JPH11136992A - Inverter control method and equipment for brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of times of occurrence of dead time and to enlarge an operation area by setting smaller the carrier frequency of inverter in response to the increase in the voltage control factor. SOLUTION: When controlling an inverter 7 for driving a brushless DC motor 5 based on a voltage control factor preset and the rotational position of a rotor 5d of a brushless DC motor 5, the carrier frequency of the inverter 7 is set in response to the voltage control factor. Also, a threshold limit value of the carrier frequency is preset and the carrier frequency is gradually reduced until the carrier frequency reaches the threshold limit value. By doing this, the number of times of the occurrence of dead time can be reduced and the output voltage of the inverter can be increased, and the operation area of the brushless DC motor 5 can be enlarged. Also, the occurrence of troubles due to a sudden increase in the inverter output voltage is prevented, thereby stabilizing the operation of the brushless DC motor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor inverter control method and apparatus, and more particularly, to a brushless DC motor based on a preset voltage control rate and a rotational position of a rotor of the brushless DC motor. The present invention relates to an inverter control method and apparatus for controlling an inverter to drive a motor.

[0002]

2. Description of the Related Art Conventionally, as a device for controlling an inverter for driving a brushless DC motor, for example,
A control device having the configuration shown in FIG. 1 has been proposed. This control device has a three-phase inverter 7 for applying an operating voltage to the brushless DC motor 5, and indicates a magnetic pole position of the rotor from a neutral point voltage of a stator winding of the brushless DC motor 5. It has rotation position detection circuits 1 and 3 for generating a rotation position detection signal. Further, it also has an integration signal level detection circuit 2a for detecting the level of the integration signal from the integration circuit 1 included in the rotation position detection circuits 1 and 3.
The microcomputer 4 performs a speed control operation and an efficiency control operation with the rotational position detection signal and the integration signal level detection signal as inputs, generates an inverter gate drive waveform, and supplies the waveform to the three-phase inverter 7 via the driver circuit 7a. Have.

If the control device having the above configuration is adopted, the brushless DC motor 5 is driven by controlling the inverter gate waveform based on the rotational position detection signal and the integrated signal level detection signal, and controlling the three-phase inverter 7. be able to.

[0004]

However, when the control device having the above-described configuration is employed, the carrier frequency of the three-phase inverter 7 is set high so that fine control can be achieved. 7, a dead time inevitably occurs, and the output voltage of the three-phase inverter 7 decreases by the dead time,
The operating area is narrowed in the area where the maximum voltage is desired.

More specifically, when a switching element having a low switching speed, such as a transistor, is used as a switching element of the three-phase inverter 7, the dead time increases, so that the output voltage of the three-phase inverter 7 decreases. The narrowing of the driving area becomes remarkable. If a switching element having a high switching speed such as an IGBT is employed as the switching element of the three-phase inverter 7, each dead time can be reduced. However, if the carrier frequency is increased in accordance with the high switching speed, the dead time is reduced. Since the number of times of occurrence of the time increases, the output voltage of the three-phase inverter 7 decreases, and the operating area becomes narrow (FIG. 3).
Middle B).

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and provides a method and an apparatus for controlling an inverter of a brushless DC motor capable of reducing the number of times of occurrence of dead time and expanding an operation area. It is intended to be.

[0007]

A brushless D according to claim 1
The method of controlling the inverter of the C motor controls the inverter to drive the brushless DC motor based on a preset voltage control rate and the rotational position of the rotor of the brushless DC motor. This is a method in which the carrier frequency of the inverter is set low in response.

According to a second aspect of the invention, there is provided a method of controlling an inverter of a brushless DC motor in which a limit value of a carrier frequency is set in advance, and the carrier frequency is gradually decreased until the carrier frequency reaches the limit value. A brushless DC motor inverter control method according to a third aspect further includes a rotation position detection unit that generates a rotation position detection signal from a neutral point voltage of a stator winding of the brushless DC motor, and is included in the rotation position detection unit. In this method, the level of the integrated signal from the integrating means is determined, and the rate of decrease of the carrier frequency is set in response to the result of the determination.

According to a fourth aspect of the present invention, it is determined whether or not the change amount of the inverter output voltage becomes larger than a predetermined amount by changing the carrier frequency. The decrease rate of the carrier frequency is set to a small value in response to the determination that the carrier frequency is greater than the predetermined amount, and the carrier frequency is reduced in response to the determination that the amount of change in the inverter output voltage is not greater than the predetermined amount. This is a method of setting a large ratio.

