Permanent magnet synchronous motor driving method and motor control device

Abstract

[Problem] To drive the rotation of a permanent magnet synchronous motor without determining in which phase a phase interruption occurred when phase interruption of the permanent magnet synchronous motor occurs. [Solution] A driving method for driving a permanent magnet synchronous motor wherein when a phase interruption occurs in one phase in a permanent magnet synchronous motor, a d-axis current id based on a d-axis current command value id* is reduced when the d-axis current id is positive, a d-axis voltage command value Vd* is reduced when the d-axis current id is negative, and a q-axis voltage command value Vq* is reduced when a q-axis current iq based on a q-axis current command value iq* flows in the opposite direction from the direction of rotation of the permanent magnet synchronous motor.

Description

Permanent magnet synchronous motor driving method and motor control device

[0001] The present invention relates to a driving method and a motor control device for a permanent magnet synchronous motor.

[0002] Patent Document 1 discloses an electric power steering device equipped with a motor control device that controls a three-phase brushless motor. When a phase loss occurs in one of the drive systems of the three-phase brushless motor, the motor control device selects a two-phase drive memory table corresponding to the two normal coils. The motor control device determines phase current command values ​​for the two normal phases from information such as a composite induced voltage obtained by referencing the selected two-phase drive memory table, and controls the rotational drive of the three-phase brushless motor based on the phase current command values ​​and the actual currents. This allows the three-phase brushless motor to maintain rotation even when a phase loss occurs in one of the drive systems of the three-phase brushless motor.

[0003] Patent No. 5282376

[0004] The motor control device described in Patent Document 1 needs to determine which of the U, V, and W phases has become missing in order to select a two-phase drive memory table corresponding to two normal phase coils. The motor control device must then selectively control the motor depending on which of the U, V, and W phases has become missing. This problem is not limited to when one phase is missing in a three-phase brushless motor, but is common to when one phase is missing in any permanent magnet synchronous motor, including a three-phase brushless motor.

[0005] An object of the present invention is to provide a driving method and a motor control device that can drive the rotation of a permanent magnet synchronous motor when a phase loss occurs in the permanent magnet synchronous motor without determining which phase has become missing.

[0006] A method for driving a permanent magnet synchronous motor according to an aspect of the present invention reduces the d-axis current when a phase loss occurs in one of the phases of the permanent magnet synchronous motor if the d-axis current based on the d-axis current command value is positive, reduces the d-axis voltage command value if the d-axis current is negative, and reduces the q-axis voltage command value if the q-axis current based on the q-axis current command value is in the opposite direction to the rotation direction of the permanent magnet synchronous motor.

[0007] Furthermore, a motor control device according to an aspect of the present invention is a motor control device that performs vector control of a permanent magnet synchronous motor, and includes: a normal state control unit that performs normal state control when no phase loss has occurred in the permanent magnet synchronous motor, outputting a d-axis voltage command value so that the d-axis current becomes the d-axis current command value, and outputting a q-axis voltage command value so that the q-axis current becomes the q-axis current command value; an abnormal state control unit that performs abnormal state control that is different from the normal state control when a phase loss has occurred; and a speed / position control unit that generates a drive signal to drive the permanent magnet synchronous motor based on the q-axis voltage command value and the q-axis voltage command value, and during the abnormal state control, the abnormal state control unit reduces the d-axis current when the d-axis current is positive, reduces the d-axis voltage command value when the d-axis current is negative, and reduces the q-axis voltage command value when the q-axis current based on the q-axis current command value is opposite to the direction of rotation of the permanent magnet synchronous motor.

[0008] The method for driving a permanent magnet synchronous motor and the motor control device according to the present invention control the motor so that a positive d-axis current does not flow, and further reduces the d-axis voltage command value when a negative d-axis current is detected, and reduces the q-axis voltage command value when a q-axis current in the opposite direction to the rotation direction is detected. With this configuration, when an abnormality occurs in one phase of the motor, it is possible to drive the motor without having to determine which of the U, V, and W phases has become missing.

[0009] In the driving method according to the above aspect, when a phase loss occurs in one phase of the permanent magnet synchronous motor, the d-axis voltage command value may be set to zero if the d-axis current is negative, and the q-axis voltage command value may be set to zero if the q-axis current is flowing in the opposite direction to the rotation direction. With this configuration, the motor can be rotated efficiently.

[0010] In the driving method according to the above aspect, when a phase loss occurs in one phase of the permanent magnet synchronous motor, if the d-axis current is positive, the d-axis current command value may be set to zero, and a d-axis voltage command value may be output such that there is no difference between the d-axis current command value set to zero and the d-axis current, thereby reducing the d-axis current.

[0011] In the driving method according to the above aspect, when the d-axis current and the q-axis current of the permanent magnet synchronous motor are controlled so that they are respectively set to predetermined values, it may be determined that a phase loss has occurred in one phase of the permanent magnet synchronous motor if at least one of the d-axis current and the q-axis current oscillates at a frequency approximately twice the frequency of the current phase current. With this configuration, it is possible to detect a phase loss without using a dedicated sensor for determining whether a phase loss has occurred.

[0012] In the motor control device according to the above aspect, the permanent magnet synchronous motor may be a drive motor for a transport vehicle that transports goods, and the emergency control unit may, in the event of a phase loss, drive the permanent magnet synchronous motor through emergency control to continue running the transport vehicle. With this configuration, it is possible to prevent interference with the transport of other transport vehicles within the logistics warehouse.

[0013] In the motor control device according to the above aspect, the abnormality control unit may, when a phase loss occurs, cause the transport vehicle to transport the item to the designated location, and continue running the transport vehicle under abnormality control until the transport vehicle retreats to the retreat position after the item has been transported. With this configuration, it is possible to prevent a decrease in retrieval efficiency within the logistics warehouse.

[0014] 1 is a schematic configuration diagram of a guided vehicle according to the present embodiment; FIG. 2 is a schematic configuration diagram of a traveling device according to the present embodiment; and FIG. 3 is a schematic configuration diagram of a motor according to the present embodiment. FIG. 4 is a diagram illustrating examples of current waveforms of U-phase current, V-phase current, W-phase current, d-axis current, and q-axis current flowing in a motor according to the present embodiment. FIG. 5 is a diagram illustrating the flow of motor phase currents when a break occurs in the W-phase power line according to the present embodiment. FIG. 6 is a flowchart illustrating a rough flow of a method for driving a motor in a guided vehicle according to the present embodiment. FIG. 7 is a flowchart illustrating an example of control when a d-axis phase is lost according to the present embodiment. FIG. 8 is a flowchart illustrating another example of control when a d-axis phase is lost according to the present embodiment. FIG. 9 is a flowchart illustrating an example of control when a q-axis phase is lost according to the present embodiment. FIG. 10 is a diagram illustrating the direction of a composite magnetic flux in normal control according to the present embodiment. FIG. 11 is a diagram illustrating the waveforms of phase currents and dq-axis currents and the direction of a composite magnetic flux in normal control according to the present embodiment. FIG. 12 is a diagram illustrating the direction of a composite magnetic flux in normal control when a W-phase is lost. FIG. 13 is a diagram illustrating the waveforms of phase currents and dq-axis currents and the direction of a composite magnetic flux in normal control when a W-phase is lost. FIG. 14 is a diagram illustrating two-phase control when a phase is lost. FIG. 1 is a diagram explaining the rotation of a motor when control is performed during a phase loss according to the present embodiment; FIG. 2 is a diagram illustrating a voltage waveform during a phase loss when the motor drive method according to the present embodiment is applied; FIG. 3 is a diagram illustrating a simulation result of speed control during control during an abnormality according to the present embodiment; FIG. 4 is a diagram illustrating a simulation result of d-axis current and q-axis current during control during an abnormality according to the present embodiment; FIG. 5 is a diagram illustrating a simulation result of U-phase current, V-phase current, and W-phase current during control during an abnormality according to the present embodiment; and FIG. 6 is a diagram illustrating a simulation result of d-axis voltage command value and q-axis voltage command value during control during an abnormality according to the present embodiment.

