JP2013162736A - Rotor stop position determination apparatus for brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a rotor stop position with high accuracy.SOLUTION: A brushless motor 2 rotatably supports a rotor with a permanent magnet in an opposite position to a stator around which a plurality of coils U, V, and W are wound. A rotor stop position determination apparatus 1 included in the brushless motor 2 comprises: a coil conduction part 3 for conducting electricity to a plurality of coil conduction paths (a UV phase, a VU phase, a VW phase, a WU phase, and a UW phase) individually; a saturation point detector 4 for detecting a saturation point of a current value at each coil conduction path; and a controller 5 for measuring time from beginning of electricity conduction to detection of the saturation point of the current value, and determining a stop position for the rotor according to the measured time of each coil conduction path. The saturation point detector 4 detects transitive decrease of the current value obtained when the current value at each coil conduction path reaches the saturation point.

Description

  The present invention relates to a rotor stop position determination device that determines a rotor stop position of a brushless motor, and more particularly to a rotor stop position determination device useful in a sensorless brushless motor.

  There is known a brushless motor configured by rotatably supporting a rotor having a permanent magnet at a position facing a stator around which a coil is wound. This type of brushless motor has a plurality of coil energization paths, and rotates the rotor by sequentially switching these coil energization paths. In order to smoothly rotate the rotor in a predetermined direction when the motor is started, it is necessary to recognize the stop position (stop range) of the rotor and select a coil energization path according to the stop position. In the method of detecting the rotor stop position by incorporating this sensor, there is a problem that not only miniaturization of the brushless motor is hindered but also the manufacturing cost is increased with the increase in the number of parts and the number of wirings.

  Therefore, a rotor stop position determination device that determines the stop position of the rotor without using a sensor has been proposed. For example, in the rotor stop position determination device disclosed in Patent Document 1, the time from the start of energization to the coil until the current value flowing through the coil reaches a predetermined threshold is measured, and the rotor stop position is determined based on this measurement time. It comes to judge. In other words, paying attention to the change in the current-carrying characteristics (ease of current flow) of the coil according to the polarity of the permanent magnet facing the coil and the strength of the magnetic field, From the time until the current value reaches a predetermined threshold value.

JP 2009-284653 A

  However, as shown in Patent Document 1, in the method of measuring the time from the start of energization until the current value reaches a predetermined threshold, good measurement accuracy cannot be obtained, and the rotor stop position is determined with high accuracy. It was difficult to do. In other words, in the above method, it is necessary to specify a current value range that does not reach the saturation point even under various conditions (coil temperature change, etc.), and to set a predetermined threshold value within this current value range. The measurement period was shortened and the measurement accuracy was limited.

The present invention has been created in view of the above circumstances and has been created for the purpose of solving these problems, and a rotor having a permanent magnet can be freely rotated at a position facing a stator around which a plurality of coils are wound. A rotor stop position determination device for a brushless motor configured to be supported by a coil, and a coil energization unit that individually energizes a plurality of coil energization paths, and a saturation point of a current value flowing through each coil energization path Saturation point detection means, time measurement means for measuring time from the start of energization until the saturation point of the current value is detected, and rotor stop position for determining the rotor stop position based on the measurement time of each coil energization path Determining means, and the saturation point detecting means detects a transient decrease in the current value that occurs when the current value flowing through each coil energization path reaches the saturation point.
Further, the saturation point detecting means detects the transient decrease in the current value based on a counter electromotive force generated in the coil energization path as the current value decreases.
In addition, the transient decrease in the current value is generated by a switching element that switches an energization state of the coil energization path.
Further, the present invention is characterized in that one switching element that causes the transient decrease in the current value is provided in a common energization path shared by all the coil energization paths.
The coil energization means, the saturation point detection means, the time measurement means, and the rotor stop position determination means are configured independently of a main control circuit that controls the brushless motor, and are requested from the main control circuit. The rotor stop position is determined in response to the determination, and the determination result is transmitted to the main control circuit.
Further, the rotor stop position determination means acquires a measurement time when a current is passed in the forward direction and a measurement time when a current is passed in the reverse direction for each of the plurality of coil energization paths. The difference between the measurement time in the direction and the measurement time in the reverse direction is calculated, and the stop position of the rotor is determined by comparing the differences between the respective coil energization paths.

