How to start a motor

Abstract

To provide a motor start method capable of improving the certainty of starting even when inertia is large.SOLUTION: In a start method of a motor including a stator and a rotor, a field coil of a stator is started as a Y connection, and when the speed of the rotor does not fall within a predetermined range from the rated value within a predetermined time (t2), the field coil is switched to the Δ connection, and when the speed of rotor is within a predetermined range from the rating, the field coil is switched to the Y connection.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a motor starting method for use in starting a synchronous reluctance motor. [Background technology]

[0002] There is known a technique in which the coil of an induction motor is star-connected and a voltage is applied to it at start-up, and then the coil is delta-connected and a voltage is applied to it after start-up (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-193702 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the technique disclosed in Patent Document 1 is used to start a synchronous reluctance motor, starting may fail if the inertia of the motor, load, etc. is large. In view of the above-mentioned problems, an object of the present invention is to provide a method for starting a motor that can improve the reliability of starting even when the inertia is large. [Means for solving the problem]

[0005] In order to solve the above problem, according to one aspect of the motor starting method of the present invention, there is provided a method for starting a motor having a stator and a rotor, characterized in that the motor is started with a field coil of the stator in a Y connection, and if the speed of the rotor does not fall within a predetermined range from the rated speed within a predetermined time (t2), the field coil is switched to a Δ connection, and if the rotational speed of the rotor falls within the predetermined range from the rated speed, the field coil is switched to a Y connection. Effect of the Invention

[0006] According to the present invention having the above configuration, it is possible to improve the reliability of starting the motor even when the inertia is large. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram showing a configuration of a motor drive system according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of the configuration of a motor. [Diagram 3] FIG. 2 is a cross-sectional view showing a detailed configuration example of a rotor core of the motor. [Figure 4] 13 is a flowchart illustrating an example of a start process. [Diagram 5] FIG. 4 is a diagram illustrating an example of the operation of each unit. [Figure 6] FIG. 4 is a diagram illustrating an example of the operation of each unit. [Figure 7] FIG. 4 is a diagram illustrating an example of the operation of each unit. [Figure 8] FIG. 13 is a diagram showing an example of inertia, load, and start-up success or failure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. <Embodiment 1> In the first embodiment, the present invention is applied to a motor drive system that drives a synchronous reluctance motor, and FIG. 1 is a block diagram showing an example of the configuration of the motor drive system of this embodiment. This motor drive system includes a synchronous reluctance motor (motor) 1 to be driven, a speed sensor 2 that detects the rotation speed of the motor 1, a timer 3 that measures a predetermined time, and a speed comparator 4 that compares the rotation speed detected by the speed sensor 2 with a predetermined speed. This motor drive system also includes a switch controller 5 that controls switches 6, 7, and 8, and a switch (SW S) 6 and a switch (SW Y ) 7, and a switch (SW Δ )8.

[0009] Fig. 2 is a cross-sectional view showing an example of the configuration of the motor 1. Fig. 2 shows an example of a four-pole motor 1. Fig. 2 also shows a cross section perpendicular to the shaft of the motor 1. This motor 1 is an inner rotor type motor, and includes an annular stator 11 that generates a field magnet (rotating field magnet), and a rotor 12 provided inside the stator 11. The stator 11 is provided with a plurality of coils, for example, three phases, that generate a field magnet. In this embodiment, the coils are wound as distributed winding, but may be wound as concentrated winding. The rotor 12 includes a shaft 13 and a rotor core 20. The rotor 12 rotates together with the shaft 13.

[0010] Fig. 3 is a cross-sectional view showing a detailed configuration example of rotor core 20. Note that Fig. 3 also shows a cross section perpendicular to shaft 13 of the synchronous reluctance motor. Rotor core 20 is configured by laminating thin plate-like magnetic materials such as silicon steel plates into a cylindrical shape having a shape shown in Fig. 3, and is attached to shaft 13. Rotor core 20 is provided with a plurality of flux barriers 21, 22, 23, 24 arranged in the q-axis direction (in this case, the radial direction of rotor core 20) for each pole.

[0011] In order to ensure the strength of the rotor core 20, the flux barriers 22, 23 are provided with rib-shaped bridges 31, 32 in the q-axis direction. The width of each bridge 31, 32 in the direction perpendicular to the q-axis is preferably set to 1 to 2 mm or greater, taking into consideration the strength required when injecting molten aluminum, copper, or other non-magnetic conductor into the flux barrier, as described below. Furthermore, each of the bridges 31, 32 is provided at the center (on the q-axis) of each of the flux barriers 22, 23, but multiple bridges may be provided on one flux barrier.

[0012] The thin plate-like magnetic material constituting rotor core 20 can be easily manufactured by punching with a press. Rotor core 20 is formed by stacking thin plate-like magnetic material into a cylindrical shape, and then injecting molten aluminum, copper, or other non-magnetic conductor into the flux barrier portion. This increases the mechanical strength of rotor core 20. Furthermore, ring-shaped conductors are provided on both axial ends of the rotor core 20. These conductors may be formed together with the conductors to be injected into the flux barrier portion.

[0013] The conductor of the flux barrier portion and the ring-shaped conductor configured as described above function similarly to the rotor of an induction squirrel-cage induction machine, and generate induced torque in a rotating magnetic field. A reluctance motor having a rotor configured in this way is sometimes called a direct-on-line synchronous reluctance motor, but in this embodiment it is simply called a synchronous reluctance motor.

[0014] The start-up process in the motor drive system configured as above will now be described. FIG. 4 is a flowchart showing an example of a starting process for starting the motor in this embodiment. When starting the motor 1, the switch controller 5 first closes the switch 7 and opens the switch 8 in S1 to switch the coil of the motor 1 to a Y connection, closes the switch 6 to supply the power supply voltage to the motor 1, and starts the motor 1. In the next step S2, the switch controller 5 determines whether or not the coils of the motor 1 are currently in a Y-connection. If they are in a Y-connection, the process proceeds to S3, and if they are not in a Y-connection, the process proceeds to S8. In S3, the switch controller 5 acquires the comparison result (speed information) from the speed comparison unit 4.

[0015] In the next S4, the switch controller 5 determines whether the current speed of the motor 1 is outside a specified range of the rated speed (e.g., outside ±5%) based on the comparison result from the speed comparison unit 4, and proceeds to S6 if it is outside ±5% of the rated speed, or proceeds to S5 if it is not outside ±5% of the rated speed. In S5, the switch controller 5 determines whether a predetermined time (for example, t1) has elapsed since the Y connection was established, and if the time has elapsed, it determines that the start-up has been successful and ends the start-up process, and if the time has not elapsed, it returns to S3. On the other hand, if it is determined in S4 that the current speed of the motor 1 is outside the rated speed of ±5%, the process proceeds to S6, where the switch controller 5 determines whether a predetermined time (e.g., t2) has elapsed since the Y connection was established. The value of t2 can be, for example, greater than 0 and within about 1 / 3 of the predicted start-up time of the motor. The value of t2 is set, for example, according to at least one of the inertia of the motor 1, etc., and the magnitude of the load.

[0016] If the time t2 has elapsed since the Y connection was established, the switch controller 5 proceeds to S7, opens the switch 7, closes the switch 8, switches the coil of the motor 1 to a Δ connection, and returns to S2. If the time t2 has not elapsed since the Y connection was established, the switch controller 5 returns to S3. As a result of the processing up to this point, in this embodiment, after starting with the coils of motor 1 in Y connection, if the speed of motor 1 does not become within ±5% of the rated speed within a predetermined time (t2), the coils of motor 1 are switched to a Δ connection.

[0017] In S2, which is executed after the coil of the motor 1 is switched to the Δ connection, the switch controller 5 determines that the coil is not in the Y connection and proceeds to S8. In S8, the switch controller 5 acquires the comparison result (speed information) from the speed comparison unit 4. In the next S9, the switch controller 5 determines whether the current speed of the motor 1 is within ±5% of the rated speed based on the comparison result from the speed comparison unit 4, and proceeds to S10 if it is within ±5% of the rated speed, and proceeds to S12 if it is not within ±5% of the rated speed.

[0018] In S10, the switch controller 5 determines whether or not the time t1 has elapsed since the Δ connection was established, and if so, proceeds to S11. In S11, the switch controller 5 closes the switch 7 and opens the switch 8, switches the coil of the motor 1 to a Y connection, and returns to S2. If the time t1 has not elapsed since the Δ connection was established, the switch controller 5 returns to S8. After switching the coil of motor 1 to the Δ connection through the operations described above, if t1 has elapsed since the current speed of motor 1 became within ±5% of the rated speed, the switch controller 5 switches the coil of motor 1 to the Y connection.

[0019] As described above, if the current speed of the motor 1 is not within ±5% of the rated speed in S9, the switch controller 5 proceeds to S12, where it determines whether the time since the Δ connection was established has passed t2, and if not, returns to S8. If the time since the Δ connection was established has passed t2, the switch controller 5 determines that the start has failed, opens the switches 6 and 8, and ends the start process. This allows the driving of the motor 1 to be stopped if starting fails.

[0020] Fig. 5 is a diagram showing an example of the operation of each part of the motor drive system of this embodiment when the inertia is relatively small. In Fig. 5, switch 6 and switch 7 are turned ON (connected) at t0, and the ON state is maintained even after t1 has passed. Switch 8 is turned OFF at t0, and the OFF state continues even after t1 has passed. The coils of motor 1 are Y-connected from t0. In this case, since the rotation speed of Motor 1 becomes within ±5% of the rated speed before t1 has elapsed since the coil of Motor 1 is connected in Y connection, the connection is not switched to Δ connection, and after t1 has elapsed, the startup process is terminated and the system transitions to steady-state operation.

[0021] Fig. 6 is a diagram showing an example of the operation of each part of the motor drive system of this embodiment when inertia is medium. In Fig. 6, switch 6 is turned ON (connected) at t0, and the ON state is maintained even after t2 and t2+t1 have passed. Switch 7 is turned ON at t0, turned OFF at t2, and turned ON at t2+t1. Switch 8 is OFF at t0, turned ON at t2, and turned OFF at t2+t1. The coils of motor 1 are Y-connected from t0 to t2, and Δ-connected from t2 to t2+t1. In this case, since the rotation speed of Motor 1 is outside the rated speed of ±5% from when the coil of Motor 1 is connected to Y until t2 has elapsed, the connection is switched to Δ after t2 has elapsed, and since the rotation speed is within the rated speed of ±5% by the time t1 has elapsed (until t2+t1), the connection is switched to Y after t1 has elapsed (when t2+t1 has occurred). Furthermore, after t1 has elapsed (when t2+2t1 has elapsed), the start-up process is terminated and the system transitions to steady operation.

[0022] Fig. 7 is a diagram showing an example of the operation of each part of the motor drive system of this embodiment when the inertia is relatively large. In Fig. 7, switch 6 is turned ON at t0 and turned OFF at 2t2. Switch 7 is turned ON at t0 and turned OFF at t2, and remains OFF even after 2t2 has passed. Switch 8 is OFF at t0, turned ON at t2, and turned OFF at 2t2. The coils of motor 1 are Y-connected from t0 to t2, and Δ-connected from t2 to 2t2. In this case, since the rotation speed of Motor 1 is outside the rated value of ±5% from the time the coil of Motor 1 is connected to Y until t2 has elapsed, the connection is switched to Δ after t2 has elapsed. However, since the rotation speed does not return to within the rated value of ±5% even after t2 has elapsed (even at 2t2), it is determined that starting has failed, the startup process is terminated, and Motor 1 is stopped.

[0023] FIG. 8 is a diagram showing examples of inertia, load, and start-up success or failure in a conventional motor drive system and the motor drive system of this embodiment. The solid lines show examples of inertia, load, and start-up success or failure in a conventional motor drive system, and the dashed lines show examples of inertia, load, and start-up success or failure in the motor drive system of this embodiment. In a conventional motor drive system, the motor starts successfully in the range of region 1. Therefore, starting fails in the ranges of regions 2 and 3. In contrast, in the motor drive system of this embodiment, the motor starts successfully within the range of area 1 and area 2. Therefore, in this embodiment, even when the inertia of the motor, load, etc. is large, the reliability of starting can be improved.

[0024] <Modification> Also, in the above-mentioned S3, the rate of increase of the rotation speed of the motor 1 may be calculated, and if the rate of increase is equal to or greater than a predetermined threshold, the connection may not be switched to the Δ connection. If the rate of increase is equal to or greater than the predetermined threshold, that is, if the inertia is relatively small and the motor 1 starts up quickly, the state shown in Fig. 5 above is reached, and the processing load can be reduced by not making a decision to switch to the Δ connection. [Explanation of symbols]

[0025] 1...motor, 2...speed sensor, 3...timer, 4...speed comparison unit, 5...switch controller, 6, 7, 8...switch, 11...stator, 12...rotor, 13...shaft, 20...rotor core, 21, 22, 23, 24...flux barrier, 31, 32...bridge

Claims

1. A method for starting a motor having a stator and a rotor, comprising the steps of: Starting the stator field coils in a Y-connection; if the speed of the rotor does not fall within a predetermined range from the rated speed within a predetermined time (t2), switching the field coil to a delta connection; When the rotation speed of the rotor falls within a predetermined range from the rated speed, the field coil is switched to a Y connection.

2. A method for starting a motor comprising:

2. 2. The method of claim 1, wherein the motor is a reluctance motor.

3. 3. The motor starting method according to claim 1, further comprising the step of determining that starting of the motor has failed if the rotor speed does not fall within a predetermined range from the rated speed within a predetermined time (t2) after the field coil is switched to the Δ connection.

4. 4. The method of claim 3, wherein the predetermined range is within ±5% of the rated rotational speed of the motor.

5. 5. The motor starting method according to claim 3, wherein the predetermined time (t2) is set in accordance with at least one of the inertia of the motor and the magnitude of the load.

6. 6. The motor starting method according to claim 3, wherein the predetermined time (t2) is greater than 0 and is within 1 / 3 of a predicted start-up time of the motor.

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