JP2004015980A - Parallel-driving circuit for dc brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parallel-driving circuit for a DC brushless motor capable of suppressing noise due to operation in an asynchronous state. <P>SOLUTION: In the parallel-driving circuit of the DC brushless motor, a switching signal generating means develops a switching signal by using a rotor position detecting signal of each motor for driving the plurality of DC brushless motors at the same speed. The rotor position detecting signal used for development of the switching signal is switched between the respective motors within a period when the rotor position detecting signal does not change. The parallel-driving circuit includes a signal selecting means for outputting a control signal so as to develop the switching signal by using the rotor position detecting signal after switching, a direct current setting circuit 70 for passing direct current through a stator coil of each of the motors within a fixed period after the motor starting, and a speed setting circuit 50 and a speed control circuit 60 for accelerating each of the motors to a predetermined speed after the fixed period passes. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a parallel drive circuit for driving a plurality of DC brushless motors connected in parallel to each other to operate a plurality of fans and pumps at the same speed, and is particularly applied to an application requiring low noise. And a person related to a suitable parallel drive circuit.
[0002]
[Prior art]
The present applicant has previously filed an application for this type of parallel drive circuit as Japanese Patent Application No. 2001-222412 (hereinafter referred to as the prior application).
First, the prior invention will be described below.
[0003]
FIG. 7 shows the entire configuration of a drive circuit according to the invention of the prior application, in which two DC brushless motors MA and MB are driven by one drive circuit. In FIG. 7, E denotes a DC power supply, and a three-phase bridge circuit including semiconductor switching elements T1 to T6 is connected to the DC power supply E. DC brushless motors MA, MB having the same configuration are connected in parallel to the respective phase output terminals U, V, W of the three-phase bridge circuit, and the Hall elements HU, HV, HW provided respectively are connected to the rotor position. It is connected to the detection circuits 21 and 22.
[0004]
The rotor position detection signals of the motors MA and MB output from the detection circuits 21 and 22 are input to a signal selection circuit 40, which can select which motor MA or MB to use. Has become. The signal selection circuit 40 outputs a control signal to the switching signal generation circuit 30 to turn on / off the switching elements T1 to T6 according to the selected motor position detection signal.
In FIG. 7, reference numeral 11 denotes a stator, 12 denotes a rotor, and CU, CV, and CW denote coils of each phase of the stator 11.
[0005]
As shown in FIG. 8, the signal selection circuit 40 includes XOR (exclusive OR) gates IC1 and IC2 to which the position detection signal of the motor MA is input, and NAND gates IC3 to IC7 connected to the output side of the XOR gate IC2. And NAND gates IC8 to IC10 to which a position detection signal of the motor MB is input, resistors R1 to R10 such as pull-up resistors, a capacitor C1, output diodes D1 to D7 of the NAND gates IC5 to IC10, and an output. And transistors TR1 to TR3 on the side.
When the rotor position detection signal of each phase of the motors MA and MB as shown in FIG. 9 is input, the signal selection circuit 40 supplies the switching signal generation circuit 30 with one or two phases of the motors MA and MB. To output a control signal for driving the switching element from the transistors TR1 to TR3.
[0006]
Hereinafter, the operation of the circuit of FIG. 7 will be described with reference to FIGS.
Now, assuming that the motors MA and MB are operating at the same speed in synchronization, the respective rotor position detection signals are output in synchronization as shown in FIG. In FIG. 9, a signal related to the motor MA is denoted by A, and a signal related to the motor MB is denoted by B.
Here, the rotor position detection signals of the motors MA and MB shown in FIG. 9 are substantially equal to the output signals of the hall elements HU, HV and HW in FIG.
[0007]
In order to operate both motors MA and MB in synchronization with the rotor position detection signal, the rotor rotation angles (space angles) in FIG. 9 are 0 °, 60 °, 120 °, 180 °, 240 °, and 300 °. It is necessary to change the switching signal output from the switching signal generation circuit 30 in accordance with the change of the position detection signal at the timing.