According to a fifth aspect of the present invention, there is provided a brushless DC motor inverter control device for controlling an inverter to drive a brushless DC motor based on a preset voltage control rate and a rotational position of a rotor of the brushless DC motor. And a carrier frequency setting means for setting the carrier frequency of the inverter to be small in response to the increase in the voltage control rate.

According to a sixth aspect of the present invention, there is provided an inverter control device for a brushless DC motor, wherein a carrier frequency limit is set in advance, and the carrier frequency is gradually reduced until the carrier frequency reaches the limit. Is adopted. The brushless DC motor inverter control device according to claim 7, further comprising: a rotation position detection means for generating a rotation position detection signal from a neutral point voltage of a stator winding of the brushless DC motor; The level of the integrated signal from the integrating means included in the position detecting means is determined, and the rate of decrease of the carrier frequency is set in response to the determination result.

According to an eighth aspect of the present invention, there is provided an inverter control device for a brushless DC motor, as a carrier frequency setting means, which determines whether or not a change amount of an inverter output voltage becomes larger than a predetermined amount by changing a carrier frequency. In response to the determination that the amount of change in the output voltage is greater than the predetermined amount, the reduction rate of the carrier frequency is set to a small value, and in response to the determination that the amount of change in the inverter output voltage is not greater than the predetermined amount. In this case, the carrier frequency reduction rate is set to be large.

[0013]

According to the brushless DC motor inverter control method of the present invention, the inverter is controlled to drive the brushless DC motor based on a preset voltage control rate and a rotational position of a rotor of the brushless DC motor. In this case, since the carrier frequency of the inverter is set to be small in response to the increase of the voltage control rate, the number of times of dead time is reduced, the inverter output voltage is increased, and the operation area of the brushless DC motor is increased. Can be spread.

According to the brushless DC motor inverter control method of the second aspect, the carrier frequency limit value is set in advance, and the carrier frequency is gradually decreased until the carrier frequency reaches the limit value. In addition to the effect of the item 1, it is possible to prevent the occurrence of inconvenience caused by the sudden increase of the inverter output voltage, and to stabilize the operation of the brushless DC motor.

According to a third aspect of the present invention, there is provided an inverter control method for a brushless DC motor, further comprising a rotational position detecting means for generating a rotational position detection signal from a neutral point voltage of a stator winding of the brushless DC motor. The level of the integrated signal from the integrating means included in the detecting means is determined, and the reduction rate of the carrier frequency is set in response to the result of the determination. The carrier frequency can be reduced within a range in which inconvenience caused by a sudden increase in voltage can be prevented, and the operating area of the brushless DC motor can be quickly expanded.

According to the brushless DC motor inverter control method of the present invention, it is determined whether or not the amount of change in the inverter output voltage becomes larger than a predetermined amount by changing the carrier frequency. The decrease rate of the carrier frequency is set to be small in response to the determination that the amount becomes larger than the predetermined amount, and the carrier frequency is set in response to the determination that the change amount of the inverter output voltage does not become larger than the predetermined amount. Therefore, in addition to the effect of any one of claims 1 to 3, the carrier frequency is reduced within a range in which the inverter output voltage does not become too large, and a sudden increase in the inverter output voltage is achieved. It is possible to prevent the occurrence of inconvenience and to stabilize the operation of the brushless DC motor.

According to the brushless DC motor inverter control device of the present invention, the inverter is controlled to drive the brushless DC motor based on a preset voltage control rate and a rotational position of a rotor of the brushless DC motor. In this case, the carrier frequency of the inverter can be set low in response to the increase in the voltage control rate by the carrier frequency setting means.

Therefore, it is possible to reduce the number of times of occurrence of the dead time, increase the output voltage of the inverter, and thereby expand the operation area of the brushless DC motor. In the brushless DC motor inverter control device according to claim 6, as the carrier frequency setting means, a carrier frequency limit value is set in advance, and the carrier frequency is gradually reduced until the carrier frequency reaches the limit value. Since this is adopted, in addition to the effect of the fifth aspect, it is possible to prevent the occurrence of inconvenience due to a sudden increase in the inverter output voltage, and to stabilize the operation of the brushless DC motor.

