JP2782481B2 - Drive circuit for brushless motor - Google Patents

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 requires a small size and low power consumption.

[0002]

2. Description of the Related Art Conventionally, as a drive system of a brushless motor for a VTR, a soft switching drive system (180.degree. Drive) which is effective in reducing noise and electromagnetic noise has been adopted. This method is to reduce the noise by flowing through currents to the upper and lower drive transistors to absorb spike currents at the point where the current flowing through the drive winding is switched, or to smooth the edges of the switched current to reduce noise. 4228
8 is disclosed. This method is an effective driving method for a motor having a detecting element for detecting the position of the field rotor, but omits the detecting element for detecting the position of the field rotor to reduce the size of the motor, and In the sensorless driving method using the electromotive voltage signal, if the current amplification factors of the upper and lower driving transistors become unbalanced, it becomes difficult to detect the back electromotive voltage, so that the soft switching driving method is difficult to apply.

Further, in a sensorless drive system, as a protection measure in the case of a start failure, a method of repeating the restart by detecting an edge at which the back electromotive voltage detection signal changes is disclosed in JP-A-58-29380. Have been. This method requires an edge detection circuit and the circuit is complicated.

[0004]

In the sensorless driving method described above, when 180 ° driving is performed, if the current amplification factor of the upper and lower driving transistors becomes unbalanced, an unbalanced current flows through the driving winding, It is difficult to detect the electromotive voltage, and it is difficult to detect the position of the rotor. In particular, at the time of start-up, the number of rotations is low, so that the back electromotive voltage is low and detection is difficult. Further, under such conditions, the reliability of the start-up is reduced. Therefore, a start-up protection measure for detecting an edge of the drive signal of the motor and restarting the motor if it is not detected for a predetermined time or more is necessary.

An object of the present invention, the three-phase brushless motor drive circuit having means for detecting a field rotor position Ri by the counter electromotive voltage, Q startup counter electromotive voltage is difficult to detect
The problem is to solve the problem.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a driving method in which a low back electromotive voltage is applied during low-speed rotation and a drive current of 120 ° without passing through current is applied, and driving is performed even if the current amplification factor of the upper and lower driving transistors becomes unbalanced. By preventing the current from flowing through the winding, the back electromotive voltage can be detected, and the reliability at the time of startup can be improved. When the three-phase brushless motor fails to start and stops, 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 at the GND level. Therefore, by determining that this potential state has continued for a certain period of time or more as a stop state,
A start failure detection circuit can be obtained without detecting an edge of a signal change.

[0007]

With the above configuration, it is possible to detect the back electromotive voltage even when the sensorless drive circuit having the soft switching function is started. Further, even if the start-up fails due to a load change or the like, a restart instruction is obtained by a simple start-up failure detection circuit, so that the motor can be started reliably and quickly.

[0008]

This embodiment shows a case where the present invention is applied to a three-phase brushless motor. FIG. 1 is a circuit configuration diagram. First, a signal for synchronous driving is generated by the oscillator 32 and the ring counter 31 in order to start. That is, the ring counter 31 is composed of three D-type flip-flops as shown in FIG.
I am getting a phase signal. This signal is selected by the data selector 30 only in the startup mode defined by the startup switching circuit 36 and is input to the three differential amplifiers 18 and 19. The third differential amplifier 18 and 19, constant current source 45 as shown in FIG. 5,
52 and transistors 46, 47, 48, 49, 50,
The current of the constant current sources 45 and 52 is distributed according to the potential difference of the input signal. These currents are amplified by the upper pre-drive 17 and the lower pre-drive 20, and the transistors 24, 25, 26, 27, 28, 29
, The driving windings 1, 2, and 3 receive voltages having phases different by 120 °, and the motor starts.

After the start-up mode has continued for a certain period of time, in order to perform sensorless driving, a command from the start-up switching circuit 36 is a self-running mode in which the data selector 30 selects an output signal of the trapezoidal wave generator 13. . Trapezoidal wave generator 13
Are output signals of comparators 21, 22, and 23 for comparing the motor terminal voltage with the motor middle point, and the motor terminal voltage and the motor middle point are respectively connected with resistors 4, 5, 6, and 7 and a capacitor 1
1 is obtained from the output signals of the comparators 14, 15, and 16, which are compared through a primary-type filter composed of 0, 11, 12, and 8.
A trapezoidal wave signal having a phase difference of 20 ° is generated. FIG. 3 is a trapezoidal wave generator, and FIG. 4 is a time chart thereof. The outputs a, b, and c of the comparators 21, 22, and 23 become square waves having phases different from each other by 120 ° as shown by a, b, and c in FIG. Further, the outputs d,
The signals e and f become signals as shown by d, e, and f in FIG.
By setting the primary 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 including the resistor 42 and the capacitor 9, a triangular wave having a frequency six times as high as that of the back electromotive voltage detection signal a can be obtained as shown in FIG. it can. The triangular wave is selected by the triangular wave selector 39 as shown by j and k in FIG. Since the same processing is performed for all three phases, only one phase will be described below. A signal for 120 ° conduction drive as shown by h and i in FIG. 4 is obtained by the 120 ° logic circuit 41 in FIG. When these signals h, i, j, and k are processed by the maximum value selector 43, signals on the upper and lower sides of the trapezoidal wave as shown by l and m in FIG. 4 can be obtained. FIG.
The trapezoidal wave n can be obtained by combining the trapezoidal wave upper signal 1 and the lower signal m with the subtraction amplifier 44 of FIG.

