JPS58119795A - Brushless motor - Google Patents

Abstract

PURPOSE:To obtain an inexpensive motor of relatively small size by energizing an armature coil only when the output rectified from an AC power source is higher than the prescribed value in case that the current of the armature coil is switched in response to the rotating position of a rotor. CONSTITUTION:An AC power source 1 is rectified by a rectifier 2, and is connected through an input voltage interrupting switch 8, an inductance 3 and a condenser 9 of relatively small capacity to armature coils 5a-5c. The output of the rectifier 2 is compared by a pulse width controller 13 with a speed command signal 10, the ON or OFF time of the switch 8 is controlled, thereby applying the high frequency voltage of the interrupted waveform to an armature coil 5, and controlling transistors 6a-6c forming a contactless commutator with a signal from a rotating position detector 11. Accordingly, the filter circuit can be extremely reduced in small size, thereby performing an inexpensive motor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless motor, and particularly to a power supply circuit for a brushless motor when an AC power source is used as a driving source.

In general, medium-sized brushless motors that use a non-contact detector to detect the rotational position of a permanent magnet rotor and switch the armature coil current according to the detection signal use a DC power source as the drive power source. A drive circuit is configured as a premise. However, as the controllability and reliability of this type of planless motor gradually attracts attention and its application fields expand, there is a growing demand for the use of brushless motors even in fields where only AC power can be used.

FIG. 1 shows an example of a conventional brushless motor drive circuit that takes into account such demands. That is, the power supplied from the AC power source 1 is supplied to silicon controlled rectifying elements (hereinafter abbreviated as SCR) 2m, 2b, and 2.
After being rectified by a rectifier circuit 2 consisting of components c and 2d and smoothed by an inductance element 3 and a capacitor 4, it is supplied to armature coils 5a, 5b, and 5c of the motor.

The currents in the armature coils 5a, 5b, and 5c flow through a transistor 6m that constitutes a non-contact commutator.

For this purpose, means for detecting the rotary position of the rotor,
The detection signal is transmitted to the commutator transistors 6m and 6b.
, 6e is required, but this part is omitted because it is not directly related to the present invention. , On the other hand, in order to control the rotational speed of the motor, 8 in the rectifier circuit 2
The firing angles of 0R2m and 2b may be controlled to make the smoothed DC output voltage level variable.

In this way, conventionally, alternating current power is rectified and smoothed to almost completely convert it into direct current power, and this direct current power is used to drive a brushless motor. Therefore, when using a single-phase AC power supply with a low frequency of 50Hz or 60Hz, a large capacity inductance element 3 is required.
The problem is that the motor is large in size and expensive in comparison to the capacity of the motor.

It is an object of the present invention to eliminate the drawbacks of the conventional circuit and to provide a power supply circuit for a planless motor that is relatively small and inexpensive.

Before describing the principle of the present invention, the basic characteristics of a brushless motor will first be explained using FIG. If the power supply l of the motor in Fig. 1 is not driven by alternating current but by direct current with voltage v0, then approximately the smoothing capacitor 4 is driven with a direct current voltage of voltage v0 applied to both ends thereof. Consider the case. At this time, each armature coil is 5m, 5m
Assuming that there is no pulsation in the induced voltage generated at b and 5C, the value E is ω (1) at g− (where @
: induced voltage constant, ω: rotor rotational angular velocity). Therefore, the current in the armature coil also does not pulsate, and its magnitude is I = (Vo-E)/R, (2) (where R1: armature DC resistance). By the way, if we consider an ideal state in which the motor has no loss other than copper loss, the motor's no-load rotational angular speed ω. is obtained when the induced voltage E reaches the drive voltage v0, so Vo = ea. t fZ b Chi, -V0/
6). (3) The following relationship is established. Therefore, the rotational angular velocity ω of the motor and the no-load rotational angular velocity ω. The ratio of S-ω/ω. If we standardize in the form of (4), we get 1, V, (1-8)/R, (51).