According to a seventh aspect of the present invention, there is provided a brushless DC motor inverter control device, further comprising: a rotational position detecting means for generating a rotational position detection signal from a neutral point voltage of a stator winding of the brushless DC motor; As the setting means, a means for judging the level of the integration signal from the integrating means included in the rotational position detecting means and setting the reduction rate of the carrier frequency in response to the judgment result is adopted. In addition to the function of claim 6, the carrier frequency can be reduced within a range in which inconvenience caused by a sudden increase in the inverter output voltage can be prevented, and the operation area of the brushless DC motor can be quickly expanded. can do.

In the inverter control apparatus for a brushless DC motor according to the present invention, the carrier frequency setting means determines whether or not the amount of change in the inverter output voltage becomes larger than a predetermined amount by changing the carrier frequency. In response to the determination that the amount of change in the inverter output voltage is larger than the predetermined amount, the reduction rate of the carrier frequency is set to be small, and it is determined that the amount of change in the inverter output voltage is not larger than the predetermined amount. In this case, the carrier frequency is set so as to increase the rate of decrease in the carrier frequency. In addition to the operation of any one of claims 5 to 7, the carrier frequency is reduced within a range where the inverter output voltage does not become too large. To prevent inconvenience caused by the sudden increase of the inverter output voltage, It is possible to stabilize the operation of the C motor.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a brushless DC motor according to an embodiment of the present invention; FIG. 1 is an electric circuit diagram showing one example of a brushless DC motor control device including a brushless DC motor inverter control device of the present invention.

This brushless DC motor control device comprises an integrator 1, a zero-cross comparator 3, and a microcomputer 4
, A brushless DC motor 5, and a Y-connected resistor circuit 6
And a three-phase inverter 7 controlled by the microcomputer 4. This will be described in more detail. The stator windings 5a, 5b, 5c of the brushless DC motor 5 are Y-connected, and a resistor 6 constituting a Y-connected resistor circuit 6 is connected.
a, 6b, 6c are connected in parallel with the stator windings 5a, 5b, 5c. The output voltage of the three-phase inverter 7 is applied to the stator windings 5a, 5b, 5c and the resistors 6a, 6b, 6
c. In addition, 5d is a rotor.

The integrator 1 has an operational amplifier 1a and a resistor 1b and a capacitor 1c connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 1a. Then, the first neutral point voltage VN obtained at the connection point between the stator windings 5a, 5b, 5c is applied to the non-inverting input terminal of the operational amplifier 1a, and the first neutral voltage VN obtained at the connection point between the resistors 6a, 6b, 6c is obtained. 2 neutral point voltage VM is applied to the inverting input terminal of the operational amplifier 1a. Therefore,
The difference voltage VMN (= VN−VM) between the two neutral point voltages is integrated by the integrator 1, and an integrated signal ∫VMNdt can be obtained.

The zero-cross comparator 3 includes an operational amplifier 3a, a resistor 3b and a light emitting diode 3c connected in series between a non-inverting input terminal and an output terminal of the operational amplifier 3a, a non-inverting input terminal of the operational amplifier 3a and a ground terminal. And a pull-up resistor 3 connected to a connection point between the resistor 3b and the light emitting diode 3c.
e, a phototransistor 3f for receiving light from the light emitting diode 3c, and a resistor 3g connected between a collector terminal of the phototransistor 3f and an operation power supply terminal. Then, the emitter terminal of the phototransistor 3f is directly connected to the ground,
Output the rotation position detection signal SINT from the collector terminal of the control circuit. However, the photocoupler including the light emitting diode 3c and the phototransistor 3f may be omitted, and the rotational position detection signal SINT may be directly output from the output terminal of the operational amplifier 3a. Therefore, it is possible to output a rotational position detection signal SINT whose level is inverted each time a zero cross of the integration signal ∫VMNdt occurs. Then, the rotational position detection signal SIN
T is supplied to the microcomputer 4.

The comparing section 2 in which the comparison level is set based on the comparison level setting signal output from the microcomputer 4
a, the integrated signal 積分 VMNdt is supplied to perform a level determination, and the level determination result signal is supplied to the flip-flop circuit 2b.
And the data (level detection signal) held by the flip-flop circuit 2 b is supplied to the microcomputer 4. The reset signal output from the microcomputer 4 is supplied to the flip-flop circuit 2b.