[0008]
On the other hand, the rotation angles in FIG. 9 are between 0 ° to 60 °, between 60 ° to 120 °, between 120 ° to 180 °, between 180 ° to 240 °, between 240 ° to 300 °, and 300 °. Between 0 ° and 0 °, the position detection signal of each of the motors MA and MB does not change and remains constant (for example, between 0 ° and 60 °, the U-phase is used as the position detection signal of the motors MA and MB). And a state in which signals of the W phase continue to be detected, and a state in which only signals of the U phase are detected as position detection signals of the motors MA and MB continues between 60 ° and 120 °).
[0009]
Therefore, there is no adverse effect even if the position detection signal of the motor MA and the position detection signal of the motor MB are switched while the rotor position detection signal does not change and remains constant as described above.
For example, a switching signal for driving the motor MA using the position detection signal of the motor MA (which may be a switching signal for driving the motor MB because the motors MA and MB are connected in parallel) is output. Is switched to the position detection signal of the other motor MB to output a switching signal for driving the motor MB (which may also be a switching signal for driving the motor MA). If it is performed during a period in which there is no change in the position detection signal, there is no fear that the voltage applied to the motor changes suddenly at the moment of switching. Further, if the drive is switched in a cycle shorter than the cycle of the rotor position detection signal, the operation is less likely to be unstable.
[0010]
Therefore, in this prior art, the angle is between 0 ° to 60 °, between 60 ° to 120 °, between 120 ° to 180 °, between 180 ° to 240 °, between 240 ° to 300 °, At 30 °, 90 °, 150 °, 210 °, 270 °, and 330 ° between 300 ° and 0 ° (360 °), the signal selection circuit 40 outputs the rotor position detection signals of the motors MA and MB. A switching signal for driving the motors MA and MB is output based on the selected rotor position detection signal.
[0011]
That is, as shown in FIG. 9, for example, the rotor position detection signal of the motor MA is selected between 330 ° and 30 °, and based on this signal, the switching signal generation circuit 30 makes the U-phase coil CU and the W-phase coil CW The switching signal is output so as to energize (different periods). Further, the rotor position detection signal of the motor MB is selected between 30 ° and 90 °, and based on this signal, the switching signal generation circuit 30 energizes the U-phase coil CU and the W-phase coil CW (the period is respectively Create a switching signal as shown in FIG.
Thereafter, similarly, the rotor position detection signal of the motor MA is selected between 90 ° and 150 °, and based on this signal, the switching signal generation circuit 30 switches the U-phase coil CU and the V-phase coil CV so that the switching signal is supplied. And the rotor position detection signal of the motor MB is selected between 150 ° and 210 °. Based on this signal, the switching signal generation circuit 30 switches the U-phase coil CU and the V-phase coil CV so that the switching signal is supplied. Create
[0012]
In FIG. 9, for convenience of explanation, the position detection signals of the motors MA and MB are switched at angles of 30 °, 90 °, 150 °, 210 °, 270 °, and 330 °, but the switching angles are limited to these values. Not between 0 ° and 60 °, between 60 ° and 120 °, between 120 ° and 180 °, between 180 ° and 240 °, between 240 ° and 300 °, The same effect can be obtained by switching at an angle that is between 0 ° and 0 ° (360 °) and does not change the position detection signals of the motors MA and MB.
[0013]
When the operation of the signal selection circuit 40 shown in FIG. 8 is confirmed, for example, the rotor position detection signals (U phase, V phase, W phase) of the motors MA and MB between 30 ° and 60 ° in FIG. Are also represented by logic (1, 0, 1). If these signals are input as the position detection signals of the motors MA and MB in FIG. 8, the output transistors TR1, TR2 and TR3 (U phase , V phase, W phase), the logic of the output signal is (1, 0, 1), and the position detection signals (U phase, V phase, W phase) of the motors MA, MB during the next 60 ° to 90 °. ) Is logic (1, 0, 0), the logic of the output signal of the output transistors TR1, TR2, TR3 (U phase, V phase, W phase) is (1, 0, 0), and FIG. Of the output (control signal) of the signal selection circuit during the period of 30 ° to 90 ° I understood.
