JP2023122381A - Driving system and control device - Google Patents

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

The present disclosure relates to an AC motor drive system and the like.

For example, there is known a system in which a driving device such as an inverter device drives an AC motor using power from a predetermined power supply through a power path provided with an opening device between the AC motor (see Patent Document 1). .

WO2009/107233

However, when the switchgear is shifted from the closed state to the open state while the AC motor is being driven by the drive, an arc is generated between the electrodes of the switchgear, and as long as the arc occurs, the drive and the AC A current flows between it and the motor. Therefore, for example, if the duration of the arc is relatively long, the life of the switchgear may be shortened, or the temperature of the switchgear may rise due to the heat generated by the arc, leading to failure of the switchgear.

Therefore, in view of the above problems, it is an object of the present invention to provide a technique capable of suppressing the shortening of the service life and the occurrence of failures of the switching device between the driving device and the AC motor.

To achieve the above objectives, in one embodiment of the present disclosure,
a driving device connected through a power path provided with an AC motor and a switchgear, and for driving the AC motor using power from a predetermined power supply;
a control device that limits the output voltage of the drive device to an upper limit value or less and changes the upper limit value according to the rotation speed of the AC motor;
A drive system is provided.

Also, in other embodiments of the present disclosure,
a driving device connected through a power path provided with an AC motor and a switchgear, and for driving the AC motor using power from a predetermined power source;
When the switchgear shifts from the closed state to the open state, the output voltage of the drive device depends on the maximum voltage required for operation according to the rotational speed of the AC motor and the arc generated between the electrodes of the switchgear. A control device that limits the output voltage of the drive device so that it is smaller than the total value of the voltage drop,
A drive system is provided.

In yet another embodiment of the present disclosure,
A control device that controls a drive device that is connected through a power path provided with an AC motor and a switchgear and that drives the AC motor using power from a predetermined power supply,
limiting the output voltage of the drive device to an upper limit value or less, and changing the upper limit value according to the rotation speed of the AC motor;
A controller is provided.

In yet another embodiment of the present disclosure,
A control device that controls a drive device that is connected through a power path provided with an AC motor and a switchgear and that drives the AC motor using power from a predetermined power supply,
When the switchgear shifts from the closed state to the open state, the output voltage of the drive device depends on the maximum voltage required for operation according to the rotational speed of the AC motor and the arc generated between the electrodes of the switchgear. limiting the output voltage of the driving device so that it is less than the sum of the voltage drop;
A controller is provided.

According to the above-described embodiment, it is possible to suppress the shortening of the service life and the occurrence of failures of the switching device between the driving device and the AC motor.

It is a figure which shows an example of a drive system. It is a functional block diagram which shows an example of a structure of a control apparatus. It is a figure explaining the control method of the alternating current motor which concerns on a comparative example. It is a figure explaining the 1st example of the control method of an alternating current motor. It is a figure explaining the 2nd example of the control method of an alternating current motor. It is a figure explaining the 3rd example of the control method of an alternating current motor. It is a figure explaining the 4th example of the control method of an alternating current motor.

Embodiments will be described below with reference to the drawings.

[Outline of drive system]
An overview of a drive system 1 according to the present embodiment will be described with reference to FIG.

FIG. 1 is a diagram showing an example of a drive system 1. As shown in FIG.

As shown in FIG. 1 , drive system 1 includes AC motor 10 , power conversion device 20 , switchgear 30 , and rotational speed sensor 40 .

The drive system 1 uses the DC power supplied from the DC power supply PS to output drive power for the AC motor 10 from the power conversion device 20 to drive the AC motor 10 .

The AC motor 10 is a target to be driven by the drive system 1 . The AC motor 10 is, for example, a synchronous motor or an induction motor.

A power conversion device 20 (an example of a drive device) converts DC power supplied from a DC power supply PS into drive power for the AC motor 10 and outputs the drive power. Power conversion device 20 includes an inverter circuit 21 , a control device 22 and a current sensor 23 .

The inverter circuit 21 converts the DC power input from the DC power supply PS into three-phase AC power of U-phase, V-phase, and W-phase with a desired voltage and frequency, and supplies it to the AC motor 10 through the power path PL. Output.

Inverter circuit 21 includes a semiconductor switch SW and a freewheeling diode DI. Specifically, three sets of series-connected bodies (switch legs) of two semiconductor switches SW corresponding to upper and lower arms are provided. connected in parallel between the lines. Then, U-phase, V-phase, and W-phase terminals are pulled out from intermediate points of the upper and lower arms of the three sets of switch legs, and are connected to the power path PL connected to the U-phase, V-phase, and W-phase terminals of the AC motor 10. Connected. The freewheeling diode DI is connected in parallel to each semiconductor switch SW such that the forward direction is from the negative line side to the positive line side.

The control device 22 drives and controls the AC motor 10 using the power conversion device 20 . Specifically, the control device 22 outputs a control command to the inverter circuit 21 (semiconductor switch SW) to cause the inverter circuit 21 to output desired drive power, thereby controlling the AC motor 10 .

The functions of the control device 22 are realized by arbitrary hardware or a combination of arbitrary hardware and software. For example, the control device 22 is configured by a computer including a CPU (Central Processing Unit), a memory device, an auxiliary storage device, and an interface device, a drive circuit for driving the gate terminal of the semiconductor switch SW, and the like. The memory device is, for example, an 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, a communication interface for communicating with other devices, and the like. The control device 22 can realize various functions by loading programs installed in the auxiliary storage device into the memory device and executing them on the CPU. Also, the control device 22 can take in and install a program from a recording medium through an external interface, or take in and install a program from another device through a communication interface.

The current sensor 23 detects the output of the inverter circuit 21, that is, the currents of the U-phase, V-phase, and W-phase. The output (detection signal) of the current sensor 23 is taken into the control device 22 .

Note that the current sensor 23 may be configured to detect the current for two phases out of the three phases of the U phase, the V phase, and the W phase. This is because the control device 22 can calculate (estimate) the remaining one-phase current from the detected values of the two-phase currents.

Switchgear 30 is provided on power path PL between power conversion device 20 and AC motor 10 .

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 cut off. The switching device 30 is, for example, an electromagnetic contactor or an electromagnetic switch.

A rotation speed sensor 40 detects the rotation speed of the AC motor 10 . The rotational speed sensor 40 is, for example, an encoder. The output (detection signal) of the rotation speed sensor 40 is input to the power conversion device 20 and taken into the control device 22 .

[Functional configuration of control device]
Next, the functional configuration of the control device 22 will be described with reference to FIG.

FIG. 2 is a functional block diagram showing an example of the functional configuration of the control device 22. As shown in FIG.

As shown in FIG. 2, it includes a speed regulator 221 , a vector converter 222 , a current regulator 223 , a voltage limiting function 224 , a voltage limiter 225 and a vector inverter 226 .

Based on the deviation between the rotational speed command value ω* of the AC motor 10 and the detected value ωdet, the speed regulator 221 issues a control command for the d-axis current and the q-axis current of the AC motor 10 to bring the deviation closer to zero. (hereinafter referred to as "current command value") Id* and Iq* are output. The detected value ωdet is acquired based on the output of the rotational speed sensor 40 . The speed controller 221 is, for example, a PI (Proportional Integral) controller.

For example, when sensorless control is employed, an estimated value ωest of the rotation speed of the AC motor 10 is used instead of the detected value ωdet of the rotation 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 regulator 221 is omitted. For example, if torque control or current control is employed, the speed regulator 221 is omitted. In this case, the current command values Id* and Iq* are generated based on the torque command values in the torque control, or based on the current command values of the U-phase, V-phase, and W-phase in the current control.

The vector converter 222 converts the detected values Iu, Iv, and Iw of the U-phase, V-phase, and W-phase phase currents into They are converted into current detection values Id and Iq and output. The detected values Iu, Iv, and Iw of the U-phase, V-phase, and W-phase phase currents are obtained based on the output of the current sensor 23 .

Based on the deviation between the current command values Id* and Iq* and the current detection values Id and Iq, the current regulator 223 issues a control command for the d-axis voltage and the q-axis voltage of the AC motor 10 to bring the deviation closer to zero. (hereinafter referred to as "voltage command value") Vd* and Vq* are output. Current regulator 223 is, for example, a PI controller.

The voltage limit function 224 uses the detected value ωdet of the rotation speed of the AC motor 10 as an argument to determine the positive limit value VLIMp and the negative limit value of the voltage applied to the AC motor 10, that is, the output voltage of the inverter circuit 21. Output VLIMn.

For example, as will be described later, an upper limit value Vo_lim (>0) is set for the output voltage of the power converter 20 (inverter circuit 21). In this case, the voltage limit function 224 outputs the upper limit value Vo_lim as the positive limit value VLIMp, and outputs a value obtained by inverting the sign of the upper limit value Vo_lim as the negative limit value VLIMn.

Voltage limiter 225 limits and outputs voltage command values Vd* and Vq* between limit value VLIMp and limit value VLIMn. Specifically, when voltage command value Vd* is within the range between limit value VLIMp and limit value VLIMn, voltage limiter 225 outputs voltage command value Vd* as it is. On the other hand, when voltage command value Vd* is greater than VLIMp, voltage limiter 225 corrects voltage command value Vd* to limit value VLIMp and outputs it. Similarly, when voltage command value Vd* is smaller than limit value VLIMn, voltage limiter 225 corrects voltage command value Vd* to limit value VLIMn and outputs it. The same applies to the voltage command value Vq*.

The vector inverter 226 converts the voltage command values Vd* and Vq* input through the voltage limiter 225 into U-phase, V-phase, and W-phase voltage command values Vu, Vv, and Vw.

The PWM signal output unit 227 generates a control command for the inverter circuit 21 , that is, a PWM (Pulse Width Modulation) signal and outputs it 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, respectively. It outputs PWM signals of phase, V-phase, and W-phase. Accordingly, the control device 22 can drive and control the AC motor 10 by outputting the PWM signal to the inverter circuit 21 .

[Control Method for AC Motor According to Comparative Example]
Next, a control method for AC motor 10 according to a comparative example will be described with reference to FIG.

FIG. 3 is a diagram for explaining a control method for the AC motor 10 according to the comparative example.

Note that the rotating speed of the AC motor 10 in a steady state is proportional to the electric frequency f in the case of a synchronous motor. Further, the rotating speed of the AC motor 10 in a steady state is roughly proportional to the electric frequency f, considering that the slip frequency is generally very small in the case of an induction motor. In either case, the constant of proportionality is the number of pole pairs of AC motor 10 . Therefore, the following description is based on the premise that a proportional relationship or an approximate proportional relationship is established between the rotation speed of the AC motor 10 and the electric frequency f.

As shown in FIG. 3, the amplitude EMF of the induced electromotive force of AC motor 10 is proportional to the rotation speed of AC motor 10 .

The terminal voltage of the AC motor 10 is the sum of the vector synthesis of the voltage drop due to the impedance of the coils (windings) caused by the current flowing through the coils (windings) and the induced electromotive force of the AC motor 10 .

The coil impedance is divided into a resistance component independent of the electric frequency f and a reactance component proportional to the electric frequency f. Here, it is generally considered that the reactance component is sufficiently larger than the resistance component except in a region where the rotation speed of the AC motor 10 is extremely low. 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 proportional to the electrical frequency f, that is, proportional to the rotation speed of the AC motor 10 . Therefore, as shown in FIG. 3, the maximum value (amplitude voltage) Vm_s of the terminal voltage of the AC motor 10 in the steady state is the amplitude EMF of the induced electromotive force and the voltage drop proportional to the rotational speed of the AC motor 10. Expressed in the form of addition. 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 approximately proportional to the rotation speed of the AC motor 10 .

The terminal voltage of the AC motor 10 in a transient state of the AC motor 10, that is, in a state in which the current amplitude of the AC motor 10 changes with time, varies depending on the rate of change with respect to the terminal voltage of the AC motor 10 in a steady state. additional voltage is added. Assuming that the rate of change in current amplitude does not depend on the rotational speed of AC motor 10, the addition corresponding to the rate of change in current amplitude can also be regarded as a constant value that does not depend on the rotational speed of AC motor 10. Therefore, as shown in FIG. 3, the maximum value (amplitude voltage) Vm_t of the terminal voltage (amplitude voltage) of the AC motor 10 in a transient state (hereinafter simply referred to as "transient state") assuming the occurrence of the expected maximum value of current amplitude is It is expressed in the form of 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 is expressed in a form that increases approximately linearly as the rotation speed of the AC motor 10 increases.

As shown in FIG. 3, in the comparative example, the upper limit value Vo_lim of the output voltage of the power converter 20 (inverter circuit 21) is set to A maximum voltage Vo_max is set. That is, the output voltage of power conversion device 20 is substantially equal to the unrestricted state.

Here, consider a case where the opening/closing device 30 shifts from the closed state to the open state during operation of the AC motor 10 for some reason.

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

The power conversion device 20 (inverter circuit 21) attempts to maintain the current corresponding to the current command values Id* and Iq* under the control of the control device 22 as described above. Therefore, as shown in FIG. 3, the power conversion device 20 attempts to increase the output voltage by the arc voltage Va. As a result, since the output voltage of the inverter circuit 21 is not substantially limited, the inverter circuit 21 can increase the output voltage by the amount of the arc voltage Va, and the arc continues. put away. For example, in FIG. 3, when the rotation speed of the AC motor 10 is a predetermined value ωa (the electric frequency f is a predetermined value fa), the switching device 30 is shifted to the open state, and the output voltage of the power conversion device 20 is the arc voltage Va reaches the predetermined value Vxa by increasing by the amount of , and this state is continued. Therefore, the continuation of the arc may shorten the life of the switchgear 30, or the temperature of the switchgear 30 may rise due to heat generation due to the continuation of the arc, leading to failure.

Also, although the arc disappears at the zero crossing of the alternating current, when the electric frequency f is relatively small, that is, when the rotation speed of the alternating current motor 10 is relatively low, the time until the zero crossing of the alternating current is relatively can be long. As a result, the duration of the arc becomes relatively long, and the arc shortens the life of the switchgear 30, and the heat generated by the arc raises the temperature of the switchgear 30, increasing the possibility of failure.

As described above, in the comparative example, since the output voltage of the inverter circuit 21 is not substantially limited, the arc generated when the switchgear 30 shifts from the closed state to the open state continues. It may lead to shortened life and failure.

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

FIG. 4 is a diagram for explaining a first example of a control method for the AC motor 10. As shown in FIG.

As shown in FIG. 4, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is the maximum value of the terminal voltage of the AC motor 10 in the transient state in the entire range of rotation speeds of the AC motor 10 equal to or higher than zero. It is set to be equal to or greater than Vm_t. The entire range of the rotational speed of the AC motor 10 means a range that is equal to or greater than zero and equal to or less than a predetermined upper limit assumed as the rotational speed of the AC motor 10 . As a result, the operation of the AC motor 10 in a transient state can be guaranteed. For example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to be somewhat larger than the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state. As a result, the operation of the AC motor 10 in the transient state can be ensured more reliably.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power converter 20 is lower than the minimum value Va_min of the output voltage of the power converter 20 required for arc continuation in the entire range of the rotation speed of the AC motor 10 equal to or higher than zero. set to be small. The minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation is the power conversion device required to continue the arc when the switching device 30 transitions from the closed state to the open state in the transient state of the AC motor 10. means the minimum of 20 output voltages. That is, the minimum value Va_min of the output voltage of the power conversion device 20 necessary for arc continuation corresponds to the sum of the maximum value Vm_t of the terminal voltage of the AC motor 10 and the arc voltage Va in the transient state. As a result, when the switching device 30 shifts from the closed state to the open state, the output voltage of the power conversion device 20 is raised to the minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation, and the current due to the arc voltage Va cannot make up for the loss. As a result, the current can reach zero, the arc can be extinguished, and the continuation of the arc can be suppressed.

The minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation when the switching device 30 shifts from the closed state to the open state in the transient state of the AC motor 10 is the terminal voltage of the AC motor 10 in the transient state. It increases linearly with an increase in the rotation speed of the AC motor 10 with the same slope as the maximum value Vm_t. Therefore, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to change in accordance with the change of the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state according to the rotation speed (electrical frequency f). . That is, the upper limit value Vo_lim of the output voltage of the power conversion device 20 has the same slope (rate of change) as the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state, and the rotational speed (electrical frequency f) of the AC motor 10 It is set so that it rises linearly with respect to the rise of . As a result, it is possible to ensure the operation of the AC motor 10 in the transient state in accordance with the change in the rotation speed of the AC motor 10, and to suppress the continuation of the arc when the switching device 30 shifts from the closed state to the open state. .

The control device 22 sets the upper limit value Vo_lim of the output voltage of the power conversion device 20 based on, for example, the detected value ωdet of the rotation speed of the AC motor 10 . Further, the control device 22 may set the upper limit value Vo_lim of the output voltage of the power conversion device 20 based on, for example, the estimated value ωest of the rotational speed of the AC motor 10 and the command value ω*. The same may be applied to second to fourth examples described later.

Further, when the AC motor 10 is an induction motor or a wound type synchronous motor, etc., since the excitation magnetic flux and the field magnetic flux are adjustable, the amplitude EMF of the induced electromotive force of the AC motor 10 generated by the excitation magnetic flux and the field magnetic flux The proportional coefficient changes with respect to the change in rotational speed. As a result, the proportional coefficient of the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state to the change in the rotation speed of the AC motor 10 also changes. In this case, the control device 22 adjusts the output of the power conversion device 20 so that the proportional coefficient with respect to the change in the rotation speed of the AC motor 10 changes according to the set values of the excitation magnetic flux and the field magnetic flux that are adjusted by itself, for example. A voltage upper limit value Vo_lim is set. Further, the proportional coefficient of the upper limit value Vo_lim of the output voltage of the power conversion device 20 with respect to the change in the rotation speed of the AC motor 10 is set in advance as a fixed value in consideration of the range of change in the amplitude EMF of the induced electromotive force. good too. The same may be applied to second and third examples described below.

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

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

FIG. 5 is a diagram for explaining a second example of the control method for the AC motor 10. As shown in FIG.

As shown in FIG. 5, in this example, as in the first example described above, in the entire range of the rotation speed of the AC motor 10 above zero, the terminal voltage of the AC motor 10 in the transient state is set to be equal to or higher than the maximum value Vm_t of the terminal voltage. is set to As a result, the operation of the AC motor 10 in a transient state can be guaranteed.

Further, in this example, as in the first example described above, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is the power conversion device 20 required for arc continuation in the entire range of the rotation speed of the AC motor 10 equal to or higher than zero. is set to be smaller than the minimum value Va_min of the output voltage of . As a result, it is possible to suppress the continuation of the arc that occurs when the switchgear 30 is switched from the closed state to the open state.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to a constant predetermined It is set to the value V1. As a result, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is kept constant in a region where the rotation speed of the AC motor 10 is relatively low, and the processing load of the control device 22 can be reduced.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is within the range where the rotation speed of the AC motor 10 is greater than the predetermined value ω1, that is, the range where the electrical frequency f is greater than the predetermined value f1. is set to linearly increase with an increase in rotational speed (electrical frequency f). Specifically, in this range, as in the case of the first example described above, the upper limit value Vo_lim of the output voltage of the power conversion device 20 has the same slope as the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state. It increases linearly as the rotation speed of the electric motor 10 increases. As a result, in a range in which the rotation speed of the AC motor 10 is relatively high, it is possible to open the switching device 30 from the closed state while ensuring the operation of the AC motor 10 in the transient state in accordance with the change in the rotation speed of the AC motor 10 . Arc continuation at the time of transition to the state can be suppressed.

Thus, in this example, as in the first example described above, it is possible to suppress the continuation of the arc when the switchgear 30 shifts from the closed state to the open state while ensuring the desired operation of the AC motor 10. can. Further, in this example, the processing load of the control device 22 can be reduced in a region where the rotational speed of the AC motor 10 is relatively low.

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

FIG. 6 is a diagram for explaining a third example of a control method for AC motor 10. In FIG.

As shown in FIG. 6, in this example, the upper limit value Vo_lim of the output voltage of the power converter 20 is set to It is set to be equal to or greater than the maximum value Vm_t of the terminal voltage of the AC motor 10 . As a result, the operation of the AC motor 10 in a transient state can be guaranteed.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is the output voltage of the power conversion device 20 necessary for arc continuation in the range where the rotational speed of the AC motor 10 is equal to or higher than zero and equal to or lower than the predetermined value ω2. It is set to be smaller than the minimum value Va_min. The range in which the rotation speed of the AC motor 10 is greater than or equal to zero and less than or equal to the predetermined value ω2 corresponds to the range in which the electrical frequency f is greater than or equal to zero and less than or equal to the predetermined value f2. This suppresses the continuation of the arc that occurs when the switching device 30 shifts from the closed state to the open state in a region where the rotation speed of the AC motor 10 is relatively low (that is, a region where the electrical frequency f is relatively low). can do.

Specifically, as shown in FIG. 6, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set within a range where the rotational speed of the AC motor 10 is equal to or higher than zero and equal to or lower than a predetermined value ω2, and With the same slope (change rate) as the maximum value Vm_t of the terminal voltage and the minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation, a linear function with respect to the increase in the rotation speed (electric frequency f) of the AC motor 10 may be set to increase exponentially.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is the minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation within a range where the rotational speed of the AC motor 10 is greater than the predetermined value ω2. is set regardless of When the electric frequency f becomes relatively large, the time from the transition from the closed state to the open state of the switchgear 30 to the zero cross becomes relatively short, and the arc extinguishes at a relatively early timing. This is because the effect on life and failure is relatively small. For example, the predetermined value f2 and the predetermined value ω2 are set by verifying the duration of the arc that does not affect the service life reduction and failure of the switchgear 30 through computer simulations and experiments using actual machines.

Specifically, as shown in FIG. 6, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to a constant value within a range where the rotational speed of the AC motor 10 is greater than the predetermined value ω2. As a result, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is kept constant in a region where the rotation speed of the AC motor 10 is relatively high, and the processing load of the control device 22 can be reduced. For example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to the maximum value Vo_max of the voltage that the power conversion device 20 can output within a range where the rotation speed of the AC motor 10 is greater than the predetermined value ω2. As a result, the desired operation of the AC motor 10 can be ensured more reliably.

Thus, in this example, as in the above-described first example, while ensuring the desired operation of the AC motor 10, the continuation of the arc when the switchgear 30 transitions from the closed state to the open state is suppressed. can be done. In addition, in this example, the processing load of the control device 22 can be reduced and the desired operation of the AC motor 10 can be ensured more reliably in a region where the rotation speed of the AC motor 10 is relatively high.

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

FIG. 7 is a diagram for explaining a fourth example of the control method for the AC motor 10. In FIG.

As shown in FIG. 7, in the same manner as the above-described first example and the like, the voltage is set to be equal to or higher than the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state in the entire range of the rotation speed of the AC motor 10 above zero. be. As a result, the operation of the AC motor 10 in a transient state can be guaranteed.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set within the range where the rotational speed of the AC motor 10 is equal to or higher than zero and equal to or lower than the predetermined value ω2, as in the third example described above. It is set to be smaller than the minimum value Va_min of the output voltage of the power conversion device 20 . This suppresses the continuation of the arc that occurs when the switching device 30 shifts from the closed state to the open state in a region where the rotation speed of the AC motor 10 is relatively low (that is, a region where the electrical frequency f is relatively low). can do.

Specifically, as shown in FIG. 7, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to a constant predetermined value V2. As a result, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is kept constant in a region where the rotation speed of the AC motor 10 is relatively low, and the processing load of the control device 22 can be reduced.

Further, in this example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set within the range where the rotation speed of the AC motor 10 is greater than the predetermined value ω2, as in the third example described above, and the power conversion device necessary for arc continuation 20 is set regardless of the minimum value Va_min of the output voltage.

As shown in FIG. 7, specifically, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is a constant value within the range where the rotation speed of the AC motor 10 is greater than the predetermined value ω2, as in the third example described above. set to the value As a result, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is kept constant in a region where the rotation speed of the AC motor 10 is relatively high, and the processing load of the control device 22 can be reduced. For example, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is the maximum value of the voltage that the power conversion device 20 can output in the range where the rotation speed of the AC motor 10 is greater than the predetermined value ω2, as in the third example described above. It is set to Vo_max. As a result, the desired operation of the AC motor 10 can be ensured more reliably.

Thus, in this example, as in the above-described first example, while ensuring the desired operation of the AC motor 10, the continuation of the arc when the switchgear 30 transitions from the closed state to the open state is suppressed. can be done. Further, in the present example, as in the third example described above, the desired operation of the AC motor 10 can be ensured more reliably in the region where the rotational speed of the AC motor 10 is relatively high. Moreover, in this example, the processing load of the control device 22 can be reduced in the entire rotation speed range of the AC motor 10 .

[Other embodiments]
Modifications and changes may be added to the above-described embodiments as appropriate.

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 conversion device 20 changes stepwise instead of linearly in response to changes in the rotational speed of the AC motor 10. may be set as Also, in the region where the rotation speed of the AC motor 10 is greater than the predetermined value ω1 in the second example of the control method described above and in the region where the rotation speed of the AC motor 10 is equal to or less than the predetermined value ω2 in the third example of the control method described above. may be similar.

Further, for example, in the above-described second example of the control method and its modification, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to It may be set to increase as the rotational speed increases. In this case, the rate of increase of the upper limit value Vo_lim of the output voltage of the power conversion device 20 with respect to the rotational speed of the AC motor 10 is set to be smaller or larger than when the rotational speed of the AC motor 10 is greater than the predetermined value ω1. good. Similarly, in the above-described third example of the control method and its modification, the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set to It may be set to increase as the speed increases. In this case, the rate of increase of the upper limit value Vo_lim of the output voltage of the power conversion device 20 with respect to the rotation speed of the AC motor 10 is set to be smaller or larger than when the rotation speed of the AC motor 10 is in the range of the predetermined value ω2 or less. good.

Further, for example, in the second example of the above-described control method and its modification, the entire range of the rotation speed of the AC motor 10 is divided into two ranges in which the upper limit value Vo_lim of the output voltage of the power conversion device 20 is set differently. However, it may be divided into three or more. The same may be applied to the above-described third example, fourth example, and modifications thereof.

Further, for example, in the above-described third example of the control method and its modification, in a region where the rotation speed of the AC motor 10 is greater than the predetermined value ω2, even if the upper limit value Vo_lim of the output voltage of the power conversion device 20 is not set, good. Further, the same may be applied to the region where the rotation speed of the AC motor 10 is greater than the predetermined value ω2 in the fourth example of the control method described above.

Further, for example, in the above-described embodiment and its modification, the control device 22 may change the method of setting the upper limit value Vo_lim of the output voltage of the power conversion device 20 according to the open/closed state of the switchgear 30 . In this case, the open/closed state of the switchgear 30 can be determined based on, for example, an auxiliary contact signal of the switchgear 30 or a signal input in conjunction with the operating portion 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 conversion device 20 to the maximum value Vo_max of the voltage that the power conversion device 20 can output. Further, the control device 22 does not have to set the upper limit value Vo_lim of the output voltage of the power conversion device 20 when the switching device 30 is in the closed state. On the other hand, when the switching device 30 shifts from the closed state to the open state, the control device 22 sets the upper limit of the output voltage of the power conversion device 20 as in the first to fourth examples of the above-described control method and the modification thereof. A value Vo_lim may be set. That is, when the switching device 30 shifts from the closed state to the open state, the control device 22 sets the upper limit value Vo_lim of the output voltage of the power conversion device 20 to be equal to or higher than the maximum value Vm_t of the terminal voltage of the AC motor 10 in the transient state. , and may be set to a range smaller than the minimum value Va_min of the output voltage of the power conversion device 20 required for arc continuation. As a result, while suppressing the processing load of the control device 22 in the closed state of the switchgear 30, it is possible to suppress the continuation of the arc that occurs when the switchgear 30 shifts from the closed state to the open state.

Further, for example, in the above-described embodiments and modifications thereof, the power conversion device 20 uses the R-phase, S-phase, and T-phase three-phase AC power may be used to generate and output drive power for the AC motor 10 . In this case, for example, the power conversion device 20 includes, in addition to the inverter circuit, a rectifier circuit that converts the power of the AC power supply to DC, and a smoothing circuit that smoothes the output of the rectifier circuit and outputs it to the inverter circuit 21 . Further, in this case, the power conversion device 20 is a matrix converter capable of directly converting three-phase AC power of R-phase, S-phase, and T-phase into three-phase AC power of U-phase, V-phase, and W-phase. may be

Also, for example, in the above-described embodiments and modifications, some or all of the functions of the control device 22 may be transferred to a control device external to the power conversion device 20 . Specifically, the function of setting the upper limit value Vo_lim of the output voltage of the power conversion device 20 may be transferred to a control device external to the power conversion device 20 . In this case, the external control device may be installed in the same building as the installation location of the AC motor 10 to be controlled (power conversion device 20) or in a building on the same site, or the AC motor 10 to be controlled and the power conversion device It may be installed at a location remote from the installation location of the device 20 . In the former case, the external control device is, for example, a PLC (Programmable Logic Controller), an edge controller, an edge server, or the like. In the latter case, the external control device is, for example, an on-premises server, a cloud server, or the like. Further, in this case, the external control device may control a plurality of AC motors 10 (power converters 20) as objects to be controlled.

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

In this embodiment, a power conversion device 20 and a control device 22 are provided. Specifically, the power conversion device 20 is connected through a power path PL provided with the AC motor 10 and the switching device 30, and drives the AC motor 10 using power from a predetermined power supply (eg, DC power supply PS). do. Then, the control device 22 limits the output voltage of the power conversion device 20 (inverter circuit 21) to be equal to or lower than the upper limit value Vo_lim, and adjusts the upper limit value according to the rotational speed of the AC motor 10 (that is, the electric frequency f). Vary the value Vo_lim.

As a result, for example, while ensuring the voltage for driving the AC motor 10 that increases according to the rotation speed, the voltage is such that the arc between the electrodes cannot be maintained when the switching device 30 shifts from the closed state to the open state. The output voltage of the power conversion device 20 can be limited so that Also, in a region where the rotation speed of the AC motor 10 is relatively low, the electrical frequency f of the power output from the power conversion device 20 is relatively low. As a result, when the switching device 30 shifts from the closed state to the open state and an arc is generated between the electrodes, the duration time until the alternating current becomes zero and the arc is extinguished becomes relatively long. will have a relatively large impact. On the other hand, in a region where the rotation speed of the AC motor 10 is relatively high, the electrical frequency f of the power output from the power conversion device 20 is relatively high. As a result, when the switching device 30 shifts from the closed state to the open state and an arc is generated between the electrodes, the duration time until the alternating current becomes zero and the arc is extinguished becomes relatively short. is relatively small. Therefore, for example, in a region where the rotation speed of the AC motor 10 is relatively low, the output voltage of the power conversion device 20 is restricted to a low level to suppress arc continuation, while in a region where the rotation speed of the AC motor 10 is relatively high, , the restriction on the output voltage of the power converter 20 can be relaxed. Therefore, it is possible to suppress the shortening of the service life and the occurrence of failure of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Further, in the present embodiment, the control device 22 may change the upper limit value Vo_lim so that the upper limit value Vo_lim increases as the rotational speed of the AC motor 10 increases.

As a result, while securing the voltage for driving the AC motor 10 that increases according to the rotation speed, the voltage becomes such that the arc between the electrodes cannot be maintained when the switchgear 30 shifts from the closed state to the open state. Thus, the output voltage of the power conversion device 20 can be limited.

Further, in the present embodiment, the control device 22 determines whether the rotation speed of the AC motor 10 is in the first range or in the second range larger than the first range. The rate of increase of the upper limit value Vo_lim with respect to the increase of may be varied.

As a result, it is possible to improve the degree of freedom of control assuming that the opening/closing device 30 shifts from the closed state to the open state.

In the present embodiment, the above-described first range is a range between the rotational speed of the AC motor 10 being zero and a predetermined value (for example, the rotational speed value when the electric frequency f is a predetermined value f1). Yes, the above-described second range may be a range in which the rotation speed of AC motor 10 is greater than a predetermined value. Then, the control device 22 sets the upper limit value Vo_lim to a constant value when the rotation speed of the AC motor 10 is in the first range, and sets the upper limit value Vo_lim to a constant value when the rotation speed of the AC motor 10 is in the second range. The upper limit value Vo_lim may be set such that it increases as the rotation speed of the AC motor 10 increases within a range where Vo_lim is greater than the above-mentioned constant value.

As a result, for example, in the first range, the voltage for driving the AC motor 10 is secured and the arc between the electrodes cannot be maintained when the switchgear 30 shifts from the closed state to the open state. The upper limit value Vo_lim of the output voltage of the power conversion device 20 can be kept constant. Therefore, it is possible to reduce the processing load of the control device 22 while suppressing the shortening of the life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Further, in the present embodiment, the above-described first range is a range between the rotation speed of the AC motor 10 being zero and a predetermined value (for example, the rotation speed value when the electric frequency f is a predetermined value f2). Yes, and the second range may be a range in which the rotation speed of AC motor 10 is greater than a predetermined value. Then, when the rotation speed of AC motor 10 is in the first range, control device 22 sets upper limit value Vo_lim such that upper limit value Vo_lim increases as the rotation speed of AC motor 10 increases. , the upper limit value Vo_lim may be set to a constant value when the rotation speed of the AC motor 10 is in the second range.

As a result, for example, in the second range, the voltage for driving the AC motor 10 is ensured and the arc between the electrodes cannot be maintained when the switching device 30 shifts from the closed state to the open state. The upper limit value Vo_lim of the output voltage of the power conversion device 20 can be kept constant. Further, as described above, in a region where the rotation speed of the AC motor 10 is relatively high, when the switching device 30 shifts from the closed state to the open state and an arc is generated between the electrodes, the effect on the switching device 30 is relatively high. significantly smaller. Therefore, for example, in the second range, the upper limit value Vo_lim of the output voltage of the power conversion device 20 can be kept constant by giving priority to securing the voltage for driving the AC motor 10 . Therefore, it is possible to reduce the processing load of the control device 22 while suppressing the decrease in life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Further, in the present embodiment, the above constant value corresponding to the upper limit value Vo_lim when the rotation speed of the AC motor 10 is in the second range is the voltage that can be output from the power conversion device 20 (inverter circuit 21). It may be the maximum value Vo_max.

Thus, in the second range, priority is given to ensuring the voltage for driving AC motor 10, and the voltage for driving AC motor 10 can be reliably ensured.

Further, in the present embodiment, when the rotation speed of the AC motor 10 is in the third range, the control device 22 sets the upper limit value Vo_lim to the first value, and the rotation speed of the AC motor 10 is in the third range. If in a fourth larger range, the upper limit value Vo_lim may be set to a second value that is greater than the first value.

As a result, for example, in the third range, the voltage for driving the AC motor 10 is ensured and the arc between the electrodes cannot be maintained when the switchgear 30 shifts from the closed state to the open state. The upper limit value Vo_lim of the output voltage of the power conversion device 20 can be kept constant. Further, for example, in the fourth range, the electric power is set so that the voltage for driving the AC motor 10 is ensured and the arc between the electrodes cannot be maintained when the switchgear 30 shifts from the closed state to the open state. The upper limit value Vo_lim of the output voltage of the converter 20 can be kept constant. Further, as described above, in a region where the rotation speed of the AC motor 10 is relatively high, when the switching device 30 shifts from the closed state to the open state and an arc is generated between the electrodes, the effect on the switching device 30 is relatively high. significantly smaller. Therefore, for example, in the fourth range, the upper limit value Vo_lim of the output voltage of the power conversion device 20 can be kept constant by giving priority to securing the voltage for driving the AC motor 10 . Therefore, it is possible to reduce the processing load of the control device 22 while suppressing the decrease in life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Further, in the present embodiment, the above-described third range is a range between the rotation speed of the AC motor 10 being zero and a predetermined value (for example, the rotation speed value when the electric frequency f is a predetermined value f2). Yes, and the second range may be a range in which the rotation speed of AC motor 10 is greater than a predetermined value. The second value may be the maximum value Vo_max of the voltage that can be output from the power converter 20 (inverter circuit 21).

Thus, in the fourth range, it is possible to ensure the voltage for driving AC motor 10 with priority given to securing the voltage for driving AC motor 10 .

Further, in the present embodiment, the control device 22 may change the upper limit value Vo_lim according to the rotation speed of the AC motor 10 when the opening/closing device 30 shifts from the closed state to the open state.

As a result, it is possible to start the control assuming that the switchgear 30 shifts from the closed state to the open state in a form corresponding to the shift of the switchgear 30 from the closed state to the open state. Therefore, it is possible to reduce the processing load of the control device 22 while suppressing the shortening of the life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Further, in the present embodiment, the control device 22 may set the upper limit value Vo_lim to the maximum value Vo_max of the voltage that the power conversion device 20 (inverter circuit 21) can output when the switching device 30 is in the closed state. .

As a result, when the switchgear 30 is in the closed state, it is not necessary to consider the arc between the electrodes of the switchgear 30, so that the voltage for driving the AC motor 10 can be reliably secured in that state. can be done.

Moreover, in this embodiment, the power conversion device 20 and the control device 22 are provided. Specifically, the power conversion device 20 is connected through a power path PL provided with the AC motor 10 and the switching device 30, and drives the AC motor 10 using power from a predetermined power supply (eg, DC power supply PS). do. Then, when the switchgear 30 shifts from the closed state to the open state, the control device 22 causes the output voltage of the power conversion device 20 (inverter circuit 21) to increase to the maximum voltage required for operation according to the rotation speed of the AC motor 10. The output voltage of the power conversion device 20 is limited so as to be smaller than the total value of the value (amplitude voltage Vm) and the voltage drop (arc voltage Va) due to the arc generated between the electrodes of the switchgear 30 .

As a result, even if the switching device 30 shifts from the open state to the closed state and an arc is generated, the rotating state of the AC motor 10 cannot be maintained, and as a result, the arc can be quickly extinguished. Therefore, it is possible to suppress the shortening of the service life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Also, in the present embodiment, the control device 22 may be mounted on the power conversion device 20 .

As a result, the control device 22 incorporated in the power conversion device 20 can complete the operation in the power conversion device 20 assuming that the switchgear 30 shifts from the closed state to the open state. Therefore, with a simpler configuration, it is possible to suppress the decrease in life and the occurrence of failures of the switching device 30 between the power conversion device 20 and the AC motor 10 .

Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the claims.

1 Drive system 10 AC motor 20 Power conversion device 21 Inverter circuit 22 Control device 23 Current sensor 30 Switchgear 40 Rotational speed sensor 221 Speed controller 222 Vector converter 223 Current controller 224 Voltage limiting function 225 Voltage limiter 226 Vector inverter 227 PWM signal output unit DI Freewheeling diode PL Power path PS DC power supply SW Semiconductor switch

Claims (14)

a driving device connected through a power path provided with an AC motor and a switchgear, and for driving the AC motor using power from a predetermined power supply;
a control device that limits the output voltage of the drive device to an upper limit value or less and changes the upper limit value according to the rotation speed of the AC motor;
drive system. The control device changes the upper limit value so that the upper limit value increases as the rotation speed of the AC motor increases.
A drive system according to claim 1 . The control device controls the upper limit value for increasing the rotation speed of the AC motor when the rotation speed of the AC motor is in a first range and when it is in a second range larger than the first range. different rate of rise of
3. A drive system according to claim 2. the first range is a range between the rotation speed of the AC motor and a predetermined value;
the second range is a range in which the rotation speed of the AC motor is greater than the predetermined value;
The control device sets the upper limit to a constant value when the rotation speed of the AC motor is in the first range, and sets the upper limit when the rotation speed of the AC motor is in the second range. setting the upper limit value so as to increase as the rotational speed of the AC motor increases within a range where the value is greater than the constant value;
4. A drive system according to claim 3. the first range is a range between the rotation speed of the AC motor and a predetermined value;
the second range is a range in which the rotation speed of the AC motor is greater than the predetermined value;
The control device sets the upper limit value such that, when the rotation speed of the AC motor is in the first range, the upper limit value increases as the rotation speed of the AC motor increases; setting the upper limit to a constant value when the rotation speed of the AC motor is in the second range;
4. A drive system according to claim 3. The constant value is the maximum value of the voltage that can be output from the driving device,
6. A drive system according to claim 5. The control device sets the upper limit value to a first value when the rotational speed of the AC motor is in a third range, and sets the rotational speed of the AC motor to a fourth range greater than the third range. setting the upper limit to a second value greater than the first value, if
3. A drive system according to claim 2. the third range is a range between the rotation speed of the AC motor and a predetermined value;
the fourth range is a range in which the rotation speed of the AC motor is greater than the predetermined value;
wherein the second value is the maximum value of voltage that can be output by the driving device;
8. A drive system as claimed in claim 7. The control device changes the upper limit value according to the rotation speed of the AC motor when the opening/closing device shifts from the closed state to the open state.
9. Drive system according to any one of the preceding claims. The control device sets the upper limit value to the maximum value of voltage that can be output by the drive device when the switching device is in a closed state.
10. Drive system according to claim 9. a driving device connected through a power path provided with an AC motor and a switchgear, and for driving the AC motor using power from a predetermined power supply;
When the switchgear shifts from the closed state to the open state, the output voltage of the drive device depends on the maximum voltage required for operation according to the rotational speed of the AC motor and the arc generated between the electrodes of the switchgear. A control device that limits the output voltage of the drive device so that it is smaller than the total value of the voltage drop,
drive system. The control device is mounted on the drive device,
12. Drive system according to any one of the preceding claims. A control device that controls a drive device that is connected through a power path provided with an AC motor and a switchgear and that drives the AC motor using power from a predetermined power supply,
limiting the output voltage of the drive device to an upper limit value or less, and changing the upper limit value according to the rotation speed of the AC motor;
Control device. A control device that controls a drive device that is connected through a power path provided with an AC motor and a switchgear and that drives the AC motor using power from a predetermined power supply,
When the switchgear shifts from the closed state to the open state, the output voltage of the drive device depends on the maximum voltage required for operation according to the rotational speed of the AC motor and the arc generated between the electrodes of the switchgear. limiting the output voltage of the driving device so that it is less than the sum of the voltage drop;
Control device.

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