JPH04317587A - Sensorless-brushless dc motor driving circuit - Google Patents

Abstract

PURPOSE:To minimize a back motion to be generated at the time of starting by transiting a synchronous operation frequency from a frequency higher than a self-starting frequency of a sensorless-.brushless DC motor to a lower frequency when the motor is started. CONSTITUTION:When a motor is started, an oscillation frequency, i.e., an exciting frequency of a VCO 7 is transited to a lower value. As the frequency is lowered, a torque tending to drive the motor is increased. If the torque is increased to a predetermined value or more due to a decrease in the exciting frequency, the motor starts rotating. That is, when the oscillating frequency of the VCO 7 is lowered to a certain frequency (<fs), the motor is self-started (point B). Thus, the motor is always started at a limit frequency (fs) capable of generating necessary minimum limit torque to self-start. Thus, a back motion to be generated at the time of starting the motor can be minimized.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a sensorless brushless DC motor drive circuit, and more particularly, to a technology that is effective when applied to the drive of a commutatorless small DC motor that does not have a sensor for detecting the rotor position. The present invention relates to a technique that is effective when used, for example, to drive a motor of a small hard disk storage device.

0002

2. Description of the Related Art In a typical brushless DC motor, energization of a stator coil is controlled based on the rotor position detected by a position sensor such as a Hall element. However, position sensors hinder motor miniaturization. Furthermore, depending on the environment in which the motor is used, it may be difficult to install a position sensor. Therefore, recently, brushless DC motors that do not use position sensors, so-called sensorless brushless DC motors, have been attracting attention.

[0003] This sensorless brushless DC motor is driven because there is no sensor to detect the position of the rotor.
The energization of the stator coil is controlled based on the induced voltage (B-EMF) appearing at the terminal of the stator coil. However, at the time of startup, energization control based on the above-mentioned induced voltage cannot be performed, so synchronous operation is performed in which energization of the stator coil is controlled externally to force rotation.

[0004] In the conventional circuit, the synchronous operation frequency when starting the motor is fixedly set in advance to a frequency that can reliably start the motor automatically, and the synchronous operation is started at this set frequency. (For example, Toshiba Corporation
Published “Toshiba Review 1990 vol.45No.
．． 9” pages 755-758, sensorless/brushless DC
(See motor drive technology).

[0005]

[Problems to be Solved by the Invention] However, the inventors have found that the above-mentioned technique has the following problems. That is, the back motion caused by the motor temporarily reversing at startup is large. The motor did not always start smoothly. For this reason, for example, in a hard disk storage device, there is a risk that the storage medium may be damaged by the impact upon startup.

An object of the present invention is to provide a technique for minimizing the back motion that occurs when starting a sensorless brushless DC motor. The above and other objects and features of the present invention will become apparent from the description herein and the accompanying drawings.

[0007]

[Means for Solving the Problems] Among the inventions disclosed in this application, a brief overview of typical inventions will be as follows.
It is as follows. That is, the synchronous operation frequency when starting a sensorless brushless DC motor is made to transition from a frequency higher than the self-starting frequency of the motor to a lower frequency.

[0008]

According to the above-described means, the sensorless brushless DC motor is always started at the limit frequency at which the motor can generate the minimum torque necessary for self-starting. This achieves the objective of minimizing the back motion that occurs when starting the sensorless brushless DC motor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In addition, in the figures, the same reference numerals include the same or equivalent parts. FIG. 1 shows an embodiment of a sensorless brushless DC motor drive circuit to which the technology of the present invention is applied.

In the figure, Lu, Lv, and Ly are stator coils arranged along the rotational direction of the rotor, 1 is a commutation generation circuit, 2 is a multiphase drive circuit, 3 is a zero level comparison circuit, and 4 5 is an edge detection circuit, 5 is a timing adjustment circuit, 6 is an edge detection control circuit, 7 is a VCO (voltage controlled variable frequency oscillator circuit), 8 is a clock switching circuit, 9
is the control section. The commutation generation circuit 1 generates a multiphase control signal, a so-called commutation signal, for controlling energization to each stator coil (Lu, Lv, Lw) based on an externally applied clock CK (CK1 or CK2). Occur.