[0014]
With the above operation, the two motors MA and MB can be stably driven in parallel by a single drive circuit in synchronization with the rotor position detection signal.
[0015]
[Problems to be solved by the invention]
However, according to the above-described related art, when the motors are stopped, the two motors MA and MB are not always stopped in synchronization (at the same rotor position).
If the operation is started from a state where both motors are not synchronized, and the speed is suddenly increased, a large circulating current flows irregularly until the motors are synchronized, and loud noise may be generated from the motors.
Further, in some cases, there is a problem that the two motors do not synchronize with each other for a long time and generate a loud noise.
[0016]
Accordingly, an object of the present invention is to provide a DC brushless motor parallel drive circuit that reduces noise caused by operation in an asynchronous state.
[0017]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 provides a switching signal generating means for driving a plurality of DC brushless motors connected in parallel at the same speed by a drive circuit having a plurality of semiconductor switching elements. Is a parallel drive circuit of a DC brushless motor that creates a switching signal of the switching element using a rotor position detection signal of each motor,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
Speed control means for accelerating each motor to a predetermined speed after the elapse of the certain period.
[0018]
In order to drive a plurality of DC brushless motors connected in parallel with each other at the same speed by a drive circuit having a plurality of semiconductor switching elements, the switching signal generating means includes a rotor position of each motor. A parallel drive circuit of a DC brushless motor that creates a switching signal of the switching element using a detection signal,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
Speed control means for operating each motor at a low speed after the elapse of the certain period, and thereafter accelerating the motor to a predetermined speed.
[0019]
In order to drive a plurality of DC brushless motors connected in parallel to each other at the same speed by a drive circuit having a plurality of semiconductor switching elements, the switching signal generating means may include a rotor position of each motor. A parallel drive circuit of a DC brushless motor that creates a switching signal of the switching element using a detection signal,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
Position signal error detection means for detecting an error of a rotor position detection signal of each motor,
Speed control means for operating each motor at a low speed after the elapse of the certain period, and accelerating each motor to a predetermined speed after an error detected by the position signal error detection means during the low speed operation becomes a specified value or less. It is provided.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 shows an entire configuration of a drive circuit according to a first embodiment of the present invention, in which two DC brushless motors MA and MB are driven by one drive circuit. The same components as those in FIG. 7 are denoted by the same reference numerals. The drive circuit of FIG. 1 corresponds to the first and second aspects of the present invention.
[0021]
In FIG. 1, a DC power supply E, a three-phase bridge circuit including semiconductor switching elements T1 to T6, DC brushless motors MA and MB, Hall elements HU, HV, HW, rotor position detection circuits 21, 22, a signal selection circuit 40, The connection configuration of the switching signal generation circuit 30 is the same as that of FIG.
A speed setting circuit 50 sets the rotation speed of the motors MA and MB in accordance with the operation command. The speed set by the circuit 50 is sent to a speed control circuit 60, and the speed control circuit 60 controls the motors MA and MB in accordance with the set speed. Of the switching elements T1 to T6 are controlled via the switching signal generation circuit 30 so as to rotate.
[0022]
Reference numeral 70 denotes a DC current setting circuit 70 for setting a DC current flowing through the stator coils CU, CV, CW of the motors MA, MB in accordance with the operation command. The output of the circuit 70 is applied to a speed control circuit 60.
That is, the set speed output from the speed setting circuit 50 and the DC current set value output from the DC current setting circuit 70 are input to the speed control circuit 60, and the speed control circuit 60 A control signal is sent to the generation circuit 30 to control the rotation speed and current of the motors MA and MB.
During operation of the DC current setting circuit 70, the output of the speed setting circuit 50 is held at zero by the control signal output from the setting circuit 70.
[0023]
Here, when the motors MA and MB are stopped while being out of synchronization, if a DC current is applied to the stator coils of the motors MA and MB, the permanent magnet of the rotor 12 is drawn to a predetermined position with respect to the stator coils. . Therefore, the positional relationship between the stator 11 and the rotor 12 of each of the motors MA and MB becomes the same, and a synchronous state can be realized.
