JPH09103090A - Drive circuit for brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit for brushless motors which can set any low speed, start at low-speed rotation without fail, increase motor efficiency and is simply constituted a low price. SOLUTION: This drive circuit for brushless motors consists of a distribution circuit 7 that distributes current to be passed thorough two stator windings 2, 3 according to signals from a magnetic pole position detecting element 1; a phase delaying means 8 that delays the phase of signals from the magnetic pole position detecting element 1; a first zero-cross comparator 14 that converts the output of the phase delaying means 8 into pulses; a logic circuit 20 that detects the amount of phase delay of the first zero-cross comparator 14; and a passed current interrupting means 21 that interrupts the initial portion of the current passed through the stator windings in every cycle. Furthermore, a phase advancing means 15 is installed in parallel with the phase delaying means 8, and a means is added which interrupts the initial and final portions of the current passed through the stator windings 2, 3 at every cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a brushless motor used for driving a fan or the like.

[0002]

2. Description of the Related Art FIGS. 5 and 6 are diagrams showing a conventional drive circuit for a brushless motor.

A conventional brushless motor drive circuit is disclosed in, for example, Japanese Patent Laid-Open No. 190908/1993. That is, there is a system in which one phase of the two-phase stator windings 2 and 3 is opened as shown in FIG. 5 and a delay system in which the time constant of the charging circuit is used as shown in FIG.

In FIG. 5, output transistors 4 and 5 for selectively switching the energization to the stator windings 2 and 3 in response to a signal from the magnetic pole position detecting element 1 of the permanent magnet rotor, and an open phase switching switch 50. A phase loss switching circuit 51 and a start compensation circuit 52 are provided. In response to the operation of the open-phase changeover switch 50, the open-phase changeover circuit 51 stops energizing the one-phase stator winding (any one of 2, 3), so that the rotation speed decreases. Also, if a restrained state occurs during this open-phase operation, a point where there is no starting torque occurs, so restart may not occur. Therefore, the start compensation circuit 52 operates by the signal from the magnetic pole position detection element 1, and the phase loss switching circuit 51 stops the phase loss operation.

In FIG. 6, the signal of the magnetic pole position detecting element 1 is amplified by the differential amplifier 6, and the output transistors 4 and 5 are driven via the distribution circuit 7. Speed command circuit 60
Is a rotation pulse generating circuit 61, a resistor 62, a capacitor 6
3, a charging circuit 65 including a transistor 64 and a comparator 14. Also, the speed switching means 66
Is composed of a transistor 67 and a resistor 68.

As shown in the figure, a rotation pulse generation circuit 60
Is a circuit for shaping the sine-wave output of the differential amplifier 6 into a rectangular wave and then generating a short-time pulse.
The electric charge charged in the capacitor 63 is extracted by. When the voltage of the capacitor 63 reaches the reference voltage divided by the resistors 12 and 13 by the charging circuit 65, the comparator 14 operates and a current flows through the stator winding. That is, the initial portion of energization is cut off from the start of energization to a certain time. The resistor 68 sets the above reference voltage value,
The transistor 67 is activated when the reference voltage value is close to the zero voltage value.

FIG. 9 shows operation waveforms (9-a).
Is the output voltage waveform of the differential amplifier 6, (9-b), (9-
c) is the output waveform of the distribution circuit 7 at full speed, (9-d) is the output waveform of the rotation pulse generating circuit 61 generated at the zero crossing of (9-a), and (9-e) is the charging circuit 6.
In the voltage waveform of the capacitor 63 of 5, the potential of V7 is the resistance 1
It is decided by 2, 13, 68. (9-f) is the comparator 1
4 is connected to the distribution circuit 7 and the result (9-
g) and the stator current as shown by the solid line in (9-h) flows.
The broken lines (9-g) and (9-h) show the stator current waveform at full speed.

[0008]

However, in the case of such a conventional drive circuit for a brushless motor, in the drive circuit of FIG. 5, the rotational speed is lowered by the open-phase operation, so an arbitrary low speed is achieved. However, there is a problem that starting compensation for the constraint in the open-phase operation is required.