The multiphase drive circuit 2 energizes and drives each stator coil (Lu, Lv, Lw) for each phase based on the above-mentioned commutation signal. The zero level comparison circuit 3 converts the induced voltages (U-N, V-N, W-N) appearing at the terminals of each stator coil (Lu, Lv, Lw) to a reference potential (
0V). This zero level comparison circuit 3 uses a comparison circuit with hysteresis having constant input threshold values VthH and VthL.

The edge detection circuit 4 detects the zero crossing point of the induced voltage waveform appearing at the terminal of the stator coil for each phase by detecting the edge of the output waveform of the comparison circuit 3. The zero crossing point detected here is output in the form of a pulse. The edge detection pulses of each phase are logically added to become the reference clock CK2 given to the commutation generation circuit 1 during autonomous operation. The timing adjustment circuit 5 receives the reference clock CK (CK1 or CK
Perform the phase adjustment in 2).

The edge detection control circuit 6 controls the edge detection circuit 4 to selectively perform edge detection during the non-energized period of the stator coil. This detection control is performed based on a status signal indicating the operating state of the commutation generation circuit 1. VCO7 is
A reference clock CK1 is generated to be given to the commutation generation circuit 1 during synchronous operation. The clock switching circuit 8 switches and selects the reference clock CK (CK1 or CK2) applied to the commutation generation circuit 1 via the timing adjustment circuit 5.

The control unit 9 is configured to perform the following control based on the operating status of each circuit described above. That is, (1) By controlling the clock switching circuit 8 based on the output state of the edge detection circuit 4, a synchronous operation is performed in which the stator coil energization is controlled based on the oscillation output (CK1) of the VCO 7 at startup. On the other hand, after startup, the stator coil is energized by the stator coil's induced voltage (CK2).
autonomous driving controlled based on

(2) By controlling the oscillation frequency of the VCO 7, as shown in FIG. 2, startup control is executed to transition the synchronous operation frequency at motor startup from a frequency higher than the motor self-starting frequency fs to a frequency lower than the motor self-starting frequency fs. do. (3) Switching to shift the operation mode to autonomous operation when a zero-crossing point is detected from the terminal voltage waveform of the stator coil by monitoring the detection state of the edge detection circuit 4 during synchronous operation. Execute control.

(4) By monitoring the detection state of the edge detection circuit 4 during autonomous operation, the operation mode can be changed when a zero-crossing point is not detected from the terminal voltage waveform of the stator coil continuously for a certain period of time or more. Execute restart control to return to the state at startup. The operation of the sensorless brushless DC motor drive circuit configured as described above will be described below. Figure 2
indicates the transition state of the synchronous operation frequency and motor drive torque when starting the motor.

FIG. 3 shows the process of clock generation based on state-specific waveforms of the voltage appearing at the terminals of the stator coil and the induced voltage. FIG. 4 shows an overview of the control procedure from the start of startup to transition to autonomous operation. 1 to 4, first, immediately after the motor is started and the motor is still stopped, the motor energization control, that is, the commutation control, is performed by the VCO.
This is performed based on the clock CK1 from 7. Although the stator coil is excited by energization, the oscillation frequency of the VCO 7 starts at a frequency sufficiently higher than the self-starting frequency fs of the motor, so the torque that attempts to drive the motor is still small. Therefore, the motor at this point is in a stopped state (point A in FIG. 2). Moreover, only the energization waveform appears at the terminals of the stator coil, as shown in FIG. 3A (step S1 in FIG. 4).

When the motor starts to start, the oscillation frequency, that is, the excitation frequency of the VCO 7 shifts to a lower value, as shown in FIG. With this decrease in excitation frequency,
The torque trying to drive the motor increases. When the torque increases above a certain level due to a decrease in the excitation frequency, the motor starts rotating. That is, when the oscillation frequency of the VCO 7 drops to a certain level (<fs), the motor starts to start automatically (point B in FIG. 2 and step S2 in FIG. 4).

[0019] In this way, the motor is always started at the limit frequency (fs) at which the motor can produce the minimum torque necessary for self-starting. This results in
Back motion that occurs when starting the motor can be minimized. After this, the oscillation frequency of the VCO 7 continues to decrease further, reaches a frequency sufficiently lower than the self-starting frequency fs of the motor, and then begins to increase. As a result, the self-started motor increases its rotational speed to a certain degree through synchronous operation (point C in FIG. 2).

When the motor starts self-starting through synchronous operation as described above, the induced voltage generated by the rotation of the rotor becomes the drive voltage at the terminals of the stator coil, as shown in FIG. They will appear superimposed. When the rotational speed of the motor increases to a certain level and the amplitude of the induced voltage exceeds a predetermined level (VthH-VthL), as shown in FIG.
As shown in (C), (D), (E), and (F), a clock (edge detection pulse) CK2 based on the induced voltage waveform is output. When this clock CK2 starts to be output, the operation mode changes to the oscillation output of VCO7 (
Due to forced synchronous operation by CK1), the above induced voltage (
CK2) to autonomous operation (steps S3 and S4 in FIG. 4).

In this case, the edge detection performed to output the clock CK2 is performed during the energization period of the stator coil and for a certain period of time (t1) after the stator coil is energized, as shown in FIG. 3(C). This is done in accordance with an edge detection control signal that prohibits detection between the edges. Note that in the illustrated embodiment, during the above period when edge detection is prohibited,
The input of the comparison circuit 3 is pulled up or down to a constant level.

[0022] In the manner described above, the motor is started by synchronous operation and transition to autonomous operation based on the induced voltage is performed. Even after the operation mode shifts from synchronous operation to autonomous operation, monitoring of the clock (edge detection pulse) CK2 based on the induced voltage continues. And clock C
If K2 is not output continuously for a certain period of time,
The operating mode is returned to the state at startup (step S5 in FIG. 4). As a result, even if starting fails or the motor once started stops, the motor can be started reliably.

[0023] Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist thereof. Needless to say. For example, edge detection control based on the state of the commutation generation circuit 1 may be performed on either the input side of the comparison circuit 3 or the input side or output side of the edge detection circuit 4.

In the above description, the invention made by the present inventor was mainly applied to the field of application of the invention, which is the motor drive of a hard disk storage device. However, the present invention is not limited to this, for example. It can also be applied to drive the rotary head motor of a small video tape recorder (8mm video).

[0025]

A brief overview of typical inventions disclosed in this application is as follows. That is, the effect of minimizing the back motion that occurs when starting the sensorless brushless DC motor can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of a sensorless brushless DC motor drive circuit to which the technology of the present invention is applied.

[Figure 2] Graph showing the transition state of synchronous operation frequency and motor drive torque when starting the motor

[Figure 3] Figure 3 is a waveform chart showing the state-specific waveform of the voltage appearing at the terminals of the stator coil and the process of clock generation based on the induced voltage.

[Figure 4] Flowchart showing the control procedure from start-up to transition to autonomous operation

[Explanation of symbols]

Lu, Lv, Ly　Stator coil 1 Commutation generation circuit 2 Multiphase drive circuit 3 Zero level comparison circuit 4 Edge detection circuit 5 Timing adjustment circuit 6 Edge detection control circuit 7 VCO 8 Clock switching circuit 9 Control section fs Motor self-starting frequency

Claims (3)

[Claims] [Claim 1] Sensorless operation that performs synchronous operation in which energization of the stator coil is externally controlled at startup, and autonomous operation in which energization of the stator coil is controlled based on the induced voltage of the stator coil after startup.・Brushless DC
What is claimed is: 1. A sensorless brushless DC motor drive circuit, characterized in that the sensorless brushless DC motor drive circuit is equipped with a control means for shifting a synchronous operation frequency at the time of motor startup from a frequency higher than a motor self-start frequency to a lower frequency. 2. Edge detection means for selectively detecting the zero-crossing point of the voltage appearing at the terminals of the stator coil during a non-energized period of the stator coil, and monitoring the detection state of the edge detection means during synchronous operation. 2. The sensorless brushless DC motor drive circuit according to claim 1, further comprising control means for shifting the operation mode to autonomous operation when the zero-crossing point is detected. 3. Edge detection means for selectively detecting a zero-crossing point of the voltage appearing at the terminal of the stator coil during a non-energized period of the stator coil, and a detection state of the edge detection means for monitoring the detection state of the edge detection means during autonomous operation. Claim 1 or 2, further comprising control means for returning the operating mode to the state at startup when the zero crossing point is no longer detected.
The sensorless brushless DC motor drive circuit described in .