JP2016123142A - Lock detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lock detection device capable of improving accuracy of lock detection.SOLUTION: An inverter control unit allows an armature to generate a first magnetic field for stopping a field magnet on a first rotational position against the armature by controlling an inverter. A position detection unit detects a first rotation detection position to be a rotational position of an electric motor in a generation state of the first magnetic field. A lock detection unit, when a difference between the first rotation detection position and the first rotational position is larger than a predetermined value, detects generation of lock in the electric motor.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lock detection device, and more particularly to a device for detecting a lock generated in an electric motor.

  Conventionally, a technique for detecting a lock of an electric motor has been proposed. For example, a method of detecting a lock by controlling an electric motor driving device that drives an electric motor has been proposed. More specifically, the first rotation position of the electric motor is detected, and the electric motor drive device is controlled so that the electric motor is stopped at a stop position separated from the first rotation position by a predetermined angle. Thereafter, the second rotational position of the electric motor is detected, and whether or not the electric motor is properly rotated to the stop position is detected to detect the presence or absence of the lock.

  Patent Document 1 describes an inverter that drives an electric motor. The inverter outputs an alternating voltage to the electric motor. In Patent Document 1, a harmonic component sufficiently larger than the fundamental wave component contributing to the rotation of the electric motor is output to the inverter, and the rotational position of the electric motor is detected based on the current flowing through the electric motor.

JP 2011-172324 A

  However, the electric motor can rotate even when the inverter 1 does not output this AC voltage. For example, when an external force acts on the motor, the motor may rotate. Specific examples of causing the external force include a difference between a low pressure and a high pressure of a compressor driven by an electric motor, and passage of wind to a fan driven by the electric motor.

  If, for example, the first rotation position is detected in a state where such an external force is applied, the first rotation position is detected with low accuracy. This reduces the accuracy of detecting the lock.

  Therefore, an object of the present application is to provide a lock detection device that can improve the accuracy of detecting a lock.

  A first aspect of the lock detection device according to the present invention includes an armature (21) having an armature winding (221), an electric motor having a field (22), and an inverter (1) for driving the electric motor. A device (3) for detecting lock of the motor, for controlling the inverter (1) to stop the field at a first rotational position relative to the armature. An inverter control unit (31) for generating a first magnetic field in the armature; and a position detection unit (32) for detecting a first rotation detection position as a rotation position of the electric motor in a state where the first magnetic field is generated; And a lock detector (33) for detecting that the electric motor is locked when a difference between the first rotation detection position and the first rotation position is larger than a predetermined value.

  A second aspect of the lock detection device according to the present invention is the lock detection device according to the first aspect, wherein the first magnetic field includes a harmonic component that does not rotate the electric motor (2), and the inverter control The unit (31) controls either the voltage or current output from the inverter (1) to generate the first magnetic field in the armature, and the position detection unit (32) includes the inverter (1). The other one of the voltage and the current output from is detected, and the first rotational position is detected based on the inclination of an elliptical locus drawn by the other vector.

  A third aspect of the lock detection device according to the present invention is the lock detection device according to the first or second aspect, wherein the inverter control unit (31) controls the inverter (1). Generating a second magnetic field in the armature (22) for locating the field to a second rotational position where a difference from the first rotational position is greater than twice the predetermined value. A detecting unit (32) detects a second rotation detection position which is a rotation position of the electric motor in a state where the second magnetic field is generated, and a difference between the first rotation detection position and the first rotation position; When the difference between the second rotation detection position and the second rotation position is smaller than the predetermined value, it is determined that it is detected that the electric motor is not locked.

  According to the first aspect of the lock detection device of the present invention, a lock can be detected with high accuracy.

  According to the second aspect of the lock detection device of the present invention, it is possible to detect the first rotational position in a state where the first magnetic field is applied.

  According to the third aspect of the lock detection device of the present invention, it is possible to detect that the lock is not locked.

It is a figure which shows an example of a lock | rock detection apparatus roughly. It is a figure which shows an example of a structure of an inverter roughly. It is a figure which shows an example of operation | movement of a lock | rock detection apparatus. It is a figure which shows an electric current vector roughly. It is a figure which shows an electric current vector roughly. It is a figure which shows an example of an electric current schematically. It is a figure which shows an electric current vector roughly. It is a figure which shows an electric current vector roughly. It is a figure which shows an electric current vector roughly.