Further, in the drive circuit of FIG. 6, although the above problems are solved, a complicated circuit configuration such as a rotation pulse generation circuit and a charging circuit is required, and in the conventional speed setting, the rotor winding is used. There is a problem in that the current supplied to the wire is only in the final stage and the motor efficiency deteriorates.

The present invention has been made in order to solve the above-mentioned problems, and can be set to an arbitrary low speed, ensures reliable starting even at low speed rotation, has high motor efficiency, and has a simple structure and is inexpensive. A brushless motor drive circuit is provided.

[0011]

To achieve this object, in the present invention, as shown in FIG. 1, a magnetic pole position detecting element of a permanent magnet rotor and a differential for amplifying a signal of the magnetic pole position detecting element. An amplifier, a distribution circuit for distributing a current flowing to the two stator windings according to the output of the differential amplifier, a phase delay means for further delaying the phase of the output of the differential amplifier, and the phase delay. A first zero-cross comparator for converting the output of the means into a pulse, a logic circuit for detecting the amount of phase delay of the first zero-cross comparator, and the output of the logic circuit for energizing the stator winding for each cycle. An energizing current interruption means for interrupting the initial portion of the electric current is provided.

Further, a phase advance means is provided in parallel with the phase delay means, and means for adding to the initial portion of the energizing current of the stator winding for each cycle and cutting off the final portion is also provided.

In this brushless motor drive circuit, as shown in FIG. 2, the speed switching transistor is turned on to start from a low speed, the phase delay means causes a phase delay, and the waveform is shaped into a rectangular waveform. The logic circuit detects the amount of phase delay, calculates the cutoff waveform, and cuts off the initial portion of the conduction current. Also in the case of phase advance, the cutoff waveform is calculated in parallel in the same manner to cut off the final part of the conduction current. After that, the speed switching transistor is turned off to start high speed operation.

When the motor is started, the output of the phase delay means
The phase difference between the stator winding energization command signals becomes zero, and the cutoff pulse does not occur. As the motor speed increases, the frequency of the magnetic pole position detection element rises, and the phase of the phase delay means gradually delays. The section is gradually shortened, and it rotates in balance at the set speed.

If the phase advance means is provided separately from the phase delay means, the cutoff pulse is not generated at the time of start-up as described above, but the phase of the phase advance means advances as the motor speed increases. The width of the terminal cutoff pulse also gradually becomes longer, and the energization period gradually becomes shorter while the terminal end part of the energization is cut off. At this time, if the initial energization portion is also cut off, the energization section is only in the vicinity of the center of the energization command signal, the set low rotation speed is achieved, and the operation can be performed at the optimum value of the motor efficiency.

[0016]

FIG. 3 is a diagram showing an embodiment of a drive circuit for a brushless motor according to the present invention. Instead of the speed command circuit 60 and the speed switching circuit 66 shown in FIG. 6 which are conventional drive circuits. The phase delay circuit 8 and the first zero-cross comparator 14 are provided. As shown in the figure, in the case of low speed rotation, the speed switching transistor 9 is in the ON state, a phase delay occurs between the resistor 10 and the capacitor 11, and the phase of the sinusoidal voltage waveform of the differential amplifier 6 becomes the resistor 10. It is delayed by the time constant of the capacitor 11. The signal having the delayed phase is shaped into a rectangular wave by the first zero-cross comparator 14, the amount of delay of the phase is detected by the logic circuit 20, and the energization current cut-off means 21 is used for the stator winding 2 only in the delayed section. A signal for shutting off the energizing current of 3 is sent to the distribution circuit 7.

FIG. 7 shows operating waveforms of the circuit of FIG.
(7-a) is the output waveform of the differential amplifier 6, (7-b),
(7-c) is the output waveform of the distribution circuit 7 at full speed, (7-c)
(d) is the output waveform of the phase delay means, (7-e) is the output waveform of the first zero-cross comparator 14, the logic circuit 20 compares (7-b) and (7-e), and outputs (7 -F)
Is generated, and the energization current interruption means 21 interrupts the energization currents of the stator windings 2 and 3 at the initial portion of the energization start as (7-g) and (7-h). As a result, the energization period is reduced and the rotation speed is reduced accordingly.

