JPS5815483A - Driving circuit for brushless motor - Google Patents

Abstract

PURPOSE:To suppress the generation of torque pulsation on the brushless motor even when it is operated at a low speed by a method wherein a resistor, having the prescribed value equal to or higher than the DC resistance value of armature coils, is commonly connected in series to each armature coil. CONSTITUTION:When the motor is started or it is operated at a low revolution speed, a resistor 10 is connected in series to armature coils 7-9, because the output signal of a level judging circuit 13, wherein a speed detecting signal sent from a frequency generator 12 will be inputted, is in a low level and a transistor 11 is in OFF position, and, accordingly, the variation in resistance value of the armature 7-9 is absorbed and no torque pulsation is generated, because the resistance value of the resistor 10 is considerably larger than that of the armatures 7-9. Subsequently, when the revolution speed of the motor is increased to the prescribed high speed, the output signal of the level judging circuit 13 is turned to the high level, ON position is given to the transistor 11, and the resistor 10 is short-circuited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive (1) circuit for a brushless motor that controls energization and disconnection of an armature coil using a semiconductor switching element.

A conventional drive circuit of this type has a configuration in which multiple phase, for example, three-phase armature coils are connected in parallel between the DC power sources, and a transistor, which is a semiconductor switching element, is connected in series to the nominal armature coil. However, since the DC resistance value of the armature coil varies due to manufacturing, this variation causes fluctuations in the armature current, especially during low speed rotation, and there is a problem in that torque pulsation occurs.

The present invention has been made in view of the above circumstances, and its object is to provide a brushless motor drive circuit that can eliminate torque pulsation even during low speed rotation.

An embodiment of the present invention will be described below with reference to the drawings.

A single DC power supply is used, and the bus bar 2°3 is connected to its positive and negative terminals. 4, 5 and 6 are PNP type transistors which are semiconductor switching elements, each emitter of which is connected to the ffl line 2. 7°8 and 9 are multi-phase three-phase armature coils, one end of each is connected to the collectors of the transistors 4, 5 and 6, respectively, and the other ends are commonly connected to the common connection point. is connected to the bus bar 5 via a resistor 10. In this case, the resistance value of the resistor 10 is set to be equal to or higher than each DC resistance value of the armature coils 7.8 and 9, for example, about nine times the DC resistance value. 11 is an NPN type transistor which is a switching element, and its emitter and collector are connected to a low resistor 1.
0 are connected in parallel. Reference numeral 12 denotes a frequency generator for detecting rotational speed, which is directly connected to a permanent magnet (not shown) that generates field magnetic flux, and its output terminal is connected to the input terminal of the level determination circuit 13. The output terminal of the level determination circuit 13 is connected to the base of the transistor 11. Here, the level determination circuit 13
converts the frequency signal, which is the speed detection signal from the frequency generator 12, into a level signal corresponding to the frequency, and raises the output signal whenever the signal exceeds a reference level indicating a predetermined high speed. It is designed to be a level. Therefore, the level determination circuit 13 sets the output signal to a low level when the level signal does not reach the reference level.

Note that the transistors 4, 5, and 6 are turned on when a position detection signal is sequentially applied to their bases from a position detection element (not shown) that detects the rotational position of the rotor. /L/4° 5 and 6 are sequentially energized 120 degrees each, thereby rotating the rotor.

By the way, when the field magnetic flux density is B and the armature current is 1, the torque T in the brushless morph is expressed as T cc B I ---------(1), and the field magnetic flux density B and the electric machine It is proportional to the child current I. Therefore, since the field magnetic flux density B normally generated by the permanent magnet is constant, variations in the trike T will be caused by the armature current I.

Furthermore, the armature current ■ at startup and low speed rotation is
When the DC power supply voltage is Vs, the saturation voltage of l-run rasters 4 to 6 is Vp, and the resistance value (i.e. DC resistance value) of armature coils 7 to 9 is R, ■=-, Ms-Vp
...(2) Indicated by a hole. Therefore, in order to prevent the armature current I flowing through the armature coils 7.8 and 9 from fluctuating and the torque T pulsating due to on/off switching of the transistors 4.5 and 6, the DC power supply voltage S must be It is conceivable to make the voltage significantly larger than the saturation voltage VF and to make the DC resistance values R of each armature coil 7 to 9 equal. however,
Depending on the mode of use, the DC power supply voltage Vs may decrease during low speed rotation.
may be 1 volt and the saturation voltage VF may be about 0.5 volts, so it is not always possible to satisfy the condition that the DC power supply voltage Vs is significantly larger than the saturation voltage VP. The DC resistance value R inevitably varies by about 5% when considering manufacturing variations of the armature coils 7 to 9 and variations in the copper wire material. At times, torque pulsations were unavoidable.

In contrast, in this embodiment, during startup and low speed rotation, the output signal of the level determination circuit 13 is low level and the transistor 11 is off, so that the resistor 10 is connected to each armature coil (L/L/ The resistance value of the resistor 10 is significantly larger than the resistance value of the armature coils 7 to 9, so that the resistance value of the armature coils 7 to 9 is The variations in torque are absorbed and do not become a problem, and torque pulsation does not occur. Thereafter, when the rotational speed increases to a predetermined high speed, the output signal of the level determination circuit 13 becomes a high level μ, so that the transistor 11 is turned on, so that the resistor 10 is short-circuited and disabled. That is, during high-speed rotation, the armature current is mostly determined by the induced voltage of each armature coil 7 to 9, so the resistor 10 has no effect, and torque pulsation is also reduced by the flywheel effect of the rotor. Therefore, the resistor 10 is disabled.

Thereby, power loss due to the resistor 10 can be eliminated during high speed rotation.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can of course be implemented with appropriate modifications.

As explained above, the present invention is a device in which armature coils of multiple phases are controlled to be turned on and off sequentially using semiconductors and switching elements, and in which the armature coils of each phase have a DC resistance value equal to or higher than the DC resistance value of the armature coil. Since the resistors having resistance values are commonly connected in series, it is possible to provide a brushless motor drive circuit that can eliminate torque pulsation even during low speed rotation.

[Brief explanation of the drawing]

The figure is an electric wiring diagram showing one embodiment of the present invention. In the figure, 4 to 6 are transistors (semiconductor switching elements), 7 to 9 are w', root fill, 10 resistors, 1
Indicates one transistor (switching not required). Applicant Tokyo Shibaura Electric Co., Ltd. (′)

Claims (1)

[Scope of Claims] 1. In a device in which armature coils of a plurality of phases are sequentially energized and de-energized by a semiconductor switching element, the armature coil of each phase has a DC resistance value equivalent to that of the armature coil. A brushless motor drive circuit consisting of resistors having the above resistance values commonly connected in series. 2. 'fXm times u of the brushless motor according to claim 1, characterized in that a switching element is connected in parallel to the resistor. 6. The brushless motor drive circuit according to claim 2, wherein the switching element is composed of a transistor.