JPH09266691A - Control method of brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent step-out and stoppage of a brushless motor. SOLUTION: The armature winding voltage R, S, T of a brushless motor 4 and reference voltage age compared by a position sensor 5, and a position sensing signal is acquired. A control circuit 10, to which the position sensing signal is input, detects the place of a rotor 4a, and conduction changeover timing is obtained as using the position sensing as a reference while the position sensing signal as the result of the comparison is masked for a fixed time after position sensing. The end edge of spike voltage is detected by the position sensing signal after the masking, and the time corresponding to current conduction changeover timing computed on the basis of the time of previous conduction changeover timing and a conduction changeover interval and the time of actually conducted current conduction changeover timing are compared when the end edge is performed at the same time as the off of a chopping signal. When the time of current conduction changeover timing is later, the next conduction changeover timing is computed on the basis of the time of previous conduction changeover timing and conduction changeover timing, and the conduction of an armature winding is changed over at the computed conduction changeover timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation control technology of a brushless motor (non-commutator motor) used for a motor of an air conditioner, and more particularly, to a brushless motor by appropriately switching the energization of armature winding current. The present invention relates to a method for controlling a brushless motor that controls the rotation of a motor.

[0002]

2. Description of the Related Art For controlling the rotation of a brushless motor, for example, a control device shown in FIG. 4 is required. In this figure, this control device converts an AC power supply 1 into a DC power supply Vdc in an AC / DC converter 2, and switches this DC power supply Vdc in an inverter circuit 3 to convert it into a three-phase AC. An alternating voltage is applied to the three-phase armature winding of the brushless motor 4.

The position detection circuit 5 compares the terminal voltages R, S, T of the armature winding of the brushless motor 4 with the reference voltage k (for example, Vdc / 2) generated by the reference voltage generation circuit 6 by a comparison circuit. , And outputs these comparison results (signals changing at intersections) to the control circuit 7 as position detection signals. The reference voltage generating circuit 6 divides the DC power supply Vdc with a resistor to generate a reference voltage k.

The control circuit 7 detects the intersection of the induced voltage and the reference voltage k (the position of the so-called rotor 4a) by the input position detection signal, and at the same time, detects the armature winding current based on this position detection timing. In order to switch the energized state to a predetermined value, the transistors U, V, W, X, and
A drive signal for controlling Y and Z is output.

Further, the control circuit 7 outputs a chopping signal having a predetermined on / off ratio to the chopping circuit 8 in order to chop and vary the applied voltage of the brushless motor 4 together with the drive signal.

The chopping circuit 8 drives a combination of an input drive signal and a chopping signal in order to perform a chopping drive on a predetermined portion of the drive section, for example, the latter half of the drive section of each of the transistors U, V, W, X, Y and Z. Output to the circuit 9.

In the control device having the above structure, for example, the voltage R of the armature winding will be described. The position detection circuit 5 compares the winding voltage R shown in FIG. The changing position detection signal is output to the control circuit 7.

In this case, when the energization is switched and the energization of the armature winding R is turned off, the armature winding R is switched to the state shown in FIG.
Spike voltage (pulse due to back electromotive force) shown in (b) h
Occurs. Since the spike voltage h intersects with the reference voltage k, the position detection signal from the position detection circuit 5 includes information on the spike voltage h. The control circuit 7 internally detects the end edge of the spike voltage h, and sets the first edge detection point after this end edge as the position detection timing of the rotor 4a.

Therefore, as shown in FIG. 5C, when the induced voltage is rising, the first rising edge after the ending edge of the spike voltage h becomes the position detection timing of the rotor 4a, and the induced voltage is decreased. During this time, the first falling edge after the end edge of the spike voltage h is the position detection timing of the rotor 4a.

In this way, the position detection timing of the rotor 4a is obtained, and the next energization switching timing is obtained based on this position detection timing. For example,
As a method of obtaining the next energization switching timing,
It is based on the time of the position detection timing interval and the time of one cycle which have already been obtained and the time of this position detection timing.

The position detection signals of other phases are also
The position of the rotor 4a is detected in the same manner as described above, and the energization switching timing is obtained based on this position detection timing.