  FIG. 1 schematically shows an example of a lock detection device 3 that detects the lock of the electric motor 2. In the illustration of FIG. 1, an electric motor drive device including an electric motor 2 and an inverter 1 that outputs an AC voltage to the electric motor 2 is also shown. A DC voltage is input to the inverter 1, and the inverter 1 converts the input DC voltage into an AC voltage and outputs the AC voltage to the electric motor 2.

  FIG. 2 is a diagram schematically showing an example of the internal configuration of the inverter 1. For example, the inverter 1 is a three-phase inverter, and outputs a three-phase AC voltage from the output terminals Pu, Pv, and Pw. These output terminals Pu, Pv, Pw are connected to the electric motor 2. The inverter 1 includes, for example, switching elements Sup and Sun, Svp, Svn, Swp, and Swn and diodes Dup, Dun, Dvp, Dvn, Dwp, and Dwn. Note that “u”, “v”, and “w” included in the reference numerals indicating the respective configurations indicate that the configurations belong to the U phase, the V phase, and the W phase, respectively. For example, the switching elements Sup, Sup, the diodes Dup, Dun, and the output terminal Pu belong to the U phase.

  The switching elements Sxp, Sxn (x represents u, v, r, hereinafter the same) are connected in series between the DC lines LH, LL to which a DC voltage is applied. The switching element Sxp is connected between the DC line LH and the output terminal Px, and controls whether or not a current flows from the DC line LH toward the output terminal Px by conduction / non-conduction. The switching element Sxn is connected between the DC line LL and the output terminal Px, and controls whether or not a current flows from the output terminal Px to the DC line LL due to conduction / non-conduction. The diodes Dxp and Dxn are connected in parallel to the switching elements Sxp and Sxn, respectively, and their forward directions are directions from the DC line LL to the DC line LH.

  By appropriately controlling the switching elements Sxp and Sxn, the inverter 1 can convert a DC voltage into an AC voltage and output it.

  Referring to FIG. 1, the electric motor 2 is, for example, a magnet-embedded electric motor, and includes a field 21 and an armature 22. The field magnet 21 has, for example, a core (not shown) and a permanent magnet (not shown) embedded in the core. The permanent magnet supplies field magnetic flux interlinking to the armature winding 221. The armature 22 has, for example, U-phase, V-phase, and W-phase armature windings 221 that are connected to the output terminals Pu, Pu, and Pw of the corresponding inverter 1, respectively. When the three-phase AC voltage from the inverter 1 is applied to the three-phase armature winding 221, the armature 22 applies a rotating magnetic field corresponding to the three-phase AC voltage to the field magnet 21. The field 21 rotates with respect to the armature 22 according to the rotating magnetic field.

  The lock detection device 3 includes, for example, an inverter control unit 31, a position detection unit 32, and a lock detection unit 33.

  Here, the lock detection device 3 includes a microcomputer and a storage device. The microcomputer executes each processing step (in other words, a procedure) described in the program. The storage device is composed of one or more of various storage devices such as a ROM (Read Only Memory), a RAM (Random Access Memory), a rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.), and a hard disk device, for example. Is possible. The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or can realize that various functions corresponding to each processing step are realized. Further, the lock detection device 3 is not limited to this, and various procedures executed by the lock detection device 3 or various means or various functions implemented may be realized by hardware.

  FIG. 3 is a flowchart showing an example of the operation of the lock detection device 3. This series of operations is started in a state where the inverter 1 is not driving the electric motor 2, that is, in a state where an AC voltage for rotating the electric motor 2 is not output. However, as described above, even when the inverter 1 does not output this AC voltage, the electric motor 2 may rotate due to, for example, an external force generated in the electric motor 2.

  In step S <b> 1, the inverter control unit 31 controls the inverter 1 to cause the armature 22 to generate a first stop magnetic field for stopping the field magnet 21 at a predetermined first rotation position. The first stop magnetic field is a magnetic field that is substantially directed in one direction regardless of the passage of time. The first stop magnetic field is applied to the field magnet 21. If the electric motor 2 is not locked, application of the first stop magnetic field causes the field 21 to rotate until the magnetic pole center of the field 21 substantially coincides with the first rotation position, and stops in that state. On the other hand, if the electric motor 2 is locked, the field 21 does not rotate despite the application of the first stop magnetic field. Alternatively, even when the position of the field 21 before the first stop magnetic field is applied coincides with the first rotation position, the field 21 does not rotate.

