JP3131157B2 - Drive circuit for brushless DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a PWM (Puls Wi)
The present invention relates to a drive circuit for a brushless DC motor that performs speed control and torque control by a dth modulation circuit.

[0002]

2. Description of the Related Art Noise reduction of a three-phase brushless DC motor has become an important issue. As a method of energizing the motor coil, a bipolar energizing method with an electrical angle of 120 degrees is currently the mainstream because it is inexpensive and efficient. In a small-sized motor having a relatively small output, the current of the motor coil is controlled, and soft switching is performed every three-phase switching to achieve low noise. However, when driving a motor with a large output to some extent, especially when controlling the speed and torque, the difference between the power supply voltage and the voltage applied between the motor coils increases, and the power transistor that drives the motor coil at the output stage of the drive circuit Since the power loss becomes extremely large, drive control by a PWM circuit is generally performed. FIG. 3 shows an example of such a PWM circuit. In the figure, 1 is a multi-pole magnetized magnet rotor in the motor, 2 is a Hall element group for detecting the position of the magnet rotor 1, 3 is an amplifier group for amplifying the signal of the Hall element group 2,
Reference numeral 4 denotes a logic circuit that generates a drive signal for energizing the power transistor group 8 by 120 degrees with a signal having a three-phase 120 ° phase difference of the amplifier group 3, 5 denotes a rotation speed command voltage generation circuit,
6 is P for converting a DC voltage to a pulse waveform width of a certain frequency.
A WM circuit, 7 is a transistor group for switching the output signal of the logic circuit 4 with a signal of the PWM circuit 6, and 8 is a power transistor group of NPN and PNP for driving a motor coil group 9. The motor coil group 9 is wound around the stator 9a.

FIG. 4 is a time chart showing signal waveforms at various parts in FIG. As shown in the figure, 4-a, 4-b, 4
Reference numeral -c denotes an output of the logic circuit 4, and reference numeral 4-d denotes a one-phase driving waveform of the motor coil group 9, in which the PNP transistor in the upper arm of the power transistor group 8 is turned on in the positive direction and in the negative direction. On the side, the NPN transistor in the lower arm of the power transistor group 8 is on, and in other states, the transistors of the power transistor group 8 are off. 4-e is an enlarged view of one cycle of 4-d, 4-f is an output waveform of the PWM circuit 6, 4-g is a current waveform of one phase of the motor coil group 9, and the other phase is located at the center of the waveform. A fall due to phase switching and a steep fall at the end are occurring.

[0004]

However, in the conventional brushless DC motor drive circuit described above, a current including harmonics is supplied to the motor coil group 9 by switching at each phase switching, and the motor coil group 9 is driven. , Stator 9
a, the motor case and the like are vibrated, and as a result, the vibration is transmitted through the air and becomes noise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to realize a drive circuit for a brushless DC motor which suppresses noise due to vibration and has low noise.

[0006]

According to the present invention, there is provided a stator having a three-phase motor coil wound thereon, a magnet rotor rotatably supported opposite to the stator, and A Hall element group for detecting the position of the magnet rotor and three drive signals each having a 180-degree conduction drive waveform are formed by three-phase signals generated from the signals of the Hall element group and having a phase difference of 120 degrees from each other. Generating means and a normal PW for controlling the rotational speed
In the drive circuit of the brushless DC motor having the M circuit, the signal of the Hall element group is used to determine that one or more of the energized drive sections
A timing circuit for detecting a timing between 20 degrees and 180 degrees, a waveform generation circuit for generating a saw-tooth wave by a signal of the timing circuit, and a software for changing a duty pulse width based on a voltage waveform of the waveform generation circuit P
Between the WM circuit and the last electrical angle of the energization, a signal obtained by gradually changing the on-duty of the soft PWM circuit is applied to each phase of the three-phase motor coil, and the on-duty of the last energization is gradually reduced. And an energizing means for energizing.

In addition, the above-mentioned PWM circuit for changing the on-duty pulse width in accordance with a command voltage and the above-mentioned soft PWM circuit for changing the on-duty pulse width at the end of energization are provided. The PWM between the normal energizing angle and the energizing end energizing angle for each energization.
It has a function of switching between the circuit and the soft PWM circuit.

