JP2000014186A - Method and apparatus for driving sensorless direct- current motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for driving a sensorless direct- current motor wherein the initial position of a rotor can be determined with accuracy in a stop state or in low speed mode and reliability at the time of driving is enhanced. SOLUTION: The driving method is for a sensorless direct-current motor provided with Y-connected phase coils 28, 30, 32 and a plurality of magnetic poles. The driving method comprises a stage in which an alternating-current voltage signal is applied to bridge circuits 12, 14, 16 connected with the phase coils, respectively, a process in which the output voltage signals of the bridge circuits are input as signals of detection of the inductance of the phase coils, a process in which the input signals of the detection of the inductance of the phase coils are amplified, a process in which the magnitudes of the amplified signals of the detection of the inductance of the phase coils are compared, and a process in which the initial position where two phase coils, except the phase coil the inductance detection signal of which has the maximum value, are magnetized to rotate the rotor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for driving a sensorless DC motor, and more particularly to a method for detecting a relative position between a phase coil and a magnetic rotor to determine the position of the rotor. The present invention relates to a method and an apparatus for driving a sensorless DC motor having a bridge-type inductance detection circuit.

[0002]

2. Description of the Related Art A video cassette recorder includes a capstan motor and a head drum motor. Conventionally, the position of the rotor is determined using a sensor such as a hall sensor or an optical sensor for driving these motors, and the commutation of the phase current applied to the motor is controlled based on the determined position information. However, the sensor method requires a space confirmation for installing the sensor, and there is a problem that the cost of the product is increased by using expensive sensor parts.

[0003] Therefore, recently, a sensorless system using no sensor has been widely adopted. Existing sensorless motors have a back electromotive force (BEMF) induced in the phase coils to determine the position of the rotor.
Is widely used to determine rotor commutation (see US Pat. No. 5,235,264).

[0004] The magnitude of the back electromotive force induced in the coil is proportional to the rotation speed of the rotor. Therefore, the back electromotive force method has no or very little back electromotive force induced when the rotor is stopped or in a low speed state. Therefore, in the back electromotive force method, the commutation control becomes inaccurate before the rotor is rotated at a certain speed or more at which the back electromotive force can be sufficiently detected.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a phase coil having a relative position based on the relative position between the phase coil and the magnetic rotor. It is an object of the present invention to provide a method and an apparatus for driving a sensorless DC motor that can accurately detect an initial position of a rotor in a stopped state or a low-speed mode by detecting inductance.

[0006]

According to a first aspect of the present invention, there is provided a method of driving a sensorless DC motor having a Y-connected phase coil and a plurality of magnetic poles. Applying an AC voltage signal to the coupled bridge circuit; inputting each output voltage signal of the bridge circuit to an inductance detection signal of each phase coil; and amplifying the input inductance detection signal of each phase coil. Comparing the magnitude of the inductance detection signal of each phase coil with the amplified phase detection signal, and excluding the phase coil having the maximum magnitude of the inductance detection signal to rotate the rotor. A step of determining an initial position at which the two phase coils are magnetized.

According to a first aspect of the present invention, there is provided a driving apparatus for a sensorless DC motor including a rotor having a Y-connected phase coil and a plurality of magnetic poles. An AC voltage power supply, a bridge circuit coupled to each phase coil for receiving the AC voltage signal and outputting a difference voltage signal between a reference voltage signal and a terminal voltage signal of the phase coil to an inductance detection signal, and the bridge circuit; An amplifier for amplifying each inductance detection signal of the circuit and the magnitude of the amplified inductance detection signal of each phase are compared, and the remaining two except for the phase where the magnitude of the inductance detection signal has the maximum value are compared. The initial position where the phase is magnetized is determined, and the magnitude of the inductance detection signal is compared for each predetermined rotation angle of the rotor and the commutation is performed. A commutation control section for determining the Shon, and characterized in that it comprises a driving unit for providing a driving current to a pair of phase coils in response to the control of the commutation control section.

