JP2010035318A - Drive system of brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate occurrence of power loss by detecting dissipation of reflux current by a system where a bidirectional diode is not inserted. <P>SOLUTION: A matching unit of an output of a comparator comparing terminal voltage of a three-phase bridge inverter with voltage which is 1/2 of input voltage of the three-phase bridge inverter, and a position detection expected value is installed. The position detection expected value is switched before and after switching of output of the three-phase bridge inverter. Dissipation of reflux current is detected by using that output of the comparator just after switching of output of the three-phase bridge inverter is the same as the position detection expected value by reflux current, and it becomes the same as the position detection expected value before output of the three-phase bridge inverter is switched when reflux current is dissipated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a drive device for a brushless motor, and more particularly to a drive device for a brushless motor that obtains a rotor position detection signal using a counter electromotive force generated in an armature winding.

  A brushless motor having a permanent magnet in the rotor is superior in efficiency and superior to an induction motor, but it is necessary to detect the magnetic pole position in order to maintain operation. As a magnetic pole position detecting means, a hall sensor for detecting a field magnetic flux is generally widely used. However, when a brushless motor is used for a hermetic compressor used for air conditioning or the like, the hall sensor is exposed to high-temperature and high-pressure refrigerant, a lead wire from the sensor is required, etc. It is difficult to use as.

  A method of obtaining a rotor position detection signal using a counter electromotive force generated in an armature winding is used for a non-printing motor. A 90 ° delay signal obtained from the terminal voltage of the three-phase bridge inverter via a first-order lag filter is used as a timing signal for switching the output of the three-phase bridge inverter. This method has a simple configuration and can control the control circuit at a relatively low speed, and can detect the position without removing the spike voltage caused by the return current generated when the output of the three-phase bridge inverter is switched. .

  A matcher between the output of the comparator that compares the terminal voltage of the three-phase bridge inverter and half the input voltage of the three-phase bridge inverter and the position detection expected value is provided, and the coincidence signal is delayed by 30 ° Then, there is a method of using a timing signal for switching the output of the three-phase bridge inverter. This method is characterized in that high-speed control is possible because a 30 ° delay signal of the terminal voltage becomes a timing signal for switching the output of the three-phase bridge inverter. However, since the spike voltage due to the return current generated when the output of the three-phase bridge inverter is switched is the same as the position detection expected value, it is necessary to remove the spike voltage.

A method of removing a spike voltage by inserting a bidirectional diode between the output of the three-phase bridge inverter and the armature winding has been proposed. A return current flows through the armature winding used for position detection by switching the energization. When this return current disappears, the bidirectional diode is turned off. By using the voltage drop of the bidirectional diode, it is possible to eliminate the period during which current flows through the armature winding, that is, the period during which the return current flows. As a result, the magnetic pole position of the rotor can be detected using the counter electromotive force obtained by removing the spike voltage from the terminal voltage.
For example, Patent Document 1 discloses an example of a drive device for a non-printer motor that detects a rotor position using a counter electromotive force generated in an armature winding.

JP-A-8-182379

  An object of the present invention is to suppress power loss caused by a bidirectional diode inserted as a means for detecting the disappearance of the return current.

  The drive device for a brushless motor according to the present invention has a position detection expectation value for detecting that the output of a comparator for comparing the terminal voltage of the three-phase bridge inverter and the voltage of one half of the input voltage is the same. The values before and after switching the output of the three-phase bridge inverter are appropriately switched.

  Since the disappearance of the return current is detected using the terminal voltage of the three-phase bridge inverter, it is possible to prevent erroneous detection of position detection due to the return current without inserting a bidirectional diode in the armature winding. Therefore, generation of power loss due to insertion of the bidirectional diode can be eliminated.

  The value before and after switching the output of the three-phase bridge inverter is the expected position detection value that detects that the output of the comparator that compares the terminal voltage of the three-phase bridge inverter with a voltage that is half the input voltage is the same. Switch as appropriate.