  Such control for generating the first stop magnetic field is known, but an example thereof will be outlined. First, the switching elements Sxp and Sxn of each phase are controlled so as to conduct exclusively. This is to prevent the DC lines LH and LL from being short-circuited. When the switching element Sxp is turned on / off by “1” and “0”, and the phases are arranged side by side, for example, (000) (001) (010) (011) (100) (101) (110) Eight switching patterns (111) can be employed.

  Hereinafter, the switching patterns represented by (000) and (111) are referred to as zero switching patterns. In this zero switching pattern, the output terminals Pu, Pv, and Pw are short-circuited with each other, so that the inverter 1 cannot output a voltage. Therefore, it is not necessary to employ the zero switching pattern in the control for applying the first stop magnetic field.

  As an example, a case where one switching pattern (110) is employed will be described. That is, the switching elements Sup and Svp are made conductive and the switching element Swn is made conductive. As a result, currents Iu, Iv, and Iw flow through the U-phase, V-phase, and W-phase armature windings 221 through current paths corresponding to the switching pattern (110), respectively. More specifically, currents Iu and Iv flow from the output ends Pu and Pv to the U-phase and V-phase armature windings 221, respectively, and they are joined together via the W-phase armature winding 221. A current Iw flows to the output terminal Pw.

  A magnetic field is generated in the armature winding 221 of each phase by the currents Iu, Iv, and Iw. A magnetic field obtained by combining these magnetic fields (hereinafter also referred to as an armature magnetic field) is generated in the entire armature 22. Since the magnetic field generated in each armature winding 221 is generated by currents Iu, Iv, and Iw corresponding to the switching pattern, the direction of the armature magnetic field of the armature 22 depends on the switching pattern.

  Here, the armature magnetic field is a concept including the first stop magnetic field and the rotating magnetic field. The first stop magnetic field means a magnetic field in which the direction of the armature magnetic field is substantially maintained in one direction, and the rotating magnetic field means a magnetic field in which the armature magnetic field is substantially rotated over time.

  For example, if one of the switching patterns (110) is continuously adopted, an armature magnetic field (first stop magnetic field) in a direction determined by the switching pattern (110) is continuously generated. Unless the motor 2 is locked and the magnetic pole center of the field 21 before the first stop magnetic field is applied coincides with the first rotation position, the first stop magnetic field is applied. Thus, the field 21 rotates until the magnetic pole center of the field 21 substantially coincides with the first rotation position.

  In the above-described example, one of the switching patterns is continuously adopted, but the present invention is not necessarily limited thereto. For example, a plurality of switching patterns may be employed at a predetermined time ratio in a predetermined cycle. That is, the direction of the magnetic field indicated by the time average of the armature magnetic field in a predetermined cycle is maintained in one direction. For example, when the switching patterns (100) and (110) are employed at a time ratio of 0.5, respectively, the direction of the armature magnetic field corresponding to the switching patterns (100) and (110) is bisected. An armature magnetic field can be generated, and the average armature magnetic field functions as the first stop magnetic field.

  Therefore, the first stop magnetic field for stopping the field magnet 21 at an arbitrary first rotational position can be generated by appropriately adjusting the switching pattern and the duty ratio thereof.

  FIG. 4 is a diagram showing the current vector I. The current vector I is a combination of vectors of the currents Iu, Iv, and Iw output from the inverter 1, and the direction thereof coincides with the direction of the vector indicating the armature magnetic field.

  In the illustration of FIG. 4, an α-β coordinate system and a dq coordinate system are also shown. The α-β coordinate system is a coordinate system fixed to a stator (for example, armature 22). For example, the α axis is set in phase with the U phase magnetic flux generated by the U phase current Iu, and the β axis is advanced by 90 degrees in phase with respect to the α axis. The dq coordinate system is a coordinate system fixed to the rotor (for example, the field 21). The d-axis is set in phase with the field magnetic flux of the field 21, and the q-axis advances 90 degrees with respect to the d-axis. As the electric motor 2 rotates, the dq coordinate system rotates in synchronization with the field 21. In the present embodiment, the rotational position of the d axis is grasped as the rotational position of the electric motor 2. Since the d axis passes through the magnetic pole center, the above description using the magnetic pole center is consistent with the following description.

