JP2023121317A - Stop method of permanent magnet-type electric motor - Google Patents

Abstract

An object of the present invention is to provide a method for stopping an electric motor that can quickly start the electric motor without requiring an operation to detect the initial position of the rotor when starting the electric motor next time. [Solution] This method executes a deceleration operation to reduce the rotational speed of a rotor 15 of a permanent magnet type electric motor 1 during steady operation, and after the rotational speed of the rotor 15 falls below a threshold value, the permanent magnet type electric motor A direct current is applied to the stator winding 17 of the rotor 1 to perform a direct current excitation operation to fix the position 15 of the rotor. [Selection diagram] Figure 3

Description

The present invention relates to a method for stopping a permanent magnet type electric motor, such as an SPM (Surface Permanent Magnet) motor and an IPM (Interior Permanent Magnet) motor, which has a permanent magnet in its rotor.

When starting a permanent magnet type motor from a stopped state, it is necessary to supply an appropriate current to the initial position of the rotor, so it is necessary to detect the initial position. Since no electromotive force is generated due to rotation of the rotor when the electric motor is stopped, techniques for detecting the position of the rotor have been conventionally proposed.

In the case of a motor in which the inductance does not change with the angle of the rotor, the shape of the magnetic path is symmetrical when viewed from the center line of the magnetic path regardless of the angle of the rotor. Therefore, there is no mutual induction between the orthogonal windings. However, when the inductance varies depending on the angle of the rotor, the shape of the magnetic path is not symmetrical when viewed from the center line of the magnetic path depending on the angle, resulting in mutual induction between the orthogonal windings. Using this property, in the case of a motor with saliency (the d-axis inductance and the q-axis inductance are different), when the windings are excited to generate an alternating magnetic field, depending on the rotor angle, the windings in the orthogonal direction of the alternating magnetic field electromotive force appears in The magnitude of this electromotive force changes according to the rotor position.

When the direction of the alternating magnetic field coincides with the d-axis of the rotor, the shape of the magnetic paths of both windings orthogonal to the d-axis is symmetrical when viewed from the magnetic path centerline. Therefore, no mutual induction occurs and no electromotive force due to mutual induction is observed. In addition, since the polarity of mutual induction changes at the boundary of the angle at which the direction of the alternating magnetic field and the d-axis of the rotor coincide, the phase of the observed electromotive force is also reversed at this angle.

Therefore, the position of the d-axis of the rotor can be estimated by applying an alternating magnetic field at a frequency sufficiently higher than the drive frequency of the motor and searching for the angle at which the electromotive force in the orthogonal direction is minimized while rotating the alternating magnetic field. However, since the direction of the d-axis magnetic pole cannot be determined, pulse voltages are applied in both positive and negative directions in the d-axis direction, and the magnetic pole direction is determined from the difference between the positive and negative response currents caused by magnetic saturation. By executing such an operation sequence, the rotor initial position can be estimated and the motor can be properly started.

Japanese Patent Application Laid-Open No. 2020-39227

However, the above-described operation sequence requires a certain amount of time to detect the rotor initial position, so that the start-up delay of the motor occurs, for example, on the order of 0.1 to 1 second. Such delay in starting may cause an adverse effect on operation depending on the application of the motor. For example, when an electric motor is connected to a pump of a water supply system, delays in starting the electric motor can lead to fluctuations in the water supply pressure.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for stopping an electric motor, which eliminates the need to detect the initial position of the rotor when starting the electric motor next time, and which can quickly start the electric motor.

In one aspect, there is provided a method for stopping a permanent magnet electric motor in steady operation, comprising executing a deceleration operation for reducing the rotational speed of a rotor of the permanent magnet electric motor in steady operation, and reducing the rotational speed of the rotor to After falling below a threshold value, a method is provided for performing a DC excitation operation to apply DC current to the stator windings of the permanent magnet motor to fix the position of the rotor.

In one aspect, the DC excitation operation is performed after the rotation speed of the rotor falls below a threshold value and before the rotation speed of the rotor reaches zero.
In one aspect, the method includes, after a rotational speed of the rotor falls below a threshold value and prior to the DC excitation operation, passing current through the stator windings to generate It further performs a pre-excitation operation that continuously or intermittently changes the direction of the applied magnetic field.
In one aspect, the method further performs a start-up preparatory operation of applying a DC current to the stator windings after the DC excitation operation and before the permanent magnet motor is next started.

In the process of stopping the electric motor from the operating state, if the electric motor is stopped in a state where the stop position of the rotor is specified, the rotor position does not need to be estimated when the electric motor is started next time. Therefore, the process of estimating the initial position of the rotor can be omitted at the time of starting, and as a result, the electric motor can be started quickly without delay.

1 is a schematic diagram showing an embodiment of an electric motor system; FIG. 1 is a cross-sectional view showing an embodiment of a permanent magnet electric motor; FIG. It is a sectional view explaining DC excitation operation.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of the electric motor system. The electric motor system includes a permanent magnet electric motor 1, an inverter 3 that supplies a variable frequency current to the permanent magnet electric motor 1, a current control section 5 that controls the operation of the inverter 3, and an inverter 3 to the permanent magnet electric motor 1. It is equipped with a current measuring device 7 for measuring the current flowing through.

The current measuring device 7 is connected to the current control section 5 so that the measured current value is sent to the current control section 5 . The current control unit 5 generates a current command value of the current to be supplied to the permanent magnet motor 1 based on the measured value of the current and the speed command value from the higher-level operation control unit (not shown). It is configured to be applied to the inverter 3 . An example of the current controller 5 is a vector controller. The inverter 3 generates current (three-phase alternating current in this embodiment) according to the current command value and supplies the current to the permanent magnet motor 1 .

FIG. 2 is a cross-sectional view showing one embodiment of the permanent magnet type electric motor 1 shown in FIG. As shown in FIG. 2, the permanent magnet electric motor 1 includes a rotor 15 having permanent magnets 12 and a stator 16 for generating a rotating magnetic field. The permanent magnet 12 is fixed to the rotor 15 and rotates together with the rotor 15 . Stator 16 has a plurality of stator windings 17 and stator core 18 arranged to surround rotor 15 . The stator windings 17 are attached to the plurality of teeth 18a of the stator core 18, respectively.

Stator winding 17 is electrically connected to inverter 3 shown in FIG. When the current supplied from the inverter 3 flows through the stator windings 17, the stator 16 generates a rotating magnetic field. A rotor 15 with permanent magnets 12 is rotated by the rotating magnetic field. A permanent magnet motor 1 is connected to a load such as a pump.

The permanent magnet electric motor 1 of this embodiment is an IPM (Interior Permanent Magnet) motor in which the permanent magnets 12 are embedded in the rotor 15 . However, the present invention is not limited to IPM motors, but may be, for example, SPM (Surface Permanent Magnet) motors in which permanent magnets are arranged on the surface of the rotor. In the following description, the permanent magnet type electric motor 1 may be simply referred to as the electric motor 1 .

The operation for stopping the electric motor 1 will be described below. A current control unit 5 controls the operation of the electric motor 1 via the inverter 3 . More specifically, upon receiving a stop command from a higher-level operation control unit (not shown), the current control unit 5 issues a command to the inverter 3 to reduce the rotational speed of the rotor 15 of the electric motor 1 during steady operation. perform an action. Furthermore, after the rotation speed of the rotor 15 has fallen below the threshold value as a result of the deceleration operation, the current control unit 5 issues a command to the inverter 3 to supply a DC current to the stator winding 17 to cause the rotor 15 to move to the position Execute the DC excitation operation to fix the Here, the position of the rotor 15 is the relative angle of the rotor 15 with respect to the stator 16 .

Steady operation of the electric motor 1 is an operating state in which a load (for example, a pump) connected to the electric motor 1 is operated in a manner capable of achieving its intended purpose. For example, steady state operation of the electric motor 1 connected to the water supply pump is the operating state of the electric motor 1 when the pump transports the liquid at the target pressure to the target point. In one example, the electric motor 1 in steady operation is operated at its rated speed.

In the sequence of stopping the rotor 15 from rotating state (sequence of decelerating and stopping), after the rotation speed of the rotor 15 falls below the threshold value, the stator winding 17 is excited with a unidirectional DC current ( That is, the DC excitation operation is performed), and the rotor 15 is stopped. If the DC excitation continues, the d-axis of the rotor 15 is attracted in the direction of the magnetic field M generated by the stator winding 17 as shown in FIG. 3, and the rotor 15 stops. That is, the rotation of the rotor 15 is stopped with the direction of the d-axis of the rotor 15 specified. Therefore, the initial position estimation of the rotor 15 becomes unnecessary when the electric motor 1 is started next time.

Known techniques can be used to determine when the rotation speed of the rotor 15 has fallen below the threshold. For example, the rotational speed of the rotor 15 can be detected by monitoring the magnitude of the terminal voltage of the electric motor 1 . A voltage sensor may be used to detect the terminal voltage. Alternatively, the terminal voltage of the electric motor 1 may be detected from the degree of modulation (duty rate) of the inverter 3 . In another example, the rotation speed of the rotor 15 can also be detected by detecting the terminal voltage of the electric motor 1 or the frequency of the winding current.

It is desirable that the DC excitation operation described above is started after the rotation speed of the rotor 15 has fallen below the threshold value and before it reaches zero. When the rotational speed of the rotor 15 is not completely zero, if DC excitation is performed in a certain direction, the rotor 15 stops after the rotor 15 rotates a little and the d-axis of the rotor 15 faces the direction of the DC excitation.

Even during the DC excitation operation, the rotation speed information of the rotor 15 can be obtained from the detected value of the voltage sensor, the degree of modulation (duty factor) during operation of the current control unit 5, or the frequency of the voltage/current. . Therefore, the rotation speed of the rotor 15 may be monitored and the DC excitation may be stopped when the stop of the rotor 15 is confirmed. However, it may be difficult or impractical to detect zero velocity. Therefore, in one embodiment, the current control unit 5 starts the DC excitation operation when a set time has elapsed since the rotation speed reached the threshold value, and the DC excitation operation is started when the preset excitation time has elapsed. The excitation operation may be stopped.