According to the first aspect of the present invention, since the stop position of the rotor is determined based on the time from the start of energization until the saturation point of the current value is detected, the current value reaches a predetermined threshold value from the start of energization. As compared with the case of measuring the time until the rotor, the measurement period can be made as long as possible, and the rotor stop position can be determined with high accuracy. In addition, since the saturation point is detected based on a transient decrease in the current value that occurs when the current value reaches the saturation point, the saturation point can be detected with high accuracy, and the determination accuracy of the rotor stop position can be further improved. it can.
According to the invention of claim 2, since the transient decrease in the current value is detected based on the counter electromotive force generated in the coil energization path as the current value decreases, the detection accuracy of the saturation point is further increased. Can be improved. In other words, the back electromotive force generated in the coil energization path with a transient current value drop has a large amount of change compared to the transient current value drop. It becomes possible to detect accurately with a circuit configuration (for example, a comparator).
According to the invention of claim 3, the transient current value drop is generated by a switching element (for example, MOSFET) that switches the energization state of the coil energization path. A drop in value can be clearly generated.
According to the invention of claim 4, since one switching element that causes a transient decrease in the current value is provided in the common energization path shared by all the coil energization paths, a switching element that differs for each coil energization path As compared with the case where a transient decrease in current value is caused, the measurement error due to the variation in the characteristics of the switching elements can be eliminated, and the determination accuracy of the rotor stop position can be further improved.
According to the invention of claim 5, the rotor stop position determination device is configured independently of the main control circuit for controlling the brushless motor, and determines the stop position of the rotor in response to a request from the main control circuit. Since the determination result is transmitted to the main control circuit, the measurement process related to the rotor stop position determination can be executed without being affected by a protection circuit (for example, a current limiting circuit) provided in the main control circuit. Moreover, it can be highly versatile and can be incorporated into various brushless motor control circuits.
According to the invention of claim 6, for each of the plurality of coil energization paths, a measurement time when a current is passed in the forward direction and a measurement time when a current is passed in the reverse direction are obtained, The difference between the measurement time in the forward direction and the measurement time in the reverse direction is calculated, and the stop position of the rotor is determined by comparing the differences between the respective coil current paths. It cancels out, and it becomes possible to determine the stop position of a rotor with high precision.

It is a circuit diagram which shows the rotor stop position determination apparatus of the brushless motor which concerns on embodiment of this invention. It is a wave form diagram which shows the saturation point detection principle which concerns on embodiment of this invention. It is a graph which shows the relationship between the measurement time of each coil electricity supply path | route which concerns on embodiment of this invention, and a rotor stop position. It is a graph which shows the relationship between the difference of the normal / reverse measurement time in each coil electricity supply path which concerns on embodiment of this invention, and a rotor stop position. It is a flowchart which shows the process sequence of the control part which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Since the configuration of the brushless motor itself and the configuration of the main control circuit for controlling the brushless motor are well known (for example, see Patent Document 1 described above), detailed description and illustration are omitted.

FIG. 1 is a circuit diagram showing a rotor stop position determination device for a brushless motor according to an embodiment of the present invention.
As shown in this figure, the rotor stop position determination device 1 according to the embodiment of the present invention has a permanent magnet at a position facing a stator (not shown) around which a plurality of coils U, V, W are wound. A device for determining a rotor stop position of a brushless motor 2 configured by rotatably supporting a rotor (not shown), wherein a plurality of coil energization paths (UV phase, VU phase, VW phase, WV phase, WU, A coil energization section (coil energization means) 3 that individually energizes each phase, UW phase), a saturation point detection section (saturation point detection means) 4 that detects a saturation point of a current value flowing through each coil energization path, The time T from the start of energization until the saturation point of the current value is detected is measured, and the stop position of the rotor is determined based on the measurement time (Tuv, Tvu, Tvw, Twv, Twu, Tuw) of each coil energization path. Judgment control unit (hours Measuring means, and a rotor stop position determining means) 5, a.

