JP3328972B2 - Position sensorless brushless DC motor controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position sensorless brushless DC motor for obtaining a commutation signal to a stator winding by using a back electromotive force generated in the stator winding as the rotor rotates. The control device is particularly suitable for performing stable rotation in the entire operation range from low speed to high speed and high efficiency rotation.

[0002]

2. Description of the Related Art In recent years, a commutation signal to a stator winding has been obtained by utilizing a back electromotive force generated in a stator winding due to rotation of a rotor. A drive system for brushless DC motors has been proposed (Suzuki, Ogasawara, and Akagi, "A Method for Configuring a Position Sensorless Brushless DC Motor", 1988, National Institute of Electrical Engineers of Japan, 1988)
o. 34).

[0003] In this type of driving system, the speed is controlled by chopper control using a voltage-source inverter circuit (motor driving circuit) of a 120-degree conduction type as a main circuit. That is, the back electromotive force e _a , e _b , e of each phase generated by the rotation of the rotor on the stator winding of each phase of U, V, W.
Due to the relationship between _c and the drive signal applied to the pair of transistors of the inverter circuit, each phase is 60 ° × 2 open periods within the electrical angle of 360 ° period (the open phase is a period during which no drive signal is applied to the transistor). ).

In order to drive the motor in such a driving system, the motor is first excited for a certain period by a drive signal of an arbitrary excitation pattern based on a starting sequence, and the rotor is moved to a position corresponding to the excitation pattern. Then, the motor is rotated by giving an arbitrary commutation signal and switching the excitation pattern. Then, based on the back electromotive force generated in the stator winding due to the rotation of the motor at this time, the position of the rotor is detected as a result. That is, when the back electromotive force is generated in the stator winding by the rotation of the rotor, the terminal voltage of the open phase changes due to the back electromotive force, and P
When the anode potential of the reflux diode side is higher than the reference voltage Ed ^+, or, the cathode potential of the freewheeling diode of the N-side reference voltage Ed ^- becomes lower than the return diode becomes conductive. Therefore, by detecting the conduction state of the open-phase diode, the mode of the current excitation pattern can be detected, and as a result, the rotor is detected. In reality, the conduction state of each diode is detected by comparing the reference voltage Ed with the terminal voltage of each diode by a mode detection circuit that detects the current mode.

The conduction state of the open-phase diode is as follows:
It is detected near 30 degrees during the 60-degree open period. That is, the conduction state is detected with a leading phase of approximately 30 degrees.
Therefore, the control circuit forms a drive signal by uniformly delaying the phase by approximately 30 degrees (phase shift) for each phase in order to perform the next commutation, and performs chopper control using the drive signal. I have.

[0006]

However, in the above-described conventional position sensorless brushless DC motor drive system, the back electromotive force is basically detected using the chopping-off period of the PWM duty. When the number of rotations is in the high rotation region, the duty becomes high, so that the period of the open phase for detecting the back electromotive force is narrowed, and the back electromotive force may not be detected properly.

If the detection of the back electromotive force is not successful, the output of the detection signal is delayed, and commutation in a normal phase cannot be performed. In the worst case, the drive is stopped without commutation. As a result, when the motor stops in the high rotation range, a current for demagnetizing the magnet flows, causing a fatal problem in the motor that the magnet performance is reduced. Further, in the above-described conventional driving method, since the phase shift amount is calculated based on the detected rotation speed,
Even when operating at the same rotational speed, if a large load torque fluctuation occurs, the reference point to be commutated becomes inaccurate and the commutation time becomes inappropriate, resulting in an invalid current at the commutation time. Increases, the power factor of the motor decreases, the motor efficiency deteriorates, and there is a risk of causing rotation failure.

Accordingly, the present invention provides a control device for a position sensorless brushless DC motor capable of reliably performing commutation and driving a stable motor even when back electromotive force is not detected when the motor is driven. The purpose is to provide.

[0009]

According to a first aspect of the present invention, there is provided a control device for a position sensorless brushless DC motor, comprising: a motor drive circuit for rotating a brushless DC motor by chopper control; A back electromotive force detection circuit for detecting a back electromotive force generated in the stator winding of each phase of V and W, a rotation speed determination circuit for determining a rotation speed of the motor based on a detection output from the back electromotive force detection circuit, Determining commutation timings corresponding to the rotational speeds of the U, V, and W phases based on outputs from the back electromotive force detection circuit and the rotation speed determination circuit, and detecting a detection output from the back electromotive force detection circuit. A phase determination circuit for temporarily storing the detection output from the back electromotive force detection circuit when there is no detection output from the back electromotive force detection circuit, and determining a commutation timing based on the stored detection output immediately before; and an output from the phase determination circuit. Based on there is a configuration in which a drive signal forming circuit for outputting a drive signal to the motor drive circuit. Further, the phase determination circuit, a storage unit for sequentially and temporarily storing the back electromotive force detection output of each phase from the back electromotive force detection circuit, and the storage unit when there is no detection output from the back electromotive force detection circuit And an input detecting unit for calling a back electromotive force detection output immediately before stored in the storage unit. The input detection unit of the phase determination circuit further detects the back electromotive force immediately before each phase stored in the storage unit. Of the outputs, the configuration is to call back electromotive force detection output of any phase, or the input detection unit of the phase determination circuit, of the back electromotive force detection output immediately before each phase stored in the storage unit, The counter electromotive force detection output of the same phase is called. Further, as the back electromotive force detection output stored in the storage unit of the phase determination circuit, the immediately preceding back electromotive force detection output averaged corresponding to the detected rotation speed is stored.

[0010]

[0011]

According to the control device for a position sensorless brushless DC motor according to the first aspect, when the rotor rotates,
A back electromotive force is generated in the stator winding of each phase, and the back electromotive force causes a current to start flowing to the open-phase freewheeling diode, thereby turning on the current. Detected by the circuit. The rotation speed determination circuit determines the current rotation speed of the motor based on the detection output from the back electromotive force detection circuit. In the phase judgment circuit,
Based on the detection output from the back electromotive force detection circuit and the output from the rotation speed judgment circuit, the mode of the PWM excitation pattern is detected, and the commutation timing of each phase of the phase advanced by approximately 30 degrees is detected. The commutation timing of each phase is determined for each phase, and a phase-shifted output for delaying the phase in accordance with the leading phase amount of each phase is transmitted.

Then, a drive signal is formed by the drive signal forming circuit based on the phase-shifted commutation timing of each phase, and the stator winding is excited by the motor drive circuit. In this case, the phase determination circuit detects whether or not the detection output from the back electromotive force detection circuit is input, and simultaneously stores the input detection output sequentially and temporarily. When the detection output is not input, the phase is determined based on the immediately preceding detection output temporarily stored, and the output of the commutation timing based on the immediately preceding detection output is sent to the drive signal forming circuit.

Therefore, even when the back electromotive force cannot be detected by the back electromotive force detection circuit and the detection output is not input to the determination circuit, for example, when the motor is rotating at a high speed, the phase can be reliably maintained at a normal phase. Commutation becomes possible, and it is possible to prevent rotation of the motor from being stopped or excitation current from flowing when the rotation of the motor is stopped, thereby reducing the performance of the magnet.

[0014]

[0015]

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a control device for a position sensorless brushless DC motor according to the present embodiment, and FIG. 2 shows a 120 ° energized voltage type inverter circuit (motor drive circuit) for driving the brushless DC motor. As shown in FIG. 2, the brushless DC motor 1 includes a rotor 2 and a stator 3
The stator 3 is provided with three-phase windings of U, V, and W, and the rotor 2 has four magnetic poles formed by permanent magnets. The inverter circuit 4 includes P-side transistors Ta ⁺ , Tb ⁺ , Tc ⁺ to which the freewheel diodes Da ⁺ , Db ⁺ , Dc ⁺ are connected, and freewheel diodes Da ⁻ , D
b ⁻ and Dc ⁻ are connected to the transistors Ta ⁻ and T on the Ν side.
b ^-, Tc ^- is composed of a.

Further, by performing a chopper control by combining a set of the P-side transistor and the Ν-side transistor of the inverter circuit 4, a three-phase DC current can be selectively supplied to two of the windings of each phase. A control circuit is provided for detecting the back electromotive force generated in each winding of the motor 1 by sequentially rotating the rotor by flowing a current through the windings to form a magnetic field. In this control circuit, as shown in FIG. 3, an output pattern mode of a drive signal corresponding to an excitation pattern for continuing normal rotation of the motor 1 is preset to 5 to 0, and each excitation pattern and commutation timing detection are performed. The relationship between the phase and the conducting diode is as shown in FIG. 3. The commutation in this order drives the motor to rotate, and based on the back electromotive force generated in each winding of the motor 1, each of the inverter circuits 4 The conduction state of the freewheeling diode is determined.

Further, the control circuit includes a back electromotive force detection circuit 5 for detecting back electromotive force generated in each winding of the motor 1,
A rotation speed judging circuit 6 for judging the rotation speed of the motor 1 based on the detection output from the back electromotive force detection circuit 5, and based on the detection output from the rotation speed judgment circuit 6 and the back electromotive force detection circuit 5. Of the phase windings U, V, and W to determine which phase winding is the back electromotive force, determine the commutation timing of each phase, and output a commutation signal shifted by a phase shift amount. A drive signal that forms a signal of six steps based on the phase determination circuit 7 and the commutation timing output from the phase determination circuit 7 and that forms a drive signal for chopper-driving the P-side and N-side transistors of the inverter circuit 4 Forming circuit 10,
Amplifier 1 for amplifying drive signal and outputting it to each transistor
1 is provided.

The phase judging circuit 7 has an input detecting section 8 for detecting whether there is a detection output from the back electromotive force detection circuit 5 and a storage section 9 for storing the detection output from the back electromotive force detection circuit 5. And When there is a detection output from the back electromotive force detection circuit 5, the input detection unit 8 sequentially stores the input detection output for each phase in the storage unit 9, and detects the detection output from the back electromotive force detection circuit 5. When there is no output, the storage unit 9
Is called, and the phase is determined based on the called detection output.

Next, a case where the operation of the motor is controlled by the control device having the above configuration will be described with reference to a flowchart shown in FIG.

In order to start the motor 1, step S1
Then, the stator winding of the motor 1 is excited with a constant excitation pattern, and for example, the inverter circuit 4 is driven so that the excitation pattern of the mode 5 becomes the excitation pattern of mode 5 among the six excitation patterns shown in FIG.
The transistors Ta + and Tb- are combined to perform chopper control, and a current flows. Then, the energized state is maintained for 0.8 seconds, and the rotor 2 is turned up to 180 electrical degrees.
The rotation is fixed in the forward or reverse direction, and the position of the rotor is determined. From this state, commutation for switching the current to another winding is performed. In this case, the commutation is performed so that the mode of the excitation pattern becomes mode 3 which is two steps ahead of mode 5.
Transistor Tb ⁺ and Tc of the inverter circuit 4 ^- and the combined commutation is performed. Accordingly, the rotor 2 is started to rotate forward and accelerated in accordance with the excitation pattern of mode 3 advanced by 120 electrical degrees in the forward direction in the forward direction. The degree of acceleration at the time of the start is determined by the magnitude of the current value to be supplied and the state of the load. In the present embodiment, for example, about 5 A at the moment of the start,
A rotation speed is reached at which the back electromotive force required for position sensorless operation can be generated.

[0022] rotor by commutation during the start rotates, counter electromotive force is generated in the stator windings, in step S2, the opening phase U- phase diode Da ^- conductive state counter electromotive force detecting circuit 5 is detected. That is, the rotor 2
If rotation normal, the reference voltage Ed (Ed ^+, Ed ^-) set to a predetermined value the forward voltage drop of the diode and by comparing the terminal voltage of each diode, the diode Da ^- conductive state is detected in the , the diode Da of the conducting state ^- by, the current excitation pattern mode is detected. The detection outputs detected by the back electromotive force detection circuit 5 are sequentially
It is input to the rotation speed judgment circuit 6 and the phase judgment circuit 7.

The rotation speed determination circuit 6 determines the rotation speed based on the detection output from the back electromotive force circuit 5 (S3).
In the phase determination circuit 7, the input detection unit 8 determines whether there is a detection output from the back electromotive force detection circuit 5 (S4). If there is a detection output, the storage unit 9 sequentially stores the detection output for each phase. The detection output is stored (S5). With this,
Detection output from counter electromotive force detection circuit 5 and rotation speed determination circuit 6
The commutation timing is detected on the basis of the detection output from, and a commutation signal having a phase delayed according to the commutation timing is formed, and the commutation signal is sent to the drive signal forming circuit 10 (S
7).