The bridge circuit has a first input terminal connected to one terminal of the AC voltage power supply and a common connection point of Y connection, and a second input terminal connected to the other terminal of the AC voltage power supply.
An input terminal, a first resistor and a first capacity connected in series between the first and second input terminals, one terminal of a phase coil of each phase, and one terminal of the AC voltage power supply; A second capacity and a second resistor connected in series between
A first output terminal provided to one terminal of the phase coil;
And a second output terminal provided to a common connection point of the first resistor and the first capacity.

According to a second aspect of the present invention, there is provided a method of driving a sensorless DC motor including a center tap-connected phase coil and a rotor having a plurality of magnetic poles. Sequentially applying an AC voltage signal to a bridge circuit respectively coupled to each of the steps, a step of inputting each output voltage signal of the bridge circuit to an inductance difference detection signal of each pair of phase coils, and Amplifying the inductance difference detection signals of the paired phase coils, comparing the magnitudes of the amplified inductance difference detection signals of the paired phase coils, and detecting the inductance difference to rotate the rotor. Determining an initial position for magnetizing the remaining phase coils except for the pair having the maximum signal magnitude. And wherein the Rukoto.

In order to achieve the above object, a second device of the present invention is to provide an AC voltage signal in a driving device for a sensorless DC motor including a rotor having a center tap-connected phase coil and a plurality of magnetic poles. An AC voltage power supply, and a bridge circuit respectively coupled to the pair of phase coils for receiving the AC voltage signal and outputting a difference voltage signal between terminal voltage signals of the two phase coils to an inductance difference detection signal, An amplifier for amplifying each inductance difference detection signal of the bridge circuit, and a magnitude of the amplified inductance difference detection signal of each phase are compared, and the magnitude of the inductance difference detection signal is a pair of phase coils having a maximum value. Is determined to be the initial position where the remaining phase coils are magnetized, and the inductance difference is detected for each predetermined rotation angle of the rotor. A commutation control section for determining a commutation by comparing the size of the item, and is characterized in that it comprises a driving unit for providing a drive current to the phase coils in response to the control of the commutation control section.

The bridge circuit includes a first input terminal connected to one terminal of the AC voltage power supply and serving as a center tap, a second input terminal connected to the other terminal of the AC voltage power supply, and a coil for each phase. And first and second resistors connected between the first terminal and the second input terminal, and one terminal of a pair of phase coils respectively connected to the first and second resistors. It is characterized by having first and second output terminals.

The above objects and other features and advantages of the present invention will become apparent from the following description of some preferred embodiments of the present invention to which reference is now made.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a sensorless DC motor driving apparatus according to a preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a drive circuit diagram of a sensorless DC motor having an Owen's bridge circuit according to the present invention. 1 includes an AC voltage power supply 10, bridge circuits 12, 14, 16 and amplifiers 18, 20, 22, a commutation control unit 24,
A drive unit 26 and Y-connected phase coils 28, 30, 32
including.

When the rotor rotates, a driving current flows through the phase coils of the motor. Temperature increases as running time increases due to resistance loss. An increase in temperature increases the resistance of the phase coil. The resistivity of copper is linearly dependent on temperature. Owen's brid
ge), causing the output voltage of the inactive phase coil to be unusable for determining rotor position. Therefore, it is desirable that the phase coil and the bridge circuit be installed together in the motor case 34 in order to compensate for the breaking of the equilibrium state of the bridge circuit due to a temperature rise due to the resistance loss of the phase coil.

FIG. 2 is a detailed circuit diagram of a bridge circuit and an amplifier for one phase coil. The bridge circuit 12 includes a first input terminal C to which one terminal of the AC voltage power supply 10 is connected and which is a common connection point of the Y connection, a second input terminal D to which the other terminal of the AC voltage power supply 10 is connected, A first resistor R connected in series between the first and second input terminals C and D;
A first capacity C1 and a second capacity C2 and a second resistor R2 connected in series between one terminal of the phase coil 28 and one terminal of the AC voltage power supply 10; 280 includes a first output terminal B provided to one side terminal and a second output terminal A provided to a common connection point of the first resistor R1 and the first capacity C1. The phase coil 28 is represented by an internal resistance Rx and an inductance Lx.