By providing two sets of comparators 21, 22, 23 and 14, 15, 16 for detecting the back electromotive force, a pulse signal having a period of 60 ° can be obtained. , O, and p. This is a feature that when the circuit is integrated, the number of external components is small. Further, as shown in trapezoidal waves n, o, and p in FIG. 4, the slope of the trapezoidal wave is １ ／ of the period of the entire trapezoidal wave.
By doing so, the relative rate of change between the phases can be minimized, and the effect of the soft switching drive can be maximized.

The trapezoidal signals n, o, and p are input to three differential amplifiers 18 and 19. FIG. 5 shows a specific example of the three differential amplifier. The three differential amplifier 18 includes PNP transistors 46, 47 and 48 and a constant current source 45, and the three differential amplifier 19 includes NPN transistors 49, 50 and 51 and a constant current source 52. These three differential amplifiers 18 and 19
The basic operation is the same except for the direction of the current. For this reason, the description will focus on the upper three differential amplifiers 18. The current of the constant current source 45 connected to the emitters of the three transistors is distributed by the difference between the base voltages. FIG. 6 shows the relationship between the potential difference input to the base and the ratio of the distributed current when there are two transistors.
When the potential difference becomes 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, it flows at the rate shown by the curve in FIG. Even if there are three transistors, the current is distributed in this relationship. Therefore, if the amplitude of the trapezoidal wave as shown by n, o, and p in FIG.
The collector currents 6, 47 and 48 are switched smoothly and sequentially. Since this current is finally applied to the bases of the upper drive transistors 24, 25, and 26, 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 phase at the midpoint potential 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 upper and lower pairs, a through current occurs to reduce the motor efficiency, but it is possible to obtain effects such as absorption of a spike voltage.

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

This problem occurs because the upper driving transistor and the lower driving transistor are simultaneously activated. To eliminate this problem, the amplitude of the trapezoidal waves n, o, and p may be increased to about 400 mVp-p. By doing so, the current of the three differential amplifier flows only in one phase, and no current flows in the remaining two phases (120 ° conduction drive), and the upper and lower transistors are simultaneously activated. There is no phase. However, in this case, the switching of the collector current is not smooth, and the effect of the soft switching drive cannot be obtained. Therefore, at the start-up time when the back electromotive force is low, the amplitude of the trapezoidal waves n, o, p is set to 400 mVp-.
p to make it easier to detect the back electromotive voltage, and when the stationary rotation is reached, the back electromotive voltage becomes higher.
The amplitude of o and p may be set to 200 mVp-p to obtain the effect of soft switching.

This operation is realized by the startup switching circuit shown in FIG. The counter electromotive force is applied to the comparators 33, 34, 35
To shape the waveform into a pulse. Comparators 33, 34,
The threshold level 35 is created by dividing the voltage Vs applied to the motor by the resistors 37 and 38. By making the resistance value of the resistor 38 smaller than the resistance 37, the output of the EOR gate 53 can be fixed at the LOW level when the motor stops. When the motor is rotating, a pulse signal can be obtained by the EOR gate 53. FIG. 8 shows a time chart of the startup switching circuit. When 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 obtained in the start-up mode. During the period from t1 to t2, the self-propelled mode is set, but the mode switching has failed and the motor is stopped. The output u of the EOR gate 53 goes low. Between t2 and t3,
In the start-up mode again, after t3, a high-frequency pulse signal can be obtained in the self-running mode when the mode switching is successful. Switching between the start mode and the self-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 is smaller than the current at the time of charging. When a pulse signal is input, the voltage continues to increase. By detecting this voltage with a comparator having hysteresis, a signal for switching between the start mode and the free running mode is obtained. The comparator 59 includes resistors 57, 58, 6
It is configured to have hysteresis by 0 and 61. In FIG. 8, threshold levels 1 and 2 are the hysteresis levels. When the threshold level 2 is exceeded, a self-running mode is set, and a driving mode based on the back electromotive voltage detection signal is entered. Here, if the mode change fails and the motor stops, the pulse signal u becomes Lo.
Since the level becomes the w level, the potential of the integration signal t drops. When the potential becomes lower than the threshold level 1, a restart function can be obtained by returning to the start mode. The signal r changing 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 successfully started and the motor continues to rotate, the integral signal t further increases. When the threshold level 3 is exceeded, the output signal r of the comparator 62 becomes Hi level, the amplification factor of the waveform synthesizer 44 of the trapezoidal wave generator is reduced, and the soft switching drive is performed.