The microcomputer 4 outputs a rotational position detection signal SI
With NT as an input, a new rotation position detection signal for inverter control is generated, and based on the newly generated rotation position detection signal, for example, speed control and efficiency control are performed to generate a voltage amplitude command and a phase command. Then, the generated pulse waveform signal is subjected to pulse width modulation based on the voltage amplitude command and the phase command to generate an inverter waveform signal, which is supplied to the three-phase inverter 7 via the drive circuit 7a. The microcomputer 4 has a carrier cycle setting function of the three-phase inverter 7. Since the speed control, efficiency control, and the like in the microcomputer 4 are conventionally known, detailed description will be omitted. The overcurrent detection circuit 7 b detects that the input current of the three-phase inverter 7 has become overcurrent, generates an overcurrent detection signal, and supplies the signal to the microcomputer 4.

Next, the operation of the rotational position detecting device having the above configuration will be described. A first neutral point voltage VN obtained at a connection point between the stator windings 5a, 5b, and 5c at which an induced voltage is generated is applied to a non-inverting input terminal of the operational amplifier 1a and a resistor 6a, 6b, and 6c. The difference voltage VMN (difference voltage between the two neutral point voltages) is integrated by applying the second neutral point voltage VM obtained at the connection point to the inverting input terminal of the operational amplifier 1a, and the integration signal ∫VMNdt
Can be obtained. Then, by supplying the integrated signal ∫VMNdt to the zero-cross comparator 3, it is possible to obtain a rotational position detection signal whose level is inverted every time a zero-cross of the integrated signal ＮVMNdt occurs.

This rotation position detection signal is supplied to the microcomputer 4 as an interrupt signal, and the microcomputer 4 controls the speed control,
Generate inverter waveform signal by performing efficiency control, etc.
It is supplied to the three-phase inverter 7 via the drive circuit 7a. The microcomputer 4 also performs a carrier frequency setting process based on the voltage control rate Ks and the integrated signal level.

FIG. 2 is a flowchart for explaining one embodiment of the carrier frequency setting process. In this embodiment and other embodiments, the carrier cycle is set, and the amount of change in the carrier cycle when the voltage control rate is 100% is set to car_up1.
When the voltage control rate is less than 99.8% and 99.6% or more, the change amount of the carrier cycle is represented by car_down1.
In addition, the change amount of the carrier cycle when the voltage control rate is less than 99.6% is set to car_down2. Note that car_up1, car_down
1. The value of car_down2 is experimentally determined based on, for example, a driven brushless DC motor. Then, the values of car_up1 and car_down1 are
It is preferable to set the value sufficiently smaller than the value of _down2 so that the inverter output voltage does not suddenly increase. Also, the value of car_down2 is set to a large value so as to obtain an appropriate carrier cycle in a short time in consideration of the fact that when the voltage control rate is reduced and the carrier cycle is long, the integrated signal becomes unstable. Is preferably set. Here, each voltage control ratio can be determined experimentally, for example.

In step SP1, the voltage control rate is 1
If the voltage control rate is 100% or higher, it is determined whether or not the integrated signal level is higher than the comparison level in step SP2. In step SP3, the carrier cycle is extended by car_up1, and in step SP4, the maximum value of the carrier cycle is limited (for example, as a result of performing the processing of step SP3, the carrier cycle exceeds the preset maximum value). In this case, the process of setting the carrier cycle to the maximum value) is performed, and the series of processes is terminated as it is.

In step SP1, the voltage control rate is 10
If it is determined that it is less than 0%, step SP5
, The voltage control rate is less than 99.8% and 99.6%
It is determined whether or not the voltage control rate is less than 99.8% and 99.6% or more. In step SP6, it is determined whether or not the integrated signal level is less than the comparison level.
If the integration signal level is lower than the comparison level, in step SP7, the carrier cycle is set to car_down.
In step SP8, the carrier cycle is reduced to the minimum value if the carrier cycle falls below a preset minimum value as a result of performing the processing in step SP7. Is performed, and the series of processing ends.

