JP3804427B2 - Rotor position detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the detection equipment which detects the rotor position of the three-phase DC brushless motor.
[0002]
[Prior art]
In recent years, a three-phase DC brushless motor has been used as a motor for high efficiency, and a method for detecting the position of the rotor with a simple circuit has been devised for cost reduction. In particular, Japanese Patent Application Laid-Open No. 2000-14181 has been filed that detects the rotor position of two phases out of three phases and calculates the remaining one phase by calculation.
[0003]
Hereinafter, a conventional rotor position detection device will be described with reference to FIGS.
[0004]
As shown in FIG. 5, a three-phase DC brushless motor 1 composed of a rotor 1a and an armature winding 1b, phase voltage detection circuits 2, 3, 4 for detecting the voltage of each phase of the armature winding 1b, The neutral point detection circuit 5 that is star-connected to the output of the voltage detection circuits 2, 3, 4 is compared with the output of 2, 4 of the phase voltage detection circuits 2, 3, 4 and the output of the neutral point detection circuit 5. Comparison means 6, 7, voltage feedback resistors 8, 9 connected between the output and input of comparison means 6, 7, microcomputer 10 for controlling the three-phase DC brushless motor 1, and outputs of comparison means 6, 7 Are insulated signal transmission circuits 11 and 12 for transmitting to a microcomputer 10 having different reference potentials.
[0005]
The operation will be described below.
[0006]
The terminal voltage of the armature winding 1b is detected by the phase voltage detection circuits 2, 3, and 4. Further, the neutral point detection circuit 5 detects the voltage at the neutral point of the armature winding 1b. The phase voltage and the neutral point voltage are compared by the comparison circuits 6 and 7, and the outputs of the comparison circuits 6 and 7 are inverted at the point where the voltage becomes the same voltage, that is, at the zero cross point of the induced voltage. This signal is transmitted to the microcomputer 10 via the insulation signal transmission circuits 11 and 12. The microcomputer 10 switches the drive pattern to the three-phase DC brushless motor 1 after a predetermined time from the timing when the signal is inverted. Further, for the remaining one phase not connected to the comparison circuits 6 and 7, the position of the rotor 1a is calculated by calculation from the other two phases and the drive pattern is switched.
[0007]
Voltage feedback resistors 8 and 9 are inserted between the outputs of the comparison circuits 6 and 7 and the + input, and the hysteresis shown in FIG. 6 is provided. Further, in the vicinity indicated by Z in the same figure, the operation waveform does not rise abruptly and the voltage change is slow.
[0008]
Further, although capacitors are inserted in the output stages of the phase voltage detection circuits 2, 3, and 4, the capacitance is set so that the time constant is sufficiently smaller than the rotational speed of the rotor 1a.
[0009]
[Problems to be solved by the invention]
However, the conventional configuration has a problem that each resistance value is very large and the voltage change of the hysteresis is slow, so that it is easily affected by noise.
[0010]
The present invention solves such a conventional problem, is less susceptible to noise, can reliably detect the position of the rotor, and can stably rotate the rotor.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is provided with a voltage feedback capacitor, whereby the voltage change of hysteresis can be made steep and a desired change amount can be obtained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, there are three phase voltage detection circuits that have a capacitor in the output stage and detect the voltage of each phase of the three-phase DC brushless motor, and two phase voltage detections among the three phase voltage detection circuits Two comparison circuits for comparing the output of the circuit and the neutral point detection circuit, a voltage feedback resistor connected between the output and the input of the comparison circuit, and a voltage feedback capacitor connected between the output and the input of the comparison circuit By adopting the configuration, it is possible to instantaneously generate a hysteresis voltage that is a divided voltage of the voltage feedback capacitor and the capacitor in the phase voltage detection circuit.
[0013]
The invention according to claim 2 has a second voltage feedback resistor between the input of the phase voltage detection circuit and the comparison circuit, and one end of the voltage feedback capacitor is connected to the phase voltage detection circuit side of the second voltage feedback resistor. As a result, a hysteresis voltage can be instantly generated as a voltage division between the voltage feedback capacitor and the capacitor in the phase voltage detection circuit, and thereafter, the hysteresis voltage generated by the voltage feedback resistor and the second voltage feedback resistor The hysteresis can be increased, and the magnitude of the hysteresis can be set to a desired value by the resistance value of the second voltage feedback resistor.
[0014]
According to a third aspect of the present invention, a second voltage feedback resistor is provided between the input of the phase voltage detection circuit and the comparison circuit, and one end of the voltage feedback capacitor is connected to the comparison circuit side of the second voltage feedback resistor. Thus, a differentiating circuit can be constituted by the series pair of the second voltage feedback resistor and the voltage feedback capacitor, and only the instantaneous hysteresis can be increased.
[0015]
According to a fourth aspect of the present invention, a capacitor is connected between the output of the neutral point detection circuit and the reference potential, and the time constant of the resistor and the capacitor of the neutral point detection circuit is set to 5 μs or less, thereby improving the position detection accuracy. Noise tolerance can be increased within a range that does not adversely affect the noise.
[0016]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
Example 1
As shown in FIG. 1, a three-phase DC brushless motor 1 comprising a rotor 1a and an armature winding 1b, phase voltage detection circuits 2, 3, 4 for detecting the voltage of each phase of the armature winding 1b, A neutral point detection circuit 5 that is star-connected to the outputs of the voltage detection circuits 2, 3, 4, and comparison means 6, 7 that compare the outputs of the phase voltage detection circuits 2, 4 and the output of the neutral point detection circuit 5; Voltage feedback resistors 8 and 9 connected between the outputs and inputs of the comparison means 6 and 7, and a second voltage feedback resistor 10 connected between the voltage feedback resistors 8 and 9 and the phase voltage detection circuits 2 and 4, 11, voltage feedback capacitors 21, 22, a capacitor 23 connected to the output of the neutral point detection circuit 5, a microcomputer 24, a power supply for the comparison circuits 6, 7 (15 V power supply in this embodiment) 25, Power source of the microcomputer 24 (5V power source in this embodiment) 26 Constitute voltage conversion circuits 28 and 29 for transmitting a common reference potential 27, a signal to the microcomputer 24 converts the output voltage of the comparator circuit 6 and 7.
[0018]
The operation will be described below.
[0019]
The terminal voltage of the armature winding 1b is detected by the phase voltage detection circuits 2, 3, and 4. Further, the neutral point detection circuit 5 detects the neutral point voltage of the armature winding 1b from the outputs of the phase voltage detection circuits 2, 3, and 4 through resistors having the same resistance value. The phase voltage and the neutral point voltage are compared by the comparison circuits 6 and 7, and the outputs of the comparison circuits 6 and 7 are inverted at the point where the same voltage is obtained. This signal is transmitted to the microcomputer 24 via the voltage conversion circuits 28 and 29. The microcomputer 24 switches the drive pattern to the three-phase DC brushless motor 1 after a predetermined time from the zero cross point of the induced voltage. The comparison circuit 6
For the remaining one phase not connected to 7, the position of the rotor 1a is calculated by calculation from the other two phases and the drive pattern is switched.
[0020]
Next, hysteresis generated by the voltage feedback resistors 8 and 9, the second voltage feedback resistors 10 and 11, and the voltage feedback capacitors 21 and 22 will be described with reference to FIGS. 2 and 3. FIG. 2B is an explanatory diagram in which a portion surrounded by a dotted line in FIG. 2A is enlarged.
[0021]
Since the two circuit operations of the comparison circuits 6 and 7 are the same, only one of them will be described. First, as shown in FIG. 2A, the output of the comparison circuit 6 is inverted at the point where the -input and the + input of the comparison circuit 6 have the same voltage. At this time, first, the voltage on the phase voltage detection circuit 2 side of the voltage feedback capacitor 21 rises by a voltage determined by the capacitance ratio with the capacitor in the phase voltage detection circuit 2 via the voltage feedback capacitor 21, and the + The voltage also rises instantaneously by the same voltage (X in FIG. 2B). Next, the + voltage of the comparison circuit 6 further rises through the voltage feedback resistor 8 and the second voltage feedback resistor 10 (Y in FIG. 2B). Further, the value of hysteresis (Y in FIG. 2B) can be finely adjusted by the resistance value of the second voltage feedback resistor 10.
[0022]
FIG. 3 shows an operation when noise is superimposed and the output of the comparison circuit 6 chatters when the hysteresis shown in the conventional example is slow. If chattering is input at a cycle earlier than the predetermined time, the input process of the microcomputer 24 may malfunction. As for chattering due to noise for a predetermined time or longer during which input processing of the microcomputer 24 can be normally performed, malfunction is prevented by performing noise processing with software.
[0023]
Further, a 2 pF capacitor 23 is connected to the output of the neutral point detection circuit 5 to suppress noise to the negative inputs of the comparison circuits 6 and 7. That is, here, the resistance on the armature winding 1b side of the phase voltage detection circuits 2, 3 and 4, the resistance of the neutral point detection circuit 5, and the voltage feedback resistance are achieved by increasing the efficiency and speeding up the position detection (digital detection). 8 and 9 are all high impedance resistances of 1 MΩ, and the time constant between the 2 pF capacitor 23 and the resistance of the neutral point detection circuit 5 is about 0.7 μs (1/3 MΩ × 2 pF). According to experiments, when this time constant exceeds 5 μs, the position detection timing begins to shift, but since the margin is taken into consideration, the position detection timing is stable.