  Here, the rotor stop position determination device 1 of the present embodiment is configured independently of the main control circuit 6 that controls the brushless motor 2, and determines the rotor stop position in response to a request from the main control circuit 6. The determination result is transmitted to the main control circuit 6. Therefore, it is possible to execute the measurement processing related to the rotor stop position determination without being affected by a protection circuit (for example, a current limiting circuit) provided in the main control circuit 6, and to various brushless motor control circuits. It can be built and highly versatile.

  The coil energization unit 3 includes a plurality of switching elements Q <b> 1 to Q <b> 6 that switch the energization state of each coil energization path according to the output signal of the control unit 5. For example, in the present embodiment, six switching elements Q1 to Q6 made of MOSFETs are provided, and three switching elements Q1 to Q3 arranged on the upstream side of each coil energization path, and downstream from each coil energization path. By switching the three switching elements Q4 to Q6 arranged on the side in a predetermined combination, a current can be individually supplied to the six coil energization paths described above.

  For example, the UV phase of the coil energization path is energized by a combination of switching elements Q3 and Q5, the VU phase is energized by a combination of switching elements Q2 and Q6, and the VW phase is energized by a combination of switching elements Q2 and Q4. The WV phase is energized by a combination of switching elements Q1 and Q5, the WU phase is energized by a combination of switching elements Q1 and Q6, and the UW phase is energized by a combination of switching elements Q3 and Q4. Yes.

  When detecting the saturation point of the current value flowing through each coil energization path, the saturation point detector 4 detects a transient decrease in the current value that occurs when the current value flowing through each coil energization path reaches the saturation point. It is like that. In other words, as a method for detecting the saturation point of the current value flowing through each coil energization path, there is a method for detecting the peak of the current value flowing through each coil energization path. In such a detection method, the current value near the saturation point is detected. Therefore, it is difficult to accurately detect the saturation point of the current value. Accordingly, in the present invention, when the current value flowing through each coil energization path reaches the saturation point, attention is paid to a clear phenomenon in which the current value decreases transiently. This makes it possible to detect the saturation point with high accuracy.

FIG. 2 is a waveform diagram showing the saturation point detection principle according to the embodiment of the present invention.
The saturation point detection unit 4 of the present embodiment detects a transient decrease in current value based on the back electromotive force generated in the coil energization path as the current value decreases. That is, as shown in FIG. 2, since the back electromotive force generated in the coil energization path with the transient current value decrease is larger than the transient current value decrease, the saturation point is clearly defined. In addition to identification, it is possible to detect with high accuracy with a simple circuit configuration (for example, a comparator).

  The transient decrease in the current value that occurs when the current value flowing through each coil energization path reaches the saturation point can be generated using the operating characteristics of the switching element Q that switches the energization state of the coil energization path. For example, paying attention to the switching element Q5 when energizing the UV phase of the coil energization path, the gate voltage of the switching element Q5 is constant and the voltage between the gate and source of the switching element Q5 is in the saturation region at the beginning of energization. The value of the current flowing through the phase increases, and the voltage increases accordingly. When the voltage between the gate and source of the switching element Q5 decreases as the voltage increases and shifts from the saturation region to the linear region, the current flowing through the coil energization path is limited (saturated), causing a transient decrease in current value. The saturation point detector 4 of the present embodiment detects the saturation point of the current value based on this transient decrease in current value.

  By the way, when performing a saturation point detection by energizing each coil energization path, if a transient decrease in the current value is caused by a different switching element Q for each coil energization path, it is caused by variations in characteristics of the switching element Q, Measurement error may occur. Therefore, in the present embodiment, one switching element Q7 is provided in a common energization path (downstream energization path of the coil energization unit 3) shared by all the coil energization paths, and the transition element in all the coil energization paths is provided by this switching element Q7. Cause a significant decrease in current value. This makes it possible to eliminate measurement errors caused by variations in the characteristics of the switching element Q.

