JPH0576190A - AC motor starting method and apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] In an AC motor starting method and device using an inverter, the boost amount at motor startup can be automatically set to an appropriate value by self-learning in accordance with the environmental temperature. [Structure] When the target AC motor 3 fails to start, the starting operation of the AC motor 3 is stopped, and after a predetermined time, it is restarted by a boost voltage obtained by adding a predetermined amount of added voltage to the previous start voltage, and the start is successful. Then, the voltage obtained by subtracting the subtraction voltage smaller than the previous addition voltage from the previous boost voltage is used as the startup voltage at the next startup. It is desirable to integrate the unit voltage in the up / down counter 12 configured such that the boost voltage is such that the down value is smaller than the up value. In addition, up-down counter 1
It is desirable to provide a memory backup function in 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for starting an AC motor, and more particularly to an apparatus which is started and operated relatively frequently and whose starting torque is easily influenced by ambient temperature, such as outdoors. A compressor that is used, such as when grease is used as lubricating oil, has a low frictional resistance when starting in summer, but has a large frictional resistance when starting in winter. The present invention relates to a starting method and a starting device thereof.

[0002]

2. Description of the Related Art In FIG. 5, which shows the relationship between the frequency and the voltage supplied to an AC motor of an inverter, the basic characteristic of the inverter that drives the AC motor is generally shown by a characteristic line K. The ratio between the frequency and the voltage supplied to the motor (hereinafter abbreviated as "motor") is controlled to be constant. In FIG. 5, the horizontal axis shows the frequency F and the vertical axis shows the voltage V. Frate is the rated frequency at which the inverter supplies power to the target motor, and Vrate is the frequency F.
It is the voltage at the rate. Fmin is the minimum frequency supplied from the inverter when starting the target motor. V
min is the voltage at the frequency Fmin. In a device in which the motor load fluctuates, the voltage at the starting frequency Fmin is increased in order to facilitate starting at low speed, that is, the boost voltage is set to Vm.
In addition to in, the starting voltage is set to voltage Vu, and a fixed booster method is used in which the motor is driven along the characteristic line U. The voltage Vu needs to be set in advance to an appropriate value so that the motor does not start because only an excessive current flows because the current is too high and the current is too low and the starting torque cannot reach the load torque. There is. Also, for loads with large torque fluctuations, an inverter that uses an auto booster system that applies a specified voltage and increases the applied voltage to a specified value when a current larger than the rated value flows There is also.

[0003]

By the way, according to the motor starting method by the inverter as described above, a device whose starting torque is easily influenced by the ambient temperature, for example, friction resistance at the time of summer start when grease is used as lubricating oil is used. However, the fixed boost method requires adjusting the boost voltage again in response to seasonal changes, etc., in order to start the motor used in a device that has high frictional resistance during winter startup.
Further, even with the auto boost method, there is a problem that it is difficult to quickly and stably start the motor in response to any change in environmental temperature. The present invention solves the above-mentioned conventional problems so that the boost amount required at the time of starting the motor can be automatically set to an appropriate value by self-learning in accordance with the environmental temperature at the time of starting. Therefore, the boost voltage is always optimized. It is an object of the present invention to obtain a method and an apparatus for starting an AC motor that can be always stably and quickly started regardless of changes in the seasonal temperature by keeping the temperature close to.

[0004]

In order to solve the above problems, in the method of starting an AC motor according to the present invention, when the AC motor fails to start at a predetermined starting voltage, the starting operation of the AC motor is stopped. After a lapse of a predetermined time, the boost voltage obtained by adding a predetermined amount of added voltage to the starting voltage is restarted, and if the starting is successful, a voltage obtained by subtracting a subtracted voltage smaller than the added voltage from the boost voltage at the time of the next starting is generated. The starting voltage is used. In order to create the boost voltage that increases or decreases, it is effective to integrate the unit voltage with an up-down counter function configured such that the down value is smaller than the up value. Further, in the AC motor starter according to the present invention, when the AC motor is started, the boost voltage created by the predetermined means is superimposed on the predetermined start voltage, and when the start failure of the AC motor is detected, the start / stop predetermined time is reached. When the boost voltage is increased by a predetermined amount and restarted, and when the startup is successful, the boost voltage is reduced by a smaller amount than the increased amount and stored in the memory for use at the next startup.
The boost voltage to be increased or decreased is configured so that the down value is smaller than the up value, and it is increased when the startup fails,
It is effective to integrate the unit voltage into an up / down counter configured to bring down the voltage when the activation is successful. Further, it is effective to provide the storage means or the up / down counter with a memory backup means for preventing the stored contents from being lost at least for a predetermined time even when the power is cut off.

[0005]

In the method of starting the AC motor according to the present invention, the method as described above is used. Therefore, if the starting fails, the restarting operation is performed by the starting voltage increased by the predetermined amount, and if the starting succeeds, the amount smaller than the increment is obtained. The reduced starting voltage can be used as the next starting voltage. Therefore, appropriate starting characteristics can be obtained by self-learning in response to environmental temperature changes in winter, summer, etc. By always maintaining the starting voltage close to the optimum value, stable stable and fast characteristics can be obtained regardless of seasonal temperature changes. Can be started.
The desired purpose can be achieved by a simple means by integrating the unit voltage in the up-down counter function configured to set the down value smaller than the up value for setting the boost voltage and the subtraction voltage. be able to. Also, in the AC motor starter according to the present invention,
With the above-described configuration, if the startup fails, the restart operation is performed with the startup voltage increased by the predetermined amount, and if the startup is successful, the startup voltage reduced by the amount smaller than the increment can be used as the next startup voltage. Therefore, appropriate starting characteristics can be obtained by self-learning in response to environmental temperature changes in winter, summer, etc. By always maintaining the starting voltage close to the optimum value, stable stable and fast characteristics can be obtained regardless of seasonal temperature changes. Can be started. The initial purpose can be achieved by a simple means by integrating the unit voltage in an up / down counter configured such that the down value is smaller than the up value to set the boost voltage and the subtraction voltage. it can. Further, by providing the storage means or the up / down counter with a memory backup means for preventing the stored contents from being lost at least for a predetermined time even when the power is cut off, the starting device can be continuously operated after a short period in which the environmental temperature changes little. When used, the motor starts successfully with the previously stored starting voltage, so the motor can be started in a short time.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a method of starting an AC motor and an apparatus therefor according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a block configuration diagram for explaining an AC motor starting device (hereinafter abbreviated as starting device) configured based on the AC motor starting method of the present invention. This block diagram shows the basic configuration in blocks to explain the function of the starter. The power supply circuit and other peripheral circuits and connection circuits, and the detailed circuits in the block showing the basic configuration are various commercially available circuits. Since the parts can be easily configured, the detailed illustration is omitted. In FIG. 1, reference numeral 1 is a DC power supply, which is converted into a predetermined frequency and voltage by an inverter 2 and supplied to an AC motor (hereinafter abbreviated as a motor) 3. Reference numeral 10 indicates a control device main body function of the inverter (hereinafter referred to as a control device main body), and for example, a storage circuit 1 in which predetermined control conditions and operation programs are stored.
0a and a storage circuit 10b for recording predetermined control data are additionally provided, and are configured by an arithmetic processing unit such as a microcomputer provided with an overcurrent detection function 10c, an inverter operation determination function 10d, a clock function 10e and the like. A signal line for transmitting the status signal 28 of the inverter 2 to the control device main body function 10 is provided between the control device main body 10 and the inverter 2. Reference numeral 11 denotes a motor start-up failure determination circuit, which is used by the control device main body 10 to detect an overcurrent detection signal 21.
And a feedback signal 22 indicating the motor start failure determination condition are input. The activation failure signal 23 is output from the activation failure determination circuit 11.
Is input to the +2 input section of the up / down counter 12, and the activation success signal 24 is input to the -1 input section of the up / down counter 12. As is well known, the up / down counter 12 has a predetermined number of addition / subtraction functions and a function of storing and accumulating calculation results. The output of the up / down counter 12 is input to a boost voltage setting integration circuit (hereinafter abbreviated as integration circuit) 13. The unit voltage signal 25 indicating the unit boost amount signal is input from the control device body 10 to the integrating circuit 13. The activation failure signal 23 from the activation failure determination circuit 11 is also transmitted to the control device body 10.