Further, in the soft PWM circuit, a voltage of a sawtooth wave during the last energization angle is superimposed on the command voltage during the normal energization angle. 3. A drive circuit for a brushless DC motor according to 2.

[0009]

FIG. 1 is a circuit diagram showing an embodiment of a drive circuit for a brushless DC motor according to the present invention. As shown in the drawing, in addition to the configuration diagram of FIG. 3, reference numeral 11 denotes a synthesizing circuit for synthesizing three-phase position signals, and 10 denotes a synthesizing circuit 1
A timing circuit for detecting the electrical angle timing of the energized drive section 120 to 180 degrees from the signal No. 1 and the six drive signals generated by the logic circuit 4a. 12 is a waveform generating circuit for generating a sawtooth voltage waveform by a signal of the timing circuit 10, and 6a is a soft PWM for changing a pulse width of a duty by an output of the waveform generating circuit 12. A circuit 13 for selecting one of a signal of the PWM circuit 6 and a signal of the soft PWM circuit 6a in accordance with a signal of the logic circuit 4a; 6 or an upper transistor group switched by the soft PWM circuit 6a, 7
b denotes a lower transistor group for switching the lower arm transistor of the power transistor group 8 by the PWM circuit 6 or the soft PWM circuit 6a. The energizing means for gradually energizing the on-duty at the end of energization and energizing the power supply includes an energization command generation circuit 13, an upper transistor group 7a, a lower transistor group 7b, and a power transistor group 8. Note that P
The function of switching between the WM circuit 6 and the soft PWM circuit 6a is incorporated in the energization command generation circuit 13.

Next, referring to the timing chart of FIG.
The operation of the circuit of FIG. As shown in FIG.
-B and 2-c are output signals of the logic circuit 4a and are three-phase signals having a phase difference of 120 degrees, and 2-d, 2-e and 2-f are outputs of the synthesizing circuit 11 and a one-phase 2- There is a positional relationship where the 2-d waveform rises at a position where the conduction angle of the a waveform is 150 degrees, and the same relationship exists for the other two phases. 2-j is 2
-A, 2-b, 2-c and outputs of the timing circuit 10 synthesized from 2-d, 2-e, 2-f, and 2-k is an output of the waveform generation circuit 12. Also, the PWM circuits 6, 6a
Have a characteristic that the on-duty becomes narrow as the input DC voltage rises.

2-l is an enlargement of the 2-k time scale.
Assuming that a section from 0 to 180 degrees is θ2, PW
As the input voltage of the M circuit 6 rises, the on-duty becomes 2-
It gradually narrows like m. The section of the conduction angle θ1 is PWM
The output of the circuit 6 is supplied to the soft PWM circuit 6a in the interval θ2.
Is selected and output by the switching function in the energization command generation circuit 13, and the motor coil group 9 is energized via the transistor group 8 by a switch signal generated by the upper transistor group 7a and the lower transistor group 7b. .

Reference numerals 2-g, 2-h, and 2-j denote one-phase current waveforms when a resistor is connected in place of the motor coil group 9 and the soft PWM circuit 6a is not provided. θ
The mesh portion 2 is a portion where the above-mentioned on-duty becomes gradually narrower, and the current in this section smoothly and gradually decreases. In the actual load of the motor coil group 9, the current waveform rises as indicated by broken lines 2-g, 2-h, and 2-j due to the inductance of the motor coil group 9 at the beginning of energization.
2-n is the actual current waveform of the motor coil group 9, and no distortion or sharp change in the current waveform is observed.

Further, since the emitter of the NPN transistor of the waveform generating circuit 12 has the same potential as the rotation speed command voltage, even if the rotation speed command voltage rises from V1 to V2 as indicated by 2-l, the current is not applied. In the section of the angle θ2, the on-duty can be smoothly reduced from that state. This means that, when the motor is used with its speed controlled, the rotation speed command voltage automatically changes according to the feedback signal, but the motor operates smoothly accordingly.