The amplifier 18 comprises an operational amplifier (U1) having a first output terminal B connected to a non-inverting terminal (+) through a resistor R4 and a second output terminal A connected to an inverting terminal (-) through a resistor R3. . The non-inverting terminal (+) of the operational amplifier U1 is grounded through the resistor R5, and the output terminal is the resistor R5.
7 is grounded. A resistor R6 is connected between the inverting terminal (-) and the output terminal. The resistors R3 and R4 have the same resistance value, and the resistors R5 and R6 have a resistance value that is m times larger than the resistance values of the resistors R3 and R4.

The circuit constants of the bridge circuit 12 are as follows: the resistance of the phase coil 28 is 22.5Ω and 813 to 846;
The inductance change having the μH range is obtained. Based on this information, the resistance values R1, R2 and the capacity values C1, C2 of the bridge system in an equilibrium state are obtained.

The voltage characteristic equation of the bridge system according to the applied AC voltage v (t) is as follows.

(Equation 1)

(Equation 2)

The value of i ₁ i _{2 is obtained from} the above equations (1) and (2). Further, the voltage V _A (t) of the output terminals A and B,
V _B (t) is obtained as follows.

## EQU3 ## v _A (t) = v (t) -R ₁ i ₁ --- (3)

(Equation 4)

In a balanced state, the voltage at the output terminal A is
And the same voltage. So there is no voltage difference between the two output terminals.

FIG. 3A shows the configuration of the phase coils 28, 30, and 32, and FIG. 3B is a sectional view showing the configuration of the magnetic rotor 36. As shown in FIG. Each phase coil has two coils 28a, 28b, 30a, 30b, 32 arranged diagonally.
a, 32b. Therefore, the six coils are distributed and arranged at 60 degrees on the same cylinder. The magnetic rotor 36 is distributed at 45 degrees on the same cylinder and eight magnetic poles are arranged. The magnetic pole has N poles and S poles arranged alternately.

Thus, when the phase coils and the magnetic rotor are overlapped in the state shown, the phase coils 28
The S pole is almost overlapped with the phase coil 30
The N pole and the S pole overlap in the phase coil 32 by が each.

When the rotor 36 rotates in such a state, the inductance of the phase coil changes due to the change in the magnetic field, and this indicates the voltage difference between the two output terminals. However, this voltage difference is very small for direct use. Thus, a differential amplifier 18 is used to amplify this signal.

The output voltage Vout of the differential amplifier is given by the following equation.

Equation 5] _{Vout = m (V A -V B} ) ------ (5) where, m is mR / R as the gain of the differential amplifier.

The AC voltage power supply 10 is a voltage source for supplying a rectangular wave having a magnitude of 10 V, a frequency of 100 kHz and a duty ratio of 25%.

FIG. 4 shows that the inductance of the phase coil is 835.
In the case of μH, an output voltage obtained by amplifying the output voltage of the bridge circuit is shown, and FIG. 5 shows a characteristic graph of the output voltage with respect to the inductance of the phase coil.

In FIG. 5, when the inductance value is 830 μH or more, the absolute value of the maximum voltage is always larger than the absolute value of the minimum voltage. However, the opposite is true for 835 μH or less. The output voltage dependent on the inductance value is measured at the elapse of 62.5 μs. The reason is that it is desirable to measure after being applied to the system for approximately six cycles to ignore the transition state.

FIG. 6 is a waveform diagram of the amplified inductance output voltage of each phase coil corresponding to the rotation angle of the magnet rotor. The solid line shows the output voltage waveform for the phase coil 28, the dotted line shows the output voltage waveform for the phase coil 30, and the dashed line shows the output voltage waveform for the phase coil 32.

In an 8-pole, three-phase (six-coil) motor, phase commutation must be performed every 15 degrees of rotor rotation. As shown in FIG.
Phase voltage profiles are well separated such that at each angle the voltage of one phase is greater than the voltage of another phase.