  The direction of the current vector I in FIG. 4 coincides with the direction of the vector indicating the first stop magnetic field. When the first stop magnetic field is applied to the field 21, the electric motor 2 is not locked, and the magnetic pole center of the field 21 and the first rotational position before the first stop magnetic field are applied are Except in the case of coincidence, the field 21 rotates along the direction of the first stop magnetic field, and the d-axis follows the direction of the first stop magnetic field (the direction of the current vector I) as shown in FIG. Rotate like so. That is, the field 21 stops at the first rotational position determined by the direction of the first stop magnetic field. Actually, a deviation may occur between the d-axis and the direction of the first stop magnetic field due to the load torque of the electric motor 2 or the like.

  On the other hand, if the electric motor 2 is locked, or if the magnetic pole center of the field 21 before the first stop magnetic field is applied coincides with the first rotation position, the field 21 rotates. For this reason, the d-axis maintains the state of FIG. 4, for example.

  The inverter control unit 31 notifies the position detection unit 32 that control for generating the first stop magnetic field has started (see FIG. 1).

  Referring to FIG. 3, in step S <b> 2, the position detection unit 32 that has received the notification detects the first rotation detection position that is the rotation position of the electric motor 2 while the first stop magnetic field is generated. This detection is performed when a predetermined time has elapsed from the start of the control for generating the first stop magnetic field. This predetermined time is a time sufficient for the field 21 that is not locked to rotate to the first rotation position.

  In the state where the first stop magnetic field is generated, even if an external force is generated in the electric motor 2, the field magnet 21 is not substantially rotated and is substantially stopped. Therefore, according to step S2, the detection can be performed with the electric motor 2 stopped, and as a result, the detection accuracy of the first rotation detection position can be improved. That is, if the electric motor 2 rotates due to the generation of an external force, the detection accuracy of the first rotation detection position decreases, but in the present embodiment, the occurrence of such a situation is avoided or suppressed.

  Note that although the rotational position detection method is arbitrary, an example thereof will be described. Here, a magnetic field of a harmonic component for detecting the rotational position (hereinafter also referred to as a detection magnetic field) is superimposed on the first stop magnetic field. The detection magnetic field rotates in the same manner as the rotating magnetic field, but the rotation speed is fast enough not to rotate the electric motor 2. In other words, the magnitude of the magnetic field of the armature winding 221 that is the basis of this detection magnetic field exhibits, for example, a three-phase sine wave, and its frequency is high enough not to rotate the electric motor 2.

  Since the detection magnetic field rotates, there is no substantial direction in consideration of the time average (for example, the average in one rotation). Therefore, even when the detection magnetic field is superimposed on the first stop magnetic field, the average direction of the magnetic field generated by the armature 22 substantially matches the direction of the first stop magnetic field. That is, the detected magnetic field does not substantially affect the direction of the first stop magnetic field. Therefore, even when such a magnetic field is applied to the field magnet 21, the field magnet 21 that is not locked maintains the stop at the first rotational position.

  In order to generate this magnetic field (a magnetic field including the first stop magnetic field and the detection magnetic field), a voltage described below may be output to the inverter 1. For example, the inverter 1 outputs a voltage in which a three-phase AC voltage component corresponding to the detected magnetic field is superimposed on a three-phase voltage component corresponding to the first stop magnetic field. The three-phase AC voltage component only needs to have a frequency high enough not to rotate the electric motor 2. Further, the three-phase voltage components corresponding to the first stop magnetic field can be grasped based on the switching pattern to be employed. For example, when only one of the switching patterns is employed, the direct current corresponding to the switching pattern is employed. Represented by ingredients.

  In order to perform such control, for example, a voltage command value for a three-phase AC voltage output from the inverter 1 is introduced. The voltage command value is a voltage obtained by superimposing the AC voltage component and the voltage component. The inverter control unit 31 generates the switching signal S of the switching elements Sxp and Sxn based on the voltage command value and outputs it. Although the generation of the switching signal S is well known, it can be performed based on, for example, a comparison between a voltage command value and a triangular wave.

  FIG. 6 shows an example of the current Ix flowing through one output terminal Px. Here, it is assumed that only one of the switching patterns is adopted to generate the first stop magnetic field. Therefore, in the illustration of FIG. 6, the current Ix includes a direct current component as a current corresponding to the first stop magnetic field. The current Ix also includes an AC component corresponding to the detected magnetic field.