The first aspect of the present invention focuses on the above-mentioned point, and directs a DC current to the stator coils of the motors MA and MB to synchronize the two motors MA and MB for a predetermined time after the start, and then sets a predetermined speed. To accelerate up to.
[0024]
FIG. 2 shows an embodiment of the first aspect of the present invention, and shows outputs of the speed setting circuit 50 and the DC current setting circuit 70 in FIG.
In FIG. 2, when an operation command is input at time t1 (during start-up), the DC current setting circuit 70 outputs a DC current set value to the speed control circuit 60 for a certain period from time t1 to time t2. A direct current is applied to the stator coils of the motors MA and MB via the switching signal generation circuit 30. As a result, as described above, the permanent magnet of each rotor 12 is attracted to a predetermined position with respect to each of the stator coils, and the positional relationship between the stator 11 and the rotor 12 of each of the motors MA and MB becomes equal to be in a synchronized state. . During this time, the output of the speed setting circuit 50 is kept at zero.
[0025]
Next, at time t2, the output of the DC current setting circuit 70 is made zero, and thereafter, the output of the speed setting circuit 50 is gradually increased to accelerate to the set speed V2.
Thus, the motors MA and MB can be accelerated in a synchronized state, so that noise can be prevented from occurring.
[0026]
However, when the motor is stopped in a state where the temperature of the lubricating oil of the bearing of the motor is low, the viscosity of the lubricating oil is high. is there. In such a case, if the motor is operated at a low speed for a while, the viscosity of the lubricating oil decreases, so that it is possible to establish synchronization during low-speed operation and then accelerate.
Therefore, in the invention described in claim 2, a direct current is supplied to the stator coils of the motors MA and MB for a certain period of time after the start, and then the motor is driven at a low speed for the same or a different period of time as described above. I accelerated.
[0027]
FIG. 3 shows an embodiment of the second aspect of the present invention, and shows outputs of the speed setting circuit 50 and the DC current setting circuit 70 in FIG.
In FIG. 3, when an operation command is input at time t4, which is a start time, the DC current setting circuit 70 outputs a DC current set value to the speed control circuit 60 for a certain period of time from time t4 to time t5. A direct current is applied to the stator coils of the motors MA and MB via the switching signal generation circuit 30. As a result, as described above, the permanent magnet of each rotor 12 is attracted to a predetermined position with respect to each stator coil, and the positional relationship between the stator 11 and the rotor 12 of each of the motors MA and MB becomes equal and synchronized. Become. During this time, the output of the speed setting circuit 50 is kept at zero.
[0028]
Next, at time t5, the output of the DC current setting circuit 70 is set to zero, and at the same time, the output of the speed setting circuit 50 is set to V1 (the output of the speed setting circuit 50 is a voltage value, but the voltage value corresponding to the set speed V1 is also convenient). The same applies to V1), and is maintained until time t6. During this period t5 to t6, the motors MA and MB are operated at a low speed at the speed V1, so that even if the synchronous operation is difficult due to the high viscosity of the lubricating oil of the bearing, the difficulty is resolved and the synchronization is sufficiently established. It becomes.
Then, after time t6, the set speed is gradually increased by the speed setting circuit 50 and accelerated to V2.
[0029]
As a result, the two motors MA and MB can be accelerated in a state in which they are reliably synchronized, and noise can be prevented from occurring.
As described above, the fixed time from time t4 to t5 and the fixed time from time t5 to t6 may be the same or different.
[0030]
Next, in the invention described in claim 3, the synchronization of the two motors MA and MB is confirmed more strictly.
That is, when the motors MA and MB are rotating synchronously, errors in the rotor position detection signals of the motors MA and MB are almost eliminated. Therefore, according to the third aspect of the present invention, a DC current is supplied to the stator coil for a certain period of time after the start, and thereafter, an error in the rotor position detection signal of each of the motors MA and MB is detected during low-speed operation, and the error is reduced to a specified value or less. When it did, it was decided that the simultaneous state had been reached and acceleration was started.