  The saturation point detector 4 of the present embodiment includes, as specific components, the switching element Q7, the resistor R1 provided in the downstream path thereof, and the increase of the back electromotive force accompanying a transient decrease in current value. Comparator 7 for detection and resistors R2 and R3 for setting a comparison voltage (saturation point detection threshold S) of comparator 7 are provided, and an output signal of comparator 7 is input to control unit 5. Yes.

  The control unit 5 of the present embodiment is configured using a microcontroller (one-chip microcomputer), and the time from the start of energization to each coil energization path until the saturation point of the current value is detected (Tuv, Tvu, Rotor stop position determination for determining a rotor stop position based on a time measurement process for measuring Tvw, Twv, Twu, Tuw) and a measurement time (Tuv, Tvu, Tvw, Twv, Twu, Tuw) of each coil energization path A program for executing processing is written.

  In the time measurement process of the present embodiment, a constant voltage is applied simultaneously to the switching element Q7 that causes a transient decrease in the current value and the switching elements Q1 to Q6 corresponding to the coil energization path to be measured. At the same time, the output signal of the comparator 7 is monitored, the time counter is stopped according to the fall of the output signal, and the count value is read. This count value corresponds to the time from the start of energization to the coil energization path until the saturation point of the current value is detected, and the above time measurement processing is executed individually for each of the six coil energization paths. The

FIG. 3 is a graph showing the relationship between the measurement time of each coil energization path and the rotor stop position according to the embodiment of the present invention.
As shown in this figure, the measurement time (Tuv, Tvu, Tvw, Twv, Twu, Tuw) of each coil energization path has a clear relationship with the rotor stop position. That is, in the 360 ° rotor stop range, the measurement time (Tuv, Tvu, Tvw, Twv, Twu, Tuw) of the six coil energization paths is a three-phase sine waveform (1 at 180 °) according to the magnetic field generated by the rotor. Period) and a large change in the amplitude of the sine waveform in accordance with the polarity of the magnetic field (S pole, N pole) created by the rotor.

  For example, paying attention to the minimum measurement time among the measurement times (Tuv, Tvu, Tvw, Twv, Twu, Tuw) of six coil energization paths, it can be seen that the minimum measurement time is switched at a 60 ° pitch. The Therefore, if the minimum measurement time is specified, it is possible to determine in which rotor stop range of the rotor stop ranges H1 to H6 divided into six at 60 ° pitches. Also, within each rotor stop range, the measurement time (Tuv, Tvu, Tvw, Twv, Twu, Tuw) changes according to the rotor stop position, so the measurement time (Tuv, Tvu, Tvw, (Twv, Twu, Tuw) may be stored in advance as a table, and the detailed rotor stop position may be specified with reference to the table.

  By the way, the plurality of coil energization paths are caused by the energization characteristics unique to the coil, and there is a possibility that the bias value varies in the time measurement. This variation affects the above-described specification of the minimum value, which may reduce the accuracy of determining the rotor stop position. Therefore, in the rotor stop position determination process of the present embodiment, for each of the plurality of coil energization paths, the difference between the measurement time when the current is passed in the forward direction and the measurement time when the current is passed in the reverse direction is calculated. The rotor stop position is determined by calculating and comparing the differences between the respective coil energization paths.

FIG. 4 is a graph showing the relationship between the difference between the forward and reverse measurement times and the rotor stop position in each coil energization path according to the embodiment of the present invention.
As shown in this figure, the difference between the forward and reverse measurement times in each coil energization path has a clear relationship with the rotor stop position. That is, in the 360 ° rotor stop range, the difference (Tuv-Tvu, Tvu-Tuv, Tvw-Twv, Twv-Tvw, Twu-Tww, Tuw-Twu) between the forward and reverse measurement times in the six coil energization paths is the rotor. Shows a six-phase sine waveform (one period at 360 °) according to the magnetic field generated by.