The commutation control unit 24 compares the magnitudes of the amplified inductance detection signals of the respective phase coils, and magnetizes the remaining two phase coils except for the phase coil having the maximum value of the inductance detection signal. Determined at the initial position.

In the stop state, input signals are sequentially applied to three phases. Then, the returned signal is amplified and the voltage value is measured at a specific time. The three phase voltage values are compared and the activation of the phase is determined based on the largest or smallest value.

When the motor is started, the commutation decision is made to rotate the rotor in the desired direction.

If the inductance detection signal of the phase coil 28 is larger than the inductance detection signal of the phase coils 30 and 32, the commutation control unit 24 controls the drive unit 26 to rotate the rotor, and
32 is magnetized by passing a drive current through it. At the next rotation angle of 15 degrees, the phase coils 28 and 32 are activated because the inductance detection signal of the phase coil 30 is the largest.
During the rotation of the motor, the inactive coil is used as a sensor. The magnetization of the corresponding phase must be performed while the output voltage is in a certain region.

FIG. 7 is a diagram showing a drive circuit of a sensorless DC motor having an inductance bridge circuit according to the present invention. 7 includes an AC voltage power supply 40, bridge circuits 42, 44, 46, amplifiers 48, 50, 52,
It includes a commutation control unit 54, a drive unit 56, and phase coils 58, 60, and 62 connected by center tap. The phase coils 58, 60, 62 are installed in the motor case 64.

FIG. 8 is a detailed circuit diagram of the inductance bridge circuit. A bridge circuit 42 for detecting an inductance difference voltage between the two phase coils 58 and 60 has a first input terminal C connected to one terminal of the AC voltage power supply 40 and serving as a center tap, and another terminal of the AC voltage power supply 40. , A first and a second resistor R1, R2 connected between one side terminal of each of the phase coils 58, 60 and the second input terminal D; First and second output terminals A and B are provided from one terminals of a pair of phase coils 58 and 60 connected to the two resistors R1 and R2, respectively. Phase coil 58 is represented by internal resistance R58 and inductance L58, and phase coil 60 is represented by internal resistance R60 and inductance L60.

The amplifier 48 comprises an operational amplifier U1 having a second output terminal B connected to a non-inverting terminal (+) through a resistor R4 and a first output terminal A connected to an inverting terminal (-) through a resistor R3. The non-inverting terminal (+) of the operational amplifier U1 is grounded through a resistor R5, and the output terminal is grounded through a resistor R7. A resistor R6 is connected between the inverting terminal (-) and the output terminal. The resistors R3 and R4 have the same resistance value, and the resistors R5 and R6 have a resistance value that is m times larger than the resistance values of the resistors R3 and R4.

The commutation control unit 54 compares the magnitudes of the amplified inductance difference detection signals of the respective phases, and removes the remaining phase coils except for a pair of phase coils in which the magnitude of the inductance difference detection signal has the maximum value. Is determined as an initial position to be magnetized, and the commutation is determined by comparing the magnitude of the inductance difference detection signal for each predetermined rotation angle of the rotor.

The driving unit 56 is a commutation control unit 54
The driving current is supplied to each phase coil 58, 60, 62 in accordance with the control of.

The output voltages of the output terminals A and B in the bridge circuit 42 can be obtained by the following equations (6) and (7).

(Equation 6)

(Equation 7)

The output voltage Vout of the amplifier is calculated according to the equations (6) and (7).
Is obtained using the following equation.

Vout = m (V _A −V _B ) −−−−− (8)

If the resistance and inductance of the two phase coils 58 and 60 are the same, there is no voltage difference between the two output terminals A and B. The inductance of the phase coil changes because the position of the magnetic pole relative to the coil changes. Even if the resistances of the two phase coils are the same, a change in inductance creates a voltage difference between the two output terminals A and B.

When a rectangular wave having a magnitude of 10 V, a frequency of 100 kHz and a duty ratio of 25% is applied to the bridge circuit by the AC voltage power supply 10, the inductance difference voltage waveforms shown in FIGS. 9 and 10 can be obtained.