[0031]
FIG. 4 is a circuit diagram showing a second embodiment of the present invention, and corresponds to the third aspect of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and different portions will be mainly described below.
[0032]
In the second embodiment, the rotor position detection signals of the motors MA and MB are input to the position signal error detection circuit 80, and the result of determining whether the error of the position detection signal is equal to or larger than a specified value or not is output. Is added to the speed setting circuit 50.
The other configuration is the same as that of FIG.
[0033]
FIG. 5 shows the relationship between the outputs of the position signal error detection circuit 80, the speed setting circuit 50, and the DC current setting circuit 70.
In FIG. 5, when an operation command is input at time t7, which is a start time, the DC current setting circuit 70 outputs a DC current set value to the speed control circuit 60 for a certain period from time t7 to time t8. A direct current is applied to the stator coils of the motors MA and MB via the switching signal generation circuit 30. As a result, as described above, the positional relationship between the stator 11 and the rotor 12 of each of the motors MA and MB is equal, and the motors MA and MB are in a synchronized state. During this time, the output of the speed setting circuit 50 is kept at zero.
[0034]
Next, at time t8, the output of the DC current setting circuit 70 is set to zero, and at the same time, the output of the speed setting circuit 50 is maintained at V1 for a while. After the time t8, the motors MA and MB are operated at the low speed at the speed V1, so that the difficulty of synchronization due to the high viscosity of the lubricating oil of the bearing before the start is eliminated, and a sufficiently synchronized state is achieved. Thereafter, when the error of the rotor position detection signal becomes equal to or less than a specified value at time t9, the output of the position signal error detection circuit 80 changes, and the speed setting circuit 50 determines that the motors MA and MB are synchronized and gradually increases the set speed. And finally accelerates to the set speed V2.
Thus, the acceleration can be started after the two motors MA and MB have reliably reached the synchronized state, so that there is no possibility of generating noise due to rapid acceleration in the asynchronous state.
[0035]
FIG. 6 is a timing chart showing an operation in a state where the synchronization of the motors MA and MB is slightly shifted in this embodiment.
An error in the rotor position detection signals of both motors MA and MB occurs for each of the U, V, and W phases. The position signal error detection circuit 80 can use all of these three-phase errors. However, in order to avoid an increase in cost due to a complicated circuit configuration, if a one-phase or two-phase error is used, good.
The error of the rotor position detection signal can be easily detected from the exclusive OR of the rotor position detection signals of the motors MA and MB.
[0036]
As shown in FIG. 6, even when the motors MA and MB are slightly out of synchronization, the rotor position detection signal remains constant without any change, for example, when the angle is between 15 ° and 60 °. 30 °, 90 ° between 75 ° to 120 °, 135 ° to 180 °, 195 ° to 240 °, 255 ° to 300 °, 315 ° to 0 ° (360 °) , 150 °, 210 °, 270 °, and 330 °, the signal selection circuit 40 alternately switches the position detection signals of the motors MA and MB between the motors and selects the motors based on the selected position detection signals. A switching signal for driving MA and MB is output.
[0037]
That is, the position detection signal of the motor MA is selected between 330 ° and 30 °, and based on this signal, the switching signal generation circuit 30 energizes the U-phase coil CU and the W-phase coil CW (periods are different). And outputs a switching signal to the switch. In addition, the position detection signal of the motor MB is selected between 30 ° and 90 °, and based on this signal, the switching signal generation circuit 30 energizes the U-phase coil CU and the W-phase coil CW (periods are different). To create a switching signal.
Thereafter, in the same manner, the position detection signal of the motor MA is selected between 90 ° and 150 °, and based on this signal, the switching signal generation circuit 30 generates a switching signal so as to energize the U-phase coil CU and the V-phase coil CV. Then, a position detection signal of the motor MB is selected between 150 ° and 210 °, and based on this signal, the switching signal generating circuit 30 generates a switching signal so as to energize the U-phase coil CU and the V-phase coil CV. I do.
