JP2007244054A - Drive unit of sensor-less brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform PWM drive control and to optimize an excitation phase, in a sensor-less brushless motor. <P>SOLUTION: The sensor-less brushless motor 1 is PWM-controlled, rotor position signals are taken out by comparators OP1 to OP3 according to an increase/decrease in an induction voltage of the motor, and the motor is commutation-controlled at excitation phase timing based on the rotor position signals. A delay phase that is magnified at a high-rotation speed side, in particular, by a first filter 7 for removing PWM noise is obtained from a map according to a rotation speed based on the rotor position signals, and the excitation phase is corrected. Furthermore, a delay of a certain time on a circuit is also corrected by the map as a delay phase that corresponds to the rotation speed. While a delay of a phase is generated in the variation of a voltage of a motor terminal due to the difference of the rotation speeds by a primary CR filter, the excitation phase (timing of excitation) in PWM drive can be optimized since the delay phase is corrected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensorless brushless motor driving apparatus that does not use a sensor for position detection of a brushless motor.

  Conventionally, when sensorless control of a three-phase brushless motor is performed in an analog manner, excitation timing is generated by phase-shifting the induced voltage signal by 90 degrees using an integration circuit using CR. When PWM driving is performed, the frequency of the PWM pulse wave becomes noise, but even in that case, the PWM noise can be removed by the integration circuit, so that the rotor position detection is not affected.

In addition, without using the CR integration circuit, the comparison result of the induced voltage signal and the (pseudo) neutral point potential of the motor sensed from the induced voltage signal by the comparator (relative to the motor terminal voltage and the motor neutral point potential) In other words, an appropriate excitation phase can be obtained at any time without depending on the rotation speed by detecting the edge of the relationship and switching the excitation after an electrical angle of 30 degrees (see, for example, Patent Document 1). .
JP 2004-304905 A

  However, in the case of using the CR integration circuit, PWM drive control is possible as described above, but there is a problem that the excitation phase cannot be made appropriate due to the frequency characteristics of the CR integration circuit. On the other hand, in the above-mentioned patent document, the excitation phase can be made appropriate, but since the circuit is configured without using the CR integration circuit, PWM noise is not removed by the CR integration circuit. Therefore, there is a problem that it is not suitable for performing PWM drive control.

  In order to solve such problems and realize that the PWM drive control is possible in the sensorless brushless motor and the excitation phase can be optimized, the present invention detects the terminal voltage of each phase of the brushless motor. A terminal voltage detecting means for detecting the rotor position from a change in the terminal voltage input to the terminal voltage detecting means, and a commutation pattern for switching the commutation pattern for driving the brushless motor according to the rotor position. A commutation control means for performing flow control; a rotational speed detection means for detecting a rotational speed of the brushless motor; and a retard angle for calculating a retard angle for retarding the commutation pattern according to the detected rotational speed. An angle calculation means, and a drive control means for driving and controlling the brushless motor with the commutation pattern based on the calculated retard angle. A sensorless brushless motor driving device, wherein the terminal voltage detecting means has a filter for removing noise contained in the terminal voltage detection signal, and the retard angle calculating means is the rotational speed of the filter. It has filter delay phase correction means for correcting the delay phase that changes in (1).

  In particular, the drive control means may perform PWM control of the brushless motor, and the filter may be a primary CR filter that removes PWM noise included in the terminal voltage detection signal. Further, it is preferable that the retard angle calculation means further includes a circuit delay phase correction means for correcting a delay phase by a circuit other than the filter.

  As described above, according to the present invention, when the noise on the motor terminal voltage for obtaining the rotor position signal is removed by the filter in the drive control of the sensorless brushless motor, the filter changes the motor terminal voltage due to the difference in the rotation speed. Although a phase delay occurs, the excitation phase (excitation timing) in the drive control can be optimized because the delay phase is corrected. As a means for correcting a delay phase that changes due to a difference in rotational speed, the delay phase can be expressed in a form including a time constant as a function of the time required to rotate the delay phase by a predetermined electrical angle. For example, by mapping the formula in advance, the calculation time by the CPU can be shortened and quick processing can be performed, so it is possible to cope with the influence of the delay phase that becomes large especially on the high rotation speed side. it can.