On the other hand, the torque of the motor is given by 7w K,・I(6) (where K: torque constant), but when the speed of the motor is expressed by the angular velocity as shown above, K - K (7)t becomes. Therefore rxK@fist V0(1-8)/R.

−P(l−8)/ω. (8) is obtained. However, P is the input power when starting the motor, and P = Vo''/R, (9).As a result, the speed-torque characteristics of the motor are as shown in Figure 2A.
shows a linear drooping characteristic as shown in a.

However, starting torque τ. is τ. =P/ω. I'm going to cry.

In addition, the input power PI when the motor rotates is p=, vo・engine, , Vo (1-8)/R, proverb P(1-8) (1
0) Furthermore, the mechanical output P0 of the motor is P −ω·τ −p(1-8) S (11). The efficiency of the motor is the ratio of this mechanical output to the input power, and is given by □ da=p0/p,=s. As a result, the speed efficiency characteristic of the motor is
This results in a linear characteristic as shown by a in Figure B.

The characteristics of a brushless motor driven by a DC power supply in this way, that is, when the capacity of the smoothing circuit is sufficiently large in Figure 1 and the brushless motor is driven under conditions without voltage pulsation, are basically that of a shunt-wound DC motor. It shows the characteristics as.

However, using such a large-capacity smoothing circuit means that the cost, size, and weight will be significantly higher.
A simple method can be considered in which the smoothing circuit is removed and the AC full-wave rectified voltage is directly used as the drive voltage. In this case, when looking at the driving voltage in the range of 0 to θ≦π as shown in Fig. 3, it is V. 5
However, during the period when the drive voltage is lower than the induced voltage level E, the non-contact commutator (6m, 6b in Figure 1)
.

When 6c) is turned on, current flows in the direction of braking the motor. Therefore, a control method is assumed in which current is supplied through the commutator only during a period in which the driving voltage level is higher than the induced voltage level E, that is, in a period when α≦θ≦π−α in FIG. At this time, the driving current of the motor is equal to the voltage difference shown in the shaded area in FIG. 3 divided by the resistance value, and is naturally intermittent.

That is, the instantaneous value of the current in the period α × θ × π−α is 1 = (V6s + tnθ−E ) / R, (12), so the instantaneous value of torque τ′ is τ′ = −1 = P ( sin θ-8)/at. It is given by (13).

Even with such pulsating torque, assuming that there is no pulsation in the rotational speed of the motor and that the motor has relatively large inertia, the average torque τ of the motor will be It is obtained by dividing the integral value of the generated torque by a period of O×θ×π, and is given by 2 π/2 τ=−·f τ7dθ π α. From this, the average mechanical output of the motor is. Also, using the instantaneous value of current 1, the motor average input power is (16), so motor efficiency can be expressed using these! =p, /p.

becomes. With respect to the torque and speed characteristics of this method shown in FIG. 2A, the device is compact, and its efficiency is comparable to that of DC drive.

There are features of the present invention. In this case, the drive voltage waveform is not particularly limited to a sinusoidal waveform.

On the other hand, as is clear from the characteristics shown in FIG. 2, when the motor is driven with a drive voltage that includes an alternating current component, a decrease in torque or output is unavoidable. However, this drawback can be sufficiently improved by the method described below. Now, when full-wave rectification is applied to a sinusoidal voltage, a voltage having the waveform shown in FIG. 4a is obtained. If this is intermittent at a constant frequency and constant pulse width as shown in the same figure, then smoothed, we get
As shown in C in the figure, an output waveform with the amplitude of a reduced is obtained. In this case, if the intermittent frequency is made sufficiently large, the capacitance of the elements required for smoothing can be reduced and the cost can be reduced. Furthermore, since it is possible to change the amplitude of the smoothed voltage by changing the width of the intermittent pulses, the speed of the motor can be controlled by supplying this smoothed voltage to the motor as a drive voltage.