  In the illustration of FIG. 6, the current Ix substantially has only a DC component before the time point t1. This means that step S1 is executed before time t1, and that step S2 is executed after time t1. However, in step S1, a magnetic field including the first stop magnetic field and the detection magnetic field may be generated. This is also because the field 21 that is not locked can be stopped by the first stop magnetic field included in the magnetic field. That is, you may start step S1, S2 simultaneously.

  FIG. 7 shows the locus of the current vector of the current flowing through the output terminals Pu, Pv, Pw. As shown in FIG. 7, the trajectory forms an ellipse centered on a point different from the origin of the α-β coordinate system. In the following, this locus will be described broadly as a vector based on a direct current component of currents Iu, Iv, and Iw and a vector based on an alternating current component of currents Iu, Iv, and Iw. First, considering only the vector of the AC component, the locus of the vector, as is well known, exhibits an ellipse centered on the origin of the α-β coordinate system, and its long axis is parallel to the d axis (also in FIG. 8). reference). On the other hand, the DC component vector I ′ (FIG. 7) is a vector that maintains a predetermined magnitude and a predetermined direction regardless of time. Therefore, the locus of the current vectors of the currents Iu, Iv, and Iw obtained by combining these vectors is expressed by translating the locus in FIG. 8 with the vector I ′. Therefore, as shown in FIG. 7, the trajectory has an ellipse centered on the point indicated by the vector I '. Even in this case, the major axis of the ellipse is parallel to the d-axis.

  Therefore, the position detection unit 32 can detect the rotational position based on the inclination of the elliptical locus of the current vector. Therefore, in the illustration of FIG. 1, a current detection unit 4 that detects an alternating current flowing through the electric motor 2 is provided. The detected alternating current is output to the position detector 32. The position detector 32 calculates a current vector based on the detected alternating current, and calculates the inclination of the ellipse (for example, the direction of the major axis) drawn by the current vector. Thereby, similarly to Patent Document 1, the rotational position of the field 21 can be detected. The detected rotational position is output to the lock detector 33.

  According to the detection method described above, the rotational position can be detected based on the current flowing through the electric motor 2 while generating the first stop magnetic field. The current detector 4 can also be used for normal control of the electric motor 2 (control for rotational operation). Therefore, compared with the case where another sensor for detecting the rotational position of the electric motor 2 is provided, the manufacturing cost can be reduced.

  In the example of FIG. 7, the direction of the vector I ′ (the direction of the first stop magnetic field) is parallel to the d-axis (= the direction of the long axis of the ellipse). On the other hand, in the example of FIG. 9, the direction of the vector I ′ is not parallel to the direction of the d axis but intersects. That is, FIG. 9 shows a case where the electric motor 2 is locked and the field 21 does not rotate to the first rotation position even though the first stop magnetic field is applied. In short, when the lock occurs, the first rotation detection position (d-axis direction) is shifted from the first rotation position (vector I ′ direction).

  Therefore, in step S3, the lock detection unit 33 determines whether or not the difference between the first rotation detection position and the first rotation position is greater than a predetermined value (for example, within several degrees). If a positive determination is made, in step S4, the lock detection unit 33 detects that the electric motor 2 is locked.

  As described above, according to the lock detection device 3, the first rotation detection position used in the determination in step S3 is detected in a state where the first stop magnetic field is applied in step S2. Therefore, the detection accuracy of the first rotation detection position can be improved, and the determination accuracy in step S3 can be improved. As a result, the lock can be detected with higher accuracy.

  As a comparative example, consider detecting the first rotation detection position without applying the first stop magnetic field. In this case, due to the disappearance of the first stop magnetic field, the field 21 may rotate as external force is applied to the electric motor 2. Such rotation increases the difference between the first rotation detection position and the first rotation position, and a positive determination can be made in the determination in step S3. In this case, the lock is erroneously detected in step S4. However, in the present embodiment, such a situation can be avoided or the frequency of occurrence thereof can be suppressed.

  In the illustration of FIG. 3, when a negative determination is made in step S3, the processing after step S5 is executed to detect the presence or absence of lock. That is, in the illustration of FIG. 3, just because the difference between the first rotation detection position and the first rotation position is smaller than a predetermined value, it is not determined that the lock has not occurred. This is because if the field 21 is stopped at the first rotation position and the lock occurs, a negative determination is made in step S3 despite the lock being generated.