  In particular, when PWM control is performed on a brushless motor, PWM signal is included in the terminal voltage detection signal. By using a primary CR filter, the PWM noise can be easily removed, and a circuit can be constructed at low cost. obtain. Further, by correcting the lagging phase caused by circuits other than the primary filter, the excitation phase (excitation timing) can be optimized with higher accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing a drive control apparatus for a brushless motor to which the present invention is applied. FIG. 1 shows drive control for a three-phase sensorless brushless motor 1. Note that the present invention is not limited to three phases.

  The drive control circuit 2 shown in the figure includes a microcomputer 2a composed of a microcomputer for generating a commutation pattern and a commutation from the microcomputer 2a in order to output a drive signal to each phase of the brushless motor 1 based on the commutation pattern. A pre-driver 2b that outputs a drive signal for each phase according to an output signal based on the flow pattern, and an inverter 2c that converts and outputs the drive signal from the pre-driver 2b are provided. Further, an induced voltage I / F circuit 2d for detecting a rotor position signal in the sensorless brushless motor is provided. The rotor position signal from the induced voltage I / F circuit 2d is input to the microcomputer 2a.

  A drive switch 4 is connected to the drive control circuit 2, and an ON signal of the drive switch 4 is input to the microcomputer 2a. Further, the drive signal from the inverter 2 c is output to the motor terminal of each phase of the motor 1 through the connection lines 3 u, 3 v, 3 w extended from the drive control circuit 2. And each branch line 5u * 5v * 5w which comprises the terminal voltage detection means branched from each connection line 3u * 3v * 3w is connected to the induced voltage I / F circuit 2d.

  When the drive switch 4 is turned on, a high level (H) signal is input to the microcomputer 2a. Upon receiving the high level signal, the microcomputer 2a performs drive control of the brushless motor 1.

  Next, the above-described induced voltage I / F circuit 2d will be described with reference to FIG. As shown in the figure, the branch lines 5u, 5v, and 5w are connected to the inverting input terminals of the corresponding comparators OP1, OP2, and OP3, respectively, and are non-inverted via predetermined resistors R1, respectively. Connected to the input terminal. The outputs of the comparators OP1, OP2, and OP3 are input to the microcomputer 2a.

  The drive control by the drive control circuit 2 performs PWM control, and in order to remove noise (PWM noise) due to a carrier wave in PWM control included in the terminal voltage detection signal, input of the induced voltage I / F circuit 2d is performed. Between the branch lines 5u, 5v, and 5w on the side and the comparators OP1, OP2, and OP3, as a filter for removing noise included in the detection signal of the terminal voltage, a primary CR by a capacitor C2 and a resistor R2 is used. A first filter 7 constituting the filter is provided. Further, a second filter 8 constituting a primary CR filter by a capacitor C3 and a resistor R3 is provided between the comparators OP1, OP2, and OP3 on the output side of the induced voltage I / F circuit 2d and the microcomputer 2a. Each is provided. The second filter 8 is for suppressing chattering at the switching edge of the output signals of the comparators OP1, OP2, and OP3 at a low rotational speed. In the illustrated example, the first filter 7 is a primary CR filter including a capacitor and a resistor. However, the first filter 7 is not limited to such a primary CR filter, and is a low-pass filter that removes high-frequency noise. As long as it constitutes. In the illustrated example, since the PWM control is performed, the primary CR filter suitable for easily removing the PWM noise is used. However, in the case of removing other noises, an appropriate filter corresponding to that may be used.

  The induced voltage I / F circuit 2d constitutes the rotor position detecting means, and the procedure for generating the excitation timing in the detection of the rotor position and the commutation control will be described with reference to FIG. FIG. 3 shows the waveforms of each phase, and the upper part of the figure shows the waveform of the terminal voltage of the stator coil (voltage waveform at branch lines 5u, 5v, and 5w). Since the waveform of each phase is the same only by shifting by an electrical angle of 120 degrees, the U phase will be shown below unless otherwise specified. Θ1 shown in the figure is an electrical angle of 120 degrees, and electricity is supplied only during that time. Θ2 and θ3 before and after that indicate a section having an electrical angle of 60 degrees.

  During the rotation of the rotor, an induced voltage is generated in the coil arranged in the stator. The induced voltage is not excited and is generated in the sections θ2 and θ3 having the electrical angle of 60 degrees, and has a waveform that gradually increases or decreases as shown by the slope of the voltage waveform in the figure, for example. By setting the threshold value Vd for the voltage change, the rotor position signal can be easily extracted.

  Further, an equivalent neutral point potential Vd equivalent to the neutral point potential waveform of the stator coil is generated by setting the resistor R1 in FIG. 2, and the induced voltage is compared with the equivalent neutral point potential Vd by the comparator OP1, The edge timing of the pulse signal output from the comparator OP1 can be used as the rotor position signal (middle upper / middle lower stage in FIG. 3). The rotational speed is obtained by the microcomputer 2a from the generation interval of the rotor position signal thus obtained.

  Further, in the microcomputer 2a, the interval between adjacent ones of the induced voltage edges of the output waveforms of the comparators OP1, OP2, and OP3 is digitally measured by, for example, a built-in counter, and the count value is converted into an electrical angle of 60 degrees. Based on this value, a count value of 30 electrical angles is calculated. In the illustrated example, excitation is switched at a timing Ew delayed by an electrical angle of 30 degrees from the W-phase edge detection timing Tw detected next to the U-phase edge detection of the rotor position signal. This timing Ew is, for example, equivalent to the timing at which the Hall sensor signal is switched in a brushless motor with a Hall sensor, and can be driven and controlled with the same excitation switching timing in a sensorless brushless motor.

  The above control may be software processing in the microcomputer 2a, and the processing procedure is shown in a block diagram in FIG. That is, based on the rotor position signal output from the induced voltage I / F circuit 2d, the excitation phase timing is set by the excitation phase setting unit 11, the motor rotation speed is obtained by the rotation speed calculation unit 12, and the commutation control unit 13 is obtained. Then, a commutation pattern control signal for PWM control is output to the pre-driver 2b in accordance with the excitation phase timing signal.

  Further, a delay phase is read from the map unit 14 in accordance with the rotation speed signal, and a correction signal for correcting the delay phase is output to the excitation phase unit 11 by the delay phase correction unit 15 in accordance with the delay phase. The excitation phase unit 11 corrects the excitation phase timing according to the correction signal and outputs the excitation phase timing signal. The procedure for correcting the delay phase is as follows.

  The first filter 7 described above is effective as PWM noise removal when performing PWM drive control. For example, when the control range of the rotational speed of the brushless motor 1 is shown by A in FIG. The cut-off frequency fc of the first filter 7 is set on the frequency side higher than the control range A. The figure is a semilogarithmic graph in which the frequency on the horizontal axis is logarithmically expressed and the vertical axis is the phase. When a cutoff frequency fc as shown in the figure is set from the relationship with the frequency of the PWM carrier wave, a lag phase is seen on the high frequency side of the control range A as shown in FIG.

  In this illustrated example, the delay phase is corrected by software processing in the microcomputer 2a, and the control procedure is shown below.

The transfer function G (s) of the first filter 7 can be expressed by the following equation using τ (= C × R).
G (s) = 1 / (τs + 1) (1)
From equation (1), the delayed phase θ1 [rad] is
θ1 = −arctan (ωτ) (2)
It becomes.

Here, the delay time due to the first filter 7 is a function of the fundamental frequency f (corresponding to the rotation speed) of the motor terminal voltage, and ω = 2πf,
The delay phase θ1 is a function of the fundamental frequency f,
θ1 = −arctan (2πτ × f) (3)
When the unit is [degree] and the phase lag is positive,
θ1 = arctan (2πτ / f) × 360 / 2π (4)
It becomes. Furthermore, it can be expressed by the following equation as a function of the time Ta required to rotate the electrical angle of 60 degrees.
θ1 = arctan (2πτ / 6 × Ta) × 360 / 2π (5)
The delay phase θ1 by the first filter 7 can be calculated by the above equation (5). This is the phase characteristic equation according to the Bode diagram shown in FIG. Therefore, specifically, since the CPU is burdened when the CPU constantly calculates, it is preferable to map FIG. 4 and obtain the delay phase θ1 from the time Ta.

Furthermore, in the present invention, other circuits other than the first filter 7 and the delay phase θ2 in software processing are also corrected. The main factors included in the delay phase θ2 include the comparators OP1 to OP3, the second filter 8, and the microcomputer (CPU) 2a. The total delay time T2, which is the sum of them, is a constant value regardless of the rotational speed, but when considered as a phase, it is a function of the time Ta required to rotate the electrical angle of 60 degrees, and the value is a constant value. It is. From the ratio of the total delay time T2 to the time Ta, the delay phase θ2 [degree] is
θ2 = (T2 / Ta) × 60 (6)
It becomes.