  FIG. 1 is an overall configuration diagram of a drive device for a brushless motor according to the present invention. Reference numeral 1 denotes an AC power source, 2 a rectifier diode, 3 a power factor improving reactor, and 4 a smoothing capacitor, which constitute a rectifying and smoothing circuit. 5 is a three-phase bridge inverter composed of a total of six semiconductor switches of three upper arms and three lower arms, 7 is a current detector, 8 is an energization switching signal generator, and 9 is the terminal voltage of the three-phase bridge inverter. 10 is a position detection expectation value, 11 is a register, 12 is a coincidence detector, and 13 is a coincidence signal. A drive device for the non-brush motor is configured. Reference numeral 6 denotes a brushless motor including a rotor having a permanent magnet and an armature winding composed of a three-phase winding.

  The AC power source 1 is rectified by a rectifying diode 2 and smoothed by a smoothing capacitor 4 to obtain a DC power source. The reactor 3 acts to improve the power factor. A DC power source for the smoothing capacitor 4 is applied to the three-phase bridge inverter 5. The output terminal of the three-phase bridge inverter 5 is connected to the armature winding 6-a of the non-printer motor 6. By detecting the magnetic pole position of the rotor 6-b having a permanent magnet and switching the energized phase of the three-phase bridge inverter 5, the direction of the current flowing through the armature winding 6-a is switched and the rotor 6-b is rotated. To do.

  FIG. 2 is an explanatory view of the position detection operation. Use pointers for illustration. The U-phase terminal voltage, the V-phase terminal voltage, and the W-phase terminal voltage each have a waveform that is 120 degrees out of phase. Here, a description will be given using the U-phase terminal voltage. When the pointers are 1 and 2, the U-phase of the upper arm is on. When the pointers are 4 and 5, the U-phase is on for the lower arm. Therefore, when the pointers are 3 and 6, the U-phase armature winding becomes a non-conducting winding, and position detection by back electromotive force can be performed. The position can be detected by comparing the terminal voltage with half the input voltage of the three-phase bridge inverter 5 by the comparator 9 and obtaining the intersection. Since the output of the comparator 9 is a digital signal as shown in the figure, it becomes a signal that can be processed by a microcomputer or the like. The energized phase of the three-phase bridge inverter 5 is switched (commutation) at a timing delayed by 30 ° in terms of the electrical angle from the half point of the terminal voltage and the input voltage of the three-phase bridge inverter 5. By performing the same processing for the V phase and the W phase, it is possible to continue the operation of the brushless motor 6. Here, at the output of the comparator 9 immediately after the commutation, the same signal as that of the half of the intersection of the terminal voltage and the input voltage of the three-phase bridge inverter 5 is generated. This is an erroneous detection of position detection based on a spike voltage due to the return current. If the spike voltage caused by the return current cannot be distinguished from the position detection based on the back electromotive force, the position detection error is detected and the operation of the non-printing motor 6 cannot be continued.

  FIG. 3 is an explanatory diagram of expected position detection values. The output of the comparator 9 in the pointers 1-6 is shown. In each pointer, the output of the comparator 9 is repeated in three patterns: an expected position detection value based on the return current, an expected return current disappearance value, and an expected position detection value based on the back electromotive force. Attention is paid to the fact that the expected position detection value by the return current and the expected position detection value by the back electromotive force are the same, and the expected return current disappearance value and the expected position detection value before commutation are the same. It is. The position detection method that compares the terminal voltage of the output of the three-phase bridge inverter with one half of the input voltage of the three-phase bridge inverter 5 detects the disappearance of the return current by using the output characteristics of the comparator 9. Thus, the comparison with the position detection expected value can be started.

  FIG. 4 is a processing flowchart. A drive device for a brushless motor that detects the magnetic pole position of the rotor by using a back electromotive force generated in the terminal voltage of the output of the three-phase bridge inverter is in a state where the rotor of the brushless motor is stopped and the rotation speed. When is small, the back electromotive force is not generated or is small, so that the magnetic pole position of the rotor cannot be detected. For this reason, a drive device for a non-printing motor that uses the back electromotive force to detect the magnetic pole position of the rotor forcibly sends a current to the armature winding, and switches the current to operate as a synchronous motor. A method of increasing the rotation speed to a rotation speed at which an electromotive force can be detected is performed. FIG. 4 is an explanatory diagram in a state where the rotational speed is sufficiently high and the magnetic pole position of the rotor is performed by the counter electromotive force.

