JPH05161388A - Drive circuit for brushless motor - Google Patents

Abstract

PURPOSE:To improve the reliability at the time of starting by making the detection of counter-electromotive force possible through performing 180 deg. drive at the time of normal rotation in a sensorless drive system and through driving by 120 deg. conduction causing no pass-through current to flow at the time of low-speed rotation, and to perform restarting surely and quickly, even in the case of failing in the start, by detecting such failure. CONSTITUTION:At the time of starting, three-phase signals differing in phase by 120 deg. for synchronous drive are obtained by an oscillator 32 and ring counter 31. These signals are selected by a data selector 30 only at the time of a starting mode specified by a starting change-over circuit 36. When a counter-electromotive force becomes higher after starting, the command of the starting change-over circuit 36 is brought to a self-advancing mode where the data selector 30 selects the output signal of a trapezoidal wave generator 13, the inclined part of the trapezoidal wave is brought to 1/3 of the period of the whole trapezoidal wave and 180 deg. conduction is performed, and the relative rate of change between respective phases is minimized and soft switching is performed. In this case, when a motor having failed in the change of the mode stops, the state of the potential of each phase counter electromotive force is detected and an apparatus is again changed-over to the starting mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly to a brushless motor suitable for use in a VTR motor or the like which is required to be small in size and consume less power.

[0002]

2. Description of the Related Art Conventionally, a soft switching drive system (180 ° drive), which is highly effective in reducing noise and electromagnetic noise, has been adopted as a drive system for a VTR brushless motor. In this method, when the current flowing through the drive winding is switched, a through current is passed through the upper and lower drive transistors to absorb spike current, and the edges of the switched current are smoothed to reduce noise. 4228
8 are disclosed. This method is an effective drive method for a motor equipped with a detection element that detects the position of the field rotor, but in order to downsize the motor, the detection element that detects the position of the field rotor is omitted, and In the sensorless drive system using the electromotive voltage signal, it is difficult to apply the soft switching drive system because it becomes difficult to detect the counter electromotive voltage when the current amplification factors of the vertical drive transistors become unbalanced.

Further, in the sensorless drive system, as a protection measure in the case of failure in starting, a method in which starting failure is detected by detecting an edge where a counter electromotive voltage detection signal changes and restarting is repeated is disclosed in Japanese Patent Laid-Open No. 58-29380. Has been done. This method requires an edge detection circuit and is complicated.

[0004]

In the sensorless drive system described above, when the current amplification factor of the upper and lower drive transistors becomes unbalanced when the 180 ° drive is performed, an unbalanced current flows in the drive winding, which causes a reverse current. It is difficult to detect the electromotive voltage, which makes it difficult to detect the position of the rotor. Especially at startup, the rotation speed is low, so the back electromotive force is low and detection is difficult. Further, under such a condition, the reliability of the start-up is lowered, so that it is necessary to take a start-up protection measure for detecting the edge of the drive signal of the motor and restarting it if it cannot be detected for a predetermined time or longer.

An object of the present invention is to reduce the noise by driving 180 ° in a VTR brushless motor drive circuit having a field rotor position detection means based on a back electromotive voltage, and to simplify the operation without using an edge detection circuit. It is to detect the start-up failure in such a circuit.

[0006]

The object of the present invention is to drive at a low speed of low back electromotive force at 120 ° conduction without passing through current, and to drive even if the current amplification factor of the vertical drive transistor becomes unbalanced. By preventing the current from flowing in the winding, the back electromotive force can be detected, and the reliability at the time of starting can be improved. When the three-phase brushless motor fails to start and is stopped, one of the three-phase winding potentials is the power supply voltage applied to the motor, the other is half the power supply voltage, and the other is the GND level. Therefore, by determining that this potential state has continued for a certain time or more as a stopped state,
It is possible to obtain the activation failure detection circuit without detecting the edge of the signal change.

[0007]

With the above structure, the counter electromotive voltage can be detected even when the sensorless drive circuit having the soft switching function is started. Further, even if the start-up fails due to load fluctuation or the like, a simple start-up failure detection circuit can be used to obtain a restart instruction, so that the motor can be started surely and quickly.

[0008]

EXAMPLE This example shows a case where the present invention is applied to a three-phase brushless motor. FIG. 1 is a circuit configuration diagram. First, in order to start up, a signal for synchronous drive is generated by the oscillator 32 and the ring counter 31. That is, the ring counter 31 comprises three D-type flip-flops as shown in FIG.
You are getting a phase signal. This signal is selected by the data selector 30 only in the start mode defined by the start switching circuit 36 and input to the three differential amplifiers 18 and 19. The three differential amplifiers 18 and 19 have a constant current source 45, as shown in FIG.
52 and transistors 46, 47, 48, 49, 50,
51, the currents of the constant current sources 45 and 52 are distributed according to the potential difference of the input signal. These currents are amplified by the upper side pre-drive 17 and the lower side pre-drive 20, and are amplified by the transistors 24, 25, 26, 27, 28, 29.
By inputting to the bases of the motors, the drive windings 1, 2 and 3 are applied with voltages having different phases of 120 °, and the motor is started.

After this start-up mode continues for a certain period of time, in order to perform sensorless drive, the start-up switching circuit 36 gives a command to the self-running mode in which the data selector 30 selects the output signal of the trapezoidal wave generator 13. .. Trapezoidal wave generator 13
Are comparators 33, 34, 35 for comparing the motor terminal voltage with the motor midpoint, and resistors 4, 5, 6, 7 and capacitors 10, 11, for the motor terminal voltage and motor midpoint, respectively.
A trapezoidal wave signal having a phase difference of 120 ° is generated from the signals of the comparators 14, 15 and 16 to be compared through a first-order filter composed of 12 and 8. FIG. 3 is a trapezoidal wave generator, and FIG. 4 is a time chart thereof. Comparators 21, 2
The outputs a, b and c of 2, 23 are square waves having different phases by 120 ° as shown by a, b and c in FIG. The outputs d, e, f of the comparators 14, 15, 16 are delayed in phase from a, b, c by the action of the first-order type filter and become signals as shown by d, e, f in FIG. By setting the first-order type filter so that the phase delay is 30 °, the energy conversion efficiency of the motor can be increased and the torque ripple can be reduced. When these six types of signals are processed by the EOR gate 40 and integrated by the integrator composed of the resistor 42 and the capacitor 9, a triangular wave having a frequency six times that of the counter electromotive voltage detection signal a can be obtained as shown in g of FIG. it can. The triangular wave is the triangular wave selector 39
Is selected as indicated by j and k in FIG. 3
Since the processing is the same for both phases, only one phase will be described below. The 120 ° logic circuit 41 of FIG. 3 obtains a 120 ° energization drive signal as indicated by h and i of FIG.
When these signals h, i, j, and k are processed by the maximum value selector 43, signals above and below the trapezoidal wave as shown by l and m in FIG. 4 can be obtained. Subtraction amplifier 44 of FIG.
The trapezoidal wave n can be obtained by combining the trapezoidal wave upper side signal 1 and the lower side signal m.

By providing two sets of comparators 21, 22, 23 and 14, 15, 16 for detecting the back electromotive voltage, a pulse signal having a period of 60 ° can be obtained, and one integrator is used to generate a trapezoidal wave n. , O, p can be obtained. This is characterized in that when this circuit is integrated, the number of external parts can be reduced. In addition, as shown by the trapezoidal waves n, o, and p in FIG. 4, the slope portion of the trapezoidal wave is ⅓ of the entire period of the trapezoidal wave.
By doing so, the relative rate of change between the phases can be minimized and the effect of soft switching drive can be maximized.

The trapezoidal wave signals n, o and p are input to the three differential amplifiers 18 and 19. FIG. 5 shows a specific example of the three differential amplifier. The 3-differential amplifier 18 includes PNP transistors 46, 47 and 48 and a constant current source 45, and the 3-differential amplifier 19 includes NPN transistors 49, 50 and 51 and a constant current source 52. The three differential amplifiers 18 and 19
Have the same basic operation except that the direction of the current is different. Therefore, the description will focus on the upper three differential amplifier 18. The current of the constant current source 45 connected to the emitters of the three transistors is distributed by the difference in the base voltage. When there are two transistors, the relationship between the potential difference input to the base and the ratio of the distributed current is as shown in FIG.
When the potential difference is 200 mV or more, it flows almost completely to one side, and when the potential difference is 0 mV, it flows evenly by 50%. In the meantime, the current flows at the rate shown by the curve in FIG. Even if the number of transistors is three, the current is distributed in this relationship. Therefore, if the amplitude of the trapezoidal wave as indicated by n, o, and p in FIG.
The collector currents of 6, 47 and 48 are smoothly and sequentially switched. Ultimately, this current is applied to the bases of the upper drive transistors 24, 25, 26, so that the collector current changes smoothly and soft switching drive can be realized. Here, the input potential of the three differential amplifiers 18 and 19 is
In a mode in which one phase has a high potential, the other phase has a low potential, and the other phase has a midpoint potential, the midpoint potential phase has a potential difference of 100 mV from the high potential phase. A small current of about 1% flows with respect to the current. Since this current flows through the pair of upper side and lower side, a through current is generated and motor efficiency is reduced, but effects such as absorption of spike voltage can be obtained.

The above description can operate without problems under ideal conditions. However, the upper drive transistors 24, 25, 26 and the lower drive transistors 27, 2
When the current amplification factors of Nos. 8 and 29 are varied, the collector currents of the upper and lower drive transistors are different in the mode in which the through current flows.
A current flows through a few points. In this case, a potential is generated at the motor terminal due to the voltage drop, and an accurate back electromotive force cannot be detected. In particular, when the rotational speed is low, the counter electromotive voltage is low, so that it is difficult to detect and the problem that it cannot be started occurs.

This problem occurs because the upper drive transistor and the lower drive transistor become active at the same time. To eliminate this problem, the amplitudes of the trapezoidal waves n, o, and p may be increased to about 400 mVp-p. By doing so, the currents of the three differential amplifiers flow only in one phase, and no current flows in the remaining two phases (120 ° energization drive), and the upper and lower transistors become active at the same time. The phase disappears. However, in this case, the switching of the collector current is not smooth, and the effect of soft switching drive cannot be obtained. Therefore, when starting with a low back electromotive force, the amplitude of the trapezoidal waves n, o, and p is 400 mVp-
p is set so that the back electromotive force can be easily detected, and when the steady rotation is reached, the back electromotive force increases, so that the trapezoidal wave n,
The amplitudes of o and p may be set to 200 mVp-p to obtain the effect of soft switching.

This operation is realized by the start switching circuit shown in FIG. The counter electromotive voltage is compared with the comparators 33, 34, 35.
The pulse shape is shaped with. Comparators 33, 34,
The threshold level of 35 is created by dividing the voltage Vs applied to the motor with resistors 37 and 38. By making the resistance value of the resistance 38 smaller than that of the resistance 37, the output of the EOR gate 53 can be fixed to the LOW level when the motor is stopped. When the motor is rotating, the pulse signal can be obtained by the EOR gate 53. FIG. 8 shows a time chart of the start switching circuit. The pulse signal u is E
This is the output of the OR gate 53. From t0 to t1, a low-frequency pulse signal is generated in the startup mode. From t1 to t2, the mode is the self-propelled mode, but the mode switching fails and the motor is stopped. The output u of the EOR gate 53 becomes LOW level. From t2 to t3,
In the startup mode again, after t3, a high-frequency pulse signal can be obtained in the state of the self-propelled mode when the mode switching is successful. The switching between the start-up mode and the free-running mode can be obtained from the signal t obtained by integrating the pulse signal u. The integrator is composed of resistors 54 and 56 and a capacitor 55 so that the current at the time of discharging becomes smaller than the current at the time of charging, and the voltage continues to rise when the pulse signal is input. By detecting this voltage with a comparator having hysteresis, it is used as a signal for switching between the start mode and the free-running mode. The comparator 59 has resistors 57, 58, 6
0 and 61 have a hysteresis. In FIG. 8, threshold levels 1 and 2 are this hysteresis level. When the threshold level 2 is exceeded, the self-running mode is set, and the drive mode based on the counter electromotive voltage detection signal is entered. Here, if the mode change fails and the motor stops, the pulse signal u changes to Lo.
Since it becomes the w level, the potential of the integrated signal t drops. When the potential becomes lower than the threshold level 1, the restart mode can be entered again to obtain the restart function. Further, the signal r which changes at the threshold level 3 is obtained by the comparator 62 and the resistors 63 and 64, and is used as a signal for switching the amplitude of the trapezoidal wave. That is, when the motor is started and succeeded in rotation, the integral signal t is further increased. When the threshold level 3 is exceeded, the output signal r of the comparator 62 becomes Hi level and the amplification factor of the waveform synthesizer 44 of the trapezoidal wave generator is lowered to perform soft switching drive.

[0015]

As described above, according to the present invention, when the counter electromotive voltage is low and the motor is rotating at a low speed, it is driven by 120 ° energization without passing through current, and it is driven even if the current amplification factor of the vertical drive transistor becomes unbalanced. By preventing it from flowing in the winding,
The back electromotive force can be detected, and the reliability at startup can be improved. When the three-phase brushless motor fails to start and is stopped, one of the three-phase winding potentials is the power supply voltage applied to the motor, the other is half the power supply voltage, and the other is the GND level. Therefore, by determining that this potential state has continued for a certain period of time or more as a stopped state, it is possible to determine the startup failure without detecting the edge of the signal change,
The motor can be started quickly and reliably. Therefore, it is possible to provide a device suitable as a drive circuit for a motor of a VTR camera or the like, which requires a shorter start-up time for improving operability.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of a drive circuit for a brushless motor according to the present invention.

FIG. 2 is a block diagram showing a configuration example of a ring counter and a data selector in FIG.

3 is a circuit diagram showing a specific configuration of the trapezoidal wave generator in FIG.

FIG. 4 is a time chart showing an operating state of the trapezoidal wave generator shown in FIG.

5 is a circuit diagram showing a specific configuration of the differential amplifier in FIG.

FIG. 6 is a characteristic diagram showing operating characteristics of the differential amplifier shown in FIG.

7 is a circuit diagram showing a specific configuration of a start switching circuit in FIG.

8 is a time chart showing an operating state of the start switching circuit in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 drive winding 2 drive winding 3 drive winding 13 trapezoidal wave generation circuit 17 upper side pre-drive circuit 18 3 differential amplification circuit 19 3 differential amplification circuit 20 lower side pre-drive circuit 30 data selector 31 ring counter 32 oscillator

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Nobuyoshi Muto 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Toshio Nagata 1410 Inada, Katsuta City, Ibaraki Hitachi Tokai Co., Ltd. In the factory (72) Hideo Zama Hideo Zama 1410 Inada, Katsuta City, Ibaraki Hitachi Ltd.Tokai Factory (72) Inventor Norihisa Ishida 2-18 Keiyo Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Masao Mizumoto 2-18, Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (14)

[Claims] 1. A counter electromotive voltage detecting means for detecting a counter electromotive voltage generated in each drive winding as the field rotor rotates,
In a drive circuit of a brushless motor of the type in which the drive current of each drive winding is changed based on the detection signal of the back electromotive voltage detection means, the current is distributed according to the signal generated by the back electromotive voltage detection means. 3. A drive circuit for a brushless motor, which has three differential amplifying means. 2. The drive circuit for a brushless motor according to claim 1, wherein the signal input to the three differential amplifier means is a trapezoidal wave. 3. The drive circuit for a brushless motor according to claim 1, wherein the amplitude of the signal input to the three differential amplifying means is changed according to the rotation speed of the motor. 4. The drive circuit for a brushless motor according to claim 1, wherein the amplitude of the signal input to the three differential amplifying means is changed in two drive modes, that is, a start-up mode and a self-feeding mode. 5. The drive current of each drive winding is changed by using a counter electromotive voltage generated in each drive winding as the field rotor rotates after a fixed time after starting the rotation. In a drive circuit for a three-phase brushless motor of a type that switches to a drive system that is one of the three-phase winding potentials, one of the three-phase winding potentials is half the power supply voltage supplied to the motor, and the other one is higher than half the power supply voltage. A drive circuit for a brushless motor, characterized in that it has means for detecting an abnormal rotation of the motor when one of the voltages is lower than half of the power supply voltage for a predetermined time or more. 6. The drive circuit for a brushless motor according to claim 5, wherein the predetermined time is equal to or longer than the cycle time of the synchronous drive signal. 7. The drive circuit for a brushless motor according to claim 1, further comprising a triangular wave generator having a frequency six times as high as a frequency at which the winding drive current changes. 8. The drive circuit for the brushless motor according to claim 2, wherein the inclined portion of the trapezoidal wave is about 1/3 of the entire period of the trapezoidal wave. 9. A field rotor and a plurality of drive windings are provided,
In a brushless motor drive circuit of a type in which a drive current of each drive winding is changed by utilizing a back electromotive voltage generated in each drive winding as the field rotor rotates, the back electromotive force is processed. A brushless motor drive circuit having two types of back electromotive force processing circuits. 10. The back electromotive force processing circuit according to claim 1, wherein one of the two types of back electromotive force processing circuits is a filter circuit that shifts the phase of the back electromotive force, and the other is a back electromotive force detection circuit. A drive circuit for the brushless motor described. 11. A counter electromotive voltage detecting means for detecting a counter electromotive voltage generated in each drive winding according to rotation of a field rotor,
In the drive circuit of the brushless motor of the type in which the drive current of each drive winding is changed based on the signal of the counter electromotive voltage detection means, the section in which the current is supplied to each drive winding is 120 ° per half wave.
A drive circuit for a brushless motor characterized by having a section that exceeds 12. A start-up mode in which low-frequency synchronous drive is performed, and after a predetermined time has elapsed after start-up, a counter electromotive voltage generated in each drive winding as the field rotor rotates is detected, and based on this signal, the counter electromotive force is detected. In the drive circuit of a brushless motor that has a free-running mode that changes the drive current of the drive winding, the current-carrying section of each drive winding in the free-running mode is made wider than the current-carrying section of each drive winding in the start-up mode. A drive circuit for a brushless motor, which is characterized in that 13. The drive circuit for a brushless motor according to claim 1, wherein the amplitude of the signal input to the three differential amplifying means is increased for a predetermined time during startup. 14. An exclusive OR circuit for performing an exclusive OR operation on the output signals of the two types of counter electromotive voltage processing circuits, and an integrating circuit for integrating the output signals of the exclusive OR circuits. The drive circuit for a brushless motor according to claim 9, wherein the drive circuit is a brushless motor.