In addition, as shown in Figure 4d, if the full-wave rectified input voltage is intermittent so that the pulse width is wide while the amplitude is small and becomes narrower as the amplitude increases, the smoothed The voltage has a waveform having a flat portion over a considerable range, as shown in FIG. When the motor is driven with such a voltage, the torque characteristics of the motor are as shown by the broken line C in Figure 2A, which is considerably improved compared to when the motor is driven with a voltage that does not smooth the sinusoidal voltage. .

The content of the present invention will be explained in more detail with reference to Examples below.

FIG. 5 shows an embodiment of the drive circuit section of the planless motor of the present invention. The input from the AC power supply l is rectified by the rectifier circuit 2. 8 is a switch for intermittent input voltage;
Transistors are used to enable intermittent operation at relatively high frequencies. The output that is turned on and off by the transistor switch 8 is smoothed by the inductance element 3 and the diode 9, and then supplied to the armature coils 5a, 5b, and 5e. In this case, the intermittent frequency of the switch 8 may be sufficient as 1. In some cases, the inductance of the armature coil can be used instead. Smoothing can be made more complete by connecting a small-capacity capacitor if necessary.

Next, the operation of the entire control circuit of the brushless motor of the present invention will be explained with reference to FIGS. 6 and 97.

The voltage full-wave rectified by the rectifier circuit 2 and the speed command signal applied to the terminal IO are applied to the comparison circuit 131 of the pulse width control circuit 13. The comparator circuit 131 produces a larger output voltage as the amplitude of the full-wave rectified voltage is larger with respect to the speed command signal. This output voltage is supplied to a monostable multivibrator 133 via an emitter follower transistor 132. The monostable multivibrator 133 is configured to be constantly triggered by a constant high frequency pulse applied to a terminal 135, and whose output pulse width can be controlled by a control voltage supplied via the emitter and Tahoroa transistors 132. ing. That is, when the control voltage is high, the output pulse width becomes large, and when the control voltage is low, the output pulse width becomes small. The output pulse of this monostable multivibrator 133 is applied to the switch circuit 8 via the emitter follower transistor 134.

Now, when the amplitude of the full-wave rectified waveform is large, the comparison circuit 131
The output voltage of the monostable multivibrator 133 also increases.
Since the output pulse width of the switch circuit 8 also increases, the off time of the switch circuit 8 becomes longer. Moreover, when the amplitude of the full-wave rectified waveform is small, the output pulse width of the monostable multivibrator 1.3B becomes small, so the off time of the switch circuit 8 becomes short. As a result, as shown in FIG. 4d, a high-frequency voltage having a waveform in which the full-wave rectified voltage is intermittent according to its amplitude is obtained, and this is supplied to the armature coil 5 as described above.

On the other hand, the rotational position detector 11 detects the occurrence.

Note that the components such as the rectifier circuit 2, the switch circuit 8, and the non-contact commutator 6 may of course be other than those shown in the above embodiments, and the method of connecting the armature coils is not limited to the above embodiments. Needless to say.

As explained above, according to the present invention, it is possible to realize a brushless motor that is relatively small and inexpensive and driven by an AC power source, which is extremely effective industrially.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional brushless motor drive circuit.
Fig. 2 is a characteristic diagram of a brushless motor, Figs. 3 and 4 are waveform diagrams for explaining the principle of the present invention, Fig. 5 is a circuit diagram showing an embodiment of the present invention, and Fig. q is a diagram of the present invention. FIG. 7 is a block diagram of the entire control circuit of a brushless motor to which this is applied, and FIG. 7 is a partial circuit diagram of FIG. 6. 1------AC power supply, 2... Rectifier circuit, 3
...Inductance element, 4...Conductor/su, 5...Armature coil, 6...-Commutator transistor, ? , , , , , , low , 8... switch circuit , 9... diode , I O -- speed command signal application terminal , 1.
1... Rotational position detector, 12... Distribution circuit. A j Eye 82 Eye 84 Face 85 Figure! f36 times

Claims (1)

[Claims] A brushless motor that switches the current flowing through the armature coil according to the rotational position of the rotor, the armature coil being energized when the output after rectification is equal to or higher than a predetermined value. 1. A brushless motor characterized by comprising: