Method of starting a motor

Abstract

A starting method of a motor having a stator and a rotor, in which a field coil of the stator is started as Y-connection, in the case where the speed of the rotor is not within a predetermined range from a rated value within a predetermined time (t2), the field coil is switched to Δ-connection, and in the case where the speed of the rotor is within the predetermined range from the rated value, the field coil is switched to Y-connection.

Description

TECHNICAL FIELD

[0001] The present application relates to a motor starting method for starting a synchronous reluctance motor. BACKGROUND

[0002] There is known a technique in which a coil of an induction motor is applied with a voltage as a star connection at the time of starting, and the coil is applied with a voltage as a delta connection after the starting (Patent Literature 1).

[0003] PRIOR ART DOCUMENT

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2010-193702 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in the case where the technique disclosed in Patent Literature 1 is applied to the starting of a synchronous reluctance motor, if the inertia of the motor or a load, etc. is large, the starting can sometimes fail.

[0008] In view of the above problem, an object of the present application is to provide a motor starting method capable of improving the reliability of starting even in the case where the inertia is large.

[0009] To solve the above problem, according to one mode of the motor starting method of the present application, there is provided a motor starting method of a motor having a stator and a rotor, characterized in that the motor is started with a field coil of the stator connected as a Y connection, the field coil is switched to a Δ connection in the case where the speed of the rotor is not within a predetermined range from a rated value for a predetermined time t2, and the field coil is switched to the Y connection in the case where the rotational speed of the rotor is within the predetermined range from the rated value.

[0010] EFFECT OF THE INVENTION

[0011] According to the present application having the above structure, the reliability of starting of a motor can be improved even in the case where the inertia is large. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a block diagram showing the structure of a motor drive system of Embodiment 1.

[0013] Figure 2 is a cross-sectional view showing a structure example of a motor.

[0014] Figure 3 is a cross-sectional view showing a detailed structure example of a rotor core of a motor.

[0015] Figure 4 is a flowchart showing an example of a starting process.

[0016] Figure 5 is a diagram showing an example of the operation of each section.

[0017] Figure 6 is a diagram showing an example of the operation of each section.

[0018] Figure 7 is a diagram showing an example of the operation of each section.

[0019] Figure 8 is a diagram showing an example of inertia, load, and success or failure of starting.

[0020] In the diagram:

[0021] 1... motor, 2... speed sensor, 3... timer, 4... speed comparison section, 5... switch controller, 6, 7, 8... switch, 11... stator, 12... rotor, 13... shaft, 20... rotor core, 21, 22, 23, 24... magnetic flux barrier, 31, 32... bridge. DETAILED DESCRIPTION

[0022] Hereinafter, with reference to the drawings, an embodiment for carrying out the present application will be described in detail.

[0023] <Embodiment 1>

[0024] Embodiment 1 is an embodiment in which the present application is applied to a motor drive system that drives a synchronous reluctance motor, Figure 1 is a block diagram showing a structure example of the motor drive system of the present embodiment.

[0025] The motor drive system is provided with a synchronous reluctance motor (motor) 1 as a drive object; a speed sensor 2 that detects the rotational speed of the motor 1; a timer 3 that measures a predetermined time; and a speed comparison section 4 that compares the rotational speed detected by the speed sensor 2 with a prescribed speed. In addition, the motor drive system is provided with a switch controller 5 that performs control of switches 6, 7, 8; a switch (SW S ) 6 that switches the supply of a three-phase (U-phase, V-phase, W-phase) power supply voltage supplied from the outside; a switch (SW Y ) 7 that switches the coil of the motor 1 to Y connection; and a switch (SW Δ ) 8 that switches the coil of the motor 1 to Δ connection.

[0026] Figure 2 is a cross-sectional view showing a structure example of the motor 1. In addition, the Figure 2 shows an example of a 4-pole motor 1. In addition, Figure 2 shows a cross section of the motor 1 perpendicular to the shaft.

[0027] The motor 1 is an internal rotor type motor, comprising an annular stator 11 that generates a magnetic field (rotating magnetic field) and a rotor 12 disposed inside the stator 11. The stator 11 is provided with multiple coils, for example, three-phase coils, that generate the magnetic field. In this embodiment, the coils are shown as distributed windings, but concentrated windings are also possible. Furthermore, the rotor 12 includes a shaft 13 and a rotor core 20. The rotor 12 rotates together with the shaft 13.

[0028] Figure 3 This is a cross-sectional view showing a detailed structural example of the rotor core 20. Additionally, this... Figure 3 A cross-section of the synchronous reluctance motor perpendicular to shaft 13 is also shown.

[0029] Rotor core 20 through Figure 3 Thin sheet-like magnetic materials, such as silicon steel plates, of the shape shown, are stacked into a cylindrical shape and mounted on the shaft 13. The rotor core 20 has multiple magnetic flux barriers 21, 22, 23, and 24 arranged in the q-axis direction (in this case, the radial direction of the rotor core 20) for each pole.

[0030] To ensure the strength of the rotor core 20, rib-shaped bridges 31 and 32 are provided on the flux barriers 22 and 23 in the q-axis direction. The width of each bridge 31 and 32 in the direction perpendicular to the q-axis is as described later, and is preferably 1 to 2 mm or larger, taking into account the strength when molten aluminum, copper, or other non-magnetic conductors are injected into the flux barrier. In addition, each bridge 31 and 32 is provided at the center (on the q-axis) of each flux barrier 22 and 23, but multiple bridges can also be provided on a single flux barrier.

[0031] The thin-plate magnetic material constituting the rotor core 20 can be easily manufactured through a stamping-based blanking process. Furthermore, the rotor core 20 is formed by stacking thin-plate magnetic materials into a cylindrical shape and then injecting molten non-magnetic conductors such as aluminum or copper into the magnetic flux barrier portion. This increases the mechanical strength of the rotor core 20.

[0032] Additionally, annular conductors are provided at both ends of the rotor core 20 along its axial direction. These conductors can be formed together with the conductors injected into the flux barrier portion.

[0033] The conductors and annular conductors of the flux barrier section, as described above, function in the same way as the rotor of the induction cage motor, generating induced torque in the rotating magnetic field.

[0034] Reluctance motors with rotors having this structure are sometimes called direct-on-line synchronous reluctance motors, but in this embodiment, they are simply referred to as synchronous reluctance motors.

[0035] Next, the start-up processing in the motor drive system configured as described above will be described.

[0036] Figure 4 is a flowchart showing an example of the start-up processing for starting the motor in the present embodiment.

[0037] When starting the motor 1, the switch controller 5 first sets the switch 7 to the closed state, sets the switch 8 to the open state, switches the coil of the motor 1 to the Y connection, closes the switch 6, and supplies the motor 1 with the power supply voltage, thereby starting the motor 1 in S1.

[0038] In the next S2, the switch controller 5 determines whether the coil of the motor 1 is currently in the Y connection, and if it is in the Y connection, proceeds to S3, and if it is not in the Y connection, proceeds to S8.

[0039] In S3, the switch controller 5 acquires the comparison result (speed information) from the speed comparison section 4.

[0040] In the next S4, the switch controller 5 determines whether the current speed of the motor 1 is outside the predetermined range of the rating (for example, ±5%) based on the comparison result from the speed comparison section 4, and if it is outside the ±5% of the rating, proceeds to S6, and if it is not outside the ±5% of the rating, proceeds to S5.

[0041] In S5, the switch controller 5 determines whether the time after the Y connection has elapsed a predetermined time (for example, tl), and if it has, the start-up is successful, and the start-up processing ends, and if it has not, returns to S3.

[0042] On the other hand, in the case where it is determined in S4 that the current speed of the motor 1 is outside the ±5% of the rating, S6 is entered, and the switch controller 5 determines whether the time after the Y connection has elapsed a predetermined time (for example, t2). The value of t2 is, for example, greater than 0, and can be within about 1 / 3 of the predicted start-up time of the motor. In addition, the value of t2 is set, for example, based on at least one of the inertia of the motor 1 and the magnitude of the load.

[0043] If the time after the Y connection has elapsed t2, the switch controller 5 proceeds to S7, sets the switch 7 to the open state, sets the switch 8 to the closed state, switches the coil of the motor 1 to the Δ connection, and returns to S2. If the time after the Y connection has not elapsed t2, the switch controller 5 returns to S3.

[0044] According to the processing thus far, in the present embodiment, in the case where the speed of the motor 1 is not within the ±5% of the rating within the predetermined time (t2) after starting the motor 1 with the coil in the Y connection, or the coil of the motor 1 is switched to the Δ connection.

[0045] In S2 performed after the coil of the motor 1 is switched to the Δ connection, the switch controller 5 judges that it is not the Y connection and proceeds to S8.

[0046] In S8, the switch controller 5 acquires the comparison result (speed information) from the speed comparison section 4.

[0047] In the following S9, the switch controller 5 determines from the comparison result from the speed comparison section 4 whether the current speed of the motor 1 is within ±5% of the rated value, and if it is within ±5% of the rated value, proceeds to S10, and if it is not within ±5% of the rated value, proceeds to S12.

[0048] In S10, the switch controller 5 determines whether the time after the Δ connection has been made has elapsed tl, and if tl has elapsed, proceeds to S11.

[0049] In S11, the switch controller 5 causes the switch 7 to be in the closed state, causes the switch 8 to be in the open state, switches the coil of the motor 1 to the Y connection, and returns to S2. If the time after the Δ connection has not elapsed tl, the switch controller 5 returns to S8.

[0050] According to the operation up to this point, in the case where tl has elapsed after the current speed of the motor 1 becomes within ±5% of the rated value after the coil of the motor 1 is switched to the Δ connection, the switch controller 5 switches the coil of the motor 1 to the Y connection.

[0051] As described above, in S9, in the case where the current speed of the motor 1 is not within ±5% of the rated value, the switch controller 5 proceeds to S12, determines whether the time after the Δ connection has been made has elapsed t2, and if it has not elapsed, returns to S8. If the time after the Δ connection has elapsed t2, the switch controller 5 determines that the start-up has failed, opens the switch 6 and the switch 8, and ends the start-up processing.