As shown in FIG. 4, the up / down counter 12 has a power storage function for backing up the power source using a capacitor or the like so that the content of the counter can be stored for a predetermined time even when the power source is cut off. In FIG. 4, 12 is an up / down counter, 12a is a positive power source, and 12b is a negative power source which is a ground. Reference numeral 17 is a capacitor having a storage capacity, 18 is a diode, and 19 is a positive power bus. Therefore, the voltage of the plus power supply bus bar 19 is equal to the capacitor 17
When the positive power source bus 19 does not supply power, the electric charge stored in the capacitor 17 is supplied to the up / down counter 12. In this case, due to the characteristics of the diode 18, the electric charge stored in the capacitor 17 is not supplied to the circuits other than the up / down counter 12. The up-down counter 12 is provided with a set circuit (not shown) that operates when the power is turned on in a state where the capacitor 17 is not charged, and that sets the counter content to specify a predetermined minimum boost voltage. The output of the integrating circuit 13 is input to the voltage setting circuit 14 so that the control device main body 1
PW after being added to the reference voltage signal 26 supplied from 0
Input to the M circuit 15. In the PWM circuit, a pulse signal having a duty ratio corresponding to the voltage signal input from the voltage setting circuit 14 at this frequency is generated by the signal 27 designating the frequency input from the control device body 10, and the trigger circuit 16 is activated. It is input to the inverter 2 via. In the inverter 2, the switching element, which is the main component of this inverter circuit, is driven by the pulse signal in the previous period, so that a predetermined voltage is supplied to the motor 3 at a predetermined frequency.

Next, a start-up method by the circuit showing the above-mentioned start-up device and its operation and action will be described with reference to the flowchart shown in FIG.
It will be described in detail with reference to the characteristic diagram shown in FIG. FIG. 3 corresponds to FIG. 5 shown in the prior art and shows the frequency F on the horizontal axis and the voltage V on the vertical axis. Frate is the rated frequency of this motor supplied from the inverter to the motor,
Vrate is the voltage at the frequency Frate. F
min is the lowest frequency that is the starting frequency of the motor supplied from the inverter to the motor, and Vmin is the reference voltage at the frequency Fmin. When the motor starts with the inverter output of frequency Fmin and voltage Vmin,
The output frequency and the voltage of the inverter 2 change according to the characteristic line K up to the frequency Frate and the voltage Vrate corresponding to this frequency Frate according to a predetermined condition output from the control device body 10. However, it is usually difficult to start the motor at the voltage Vmin at the frequency Fmin, and the starting operation is performed at the voltage b, for example, in addition to the boost voltage Vmin. When a start switch (not shown) of the control device main body 10 is turned on to start the motor, the sequence condition stored in the storage device 10a in advance and the control data stored in the storage device 10b are displayed as shown in FIG. The inverter is activated as shown. A status signal 28 indicating the operating status of the inverter 2 is transmitted to the control device body 10. An overcurrent detection signal 21 and a feedback signal 22 indicating a motor start failure determination condition are input from the control device body 10 to the start failure determination circuit 11. The up / down counter 12 operates even when the power is cut off by the electric charge stored in the capacitor 17 that backs up the power supply, and stores the counter content for a predetermined period. Therefore, the counter content of the previous day is input to the integrating circuit 13, and the control device main body 10 A boost voltage is created by integrating the unit voltage signal 25 input from the counter contents of the counter. This boost voltage is input to the voltage setting circuit 14 and added to the reference voltage signal 26 supplied from the control device body 10, and then the PWM circuit 1
Enter in 5. In the PWM circuit, the controller body 1
A PWM pulse signal having a duty ratio corresponding to the voltage signal input from the voltage setting circuit 14 at a predetermined frequency is created by the signal 27 specifying the starting frequency input from 0 and the output signal from the voltage setting circuit 14. Then, it is input to the inverter 2 via the trigger circuit 16. Therefore,
From the inverter 2, the motor 3 is supplied with a voltage at which a boost voltage according to the contents set in the up / down counter 12 and a reference voltage corresponding to the startup frequency are added to the motor 3 at a predetermined startup frequency. That is, in FIG. 3, the voltage a at the starting frequency Fmin is supplied from the inverter 2 to the motor 3. The output current value of the inverter 2 is detected and transmitted as a status signal 28 to the control device body 10. In the overcurrent detection function 10c, the storage device 10b
The contents of the status signal 28 and the reference current value under the output condition of the inverter 2 stored in
If the output current of is larger than the reference current value, the overcurrent detection signal 21 is input to the motor start failure determination circuit 11.

Further, the clock function 10e provided in the control device body 10 is activated. This clock function 10e measures a predetermined time set in advance, or an inverter operation determination function 10d also provided in the control device body 10 is included in the status signal 28 from the inverter 2 to send a signal to the inverter 2 When the trip is detected, the feedback signal 22 is input to the motor start failure determination circuit 11. In the motor start failure determination circuit 11, the overcurrent detection signal 2
When it is detected that both 1 and the feedback signal 22 are input, it is determined that the motor has failed to start, and a signal is sent to the +2 input portion of the up / down counter 12 to add 2 to the up / down counter 12. The activation failure signal 23 from the activation failure determination circuit 11 is also input to the control device body 10 to restart the clock function 10e. That is, in FIG. 2, when it is determined that the motor has failed to start after the motor has been operated to start the inverter, 2 is added to the counter and the clock is set. When this clock function measures a predetermined time set in advance, the control device body 10 restarts the above-described operation so as to restart the inverter 2. Since the set content of the up / down counter 12 has increased by 2 from the beginning, the voltage b is output from the inverter 2 and supplied to the motor 3 as shown in FIG. As shown in FIG. 3, if the motor startup fails again this time, the voltage c is output from the inverter 2 and supplied to the motor 3. The controller main body 10 continuously changes the signal 27 designating the frequency of the inverter according to the predetermined conditions stored in the storage devices 10a and 10b, and changes the unit voltage signal 25 and the reference voltage signal 26 corresponding to this frequency. Let Therefore, the inverter 2
The frequency and voltage supplied from the to the motor 3 vary along the characteristic line C. When the status signal 28 of the inverter 3 does not transmit an abnormal signal and the frequency becomes Fo shown in FIG. 3, the inverter operation determination function 10d inputs a predetermined signal to the motor start failure determination circuit 11 by the feedback signal 22. In the motor start-up failure judgment circuit 11, the feedback signal 22 and the overcurrent signal 21 are not present, so that it is judged that the motor start-up is successful, and the result is input to the -1 input section of the up-down counter 12. Therefore, as shown in FIG. 2, 1 is subtracted from the contents of the counter. The contents of the up / down counter 12 are used at the next startup. That is, at the next startup, the output voltage of the inverter 2 is the voltage c as shown in FIG.
The voltage d obtained by subtracting the unit voltage from is supplied to the motor 3. Since the power source of the up / down counter 12 has a power storage function using a capacitor or the like that can store the counter contents for a predetermined time as described above, when restarting after a short period with a small change in environmental temperature, It is activated by the appropriate boost voltage. In the case of starting after a long period of time, if the stored voltage decreases and the contents of the up / down counter 12 are erased, the voltage is set to a predetermined value when the power is turned on, so that it is started by the voltage a. Therefore, it is possible to prevent the excessive boost voltage from being output from the beginning when the environmental temperature changes. In addition, even in an inverter that accelerates at a steep slope, it is possible to respond appropriately and reliably and stably.

The circuit shown in FIG. 1 shows the functions according to the present invention. Each functional block may be formed by a circuit individually, or by using a circuit element formed by appropriately combining them, a control device. It may be absorbed by the main body 10. The control device main body 10 is additionally provided with a storage circuit 10a that stores predetermined control conditions and operation programs and a storage circuit 10b that stores predetermined control data, and an overcurrent detection function 10c, an inverter operation determination function 10d, and a clock function. Although it has been described as being configured by an arithmetic processing device including 10e and the like, any other suitable configuration may be used as long as it is configured to have a predetermined function according to the present invention. Although it has been described that the up-down counter is incremented by 2 when the activation fails, and the up-down counter is decremented by 1 when the activation is successful, the up-down counter function may be provided in the control device main body. The storage means may be stored in the storage means, and the storage means may be provided with a power backup function at the time of power shutdown. Further, a numerical value other than 2 may be added when the start fails, and a numerical value other than 1 that is less than or equal to the added value may be subtracted when the start is successful. In that case, the number of additions and the number of subtractions may be appropriately changed instead of being a fixed number in accordance with the number of contents of the calculation result. Further, although it has been described that the contents of the up / down counter are set to a predetermined value when the power of the up / down counter is turned on, when the power is turned on, the up / down counter is completely reset to the reference voltage 2 a. Any suitable means can be adopted within the scope of the technical idea of the present invention, such as transmitting the voltage signal 26 for designating. Further, the above functions may be realized by using a microprocessor. Further, although the capacitor is used for the power source backup, a battery other than the capacitor, for example, a battery may be used depending on the application condition. It goes without saying that the boost voltage setting means based on the present invention can be applied to an inverter having an inverter output frequency / voltage characteristic other than that shown in FIG. 3 and an inverter having a configuration other than PWM.