  First, initialize the pointer. Also, a position detection expected value corresponding to the pointer is set. This expected position detection value is the expected position detection value based on the back electromotive force, and is the same as the expected position detection value based on the return current. Immediately after commutation, the value of the register 11 is equal to the output of the comparator 9 and the coincidence detector 12 generates a coincidence signal 13. In the first coincidence signal generation determination of FIG. 4, loop processing is performed during coincidence signal generation. When the output of the comparator 9 changes, the coincidence signal 13 from the coincidence detector 12 disappears. Then, the process of FIG. 4 proceeds downward, and the position detection expected value is updated to the return current disappearance expected value. According to the explanation of FIG. 3, since the output of the comparator 9 changes with the disappearance of the return current, the output of the comparator 9 after the change should match the expected return current disappearance value. However, it is also expected that the output of the comparator 9 changes due to the influence of noise or the like. Therefore, in the second coincidence signal generation determination of FIG. 4, it is confirmed that the output of the comparator 9 matches the expected return current disappearance value. When the output of the comparator 9 does not match the expected return current disappearance value, the process returns to the first coincidence signal generation determination as an erroneous detection due to noise or the like. When the output of the comparator 9 matches the expected return current disappearance value, the process of FIG. 4 proceeds downward, and the position detection expected value is updated to the position detection expected value by the back electromotive force. Then, in the third coincidence signal generation determination of FIG. 4, loop processing is performed until the coincidence signal 13 is generated. A coincidence signal 13 is generated at the intersection of the terminal voltage of the three-phase bridge inverter 5 and the half voltage of the input voltage of the three-phase bridge inverter 5. When the coincidence signal 13 is generated, the processing of FIG. 4 proceeds downward, and after performing the electrical angle 30 ° delay waiting processing, the energized phase of the three-phase bridge inverter 5 is switched (commutation). Subsequently, the pointer and the position detection expected value are updated, and the process returns to the first coincidence signal generation determination.

  By the above processing, the disappearance of the return current can be detected reliably only by comparing the terminal voltage of the three-phase bridge inverter 5 and the half voltage of the input voltage of the three-phase bridge inverter 5, and the rotor magnetic pole position is erroneous. It is possible to configure a drive device for a brushless motor that is not likely to be detected.

1 is an overall configuration diagram of a drive device for a brushless motor according to the present invention. FIG. Position detection operation explanatory drawing. Position detection expectation value explanatory drawing. Processing flowchart.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Diode for rectification 3 Reactor 4 Smoothing capacitor 5 Three-phase bridge inverter 6 Brushless motor 7 Current detector 8 Energization switching signal generator 9 Comparator 10 Expected position detection value 11 Numerator 12 Matching detector 13 Coincidence signal

Claims (2)

  A three-phase bridge inverter is connected to a DC power source obtained by rectifying and smoothing an AC power source, and the output of the three-phase bridge inverter is a rotor of a permanent magnet and an armature winding composed of a three-phase winding. Comparison comparing the output of the three-phase bridge inverter with the terminal voltage of the terminal connecting the armature winding and the voltage half the input voltage of the three-phase bridge inverter connected to the armature winding And an energization switching signal generator for generating the next position detection expected value set in advance corresponding to the output of the three-phase bridge inverter, and the magnetic pole position of the rotor based on the comparison result The output of the comparator immediately after switching the output of the three-phase bridge inverter is the same as the position detection expected value due to the return current, and before the return current disappears. A brushless motor characterized by detecting the disappearance of the return current by using the same value as the position detection expected value before switching the output of the three-phase bridge inverter and starting comparison with the position detection expected value Drive device.   A three-phase bridge inverter is connected to a DC power source obtained by rectifying and smoothing the AC power source, and the output of the three-phase bridge inverter is a rotor of a permanent magnet and an armature winding composed of a three-phase winding. Comparison comparing the terminal voltage of the terminal connected to the armature winding and the output of the three-phase bridge inverter and the terminal connecting the armature winding with half the input voltage of the three-phase bridge inverter And an energization switching signal generator for generating the next position detection expected value set in advance corresponding to the output of the three-phase bridge inverter, and the magnetic pole position of the rotor based on the comparison result When the output of the comparator immediately after switching the output of the three-phase bridge inverter is the same as the position detection expected value due to the return current, and the return current disappears, By detecting the disappearance of the circulating current by utilizing the fact that different from the detected expected value, drive of brushless motor, characterized in that to start the comparison of the position detection expected value.

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