage generated when energization of the armature winding is switched is detected based on the position detection signal, and a time between the position detection points is calculated. On the other hand, while predicting the detection time of the position detection point, the generation time of the counter electromotive voltage and the predetermined time are subtracted from the prediction time to obtain the energization switching time of the armature winding current, and the position The method of the brushless motor generation of the output temae the counter electromotive voltage is characterized in that to switch the energization of the armature winding current to exit. 5. The position detection signal is obtained by comparing a terminal voltage of one of the armature windings of the brushless motor with a reference voltage, and other than the energization switching time. 5. The method for controlling a brushless motor according to claim 4, wherein the energization switching time is calculated by taking into consideration the generation time of the back electromotive voltage and a predetermined time.