[0011]

Since the method of starting the AC motor according to the present invention has the above-described method and the apparatus has the above-described configuration, the following excellent effects can be obtained. The boost voltage can always be optimally maintained even in an inverter that starts frequently and accelerates with a steep gradient. Since an appropriate boost voltage is automatically obtained in response to environmental temperature changes in winter or summer, excellent starting characteristics can be obtained. The boost voltage can be easily and reliably obtained by automatic self-learning in response to environmental temperature changes in winter or summer. As described in detail for obtaining the boost voltage, when the unit voltage is integrated with the content value of the up / down counter in which the up value and the down value are changed, the self-learning can be performed with a simple configuration. When the power source of the up / down counter or the power source of the storage means is provided with the power source backup function, the motor can be quickly started by the boost voltage suitable for each environmental temperature even in the case of seasonal fluctuations such as winter or summer.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an AC motor starting device configured based on an AC motor starting method of the present invention.

FIG. 2 is a flowchart illustrating a method for starting an AC motor according to the present invention with reference to the block diagram shown in FIG.

FIG. 3 is a characteristic diagram showing a frequency-voltage characteristic of an inverter output for explaining a self-learning situation of a boost voltage according to the present invention.

4 is a block diagram illustrating a power supply backup circuit of the up / down counter shown in FIG.

FIG. 5 is a characteristic diagram showing frequency-voltage characteristics of a general inverter for driving an AC motor.

[Explanation of symbols]

 1: DC power supply 2: Inverter 3: AC motor 10: Inverter control device main body function (control device main body) 11: Startup failure determination circuit 12: Up / down counter 13: Boost voltage setting integration circuit 14: Voltage setting circuit 15: PWM circuit 17: Power supply backup capacitor

Claims (5)

[Claims] 1. A method of starting an AC motor supplied with electric power by an inverter, wherein when the starting of the AC motor fails with a starting voltage obtained by adding a boost voltage created by a predetermined means to a predetermined reference voltage. ，
After the start operation of the AC motor is stopped, after a predetermined time, the boost voltage is superposed with a predetermined addition voltage and restarted by an increased restart voltage, and if the start is successful, the addition voltage is decreased by a predetermined value. A method for starting an AC motor, characterized in that a voltage obtained by subtracting and subtracting the subtracted voltage from the boost voltage is stored for at least a predetermined time as the boost voltage for the next startup. 2. The method of starting an AC motor according to claim 1, wherein the boost voltage to be increased or decreased is a predetermined unit voltage for a content value of an up-down counter function configured such that a down value is smaller than an up value. The method of starting an AC motor according to claim 1, wherein the method is performed by integrating. 3. A controller for an AC motor supplied with electric power by an inverter, a means for storing a starting frequency of the inverter and a predetermined starting voltage corresponding to the frequency when the AC motor is started, and the AC. A means for superimposing a boost voltage created by a predetermined means on the starting voltage and applying it to the AC motor when the motor is started, and a means for stopping the power supply to the AC motor when a failure to start the AC motor is detected. A means for instructing a restart operation of the AC motor after a predetermined time has elapsed after the AC motor fails to start, and a means for creating a predetermined amount of increase to increase the boost voltage when the AC motor fails to start,
A starting device for an AC motor, comprising means for generating a predetermined amount of decrease smaller than the increment for decreasing the boost voltage and storing the decreased amount for at least a predetermined time when the AC motor is successfully started. 4. The start-up device for an AC motor according to claim 3, wherein the boost voltage is configured such that a down value is smaller than an up value, and when the start fails, the boost voltage is increased by a predetermined amount. 4. The unit voltage is increased as a means for creating, and as a means for creating a decrease amount for decreasing the boost voltage when starting is successful, an up-down counter configured so as to be down is obtained by accumulating unit voltages. AC motor starter described. 5. The AC motor starter according to claim 3 or 4, further comprising a power supply backup means for preventing the stored contents from being lost at least for a predetermined time even when the storage means or the up / down counter is powered off. The AC motor starting device according to claim 3, wherein the AC motor starting device is provided.