Drive system, control device

Abstract

To provide a technique for suppressing reduction in the lifetime of a switch device between a driving device and an AC motor, and suppressing occurrence of a failure.SOLUTION: A driving system 1 according to one embodiment of the present disclosure includes: a power conversion device 20 (inverter circuit 21) that is connected to an AC motor 10 via a power path PL provided with a switch device 30, and drives the AC motor 10 by using power from a DC power source PS; and a control device 22 that restricts an output voltage of the power conversion device 20 to be equal to or lower than an upper limit value Vo_lim, and changes the upper limit value Vo_lim according to the rotational speed of the AC motor 10.SELECTED DRAWING: Figure 4

Description

Technical Field

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[0001] The present disclosure relates to a drive system for an alternating current motor and the like.

Background Art

[0002] For example, a system is known in which a drive device such as an inverter device drives an alternating current motor using electric power from a predetermined power source through a power path provided with an opening / closing device between the drive device and the alternating current motor (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the opening / closing device is shifted from the closed state to the open state while the alternating current motor is being driven by the drive device, an arc is generated between the electrodes of the opening / closing device, and as long as the arc is generated, a current flows between the drive device and the alternating current motor. Therefore, for example, if the duration of the arc becomes relatively long, the life of the opening / closing device may be shortened, or the temperature of the opening / closing device may rise due to heat generation by the arc, leading to a failure of the opening / closing device.

[0005] Therefore, in view of the above problems, an object is to provide a technology capable of suppressing a decrease in the life and occurrence of failures of the opening / closing device between the drive device and the alternating current motor.

Means for Solving the Problems

[0006] To achieve the above object, in one embodiment of the present disclosure, a drive device that is connected through a power path provided with an opening / closing device to an alternating current motor and drives the alternating current motor using electric power from a predetermined power source, and The output voltage of the drive device is at the upper limit Do not exceed The system includes a control device that limits the rotation speed and changes the upper limit according to the rotation speed of the AC motor. 、 The aforementioned upper limit is the output voltage of the drive device that can suppress the continuation of the arc generated between the electrodes of the switchgear when the switchgear transitions from a closed state to an open state while the AC motor is being driven. ru, A drive system is provided.

[0007] In other embodiments of this disclosure, A drive unit is connected to an AC motor and a switchgear via a power path, and drives the AC motor using power from a predetermined power source. When the switchgear transitions from a closed state to an open state, if the output voltage of the drive unit exceeds the sum of the maximum voltage required for operation according to the rotational speed of the AC motor and the voltage drop due to the arc generated between the electrodes of the switchgear, the output voltage of the drive unit is limited to be less than the sum of the two values. and suppress the continuation of the arc. A control device comprising, A drive system is provided.

[0008] Furthermore, in yet another embodiment of this disclosure, A control device that controls a drive device that drives an AC motor, which is connected to an AC motor and a switchgear via a power path, and uses power from a predetermined power source to drive the AC motor, The output voltage of the drive device is at the upper limit Do not exceed The limit is restricted in such a way, and the upper limit is changed according to the rotational speed of the AC motor. 、 The aforementioned upper limit is the output voltage of the drive device that can suppress the continuation of the arc generated between the electrodes of the switchgear when the switchgear transitions from a closed state to an open state while the AC motor is being driven. ru, A control device is provided.

[0009] Furthermore, in yet another embodiment of this disclosure, A control device that controls a drive device that drives an AC motor, which is connected to an AC motor and a switchgear via a power path, and uses power from a predetermined power source to drive the AC motor, When the opening / closing device transitions from the closed state to the open state, if the output voltage of the drive device exceeds the sum of the maximum value of the voltage required for operation according to the rotational speed of the AC motor and the voltage drop due to the arc generated between the electrodes of the opening / closing device, the output voltage of the drive device is limited so as to be smaller than the sum value. and suppress the continuation of the arc. to perform a control device is provided.

Advantages of the Invention

[0010] According to the above-described embodiment, it is possible to suppress a decrease in the lifespan and occurrence of failures of the opening / closing device between the drive device and the AC motor.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a diagram showing an example of a drive system. [Figure 2] FIG. 2 is a functional block diagram showing an example of the configuration of the control device. [Figure 3] FIG. 3 is a diagram for explaining a control method of an AC motor according to a comparative example. [Figure 4] FIG. 4 is a diagram for explaining a first example of a control method of an AC motor. [Figure 5] FIG. 5 is a diagram for explaining a second example of a control method of an AC motor. [Figure 6] FIG. 6 is a diagram for explaining a third example of a control method of an AC motor. [Figure 7] FIG. 7 is a diagram for explaining a fourth example of a control method of an AC motor.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments will be described with reference to the drawings.

[0013] [Overview of the Drive System] Referring to FIG. 1, the overview of the drive system 1 according to the present embodiment will be described.

[0014] FIG. 1 is a diagram showing an example of the drive system 1.

[0015] As shown in Figure 1, the drive system 1 includes an AC motor 10, a power converter 20, a switchgear 30, and a rotational speed sensor 40.

[0016] The drive system 1 uses DC power supplied from the DC power supply PS to output drive power for the AC motor 10 from the power converter 20, thereby driving the AC motor 10.

[0017] The AC motor 10 is the drive target of the drive system 1. The AC motor 10 is, for example, a synchronous motor or an induction motor.

[0018] The power converter 20 (an example of a drive device) converts the DC power supplied from the DC power supply PS into drive power for the AC motor 10 and outputs it. The power converter 20 includes an inverter circuit 21, a control device 22, and a current sensor 23.

[0019] The inverter circuit 21 converts the DC power input from the DC power supply PS into three-phase AC power of the desired voltage and frequency (U-phase, V-phase, and W-phase), and outputs it to the AC motor 10 through the power path PL.

[0020] The inverter circuit 21 includes semiconductor switches SW and freewheeling diodes DI. Specifically, three sets of series connections (switch legs) of two semiconductor switches SW corresponding to the upper and lower arms are provided, and the three sets of switch legs are connected in parallel between the positive and negative lines extending from the positive and negative terminals of the DC power supply PS, respectively. Then, terminals for the U phase, V phase, and W phase are drawn out from the midpoint of the upper and lower arms of the three sets of switch legs and connected to the power path PL which is connected to the U phase, V phase, and W phase terminals of the AC motor 10. The freewheeling diodes DI are connected in parallel to each semiconductor switch SW with the forward direction from the negative line side to the positive line side.

[0021] The control device 22 drives and controls the AC motor 10 using the power converter 20. Specifically, the control device 22 drives and controls the AC motor 10 by outputting a control command to the inverter circuit 21 (semiconductor switch SW), causing the inverter circuit 21 to output the desired drive power.

[0022] The functions of the control device 22 are realized by any hardware or any combination of hardware and software. For example, the control device 22 is composed of a computer including a CPU (Central Processing Unit), a memory device, an auxiliary storage device, and an interface device, as well as a drive circuit that drives the gate terminals of a semiconductor switch SW. The memory device is, for example, SRAM (Static Random Access Memory). The auxiliary storage device is, for example, EEPROM (Electrically Erasable Programmable Read-Only Memory) or flash memory. The interface device includes, for example, an external interface for connecting to an external recording medium and a communication interface for communicating with other devices. The control device 22 can realize various functions by loading a program installed in the auxiliary storage device into the memory device and executing it on the CPU. The control device 22 can also retrieve and install programs from a recording medium via the external interface, or retrieve and install programs from other devices via the communication interface.

[0023] The current sensor 23 detects the output of the inverter circuit 21, i.e., the currents of the U-phase, V-phase, and W-phase. The output (detection signal) of the current sensor 23 is input to the control device 22.

[0024] Furthermore, the current sensor 23 may be configured to detect the current of two of the three phases: U-phase, V-phase, and W-phase. This is because the control device 22 can calculate (estimate) the current of the remaining phase from the detected current values ​​of the two phases.

[0025] The switchgear 30 is installed in the power path PL between the power converter 20 and the AC motor 10.

[0026] The switchgear 30 switches between a closed state in which the power path PL is electrically connected and an open state in which the power path PL is disconnected. The switchgear 30 is, for example, an electromagnetic contactor or an electromagnetic switch.

[0027] The rotational speed sensor 40 detects the rotational speed of the AC motor 10. The rotational speed sensor 40 is, for example, an encoder. The output (detection signal) of the rotational speed sensor 40 is input to the power converter 20 and taken up by the control device 22.

[0028] [Control device function configuration] Next, the functional configuration of the control device 22 will be described with reference to Figure 2.

[0029] Figure 2 is a functional block diagram showing an example of the functional configuration of the control device 22.

[0030] As shown in Figure 2, the system includes a speed controller 221, a vector converter 222, a current controller 223, a voltage limiting function 224, a voltage limiter 225, and a vector inverse converter 226.

[0031] The speed controller 221 outputs control commands (hereinafter referred to as "current command values") Id* and Iq* for the d-axis current and q-axis current of the AC motor 10, based on the deviation between the command value ω* of the rotational speed of the AC motor 10 and the detected value ωdet, in order to bring the deviation closer to zero. The detected value ωdet is obtained based on the output of the rotational speed sensor 40. The speed controller 221 is, for example, a PI (Proportional Integral) controller.

[0032] Furthermore, if sensorless control is employed, for example, the estimated value ωest of the rotational speed of the AC motor 10 is used instead of the detected value ωdet of the rotational speed of the AC motor 10. In this case, the rotational speed sensor 40 is omitted. Also, if speed control is not employed, the speed controller 221 is omitted. For example, if torque control or current control is employed, the speed controller 221 is omitted. In this case, the current command values ​​Id*,Iq* are generated based on the torque command value in torque control, or based on the U-phase, V-phase, and W-phase current command values ​​in current control.

[0033] The vector converter 222 converts the detected phase currents Iu, Iv, and Iw of the U-phase, V-phase, and W-phase into current detection values ​​Id and Iq in the dq coordinate system, based on information such as the electrical phase angle θ and magnetic pole position of the AC motor 10, and outputs them. The detected phase currents Iu, Iv, and Iw of the U-phase, V-phase, and W-phase are obtained based on the output of the current sensor 23.

[0034] The current regulator 223 outputs control commands (hereinafter referred to as "voltage command values") Vd*, Vq* for the d-axis voltage and q-axis voltage of the AC motor 10, based on the deviation between the current command values ​​Id*, Iq* and the current detection values ​​Id, Iq, in order to bring the deviation closer to zero. The current regulator 223 is, for example, a PI controller.

[0035] The voltage limiting function 224 takes the detected rotational speed ωdet of the AC motor 10 as an argument and outputs the positive limit value VLIMp and the negative limit value VLIMn of the voltage applied to the AC motor 10, i.e., the output voltage of the inverter circuit 21.

[0036] For example, as described later, the output voltage of the power converter 20 (inverter circuit 21) is set to an upper limit value Vo_lim (>0). In this case, the voltage limiting function 224 outputs the upper limit value Vo_lim as the positive limit value VLIMp, and the value of the upper limit value Vo_lim with its sign reversed as the negative limit value VLIMn.

[0037] The voltage limiter 225 limits the voltage command values ​​Vd* and Vq* to between the limit values ​​VLIMp and VLIMn and outputs them. Specifically, if the voltage command value Vd* is within the range between the limit values ​​VLIMp and VLIMn, the voltage limiter 225 outputs the voltage command value Vd* as is. On the other hand, if the voltage command value Vd* is greater than VLIMp, the voltage limiter 225 corrects the voltage command value Vd* to the limit value VLIMp and outputs it. Similarly, if the voltage command value Vd* is less than the limit value VLIMn, the voltage limiter 225 corrects the voltage command value Vd* to the limit value VLIMn and outputs it. The same applies to the voltage command value Vq*.

[0038] The vector inverse converter 226 converts the voltage command values ​​Vd* and Vq*, which are input after passing through the voltage limiter 225, into U-phase, V-phase, and W-phase voltage command values ​​Vu, Vv, and Vw, respectively, based on information such as the electrical phase angle θ and magnetic pole position of the AC motor 10, and outputs them.

[0039] The PWM signal output unit 227 generates control commands for the inverter circuit 21, i.e., PWM (Pulse Width Modulation) signals, and outputs them to the inverter circuit 21. For example, the PWM signal output unit 227 includes comparators corresponding to the U-phase, V-phase, and W-phase, and the comparators output PWM signals for the U-phase, V-phase, and W-phase by comparing the voltage command values ​​Vu, Vv, and Vw with the carrier wave. As a result, the control device 22 can drive and control the AC motor 10 by outputting PWM signals to the inverter circuit 21.

[0040] [Control method for AC motors according to comparative examples] Next, with reference to Figure 3, a control method for the AC motor 10 according to a comparative example will be described.

[0041] Figure 3 is a diagram illustrating a control method for an AC motor 10 in a comparative example.

[0042] Furthermore, the steady-state rotational speed of the AC motor 10 is proportional to the electrical frequency f in the case of a synchronous motor. Also, in the case of an induction motor, the steady-state rotational speed of the AC motor 10 is generally proportional to the electrical frequency f, considering that the slip frequency is generally very small. In either case, the proportionality constant is the number of pole pairs of the AC motor 10. Therefore, the following explanation will be based on the premise that a proportional relationship, or an approximately proportional relationship, exists between the rotational speed of the AC motor 10 and the electrical frequency f.

[0043] As shown in Figure 3, the amplitude EMF of the induced electromotive force of the AC motor 10 is proportional to the rotational speed of the AC motor 10.

[0044] The terminal voltage of the AC motor 10 is the sum of the vector sum of the voltage drop due to the impedance of the coil (winding) caused by the current flowing through the coil and the induced electromotive force of the AC motor 10.

[0045] The impedance of a coil can be divided into a resistive component that does not depend on the electrical frequency f and a reactance component that is proportional to the electrical frequency f. Here, except in the region where the rotational speed of the AC motor 10 is very low, it is generally the case that the reactance component is sufficiently large compared to the resistive component. Therefore, the voltage drop due to the impedance of the coil is dominated by the voltage drop due to the reactance component and can be considered to be proportional to the electrical frequency f, that is, proportional to the rotational speed of the AC motor 10. Thus, as shown in Figure 3, the maximum value (amplitude voltage) Vm_s of the terminal voltage of the AC motor 10 in the steady state is expressed as the sum of the amplitude EMF of the induced electromotive force and the voltage drop component that is proportional to the rotational speed of the AC motor 10. As a result, the maximum value Vm_s of the terminal voltage of the AC motor 10 in the steady state is expressed in a form that is approximately proportional to the rotational speed of the AC motor 10.

[0046] In the transient state of the AC motor 10, that is, in the state in which the current amplitude of the AC motor 10 changes over time, the terminal voltage of the AC motor 10 is further increased by a voltage corresponding to the rate of change compared to the terminal voltage of the AC motor 10 in the steady state. Assuming that the rate of change of the current amplitude does not depend on the rotational speed of the AC motor 10, the addition corresponding to the rate of change of the current amplitude can also be considered a constant value that does not depend on the rotational speed of the AC motor 10. Therefore, as shown in Figure 3, the maximum value (amplitude voltage) Vm_t of the terminal voltage of the AC motor 10 in the transient state (hereinafter simply referred to as the "transient state"), assuming the occurrence of the expected maximum value of the current amplitude, can be expressed by adding a constant value to the maximum value Vm_s of the terminal voltage of the AC motor 10 in the steady state. As a result, the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state can be expressed as increasing approximately linearly with increasing rotational speed of the AC motor 10.

[0047] As shown in Figure 3, in the comparative example, the upper limit Vo_lim of the output voltage of the power converter 20 (inverter circuit 21) is set to the maximum value Vo_max of the voltage that the power converter 20 (inverter circuit 21) can output using power from the DC power supply PS. In other words, the output voltage of the power converter 20 is effectively equivalent to being unlimited.

[0048] Now, let's consider a case where, for some reason, the switchgear 30 transitions from a closed state to an open state while the AC motor 10 is in operation.

[0049] When the switchgear 30 transitions from a closed state to an open state, an arc is generated between the electrodes of the switchgear 30. When an arc is generated, a voltage drop due to the arc (hereinafter referred to as "arc voltage") Va occurs in the switchgear 30.

[0050] As described above, the power converter 20 (inverter circuit 21) attempts to maintain a current corresponding to the current command values ​​Id* and Iq* under the control of the control device 22. Therefore, as shown in Figure 3, the power converter 20 attempts to increase the output voltage by the amount of the arc voltage Va. As a result, since the output voltage of the inverter circuit 21 is not substantially limited, the inverter circuit 21 is able to increase the output voltage by the amount of the arc voltage Va, and the arc continues. For example, in Figure 3, when the rotational speed of the AC motor 10 is at a predetermined value ωa (electrical frequency f is a predetermined value fa), the switchgear 30 is switched to the open state, and the output voltage of the power converter 20 rises by the amount of the arc voltage Va to reach a predetermined value Vxa, and this state continues. Therefore, the continuation of the arc may shorten the lifespan of the switchgear 30, or the heat generated by the continuation of the arc may cause the temperature of the switchgear 30 to rise, potentially leading to failure.

[0051] Furthermore, although the arc disappears when the AC current crosses zero, if the electrical frequency f is relatively small, that is, if the rotational speed of the AC motor 10 is relatively small, the time until the AC current crosses zero may be relatively longer. As a result, the duration of the arc becomes relatively longer, increasing the likelihood that the lifespan of the switchgear 30 will be shortened due to the arc, or that the temperature of the switchgear 30 will rise due to the heat generated by the arc, leading to failure.

[0052] Thus, in the comparative example, since the output voltage of the inverter circuit 21 is not substantially limited, the arc generated when the switchgear 30 transitions from the closed state to the open state continues, which may result in a reduced lifespan or failure of the switchgear 30.

[0053] [First example of an AC motor control method] Next, with reference to Figure 4, a first example of a control method for the AC motor 10 by the control device 22 will be described.

[0054] Figure 4 illustrates a first example of a control method for the AC motor 10.

[0055] As shown in Figure 4, in this example, the upper limit of the output voltage Vo_lim of the power converter 20 is set to be greater than or equal to the maximum value Vm_t of the terminal voltage of the AC motor 10 in a transient state across the entire range of rotational speeds of the AC motor 10 above zero. The entire range of rotational speeds of the AC motor 10 means the range from zero or above, and below a predetermined upper limit value assumed to be the rotational speed of the AC motor 10. This ensures the operation of the AC motor 10 in a transient state. For example, the upper limit of the output voltage Vo_lim of the power converter 20 is set to be somewhat greater than the maximum value Vm_t of the terminal voltage of the AC motor 10 in a transient state. This ensures the operation of the AC motor 10 in a transient state more reliably.

[0056] In this example, the upper limit of the output voltage of the power converter 20, Vo_lim, is set to be smaller than the minimum output voltage of the power converter 20 required to maintain the arc, Va_min, across the entire range of rotational speeds of the AC motor 10 above zero. The minimum output voltage of the power converter 20 required to maintain the arc, Va_min, represents the minimum output voltage of the power converter 20 required to maintain the arc when the switchgear 30 transitions from the closed state to the open state during the transient state of the AC motor 10. In other words, the minimum output voltage of the power converter 20 required to maintain the arc, Va_min, corresponds to the sum of the maximum terminal voltage Vm_t of the AC motor 10 during the transient state and the arc voltage Va. As a result, when the switchgear 30 transitions from the closed state to the open state, the output voltage of the power converter 20 cannot be raised to the minimum output voltage of the power converter 20 required to maintain the arc, Va_min, to compensate for the current reduction due to the arc voltage Va. Consequently, the current can be reduced to zero, extinguishing the arc and suppressing its continuation.

[0057] When the AC motor 10 transitions from the closed state to the open state of the switchgear 30 during a transient state, the minimum output voltage Va_min of the power converter 20 required to maintain arc increases linearly with increasing rotational speed of the AC motor 10, with the same slope as the maximum terminal voltage Vm_t of the AC motor 10 during the transient state. Therefore, the upper limit of the output voltage Vo_lim of the power converter 20 is set to change in accordance with the change in the maximum terminal voltage Vm_t of the AC motor 10 during the transient state, corresponding to the rotational speed (electrical frequency f). In other words, the upper limit of the output voltage Vo_lim of the power converter 20 is set to increase linearly with increasing rotational speed (electrical frequency f) of the AC motor 10, with the same slope (rate of change) as the maximum terminal voltage Vm_t of the AC motor 10 during the transient state. This makes it possible to suppress arc maintenance when the switchgear 30 transitions from the closed state to the open state, while ensuring the operation of the AC motor 10 during the transient state, in accordance with changes in the rotational speed of the AC motor 10.

[0058] The control device 22 sets the upper limit value Vo_lim of the output voltage of the power converter 20 based on, for example, the detected value ωdet of the rotational speed of the AC motor 10. Alternatively, the control device 22 may set the upper limit value Vo_lim of the output voltage of the power converter 20 based on, for example, the estimated value ωest of the rotational speed of the AC motor 10 or the command value ω*. The same may apply to the second to fourth examples described later.

[0059] Furthermore, if the AC motor 10 is an induction motor or a wound-type synchronous motor, the excitation flux and field flux are adjustable, so the proportionality coefficient of the amplitude EMF of the induced electromotive force of the AC motor 10, which is generated by the excitation flux and field flux, with respect to the change in rotational speed changes. As a result, the proportionality coefficient of the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state with respect to the change in rotational speed of the AC motor 10 also changes in the same way. In this case, the control device 22 sets the upper limit value Vo_lim of the output voltage of the power converter 20 so that the proportionality coefficient with respect to the change in rotational speed of the AC motor 10 changes according to the set values ​​of the excitation flux and field flux that it adjusts. Alternatively, the proportionality coefficient of the upper limit value Vo_lim of the output voltage of the power converter 20 with respect to the change in rotational speed of the AC motor 10 may be set as a fixed value in advance, taking into account the range of change in the amplitude EMF of the induced electromotive force. The same may apply in the second example, third example, etc., described later.

[0060] Thus, in this example, unlike the comparative example described above, it is possible to suppress the continuation of arcing when the switchgear 30 transitions from the closed state to the open state while ensuring the desired operation of the AC motor 10.

[0061] [Second example of an AC motor control method] Next, with reference to Figure 5, a second example of a control method for the AC motor 10 by the control device 22 will be described.

[0062] Figure 5 illustrates a second example of a control method for the AC motor 10.

[0063] As shown in Figure 5, in this example, similar to the first example described above, the terminal voltage of the AC motor 10 is set to be greater than or equal to the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state across the entire range of rotational speeds of the AC motor 10 above zero. This ensures the operation of the AC motor 10 in the transient state.

[0064] Furthermore, in this example, similar to the first example described above, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to be smaller than the minimum value Va_min of the output voltage of the power converter 20 required to maintain the arc, across the entire range of rotational speeds of the AC motor 10 above zero. This makes it possible to suppress the continuation of the arc that occurs when the switchgear 30 transitions from the closed state to the open state.

[0065] Furthermore, in this example, when the rotational speed of the AC motor 10 is within a range of a predetermined value ω1 or less, that is, when the electrical frequency f is within a range of a predetermined value f1 or less, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to a constant predetermined value V1. As a result, in the region where the rotational speed of the AC motor 10 is relatively small, the upper limit value Vo_lim of the output voltage of the power converter 20 is kept constant, and the processing load of the control device 22 can be reduced.

[0066] Furthermore, in this example, in the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω1, that is, in the range where the electrical frequency f is greater than a predetermined value f1, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to increase linearly with respect to the increase in the rotational speed (electrical frequency f) of the AC motor 10. Specifically, in this range, as in the first example described above, the upper limit value Vo_lim of the output voltage of the power converter 20 increases linearly with respect to the increase in the rotational speed of the AC motor 10 with the same slope as the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state. This makes it possible to suppress arc continuity when the switchgear 30 transitions from the closed state to the open state, while ensuring the operation of the AC motor 10 in the transient state in accordance with the change in the rotational speed of the AC motor 10.

[0067] Thus, in this example, similar to the first example described above, it is possible to suppress the continuation of arcing when the switchgear 30 transitions from the closed state to the open state while ensuring the desired operation of the AC motor 10. Furthermore, in this example, the processing load of the control device 22 can be reduced in the region where the rotational speed of the AC motor 10 is relatively low.

[0068] [Third example of an AC motor control method] Next, with reference to Figure 6, a third example of a control method for the AC motor 10 by the control device 22 will be described.

[0069] Figure 6 illustrates a third example of a control method for the AC motor 10.

[0070] As shown in Figure 6, in this example, the upper limit of the output voltage Vo_lim of the power converter 20 is set to be greater than or equal to the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state, across the entire range of rotational speeds of the AC motor 10 above zero, similar to the first example described above. This ensures the operation of the AC motor 10 in the transient state.

[0071] Furthermore, in this example, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to be smaller than the minimum value Va_min of the output voltage of the power converter 20 required for arc continuation, within the range where the rotational speed of the AC motor 10 is zero or greater and less than or equal to a predetermined value ω2. The range where the rotational speed of the AC motor 10 is zero or greater and less than or equal to a predetermined value ω2 corresponds to the range where the electrical frequency f is zero or greater and less than or equal to a predetermined value f2. This makes it possible to suppress the continuation of arc that occurs when the switchgear 30 transitions from the closed state to the open state in the region where the rotational speed of the AC motor 10 is relatively small (i.e., the region where the electrical frequency f is relatively small).

[0072] Specifically, as shown in Figure 6, the upper limit of the output voltage of the power converter 20, Vo_lim, may be set to increase linearly with respect to the increase in the rotational speed (electrical frequency f) of the AC motor 10, with the same slope (rate of change) as the maximum value Vm_t of the terminal voltage of the AC motor 10 in a transient state and the minimum value Va_min of the output voltage of the power converter 20 required to maintain the arc, within the range where the rotational speed of the AC motor 10 is zero or greater and less than or equal to a predetermined value ω2.

[0073] Furthermore, in this example, the upper limit of the output voltage of the power converter 20, Vo_lim, is set independently of the minimum output voltage of the power converter 20, Va_min, required for arc continuation, within the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2. This is because, as the electrical frequency f becomes relatively larger, the time from the transition of the switchgear 30 from the closed state to the open state to zero crossing becomes relatively shorter, and the arc extinguishes at a relatively earlier timing, thus having a relatively small impact on the lifespan and failure of the switchgear 30. For example, the predetermined values ​​f2 and ω2 are set by verifying the duration of the arc that does not affect the lifespan reduction or failure of the switchgear 30 through computer simulations and experiments with actual equipment.

[0074] As shown in Figure 6, specifically, the upper limit of the output voltage Vo_lim of the power converter 20 is set to a constant value in the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2. This ensures that in the range where the rotational speed of the AC motor 10 is relatively high, the upper limit of the output voltage Vo_lim of the power converter 20 remains constant, reducing the processing load on the control device 22. For example, the upper limit of the output voltage Vo_lim of the power converter 20 is set to the maximum value Vo_max of the voltage that the power converter 20 can output in the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2. This ensures more reliable operation of the AC motor 10.

[0075] Thus, in this example, similar to the first example described above, it is possible to suppress the continuation of arcing when the switchgear 30 transitions from the closed state to the open state while ensuring the desired operation of the AC motor 10. Furthermore, in this example, in the region where the rotational speed of the AC motor 10 is relatively high, the processing load of the control device 22 can be reduced, and the desired operation of the AC motor 10 can be more reliably guaranteed.

[0076] [Fourth example of an AC motor control method] Next, with reference to Figure 7, a fourth example of a control method for the AC motor 10 by the control device 22 will be described.

[0077] Figure 7 illustrates a fourth example of a control method for the AC motor 10.

[0078] As shown in Figure 7, similar to the first example described above, the terminal voltage of the AC motor 10 is set to be greater than or equal to the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state across the entire range of rotational speeds of the AC motor 10 above zero. This ensures the operation of the AC motor 10 in the transient state.

[0079] Furthermore, in this example, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to be smaller than the minimum value Va_min of the output voltage of the power converter 20 required for arc continuation, in the range where the rotational speed of the AC motor 10 is greater than or equal to zero and less than or equal to a predetermined value ω2, similar to the third example described above. This makes it possible to suppress the continuation of arc that occurs when the switchgear 30 transitions from the closed state to the open state in a region where the rotational speed of the AC motor 10 is relatively small (i.e., a region where the electrical frequency f is relatively small).

[0080] Specifically, as shown in Figure 7, the upper limit of the output voltage Vo_lim of the power converter 20 is set to a constant predetermined value V2. This ensures that in regions where the rotational speed of the AC motor 10 is relatively low, the upper limit of the output voltage Vo_lim of the power converter 20 remains constant, thereby reducing the processing load on the control device 22.

[0081] Furthermore, in this example, the upper limit value Vo_lim of the output voltage of the power converter 20 is set independently of the minimum value Va_min of the output voltage of the power converter 20 required to maintain the arc, within the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2, similar to the third example described above.

[0082] As shown in Figure 7, specifically, the upper limit of the output voltage Vo_lim of the power converter 20 is set to a constant value in the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2, similar to the third example described above. This ensures that the upper limit of the output voltage Vo_lim of the power converter 20 remains constant in the range where the rotational speed of the AC motor 10 is relatively high, thereby reducing the processing load on the control device 22. For example, the upper limit of the output voltage Vo_lim of the power converter 20 is set to the maximum value Vo_max of the output voltage that the power converter 20 can output in the range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2, similar to the third example described above. This ensures more reliable operation of the AC motor 10.

[0083] Thus, in this example, similar to the first example described above, it is possible to suppress the continuation of arcing when the switchgear 30 transitions from the closed state to the open state while ensuring the desired operation of the AC motor 10. Furthermore, in this example, similar to the third example described above, the desired operation of the AC motor 10 can be more reliably guaranteed in the region where the rotational speed of the AC motor 10 is relatively high. In addition, in this example, the processing load of the control device 22 can be reduced across the entire range of rotational speeds of the AC motor 10.

[0084] [Other embodiments] The embodiments described above may be modified or altered as appropriate.

[0085] For example, in the first example of the control method described above, the upper limit value Vo_lim of the output voltage of the power converter 20 may be set to change in a stepwise manner instead of linearly in response to the change in the rotational speed of the AC motor 10. The same may apply to the region in the second example of the control method described above where the rotational speed of the AC motor 10 is greater than a predetermined value ω1, and to the region in the third example of the control method described above where the rotational speed of the AC motor 10 is less than or equal to a predetermined value ω2.

[0086] Furthermore, for example, in the second example of the control method described above and its modifications, the upper limit value Vo_lim of the output voltage of the power converter 20 may be set to increase in accordance with the increase in the rotational speed of the AC motor 10, within a range where the rotational speed of the AC motor 10 is ω1 or less. In this case, the rate of increase of the upper limit value Vo_lim of the output voltage of the power converter 20 with respect to the rotational speed of the AC motor 10 may be set to be smaller or larger than when the rotational speed of the AC motor 10 is in a range greater than the predetermined value ω1. Similarly, in the third example of the control method described above and its modifications, the upper limit value Vo_lim of the output voltage of the power converter 20 may be set to increase in accordance with the increase in the rotational speed of the AC motor 10, within a range where the rotational speed of the AC motor 10 is greater than a predetermined value ω2. In this case, the rate of increase of the upper limit value Vo_lim of the output voltage of the power converter 20 with respect to the rotational speed of the AC motor 10 may be set to be smaller or larger than when the rotational speed of the AC motor 10 is in a range where the rotational speed of the AC motor 10 is ω2 or less.

[0087] Furthermore, for example, in the second example of the control method described above and its modified form, the entire range of rotational speed of the AC motor 10 is divided into two ranges in which the setting mode of the upper limit value Vo_lim of the output voltage of the power converter 20 is different from each other, but it may be divided into three or more ranges. The same may apply to the third example, the fourth example, and their modified forms described above.

[0088] Furthermore, for example, in the third example of the control method described above and its modified form, the upper limit value Vo_lim of the output voltage of the power converter 20 does not need to be set in the region where the rotational speed of the AC motor 10 is greater than a predetermined value ω2. The same may also apply to the region where the rotational speed of the AC motor 10 is greater than a predetermined value ω2 in the fourth example of the control method described above.

[0089] Furthermore, in the embodiments and their modifications described above, the control device 22 may set the upper limit value Vo_lim of the output voltage of the power converter 20 differently depending on the open / closed state of the switchgear 30. In this case, the open / closed state of the switchgear 30 can be determined, for example, based on the auxiliary contact signals of the switchgear 30 or signals input in conjunction with the operating section of the switchgear 30. Specifically, when the switchgear 30 is in the closed state, the control device 22 may set the upper limit value Vo_lim of the output voltage of the power converter 20 to the maximum value Vo_max of the voltage that the power converter 20 can output. Alternatively, when the switchgear 30 is in the closed state, the control device 22 may not set the upper limit value Vo_lim of the output voltage of the power converter 20. On the other hand, when the switchgear 30 transitions from the closed state to the open state, the control device 22 may set the upper limit value Vo_lim of the output voltage of the power converter 20, as in the first to fourth examples and their modifications described above. In other words, when the switchgear 30 transitions from a closed state to an open state, the control device 22 may set the upper limit Vo_lim of the output voltage of the power converter 20 to a range that is greater than or equal to the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state, and smaller than the minimum value Va_min of the output voltage of the power converter 20 required to maintain the arc. This suppresses the processing load on the control device 22 when the switchgear 30 is in a closed state, while also suppressing the continuation of the arc that occurs when the switchgear 30 transitions from a closed state to an open state.

[0090] Furthermore, in the embodiments and their modifications described above, the power converter 20 may generate and output the drive power for the AC motor 10 using three-phase AC power of R, S, and T phases input from an AC power source (an example of a predetermined power source) instead of DC power from a DC power source PS. In this case, for example, the power converter 20 includes, in addition to the inverter circuit, a rectifier circuit that converts the power from the AC power source to DC, and a smoothing circuit that smooths the output of the rectifier circuit and outputs it to the inverter circuit 21. In this case, the power converter 20 may also be a matrix converter capable of directly converting three-phase AC power of R, S, and T phases into three-phase AC power of U, V, and W phases.

[0091] Furthermore, in the embodiments and modifications described above, for example, some or all of the functions of the control device 22 may be transferred to an external control device of the power converter 20. Specifically, the function of setting the upper limit value Vo_lim of the output voltage of the power converter 20 may be transferred to an external control device of the power converter 20. In this case, the external control device may be installed in the same building or on the same premises as the AC motor 10 (power converter 20) to be controlled, or it may be installed in a location away from the AC motor 10 and power converter 20 to be controlled. In the former case, the external control device may be, for example, a PLC (Programmable Logic Controller), an edge controller, or an edge server. In the latter case, the external control device may be, for example, an on-premise server or a cloud server. In this case, the external control device may control multiple AC motors 10 (power converters 20) as the controlled objects.

[0092] [Effect] Next, the operation of the drive system 1 (control device 22) according to this embodiment will be described.

[0093] In this embodiment, the system includes a power converter 20 and a control device 22. Specifically, the power converter 20 is connected to the AC motor 10 through a power path PL through which a switchgear 30 is provided, and drives the AC motor 10 using power from a predetermined power source (for example, a DC power source PS). The control device 22 limits the output voltage of the power converter 20 (inverter circuit 21) to be less than or equal to an upper limit value Vo_lim, and changes the upper limit value Vo_lim according to the rotational speed (i.e., electrical frequency f) of the AC motor 10.

[0094] This allows the output voltage of the power converter 20 to be limited so that, for example, it is not possible to maintain an arc between the electrodes when the switchgear 30 transitions from a closed state to an open state, while still ensuring sufficient voltage to drive the AC motor 10, which increases in proportion to its rotational speed. Furthermore, in the region where the rotational speed of the AC motor 10 is relatively low, the electrical frequency f of the power output from the power converter 20 is relatively low. As a result, when the switchgear 30 transitions from a closed state to an open state and an arc occurs between the electrodes, the duration until the AC current becomes zero and the arc disappears becomes relatively longer, resulting in a relatively larger impact on the switchgear 30. On the other hand, in the region where the rotational speed of the AC motor 10 is relatively high, the electrical frequency f of the power output from the power converter 20 is relatively high. As a result, when the switchgear 30 transitions from a closed state to an open state and an arc occurs between the electrodes, the duration until the AC current becomes zero and the arc disappears becomes relatively shorter, resulting in a relatively smaller impact on the switchgear 30. Therefore, for example, in regions where the rotational speed of the AC motor 10 is relatively low, the output voltage of the power converter 20 can be limited to suppress arc continuation, while in regions where the rotational speed of the AC motor 10 is relatively high, the limitation on the output voltage of the power converter 20 can be relaxed. Thus, it is possible to suppress the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10.

[0095] Furthermore, in this embodiment, the control device 22 may change the upper limit value Vo_lim so that the upper limit value Vo_lim increases in accordance with the increase in the rotational speed of the AC motor 10.

[0096] This allows the output voltage of the power converter 20 to be limited to a level that does not allow the arc between the electrodes to be maintained when the switchgear 30 transitions from a closed state to an open state, while still ensuring sufficient voltage to drive the AC motor 10, which increases in accordance with its rotational speed.

[0097] Furthermore, in this embodiment, the control device 22 may set the rate of increase of the upper limit value Vo_lim for the increase in the rotational speed of the AC motor 10 to be different depending on whether the rotational speed of the AC motor 10 is in a first range or in a second range greater than the first range.

[0098] This improves the degree of control when the opening / closing device 30 transitions from a closed state to an open state.

[0099] Furthermore, in this embodiment, the first range described above is the range between zero and a predetermined value (for example, the value of the rotational speed when the electrical frequency f is a predetermined value f1), and the second range described above may be the range in which the rotational speed of the AC motor 10 is greater than the predetermined value. The control device 22 may set the upper limit value Vo_lim to a constant value when the rotational speed of the AC motor 10 is in the first range, and when the rotational speed of the AC motor 10 is in the second range, the upper limit value Vo_lim may be set to increase in proportion to the increase in the rotational speed of the AC motor 10 in a range greater than the constant value described above.

[0100] This allows the upper limit value Vo_lim of the output voltage of the power converter 20 to be kept constant, for example, in the first range, so as to ensure a voltage for driving the AC motor 10 and to prevent the arc between the electrodes from being maintained when the switchgear 30 transitions from a closed state to an open state. As a result, the processing load on the control device 22 can be reduced while suppressing the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10.

[0101] Furthermore, in this embodiment, the first range described above is the range between zero and a predetermined value (for example, the value of the rotational speed when the electrical frequency f is a predetermined value f2), and the second range may be the range in which the rotational speed of the AC motor 10 is greater than the predetermined value. The control device 22 may set the upper limit value Vo_lim such that when the rotational speed of the AC motor 10 is in the first range, the upper limit value Vo_lim increases in proportion to the increase in the rotational speed of the AC motor 10, and may set the upper limit value Vo_lim to a constant value when the rotational speed of the AC motor 10 is in the second range.

[0102] This allows the upper limit value Vo_lim of the output voltage of the power converter 20 to be kept constant, for example, in the second range, in order to secure the voltage necessary to drive the AC motor 10 and to prevent the arc between the electrodes from being maintained when the switchgear 30 transitions from a closed state to an open state. Furthermore, as described above, in the region where the rotational speed of the AC motor 10 is relatively high, the impact on the switchgear 30 becomes relatively small when the switchgear 30 transitions from a closed state to an open state and an arc is generated between the electrodes. Therefore, for example, in the second range, the upper limit value Vo_lim of the output voltage of the power converter 20 can be kept constant by prioritizing the securing of the voltage necessary to drive the AC motor 10. Thus, the processing load of the control device 22 can be reduced while suppressing the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10.

[0103] Furthermore, in this embodiment, the above-mentioned constant value corresponding to the upper limit Vo_lim when the rotational speed of the AC motor 10 is within the second range may also be the maximum value Vo_max of the output voltage of the power converter 20 (inverter circuit 21).

[0104] This allows prioritizing the securing of voltage for driving the AC motor 10 within the second range, thereby ensuring that the voltage for driving the AC motor 10 is reliably secured.

[0105] Furthermore, in this embodiment, the control device 22 may set the upper limit value Vo_lim to a first value when the rotational speed of the AC motor 10 is in a third range, and set the upper limit value Vo_lim to a second value greater than the first value when the rotational speed of the AC motor 10 is in a fourth range greater than the third range.

[0106] This allows, for example, in the third range, to maintain a constant upper limit Vo_lim of the output voltage of the power converter 20 so as not to maintain an arc between the electrodes when the switchgear 30 transitions from a closed state to an open state. Also, for example, in the fourth range, to maintain a constant upper limit Vo_lim of the output voltage of the power converter 20 so as not to maintain an arc between the electrodes when the switchgear 30 transitions from a closed state to an open state. Furthermore, as described above, in the region where the rotational speed of the AC motor 10 is relatively high, the impact on the switchgear 30 becomes relatively small when the switchgear 30 transitions from a closed state to an open state and an arc is generated between the electrodes. Therefore, for example, in the fourth range, priority can be given to securing the voltage to drive the AC motor 10, and the upper limit Vo_lim of the output voltage of the power converter 20 can be maintained constant. Therefore, it is possible to reduce the processing load on the control device 22 while suppressing the reduction in the lifespan and occurrence of failures of the switchgear 30 between the power converter 20 and the AC motor 10.

[0107] Furthermore, in this embodiment, the third range described above is the range between zero and a predetermined value (for example, the value of the rotational speed when the electrical frequency f is a predetermined value f2), and the second range may be the range in which the rotational speed of the AC motor 10 is greater than the predetermined value. The second value may also be the maximum value Vo_max of the output voltage of the power converter 20 (inverter circuit 21).

[0108] This allows prioritizing the securing of voltage for driving the AC motor 10 within the fourth range, thereby ensuring that the voltage for driving the AC motor 10 is reliably secured.

[0109] Furthermore, in this embodiment, the control device 22 may change the upper limit value Vo_lim according to the rotational speed of the AC motor 10 when the switching device 30 transitions from a closed state to an open state.

[0110] This allows control to be initiated that assumes the switchgear 30 has transitioned from a closed state to an open state, in response to the switchgear 30 transitioning from a closed state to an open state. As a result, the processing load on the control device 22 can be reduced while suppressing the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10.

[0111] Furthermore, in this embodiment, when the switchgear 30 is in the closed state, the control device 22 may set the upper limit value Vo_lim to the maximum value Vo_max of the voltage that the power converter 20 (inverter circuit 21) can output.

[0112] As a result, when the switchgear 30 is in the closed state, there is no need to consider the arc between the electrodes of the switchgear 30, and therefore, a voltage for driving the AC motor 10 can be reliably secured in that state.

[0113] Furthermore, this embodiment includes a power converter 20 and a control device 22. Specifically, the power converter 20 is connected to the AC motor 10 and the switchgear 30 via a power path PL, and drives the AC motor 10 using power from a predetermined power source (for example, a DC power source PS). The control device 22 then limits the output voltage of the power converter 20 (inverter circuit 21) so that when the switchgear 30 transitions from a closed state to an open state, the output voltage of the power converter 20 (inverter circuit 21) becomes smaller than the sum of the maximum voltage required for operation according to the rotational speed of the AC motor 10 (amplitude voltage Vm) and the voltage drop due to the arc generated between the electrodes of the switchgear 30 (arc voltage Va).

[0114] As a result, even if the switchgear 30 transitions from the open state to the closed state and an arc is generated, the rotation state of the AC motor 10 cannot be maintained, and consequently, the arc can be extinguished quickly. Therefore, it is possible to suppress the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10.

[0115] Furthermore, in this embodiment, the control device 22 may be mounted on the power converter 20.

[0116] This allows the control device 22 built into the power converter 20 to complete the operation assuming that the switchgear 30 transitions from a closed state to an open state. Therefore, it is possible to suppress the reduction in the lifespan and failure of the switchgear 30 between the power converter 20 and the AC motor 10 with a simpler configuration.

[0117] Although embodiments have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist described in the claims. [Explanation of symbols]

[0118] 1. Drive System 10 AC motor 20 Power converter 21 Inverter Circuit 22 Control device 23 Current Sensor 30 Switching device 40 Rotation speed sensor 221 Speed ​​regulator 222 Vector Converters 223 Current regulator 224 Voltage Limiting Function 225 Voltage Limiter 226 Vector Inverse Converter 227 PWM signal output section DI freewheel diode PL Power Path PS DC power supply SW Semiconductor Switch

Claims

1. A drive unit is connected to an AC motor and a switchgear via a power path, and drives the AC motor using power from a predetermined power source. The system includes a control device that limits the output voltage of the drive device so as not to exceed an upper limit, and changes the upper limit according to the rotational speed of the AC motor, The aforementioned upper limit is the output voltage value of the drive device that can suppress the continuation of the arc generated between the electrodes of the switchgear when the switchgear transitions from a closed state to an open state while the AC motor is being driven. Drive system.

2. The control device changes the upper limit value such that the upper limit value increases as the rotational speed of the AC motor increases. The drive system according to claim 1.

3. The control device makes the rate of increase of the upper limit value with respect to the increase in the rotational speed of the AC motor different when the rotational speed of the AC motor is in a first range and when it is in a second range greater than the first range. The drive system according to claim 2.

4. The first range is the range in which the rotational speed of the AC motor is between zero and a predetermined value. The second range is the range in which the rotational speed of the AC motor is greater than the predetermined value. The control device sets the upper limit to a constant value when the rotational speed of the AC motor is within the first range, and sets the upper limit to a constant value when the rotational speed of the AC motor is within the second range, such that the upper limit increases in proportion to the increase in the rotational speed of the AC motor, within a range greater than the constant value. The drive system according to claim 3.

5. The first range is the range in which the rotational speed of the AC motor is between zero and a predetermined value. The second range is the range in which the rotational speed of the AC motor is greater than the predetermined value. The control device sets the upper limit value such that, when the rotational speed of the AC motor is within the first range, the upper limit value increases in proportion to the increase in the rotational speed of the AC motor, and sets the upper limit value to a constant value when the rotational speed of the AC motor is within the second range. The drive system according to claim 3.

6. The aforementioned constant value is the maximum output voltage of the drive device. The drive system according to claim 5.

7. The control device sets the upper limit to a first value when the rotational speed of the AC motor is in a third range, and sets the upper limit to a second value that is greater than the first value when the rotational speed of the AC motor is in a fourth range that is greater than the third range. The drive system according to claim 2.

8. The third range is the range in which the rotational speed of the AC motor is between zero and a predetermined value. The fourth range is the range in which the rotational speed of the AC motor is greater than the predetermined value. The second value is the maximum output voltage of the drive device. The drive system according to claim 7.

9. The control device changes the upper limit value according to the rotational speed of the AC motor when the opening / closing device transitions from a closed state to an open state. The drive system according to any one of claims 1 to 8.

10. The control device, when the switching device is in the closed state, sets the upper limit to the maximum voltage that the drive device can output. The drive system according to claim 9.

11. A drive unit is connected to an AC motor and a switchgear via a power path, and drives the AC motor using power from a predetermined power source. The control device includes, when the switchgear transitions from a closed state to an open state, and the output voltage of the drive device exceeds the sum of the maximum voltage required for operation according to the rotational speed of the AC motor and the voltage drop due to the arc generated between the electrodes of the switchgear, the control device limits the output voltage of the drive device to be less than the sum of the above values, thereby suppressing the continuation of the arc. Drive system.

12. The control device is mounted on the drive unit, The drive system according to any one of claims 1 to 11.

13. A control device that controls a drive device that drives an AC motor, which is connected to an AC motor and a switchgear via a power path, and uses power from a predetermined power source to drive the AC motor, The output voltage of the drive device is limited so as not to exceed an upper limit, and the upper limit is changed according to the rotational speed of the AC motor. The aforementioned upper limit is the output voltage value of the drive device that can suppress the continuation of the arc generated between the electrodes of the switchgear when the switchgear transitions from a closed state to an open state while the AC motor is being driven. Control device.

14. A control device that controls a drive device that drives an AC motor, which is connected to an AC motor and a switchgear via a power path, and uses power from a predetermined power source to drive the AC motor, When the switchgear transitions from a closed state to an open state, if the output voltage of the drive unit exceeds the sum of the maximum voltage required for operation according to the rotational speed of the AC motor and the voltage drop due to the arc generated between the electrodes of the switchgear, the output voltage of the drive unit is limited to be less than the sum of the two values, thereby suppressing the continuation of the arc. Control device.

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