  For example, pay attention to the difference which becomes the minimum or the maximum among the differences (Tuv-Tvu, Tvu-Tuv, Tvw-Twv, Twv-Tvw, Twu-Tuw, Tuw-Twu) of forward / reverse measurement times in six coil energization paths. Then, it can be seen that the minimum or minimum difference is switched at a 60 ° pitch. Therefore, if the difference which becomes the minimum or the maximum is specified, it becomes possible to determine in which rotor stop range of the rotor stop ranges H1 to H6 divided into six at 60 ° pitch. . If attention is paid to the second smallest difference or the second largest difference, it can be seen that the second smallest difference or the second largest difference is switched at a pitch of 30 °. Therefore, if the second smallest difference or the second largest difference is specified, it is determined in which rotor stop range of the rotor stop ranges h1 to h12 divided into 12 at 30 ° pitch. Is possible.

  Next, the processing procedure of the control unit 5 will be described with reference to FIG.

FIG. 5 is a flowchart showing a processing procedure of the control unit according to the embodiment of the present invention.
As shown in this figure, the controller 5 first determines whether a request signal from the main control circuit 6 has been received (S1). When this determination result is YES, in the six coil energization paths (UV phase, VU phase, VW phase, WV phase, WU phase, UW phase), from the start of energization until the saturation point of the current value is detected. Time T is measured (S2 to S7).

  In the time measurement process, energization of a predetermined coil energization path is started (S21), the time counter is started (S22), and the output signal of the comparator 7 is monitored (S23). Thereafter, when the output signal of the comparator 7 falls, the time counter is stopped (S24). When the predetermined timer time has elapsed (S25), the energization to the predetermined coil energization path is stopped (S26), and the count value of the time counter is read (S27).

  When the time measurement of each coil energization path is completed, the difference between the forward and reverse measurement times of each coil energization path (Tuv-Tvu, Tvu-Tuv, Tvw-Twv, Twv-Tvw, Twu-Tuw, Tuw-Twu) is calculated. At the same time (S8), the minimum or maximum difference, the second smallest difference or the second largest difference is specified from these differences, and the rotor stop ranges H1 to H6 and the rotor stop range are determined based on the specified differences. h1 to h12 are determined (S9). Thereafter, the determination result is transmitted to the main control circuit 6 (S10), and the process returns to the first processing step S1.

  According to the present embodiment configured as described, the brushless motor 2 is configured by rotatably supporting a rotor having a permanent magnet at a position facing a stator around which a plurality of coils U, V, and W are wound. Rotor stop position determination apparatus 1, and a coil energization section 3 that individually energizes a plurality of coil energization paths (UV phase, VU phase, VW phase, WV phase, WU phase, UW phase), and each coil A saturation point detection unit 4 that detects a saturation point of the current value flowing through the energization path, and measures the time from the start of energization until the saturation point of the current value is detected, and based on the measurement time of each coil energization path And a control unit 5 that determines a stop position of the rotor, and the saturation point detection unit 4 detects a transient decrease in current value that occurs when the current value flowing through each coil energization path reaches the saturation point. It is as.

  That is, the rotor stop position determination device 1 according to the embodiment of the present invention determines the rotor stop position based on the time from the start of energization until the saturation point of the current value is detected. Compared to the case where the time until the value reaches a predetermined threshold is measured, the measurement period can be made as long as possible, and the rotor stop position can be determined with high accuracy. In addition, since the saturation point is detected based on a transient decrease in the current value that occurs when the current value reaches the saturation point, the saturation point can be detected with high accuracy, and the determination accuracy of the rotor stop position can be further improved. it can.

  In addition, the saturation point detection unit 4 detects a transient decrease in the current value based on the back electromotive force generated in the coil energization path as the current value decreases, so that the saturation point detection accuracy is further improved. be able to. In other words, the back electromotive force generated in the coil energization path with a transient current value drop has a large amount of change compared to the transient current value drop. It becomes possible to detect with high accuracy by the circuit configuration.