By switching the energization of the armature winding current of the brushless motor 4 at the energization switching timing thus obtained, the brushless motor 4 can be controlled in a predetermined rotation and the on / off ratio of the chopping signal can be controlled. It is possible to control the rotation speed to a desired value by changing the value.

[0013]

However, in the brushless motor control method, there is no problem if the ending edge of the spike voltage h is in the off section of the chopping signal as shown in FIG. 5 (b). As shown in FIG. 6B, for example, if the end edge of the spike voltage h becomes the ON section of the chopping signal due to a change in the load and the original position detection is hidden by the spike voltage h, problems such as step-out may occur. Occurs.

As shown in FIG. 6C, the spike voltage h
Is applied to the induced voltage, the end edge of the spike voltage h becomes the same as when the chopping signal is turned off, and the detection of the end edge is delayed.

As a result, the original position detection timing cannot be obtained, and erroneous position detection timing is obtained. It should be noted that this erroneous position detection timing is also caused by noise or the like (including noise accompanying the generation of the spike voltage h).

Further, the energization switching timing of the brushless motor 4 is delayed, and therefore the end edge of the spike voltage h is delayed to reach the ON section of the chopping signal, thereby obscuring the original position detection and obtaining the erroneous position detection timing. There is also.

As described above, in the state where the end edge of the spike voltage h hides the original position detection and the erroneous position detection timing is obtained, the brushless motor 4 is already out of step, and finally the brushless motor 4 comes out. Not only start and stop, various adverse effects occur.

The present invention has been made in view of the above problems, and an object thereof is to perform appropriate energization switching even in a state where an incorrect position detection timing is obtained due to spike voltage, noise, etc. It is an object of the present invention to provide a brushless motor control method capable of preventing the motor from being out of step and stopped.

[0019]

To achieve the above object, the present invention compares a voltage of an armature winding of a brushless motor with a reference voltage while switching a DC power supply to supply the brushless motor. , A brushless that obtains a position detection signal of the comparison result, detects the position of the rotor of the brushless motor by the position detection signal, and switches energization of the armature winding current of the brushless motor based on the timing of the position detection. A method of controlling a motor,
While the comparison result is masked for a predetermined time after the position detection, the energization of the armature winding is switched at a predetermined time when the comparison result is not obtained even after a predetermined time has passed from the current energization switching. It is characterized by having done.

Further, according to the brushless motor control method of the present invention, the comparison result is masked for a time shorter than the interval between the position detection and the previous position detection, while the time of the energization switching timing before and after the current energization switching and The time of the next energization switching timing is calculated based on the energization switching interval, and when the comparison result is not obtained even after a predetermined time has elapsed from the current energization switching, the electric power is switched at the calculated energization switching timing time. The feature is that the energization of the subsidiary winding is switched.

According to the present invention, when the DC power supply is switched to be supplied to the brushless motor to control the inverter, the applied voltage of the brushless motor is changed by a predetermined chopping signal, while the voltage of the armature winding of the brushless motor is changed. The position detection signal of the comparison result is obtained by comparing with a reference voltage, the position of the rotor of the brushless motor is detected by the position detection signal, and the armature winding of the brushless motor is based on the timing of the position detection. A method of controlling a brushless motor that switches between energization of a current, wherein the comparison result is masked for a time shorter than a position detection interval before the position detection, while the end of a spike voltage generated by the energization switching is detected by the position detection. Detecting from the signal that the end of the detected spike voltage is after the mask and the chopping When the signal is turned off at the same time, the armature winding timing is set at the previous energization switching timing time and energization switching interval or at the previous position detection timing time and energization switching timing calculated based on the position detection interval. The feature is that the power supply to the wire is switched.

Further, in the brushless motor control method of the present invention, the comparison result is masked for a time shorter than the position detection interval before the position detection, while the end of the spike voltage generated by the energization switching is detected by the position. When the end of the spike voltage generated by the current switching is detected after the mask and at the same time when the chopping signal is turned off, the time of the previous power switching timing and the power switching interval are also detected. Then, the time corresponding to the current energization switching timing is calculated, and the calculated time is compared with the time of the current energization switching timing. If the time of the current energization switching timing is late, the previous energization is performed. At the next energization switching timing based on the switching timing time and energization switching interval It is calculated and is characterized in at the time of energization switching timing out the calculated that to switch the energization of the armature winding.