In the case of full speed rotation, the speed switching transistor 9 is in the off state, the capacitor 11 does not function and the phase does not change. Therefore, the energization interruption section disappears like the waveforms of the broken lines (7-g) and (7-h), and the motor rotates at full speed.

When the motor is started or locked, the frequency of the sine wave voltage of the differential amplifier 6 is zero, and there is no phase delay. As a result, there is no particular need for startup compensation.

FIG. 4 shows a phase lead circuit 15 added to the drive circuit shown in FIG.
The phase is advanced by 6 and 17, the waveform is shaped into a rectangular wave by the second zero-cross comparator 19, and the terminal portion of the energizing current is interrupted by the logic circuit 20 and the energizing current interrupting means 21.

FIG. 8 shows operating waveforms of the circuit of FIG.
(8-f) is the output waveform of the phase advance circuit 15, (8-g)
Is the output waveform of the second zero-cross comparator 19, (8
-H) is the logic circuit 20 (8-b), (8-e), (8
-G) is a waveform generated by comparison. The energization currents of the stator windings 2 and 3 are cut off at the initial part of the energization start and the end part of the energization as shown in (8-i) and (8-j).
As a result, the number of revolutions is reduced, and at the same time, the current value is extremely reduced by energizing only the section where the torque is strongest in the motor, and the motor efficiency is significantly improved.

[0022]

As described above, in the brushless motor drive circuit according to the present invention, the low speed can be set to an arbitrary speed, the start can be surely performed even at the low speed rotation, the motor efficiency is improved, and the simplification is simplified. And an inexpensive circuit configuration becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of a drive circuit for a brushless motor according to the present invention.

FIG. 2 is a flow chart of the circuit operation of the present invention.

FIG. 3 is a diagram showing an embodiment of claim 1 of the present invention.

FIG. 4 is a diagram showing an embodiment of claim 2 of the present invention.

FIG. 5 is an example of a drive circuit for a brushless motor according to the related art.

FIG. 6 is another example of the drive circuit of the brushless motor according to the related art.

7 is an operation waveform of FIG.

8 is an operation waveform of FIG.

9 is an operation waveform of FIG.

[Explanation of symbols]

 1 Magnetic Pole Position Detection Element 2 Stator Winding 3 Stator Winding 4 Output Transistor 5 Output Transistor 6 Differential Amplifier 7 Distribution Circuit 8 Phase Delay Circuit 9 Speed Switching Transistor 10 Resistor 11 Capacitor 12 Resistor 13 Resistor 14 First Zero-Cross Comparator 15 phase advance circuit 16 resistance 17 resistance 18 capacitor 19 second zero-cross comparator 20 logic circuit 21 energizing current interruption means

Claims (2)

[Claims] 1. A drive circuit of a brushless motor having a permanent magnet rotor, comprising: a magnetic pole position detecting element of the permanent magnet rotor; a differential amplifier for amplifying a signal of the magnetic pole position detecting element; and a differential amplifier of the differential amplifier. A distribution circuit that distributes a current flowing to the two stator windings according to the output, a phase delay means that further delays the phase of the output of the differential amplifier, and an output of the phase delay means to a pulse. A first zero-cross comparator, a logic circuit that detects a phase delay amount of the first zero-cross comparator, and an energization that cuts off the initial portion of the energization current of the stator winding for each cycle by the output of the logic circuit. A drive circuit for a brushless motor, comprising: a current cutoff means. 2. A phase advance means provided in parallel with the phase delay means, a second zero cross comparator for converting the output of the phase advance means into a pulse, and a phase advance amount of the second zero cross comparator. It has the above-mentioned logic circuit added with a function, and the above-mentioned conduction current interruption means added with a function of interrupting the terminal part of the conduction current of the stator winding for each cycle by the output of the above-mentioned logic circuit. The drive circuit for the brushless motor according to claim 1.