  From this equation (6), when the rotational speed is increased, the time Ta is shortened, whereas the total delay time T2 is constant. Therefore, the value of T2 / Ta is increased, and the delay phase θ2 when the rotational speed is high. It turns out that becomes large. Even in the equation (6), it is preferable to map it.

Therefore, preferably, the above formulas (5) and (6) are added as a formula for obtaining the delay phase θ of the rotor position detection signal,
θ = arctan (2πτ / 6 × Ta) × 360 / 2π + (T2 / Ta) × 60 (7)
It becomes. In executing this equation (7), it is sufficient to add the values obtained from the map of equation (5) and the map of equation (6) as described above, and the lag phase θ of the rotor position detection signal can be easily obtained. Can be requested. In the specific control, the delay phase θ is considered at the timing Ew for switching the excitation in FIG. 3 (30−θ).

  Since each of the delayed phases θ1 and θ2 is processed using a map (table) in this way, Equation (7) can be processed at high speed, and in the commutation control of the microcomputer 2a even in a high rotational speed range. Since it is not affected by the calculation time, it is not necessary to use a high-speed CPU, that is, an expensive CPU, and the apparatus can be prevented from rising.

  In addition, the result of obtaining the excitation phase (30−θ) using the above equation (7) and the edge timing (rising edge) of the sensor signal based on the actual measurement value of the brushless motor provided with the Hall sensor may substantially coincide. confirmed. As a result, even with the terminal voltage waveform of the stator coil, it became a trapezoidal wave equivalent to the case of driving using a hall sensor, and it was confirmed that PWM control of a sensorless brushless motor can be driven equivalent to a brushless motor with a sensor. .

  It is conceivable to apply the control method for correcting the above to a coreless brushless motor. In that case, the coreless motor has a small mechanical time constant due to low inertia and a small electrical time constant due to low inductance, so acceleration is good, and rotor position detection and excitation timing generation control using the above correction. By applying the above, there is also an effect that it is possible to obtain a responsive (high-speed) starting characteristic.

  The sensorless brushless motor drive apparatus according to the present invention can perform accurate drive control by preventing delay of PWM control and excitation timing of the sensorless brushless motor, and technical fields of various motor apparatuses using the sensorless brushless motor. Useful as.

It is a schematic block diagram which shows the drive control apparatus of the brushless motor to which this invention was applied. It is a figure which shows an induced voltage I / F circuit. It is a wave form diagram which shows the excitation timing of each phase. It is a figure which shows the delay phase of the motor terminal voltage waveform with respect to a frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Drive control circuit, 2a Microcomputer, 2b Pre-driver, 2c Inverter 3u * 3v * 3w Connection line 4 Drive switch 5u * 5v * 5w Branch line 7 1st filter 8 2nd filter 11 Excitation phase setting part 12 Rotational speed calculation unit 13 Commutation control unit 14 Map unit 15 Phase correction unit

Claims (3)

A terminal voltage detecting means for detecting a terminal voltage of each phase of the brushless motor; a rotor position detecting means for obtaining a rotor position from a change in the terminal voltage input to the terminal voltage detecting means; and a commutation for driving the brushless motor. Commutation control means for performing commutation control for switching the pattern according to the rotor position, rotational speed detection means for detecting the rotational speed of the brushless motor, and delaying the commutation pattern according to the detected rotational speed. A sensorless brushless motor drive device comprising: a retard angle calculation means for calculating a retard angle to be angled; and a drive control means for driving and controlling the brushless motor with the commutation pattern based on the calculated retard angle. ,
The terminal voltage detection means has a filter for removing noise included in the detection signal of the terminal voltage;
The sensorless brushless motor driving apparatus, wherein the retard angle calculating means includes a filter delay phase correcting means for correcting a delay phase changing at the rotation speed of the filter. The drive control means performs PWM control on the brushless motor,
The sensorless brushless motor driving apparatus according to claim 1, wherein the filter is a primary CR filter that removes PWM noise included in a detection signal of the terminal voltage.   The sensorless brushless motor driving apparatus according to claim 1, wherein the retard angle calculation unit further includes a circuit delay phase correction unit that corrects a delay phase by a circuit other than the filter.

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