  In addition, since the transient decrease in the current value is generated by the switching element Q that switches the energization state of the coil energization path, the transient decrease in the current value can be clearly generated by selecting the switching element Q.

  In addition, since the single switching element Q7 that causes the transient current value to decrease is provided in the common energization path shared by all the coil energization paths, the transient current value of the switching element Q is different for each coil energization path. Compared with the case where the reduction occurs, the measurement error due to the variation in the characteristics of the switching element Q can be eliminated, and the determination accuracy of the rotor stop position can be further improved.

  The rotor stop position determination device 1 of the present embodiment is configured independently of the main control circuit 6 that controls the brushless motor 2, determines the stop position of the rotor in response to a request from the main control circuit 6, Since the determination result is transmitted to the main control circuit 6, it is possible to execute the measurement process related to the rotor stop position determination without being affected by a protection circuit (for example, a current limiting circuit) provided in the main control circuit 6. Moreover, it can be highly versatile and can be incorporated into various brushless motor control circuits.

  Further, the control unit 5 acquires, for each of the plurality of coil energization paths, a measurement time when a current is passed in the forward direction and a measurement time when a current is passed in the reverse direction, and the measurement in the forward direction. Since the rotor stop position is determined by calculating the difference between the time and the measurement time in the reverse direction and comparing the differences between the coil energization paths, the variation in the energization characteristics of each coil energization path is canceled out. Can be determined with high accuracy.

  Needless to say, the present invention is not limited to the above-described embodiment, and the configuration can be changed or added as appropriate without departing from the scope of the claims.

  For example, in the above-described embodiment, the Y-connection brushless motor is exemplified, but the coil connection method may be Δ connection. Further, the number of magnetic poles of the rotor and the number of coils of the stator in the brushless motor are arbitrary.

DESCRIPTION OF SYMBOLS 1 Rotor stop position determination apparatus 2 Brushless motor 3 Coil energization part 4 Saturation point detection part 5 Control part 6 Main control circuit 7 Comparator Q Switching element

Claims (6)

A rotor stop position determination device for a brushless motor configured to rotatably support a rotor having a permanent magnet at a position facing a stator around which a plurality of coils are wound,
A coil energization means for energizing individually a plurality of coil energization paths;
Saturation point detection means for detecting a saturation point of a current value flowing through each coil energization path;
Time measuring means for measuring the time from the start of energization until the saturation point of the current value is detected;
Rotor stop position determination means for determining the rotor stop position based on the measurement time of each coil energization path,
The said saturation point detection means detects the transient fall of the current value which arises when the current value which flows through each coil energization path reaches a saturation point, The rotor stop position determination apparatus of the brushless motor characterized by the above-mentioned.   2. The brushless motor according to claim 1, wherein the saturation point detecting unit detects the transient decrease in the current value based on a back electromotive force generated in the coil energization path as the current value decreases. Rotor stop position determination device.   The brush stop motor rotor stop position determination device according to claim 1 or 2, wherein the transient decrease in the current value is generated by a switching element that switches an energization state of a coil energization path.   4. The rotor stop position determination device for a brushless motor according to claim 3, wherein one switching element for generating the transient decrease in the current value is provided in a common energization path shared by all the coil energization paths.   The coil energization means, the saturation point detection means, the time measurement means, and the rotor stop position determination means are configured independently of a main control circuit that controls the brushless motor, and according to a request from the main control circuit The rotor stop position determination device for a brushless motor according to any one of claims 1 to 4, wherein the stop position of the rotor is determined and the determination result is transmitted to the main control circuit.   The rotor stop position determination means acquires a measurement time when a current is passed in the forward direction and a measurement time when a current is passed in the reverse direction for each of the plurality of coil energization paths, The rotor stop position is determined by calculating the difference between the measurement time and the measurement time in the opposite direction, and comparing the differences between the respective coil energization paths. The rotor stop position determination apparatus of the brushless motor as described.

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