Further, according to the brushless motor control method of the present invention, the comparison result is masked for a time shorter than the position detection interval before the position detection, while the end of the spike voltage generated by the energization switching is detected by the position. When the end of the spike voltage generated by the current switching is detected after the mask and at the same time when the chopping signal is turned off, the time and position detection interval of the previous position detection timing are also detected. And calculate the time corresponding to the current energization switching timing,
The calculated time is compared with the time of the current energization switching timing, and if the time of the current energization switching timing is late, the next energization switching is performed based on the time of the previous position detection timing and the position detection interval. The timing is calculated, and the energization of the armature winding is switched at the calculated energization switching timing.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. In the figure,
The same parts as those in FIGS. 4 to 6 and the corresponding parts are designated by the same reference numerals, and a duplicate description will be omitted.

In FIG. 1, the control device to which the brushless motor control method of the present invention is applied, when the position of the rotor 4a is detected by a position detection signal in addition to the function of the control circuit 7 shown in FIG. While the result of comparison between the terminal voltages R, S, T and the reference voltage k is masked for a time shorter than the position detection timing before the position detection timing, a predetermined time (time later than the mask time) has passed since the current energization switching. Even if the comparison result (the position of the rotor 4a) of the terminal voltages R, S, T and the reference voltage k cannot be obtained, a control circuit (microcomputer) 10 having a function of forcibly switching the energization is provided. There is.

Further, the control circuit 10 stores a predetermined number of energization switching timing times, energization switching intervals, position detection timing times, and position detection intervals, and a spike voltage (pulse of counter electromotive voltage) generated by energization switching is stored. ) The end edge of h (the first edge of the position detection signal after switching the energization) is detected, and it is determined whether or not this end edge is the same as when the chopping signal is off.

If the end edge is not at the same time as when the chopping signal is turned off, the energization switching timing is obtained with reference to the position detection timing obtained thereafter, and the energization switching is performed at this energization switching timing.

If the end edge is at the same time as when the chopping signal is turned off, this is performed this time based on a predetermined number of times of the energization switching timing and the time of the energization switching interval (or the position detection edge interval). The time corresponding to the energization switching timing is calculated. The calculated time point of the energization switching timing is compared with the time point of the energization switching timing performed this time.

When the energization switching timing performed this time is earlier, the position of the rotor 4a is detected by the position detection signal after the end edge, and the energization switching timing is calculated with this position detection timing as a reference. The energization of the armature winding current is switched at the switching timing.

When the energization switching timing performed this time is later, the energization switching timing is calculated based on the time of the previous energization switching timing and the energization switching interval (or the position detection edge interval). Forced switching of armature winding current energization at the timing.

Specifically, referring to the time chart of FIG. 2 and the flowchart of FIG. 3, it is assumed that the brushless motor 4 is rotationally controlled in the position detection mode.

Then, the armature winding of the brushless motor 4 has a winding voltage R, shown in FIGS. 2 (a), 2 (b) and 2 (c).
Since S and T are generated, the position detection circuit 5 causes the winding voltage R,
S and T are compared with the reference voltage k, and the position detection signal of the comparison result is output to the control circuit 10 ((e) in the figure,
(See (f) and (g)).

The control circuit 10 detects the position of the rotor 4a based on the input position detection signal. If the induced voltage generated in the armature winding is rising, the control circuit 10 positions the first rising edge after energization switching. It is obtained as the detection timing, and when the induced voltage generated in the armature winding is falling, the first falling edge after switching the energization is obtained as the position detection timing. The energization switching timing is calculated based on the position detection timing thus obtained, and energization of the armature winding current is switched at this energization switching timing.

At this time, each time the energization is switched, a predetermined number of times (tan) are stored, and the energization switching interval (tan- (tan-1) = TAn-1) is calculated and stored in a predetermined number. Time of position detection timing (tbn)
Is stored in a predetermined number, and the position detection interval (tbn- (tbn
-1) = TBn-1) is stored in a predetermined number. Note that n
Is a positive integer.

