JP2020127340A - Motor control system - Google Patents

Abstract

To prevent the whole system from stopping due to overload trip of an inverter device by a starting current of a motor when a stopping motor is additionally started with one or a plurality of motors having been operated.SOLUTION: When a stopping motor 9_K is additionally started with one or a plurality of motors having been operated, an operation frequency of an inverter device 3 is first lowered. After a difference between a rated current value of the inverter device 3 and an actual load current value of the inverter device 3 reaches at least a starting current value generated when a stopping motor 9_K is started, the stopping motor 9_K is additionally started.SELECTED DRAWING: Figure 1

Description

The present invention relates to a motor control system that drives a plurality of motors with a single inverter device.

For example, the patent documents listed below disclose systems in which one inverter device drives a plurality of electric motors. In such a system, a stopped electric motor may be additionally started in a situation where some electric motors are already in operation. A problem in such a case is an overload trip of the inverter device due to the starting current of the electric motor. When starting the electric motor, a starting current having a magnitude several times larger than the rated current of the electric motor is generated. When this starting current is added to the total current value of the motor that is already operating, the load current value flowing in the inverter device may exceed the rated current of the inverter device. In this case, the overload protection function of the inverter device may operate to trip the inverter device, and the entire system may stop.

Regarding the above-mentioned problem, for example, Patent Document 1 discloses a conventional technique of monitoring a current flowing through an inverter device (motor driver) when an electric motor is additionally activated and reducing a frequency output to the electric motor when the electric current exceeds a threshold value. Has been done. Further, in Patent Document 2, at the time of a momentary power failure restart of a group operating electric motor, a detected value of a current flowing through an inverter device is compared with a current limit level, and the current is limited when the detected current value exceeds the current limit level. At the same time, a conventional technique for reducing the output frequency of the inverter device is disclosed.

However, since the above-mentioned conventional technique is a posterior measure after the current flowing through the inverter device exceeds the threshold value, it cannot always be said that the overload trip of the inverter device can be prevented in consideration of the response delay of the system.

JP, 2002-101694, A JP, 10-112996, A JP 2000-228898 A

The present invention has been made in view of the above-described problems, and in the case of additionally starting a stopped motor in a state where one or a plurality of electric motors are already operating, an inverter device according to a starting current of the electric motor is provided. An object of the present invention is to provide an electric motor control system capable of preventing the entire system from stopping due to an overload trip.

In order to achieve the above object, the electric motor control system according to the present invention is an electric motor control system that drives a plurality of electric motors with one inverter device, and in a state where one or a plurality of electric motors are already operating. When the stopped motor is additionally started, the operating frequency of the inverter device is lowered, and the difference between the rated current value of the inverter device and the actual load current value of the inverter device occurs when the stopped motor is started. The feature is that the motor that is stopped is additionally started after the current exceeds the starting current value.

When the additional start of the stopped electric motor is performed, the operating frequency of the inverter device may be increased to the frequency before the additional start is performed after a predetermined start completion time has elapsed from the execution of the additional start. Alternatively, after the change rate of the actual load current value of the inverter device falls below a predetermined allowable current change rate, the operating frequency of the inverter device may be increased to the frequency before the additional start. However, if the predetermined start completion time has elapsed from the execution of additional startup before the rate of change of the actual load current value of the inverter device falls below the allowable current change rate, the additionally activated motor is restarted. After stopping, the operating frequency of the inverter device may be increased to the frequency before the additional startup is performed.

According to the electric motor control system of the present invention, the operating frequency of the inverter device is lowered prior to additionally starting the stopped motor, and the difference between the rated current value of the inverter device and the actual load current value of the inverter device is: Since the stopped motor is additionally started after the current exceeds the starting current value generated when the stopped motor is started, the load current value of the inverter device will exceed the rated current value due to the starting current when the motor is additionally started. Overrun is suppressed. Therefore, according to the electric motor control system of the present invention, it is possible to prevent the entire system from being stopped due to the overload trip of the inverter device due to the starting current of the electric motor.

It is a figure which shows the structure of the electric motor control system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the control flow of the additional starting control which concerns on the 1st Embodiment of this invention. It is an operation explanatory view explaining operation of an electric motor control system concerning a 1st embodiment of the present invention. It is an operation explanatory view explaining operation of a comparative example. It is a flowchart which shows the control flow of the additional starting control which concerns on the 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings. However, in the following embodiments, when the number of each element, the number, the amount, the range, or the like is referred to, the reference is made unless otherwise specified or in principle specified by the number. The invention is not limited to a number. Further, the structures and steps described in the embodiments below are not necessarily essential to the present invention, unless otherwise specified or clearly specified in principle.

1. First Embodiment FIG. 1 is a diagram showing a configuration of an electric motor control system according to a first embodiment of the present invention. The electric motor control system according to the present embodiment is a system that controls the operation of a plurality of (here, N) electric motors (motors) 9 with one electric power conversion device 3. The electric motor control system according to the present embodiment frequency-converts the alternating-current power received from the commercial three-phase alternating-current power supply 1 by the power converter 3 and outputs the frequency-converted alternating-current power from the power converter 3 to the electric motor 9. Thus, the electric motor 9 is driven at a variable speed. In FIG. 1, for example, 9_1 means the first electric motor 9, and 9_N means the Nth electric motor 9.

The power conversion device 3 is an inverter device including a converter 31, an inverter 32, and a converter control device 33. The AC power input to the power conversion device 3 is converted into DC power by the converter 31. The DC power output from the converter 31 is smoothed by a capacitor (not shown), converted into AC power by the inverter 32, and output from the power conversion device 3. The converter control device 33 controls the inverter 32 so as to match the output frequency of the power conversion device 3 with the frequency command according to the frequency command given from the additional startup control device 10 described later.

The AC power supply 1 and the power converter 3 are connected via a transformer 2. The power conversion device 3 and each electric motor 9 are connected via an output switch 50 and an individual switch 52. The output switch 50 is provided in the main line of the power line that connects the power conversion device 3 and each electric motor 9. However, in the following description, it is assumed that the output switch 50 is always closed. The individual switch 52 is provided in a branch line in which a power line is branched for each electric motor 9. A current detector 6 is provided on the electric motor side of the output switch 50. Note that, in FIG. 1, for example, 52_1 means the first individual switch 52, and 52_N means the Nth individual switch 52.

The electric motor control system according to this embodiment includes an additional start control device 10. The additional activation control device 10 is a control device that additionally activates the stopped electric motor 9 in accordance with an instruction from a host device (not shown). The higher-level device is, for example, a device that manages the entire electric motor control system or a larger system including the electric motor control system. The additional startup of the electric motor 9 is realized by the host device interface 11, the current signal interface 12, the frequency command output unit 13, the opening/closing command output unit 14, the storage unit 15, and the calculation unit 16 included in the additional startup control device 10. Although the additional startup control device 10 is an independent device in FIG. 1, the additional startup control device 10 may be incorporated in the converter control device 33 or may be incorporated in a host device.

The inter-upper-device interface 11 is an interface for transmitting and receiving signals to and from the upper-level device. A frequency command F_REF and a motor start command M_ON are input from the host device to the host device interface 11. The frequency command F_REF is a frequency reference command that determines the operating frequency of the electric motor 9. The motor start command M_ON is a signal that specifies the electric motor 9 to be started, and N kinds of signals from M_ON_1 to M_ON_N are input for each electric motor 9. For example, when activating the Kth electric motor 9_K, the motor activation command M_ON_K is input from the upper device to the upper device interface 11.

The motor start completion signal M_F and the motor start disable signal M_NG are output from the interface 11 between the upper devices to the upper device. The motor start-up completion signal M_F is a signal for reporting the completion of start-up of the electric motor 9 to the host device, and N kinds of signals from M_F_1 to M_F_N are output for each electric motor 9. For example, when the activation of the Kth electric motor 9_K is completed, the motor activation completion signal M_F_K is output from the inter-upper device interface 11 to the upper device. The motor start disable signal M_NG is a signal that reports to the host device that the electric motor 9 could not be started, and N types of signals from M_NG_1 to M_NG_N are output for each electric motor 9. For example, when the Kth electric motor 9_K cannot be started, the motor start prohibition signal M_NG_K is output from the higher-level device interface 11 to the higher-level device.

The current signal interface 12 is an interface for receiving the output current signal I_OUT of the current detector 6. The output current signal I_OUT of the current detector 6 indicates the load current value that actually flows in the power conversion device 3, that is, the total current value of all the electric motors 9 that are currently operating.

The frequency command output unit 13 is an interface for outputting the frequency command F_M_REF to the converter control device 33 of the power conversion device 3. The frequency command F_M_REF output from the frequency command output unit 13 is matched with the frequency command F_REF input from the host device during normal operation. However, when additionally starting the stopped electric motor 9, a frequency different from the frequency command F_REF input from the host device is set. Hereinafter, the frequency command F_REF input from the host device will be referred to as a first frequency command, and the frequency command F_M_REF output from the frequency command output unit 13 will be referred to as a second frequency command.

The open/close command output unit 14 is an interface for outputting a switch operation signal S_ON to each individual switch 52. The switch operation signal S_ON is a signal for opening and closing the individual switch 52, and when the switch operation signal S_ON is at L level, the individual switch 52 is opened, and when the switch operation signal S_ON is at H level, individual The switch 52 is turned on. The switching command output unit 14 outputs N kinds of signals from S_ON_1 to S_ON_N for each individual switch 52. For example, when the K-th individual switch 52_K is turned on, an H-level switch operation signal S_ON_K is output to the individual switch 52_K.

The storage unit 15 stores various information necessary for additional startup control. Specifically, the open/closed state of the individual switch 52, that is, the operating/stopping state of each electric motor 9 is stored in the storage unit 15. Further, the storage unit 15 stores the starting current value I_MOT of each electric motor 9. The starting current value I_MOT that flows when the electric motor 9 is started is determined by the type (including size) of the electric motor 9. The storage unit 15 includes a lookup table that associates the type of the electric motor 9 with the starting current value I_MOT. Since the starting current value I_MOT changes between the voltage V and the frequency F, and the voltage V is controlled to be constant V/F, the starting current value I_MOT may be stored as a function of the frequency F.

The storage unit 15 also stores the start-up completion time TR of each electric motor 9. The time required to complete the activation of the electric motor 9, that is, the activation completion time TR is determined by the type (including the size) of the electric motor 9. The storage unit 15 includes a lookup table that associates the type of the electric motor 9 with the activation completion time TR. The start-up completion time TR is determined by the total moment of inertia and torque of the electric motor 9 and the load, and the load may depend on the frequency F (voltage). Therefore, the startup completion time TR may be stored as a function of the load and the frequency F.

Further, the storage unit 15 stores an allowable current change rate ΔI which is an allowable value of the change rate of the starting current of each electric motor 9. The starting current is a large current that flows temporarily, and converges to a steady current as time elapses after starting. The allowable current change rate ΔI is the change rate of the current value that can be considered that the starting current has converged to the steady current. The allowable current change rate ΔI depends on the output characteristic of the starting current of the electric motor 9 and is therefore determined by the type (including size) of the electric motor 9. The storage unit 15 includes a lookup table that associates the type of the electric motor 9 with the allowable current change rate ΔI. However, since the allowable current change rate ΔI changes depending on the frequency F (voltage) and the load, the allowable current change rate ΔI may be stored as a function thereof.

The calculation unit 16 performs a calculation for additional startup control. FIG. 2 is a flowchart showing the control flow of the additional activation control according to this embodiment. The calculation unit 16 performs calculation for additional startup control according to the control flow shown in this flowchart. Hereinafter, the content of the calculation performed by the calculation unit 16 will be described based on the flowchart.

In step S101, the second frequency command F_M_REF output from the frequency command output unit 13 is matched with the first frequency command F_REF input from the host device. In step S102, it is determined whether or not the motor start instruction M_ON_K for the stopped Kth electric motor 9_K is received from the host device. Until the new motor start command M_ON_K is received, the processes of steps S101 and S102 are repeatedly executed.

When a new motor start command M_ON_K is received in step S102, the start current value I_MOT of the Kth electric motor 9_K is read from the storage unit 15 in step S103. Subsequently, in step S104, the output current signal I_OUT indicating the load current value of the power conversion device 3 is read from the current detector 6.

In step S105, it is determined whether or not the difference between the rated current value I_INV of the power conversion device 3 and the output current signal I_OUT is greater than or equal to the starting current value I_MOT of the Kth electric motor 9_K. If there is a sufficient margin between the rated current value I_INV of the power conversion device 3 and the output current signal I_OUT, the determination result of step S105 becomes a positive result.

If the determination result of step S105 is negative, that is, if there is no sufficient margin between the rated current value I_INV of the power conversion device 3 and the output current signal I_OUT, the processes of steps S113 and S114 are performed.

In step S113, it is determined whether the second frequency command F_M_REF is equal to or higher than a predetermined minimum frequency F_MIN. The minimum frequency F_MIN is determined, for example, from the allowable minimum rotation speed of the electric motor 9. When the second frequency command F_M_REF is equal to or higher than the minimum frequency F_MIN, the second frequency command F_M_REF is reduced by the predetermined reduction rate ΔF in step S114. The reduction rate ΔF is the frequency reduction amount per unit time.

By reducing the second frequency command F_M_REF, the current flowing through each electric motor 9 in operation decreases, and the output current signal I_OUT read in step S104 decreases. The decrease in the output current signal I_OUT increases the margin between the rated current value I_INV and the output current signal I_OUT. The calculation unit 16 repeats the processes of step S113, step S114, step S104, and step S105 until the difference between the rated current value I_INV and the output current signal I_OUT becomes equal to or greater than the starting current value I_MOT of the Kth electric motor 9_K.

If the determination result of step S105 is a positive result, the processes from step S106 to step S112 are performed.

In step S106, the opening/closing command output unit 14 outputs an H-level operation signal S_ON_K to the individual switch 52_K corresponding to the Kth electric motor 9_K. As a result, the individual switch 52_K is closed, power is supplied to the electric motor 9_K, and activation of the electric motor 9_K is started.

In step S107, the activation completion time TR_K corresponding to the Kth electric motor 9_K is called from the storage unit 15. Then, in step S108, the timer T1 is reset. In step S109, the timer T1 is counted up, and in step S110, it is determined whether the count time of the timer T1 is equal to or longer than the activation completion time TR_K. The processes of step S109 and step S110 are repeatedly executed until the count time of the timer T1 becomes equal to or longer than the activation completion time TR_K.

When the count time of the timer T1 is equal to or longer than the activation completion time TR_K in step S110, the process of step S111 is performed. When there is no sufficient margin between the rated current value I_INV of the power conversion device 3 and the output current signal I_OUT, and the second frequency command F_M_REF is made lower than the first frequency command F_REF by the process of step S114, in step S111. , The second frequency command F_M_REF is gradually increased until it becomes the same value as the first frequency command F_REF. When the process of step S114 is not performed, that is, when there is a sufficient margin between the rated current value I_INV of the power conversion device 3 and the output current signal I_OUT, the second frequency command F_M_REF is set to the first value in step S111. The frequency command F_REF is maintained. Then, in step S112, the motor start completion signal M_F_K corresponding to the Kth electric motor 9_K is output from the higher-level inter-device interface 11.

When the determination result of step S113 is a negative result, that is, before the difference between the rated current value I_INV and the output current signal I_OUT is equal to or more than the starting current value I_MOT of the Kth electric motor 9_K, the second frequency command is generated. When F_M_REF becomes equal to or lower than the minimum frequency F_MIN, the processes from step S115 to step S117 are performed.

In step S115, the motor start prohibition signal M_NG_K corresponding to the Kth electric motor 9_K is output from the higher-level device interface 11. In step S116, the L level operation signal S_ON_K is output from the opening/closing command output unit 14 to the individual switch 52_K corresponding to the Kth electric motor 9_K. As a result, the individual switch 52_K is maintained in the open state, and the electric motor 9_K is not activated. In step S117, the second frequency command F_M_REF lowered to the lowest frequency F_MIN is gradually increased until it becomes the same value as the first frequency command F_REF.

Next, the effect obtained by executing the additional startup control according to the above-described flowchart will be described based on comparison with the comparative example. FIG. 3 is an operation explanatory diagram illustrating the operation of the electric motor control system when the additional start control is performed according to the above-described flowchart. FIG. 4 is an operation explanatory diagram illustrating the operation of the comparative example. In the comparative example, the K-th electric motor 9_K is started in a state where one or more electric motors 9 are already in operation, and then, when the load current value of the electric power converter 3 reaches the rated current value, the electric power converter 3 The frequency command is reduced.

Since the system has a response delay, a time delay occurs after the frequency command to the power conversion device 3 is changed until the load current value of the power conversion device 3 changes. As shown in FIG. 4, in the comparative example, the frequency command is reduced after the starting current is generated, but since the speed of increase of the starting current at the rising time is large, the load current is immediately increased even after the frequency command is lowered. The value does not decrease. Therefore, in the comparative example, the load current value may temporarily overshoot the rated current value. When the load current value exceeds the rated current value, the entire system may be stopped due to the overload trip of the power conversion device 3.

According to the additional startup control according to the present embodiment, as shown in FIG. 3, by reducing the frequency command to the power conversion device 3, the load current value of the power conversion device 3 is also reduced, and the power conversion device 3 is reduced. The difference between the rated current value and the load current value is increased. Then, by additionally starting the electric motor 9_K after the difference becomes equal to or larger than the starting current value of the electric motor 9_K, the load current value of the power conversion device 3 falls within the rated current value even when the starting current is generated. This prevents the entire system from being stopped due to the overload trip of the power converter 3.

2. Second Embodiment A second embodiment of the present invention will be described. The second embodiment of the present invention is common to the first embodiment in the configuration of the electric motor control system (see FIG. 1) and is different in the content of the additional start control. FIG. 5 is a flowchart showing a control flow of the additional activation control according to this embodiment. In the second embodiment, the calculation unit 16 performs a calculation for additional startup control according to the control flow shown in this flowchart. Hereinafter, the contents of the calculation performed by the calculation unit 16 will be described based on the flowchart. However, regarding the processing common to the additional startup control according to the second embodiment and the additional startup control according to the first embodiment, the step numbers common to the flowchart of FIG. 5 and the flowchart of FIG. Is attached.

In the second embodiment, in step S106, when the electric motor 9_K is activated by outputting the H-level operation signal S_ON_K to the individual switch 52_K corresponding to the Kth electric motor 9_K, then, in step S201. The process of is executed. In step S201, the start-up completion time TR_K and the allowable current change rate ΔI_K corresponding to the Kth electric motor 9_K are called from the storage unit 15. Then, in step S202, the timer T1 is reset.

In step S203, the timer T1 is counted up. Then, in step S204, the output current signal I_OUT indicating the load current value of the power conversion device 3 is read from the current detector 6. In step S205, the change rate ΔI_OUT of the output current signal I_OUT read in step S204 is calculated. The output current signal change rate ΔI_OUT is the change rate of the output current signal I_OUT per unit time.

In step S206, it is determined whether the output current signal change rate ΔI_OUT has become equal to or lower than the allowable current change rate ΔI_K of the Kth electric motor 9_K. If the output current signal change rate ΔI_OUT becomes equal to or lower than the allowable current change rate ΔI_K, it can be considered that the starting current generated by the additional start of the electric motor 9_K has converged to the steady current.

If the output current signal change rate ΔI_OUT is not less than or equal to the allowable current change rate ΔI_K, the determination in step S207 is performed. In step S207, it is determined whether the count time of the timer T1 is equal to or longer than the activation completion time TR_K. If the count time of the timer T1 has not reached the activation completion time TR_K, after waiting for a predetermined time in step S208, the processes of step S203, step S204, and step S205 are performed again. Then, again in step S206, it is determined whether or not the output current signal change rate ΔI_OUT has become equal to or lower than the allowable current change rate ΔI_K of the Kth electric motor 9_K.

That is, in the additional start control according to the second embodiment, the first determination whether the output current signal change rate ΔI_OUT becomes equal to or lower than the allowable current change rate ΔI_K of the additionally started Kth electric motor 9_K, and the Kth. A second determination is made as to whether or not the elapsed time from the additional activation of the electric motor 9_K (the count time of the timer T1) is equal to or greater than the activation completion time TR_K.

When the condition of the first determination is satisfied before the condition of the second determination is satisfied, that is, the output current signal change rate ΔI_OUT becomes equal to or less than the allowable current change rate ΔI_K of the Kth electric motor 9_K. In this case, the processes of steps S111 and S112 are performed to complete the additional activation of the Kth electric motor 9_K. In step S111, the second frequency command F_M_REF is gradually increased until it becomes the same value as the first frequency command F_REF. In step S112, the motor start-up completion signal M_F_K corresponding to the Kth electric motor 9_K is output from the host-machine interface 11.

If the condition of the second determination is satisfied before the condition of the first determination is satisfied, that is, if the count time of the timer T1 is equal to or more than the activation completion time TR_K, steps S115, S116 and steps The process of S117 is performed to stop the additional activation of the Kth electric motor 9_K. In step S115, the motor start prohibition signal M_NG_K corresponding to the Kth electric motor 9_K is output from the higher-level device interface 11. In step S116, the L level operation signal S_ON_K is output from the opening/closing command output unit 14 to the individual switch 52_K corresponding to the Kth electric motor 9_K. As a result, the individual switch 52_K is opened and the electric motor 9_K is stopped from starting. In step S117, the second frequency command F_M_REF lowered to the lowest frequency F_MIN is gradually increased until it becomes the same value as the first frequency command F_REF.

1 AC power supply 2 Transformer 3 Power conversion device (inverter device)
31 converter 32 inverter 33 converter control device 52 switch 6 current detector 50 output switch 52_1 to 52_N individual switches 9_1 to 9_N electric motor 10 additional startup control device 11 upper device interface 12 current signal interface 13 frequency command output unit 14 Open/close command output unit 15 storage unit 16 calculation unit

Claims (4)

A motor control system for driving a plurality of motors with one inverter device,
When additionally starting a motor that is stopped while one or more motors are already operating, the operating frequency of the inverter device is lowered, and the rated current value of the inverter device and the actual load current of the inverter device are reduced. A motor control system characterized in that the difference between the value and a value becomes equal to or more than a starting current value generated when the stopped motor is started, and the stopped motor is additionally started. When the additional start of the stopped motor is performed, the operating frequency of the inverter device is increased to the frequency before the additional start after a predetermined start completion time has elapsed from the execution of the additional start. The electric motor control system according to claim 1. When the additional start of the stopped motor is performed, after the change rate of the actual load current value of the inverter device is reduced to a predetermined allowable current change rate or less, the operating frequency of the inverter device is before the additional start is performed. 2. The electric motor control system according to claim 1, wherein the electric motor control system increases the frequency up to the frequency. If the predetermined start completion time has elapsed from the execution of additional startup before the rate of change of the actual load current value of the inverter device falls below the allowable rate of change of current, the additionally activated motor is stopped again. The motor control system according to claim 3, wherein the operating frequency of the inverter device is increased to a frequency before the additional start is performed.

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