[0015] The present invention will be described below through embodiments, but the following embodiments are not limited to the inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In the drawings, identical or similar parts may be designated by the same reference numerals, and redundant explanations may be omitted. Furthermore, the shapes and sizes of elements in the drawings may be exaggerated for clarity, and may differ in shape and size from the actual product.

[0016] A drive method for a permanent magnet synchronous motor (hereinafter simply referred to as a "motor drive method") and a motor control device according to this embodiment will be described below. In recent years, with the expansion of e-commerce businesses, the importance of logistics warehouses, which handle everything from storage to shipping of merchandise, has increased. In e-commerce businesses, speed from order to delivery is required, and shipping volume is also increasing. Therefore, in e-commerce logistics warehouses, transport vehicles such as AGVs and robots move freely in all directions to improve the efficiency of shipping merchandise.

[0017] If a phase loss occurs in a permanent magnet synchronous motor used to drive a transport vehicle, the motor cannot be driven, and the transport vehicle may stop moving. As a result, logistics may be interrupted. For example, if a phase loss occurs in a transport vehicle transporting an item, the transport vehicle may stop with the item still loaded, and may be unable to transport the item. Furthermore, if a phase loss occurs in a transport vehicle, the transport vehicle may stop on the transport path of the item, interfering with the transport of other transport vehicles.

[0018] Therefore, the motor drive method and motor control device according to this embodiment allows the transport vehicle to continue traveling without stopping when a phase loss occurs due to a break in the power line of the permanent magnet synchronous motor, etc. Below, an example will be described in which the motor drive method and motor control device according to this embodiment are applied to a transport vehicle, but the present invention is not limited to this and can also be applied to driving permanent magnet synchronous motors provided in vehicles and devices other than transport vehicles.

[0019] A specific example of the motor drive method and motor control device according to this embodiment will be described below. The motor drive method and motor control device according to this embodiment controls the drive of the motor 5 for travel mounted on the transport vehicle 100, for example.

[0020] The transport vehicle 100 transports an item M. The transport vehicle 100 is, for example, an automatic guided vehicle (AGV) or a robot. The transport vehicle 100 travels, for example, within a warehouse and loads and unloads the item M. The transport vehicle 100 travels, for example, along a travel path established within the warehouse. This travel path is, for example, a route for the transport vehicle 100 set on the floor. For example, the travel path may be a two-dimensional code, a magnetic tape (magnetic marker), a laser reflector, a floor track, a rail, or the like. However, the travel path does not have to be established on the floor, and may be located at a predetermined height.

[0021] There are no particular limitations on the size, shape, weight, etc. of the item M transported by the transport vehicle 100, and any object can be applied as the item M. For example, the item M may be a commodity in a warehouse or a container box capable of storing multiple commodities.

[0022] 1 is a schematic diagram of a transport vehicle 100 according to this embodiment. The transport vehicle 100 includes, for example, a vehicle body 1, wheels 2, and a traveling device 3.

[0023] The vehicle body 1 is provided with a plurality of wheels 2 for traveling along the travel route. The transport vehicle 100 is capable of traveling by the rolling of the wheels 2. The vehicle body 1 is provided with a storage section for placing an article M thereon.

[0024] 2 is a schematic diagram of the traveling device 3 according to this embodiment. As shown in FIG. 2, the traveling device 3 includes a power supply device 4, a motor 5, and a motor drive device 6.

[0025] The power supply device 4 is disposed inside the vehicle body 1. The power supply device 4 includes, for example, a battery. The power supply device 4 supplies a DC voltage to the motor drive device 6. The power supply device 4 may include one or more DC / DC converters for stepping up or stepping down the voltage.

[0026] The motor 5 is a drive motor that drives at least one of the multiple wheels 2. This allows the transport vehicle 100 to travel along the above-mentioned travel route. The transport vehicle 100 can move forward, backward, turn left and right, etc. The motor 5 is a permanent magnet synchronous motor. A permanent magnet synchronous motor is a synchronous motor (PM motor) that uses a permanent magnet in the field magnet. For example, the motor 5 is an SPMSM (Surface Permanent Magnet Synchronous Motor).

[0027] In the following, an example will be described in which the motor 5 is a three-phase permanent magnet synchronous motor and an SPMSM. The number of slots in the motor 5 and the number of poles of the permanent magnets in the rotor 10 can be changed as desired. For convenience of explanation, the following will be described as an example in which the motor 5 is a three-phase, two-pole, three-slot motor.

[0028] Fig. 3 is a schematic diagram of a motor 5 according to this embodiment. As shown in Fig. 3, the motor 5 includes a rotor 10 and a stator 11. The rotor 10 is supported by a housing (not shown) of the motor 5 via bearings so as to be rotatable about the central axis of the rotor 10. The rotor 10 includes, relative to the stator 11, a plurality of permanent magnets spaced apart in the circumferential direction around the central axis of the rotor 10, and an iron core that holds the plurality of permanent magnets.

[0029] The stator 11 is disposed relative to the rotor 10 at a radial distance from the rotor 10, centered on the central axis of the rotor 10. In this embodiment, the stator 11 is disposed radially outside the rotor 10 so as to surround the rotor 10. The stator 11 is fixed to a motor housing (not shown). The stator 11 has three phases (U-phase, V-phase, and W-phase): a U-phase winding 12u, a V-phase winding 12v, and a W-phase winding 12w. The U-phase winding 12u, the V-phase winding 12v, and the W-phase winding 12w are star-connected. When the U-phase winding 12u, the V-phase winding 12v, and the W-phase winding 12w are not to be distinguished from one another, they may be simply referred to as "windings 12."

[0030] Returning to FIG. 2, the motor drive device 6 includes an inverter 20, a current sensor 21, a rotation angle sensor 22, and a motor control device 23.

[0031] The inverter 20 converts the DC voltage supplied from the power supply 4 into three-phase AC voltages Vu, Vv, and Vw. The inverter 20 outputs the three-phase AC voltages Vu, Vv, and Vw to the motor 5. This causes an AC current (hereinafter referred to as "phase current") to flow through the windings 12, generating magnetic flux for rotating the rotor 10. The rotor 10 then rotates so that the direction of the composite magnetic flux MF, which is the composite of the multiple magnetic fluxes generated in the motor 5, is the same as the direction of the N pole of the permanent magnet in the rotor.

[0032] The inverter 20 has, for example, a switching pair for each of the U-phase, V-phase, and W-phase (see FIG. 5 ). Each switching pair has a switching element (upper arm) arranged on the high-voltage side and a switching element (lower arm) arranged on the low-voltage side, and the two switching elements are connected in series.

[0033] Each switching pair is driven by a drive signal from the motor control device 23. The drive signal is, for example, a PWM (Pulse Width Modulation) signal. By driving each switching pair with the drive signal, the inverter 20 generates a U-phase AC voltage Vu, a V-phase AC voltage Vv, and a W-phase AC voltage Vw and supplies the generated AC voltages to the U-phase winding 12u, the V-phase winding 12v, and the W-phase winding 12w. As a result, a phase current (hereinafter referred to as the "U-phase current iu") flows through the U-phase winding 12u, a phase current (hereinafter referred to as the "V-phase current iv") flows through the V-phase winding 12v, and a phase current (hereinafter referred to as the "W-phase current iw") flows through the W-phase winding 12w.

[0034] The current sensor 21 detects the phase currents flowing through at least two of the windings 12, namely the U-phase winding 12u, the V-phase winding 12v, and the W-phase winding 12w. In the present embodiment, as an example, the current sensor 21 detects a U-phase current iu flowing through the U-phase winding 12u and a V-phase current iv flowing through the V-phase winding 12v.

[0035] The current sensor 21 outputs the detected U-phase current iu and V-phase current iv to the motor control device 23. For example, the current sensor 21 may be a resistance detection type sensor or a magnetic field detection type sensor. As an example, the current sensor 21 includes a magnetic field detection type current sensor 21u provided on the connection line connecting the inverter 20 and the U-phase winding 12u, and a magnetic field detection type current sensor 21v provided on the power line connecting the inverter 20 and the V-phase winding 12v.

[0036] The rotation angle sensor 22 is attached to the motor 5. The rotation angle sensor 22 outputs a signal corresponding to the rotational position of the rotor 10 of the motor 5 (hereinafter referred to as the "rotational position signal") to the motor control device 23. The rotation angle sensor 22 detects the rotational position of the rotor 10 of the motor 5 as an electrical angle. For example, the rotation angle sensor 22 outputs a rotational position signal corresponding to the detected electrical angle to the motor control device 23. Note that if the motor control device 23 can estimate the electrical angle of the rotor 10, the configuration of the rotation angle sensor 22 may be omitted. The rotation angle sensor 22 is, for example, a sensor using an encoder or a Hall element. The rotational position signal is, for example, a pulse signal indicating the rotational position of the rotor 10.

[0037] The motor control device 23 controls the motor 5 by vector control. The motor control device 23 includes, for example, a speed / position control unit 30, a missing phase detection unit 31, a dq command value generation unit 32, a subtraction unit 33, and a dq axis current control unit 34. These components are realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Furthermore, some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integrated Circuit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware. The program may be stored in advance in a storage device (a storage device having a non-transitory storage medium) such as an HDD (Hard Disk Drive) or flash memory, or may be stored in a removable storage medium (a non-transitory storage medium) such as a DVD or CD-ROM, and installed in the storage device by inserting the storage medium into a drive device. The storage device may be configured, for example, by a HDD, a flash memory, an EEPROM (Electrically Erasable Programmable Read Only Memory), a ROM (Read Only Memory), or a RAM (Random Access Memory).

[0038] The speed / position control unit 30 includes AD converters 40 a and 40 b, a feedback unit 41 , a first coordinate conversion unit 42 , a second coordinate conversion unit 43 , and a drive signal generation unit 44 .

[0039] The AD converter 40a converts the U-phase current iu detected by the current sensor 21u into digital data. Hereinafter, the U-phase current converted into digital data may be referred to as the "U-phase current iu_dd." The AD converter 40a outputs the U-phase current iu_dd to the first coordinate conversion unit 42 and the missing-phase detection unit 31.

[0040] The AD converter 40b converts the V-phase current iv detected by the current sensor 21v into digital data. Hereinafter, the converted V-phase current value may be referred to as a "V-phase current iv_dd." The AD converter 40b outputs the V-phase current iv_dd to the first coordinate conversion unit 42 and the missing-phase detection unit 31.

[0041] The feedback unit 41 calculates the electrical angle θ and the rotational speed ω of the rotor 10 based on the rotational position signal from the rotational angle sensor 22. The feedback unit 41 outputs the electrical angle θ of the rotor 10 to the first coordinate conversion unit 42 and the second coordinate conversion unit 43. The feedback unit 41 outputs the rotational speed ω of the rotor 10 to the dq command value generation unit 32.

[0042] The first coordinate conversion unit 42 acquires the U-phase current iu_dd from the AD converter 40a. The first coordinate conversion unit 42 acquires the V-phase current iv_dd from the AD converter 40b. The first coordinate conversion unit 42 calculates the W-phase current iw_dd from the U-phase current iu_dd and the V-phase current iv_dd based on Kirchhoff's law (iu_dd + iv_dd + iw_dd = 0). The first coordinate conversion unit 42 acquires the electrical angle θ of the rotor 10 from the rotation angle sensor 22.

[0043] The first coordinate transformation unit 42 transforms the U-phase current iu_dd, V-phase current iv_dd, and W-phase current iw_dd into a d-axis / q-axis rotating coordinate system using the electrical angle θ to determine a direct current (DC) d-axis current id and a q-axis current (DC) iq. That is, the first coordinate transformation unit 42 transforms the three-phase currents, i.e., the U-phase current iu_dd, V-phase current iv_dd, and W-phase current iw_dd, into DC d-axis current id and q-axis current iq. The d-axis current id is the phase difference between the expected phase current value of each phase and the actual phase current value. The q-axis current iq is a current component corresponding to the output torque of the motor 5.

[0044] The first coordinate conversion unit 42 outputs the d-axis current id and the q-axis current iq to the subtraction unit 33. The first coordinate conversion unit 42 outputs the d-axis current id to the open-phase detection unit 31.

[0045] The second coordinate converter 43 acquires a d-axis voltage command value (hereinafter referred to as the "d-axis voltage command value") Vd* and a q-axis voltage command value (hereinafter referred to as the "q-axis voltage command value") Vq* from the dq-axis current controller 34. The second coordinate converter 43 generates a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw* by performing three-phase conversion on the d-axis voltage command value Vd* and the q-axis voltage command value Vq* using the d-axis voltage command value Vd*, the q-axis voltage command value Vq*, and the electrical angle θ of the rotor 10. The second coordinate converter 43 outputs the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw* to the drive signal generator 44.

[0046] The drive signal generation unit 44 acquires the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw* from the second coordinate transformation unit 43. The drive signal generation unit 44 generates a drive signal for driving the inverter 20 based on the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw*. The drive signal generation unit 44 generates a PWM signal from the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw*, for example, by pulse width modulation. The PWM signal is an example of a drive signal. The drive signal generation unit 44 outputs the generated drive signal to the inverter 20.

[0047] The phase loss detection unit 31 detects a phase loss when one of the three phases of the motor 5 is lost. In this embodiment, a phase loss refers to a loss of phase current in one of the phases of the motor 5 due to some kind of abnormality. Examples of abnormalities that can cause a phase loss include a break in any one of the U-phase winding 12u, V-phase winding 12v, and W-phase winding 12w, a break in the power cable connecting any one of the windings 12 to the inverter 20, or plastic deformation of a metal contact in a connector due to device vibration. When the phase loss detection unit 31 detects a phase loss, it outputs a signal SL to the dq-axis current control unit 34.

[0048] In this embodiment, the phase loss detection by the phase loss detection unit 31 is to detect that a phase loss has occurred, and does not include processing to determine which phase has become missing. However, the phase loss detection unit 31 may perform processing to determine which phase has become missing after performing the phase loss detection. In other words, the processing to determine which phase has become missing may be performed by the phase loss detection unit 31, but is not required to do so.

[0049] An example of phase loss detection by the phase loss detection unit 31 will be described below with reference to Figures 4 and 5. Figure 4 is a diagram showing example current waveforms of the U-phase current iu, V-phase current iv, W-phase current iw, d-axis current id, and q-axis current iq flowing through the motor 5 before and after a W-phase loss occurs. Period T1 in Figure 4 is a period in which no phase loss occurs in any phase. Period T2 in Figure 4 is a period in which a phase loss occurs only in the W-phase. Figure 5 is a diagram showing the flow of motor phase currents when a break occurs in the W-phase power line.

[0050] When no phase loss occurs in any of the phases, the U-phase current iu, the V-phase current iv, and the W-phase current iw are shifted in phase from one another by 120 degrees, as shown in period T1 in Figure 4. In other words, when no phase loss occurs in any of the phases, the phase difference D between the two phases is maintained at 120 degrees.

[0051] 5, if the power line connecting the W-phase winding 12w and the inverter 20 is broken, the AC voltage supplied from the inverter 20 is not applied to the W-phase winding 12w, and the AC voltage is applied only to the U-phase winding 12u and the V-phase winding 12v. As a result, phase currents flow through the U-phase winding 12u and the V-phase winding 12v, but not through the W-phase winding 12w, resulting in a W-phase loss.