  If a negative determination is made in step S3, the lock detection unit 33 notifies the inverter control unit 31 of the determination result. In step S <b> 5, the inverter control unit 31 that has received the notification controls the inverter 1 to cause the armature 22 to generate a second stop magnetic field for stopping the field 21 at the predetermined second rotation position. The second rotational position is set so that the difference from the first rotational position is greater than the predetermined value. For example, 90 degrees can be adopted as the difference.

  Since the control for generating the second stop magnetic field is the same as the control for generating the first stop magnetic field, repeated description is avoided. The inverter control unit 31 notifies the position detection unit 32 that control for generating the second stop magnetic field has started.

  In step S <b> 6, the position detection unit 32 that has received the notification detects the second rotation detection position that is the rotation position of the electric motor 2 in a state where the second stop magnetic field is generated. As in step S2, this detection is performed when a predetermined time has elapsed since the start of the control for generating the second stop magnetic field. Since the second rotation detection position is detected in a state where the second stop magnetic field is applied, the second rotation detection position can be detected with high accuracy as in step S2. The detected second rotation detection position is output to the lock detection unit 33.

  Next, in step S7, the lock detector 33 determines whether or not the difference between the second rotation detection position and the second rotation position is greater than a predetermined value. If a positive determination is made, in step S8, the lock detector 33 detects that the electric motor 2 is locked.

  If a negative determination is made in step S7, in step S9, the lock detector 33 detects that the electric motor 2 is not locked. That is, the electric motor 2 is locked when both the difference between the first rotation detection position and the first rotation position and the difference between the second rotation detection position and the second rotation position are smaller than a predetermined value. It detects that there is no.

  In addition, the second rotation detection position used in the determination in step S7 is detected in a state where the second stop magnetic field is generated in step S6. Therefore, the detection accuracy of the second rotation detection position can be improved, and the determination accuracy of step S7 can be improved. As a result, the accuracy of detecting the presence or absence of locking can be improved.

  In the above specific example, in steps S2 and S6, the inverter control unit 31 controls the output voltage output from the inverter 1, and the position detection unit 32 detects the rotational position based on the detected current. However, the control target and the detection target may be reversed. That is, the inverter control unit 31 provides a voltage detection unit that controls the output current output from the inverter 1 and detects the output voltage of the inverter 1, and the position detection unit 32 detects the rotational position based on the voltage. Also good. In this case, the output current includes an AC component for detecting the rotational position and a component for a stop magnetic field. The frequency of this alternating current component is high enough that the electric motor 2 cannot be started. The locus of the voltage vector detected at this time has an ellipse, and its long axis corresponds to the d-axis.

  In the present invention, the above-described various embodiments can be appropriately modified and omitted within the scope of the present invention as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Inverter 3 Lock detection apparatus 31 Inverter control part 32 Position detection part 33 Lock detection part

Claims (3)

In an electric motor drive device comprising an armature (21) having an armature winding (221), an electric motor having a field (22), and an inverter (1) for driving the electric motor, the lock of the electric motor is detected. A device (3) to perform,
An inverter control unit (31) for controlling the inverter (1) to cause the armature to generate a first magnetic field for stopping the field at a first rotational position with respect to the armature;
A position detection unit (32) for detecting a first rotation detection position which is a rotation position of the electric motor in a state where the first magnetic field is generated;
A lock detection apparatus comprising: a lock detection unit (33) that detects that the electric motor is locked due to a difference between the first rotation detection position and the first rotation position being greater than a predetermined value. The first magnetic field includes a harmonic component that does not rotate the electric motor (2),
The inverter control unit (31) controls either one of the voltage and current output from the inverter (1) to generate the first magnetic field in the armature,
The position detection unit (32) detects the other of the voltage and the current output from the inverter (1), and determines the first rotation position based on the inclination of an elliptical locus drawn by the other vector. The lock detection device according to claim 1, which detects the lock detection device. The inverter control unit (31) controls the inverter (1) to secondly position the field to a second rotational position where the difference from the first rotational position is larger than the predetermined value. A magnetic field is generated in the armature (22),
The position detector (32) detects a second rotation detection position which is a rotation position of the electric motor in a state where the second magnetic field is generated;
When the difference between the first rotation detection position and the first rotation position and the difference between the second rotation detection position and the second rotation position are both smaller than the predetermined value, the motor is locked. The lock detection device according to claim 1, wherein the lock detection device detects that no occurrence has occurred.

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