FIG. 9 is a waveform diagram of the maximum voltage of each inductance bridge circuit corresponding to the rotation angle of the magnet rotor when a rectangular wave is input, and FIG. 10 is a diagram illustrating each inductance corresponding to the rotation angle of the magnet rotor when a rectangular wave is input. It is a waveform diagram of the minimum voltage of a bridge circuit.

In FIG. 9, the solid line indicates the maximum inductance difference voltage between the phase coils 60 and 62, and the dashed line indicates the phase coil 6
The maximum inductance difference voltage between 0 and 58 is shown, and the dotted line shows the maximum inductance difference voltage between the phase coils 58 and 60. In FIG. 10, the solid line indicates the minimum inductance difference voltage between the phase coils 60 and 62, and the dashed line indicates the phase coils 60 and 58.
The dotted line shows the minimum inductance difference voltage between the phase coils 58 and 60, and the dotted line shows the minimum inductance difference voltage between the phase coils 58 and 60.

In the stopped state, an input signal is applied to three pairs of two phase coils. The signals returned from each pair of phase coils are measured and compared and commutation based on the maximum or minimum voltage is performed to rotate the rotor.
However, two phase coils are used to determine the rotor position and the other phase coil is magnetized. In this case, the maximum voltage is used to determine the phase coil to be magnetized.

For example, when the voltage difference between the two phase coils 60-62 is larger than 62-58, 58-60, a driving current is applied to the phase coils 58 for rotation of the rotor, and the phase coils 58 are magnetized. At the next rotor rotation angle of 15 degrees, the phase coil 60 is activated.

It is difficult to decide to activate a phase if there are two maxima. In this case, the minimum voltage is used for commutation. For example, 1
At 5 degrees, there is a commutation change point P in phase coils 62-58. The output voltage at this time is the same. But,
The output voltage at 62-58 is lower than the output voltage at 60-62 and 58-60. If the commutation magnetizes the phase coils, the rotor rotates in the desired direction.

FIG. 11 is a waveform diagram of an inductance difference voltage between two phase coils when a sine wave is input. The solid line indicates the inductance difference voltage between the two phase coils 58-60, the dashed line indicates the inductance difference voltage between the two phase coils 60-62, and the dotted line indicates the two phase coils 62-58.
The minimum inductance difference voltage is shown. In FIG. 11, a 10 V, 50 kHz sine wave is provided to the bridge circuit from the AC voltage power supply 40.

The difference voltage in FIG. 11 is a voltage magnitude measured at T = 15 μs when the input signal reaches the minimum value for a specific time.

For example, at a rotor rotation angle of 36 degrees, the voltage difference between the two phase coils 62-58 is greater than another voltage output.
Thus, the phase coil 60 must be magnetized to rotate the rotor. Phase coil 60 is subsequently magnetized while the differential voltage between phase coils 62-58 is greater than the differential voltage of another phase coil pair.

Referring to FIG. 12, it can be seen that during 28-43 degrees when the phase coil 60 is magnetized, the inductance of the phase coil 60 is reduced as compared to increasing the inductance of the other two phase coils. I understand. FIG. 12 shows the inductance of each phase coil depending on the rotor rotation angle.

FIG. 13 is a diagram showing the phase relationship between the input signal and the differential voltage signal under the condition that L60> L58. That is, it can be seen that the input signal and the difference voltage signal have the same phase.

FIG. 14 is a diagram showing the phase relationship between the input signal and the differential voltage signal under the condition that L58> L60. That is, it can be seen that the input signal and the difference voltage signal have different phases.

Such phase angle transition information in addition to the maximum difference voltage can be used for correct commutation.

FIG. 15 shows the magnetization sequence of the phase coil. First, a driving current in the positive direction is applied to the phase coil 58 during the first 15 degrees, a driving current in the negative direction is applied to the phase coil 60 during the next 15-30 degrees, and the next 30-degree. During 45 degrees, a drive current in the positive direction is applied to the phase coil 62. Therefore, the phase coil is 5
The commutation is determined so as to be sequentially magnetized in the order of 8-60-62-58.