[0052] When the W phase is lost, no voltage is applied to the W-phase winding 12w, and voltage is applied only between the U and V phases. As a result, phase current flows only between the U and V phases. As shown in Figure 5, current sensors 21u and 21v provided in the U and V phases measure the phase current flowing between the U and V phases.

[0053] If the positive direction of current sensor 21 is the direction of current flow from inverter 20 to motor 5, then in the example of FIG. 5 , the U-phase current sensor 21u and the V-phase current sensor 21v measure the same current. Therefore, the positive and negative signs of the U-phase current iu measured by current sensor 21u and the V-phase current iv measured by current sensor 21v are reversed, resulting in a 180-degree phase difference between the U-phase current iu and the V-phase current iv. Thus, when the W-phase is lost, the phase difference D between the U-phase current iu and the V-phase current iv changes from 120 degrees to 180 degrees, as shown in period T2 of FIG. 4 . That is, the phase difference D, which had been maintained at 120 degrees, is disrupted and becomes 180 degrees.

[0054] The event in which the phase difference D changes from 120 degrees to 180 degrees is not limited to the loss of the W phase, but is common to any loss of one of the three phases. In other words, when one phase is lost, the phase difference between the phase currents of the two phases other than the lost phase changes from 120 degrees to 180 degrees. Therefore, the phase loss detection unit 31 detects the loss of one phase by directly or indirectly detecting this change in phase difference from 120 degrees to 180 degrees.

[0055] As an example, the phase loss detection unit 31 detects whether or not one of the three phases is missing using the d-axis current id and the q-axis current iq acquired from the first coordinate conversion unit 42. That is, the phase loss detection unit 31 detects whether or not a phase is missing using the d-axis current id and the q-axis current iq converted into direct current instead of alternating current.

[0056] Here, during normal operation when no phase loss occurs, motor control device 23 controls d-axis current id and q-axis current iq so that they are each at a specified value. As a specific example, during normal operation when no phase loss occurs, motor control device 23 controls d-axis current id to approximately 0 (zero) so that operation can be performed at maximum efficiency, and controls q-axis current iq to be constant at an arbitrary value.

[0057] When a phase loss occurs during normal operation, the phase difference between the phase currents of the other two phases changes from 120 degrees to 180 degrees. When the phase difference between the phase currents of the other two phases becomes 180 degrees, the d-axis current id and the q-axis current iq oscillate sinusoidally, as shown in period T2 in Figure 4 . That is, the d-axis current id and the q-axis current iq are direct currents during normal operation when no phase loss occurs, but they oscillate sinusoidally when a phase loss occurs. For example, when a phase loss occurs, the d-axis current id and the q-axis current iq oscillate at a frequency approximately twice the frequency of the current phase current. The current phase current is the phase current when a phase loss occurs, and in the example shown in Figure 4 , it is the U-phase current iu or the V-phase current iv, with a phase difference D of 180 degrees.

[0058] The phase loss detection unit 31 monitors whether at least one of the d-axis current id and the q-axis current iq is oscillating at a frequency approximately twice the frequency of the current phase current. If at least one of the d-axis current id and the q-axis current iq is oscillating at a frequency approximately twice the frequency of the current phase current, the phase loss detection unit 31 determines that one of the three phases is missing. In the example shown in FIG. 2 , the phase loss detection unit 31 monitors whether the d-axis current id is oscillating at a frequency approximately twice the frequency of either the current U-phase current iu_dd or the V-phase current iv_dd as the current phase current. However, without being limited thereto, the phase loss detection unit 31 may monitor whether the q-axis current iq is oscillating at a frequency approximately twice the frequency of the current phase current, or both.

[0059] The dq command value generation unit 32 generates a d-axis current command value id*, which is a target value for the d-axis current id, and a q-axis current command value iq*, which is a target value for the q-axis current iq, based on an external speed command ω* and the rotational speed ω from the feedback unit 41. The dq command value generation unit 32 outputs the d-axis current command value id* and the q-axis current command value iq* to the subtraction unit 33. The speed command ω* is a target value for the rotational speed of the motor 5. An example will be described in which the dq command value generation unit 32 is a device (external device) separate from the motor control device 23.

[0060] The subtraction unit 33 includes a first subtraction unit 33d and a second subtraction unit 33q.

[0061] The first subtraction unit 33d obtains the d-axis current command value id* from the dq command value generation unit 32. The first subtraction unit 33d obtains the d-axis current id from the first coordinate transformation unit 42. The first subtraction unit 33d calculates the difference Δd between the d-axis current command value id* and the d-axis current id. The first subtraction unit 33d outputs the difference Δd to the dq-axis current control unit 34.

[0062] The second subtraction unit 33q obtains the q-axis current command value iq* from the dq command value generation unit 32. The second subtraction unit 33q obtains the q-axis current iq from the first coordinate transformation unit 42. The second subtraction unit 33q calculates the difference Δq between the q-axis current command value iq* and the q-axis current iq. The second subtraction unit 33q outputs the difference Δq to the dq-axis current control unit 34.

[0063] When no phase loss occurs, the dq-axis current control unit 34 performs feedback control so that the difference Δd and the difference Δq each approach zero, and outputs the d-axis voltage command value Vd* and the q-axis voltage command value Vq* obtained by this feedback control to the second coordinate transformation unit 43. The d-axis voltage command value Vd* is the target value of the voltage of the d-axis component. The q-axis voltage command value Vq* is the target value of the voltage of the q-axis component. The feedback control performed by the dq-axis current control unit 34 when no phase loss occurs may be referred to as "normal control." Furthermore, the state when no phase loss occurs may be referred to as "normal."

[0064] When a phase loss occurs, the dq-axis current control unit 34 executes control different from normal control (hereinafter referred to as "phase loss control"). As phase loss control, the dq-axis current control unit 34 outputs a d-axis voltage command value Vd* so as to reduce the d-axis current id when the d-axis current id is positive, reduces the d-axis voltage command value Vd* when the d-axis current id is negative, and reduces the q-axis voltage command value Vq* when the q-axis current iq is in the opposite direction to the rotation direction of the motor 5. The occurrence of a phase loss may be referred to as an "abnormal state."

[0065] The dq-axis current control unit 34 according to this embodiment will be specifically described below. The dq-axis current control unit 34 includes a d-axis current control unit 51, a q-axis current control unit 52, and a switching unit 50.

[0066] The d-axis current control unit 51 calculates the d-axis voltage command value Vd* using the difference Δd output from the first subtraction unit 33d. The d-axis current control unit 51 includes, for example, a d-axis normal state control unit 60 and a d-axis abnormal state control unit 61.

[0067] The d-axis normal state control unit 60 calculates the d-axis voltage command value Vd* in normal state based on the difference Δd calculated by the first subtraction unit 33 d. The d-axis normal state control unit 60 outputs the d-axis voltage command value Vd* to the second coordinate conversion unit 43 in normal state.

[0068] During normal operation, the difference Δd is input from the first subtractor 33d to the d-axis normal operation control unit 60 at regular intervals. The d-axis normal operation control unit 60 calculates the d-axis voltage command value Vd* so that the input difference Δd becomes zero. In this way, the d-axis normal operation control unit 60 performs feedback control so that the d-axis current id follows the d-axis voltage command value Vd*. For example, the d-axis normal operation control unit 60 performs PI control so that the difference Δd becomes zero, thereby outputting the d-axis voltage command value Vd* to the second coordinate transformation unit 43. PI control is an example of feedback control.

[0069] The d-axis abnormality control unit 61 performs control (hereinafter referred to as "d-axis open-phase control") to calculate a d-axis voltage command value Vd* in the event of an abnormality and output the calculated d-axis voltage command value Vd* to the second coordinate conversion unit 43. The d-axis open-phase control performed in the event of an abnormality will be described below.

[0070] The d-axis abnormality control unit 61 monitors the d-axis current id output from the first coordinate conversion unit 42. As a d-axis open-phase control, the d-axis abnormality control unit 61 performs a first control to reduce the positive d-axis current, and a second control to reduce the d-axis voltage command value Vd* when the d-axis current id is negative.

[0071] As an example of the first control, the d-axis abnormality control unit 61 performs control so that the positive d-axis current id does not flow as much as possible. For example, as the first control, the d-axis abnormality control unit 61 performs control so that the d-axis current id becomes zero. However, the first control does not necessarily require the d-axis current id to be zero; it is sufficient to reduce the d-axis current id. Note that the d-axis abnormality control unit 61 may perform the first control even when the d-axis current id is zero.

[0072] One example of a method for reducing the d-axis current id is to set the d-axis current command value id* to 0. As a specific example, when the d-axis abnormality control unit 61 determines that the d-axis current id is not a negative value or that the d-axis current id is a positive value, it notifies the dq command value generating unit 32 of this fact.

[0073] When the dq command value generator 32 receives a notification from the d-axis abnormality controller 61, it sets the d-axis current command value id* to zero. Then, the dq command value generator 32 outputs the d-axis current command value id* set to zero to the first subtractor 33d. However, this is not limiting, and the d-axis abnormality controller 61 may set the d-axis current command value id* to zero.

[0074] The d-axis abnormality control unit 61 calculates the d-axis voltage command value Vd* based on the difference Δd when the d-axis current command value id* is set to zero, and outputs the calculated d-axis voltage command value Vd* to the second coordinate conversion unit 43. That is, in the first control, the d-axis normality control unit 60 outputs the d-axis voltage command value Vd* to the second coordinate conversion unit 43 by performing feedback control such as PI control so that the d-axis current id becomes zero.

[0075] When the d-axis abnormality control unit 61 determines that the d-axis current id is negative, it performs a second control to reduce the d-axis voltage command value Vd*. As an example of the second control, when the d-axis abnormality control unit 61 determines that the d-axis current id is negative, it reduces the d-axis voltage command value Vd* by setting the d-axis voltage command value Vd* to zero regardless of the value of the difference Δd. In other words, when the d-axis current id is negative, the d-axis abnormality control unit 61 outputs the d-axis voltage command value Vd* set to zero to the second coordinate transformation unit 43.

[0076] Next, the q-axis current control unit 52 according to this embodiment will be described.

[0077] The q-axis current control unit 52 calculates the q-axis voltage command value Vq* using the difference Δq output from the second subtraction unit 33q. The q-axis current control unit 52 includes, for example, a q-axis normal state control unit 70 and a q-axis abnormal state control unit 71.

[0078] The q-axis normal state control unit 70 calculates the q-axis voltage command value Vq* in normal state based on the difference Δq calculated by the second subtraction unit 33q. The q-axis normal state control unit 70 outputs the q-axis voltage command value Vq* to the second coordinate conversion unit 43 in normal state.

[0079] During normal operation, the difference Δq is input from the second subtractor 33q to the q-axis normal operation control unit 70 at regular intervals. The q-axis normal operation control unit 70 calculates the q-axis voltage command value Vq* so that the input difference Δq becomes zero. In this way, the q-axis normal operation control unit 70 performs feedback control so that the q-axis current iq follows the q-axis voltage command value Vq*. For example, the q-axis normal operation control unit 70 performs PI control so that the difference Δq becomes zero, thereby outputting the q-axis voltage command value Vq* to the second coordinate transformation unit 43.

[0080] The q-axis abnormality control unit 71 performs q-axis phase-open control by calculating a q-axis voltage command value Vq* in the event of an abnormality and outputting the calculated q-axis voltage command value Vq* to the second coordinate conversion unit 43. The q-axis phase-open control performed in the event of an abnormality will be described below.

[0081] The q-axis abnormality control unit 71 acquires the q-axis current iq from the first coordinate conversion unit 42. When the q-axis abnormality control unit 71 acquires, from the first coordinate conversion unit 42, the q-axis current iq that is opposite to the rotation direction of the motor 5 (hereinafter simply referred to as the "rotation direction") during an abnormality, the q-axis abnormality control unit 71 executes q-axis open-phase control, which outputs the q-axis voltage command value Vq* set to zero to the second coordinate conversion unit 43.

[0082] When the q-axis abnormality control unit 71 acquires, from the first coordinate conversion unit 42, a q-axis current iq that is oriented in the same direction as the direction of rotation during an abnormality, the q-axis abnormality control unit 71 outputs the q-axis voltage command value Vq* to the second coordinate conversion unit 43 in the same manner as the q-axis normality control unit 70. That is, when the q-axis abnormality control unit 71 acquires, from the first coordinate conversion unit 42, a q-axis current iq that is oriented in the same direction as the direction of rotation during an abnormality, the q-axis abnormality control unit 71 outputs the q-axis voltage command value Vq* to the second coordinate conversion unit 43 by performing feedback control such as PI control so that the difference Δq becomes zero.

[0083] For example, assume that the sign of the q-axis current iq, which is in the same direction as the direction of rotation, is positive. In such a case, when the sign of the q-axis current iq acquired from the first coordinate transformation unit 42 is negative, the q-axis abnormality control unit 71 outputs the q-axis voltage command value Vq* set to zero to the second coordinate transformation unit 43. On the other hand, when the sign of the q-axis current iq acquired from the first coordinate transformation unit 42 is positive, the q-axis abnormality control unit 71 calculates the q-axis voltage command value Vq* so that the difference Δq becomes zero, and outputs the calculated q-axis voltage command value Vq* to the second coordinate transformation unit 43.

[0084] In this way, the d-axis normal operation control unit 60 and the q-axis normal operation control unit 70 execute normal operation control during normal operation when no phase loss occurs. The d-axis abnormal operation control unit 61 and the q-axis abnormal operation control unit 71 execute open-phase operation control during abnormal operation when a phase loss occurs. Note that open-phase operation control includes d-axis open-phase operation control and q-axis open-phase operation control.

[0085] The switching unit 50 is capable of switching between a normal state and an abnormal state. The normal state is the connection state of the switching unit 50 that is set when normal control is performed. The abnormal state is the connection state of the switching unit 50 that is set when open-phase control is performed rather than normal control. In other words, the normal state is set when no open phase has occurred. The abnormal state is set when a open phase has occurred. When the switching unit 50 receives a signal SL from the open-phase detection unit 31, it switches from the normal state to the abnormal state. Note that the switching unit 50 according to this embodiment is realized by software, but may also be realized by hardware.

[0086] The switching unit 50 includes a front-stage switch unit 55 and a rear-stage switch unit 56. The front-stage switch unit 55 includes a front-stage d-axis switch unit 80 and a front-stage q-axis switch unit 81. The rear-stage switch unit 56 includes a rear-stage d-axis switch unit 82 and a rear-stage q-axis switch unit 83.

[0087] Each of the front stage d-axis switch unit 80, the front stage q-axis switch unit 81, the rear stage d-axis switch unit 82, and the rear stage q-axis switch unit 83 has a normal state and an abnormal state. Each of the front stage d-axis switch unit 80, the front stage q-axis switch unit 81, the rear stage d-axis switch unit 82, and the rear stage q-axis switch unit 83 is switched from the normal state to the abnormal state simultaneously or almost simultaneously by signal SL.

[0088] The front-stage d-axis switch unit 80 has a normal state in which the difference Δd calculated by the first subtraction unit 33 d is input to the d-axis normal state control unit 60, and an abnormal state in which the difference Δd calculated by the first subtraction unit 33 d is input to the d-axis abnormal state control unit 61. When the SL signal is input to the switching unit 50, the front-stage d-axis switch unit 80 switches from the normal state to the abnormal state.

[0089] The front-stage q-axis switch unit 81 has a normal state in which the difference Δq calculated by the second subtraction unit 33q is input to the q-axis normal state control unit 70, and an abnormal state in which the difference Δq calculated by the second subtraction unit 33q is input to the q-axis abnormal state control unit 71. When the SL signal is input to the switching unit 50, the front-stage q-axis switch unit 81 switches from the normal state to the abnormal state.

[0090] The rear-stage d-axis switch unit 82 has a normal state in which the d-axis voltage command value Vd* calculated by the d-axis normal operation control unit 60 is input to the second coordinate conversion unit 43 as the d-axis voltage command value Vd* to be input to the second coordinate conversion unit 43, and an abnormal state in which the d-axis voltage command value Vd* calculated by the d-axis abnormal operation control unit 61 is input to the second coordinate conversion unit 43 as the d-axis voltage command value Vd* to be input to the second coordinate conversion unit 43. When an SL signal is input to the switching unit 50, the rear-stage d-axis switch unit 82 switches from the normal state to the abnormal state.

[0091] The rear-stage q-axis switch unit 83 has a normal state in which the q-axis voltage command value Vq* calculated by the q-axis normal state control unit 70 is input to the second coordinate transformation unit 43 as the q-axis voltage command value Vq* to be input to the second coordinate transformation unit 43, and an abnormal state in which the q-axis voltage command value Vq* calculated by the q-axis abnormal state control unit 71 is input to the second coordinate transformation unit 43 as the q-axis voltage command value Vq* to be input to the second coordinate transformation unit 43. The rear-stage q-axis switch unit 83 switches from the normal state to the abnormal state when an SL signal is input to the switching unit 50. Note that the front-stage d-axis switch unit 80, the front-stage q-axis switch unit 81, the rear-stage d-axis switch unit 82, and the rear-stage q-axis switch unit 83 are all linked together and switch from the normal state to the abnormal state simultaneously or almost simultaneously.

[0092] The general flow of the method for driving the motor 5 mounted on the transport vehicle according to this embodiment will be described below with reference to Fig. 6. Fig. 6 is a flow chart for explaining the general flow of the method for driving the motor 5 in the transport vehicle according to this embodiment. In Fig. 6, it is assumed that the transport vehicle 100 travels within a warehouse to store and retrieve an article M.

[0093] When the transport vehicle 100 travels within the warehouse, the motor drive device 6 executes normal operation control to drive the motor 5 (step S101). As a result, the transport vehicle 100 moves within the warehouse and transports the item M. At this time, the connection state of the switching unit 50 is in the normal operation state. Therefore, the speed / position control unit 30 generates a drive signal based on the d-axis voltage command value Vd* obtained from the d-axis normal operation control unit 60 and the q-axis voltage command value Vq* obtained from the q-axis normal operation control unit 70, and outputs the generated drive signal to the inverter 20 to drive the motor 5.

[0094] The motor drive device 6 determines whether a phase loss has occurred in the phase loss detection unit 31 (step S102). If the motor drive device 6 determines that a phase loss has not occurred, it continues driving the motor 5 under normal control (step S103). If the motor drive device 6 determines in step S102 that a phase loss has occurred, it switches the dq-axis current control for driving the motor 5 from normal control to phase loss control (step S104).

[0095] As a specific example, when it is determined in step S102 that a phase loss has occurred, the open-phase detection unit 31 outputs a signal SL to the switching unit 50. When the switching unit 50 receives the signal SL, the connection state of the switching unit 50 switches from the normal state to the abnormal state. Therefore, the speed / position control unit 30 generates a drive signal based on the d-axis voltage command value Vd* obtained from the d-axis abnormality control unit 61 and the q-axis voltage command value Vq* obtained from the q-axis abnormality control unit 71, and outputs the generated drive signal to the inverter 20 to drive the motor 5.

[0096] This allows the transport vehicle 100 to rotate the motor 5 even if a phase loss occurs. As a result, the motor drive device 6 can continue running the transport vehicle 100 without stopping it, even if a phase loss occurs in the motor 5. For example, if a phase loss occurs while the transport vehicle 100 is transporting an article M, the motor drive device 6 may continue running the transport vehicle 100 using phase loss control until the article M has been transported to a designated location. If a phase loss occurs, the motor drive device 6 may run the transport vehicle 100 to a predetermined evacuation position using phase loss control.

[0097] For example, if a phase loss occurs while the transport vehicle 100 is transporting the item M to a designated location, the transport vehicle 100 continues traveling using phase loss control to transport the item M to the designated location. Then, when the transport vehicle 100 has completed transporting the item M to the designated location, it may send a notification of the failure to an external device via a communication network. The external device may be, for example, a computer. The external device may be, for example, a server device or a communication terminal (such as a smartphone or a tablet terminal).

[0098] For example, if a phase loss occurs while the transport vehicle 100 is transporting the item M to a designated location, the transport vehicle 100 continues traveling under the control during a phase loss and transports the item M to the designated location. After transporting the item M to the designated location, the transport vehicle 100 travels to a sheltered position under the control during a phase loss. Then, when the transport vehicle 100 arrives at the sheltered position, it may stop traveling and send a notification of a malfunction to the external device via a communication network.

[0099] When switching from normal control to open-phase control, the motor drive device 6 may cause the transport vehicle 100 to operate in a degenerated manner. In other words, the motor drive device 6 may cause the transport vehicle 100 to operate in a degenerated manner while the transport vehicle 100 is traveling using the open-phase control.

[0100] The operation flow of the control when a phase is lost according to this embodiment will be described below. The control when a phase is lost is roughly divided into d-axis control when a phase is lost and q-axis control when a phase is lost. The d-axis control when a phase is lost and the q-axis control when a phase is lost are executed in parallel. First, the operation flow of the control when a phase is lost according to this embodiment will be described. Figure 7 is a flow chart of an example of the control when a phase is lost according to this embodiment.

[0101] When the d-axis abnormality control unit 61 starts the d-axis open-phase control, it acquires the d-axis current id output from the first coordinate conversion unit 42 (step S201). The d-axis abnormality control unit 61 determines whether the acquired d-axis current id is equal to or greater than 0 (step S202). If the d-axis current id is equal to or greater than 0, the d-axis abnormality control unit 61 controls the d-axis current id so that a positive d-axis current id does not flow (step S203).

[0102] For example, in step S203, the d-axis abnormality control unit 61 directly or indirectly sets the d-axis current command value id* to zero. The d-axis abnormality control unit 61 calculates the d-axis current command value id* so that the difference Δd between the d-axis current command value id* set to zero and the d-axis current id obtained from the first coordinate transformation unit 42 becomes zero. The d-axis abnormality control unit 61 then outputs the calculated d-axis current command value id* to the speed / position control unit 30. This allows the d-axis abnormality control unit 61 to perform control so that a positive d-axis current id does not flow. After executing step S203, the d-axis abnormality control unit 61 returns to the processing of step S201.

[0103] If the d-axis abnormality control unit 61 determines in step S202 that the d-axis current id is less than 0 (negative), it sets the d-axis voltage command value Vd* to zero regardless of the value of the difference Δd. Then, the d-axis abnormality control unit 61 outputs the d-axis voltage command value Vd* set to zero to the speed / position control unit 30 (step S204). After executing step S203, the d-axis abnormality control unit 61 returns to the processing of step S201.

[0104] As a modified example, the process of step S203 may be replaced with the process of step S302 shown in FIG. 8 . For example, as shown in FIG. 8 , in step S302, the d-axis abnormality control unit 61 may determine whether the acquired d-axis current id is positive or negative. The d-axis abnormality control unit 61 may then perform step S203 if the d-axis current id is positive, execute step S204 if the d-axis current id is negative, and return to step S201 if the d-axis current id is positive. Furthermore, in the example shown in FIG. 8 , the d-axis abnormality control unit 61 may execute step S204 instead of returning to step S201 if the d-axis current id is 0.

[0105] The flow of the operation of the control when the q-axis phase is open according to this embodiment will be described below with reference to Fig. 9. Fig. 9 is a flow chart showing an example of the control when the q-axis phase is open according to this embodiment.

[0106] When the q-axis abnormality control unit 71 starts the q-axis open-phase control, it acquires the q-axis current iq output from the first coordinate conversion unit 42 (step S401). Based on the acquired q-axis current iq, the q-axis abnormality control unit 71 determines whether the direction of the q-axis current flowing through the motor 5 is opposite to the direction of rotation (step S402). For example, if the sign of the acquired q-axis current iq is positive, the q-axis abnormality control unit 71 determines that the direction of the q-axis current flowing through the motor 5 is the direction of rotation. For example, if the sign of the acquired q-axis current iq is negative, the q-axis abnormality control unit 71 determines that the direction of the q-axis current flowing through the motor 5 is opposite to the direction of rotation.

[0107] When the direction of the q-axis current flowing through the motor 5 is the rotation direction, the q-axis abnormality control unit 71 performs feedback control such as PI control so that the difference Δq obtained from the second subtraction unit 33q becomes zero, thereby outputting the q-axis voltage command value Vq* to the second coordinate conversion unit 43 (step S403). After executing step S403, the q-axis abnormality control unit 71 returns to step S401.

[0108] When the direction of the q-axis current flowing through the motor 5 is opposite to the direction of rotation, the q-axis abnormality control unit 71 outputs the q-axis voltage command value Vq* set to zero to the second coordinate conversion unit 43 (step S404). After executing step S404, the q-axis abnormality control unit 71 returns to step S401.

[0109] Next, the effects of this embodiment will be described. FIG. 10 is a diagram showing the direction of the composite magnetic flux under normal control according to this embodiment. FIG. 11 is a diagram showing the waveforms of the phase currents and d-axis and q-axis currents under normal conditions, and the direction of the composite magnetic flux under normal conditions according to this embodiment. Under normal control, as shown in FIG. 11 , AC voltages having a phase difference of 120 degrees are applied to the motor 5. When the windings 12 are excited by these AC voltages, a magnetic force is generated. The composite magnetic flux MF, which is the combination of the magnetic fluxes generated in the windings 12, rotates as shown in FIGS. 10 and 11 . The direction of the composite magnetic flux MF is the direction of the d-axis, and the rotation of the rotor 10 is controlled so that the direction of the d-axis and the direction of the N pole of the rotor 10 coincide. In other words, the rotor 10 rotates so that the direction of the N pole of the rotor 10 coincides with the direction of the composite magnetic flux MF.

[0110] Fig. 12 is a diagram showing the direction of the composite magnetic flux when normal control is performed in the event of a W-phase loss. Fig. 13 is a diagram showing the waveforms of the phase currents and dq-axis currents, and the direction of the composite magnetic flux when normal control is performed in the event of a W-phase loss.

[0111] Suppose that a W-phase loss occurs during normal control. When a phase loss occurs, if normal control is executed in the same manner as in normal operation, the direction of the composite magnetic flux MF generated by the motor 5 does not rotate, as shown in Figures 12 and 13 . That is, if the same sinusoidal AC voltage as in normal operation is applied during a phase loss, the direction of the composite magnetic flux MF is controlled to a fixed direction as shown in Figures 12 and 13 , and the composite magnetic flux MF does not rotate. Furthermore, as shown in Figure 13 , the composite magnetic flux MF near an electrical angle of 120 degrees and the composite magnetic flux MF near an electrical angle of 300 degrees act in the opposite direction to the direction of the composite magnetic flux MF in normal operation as shown in Figure 11 , interfering with the rotor 10 that has begun to rotate. As a result, the rotor 10 cannot rotate, the motor 5 stops, and the motor 5 cannot accelerate again.

[0112] In the event of a phase loss, the inventors have devised a method for rotating the rotor 10 using the remaining two phases other than the lost phase by providing a section in which current is applied (hereinafter referred to as a "current application section") and a section in which the current is zero (hereinafter referred to as a "zero current section"), as shown in Figure 14. In this method, only sections that contribute to rotation (e.g., around 60 degrees and 240 degrees when the W phase is lost) are set as current application sections, and the rotor 10 is rotated by repeatedly generating magnetic flux in the current application section and stopping magnetic flux generation in the zero current section. This allows the motor 5 to be driven even when a phase loss occurs, without generating a composite magnetic flux MF that would interfere with the rotor 10 once it has started to rotate.

[0113] 14 , when a phase is lost, it is necessary to perform a lost phase determination process to determine which phase is lost and a voltage waveform generation process to generate voltage waveforms for the remaining two phases other than the lost phase. Furthermore, in the voltage waveform generation process, it is necessary to set up the software so that it can generate three patterns of voltage waveforms when the lost phase is U, V, or W, so that it can handle any phase that is lost among U, V, or W. This can make the software complicated.

[0114] FIG. 15 illustrates motor rotation when control is performed in the event of a phase loss according to this embodiment. FIG. 16 illustrates voltage waveforms when a phase loss occurs when the motor drive method according to this embodiment is applied. When a phase loss occurs, the motor drive method and motor control device according to this embodiment change the control so that a positive d-axis current i d does not flow. Furthermore, when a negative d-axis current i d is detected, the d-axis voltage command value v d * is set to zero. When a q-axis current i q opposite to the direction of rotation is detected, the q-axis voltage command value v q * is set to zero. This creates a section VZ in which no voltage is applied to the winding 12. During the section VZ in which no voltage is applied to the winding 12, the motor 5 coasts, as shown in FIG. 15 . With these configurations, this embodiment can drive the motor 5 without generating a composite magnetic flux that would interfere with the rotation of the rotor 10, without performing a phase loss determination process or a voltage waveform generation process.

[0115] As shown in Figure 16, when the W phase is lost, the sections where the electrical angle is from 105 degrees to 155 degrees and from 285 degrees to 335 degrees are sections where no voltage is applied. Note that while the explanation has been given assuming that the W phase is lost, the same applies when the U and V phases are lost. For example, when the U phase is lost, the sections where the electrical angle is from 45 degrees to 95 degrees and from 225 degrees to 275 degrees are sections where no voltage is applied. For example, when the V phase is lost, the sections where the electrical angle is from 75 degrees to 125 degrees and from 255 degrees to 305 degrees are sections where no voltage is applied.

[0116] Below are shown the results of a simulation when the motor drive method according to this embodiment is applied. The simulation results shown below are the results of simulating abnormality control by assuming a state in which the W phase is lost and providing a speed command ω* when the motor is stopped. FIG. 17 is a diagram showing the results of a simulation of speed control during abnormality control according to this embodiment. The results shown in FIG. 17 confirm that during abnormality control, the rotational speed ω follows the speed command ω*, and speed control is possible even when one phase is lost.

[0117] 18, 19, and 20 are diagrams showing simulation results of current control during abnormality control according to this embodiment. Fig. 18 shows simulation results of the d-axis current id and the q-axis current iq during abnormality control according to this embodiment. Fig. 19 shows simulation results of the U-phase current iu, the V-phase current iv, and the W-phase current iw during abnormality control according to this embodiment. Fig. 20 shows simulation results of the d-axis voltage command value Vd* and the q-axis voltage command value Vq* during abnormality control according to this embodiment.

[0118] As shown in FIG. 18 , the d-axis current id and the q-axis current iq are distorted waveforms that are deformed from sine waves. Furthermore, as shown in FIG. 19 , the U-phase current iu and the V-phase current iv are also distorted. This causes the motor rotation speed to oscillate, but this oscillation is within a range that does not interfere with the degenerate operation of the guided vehicle 100. Note that the first half of the H-shaped waveforms of the U-phase current iu and the V-phase current iv shown in FIG. 19 are current waveforms generated by induced voltage. This is because, as shown in FIG. 20 , there is a section where both the d-axis voltage command value Vd* and the q-axis voltage command value Vq* are 0 (zero), and during this section, a current is generated from the rotating motor 5 due to the induced voltage.

[0119] The simulation results revealed that by modifying part of the dq-axis current control section for use in the event of a phase loss, it is possible to drive the motor using the remaining two phases even when one phase is lost. The motor drive method and motor control device according to this embodiment are capable of rotating the motor 5 forward and reverse even when a phase is lost, and are capable of making the rotational speed of the motor 5 follow the speed command ω* even when the speed command ω* is changed. The simulation results also confirmed that degenerate operation is possible by manipulating the dq-axis currents alone, regardless of which of the U, V, or W phases is lost.

[0120] The above-described embodiment discloses the following configuration. (Configuration 1) A driving method according to this embodiment is a method for driving a permanent magnet synchronous motor (motor 5). The driving method according to this embodiment includes: (1) reducing the d-axis current id when a phase loss occurs in one phase of the permanent magnet synchronous motor and the d-axis current id based on the d-axis current command value id* is positive; (2) reducing the d-axis voltage command value Vd* when the d-axis current id is negative when the phase loss occurs; and (3) reducing the q-axis voltage command value Vq* when the q-axis current iq based on the q-axis current command value iq* is opposite to the rotation direction of the permanent magnet synchronous motor when the phase loss occurs. Note that while the motor 5 is an SPMSM in the above description, the present invention is not limited to this and may be, for example, an IPMSM (Interior Permanent Magnet Synchronous Motor). (Configuration 2) In the above (2), if the d-axis current id is negative, the d-axis voltage command value Vd* may be set to zero, and in the above (3), if the q-axis current iq is directed opposite to the direction of rotation, the q-axis voltage command value Vq* may be set to zero. (Configuration 3) In the above (1) of configuration 1 or configuration 2, if the d-axis current id is positive, the d-axis current command value id* may be set to zero, and a d-axis voltage command value Vd* may be output that eliminates a difference between the d-axis current id and the d-axis current id, thereby reducing the d-axis current id. (Configuration 4) In any of configurations 1 to 3, the driving method according to the present embodiment may further include determining that a phase loss has occurred in one phase of the permanent magnet synchronous motor when at least one of the d-axis current id and the q-axis current iq of the motor 5 oscillates at a frequency approximately twice the frequency of the current phase current while controlling the d-axis current id and the q-axis current iq of the motor 5 to be respective specified values. (Configuration 5) The motor control device 23 performs vector control of the motor 5. The motor control device 23 includes a normal state control unit, an abnormal state control unit, and a speed / position control unit 30.The normal-state control unit includes, for example, a d-axis normal-state control unit 60 and a q-axis normal-state control unit 70, and when no phase loss occurs in the motor 5, performs normal-state control by outputting a d-axis voltage command value Vd* so that the d-axis current id becomes the d-axis current command value id* and outputting a q-axis voltage command value Vq* so that the q-axis current iq becomes the q-axis current command value iq*. The abnormal-state control unit includes a d-axis abnormal-state control unit 61 and a q-axis abnormal-state control unit 71, and when a phase loss occurs, performs abnormal-state control that differs from the normal-state control. In the abnormal-state control, the abnormal-state control unit reduces the d-axis current id when the d-axis current id is positive, reduces the d-axis voltage command value Vd* when the d-axis current id is negative, and reduces the q-axis voltage command value Vq* when the q-axis current iq based on the q-axis current command value iq* is opposite to the rotation direction of the permanent magnet synchronous motor. (Configuration 6) In configuration 5, the motor 5 is a drive motor of the transport vehicle 100 that transports the article W, and the abnormality control unit may, in the event of a phase loss, continue running the transport vehicle 100 by driving the motor 5 under abnormality control. (Configuration 7) Furthermore, in configuration 5 or 6, in the event of a phase loss, the abnormality control unit may transport the article W to a designated location by the transport vehicle 100, and continue running the transport vehicle 100 under abnormality control until the transport vehicle 100 retreats to a retreat position after the article W has been transported.

[0121] One or more of the requirements described in the above-described embodiments may be omitted. Furthermore, the requirements described in the above-described embodiments may be combined as appropriate. Furthermore, the execution order of each procedure shown in this embodiment can be realized in any order as long as the results of a previous procedure are not used in a subsequent procedure. Furthermore, even if the operations in the above-described embodiments are described using terms such as "first," "next," and "subsequently" for convenience, it is not necessary to perform the operations in this order. Furthermore, to the extent permitted by law, the disclosures of Japanese Patent Application No. 2024-029362 and all documents cited in the above-described embodiments are incorporated herein by reference.

[0122] 5... Motor, 23... Motor control device, 30... Speed / position control unit, 31... Open-phase detection unit, 32... dq command value generation unit, 33... Subtraction unit, 34... dq axis current control unit

Claims

1. A method for driving a permanent magnet synchronous motor, comprising the steps of: when a phase loss occurs in one of the phases of the permanent magnet synchronous motor, reducing the d-axis current if the d-axis current based on a d-axis current command value is positive; reducing the d-axis voltage command value if the d-axis current is negative; and reducing the q-axis voltage command value if the q-axis current based on a q-axis current command value is in the opposite direction to the rotation direction of the permanent magnet synchronous motor.

2. A method for driving a permanent magnet synchronous motor according to claim 1, wherein, when a phase loss occurs in one phase of the permanent magnet synchronous motor, if the d-axis current is negative, the d-axis voltage command value is set to zero, and if the q-axis current is in the opposite direction to the rotation direction, the q-axis voltage command value is set to zero.

3. A method for driving a permanent magnet synchronous motor according to claim 1 or 2, wherein when a phase loss occurs in one phase of the permanent magnet synchronous motor, if the d-axis current is positive, the d-axis current command value is set to zero, and the d-axis voltage command value is output so that there is no difference between the d-axis current command value set to zero and the d-axis current, thereby reducing the d-axis current.

4. A method for driving a permanent magnet synchronous motor according to claim 1, wherein, when the d-axis current and the q-axis current of the permanent magnet synchronous motor are controlled to be set to respective specified values, if at least one of the d-axis current and the q-axis current oscillates at a frequency approximately twice the frequency of the current phase current, it is determined that a phase loss has occurred in one of the phases of the permanent magnet synchronous motor.

5. A motor control device that performs vector control of a permanent magnet synchronous motor, comprising: a normal state control unit that performs normal state control when no phase loss has occurred in the permanent magnet synchronous motor, outputting a d-axis voltage command value so that the d-axis current becomes the d-axis current command value, and outputting a q-axis voltage command value so that the q-axis current becomes the q-axis current command value; an abnormal state control unit that performs abnormal state control different from the normal state control when the phase loss has occurred; and a speed / position control unit that generates a drive signal to drive the permanent magnet synchronous motor based on the q-axis voltage command value and the q-axis voltage command value, wherein the abnormal state control unit reduces the d-axis current when the d-axis current is positive, reduces the d-axis voltage command value when the d-axis current is negative, and reduces the q-axis voltage command value when the q-axis current based on the q-axis current command value is opposite to the rotation direction of the permanent magnet synchronous motor, in the abnormal state control.

6. The motor control device according to claim 5, wherein the permanent magnet synchronous motor is a drive motor for a transport vehicle that transports goods, and the abnormality control unit, when the phase loss occurs, continues the travel of the transport vehicle by driving the permanent magnet synchronous motor through the abnormality control.

7. The motor control device according to claim 6, wherein the abnormality control unit, when the phase loss occurs, causes the transport vehicle to transport the item to a designated location, and continues the transport vehicle's running under the abnormality control until the transport vehicle retreats to a retreat position after the item has been transported.

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