Then, the result of comparison between the terminal voltage and the reference voltage is masked for a predetermined time from the position detection of the rotor 4a,
That is, the position detection of the rotor 4a is prohibited. As the mask time, when the current position detection time is (tb2), a time (TB1 × α / 100) shorter than the previous position detection interval (tb2-tb1 = TB1) is set (FIG. 2).
(H)). It should be noted that α is determined in consideration of the load state, the use state, and the like.

Thus, within the mask time, erroneous position detection due to the occurrence of noise or the like is eliminated, the energization of the brushless motor 4 can be switched appropriately, and proper rotation control can be performed.

On the other hand, every time the energization switching is performed, a predetermined number of energization switching timing times (tan) are stored, and the energization switching interval (TAn-1) is calculated and stored for a predetermined number (step ST1). The input edge detection signal is used to detect the ending edge of the spike voltage h generated by switching the energization (step ST2).

Subsequently, it is determined whether or not the ending edge of the spike voltage h is the same as when the chopping signal is off (step ST3). That is, as described in the conventional example, when the end of the spike voltage h is applied to the ON section of the chopping signal, the detection of the end edge of the spike voltage h is the maximum and the ON section is delayed. Because it will be hidden.

[0039] Spike voltage h due to current switching
When the end edge of is not at the same time as when it is off, the process proceeds from step ST3 to ST4, and the position of the rotor 4a is detected by the position detection signal after the mask time. When this position detection timing is obtained, the energization switching timing is calculated with reference to the time (tbn) of the position detection timing as described above, and energization is switched at this energization switching timing (step ST5).

Subsequently, when the ending edge of the spike voltage h is the same as the off-time, the steps ST3 to S3 are performed.
Proceeding to T6, the current energization switching timing (time ta
m) to n times before the energization switching timing (ta)
m−n) and energization switching interval (TAm−n) × n, which corresponds to the current energization switching timing and current energization switching timing (tam).
To determine if is faster. Note that m and n are positive integers.

For example, as shown in FIG. 2A, when the ending edge of the spike voltage h due to the energization switching at time (tam = ta9) is at the same time as when the chopping signal is turned off, four times before (y = 4). 4) the previous energization switching interval (TA5) is added to the time (ta5) of the energization switching timing of 4) and added to calculate the time (ta5 + TA5 × 4) corresponding to the time of the current energization switching timing. The calculated time (ta5 + TA5 × 4) is compared with the current time (ta9) of the current energization switching timing.

The current energization switching timing time (t
When am = ta9) is later, the time of the next energization switching timing is calculated based on the time of the previous energization switching timing and the energization switching interval. That is, the fact that the time (ta9) at the current energization switching timing is late means that the rotation of the brushless motor 4 is not normal and there is a high possibility that, for example, a step-out is occurring, and the original position within the ending edge of the spike voltage h. This is because the detection will be hidden, and if the current state continues, the step will be lost.

For example, ta5 + (4 + 1) × TA5 is set to the time of the next energization switching timing, and energization of the armature winding current is forcibly switched at this time (step ST
7). In this way, since the energization can be forcibly switched within a predetermined time after the energization switching, even in the conventional case of FIG. 6, the energization switching is not performed based on the incorrect position detection timing, and the appropriate energization switching is performed. It is possible to prevent the step-out of the brushless motor 4 and the like.

The time of the current energization switching timing (t
am) is earlier, steps ST6 to ST4
Then, the processing described above is executed. That is, even if the spike voltage h is applied to the ON section of the chopping signal, the subsequent position detection timing is not necessarily the original one, that is, the position detection timing obtained thereafter can be regarded as normal. This is because, for example, refer to the position detection timing (tb5) in the energization switching interval (TA5) in FIG. 2) and there is no step out.

In step ST6, the time corresponding to the current energization switching timing calculated by the time (tam-n) at the energization switching timing n times before and the energization switching interval (TAm-n) × n and the current energization. It is determined whether or not the time (tam) of the switching timing is earlier, but the times may be the same.

In this case, depending on the rotation state of the brushless motor 4, it may be determined whether the current energization switching timing is to be later or earlier, but if the rotation control is stable. , I can judge that I am not out of tune and can put in the earlier one.