[0056]

As described above, according to the method and apparatus for driving a sensorless DC motor having a bridge-type inductance detecting circuit of the present invention, it is possible to accurately determine the initial position of the rotor in the stop state or the low-speed mode. There is an advantage that reliability can be improved when the motor is driven because it can be performed.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to the embodiments, and any person having ordinary knowledge in the technical field to which the present invention belongs may depart from the spirit and spirit of the present invention. Rather, the invention could be modified or changed.

[Brief description of the drawings]

FIG. 1 shows Owen's bridg according to the present invention.
e) A drive circuit diagram of a sensorless DC motor having a circuit.

FIG. 2 is a detailed circuit diagram of the Owen bridge circuit of FIG. 1;

FIG. 3A is a diagram showing a configuration of a phase coil. B is a cross-sectional view showing the configuration of the magnetic rotor.

FIG. 4 is a diagram showing a waveform diagram of an output voltage of a bridge circuit when the inductance of a phase coil is 835 μH.

FIG. 5 is a waveform diagram of an output voltage with respect to an inductance of a phase coil.

FIG. 6 is a waveform diagram of an amplified inductance output voltage of each phase coil corresponding to a rotation angle of a magnetic rotor.

FIG. 7 is a diagram showing a drive circuit of a sensorless DC motor having an inductance bridge circuit according to the present invention.

FIG. 8 is a detailed circuit diagram of an inductance bridge circuit.

FIG. 9 is a waveform diagram of the maximum voltage of each inductance bridge circuit corresponding to the rotation angle of the magnet rotor when a rectangular wave is input.

FIG. 10 is a waveform diagram of a minimum voltage of each inductance bridge circuit corresponding to a rotation angle of a magnet rotor when a rectangular wave is input.

FIG. 11 is a waveform diagram of an inductance difference voltage between two phase coils when a sine wave is input.

FIG. 12 is a diagram showing inductance corresponding to a rotor rotation angle of each phase coil.

FIG. 13 is a diagram illustrating a phase relationship between an input signal and a difference voltage signal under a condition of L1> L2.

FIG. 14 is a diagram illustrating a phase relationship between an input signal and a differential voltage signal under a condition of L2> L1.

FIG. 15 is a diagram showing an energizing sequence of each phase coil.

[Explanation of symbols]

 Reference Signs List 10 AC voltage power supply 12, 14, 16 Bridge circuit 18, 20, 22 Amplifier 24 Commutation control unit 26 Drive unit 28, 30, 32 phase coil 34 Motor case

Claims (13)