[0024]
Further, voltage conversion circuits 28 and 29 are inserted between the comparison circuits 6 and 7 and the microcomputer 24 to convert the 15V signal of the comparison circuits 6 and 7 into the 5V signal of the microcomputer 24. As a result, it is possible to make the reference potential 27 the same, eliminate the need for an expensive insulation signal transmission circuit, and transmit circuit signals of different power supply voltages. By setting the power supply of the comparison circuits 6 and 7 to 15V instead of 5V, the input voltage range of the comparison circuits 6 and 7 is increased and the detection accuracy is improved.
[0025]
(Example 2)
The description will be made with reference to FIG. 4, but the constituent elements are omitted except for the differences from FIG. Since the operation of the comparison circuit 7 is the same as that of the comparison circuit 6, it is omitted as in the first embodiment.
[0026]
When the connection point of the voltage feedback capacitor 21 is the + input of the comparison circuit 6 as shown in FIG. 4A, the hysteresis is as shown in FIG. That is, by forming a differentiation circuit with the voltage feedback capacitor 21 and the second voltage feedback resistor 10, the hysteresis is increased only for a short time immediately after the output of the comparison circuit 6 is inverted (A in FIG. 4B). It becomes possible. By setting the time when the hysteresis becomes large to be longer than the time when the input of the microcomputer 24 does not malfunction, erroneous detection due to the chattering of the input of the microcomputer 24 can be prevented.
[0027]
【The invention's effect】
As is clear from the above embodiments, according to the present invention, the voltage change of the hysteresis can be made steep by providing the voltage feedback capacitor.
[0028]
In addition, since the second voltage feedback resistor is provided, the hysteresis change amount can be set to a desired change amount by adjusting the resistance value of the second voltage feedback resistor. An arbitrary optimum hysteresis waveform can be obtained depending on the position. By providing the above hysteresis, noise resistance can be improved.
[0029]
Further, by connecting a capacitor having a time constant of 5 μs or less to the neutral point detection circuit, it is possible to perform position detection that is resistant to noise and stable.
[0030]
Further, by providing the voltage conversion circuit, the comparison circuit and the microcomputer can be operated with different power supply voltages even when the reference potential is the same, and position detection with high detection accuracy can be realized at low cost.
[0031]
As described above, the three-phase DC brushless motor can be stably rotated by detecting the position of the rotor which is resistant to noise and has high detection accuracy.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a rotor position detecting device showing a first embodiment of the present invention. FIG. 2 is a diagram of operation waveforms of the first embodiment of the present invention. FIG. 1B is a first embodiment of the present invention. FIG. 3 is an operation waveform diagram showing a first embodiment of the present invention. FIG. 4A is a circuit diagram of a rotor position detecting device showing a second embodiment of the present invention. (B) Operation waveform diagram of second embodiment of the present invention FIG. 5 is a circuit diagram of a rotor position detection device showing a conventional example. FIG. 6 is an operation waveform diagram of a rotor position detection device showing a conventional example. ]
DESCRIPTION OF SYMBOLS 1 3 phase DC brushless motor 2, 3, 4 phase voltage detection circuit 5 Neutral point detection circuit 6, 7 Comparison circuit 8, 9 Voltage feedback resistance 10, 11 Second voltage feedback resistance 21, 22 Voltage feedback capacitor 23 Capacitor

Claims (4)

  A three-phase DC brushless motor, a three-phase voltage detection circuit that has a capacitor in the output stage and detects the voltage of each phase of the three-phase DC brushless motor, and one point from each output of the phase voltage detection circuit via a resistor Connected to the neutral point detection circuit for detecting the neutral potential of the three-phase DC brushless motor, and outputs of the two phase voltage detection circuits and the neutral point detection circuit among the three phase voltage detection circuits. The three-phase DC circuit includes two comparison circuits to be compared, a voltage feedback resistor connected between the output and input of the comparison circuit, and a voltage feedback capacitor connected between the output and input of the comparison circuit. A rotor position detecting device for detecting a rotor position of a brushless motor.   A second voltage feedback resistor is provided between the phase voltage detection circuit and the input of the comparison circuit, and one end of the voltage feedback capacitor is connected to the phase voltage detection circuit side of the second voltage feedback resistor. The rotor position detecting device according to claim 1.   A second voltage feedback resistor is provided between the phase voltage detection circuit and the input of the comparison circuit, and one end of a voltage feedback capacitor is connected to the comparison circuit side of the second voltage feedback resistor. Item 2. The rotor position detection device according to Item 1.   4. A capacitor is connected between the output of the neutral point detection circuit and a reference potential, and the time constant of the resistance of the neutral point detection circuit and the capacitor is 5 μs or less. Rotor position detector.

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