The same processing can be performed by using the position detection timing and the position detection interval instead of the power supply switching timing and the power supply switching interval. In this case, the position detection interval (TBz × z) is added to the energization switching time (tbz) z times before, and the time ((tbz) + (TBz × z)) obtained by this addition and the current energization switching time tam. = Ta9), and the same processing as described above may be performed based on the comparison result.

[0048]

As described above, according to the first aspect of the brushless motor control method of the present invention, the armature winding voltage is compared with the reference voltage, and the rotor position is detected by the position detection signal of the comparison result. When detecting the position While masking the comparison result for a predetermined time after position detection, if the comparison result is not obtained even after a lapse of a predetermined time from this energization switching, the armature winding is energized at the predetermined time. Since the power supply is switched, the power supply can be switched even when the incorrect position detection timing is obtained due to the spike voltage, noise, etc. generated by the power supply switching, and thus the step-out and stop of the brushless motor can be prevented. The effect is that you can.

According to the second aspect of the present invention, when the armature winding voltage and the reference voltage are compared and the position of the rotor is detected by the position detection signal of the comparison result, the comparison result is obtained for a predetermined time from the position detection. When masking is performed and the comparison result is not obtained even after this mask time has elapsed, the armature winding is energized at the time of the previous energization switching timing and the energization switching timing calculated based on the energization switching interval. Since it is switched, even if the incorrect position detection timing is obtained due to spike voltage, noise, etc. generated by switching the energization, it is possible to switch the energization appropriately and prevent the step-out and stop of the brushless motor. There is an effect that can be done.

According to the third aspect of the present invention, when the DC power supply is switched and supplied to the brushless motor for inverter control, and the applied voltage of the brushless motor is changed by a predetermined chopping signal, the armature winding voltage is changed. When the rotor position is detected by the position detection signal of the comparison result, the comparison result is masked for a predetermined time from the position detection, while the end of the spike voltage generated by the energization switching is detected, When the detection spike voltage ends after the mask and at the same time as when the chopping signal is turned off, the power-on switching timing is calculated based on the previous power-on switching timing and the power-on switching timing. Since the energization of the armature winding is switched, incorrect position due to spike voltage, noise, etc. Even in a state in which output timing can be obtained, particularly even when the end edge of the spike voltage had concealed situ detection timing delayed by chopping signals, it is possible to perform appropriate energization switching,
As a result, it is possible to prevent the step-out and stop of the brushless motor.

According to claim 4 of the present invention, in addition to claim 3, the time corresponding to the current energization switching timing is calculated based on the time of the previous energization switching timing and the energization switching interval, and the calculated time is calculated. And the current energization switching timing time are compared, and if the current energization switching timing time is late, the next energization switching timing time is calculated based on the previous energization switching timing time and the energization switching interval. However, since the energization of the armature winding is switched at the time of the calculated energization switching timing, in addition to the effect of claim 3, a function of determining whether or not the spike voltage hides the original position detection timing is added. By doing so, there is an effect that more appropriate energization switching can be performed.

According to a fifth aspect of the present invention, instead of calculating the time corresponding to the current energization switching timing time from the previous energization switching timing time and energization switching interval in the fourth aspect, the previous position detection timing is calculated. Since the time corresponding to the time of the current energization switching timing is calculated using the position detection interval and the position detection interval, the same effect as in claim 4 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, to which a control method of a brushless motor is applied.

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

3 is a schematic flowchart for explaining the operation of the brushless motor control device shown in FIG. 1. FIG.

FIG. 4 is a schematic block diagram of a conventional brushless motor control device.