On the other hand, after the rotational speed of the rotor 15 has fallen below the threshold value, the rotor 15 may have already stopped before the DC excitation operation is started. For example, this is the case when the load connected to the electric motor 1 is temporarily increased. In this case, unlike the above, the stop position of the rotor 15 cannot be grasped, so even if DC excitation is performed in a certain direction, torque may not be generated depending on the angle of the rotor 15, and the d-axis of the rotor 15 is It may not be possible to attract and grasp.

Therefore, in one embodiment, after the rotation speed of the rotor 15 has fallen below the threshold value and before the DC excitation operation, the current control unit 5 issues a command to the inverter 3 so that the stator winding 17 to perform a pre-excitation operation in which the direction of the magnetic field generated by the stator winding 17 is changed continuously or intermittently. Specifically, the current control unit 5 issues a command to the inverter 3 to rotate (change) the direction of DC excitation continuously or intermittently to generate torque in an open loop, thereby slightly rotating the rotor 15. After that, DC excitation is performed in a certain direction to complete the excitation. By doing so, it is possible to stop the rotor 15 in a specified stop position.

In applications where the rotor 15 is not rotated from the load side when the electric motor 1 is stopped, the position of the rotor 15 is not lost if the electric motor 1 is stopped by the above operation. However, it is possible that the rotor 15 is turned slightly when the electric motor 1 is stopped. For example, the fan connected to the electric motor 1 may rotate slightly due to the airflow, causing the rotor 15 to be displaced.

Therefore, in one embodiment, after the DC excitation operation and before the motor 1 is next started, the current control unit 5 issues a command to the inverter 3 to prepare for starting by supplying a DC current to the stator winding 17. Perform more actions. For example, by executing a startup preparation operation in which DC excitation is repeated at appropriate time intervals, the magnetic pole position of the rotor 15 that has been slightly rotated is corrected, and the position of the rotor 15 can be completely specified. be able to. However, there is a possibility that a start command for the electric motor 1 will be issued during this short start preparation operation. If the current control unit 5 receives a start command for the electric motor 1 during this start preparation operation, the current control unit 5 must immediately stop this start preparation operation. must be monitored.

According to each embodiment described above, the position of the d-axis of the rotor 15 when the electric motor 1 is stopped can be grasped. Therefore, when the electric motor 1 is started next time, it is not necessary to estimate the initial position of the rotor 15 based on inductance measurement by applying a high-frequency current, for example. Since initial position estimation does not take time, the electric motor 1 can be quickly started by generating a magnetic field on the q-axis orthogonal to the d-axis. In addition, there is an advantage that the initial position can be grasped even in a permanent magnet type motor having no saliency.

After the electric motor 1 stops, the position of the rotor 15 may be displaced for some reason before the electric motor 1 is restarted. Therefore, after the DC excitation operation is performed to stop the electric motor 1 and before the next start of the electric motor 1, the current control unit 5 further performs a start preparation operation for supplying a DC current to the stator windings 17. You may That is, before starting the electric motor 1, the current control unit 5 issues a command to the inverter 3 to supply a DC current to the stator winding 17 to reliably determine the position of the rotor 15 on the d-axis, and then on the q-axis. A sequence to start the excitation of The q-axis of the rotor 15 can be reliably grasped by such a start preparation operation. This start preparation operation takes a little time, but the time is shorter than the conventional initial position estimation. Therefore, the electric motor 1 can be quickly started.

The above-described embodiments are described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiments can be made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments, but is to be construed in its broadest scope in accordance with the technical spirit defined by the claims.

1 Permanent Magnet Motor 3 Inverter 5 Current Control Section 7 Current Measuring Device 12 Permanent Magnet 15 Rotor 16 Stator 17 Stator Winding 18 Stator Core

Claims (4)

A method for stopping a permanent magnet motor in steady operation, comprising:
performing a deceleration operation to reduce the rotation speed of the rotor of the permanent magnet type electric motor during steady operation;
After the rotation speed of the rotor falls below a threshold, a DC excitation operation is performed by applying a DC current to a stator winding of the permanent magnet motor to fix the position of the rotor. 2. The method of claim 1, wherein the DC excitation operation is performed after the rotation speed of the rotor falls below a threshold and before the rotation speed of the rotor reaches zero. After the rotation speed of the rotor falls below a threshold value and before the DC excitation operation, current is passed through the stator windings to continuously change the direction of the magnetic field generated by the stator windings. 3. The method according to claim 1 or 2, further comprising intermittently changing pre-excitation operation. 4. The motor according to any one of claims 1 to 3, further comprising: after the DC excitation operation and before starting the permanent magnet motor next time, a start preparation operation for supplying a DC current to the stator winding is further performed. The method described in section.

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