It is well known that the current waveform of the motor coil group 9 can be further improved by detecting and feeding back the current flowing through the entire motor and the midpoint voltage of the star-connected motor coil.

[0015]

As described above, in the drive circuit of the brushless DC motor according to the present invention, it is possible to smoothly lower the end of energization when the energized phase of the motor coil is switched while driving the soft PWM circuit. As a result, distortion including a harmonic and a steep change in the current waveform of the motor coil are eliminated, so that motor noise can be significantly reduced.

Further, noise is further reduced by switching between a PWM circuit having a normal energization angle and a soft PWM circuit at the end of energization.

Further, even when the motor is controlled in speed by superimposing a sawtooth voltage at the end of energization on a normal command voltage, the motor coil current at the end of energization can be smoothly reduced, so that noise is further reduced. Can be done.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a brushless DC motor drive circuit according to the present invention.

FIG. 2 is a diagram showing an operation timing chart of a drive circuit of a brushless DC motor according to the present invention and waveforms of respective parts.

FIG. 3 is a circuit configuration diagram according to a conventional technique.

4 is a diagram showing an operation timing chart of the circuit of FIG. 3 and a waveform of each part.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnet rotor 2 ... Hall element group 3 ... Amplifier group 4 ... Logic circuit 4a ... Logic circuit of 180 degree conduction 5 ... Rotation speed command voltage generation circuit 6 ... PWM circuit 6a ... Soft PWM circuit 7 ... ... Transistor group 7a ... Upper transistor group 7b ... Lower transistor group 8 ... Power transistor group 9 ... Motor coil group 9a ... Stator 10 ... Timing circuit 11 ... Synthesis circuit 12 ... Waveform generation circuit 13 ... Energization command generation circuit 2- Output signal a ... 4 2-b ... 4 output signal 2-c ... 4 output signal 2-d ... 11 output signal 2-e ... 11 output signal 2-f ... 11 output signal 2-g ... One-phase current waveform with resistive load 2-h ... One-phase current waveform with resistive load 2-i ... One-phase current waveform with resistive load 2-j ... 10 output signal 2-k ... 12 2-l ... 2-k time scale enlarged view 2-m ... 6a output signal 2-n ... a certain phase motor coil current waveform 4-a ... 4 output signal 4-b ... 4 output Signal 4-c ... 4 output signal 4-d ... one-phase current waveform with resistance load 4-e ... 4-d time scale enlarged view 4-f ... 6 output signal 4-g ... one phase Motor coil current waveform

Claims (3)

(57) [Claims] 1. A stator on which a three-phase motor coil is wound, a magnet rotor rotatably supported opposite the stator, a hall element group for detecting the position of the magnet rotor, and the hall element Means for generating six drive signals each having a 180-degree conduction drive waveform by three-phase signals having a phase difference of 120 electrical degrees formed from the group of signals, and a normal PWM circuit for controlling the rotation speed And a timing circuit for detecting an electrical angle timing of an end period of energization of approximately 120 degrees to 180 degrees of an energization drive period from a signal of the Hall element group, and a sawtooth signal based on a signal of the timing circuit. A waveform generating circuit for generating a waveform, a soft PWM circuit for changing a duty pulse width according to a voltage waveform of the waveform generating circuit, Between the electricity end-stage electrical angle, the soft PW
And an energizing means for energizing the three-phase motor coil driving transistor group by adding a signal obtained by gradually changing the on-duty of the M circuit, and gradually reducing the on-duty at the end of energization. And a brushless DC motor drive circuit. 2. The PWM circuit for changing an on-duty pulse width according to a command voltage, and the soft PWM for changing an on-duty pulse width at the end of energization.
Wherein the energizing means has a function of switching between the PWM circuit and the soft PWM circuit between the normal energizing angle and the last energizing angle for each phase energization. Item 2. A brushless DC motor drive circuit according to item 1. 3. The soft PWM circuit according to claim 1, wherein a sawtooth voltage during the last energization angle is superimposed on the command voltage during the normal energization angle.
A driving circuit for a brushless DC motor according to claim 2.