[0052] Thus, in the case where the start-up has failed, the driving of the motor 1 can be stopped.

[0053] Figure 5 is an example showing the operation of each part of the motor driving system of the present embodiment in the case where the inertia is small. In Figure 5 , the switch 6 and the switch 7 are turned on (connected) at to, and the on state is maintained even if tl elapses. In addition, the switch 8 is open at to, and the open state is continued even if tl elapses. The coil of the motor 1 is in the Y connection from to.

[0054] In this case, the rotational speed of the motor 1 becomes within ±5% of the rated value before tl elapses after the coil of the motor 1 is in the Y connection, so switching to the Δ connection is not performed, and after tl elapses, the start-up processing is ended and the stable operation is shifted to.

[0055] Figure 6 is an example of the operation of each part of the motor drive system of the present embodiment in the case where the inertia is moderate. In Figure 6 , the switch 6 is on (connected) at tO, and remains on even after t2 and t2 + ti. The switch 7 is on at tO, off at t2, and on at t2 + ti. The switch 8 is off at tO, on at t2, and off at t2 + ti. The coil of the motor 1 is connected in Y from tO to t2, and connected in Δ from t2 to t2 + ti.

[0056] In this case, the rotational speed of the motor 1 is outside the range of ±5% of the rated value from when the coil of the motor 1 is connected in Y until t2 elapses, so the connection is switched to Δ after t2 elapses, and the rotational speed is within the range of ±5% of the rated value during the period until ti elapses (until t2 + ti) after that, so the connection is switched to Y at ti (t2 + ti). Further, the start-up processing ends and the stable operation is shifted to after ti elapses (t2 + 2ti).

[0057] Figure 7 is an example of the operation of each part of the motor drive system of the present embodiment in the case where the inertia is moderate. In Figure 7 , the switch 6 is on (connected) at tO, and remains on even after t2 and t2 + ti. The switch 7 is on at tO, off at t2, and on at t2 + ti. The switch 8 is off at tO, on at t2, and off at t2 + ti. The coil of the motor 1 is connected in Y from tO to t2, and connected in Δ from t2 to t2 + ti.

[0058] In this case, the rotational speed of the motor 1 is outside the range of ±5% of the rated value from when the coil of the motor 1 is connected in Y until t2 elapses, so the connection is switched to Δ after t2 elapses, and the rotational speed is within the range of ±5% of the rated value during the period until ti elapses (until t2 + ti) after that, so the connection is switched to Y at ti (t2 + ti). Further, the start-up processing ends and the stable operation is shifted to after ti elapses (t2 + 2ti).

[0059] Figure 8 is an example of the operation of each part of the motor drive system of the present embodiment in the case where the inertia is moderate. In

[0060] The example of the inertia, load, and success or failure of the start-up in the conventional motor drive system is shown in solid lines, and the example of the inertia, load, and success or failure of the start-up in the motor drive system of the present embodiment is shown in dashed lines.

[0061] In the existing motor drive system, the start-up of the motor is successful in the range of region 1. Therefore, the start-up is unsuccessful in the ranges of region 2 and region 3.

[0062] On the contrary, in the motor drive system of the present embodiment, the start of the motor is successful in the range of the region 1 and the region 2.

[0063] Therefore, in the present embodiment, even in the case where the inertia of the motor or the load is large, it is possible to improve the reliability of the start.

[0064] <Modification Example>

[0065] Further, in the above S3, it is also possible to calculate the rate of increase of the rotation speed of the motor 1, and in the case where the rate of increase is equal to or higher than a predetermined threshold value, not to switch to the delta connection. In the case where the rate of increase is equal to or higher than the predetermined threshold value, that is, in the case where the inertia is small and the start of the motor 1 is fast, the above-described state is achieved, and therefore by not performing the judgment of switching to the delta connection, it is possible to reduce the processing load. Figure 5 the state shown in FIG. 8, and therefore by not performing the judgment of switching to the delta connection, it is possible to reduce the processing load.

Claims

1. A starting method of a motor having a stator and a rotor, characterized by, starting an exciting coil of the stator as Y-connection; switching the exciting coil to Δ-connection in a case where the speed of the rotor is not within a predetermined range from a rated value for a predetermined time t2; switching the exciting coil to Y-connection in a case where the rotational speed of the rotor is within a predetermined range from a rated value for a predetermined time tl after switching the exciting coil to Δ-connection, determining that the starting of the motor has failed in a case where the speed of the rotor is not within a predetermined range from a rated value for a predetermined time t2 after switching the exciting coil to Δ-connection.

2. The starting method of a motor according to claim 1, characterized in that, the motor is a reluctance motor.

3. The starting method of a motor according to claim 1, characterized in that, the predetermined range is a range of plus or minus 5% of a rated rotational speed, i.e., speed, of the motor.

4. The starting method of a motor according to claim 1, characterized in that, the predetermined time t2 is set in accordance with at least one of an inertia and a magnitude of a load of the motor.

5. The starting method of a motor according to claim 1, characterized in that, the predetermined time t2 is greater than 0 and is within 1 / 3 of a predicted starting time of the motor.

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