In step SP5, the voltage control rate is 9
If it is determined that it is less than 9.8% and not more than 99.6%, in step SP9, the voltage control rate is 99.
It is determined whether it is less than 6%, and the voltage control rate is 99.6.
%, The carrier cycle is shortened by car_down2 in step SP10, and the process of limiting the minimum value of the carrier cycle in step SP11 (for example, as a result of performing the process of step SP7, the carrier cycle is set in advance) If the value falls below the set minimum value, the process of setting the carrier cycle to the minimum value is performed, and the series of processes ends.

When it is determined in step SP2 that the integrated signal level is not higher than the comparison level, when it is determined in step SP6 that the integrated signal level is not lower than the comparison level, or when the voltage control rate is 99.6 in step SP9. If it is determined that the value is not less than%, the series of processing ends. Therefore, by extending the carrier period while keeping the inverter output voltage from suddenly increasing, the dead time is reduced, the inverter output voltage is sufficiently increased, and the voltage in the high-speed and high-load region is maximized. The operation area can be widened in a desired region (the operation area can be increased by about 5 to 10% as compared with the case where the conventional method is adopted). When the voltage control ratio decreases,
By shortening the carrier cycle, the integration signal can be prevented from becoming unstable, and the brushless DC motor can be stably controlled.

Next, a further explanation will be given with reference to FIGS. FIG. 4 is a signal waveform diagram showing a rotational position detection signal and an inverter gate driving waveform of an ideal 100% voltage control rectangular wave. In the signal waveform of FIG. 4, the switching elements of the upper arm and the lower arm of the corresponding phase are controlled at the timing when the phase correction is applied to the edge of the rotation position detection signal, and the signal is caused by the carrier cycle. There is no dead time, and only a dead time associated with switching of the switching elements of the upper arm and the lower arm exists.

Therefore, the output voltage of the inverter can be made sufficiently large, and as shown by A in the load-speed characteristic of FIG. be able to. FIG. 5 is a signal waveform diagram showing a rotation position detection signal and a conventional inverter gate driving waveform of a rectangular wave having a voltage control rate of 100%.

In the signal waveform of FIG. 5, the switching elements of the upper arm and the lower arm of the corresponding phase are controlled at the timing when the phase of each edge of the rotational position detection signal is corrected, and the carrier period is adjusted. There are many dead times caused by the switching of the switching elements of the upper arm and the lower arm.

Therefore, the inverter output voltage is reduced by the amount of the dead time, and as shown by B in the load-speed characteristic of FIG. Becomes narrower. FIG. 6 is a signal waveform diagram showing the rotational position detection signal and the inverter gate drive waveform of the rectangular wave of the voltage control rate of 100% of this embodiment.

In the signal waveform of FIG. 6, the switching elements of the upper arm and the lower arm of the corresponding phase are controlled at the timing when the phase of the edge of the rotational position detection signal is corrected, and the carrier cycle And a dead time associated with switching of the switching elements of the upper arm and the lower arm. However, the number of dead times due to the carrier cycle is smaller than the number of dead times in the signal waveform of FIG.

Therefore, the output voltage of the inverter becomes larger than that of the signal waveform of FIG. 5 by the reduced dead time, and as shown by C in the load-rotational speed characteristic of FIG.
The operating area can be expanded in a region where the voltage in a high speed / high load region is desired to be maximized. FIG. 7 is a flowchart illustrating another embodiment of the carrier frequency setting process.
In the flowchart of FIG. 7, the value of car_up0 is set to be larger than the value of car_up1,
The values of r_down0 are car_down1, car_
It is set larger than the value of down2.

In step SP1, it is determined whether the carrier cycle can be largely changed. More specifically, whether the inverter output voltage does not change at all even if the carrier cycle is changed, or the change width of the inverter output voltage is extremely small (the change width of the inverter output voltage is smaller than a predetermined reference value that is sufficiently small). It is sufficient to determine whether or not it is smaller. For example, the determination can be made by calculating the change width of the inverter output voltage from the carrier cycle at the corresponding time and comparing the magnitude with a predetermined reference value.

If it is determined in step SP1 that the carrier cycle may be largely changed, it is determined in step SP2 whether or not the voltage control rate is 100% or more. If there is, in step SP3, the carrier cycle is set to car_up0
Then, in step SP4, a process for limiting the maximum value of the carrier cycle is performed, and the series of processes is ended as it is.

In step SP2, the voltage control rate is 10
If it is determined that it is not 0% or more, step SP5
In, it is determined whether or not the voltage control rate is less than 99.8%. If the voltage control rate is less than 99.8%,
In step SP6, the carrier cycle is set to car_do
In step SP7, a process for limiting the minimum value of the carrier cycle is performed, and the series of processes is completed.