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

1 AC power supply 2 AC / DC converter 3 Inverter circuit 4 Brushless motor (commutator motor) 4a Rotor 4a (of brushless motor 4) 5 Position detection circuit 6 Reference voltage generation circuit 7, 10 Control circuit (microcomputer) 8 Chopping circuit 9 Drive circuit h Spike voltage k Reference voltage (Vdc / 2) R, S, T Winding voltage (terminal voltage of brushless motor 4)

Claims (5)

[Claims] 1. A DC power supply is switched to be supplied to a brushless motor, and a voltage of an armature winding of the brushless motor is compared with a reference voltage to obtain a position detection signal of the comparison result. The position of the rotor of the brushless motor is detected by the method, and a brushless motor control method that switches the energization of the armature winding current of the brushless motor based on the timing of the position detection is used. While the comparison result is masked for a period of time, the energization of the armature winding is switched at a predetermined time when the comparison result is not obtained even after a predetermined time has passed from the current energization switching. Motor control method. 2. A DC power supply is switched to supply it to a brushless motor, and a voltage of an armature winding of the brushless motor is compared with a reference voltage to obtain a position detection signal of the comparison result. A method of controlling a brushless motor that detects the position of the rotor of the brushless motor, and switches energization of the armature winding current of the brushless motor with reference to the timing of the position detection, wherein the position before the position detection While the comparison result is masked for a time shorter than the detection interval, the time of the next energization switching timing is calculated based on the time of the energization switching timing before the current energization switching and the energization switching interval, When the comparison result is not obtained even after a lapse of a predetermined time from the energization switching, the calculated energization switching timing The method of the brushless motor, characterized in that to switch the energization of the armature winding in time. 3. When switching a DC power supply to a brushless motor for inverter control, the applied voltage of the brushless motor is varied by a predetermined chopping signal, while the voltage of an armature winding of the brushless motor and a reference voltage are changed. A voltage is compared, a position detection signal of the comparison result is obtained, the position of the rotor of the brushless motor is detected by the position detection signal, and the armature winding current of the brushless motor is based on the position detection timing. The method of controlling a brushless motor for switching the energization of, wherein the comparison result is masked for a time shorter than the previous position detection interval from the position detection, while the end of the spike voltage generated by the energization switching is detected by the position detection signal. And the end of the detected spike voltage is after the mask,
Further, when the chopping signal is turned off at the same time, the time of the previous energization switching timing and the energization switching interval or the time of the previous position detection timing and the energization switching timing calculated based on the position detection interval are A method for controlling a brushless motor, characterized in that energization of an armature winding is switched. 4. When the DC power supply is switched to be supplied to the brushless motor for inverter control, the applied voltage of the brushless motor is varied by a predetermined chopping signal, while the voltage of the armature winding of the brushless motor and the reference voltage are changed. A voltage is compared, a position detection signal of the comparison result is obtained, the position of the rotor of the brushless motor is detected by the position detection signal, and the armature winding current of the brushless motor is based on the position detection timing. The method of controlling a brushless motor for switching the energization of, wherein the comparison result is masked for a time shorter than the previous position detection interval from the position detection, while the end of the spike voltage generated by the energization switching is detected by the position detection signal. , The end of the spike voltage generated by the current switching is detected after the mask, and When the chopping signal is turned off at the same time, the time corresponding to the current energization switching timing is calculated based on the time of the previous energization switching timing and the energization switching interval, and the calculated time and the current energization are calculated. When the time of the current energization switching timing is late, the time of the next energization switching timing is calculated based on the time of the previous energization switching timing and the energization switching interval. A method of controlling a brushless motor, wherein energization of the armature winding is switched at a time of a calculated energization switching timing. 5. When switching a DC power supply to a brushless motor for inverter control, the applied voltage of the brushless motor is varied by a predetermined chopping signal, while the voltage of an armature winding of the brushless motor and a reference A voltage is compared, a position detection signal of the comparison result is obtained, the position of the rotor of the brushless motor is detected by the position detection signal, and the armature winding current of the brushless motor is based on the position detection timing. The method of controlling a brushless motor for switching the energization of, wherein the comparison result is masked for a time shorter than the previous position detection interval from the position detection, while the end of the spike voltage generated by the energization switching is detected by the position detection signal. , The end of the spike voltage generated by the current switching is detected after the mask, and When the chopping signal is turned off at the same time, the time corresponding to the current energization switching timing is calculated based on the time of the previous position detection timing and the position detection interval, and the calculated time and the current energization are calculated. When the time of the current energization switching timing is late, the time of the next energization switching timing is calculated based on the time of the previous position detection timing and the position detection interval, A method of controlling a brushless motor, wherein energization of the armature winding is switched at a time of a calculated energization switching timing.