[Claims] 1. A method of driving a sensorless DC motor having a Y-connected phase coil and a plurality of magnetic poles, comprising: applying an AC voltage signal to bridge circuits respectively coupled to the phase coils; A step of inputting each output voltage signal to the inductance detection signal of each phase coil, a step of amplifying the input inductance detection signal of each phase coil, and comparing the magnitude of the amplified inductance detection signal of each phase coil. And determining the initial position for magnetizing the remaining two phase coils excluding the phase coil having the maximum value of the inductance detection signal in order to rotate the rotor. Method of driving a sensorless DC motor. 2. The method according to claim 1, further comprising the step of: rotating the rotor according to the initial position determination; and determining the commutation by comparing the magnitude of an inductance detection signal at each predetermined rotation angle of the rotor. The method for driving a sensorless DC motor according to claim 1. 3. The method according to claim 1, wherein the bridge circuit has an Owen bridge structure. 4. A driving apparatus for a sensorless DC motor including a rotor having a Y-connected phase coil and a plurality of magnetic poles, comprising: an AC voltage power supply for providing an AC voltage signal; A bridge circuit respectively coupled to each phase coil to output a difference voltage signal between a reference voltage signal and a terminal voltage signal of the phase coil to an inductance detection signal; and an amplifier for amplifying each inductance detection signal of the bridge circuit. The magnitudes of the amplified inductance detection signals of the respective phases are compared, and the two phases other than the phase having the maximum value of the inductance detection signal are determined as initial positions for magnetizing the two phases, and a predetermined position of the rotor is determined. Commutation control that determines the commutation by comparing the magnitude of the inductance detection signal for each rotation angle When, and sensorless DC motor driving apparatus characterized by comprising a driving unit for providing a driving current to a pair of phase coils in response to the control of the commutation control section. 5. The bridge circuit, wherein: a first input terminal connected to one terminal of the AC voltage power supply and serving as a common connection point of Y connection; and a second input connected to the other terminal of the AC voltage power supply. A first resistor and a first capacity connected in series between the first and second input terminals; and a first terminal of a phase coil of each phase and a first terminal of the AC voltage power supply. A second capacity and a second capacity connected in series between
A resistor; a first output terminal provided to one terminal of the phase coil;
5. The driving apparatus of claim 4, further comprising a second output terminal provided at a common connection point between the first resistor and the first capacity. 6. The driving apparatus according to claim 5, wherein the bridge circuit is installed in the same space as the phase coil to satisfy the same temperature condition. 7. A method for driving a sensorless DC motor including a center tap-connected phase coil and a rotor having a plurality of magnetic poles, wherein an AC voltage signal is sequentially applied to bridge circuits respectively coupled to each pair of the phase coils. Applying each output voltage signal of the bridge circuit to the inductance difference detection signal of each pair of phase coils, and amplifying the input inductance difference detection signal of each pair of phase coils. Comparing the magnitude of the amplified inductance difference detection signal of each pair of phase coils; and removing the pair having the largest magnitude of the inductance difference detection signal to rotate the rotor. Of a sensorless DC motor, comprising a step of determining an initial position for magnetizing three phase coils. Method. 8. The method according to claim 1, further comprising the step of rotating the rotor according to the initial position determination, and comparing the magnitude of the inductance difference detection signal at each predetermined rotation angle of the rotor to determine commutation. The method for driving a sensorless DC motor according to claim 7. 9. A driving apparatus for a sensorless DC motor including a rotor having a center tap-connected phase coil and a plurality of magnetic poles, comprising: an AC voltage power supply for providing an AC voltage signal; A bridge circuit respectively coupled to the pair of phase coils to output a difference voltage signal between the terminal voltage signals of the two phase coils to an inductance difference detection signal; andamplifying each inductance difference detection signal of the bridge circuit. The amplifier compares the magnitude of the amplified inductance difference detection signal of each phase, and returns to the initial position where the remaining phase coils are magnetized except for a pair of phase coils in which the magnitude of the inductance difference detection signal has a maximum value. And commutation by comparing the magnitude of the inductance difference detection signal for each predetermined rotation angle of the rotor. A commutation control for constant and sensorless DC motor driving apparatus characterized by comprising a driving unit for providing a drive current to the phase coils in response to the control of the commutation control section. 10. The bridge circuit includes: a first input terminal connected to one terminal of the AC voltage power supply and being a center tap; a second input terminal connected to the other terminal of the AC voltage power supply; First and second resistors connected between one terminal of a phase coil and the second input terminal, and one terminal of a pair of phase coils connected to the first and second resistors, respectively. The driving device for a sensorless DC motor according to claim 9, further comprising a first output terminal and a second output terminal. 11. The apparatus according to claim 1, wherein the rotor has eight magnetic poles, and each phase coil is formed of two coils, and the commutation is determined for each rotation angle of the rotor of 15 degrees. 10. The driving device for a sensorless DC motor according to any one of claims, 4, 7 and 9. 12. The sensorless DC motor according to claim 1, wherein the AC voltage signal is a rectangular wave having a magnitude of 10 V, a frequency of 100 kHz, and a duty ratio of 25%. Drive. 13. The sensorless DC motor driving apparatus according to claim 9, wherein the AC voltage signal is a sine wave having a magnitude of 10 V and a frequency of 50 kHz.