In step SP5, the voltage control rate is 9
If it is determined that the difference is not less than 9.8%, the series of processing ends. If it is determined in step SP1 that the carrier cycle should not be significantly changed, it is determined in step SP8 whether the voltage control rate is 100% or more. If the voltage control rate is 100%, In step SP9, it is determined whether or not the integrated signal level is equal to or higher than the comparison level. If the integrated signal level is equal to or higher than the comparison level, in step SP10, the carrier cycle is extended by car_up1, and step SP1 is performed.
In step 1, a process for limiting the maximum value of the carrier cycle is performed, and the series of processes is terminated as it is.

In step SP8, the voltage control rate is 10
If it is determined that it is less than 0%, step SP1
2, the voltage control ratio is less than 99.8% and 99.6%
%, And if the voltage control rate is less than 99.8% and 99.6% or more, it is determined in step SP13 whether or not the integrated signal level is less than the comparison level. If the level is below the comparison level,
In step SP14, the carrier cycle is set to car_d
In step SP15, a process for limiting the minimum value of the carrier cycle is performed, and the series of processes is completed.

In step SP12, when it is determined that the voltage control rate is less than 99.8% and not more than 99.6%, in step SP16, the voltage control rate becomes 9
It is determined whether or not the voltage control rate is less than 9.6%.
If it is less than 9.6%, in step SP17, the carrier cycle is shortened by car_down2, and in step SP18, processing for limiting the minimum value of the carrier cycle is performed, and the series of processing is ended as it is.

When it is determined in step SP9 that the integrated signal level is not higher than the comparison level, when it is determined in step SP13 that the integrated signal level is not lower than the comparison level, or when the voltage control ratio is 99.6 in step SP16. If it is determined that the value is not less than%, the series of processing ends. Therefore, if the inverter output voltage does not change or the inverter output voltage hardly changes even if the carrier cycle is changed, the change width of the carrier cycle is set to be large, and if the carrier cycle is changed, the inverter output voltage is changed. If the voltage fluctuates to a non-negligible level, extend the carrier period while keeping the inverter output voltage from suddenly increasing to reduce the dead time, increase the inverter output voltage sufficiently, and increase the speed. -The operating area can be widened in the area where the voltage in the high load area is desired to be maximized (the operating area can be expanded by about 5 to 10% as compared with the case where the conventional method is adopted). Also,
When the voltage control rate is reduced, the carrier cycle is shortened to prevent the integrated signal from becoming unstable, and the brushless DC motor can be controlled stably.

[0047]

According to the first aspect of the present invention, the number of dead times can be reduced, the inverter output voltage can be increased, and the operating area of the brushless DC motor can be extended. According to the second aspect of the present invention, in addition to the effect of the first aspect, it is possible to prevent the occurrence of inconvenience caused by a sudden increase in the output voltage of the inverter and to stabilize the operation of the brushless DC motor. To play.

According to a third aspect of the present invention, in addition to the effects of the first or second aspect, the carrier frequency is reduced within a range in which inconvenience caused by a rapid increase in the inverter output voltage can be prevented. This has a unique effect that the operation area of the brushless DC motor can be quickly expanded. According to a fourth aspect of the present invention, in addition to the effect of any one of the first to third aspects, the carrier frequency is reduced within a range where the inverter output voltage does not become too large.
As a result, it is possible to prevent the occurrence of inconvenience due to a sudden increase in the inverter output voltage, and to stabilize the operation of the brushless DC motor.

The invention of claim 5 has a specific effect that the number of occurrences of dead time can be reduced, the output voltage of the inverter can be increased, and the operating area of the brushless DC motor can be expanded. The invention of claim 6 is
In addition to the effect of the fifth aspect, the present invention has a unique effect that it is possible to prevent the occurrence of inconvenience due to a sudden increase in the inverter output voltage and to stabilize the operation of the brushless DC motor.

According to a seventh aspect of the present invention, in addition to the effects of the fifth or sixth aspect, the carrier frequency is reduced within a range in which the occurrence of inconvenience due to a sudden increase in the inverter output voltage can be prevented. This has a unique effect that the operation area of the brushless DC motor can be quickly expanded. According to an eighth aspect of the present invention, in addition to the effect of any of the fifth to seventh aspects, the carrier frequency is reduced within a range where the inverter output voltage does not become too large.
As a result, it is possible to prevent the occurrence of inconvenience due to a sudden increase in the inverter output voltage, and to stabilize the operation of the brushless DC motor.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one example of a brushless DC motor control device including a brushless DC motor inverter control device of the present invention.

FIG. 2 is a flowchart illustrating one embodiment of a carrier frequency setting process.

FIG. 3 is a diagram showing load-speed characteristics.

FIG. 4 shows a rotational position detection signal and an ideal voltage control rate of 100.
FIG. 7 is a signal waveform diagram showing a% square wave inverter gate driving waveform.

FIG. 5 shows a rotational position detection signal and a conventional voltage control rate of 100%.
It is a signal waveform diagram which shows the inverter-gate drive waveform of a square wave.

6 is a signal waveform diagram showing a rotational position detection signal and a 100% rectangular voltage inverter gate drive waveform of the embodiment of FIG. 1;

FIG. 7 is a flowchart illustrating another embodiment of a carrier frequency setting process.

[Explanation of symbols]

 Reference Signs List 1 integration circuit 3 zero cross comparator 4 microcomputer 5 brushless DC motor 5a, 5b, 5c stator winding 5d rotor 7 three-phase inverter

Claims (8)

[Claims] An inverter control for controlling an inverter (7) to drive a brushless DC motor (5) based on a preset voltage control rate and a rotational position of a rotor (5d) of the brushless DC motor (5). A method of controlling an inverter for a brushless DC motor, comprising: setting a carrier frequency of an inverter (7) to be small in response to an increase in the voltage control ratio. 2. The brushless D according to claim 1, wherein a limit value of the carrier frequency is set in advance, and the carrier frequency is gradually reduced until the carrier frequency reaches the limit value.
Inverter control method for C motor. 3. A rotation position detection means (1) (3) for generating a rotation position detection signal from a neutral point voltage of the stator windings (5a) (5b) (5c) of the brushless DC motor (5). And determining the level of the integration signal from the integration means (1) included in the rotational position detection means (1) and (3), and setting the reduction rate of the carrier frequency in response to the determination result. An inverter control method for a brushless DC motor according to claim 2. 4. It is determined whether or not the amount of change in the inverter output voltage is greater than a predetermined amount by changing the carrier frequency, and it is determined that the amount of change in the inverter output voltage is greater than the predetermined amount. The method according to claim 1, wherein the decrease rate of the carrier frequency is set to be small in response to the determination, and the decrease rate of the carrier frequency is set to be large in response to the determination that the amount of change in the inverter output voltage is not larger than the predetermined amount. 3. Brushless D according to any one of 3.
Inverter control method for C motor. 5. Inverter control for controlling an inverter (7) to drive a brushless DC motor (5) based on a preset voltage control rate and a rotational position of a rotor (5d) of the brushless DC motor (5). An inverter control device for a brushless DC motor, comprising: a carrier frequency setting means (4) for setting a carrier frequency of an inverter (7) small in response to an increase in the voltage control ratio. 6. The carrier frequency setting means according to claim 5, wherein the carrier frequency setting means sets a limit value of the carrier frequency in advance and gradually decreases the carrier frequency until the carrier frequency reaches the limit value. Inverter control device for brushless DC motor. 7. A rotation position detecting means (1) (3) for generating a rotation position detection signal from a neutral point voltage of the stator windings (5a) (5b) (5c) of the brushless DC motor (5). The carrier frequency setting means (4) determines the level of the integrated signal from the integrating means (1) included in the rotational position detecting means (1) and (3), and responds to this determination result to determine the carrier frequency. 6. The method according to claim 5, wherein a reduction ratio is set.
7. An inverter control device for a brushless DC motor according to claim 6. 8. A carrier frequency setting means (4) for judging whether or not the change amount of the inverter output voltage is larger than a predetermined amount by changing the carrier frequency. The decrease rate of the carrier frequency is set to be small in response to the determination that the carrier frequency has become larger than the predetermined value, and the decrease rate of the carrier frequency is set to be small in response to the determination that the amount of change in the inverter output voltage does not become larger than the predetermined amount. The inverter control device for a brushless DC motor according to any one of claims 5 to 7, which is set to be large.