JPH08223959A - System and method for controlling speed of ac motor and power inversion unit employed therein - Google Patents

Abstract

PURPOSE: To suppress fluctuation in the output voltage from a power inverter due to abrupt variation of speed command in a system for controlling the speed of an AC machine by feeding inverted AC power thereto. CONSTITUTION: The power inverter unit comprises a power converter 11 and a power inverter 14 and controls an AC rotating machine 15 by feeding AC rotating machine 15 with AC power of desired frequency obtained by inverting power from an AC power supply 10. The power inversion unit further comprises a speed control system 20 for the power inverter 14 and a voltage control system 30 for the power converter 11. In the speed control system 20, a speed command delay unit 22 receives a speed command Wr* and outputs the speed command Wr* with a predetermined time lag, while at the same time, an acceleration/ deceleration current operating unit 23 and a power operating unit 24 calculate an inverter output power Pconv. In the voltage control system 30, a power supply current operating unit 34 operates a power supply current compensation command value Idc* from the inverter output power Pconv. The Idc* is added to a control output Id* from a voltage control operating unit 32 determined from the difference between a voltage command V* and the voltage Vfb across a smoothing capacitor 13 thus producing a power supply current command value Id* for controlling the output from the power converter 11 stably.

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 controlling an AC motor, and more particularly, it is suitable for converting output power of a converter into AC power by an inverter and driving the AC motor with this AC power. The present invention relates to a control method for an AC electric motor and a control device therefor.

[0002]

2. Description of the Related Art Conventionally, as a control device for controlling the speed of an AC electric motor using a converter and an inverter, for example, the one described in JP-A-3-190594 is already known.

FIG. 4 shows an example of the configuration of such a conventional motor control device. This device includes a converter voltage controller 32, a converter current controller 33, a power calculator 24,
An inverter converter 14, a smoothing capacitor 13, an inductance 12, an AC motor 15, a converter converter 11,
Inverter calculator 46, power supply current compensation command calculator 34,
The subtraction means 35 and 36 and the AC power supply 10 are included. In this conventional control device, the output power Pconv of the inverter 14 is calculated from the AC current of the AC motor 15, and the power supply current value I to be output by the converter 11 is calculated from the calculated output power.
Calculate dc *. Then, a method of using this power supply current value as a part of the current command Id * of the converter 11 is adopted.

According to such a conventional method,
When the load torque sharply increases, the output current of the converter 11 also increases according to the load torque, so that the voltage fluctuation across the smoothing capacitor 13 corresponding to the output voltage of the converter can be reduced.

[0005]

However, in the above-mentioned prior art, no consideration is given to the operation delay of the power converter, particularly the control response delay of the converter, and therefore the speed command of the electric motor is suddenly increased. The converter output voltage fluctuates remarkably with respect to the change of Wr *, so that there is a problem that the above-mentioned effect cannot be sufficiently obtained.

This is because, for example, when the thyristor converter of the anti-parallel connection is adopted as the converter 11, the necessary power signal is generated, and even if this is immediately transmitted to the control system of the converter, the converter is operated. Due to the operation delay due to the dead time of the antiparallel switching of the constituent thyristors and the control response delay of the converter, the converter 11
Cannot supply power quickly, which causes the output voltage to fluctuate.

The fluctuation of the output voltage of the converter 11 also causes the fluctuation of the voltage across the smoothing capacitor 13 for smoothing the converter output. Therefore, it is necessary to improve the withstand voltage of the smoothing capacitors 13, and it is necessary to take measures to increase the number of the smoothing capacitors 13.
The cost increase for that was also a problem.

Therefore, in view of the above problems in the prior art, an object of the present invention is to control an AC electric motor when there is a power conversion operation delay of a converter constituting a power converter and a control response delay thereof. AC motor speed control system and its method that can suppress fluctuations in the output voltage of the converter even when the speed command changes rapidly, and do not increase the cost of the device, and the power used for such a system. It is to provide a conversion device.

[0009]

In order to achieve the above object of the present invention, what is provided by the present invention is as follows.
An AC motor that includes a converter and an inverter, converts the DC output power converted from AC by the converter into AC power having a desired frequency by the inverter, and supplies the AC power to the AC motor to drive and control the AC motor. A speed control system, wherein the converter has an operation delay or a control response delay, a voltage control system for outputting a conversion control signal to the converter based on a given voltage command, and a given speed command And a speed control system for outputting a conversion control signal to the inverter based on the above, the speed control system includes a speed command delay device for delaying the given speed command for a predetermined time. It is a speed control system of an AC electric motor.

In order to achieve the above-mentioned object of the present invention, according to the present invention, after converting the AC power into DC power by the converter, the converted DC output power is converted into AC power of a desired frequency by the inverter. In the speed control method of the AC electric motor for converting the AC electric power to the AC electric motor to drive and control the AC electric motor, the speed control system for converting the DC output electric power into the AC electric power by the inverter is converted into the AC electric power. There has been proposed a speed control method for an AC electric motor that controls the power conversion of the inverter by delaying the speed command for controlling the power conversion by the converter in consideration of the operation delay or the control response delay.

Further, as means for achieving the above-mentioned object of the present invention, a converter, an inverter, and
The converter includes a voltage control system that outputs a conversion control signal to the converter based on a given voltage command, and a speed control system that outputs a conversion control signal to the inverter based on a given speed command, and the converter operates. It is composed of a power conversion device having a delay or a control response delay,
A power conversion device has been proposed in which the speed control system includes speed command delay means for delaying the given speed command for a predetermined time.

That is, in the present invention, the required power of the AC motor to be controlled is divided into acceleration / deceleration output power for following changes in the speed command and disturbance suppression output power due to load fluctuation, and Acceleration / deceleration output power pays attention to the fact that it can be calculated by the acceleration / deceleration current command value of the electric motor, and the speed command value that generates the torque flow command value of the electric motor is
By delaying the acceleration / deceleration current command value with respect to the speed command value to be generated, it is possible to compensate for the operation delay and control response delay of the converter, and further, as will be apparent from the following embodiments of the present invention. The converter promptly compensates the necessary acceleration / deceleration electric power at the same time when the acceleration / deceleration of the electric motor is started.

[0013]

According to the speed control system and method for an AC electric motor provided by the present invention as described above, and the electric power converter used in such a system, the electric motor with respect to the speed command value for generating the acceleration / deceleration current command value The speed command value for generating the torque current command value of is delayed. Also, since the power supply current value is calculated using the output power generated from the acceleration / deceleration current command value and made a part of the converter current command, the converter can supply the necessary acceleration / deceleration power at the same time when the motor starts acceleration / deceleration. Even if the speed command value of the electric motor suddenly changes, it is possible to suppress the fluctuation of the output voltage of the converter due to the control response delay of the converter and the operation delay of the converter.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of one embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a main circuit configuration of a speed control device for an electric motor according to the present invention. In this figure, a three-phase AC power source 10 (U phase, V phase,
An inductor 12 and a smoothing capacitor 13 are connected to a converter 11 connected to the (W phase), and both ends of the smoothing capacitor 13 are connected to an inverter 14, so that the AC output from the inverter 14 is an AC motor. It has a structure to be supplied to 15. That is,
The power supplied from the three-phase AC power supply 10 is converted into DC by the converter 11, and then the inverter 1 is used again.
It is converted into an alternating current having a desired frequency by 4 and supplied to the alternating current electric motor 15, so that the alternating current electric motor 15 is controlled to a desired rotational speed.

In the circuit configuration of the speed control device for the electric motor, at least the converter 11 is configured by adopting an antiparallel thyristor converter (not shown), and an inverter is used as a control system for the electric motor. 14
A speed control system 20 is provided to control the voltage control system, and a voltage control system 30 is provided to control the converter 11.

First, the speed control system 20 for controlling the inverter 14 will be described. This speed control system 20 will be described.
Is a speed detector 21, a speed command delay device 22, an acceleration / deceleration current command calculator 23, a power calculator 24, a speed control calculator 25, an inverter current, which detects and outputs the rotation speed of the rotating shaft of the AC motor 15. It is composed of a control calculator 26 and a subtractor 27. In the speed control system 20 having such a configuration, when the speed command Wr * is input, the speed command Wr * is input to the speed command delay device 22.
The speed command delay device 22 is a speed command Wr * considering the operation delay of the converter 11 and the control delay of the voltage control system 30.
Output *. Here, the anti-parallel connection thyristor converter has two thyristor bridges, and these two thyristor bridges are switched to perform power supply and regeneration. The time for this switching is necessary, and this is the operation delay (the time from the application of the power line command to the start of the operation). In addition, a speed command is given as a time-dependent correction in consideration of this delay. That is, the speed command is such that the speed command is given at the operation start timing of the converter.

That is, the speed command delay device 22 delays the speed command Wr * by a delay time corresponding to the operation delay of the converter 11 and the control response delay. After that, the speed command Wr ** output from the speed command delay device 22 is output.
Is calculated in the subtracter 27 from the deviation from the motor speed Wr output from the speed detector 21, and this speed deviation is input to the speed control calculator 25, where the torque current command It * is output. . The torque current command It * is input to the inverter current control calculator 26, and the current control calculator 26 controls the output voltage / current of the inverter 14 according to the torque current command It *, that is, a desired AC current. The electric power is output to drive and control the AC motor 15.

On the other hand, according to the present invention, the speed command Wr *
Is input to the acceleration / deceleration current calculator 23 together with the speed command delay unit 22. That is, the acceleration / deceleration current calculator 23 inputs the speed command Wr *, and outputs, as its output, the acceleration / deceleration current command value Ia * indicated by the following equation 1 which is a differential value thereof so as to correspond to the rapid acceleration / deceleration. Is output.

[Equation 1] Here, K1 is a constant and represents the moment of inertia of the motor and the load.

Further, the acceleration / deceleration current command value Ia * from the acceleration / deceleration current calculator 23 is inputted to the electric power calculator 24, and further the converter output power Pconv is calculated and outputted. First, here, the inverter output power Pinv is calculated by the following equation 2.

[Equation 2] Here, V1 is the primary voltage of the electric motor or its command. The inverter output power Pinv is also calculated by the following expression 3.

(Equation 3) Here, τ is the motor torque, and η1 is the motor efficiency.

Next, the converter output power Pconv to be output by the converter 11 is calculated according to the following equation 4 or 5.

[Equation 4]

(Equation 5) In the above equation, η2 is the efficiency of the main circuit. The converter output power Pconv is output to the voltage control system 30.

The voltage control system 30 for controlling the converter 11 is, as shown in the figure, a voltage detector 31, a voltage control calculator 32, for detecting the voltage across the smoothing capacitor 13.
It is composed of a converter current control calculator 33, a power supply current compensation command value calculator 34, and two adders / subtractors 35 and 36.

In the voltage control system 30, when the voltage command V * is inputted, the deviation from the voltage Vfb across the smoothing capacitor 13 which is the output of the voltage detector 31 is obtained by the subtractor 35, and the deviation is obtained. The deviation is input to the voltage control calculator 32, which outputs the power supply current command value Id *.

On the other hand, the power supply current compensation command value calculator 34 is
The converter output power Pconv from the speed control system 20 is input, and thereby the power supply current compensation command value Idc * is calculated and output according to the following Equation 6.

(Equation 6) Here, Ve is a power supply voltage.

Further, the power supply current command value Id * from the voltage control calculator 32 and the power supply current compensation command value calculator 34.
The power supply current compensation command value Idc * is added to each other by the adder 36 (Id * + Idc *), and is output as the power supply current command value Id **.

After that, the converter current control calculator 33
Will input the power supply current command value Id ** and control the conversion output of the converter 14 according to the power supply current command value Id **.

As described above, in this embodiment, the electric power required for accelerating and decelerating the electric motor is obtained from the speed instruction Wr *, and the electric power source current for compensating the electric power source current instruction value Id * for controlling the converter 14 is obtained from the obtained electric power. Calculate the compensation value Idc *. Then, this power supply current compensation value Idc * is added to the power supply current command Id *, whereby the final converter current command value Id * is obtained.
Therefore, the necessary electric power for acceleration / deceleration is promptly supplied from the converter 11. The speed command Wr ** input to the speed control calculator 25 is delayed by the speed command delay device 22.

From the above, even if the speed command value Wr * of the electric motor 15 suddenly changes, the AC current is supplied to the converter 11 at an appropriate timing by considering the control response delay of the converter 11 and the operation delay of the inverter 14. Can be flowed in, and thus fluctuations in the output voltage of the converter 11 can be suppressed.

Another embodiment of the present invention will be described below with reference to the attached FIG. Since the operation of each part in the other embodiments is almost the same as that of the embodiment of FIG. 1, the difference will be mainly described below.

Another embodiment of the present invention, as shown in FIG.
For one converter 11, a plurality of inverters 14
a, 14b, 14c ... Are connected. In this system, each speed control system 20a, 20b, 20c
The signals output from the power calculators 24a, 24b, 24c, ... Are added by the adder 41 of the voltage control system 30, and this is the converter output power Pconv. Therefore, in the other embodiments as well, similar to the embodiment of FIG.
Even if there is a rapid change in the speed command value Wr *, the speed command delay devices 22a, 2a, 2c of the speed control systems 20a, 20b, 20c ...
It will be apparent that the functions of 2b, 22c ... Can suppress fluctuations in the output voltage of the converter 11.

Next, still another embodiment of the present invention will be described with reference to the attached FIG. Also in this third embodiment, the operation of each part is almost the same as that of the embodiment shown in FIGS. 1 and 2, so that the main differences will be mainly described.

As is apparent from FIG. 3, in the third embodiment, a plurality of inverters 14a, 14b, 14c ... Are connected to one converter 11. AC motors 15a, 15b, 15c ... Are connected to the plurality of inverters 14a, 14b, 14c. Then, the plurality of AC motors 15a, 1
5b, 15c, ... Have rolls 42a, 42, respectively.
b, 42c ... Are connected, and these rolls 42a, 42b, 42c.
They are connected by 3. In the equipment having such a configuration, the AC motors 15a, 15b, 15c ...
Is operated in synchronization with (proportional to) a line speed command (plate speed command) SP * which is a line moving speed of the plate 43.

By the way, in the embodiments of FIGS. 1 and 2, the required electric power of each AC motor (or inverter) is obtained from the speed command Wr *. Speed command) SP * electric motor 15a,
The electric power required for acceleration / deceleration of 15b, 15c ... Is obtained. Here, line speed SP *
Is input to the speed command delay device 22, a line speed command SP ** is output as its output in consideration of the operation delay of the power converter and the control delay of the voltage control system. Therefore,
The proportional converters 44a, 44b, 44c ... Input this line speed command SP **, and the speed command W of the AC motor is input there.
Convert to ra *, Wrb *, Wrc * ...

On the other hand, the acceleration / deceleration current calculator 23 receives the line speed command SP * as an input and outputs the acceleration / deceleration current command value Ia * expressed by the following equation 7.

(Equation 7) Here, K2 represents a constant.

Further, the power calculator 24 receives the acceleration / deceleration current command value Ia * output from the acceleration / deceleration current calculator 23 as an input, and calculates the total inverter output power Pin by the following equation 8.
Calculate v.

(Equation 8) Here, V1 is the primary voltage of the representative motor or its command, and K3 is a constant.

Also, this total inverter output power Pinv
Is also calculated by the following equation 9.

[Equation 9] In this equation 9, τ is the representative motor torque, η
1 is the efficiency of the representative motor, and K4 is a constant.

Next, the power calculator 24 calculates the converter output power Pconv by the following formula 10 or formula 11.

[Equation 10]

[Equation 11] Here, η2 is the efficiency of the representative main circuit, and K5 is a constant.

Thereafter, the voltage control system 30 inputs the converter output power Pconv calculated as described above, and here, as in the embodiment of FIG. 1, the converter output power Pconv is divided by the power supply voltage. By doing so, the power supply current compensation command value Idc * is calculated, and this power supply current compensation command value Idc * is added to the power supply current command value Id ** to obtain the final converter current command value. For this reason,
Also in the present embodiment, as in the above-described various embodiments, even if there is a rapid change in the line speed command (plate speed command) SP *, the fluctuation of the output voltage of the converter 11 can be suppressed.

The above FIG. 3 shows a plurality of motors 15a to 15a for the same processing step in a production line processing system including a rolling mill or the like.
Although the installation example of c has been described, separate processing steps (for example, two separate steps of tension control step and rolling processing step)
It can also be applied to the case where the motors are separately installed in and the control of these motors is performed.

[0039]

As is apparent from the above detailed description, according to the present invention, even when the speed command value of the AC motor to be controlled changes abruptly, the speed command is delayed for a predetermined time and at the same time. By configuring the converter to supply power for acceleration / deceleration promptly, it is possible to supply a high-quality power supply with suppressed fluctuations in the converter output voltage to the inverter, which is also technically excellent. To do. Furthermore, this not only improves the control characteristics of the speed control device, but also reduces the capacity of the smoothing capacitor that suppresses fluctuations in the output voltage, and thus has the effect of making the device more inexpensive.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a speed control device for an electric motor, which is a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a speed control device for an electric motor that is another embodiment of the present invention.

FIG. 3 is a block diagram showing a circuit configuration of a speed control device for an electric motor which is still another embodiment of the present invention.

FIG. 4 is a block diagram showing an example of a circuit configuration of a conventional motor control device.

[Explanation of symbols]

 10 AC power supply 11 Converter 12 Inductance 13 Smoothing capacitor 14 Inverter 15 AC motor 20 Speed control system 21 Speed detector 22 Speed command delay device 23 Acceleration / deceleration current calculator 24 Power calculator 25 Speed control calculator 26 Inverter current control calculator 27 Adder / subtractor 30 Voltage control system 31 Voltage detector 32 Converter voltage control calculator 33 Converter current control calculator 34 Power supply current compensation command calculator 35, 36 Adder / subtractor 41 Adder 42 Roll 43 Plate 44 Proportional converter 45 Current detector 46 Inverter controller

Claims (12)

[Claims] 1. A converter and an inverter, wherein the converter converts DC output power converted from AC to AC power of a desired frequency, and supplies the AC power to the AC motor to drive the AC motor. A speed control system of an AC motor for drive control, wherein the converter has an operation delay or a control response delay, and a voltage control system that outputs a conversion control signal to the converter based on a given voltage command, A speed control system for outputting a conversion control signal to the inverter based on a given speed command, wherein the speed control system is a speed command delay for delaying the given speed command for a predetermined time. A speed control system for an AC electric motor, characterized by being equipped with a controller. 2. The speed control system for an AC motor according to claim 1, wherein the voltage control system is based on the given voltage command based on a compensation command value obtained based on the speed command from the speed control system. A speed control system for an AC electric motor, comprising means for correcting a current command value obtained by the above. 3. The speed control system for an AC electric motor according to claim 2, wherein the speed control system further comprises means for calculating electric power required for acceleration / deceleration of the AC electric motor from the given speed command. The speed control system for an AC electric motor, wherein the voltage control system includes means for calculating the compensation command value based on electric power required for acceleration / deceleration from the calculation means. 4. The speed control system for an AC electric motor according to claim 1, wherein the AC electric motor is plural, and
The speed control system for an AC electric motor, wherein each of the plurality of AC electric motors is provided with the inverter, and is driven and controlled by the AC output power from each inverter. 5. The speed control system for an AC electric motor according to claim 1, wherein a plurality of the AC electric motors are provided, and
Each AC motor is directly connected to a plurality of rolls mechanically connected by one plate, so that by rotating the plurality of AC motors to move the one plate at a desired line speed In the above, the speed control system is configured to control the rotational speeds of the plurality of AC motors by using the desired line speed as the speed command. 6. The converter converts AC power into DC power, and then the converted DC output power is converted into AC power of a desired frequency by an inverter, and the AC power is supplied to the AC motor to drive the AC motor. In the speed control method of an AC motor for drive control, a speed control system for converting DC output power to AC power by the inverter,
A speed control method for an AC electric motor, comprising controlling a power conversion of the inverter by delaying a speed command for converting to AC power by a time taking into consideration an operation delay or a control response delay of the converter. 7. The speed control method for an AC electric motor according to claim 6, wherein the voltage control system for controlling the power conversion of the converter generates AC power based on a current command value obtained based on a given voltage command. A speed control method for an AC electric motor, wherein the voltage control system corrects the current command value with a compensation command value according to the speed command from the speed control system. 8. The AC motor speed control method according to claim 7, wherein the speed control system calculates electric power required for acceleration / deceleration of the AC motor from the given speed command,
The speed control method for an AC electric motor, wherein the voltage control system calculates the compensation command value based on electric power required for the acceleration / deceleration. 9. The speed control method for an AC motor according to claim 8, wherein the speed control system obtains an acceleration / deceleration current value required for acceleration / deceleration of the AC motor by differentiating the given speed command. A speed control method for an AC motor, characterized in that electric power required for the acceleration / deceleration is calculated based on the obtained acceleration / deceleration current value. 10. The speed control method for an AC electric motor according to claim 9, wherein the speed control system further obtains output power to be output by the converter from the calculated power required for acceleration / deceleration, and obtains this. A method for controlling a speed of an AC motor, wherein the compensation command value is calculated from converter output power. 11. The AC motor speed control method according to claim 10, wherein the speed control system further calculates the compensation command value by dividing the obtained converter output power by a power supply voltage. AC motor speed control method. 12. A converter, an inverter, a voltage control system for outputting a conversion control signal to the converter based on a given voltage command, and a conversion control signal to the inverter based on a given speed command. A speed control system, wherein the converter is composed of a power converter having an operation delay or a control response delay, and the speed control system delays the given speed command by a predetermined time. A power conversion device comprising: