JPH04208092A - Brushless dc motor driving circuit - Google Patents

Abstract

PURPOSE:To detect the rotational position of a motor accurately by a method wherein the changing point of the polarity of a voltage waveform at a coil end is detected to obtain the rotational position of the rotor. CONSTITUTION:Low-pass filters(LPF) 5u, 5v and 5w, differential circuits 6u, 6v and 6w, comparators 7u, 7v and 7w and a logic circuit 11 are provided. A detecting circuit which detects the rotational position of a rotor is composed of the LPF's 5u, 5v and 5w, the differential circuits 6u, 6v and 6w and the comparator 7u, 7v and 7w and, further, a switching signal which switches the current application of a stator coil in accordance with a positional signal obtained by the rotor rotational position detecting circuit is generated by the logic circuit 11. Moreover, for instance, a driving voltage V+ is applied to the one end of a coil 1u and a coil terminal voltage is detected from the other end of the coil 1u through the LPF 5u. With this constitution, the rotational position of the rotor can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a three-phase half-wave brushless DC motor used, for example, in air-conditioning fan motors, office automation equipment, and the like.

[Prior Art] Generally, in a brushless DC motor, a plurality of permanent magnets are arranged in a rotor, and a three-phase star-connected wire-wound coil is arranged in a stator. In order to rotate a motor, it is necessary to send current to an appropriate coil determined by the relationship between the rotor's magnet position and the stator's coil position. Furthermore, as the rotor rotates, it is necessary to sequentially switch the filters through which current flows.

As described above, in a brushless DC motor, the positional relationship between the magnet and the coil is important, and for this purpose, the rotational position of the rotor must be accurately detected. Conventionally, there are the following rotor position detection methods.

(1) A sensor such as a Hall element is provided inside the motor to detect the rotational position of the rotor.

(2) A slit plate attached to the rotating shaft of the rotor allows
The rotational position of the rotor is detected optically.

Here, the method (1) above will be taken as an example. FIG. 5 shows a principle diagram of a conventional brushless DC motor drive circuit using a Hall element as a sensor.

In FIG. 5, the rotor is made up of a two-pole magnet 2, with the right half being the north pole and the left half being the south pole. The stator has coils lu, lv arranged around the rotor at 120° intervals.

It is composed of 1w. Each coil lu, lv.

One end of 1W is connected to the positive side (V+) of the motor drive power supply, and the other end is connected to a switching transistor 8u,
It is grounded to the negative side of the drive power source via 8V and 8W.

Here, the Hall elements 3u, 3v, and 3w as rotor rotational position detection sensors are arranged around the rotor at intervals of 120'. Each coil lu.

lv, 1w and Hall elements 3u, 3v, 3w are respectively arranged appropriately for position detection. The output of the Hall element 3u is transmitted through an amplifier 4u to a transistor 8u.
It is connected to the. When the Hall element 3u faces the ON pole of the rotor magnet 2, it turns on the transistor 8u and energizes the coil 1u. The other Hall elements 3v and 3w also have a similar configuration.

In the state shown in FIG. 5, the Hall elements 3i and 3v face the north pole of the magnet 2, the coils 1u and 1v are energized, and rotational torque is generated.

When the Hall element 3v faces the south pole due to the rotation of the rotor, the coil 12 is energized or cut off. Then, when the Hall element 3w faces the north pole, the coil IW starts to be energized, and rotational torque is obtained by the coil IW. Thereafter, coil lu is connected in the same manner.

The energization is sequentially switched between 1'v and 1w, and the motor continues to rotate.

[Problems to be Solved by the Invention] As described above, conventionally, the rotational position of the rotor has been detected using a sensor, but this has the following problems.

(1) When trying to make the motor smaller and thinner, the installation space for the sensor cannot be ignored.

(2) Since the sensor is built into the motor, maintenance of the sensor section after the motor is assembled becomes difficult.

(3) In addition to the wiring for driving the motor, wiring for the sensor is required, which poses problems such as wiring space and incorrect wiring.

The present invention has been made in view of the above points, and an object of the present invention is to provide a brushless D/C motor drive circuit that can accurately detect the rotational position of a rotor without requiring any dedicated sensors.

[Means and Operations for Solving the Problems] The present invention provides a brushless DC motor in which a plurality of coils arranged as a stator are sequentially energized and rotated to rotate a rotor, in which a point of change in polarity of a voltage waveform at the ends of the coils is detected. The rotational position of the rotor is determined by detection, and with such a configuration, the rotational position of the rotor can be accurately detected without the need for dedicated sensors.

[Embodiment] A brushless DC motor drive circuit according to an embodiment of the present invention will be described below with reference to the drawings.

First, the principle of the brushless DC motor drive circuit of the present invention will be explained with reference to FIG. In addition, here, in a three-phase half-half wave drive type as shown in Fig. 1, three coils l
The explanation will be focused on the coil 1u among the coils u, lv, , 1w.

The motor drive circuit of the present invention includes a low-pass filter (hereinafter referred to as
(referred to as LPF) 5u, a differentiation circuit 6u, a comparator 7u, and a logic circuit 11. Of these, the LPF 5u, the differential circuit 6u, and the comparator 7u constitute a detection circuit for detecting the rotational positions of the mouth and the mouth. Furthermore, the logic circuit 11 generates a switching signal for switching the energization of the stator coil based on the position signal obtained by the rotor rotational position detection circuit.

Here, a drive voltage V+ is applied to one end of the coil 1u, and a coil terminal voltage is detected from the other end of the coil 1u through an LPF 5u. LPF
5u is for removing noise in the voltage waveform. In this case, since the period of the voltage waveform is determined by the number of poles and rotation speed of the motor, appropriate filter characteristics for removing noise components are set depending on the motor used.

The voltage waveform Au at the coil end at this time is shown in FIG. Here, a waveform in an ideal state with no noise is shown. coil 1
When the power supply u is cut off, the induced voltage generated in the coil 1u is superimposed on the power supply voltage, so the voltage waveform becomes a convex curve as shown by Au in FIG. At the peak point of this voltage waveform, the other two phase coils lv
, 1W energization is being switched. therefore,
By detecting this peak point, the rotational position of the rotor can be known.

Therefore, in order to detect this peak point, the rate of change of the voltage waveform is determined by the differentiating circuit 6u, and the point of change in polarity is determined by the comparator 7u. The output potential of the differentiating circuit 6u is higher than Vre when the rate of change is positive with respect to the reference potential V ref, and lower than Vre when it is negative. Also,
When the rate of change is 0, the output potential becomes Vre. Au
The output waveform of the differentiating circuit 6u with the input waveform Bu shown in FIG. 2 is as shown in FIG. Here, when the differential waveform Bu and the reference potential V ref are compared by the comparator 7u, Bu>V
rHJ level when rer, rL when Buku Vref
Obtain J level output. As a result, the output waveform of the comparator 7u becomes like Cu shown in FIG.

In this way, the peak point of the coil terminal voltage waveform Au can be detected from the falling edge of the output waveform Cu of the comparator 7u. The logic circuit 11 inputs this detection signal Cu as a rotational position detection signal of the rotor, and generates an energization switching signal Cu for the coil 1u based on the signal.

FIG. 1 shows the specific configuration of this embodiment.

When the motor is rotated by the motor drive control circuit 12, an induced voltage is generated in the coils 1u, lv, and 1w. When the current is cut off, the waveform of this induced voltage is the same as that in the coils ILI, IV', and IW. The voltage waveform at each coil end is the corresponding LPF5u,'
Detected through 5v and 5w. The voltage waveform at this time is shown in Fig. 2 for Au.

Shown in AV and AW. Voltage waveforms Au and Av of each phase.

Aw is shifted by 2π/3 periods.

A differentiating circuit 6u separates each voltage waveform Au, Av, and Aw.

By differentiating with 6v and 6w and detecting the zero crossing point of the differentiated waveform with comparators 7u, 7v, and 7w,
Rotor rotational position detection signals such as those shown by Cu, Cv, and Cw in FIG. 2 are obtained. FIG. 3 shows a specific example of a rotor rotational position detection circuit composed of an LPF, a differentiation circuit, and a comparator. Note that the rotor rotational position detection circuit of the present invention is not limited to this circuit example.

Next, the logic circuit 11 will be explained.

The logic circuit 11 includes R-S flip-flops 9u, 9
v, 9w and AND circuit 10. u, 10v.

10W, and each position detection signal Cu, Cv.

Transistor 8u from the falling edge of Cw.

Signals Du and Dv for driving 8v and 8w.

Generate Dw. Here, the process of generating the signals Dv and Dw for switching the energization of the V phase and W phase at the falling edge of the position detection signal Cu at time T shown in FIG. 2 will be described as an example.

Until the Cu falling signal is output, the ■ phase transistor 8v is in the on state, and the other transistors 8u and 8 are in the on state.
w is in the off state. This Du.

The off signal of Dw is output from AND circuit 1. Ov, 10w (7)
The output is rLJ level, and the position detection signal Cv.

Invalidates Cw input. This is to prevent over-operation due to an unexpected signal. At this time, the AND circuit 10
u is set to "H" by the Dv on signal and the Cu rHJ signal.
Outputs a level signal.

Here, at time T, when the position detection signal Cu reaches the rLJ level, the output of the AND circuit 10u also becomes the rLJ level. The falling edge at this time resets the flip-flop 9u and sets the flip-flop 9W, turning off the transistor 8v and turning on the transistor 8w. As a result, each AND circuit 10u, 10
V, the feed of the signals Du, Dv, Dw to 10w changes, the output of the AND circuit 10v, 10u is rL
J level, the output of the AND circuit 10v becomes rHJ level. Thereafter, the motor continues to rotate by repeating this process.

[Effects of the Invention] As described above, according to the present invention, the sensor for detecting the rotational position of the rotor can be eliminated in the brushless DC motor drive circuit, and the following effects can be obtained.

(1) The motor can be made smaller and thinner.

(2) Since no sensor is required, costs can be reduced overall.

(3) Sensor installation eliminates rotational unevenness due to position.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a brushless DC motor drive circuit according to an embodiment of the present invention, Fig. 2 is a timing chart for explaining the operation of the embodiment, and Fig. 3 is a rotor rotation in the embodiment. FIG. 4 is a diagram showing the configuration of the position detection circuit, FIG. 4 is a diagram for explaining the rotor rotational position detection method of the same embodiment, and FIG. 5 is a principle diagram of a conventional brushless DC motor drive circuit. lu, 1v, 1w-coil, 5u, 5v, 5w-LPF
(o-pass filter), 6u, 6v. 6w... Differential circuit, 7u, 7v, 7w... Comparator, 8
u, 8v, 8w...transistor, 9u, 9v. 9w...Flip-flop, 10u, lQy. 10w...AND circuit, 11...logic circuit, U2...motor drive control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 5

Claims (1)

[Claims] In a brushless DC motor that rotates a rotor by sequentially controlling energization of a plurality of coils arranged as a stator, a voltage waveform detection means for detecting a voltage waveform at the end of the coil; rotor rotational position detection means for detecting a point of change in polarity of the voltage waveform by differentiating the detected voltage waveform and comparing the differentiated waveform with a reference potential; A brushless DC motor drive circuit that detects the rotational position of the rotor based on a detection signal.