[0038]
When both motors MA and MB are synchronized, the rotor position detection signal becomes as shown in FIG. 9 described above, and there is no error in the rotor position detection signal. In this embodiment, even after the motors MA and MB are synchronized, the signal detection circuit 40 alternately outputs the position detection signals of the motors MA and MB between the motors at, for example, 30 °, 90 °, 150 °,. Switching and selection may be performed, and the switching signal generation circuit 30 may output a switching signal based on the selected position detection signal.
[0039]
Note that a sine wave PWM control method for performing PWM (pulse width modulation) control on the switching elements so that the voltages applied to the motors MA and MB become sine waves equivalently is well known. If this method is applied to the switching signal generation circuit 30 and the switching elements are driven by PWM pulses, the motors MA and MB can operate more stably.
In the above embodiment, the case where two DC brushless motors are operated in parallel has been described, but the present invention is also applicable to the case where three or more motors are operated in parallel.
[0040]
【The invention's effect】
As described above, according to the present invention, a plurality of DC brushless motors can be stably driven in parallel with low noise by a single drive circuit, and a plurality of fans, pumps, etc. which require low noise are required. Can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
FIG. 2 is an operation explanatory diagram of a speed setting circuit and a DC current setting circuit in FIG. 1;
FIG. 3 is an operation explanatory diagram of a speed setting circuit and a DC current setting circuit in FIG. 1;
FIG. 4 is a circuit diagram showing a second embodiment of the present invention.
FIG. 5 is an operation explanatory diagram of a speed setting circuit, a position signal error detection circuit, and a DC current setting circuit in FIG. 4;
FIG. 6 is a timing chart showing an operation when there is an error in a rotor position detection signal of each motor.
FIG. 7 is a circuit diagram showing a conventional technique.
FIG. 8 is a circuit diagram showing a configuration of a signal selection circuit in FIG. 7;
FIG. 9 is a timing chart showing the operation of FIG.
[Explanation of symbols]
E DC power supplies T1 to T6 Switching elements U, V, W Output terminals MA, MB DC brushless motors CU, CV, CW coils HU, HV, HW Hall element 11 Stator 12 Rotor 21, 22 Rotor position detection circuit 30 Switching signal generation circuit 40 signal selection circuit 50 speed setting circuit 60 speed control circuit 70 DC current setting circuit 80 position signal error detection circuit

Claims (3)

In order to drive a plurality of DC brushless motors connected in parallel with each other at the same speed by a drive circuit having a plurality of semiconductor switching elements, a switching signal generating unit uses the rotor position detection signal of each motor to generate a signal for the switching elements. A parallel drive circuit of a DC brushless motor for generating a switching signal,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
Speed control means for accelerating each motor to a predetermined speed after the lapse of the certain period, a parallel drive circuit for a DC brushless motor. In order to drive a plurality of DC brushless motors connected in parallel with each other at the same speed by a drive circuit having a plurality of semiconductor switching elements, a switching signal generating unit uses the rotor position detection signal of each motor to generate a signal for the switching elements. A parallel drive circuit of a DC brushless motor for generating a switching signal,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
A DC brushless motor parallel drive circuit, comprising: speed control means for operating each motor at a low speed after the lapse of the certain period, and thereafter accelerating the motor to a predetermined speed. In order to drive a plurality of DC brushless motors connected in parallel with each other at the same speed by a drive circuit having a plurality of semiconductor switching elements, a switching signal generating unit uses the rotor position detection signal of each motor to generate a signal for the switching elements. A parallel drive circuit of a DC brushless motor for generating a switching signal,
During the period in which the rotor position detection signal of each motor does not change, the rotor position detection signal used for generating the switching signal is switched between the motors, and the switching signal is generated using the rotor position detection signal of the switched motor. A parallel drive circuit including a signal selection unit that outputs a control signal to the switching signal generation unit;
Means for flowing a direct current to the stator coil of each motor for a certain period after starting,
Position signal error detection means for detecting an error of a rotor position detection signal of each motor,
Speed control means for operating each motor at a low speed after the elapse of the certain period, and accelerating each motor to a predetermined speed after an error detected by the position signal error detection means during the low speed operation becomes a specified value or less. A parallel drive circuit for a DC brushless motor, comprising:

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