That is, in the back electromotive force detection circuit 5, since the back electromotive force is detected at about 30 degrees in the open period of 60 degrees, the phase is substantially the same as the next commutation point in the next excitation pattern mode 2. Since the phase is advanced by 30 degrees, the phase determination circuit 7 performs a phase shift of delaying the phase in accordance with the commutation timing to form a commutation signal.

On the other hand, when no detection output is input,
The immediately preceding detection output for each phase stored in the storage unit 9 is called (S6), and a phase shift is performed based on the immediately preceding detection output to form a commutation signal (S7).

Then, in the drive signal forming circuit 10,
A drive signal for driving a set of transistors is formed based on these commutation signals (S8), and sensorless operation is continued in step S9, and during operation, steps S2 to S9 are performed.
Is repeated.

Therefore, especially in the high-speed rotation range,
Even when the PWM off period becomes narrow and the back electromotive force cannot be detected properly, the phase is determined based on the temporarily stored immediately preceding detection output, and a commutation signal based on the immediately preceding detection output is obtained. Commutation at a normal phase according to the number of rotations is possible, and the worst case of stopping the motor drive at high speed rotation can be prevented from occurring, and the performance of the magnet can be prevented from deteriorating due to the demagnetization current.

In the above embodiment, on the assumption that the shift amounts of the U, V, and W phases are different, the storage section of the phase determination circuit stores the detection output from the back electromotive force detection circuit for each phase. However, the present invention is not limited to this. For example, when there is not much difference between the shift amounts of the respective phases, the stored detection outputs of different phases may be called and used.
Further, when storing in the storage unit, an average detection output corresponding to the average speed may be stored in the storage unit and used.

Next, another embodiment of the present invention will be described with reference to FIGS. The control device for the position sensorless brushless DC motor according to the present embodiment achieves higher efficiency of the motor by setting an appropriate phase shift amount based on the motor rotation speed and the load torque determined from the duty ratio. Things.

That is, FIG. 5 shows a schematic functional block diagram of the position sensorless brushless DC motor according to the present embodiment. The brushless DC motor main body 1, a drive circuit section 21 for supplying a drive current to the motor 1, and a A detection circuit unit 22 that detects an actual driving state of the motor and collects data used for control, and based on the detection data, maintains a required number of rotations or enables highly efficient motor operation.
And a control circuit section 23 for controlling the drive circuit section 21.

The driving section 21 is provided with a control circuit section 2 to be described later.
3 based on a duty ratio setting signal from the chopper switching circuit and a chopper signal generation circuit 24 for switching the duty ratio and a commutation signal from the control circuit unit 23.
An output pattern mode selection circuit 25 for selecting and outputting a commutation mode, a drive signal forming circuit 26 for outputting a signal for performing a switching operation of each transistor of the inverter circuit 4 based on this mode, and a DC power supply unit, ,
An inverter circuit 4 that switches the transistor in accordance with the operation signal and switches and supplies an exciting current to each motor coil. That is, the next excitation pattern mode is output from the output pattern mode selection circuit 25 based on the commutation signal finally corrected from the control circuit unit 23 and output at the timing determined by the phase shift amount. Has become. Next, based on this mode, a signal for switching operation of each transistor of the inverter circuit 4 is output from the drive signal forming circuit 26. The exciting current is switched and supplied to each coil unit according to the mode by the inverter circuit 4, and the motor 1 is driven to rotate. Further, the chopper signal generation circuit 24 generates a chopper signal based on a chopper switching command from the control circuit unit 23 and a duty ratio setting signal indicating a rotation speed of the motor, and outputs the generated chopper signal to the drive signal forming circuit 26.

The detection circuit section 22 includes an inverter circuit 4
Connected in parallel to the supply lines from
The mode electromotive force of each motor coil is determined by the conduction state of the freewheeling diode, thereby determining the state of current supply to the motor coil. A reference point determination circuit 29 for determining a detection point serving as a reference point of the flow signal.

The control circuit section 23 is provided outside the motor device and the like, and is operated by a user or the like to input an operation and output a required value according to the operation.
And a microcomputer 30 connected to the controller 30 and the detection unit. The microcomputer 31 includes an A / D converter for digitally converting each input signal, an I / O port, a CPU,
It has a memory and the like,
An appropriate amount of phase shift is set based on the rotation speed and the load torque from the detection unit.

That is, the microcomputer 31
, The rotation speed based on the request speed command from the controller 30 is automatically controlled by another built-in program in the microcomputer 31 so as to be kept constant. Specifically, the actual motor speed is detected,
The difference between the rotation speed and the required rotation speed is determined, and the duty ratio is corrected and changed so as to reduce the difference, so that the supply voltage to the motor 1 is increased or decreased so that the motor 1 reaches the required rotation speed. Controlling. This is generally D
As shown in FIG. 6A, when the voltage value supplied to the exciting coil changes to high or low, the motor speed of the C motor increases or decreases in direct proportion. Utilizing this, the average supply voltage to the motor is adjusted by chopper control to control the rotation speed of the motor. Therefore, due to fluctuations in motor load due to external factors and changes in the required number of revolutions,
If the actual speed does not match the required speed,
This duty ratio is newly reset according to the difference in the number of rotations. That is, the duty ratio reflects the influence of the load torque in order to maintain the rotation speed.

Then, according to the duty ratio set in the microcomputer 31 and the detected rotation speed, the processing of the present embodiment is performed such that an appropriate phase shift amount corresponding to the load torque and the rotation speed is obtained. Are performed inside the microcomputer 31.

That is, referring to FIG. 6B, in this type of DC motor, when the supply voltage is constant, the rotation speed and the load torque are in inverse proportion to each other. In other words, if one of these can be determined,
The other will be able to determine. Therefore, if the supply voltage and the rotation speed can be determined, the load torque can be determined. Then, in the present embodiment, the voltage value defining the rotation speed is increased or decreased by chopper control. That is, this voltage value is set by the duty ratio. Therefore, the duty ratio and the load torque according to the rotation speed can be easily determined. That is, it is possible to directly determine the load torque from the duty ratio and the number of revolutions without converting the duty ratio into a voltage value.

The data of the appropriate phase shift amount corresponding to the actual load torque and the rotation speed, which are expected to differ depending on the size and weight of each motor, are collected and set in advance by experiments and the like. I have. That is, FIG.
As shown in (a), (b), and (c), the phase shift amount is corrected as shown by a solid curve in FIG. I have. Specifically, at each rotation speed, the load torque is 2
When the rotation speed is equal to or more than Nm, at 1000 rpm, the phase shift amount becomes −10 ° in electrical angle from the phase shift correction amount based on the normal rotation speed, and becomes −5 ° at 3500 rpm, and −8 ° at 7000 rpm. The phase shift amount is set by each rotation speed and load torque. Such a data table is registered in advance in a memory such as the ROM of the microcomputer 31 described above. That is, the optimal phase shift amount is recorded at the intersection of the two-dimensional coordinate system represented by the two elements of the rotational speed and the load torque, and the phase shift amount is compared with these two elements and referred to. Has become.

Next, the operation of controlling the driving of the motor by the control device for such a position sensorless brushless DC motor will be described with reference to the flowchart shown in FIG.

First, in step P101, the motor rotation speed is read from the detection circuit section 22. Next, in step P102, the load torque is determined directly from the duty ratio set in the microcomputer 31 and the rotation speed. Then, Step P103
Then, based on the load torque and the rotation speed, an optimum phase shift amount is set by referring to a correction data table stored in a memory prepared in advance. Further, the process proceeds to Step P104, where the timer time of the microcomputer 31 for determining the commutation signal and the output time is set based on the set phase shift amount, and the time count is started. Then, Step P105
This time is counted. Next, step P1
In step 06, the elapse of the timer time is determined. If the time is not up, the process returns to step P105 to continue counting the time.
The process shifts to 7. Then, in this step P107, a commutation signal is output, and the control of this one commutation cycle ends.

As described above, according to the present embodiment,
The load torque is determined from the motor supply voltage and the number of rotations, and a data table in which an appropriate correction phase shift amount is set in advance according to the load torque and the number of rotations of the motor is prepared in advance. Since the appropriate phase shift amount is determined with reference to this table, the optimal phase shift amount can be set according to the load torque and the rotation speed of each region in the entire operation region of the motor, and at the optimal timing. Since commutation is possible, the power factor of the motor is increased, and high efficiency can be achieved.

Further, even when the rotational speed and the load torque fluctuate significantly, the optimum amount of phase shift that can follow the fluctuation can be selected, so that the ineffective current at the commutation point is suppressed. Power saving of the motor can be achieved.

Further, since the actual number of rotations of the motor is determined by the mode signal, a separately provided number of rotations detector is not required, so that the circuit configuration can be simplified, cost can be reduced, and the number of rotations can be reduced. Failure can be prevented.

Further, since the load torque is determined from the duty ratio and the number of revolutions, a separately provided load detector becomes unnecessary. Since the table is stored in the storage unit, the table can be easily updated / changed, and the maintenance and design change can be performed more flexibly than when a table is created by a general electronic circuit configuration.

[0044]

As described above, according to the present invention,
Even if back electromotive force is not detected when driving the motor in the high rotation range, commutation can be performed reliably, so that the motor can be operated stably even in the high speed rotation range and the motor stops at high speed rotation. Therefore, it is possible to prevent the demagnetizing current from flowing due to the stoppage and reduce the performance of the magnet as in the related art.

[0045]

[Brief description of the drawings]

FIG. 1 is a block diagram of a control device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a brushless DC motor and an inverter circuit.

FIG. 3 is a diagram showing an excitation pattern and its mode.

FIG. 4 is a flowchart of motor rotation control.

FIG. 5 is a block diagram of a control device according to another embodiment of the present invention.

FIG. 6A is a diagram showing the rotation speed and voltage of a DC motor, and FIG.
FIG. 4 is a characteristic diagram showing a relationship between voltage and load torque.

FIGS. 7A to 7C are diagrams showing a relationship between a load torque and an optimal phase shift amount at each rotation speed.

FIG. 8 is a flowchart showing a control process for selecting an optimal phase shift amount.

[Explanation of symbols]

1 brushless DC motor 2 rotor 4 motor drive circuit 5 counter electromotive force detecting circuit 6 rpm judging circuit 7 phase determining circuit 8 input detecting unit 9 memory 10 the drive signal forming circuit ^{Da +, Db +, Dc +} , Da -, db ^-, Dc ^- freewheeling diode U, V, W phases of the stator winding

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-99491 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 6/18

Claims (5)

(57) [Claims] 1. A motor drive circuit for rotating a brushless DC motor by chopper control, and a back electromotive force detecting back electromotive force generated in stator windings of U, V, and W phases as the rotor rotates. A power detection circuit, a rotation speed determination circuit that determines the rotation speed of the motor based on the detection output from the back electromotive force detection circuit, and U, V based on the outputs from the back electromotive force detection circuit and the rotation speed determination circuit. , W and the commutation timing corresponding to the rotation speed of each phase are determined, and the detection output from the back electromotive force detection circuit is temporarily stored sequentially, and when there is no detection output from the back electromotive force detection circuit, A phase determination circuit that determines a commutation timing based on the stored immediately preceding detection output, and a drive signal forming circuit that outputs a drive signal to the motor drive circuit based on an output from the phase determination circuit , The detection output from the back electromotive force detection circuit is
In some cases, based on the detection output,
Stored when there is no detection output from the power detection circuit
Based on the immediately preceding detection output,
The commutation timing is determined by
Based on these outputs, the drive signal forming circuit outputs the
A control device for a position sensorless brushless DC motor, wherein a driving signal is output to a motor driving circuit . 2. The memory according to claim 1, wherein the phase determination circuit temporarily and temporarily stores the back electromotive force detection output of each phase from the back electromotive force detection circuit, and there is no detection output from the back electromotive force detection circuit. 2. The control device for a position sensorless brushless DC motor according to claim 1, further comprising: an input detection unit that sometimes reads the immediately preceding back electromotive force detection output stored in the storage unit. 3. The phase detection circuit according to claim 1, wherein the input detection unit of the phase determination circuit calls back electromotive force detection output of an arbitrary phase among the back electromotive force detection outputs immediately before each phase stored in the storage unit. Item 2. A control device for a position sensorless brushless DC motor according to item 2. 4. An input detection section of said phase determination circuit, wherein a back electromotive force detection output of the same phase is called out of back electromotive force detection outputs immediately before each phase stored in said storage section. A control device for the position sensorless brushless DC motor according to the above description. 5. The position sensorless brushless DC motor according to claim 1, wherein the storage unit of the phase determination circuit stores an immediately preceding averaged back electromotive force detection output corresponding to the detected rotation speed. Control device.