[0015]

As described above, according to the present invention, when the motor is rotated at a low speed with a low back electromotive voltage, the motor is driven at a current of 120.degree. Without passing through current, and is driven even when the current amplification factor of the upper and lower driving transistors becomes unbalanced. By not flowing to the winding,
The back electromotive voltage can be detected, and the reliability at the time of starting can be improved. When the three-phase brushless motor fails to start and stops, 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 at the GND level. Therefore, by determining that this potential state has continued for a certain period of time or more as a stop state, it is possible to determine a start failure without detecting an edge of a signal change,
The motor can be started quickly and reliably. Therefore, it is possible to provide a device suitable as a motor drive circuit of a VTR camera or the like that requires a shorter startup time in order to improve operability.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a configuration example of a ring counter and a data selector in FIG. 1;

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

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

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

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

FIG. 7 is a circuit diagram showing a specific configuration of a startup switching circuit in FIG. 1;

8 is a time chart showing an operation state of a start-up switching circuit in FIG. 7;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drive winding 2 drive winding 3 drive winding 13 trapezoidal wave generation circuit 17 upper side pre-drive circuit 18 3 differential amplifier circuit 19 3 differential amplifier circuit 20 lower side pre-drive circuit 30 data selector 31 ring counter 32 oscillator

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyoshi Muto 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. Inside the factory (72) Inventor Hideo Zama 1410 Inada, Katsuta-shi, Ibaraki Pref.Hitachi, Ltd.Tokai Plant 72) Inventor Masao Mizumoto 2-18, Keihanhon-dori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-62-221894 (JP, A) JP-A-3-243197 (JP, A) JP-A-1-255494 (JP, A) JP-A-62-239891 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02P 6/18

Claims (4)

(57) [Claims] 1. A three-phase brushless motor for driving a three-phase brushless motor.
Generates three-phase synchronous drive signals for upper and lower drive transistors and 120 ° conduction mode
Synchronous drive signal generating circuit, and a back electromotive force detection value of each winding of the three-phase brushless motor
Trapezoidal signal for three phases for 180 ° conduction mode based on
A trapezoidal wave signal generating circuit for generating the synchronous drive signal generating circuit and the trapezoidal wave signal generating circuit
One of the synchronous drive signal and trapezoidal wave signal
And a selector circuit for outputting the signal according to the difference between the three phases of the signal output from the selector circuit.
To control the current distributed to the three-phase upper and lower drive transistors.
Controlling the three differential amplifier circuits, and at the time of startup, the selection circuit selects the synchronous drive signal.
Command, and after startup, the trapezoidal wave
A switching circuit that outputs a command to select a signal.
3 phase brushless motor drive circuit. 2. The three-phase brushless mode switching circuit according to claim 1 , wherein
The pulse voltage is generated by shaping the terminal voltage of each winding of the motor.
Means for integrating the pulse signal;
When the output signal of the integration means is equal to or less than the first set value, the selection is performed.
Output a command to select the synchronous drive signal to the selection circuit,
When the first set value is exceeded, the trapezoidal wave is applied to the selection circuit.
Output a command to select a signal.
The driving circuit for a three-phase brushless motor according to claim 1, wherein: 3. The trapezoidal wave generation circuit according to claim 2, wherein
The switching circuit is configured to generate one trapezoidal wave signal, and the output signal of the integrating means is set to a first setting signal.
A second set value that exceeds the value and is greater than the first set value
Generates the trapezoidal wave signal with the larger amplitude in the following cases.
Output to the trapezoidal wave generation circuit,
When the output signal of the stage exceeds the second set value, the trapezoid
The command to generate the smaller wave signal amplitude is
Output to the generator circuit.
A drive circuit for the three-phase brushless motor according to claim 2 . 4. The switching circuit includes a trapezoidal wave provided to the selection circuit.
After outputting the command to select the signal,
Is smaller than the third set value, which is smaller than the third set value.
The circuit outputs a command to select the synchronous drive signal.
4. The driving circuit for a three-phase brushless motor according to claim 2 , wherein the driving circuit comprises: