JPH07322666A - Controller for variable speed drive system - Google Patents

Abstract

PURPOSE:To improve follow-up to a speed command by computing a required value of the input or outlet current from the operating command signal and the load characteristics of an electric motor, and setting it as the output value of an integrator or the primary delay factor in a voltage control part. CONSTITUTION:Torque increases with the square of the speed in an electric motor, so it is possible to obtain a current command value which maintains speed at the time of restarting operation as an output when a speed command value is inputted in a square-law operating device 27 with coefficient. The current command value is inputted in a switch 28, and is set as the output of the operating device of a proportional integrator 17 during stopping. Because a required value to maintain a speed is given beforehand as the output of the proportional integrator 17 generated at the time of restarting operation, response delay is shortened, and the current required to maintain a speed is injected with only the response delay of the proportional integrator 20 for current control. It is thus possible to enhance the speed response characteristics of an induction motor 7 and improve it regardless of the response characteristics of the proportional integrator 17 for voltage control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device having an improved speed response characteristic of a variable speed drive system composed of a voltage source and a variable speed controlled motor load which is its load.

[0002]

2. Description of the Related Art A variable speed drive system composed of a voltage source and a variable speed controlled motor load is disclosed in, for example, Shibata et al., "Variable speed drive of AC electric motor by power electronics" (published by Tokyo Denki University Press). P.121 Figure 3.4
2, P.126 Figure 3.51 and P.128 Figure 3.56. Here, an induction motor connected to a current type inverter is used as a variable speed controlled motor load.

In such a conventional system, in order to maintain stability of the control system, the response speed of the voltage control unit is slower than that of the current control unit which is a minor loop. That is, the control characteristics when the operation is restarted in the case of the conventional method will be described with reference to FIG. The speed command during stop is naturally decelerating due to the load. When the operation is restarted, the speed command becomes constant or tends to increase, so that a break point occurs in the speed command at the moment when the operation is restarted. In order to follow this speed command, it is theoretically necessary that the torque generated by the electric motor changes discontinuously as shown in FIG. In order to change the torque of the induction motor of FIG. 1 discontinuously, not only the frequency but also the terminal voltage must follow the polygonal line similar to the speed command because of the constant V / f control. However, since the response speed of the terminal voltage is affected by the response delay as long as the voltage control system is the feedback control system, the torque change is delayed as shown in FIG. 5, and the speed followability is deteriorated. This has been an unavoidable problem in the feedback control system.

[0004]

In this case, for example, when the voltage command rises / falls as the speed command rises / falls in the induction motor controlled by a constant voltage / frequency ratio, the power from the forward converter is increased. Has a drawback that the response characteristic of the voltage control unit delays the injection / narrowing of, and as a result, the followability of the motor speed to the speed command is deteriorated. This delay in speed response is a problem especially when high operational continuity reliability is required when an instantaneous power failure or switching between multiple control systems occurs, such as control of an internal reactor pump. .

It is an object of the present invention to provide a control device for a variable speed drive system which has good followability to a speed command.

[0006]

A necessary value of an input or output current of a forward converter is calculated from an operation command signal of a motor including a speed command value and a load characteristic, and this is calculated by an integrator or a first-order delay in a voltage control unit. Set as the output value of the element.

[0007]

The time required for the output of the integrator or the first-order lag element in the voltage control unit to reach a stable value after the operation mode is changed is shortened, and the power injection / narrowing is accelerated.

[0008]

FIG. 1 shows a first embodiment of the present invention. Here, an induction motor connected to a voltage type inverter is used as a variable speed controlled electric motor load, and the load of the electric motor is such that the torque increases with the square of the speed like a pump.

The power circuit has a converter 2 which serves as a voltage source.
A three-phase AC input terminal of (three-phase bridge converter having six thyristors as main constituent elements) is connected to a three-phase AC voltage source 1 with a frequency f _AC , and an inductor 3 and a capacitor 4 are connected to a DC output terminal of the converter 2. Inverter 5 with variable frequency control by connecting a filter consisting of a series body (3 phase bridge inverter in which two groups of GTO thyristor and reverse polarity parallel body of diodes are connected in series for one phase)
The DC input terminal of is connected to both ends of the capacitor 4. The three-phase AC output terminal of the inverter 5 is connected to the input terminal of the induction motor 7.

Next, the frequency control system inputs the output of the speed command unit 11 to the rate of change limiter 12 to convert it into a speed pattern below the allowable maximum acceleration / deceleration, and inputs the speed pattern to the frequency command generator 13. Frequency command f according to speed pattern
* To generate the frequency command f * and the inverter controller 1
Enter in 4. The inverter control device 14 controls the thyristor switch forming the inverter 5 based on the frequency command f * as a so-called square wave inverter,
The frequency f * and the inverter 5 are applied to the output terminal of the inverter 5.
6 step three-phase AC voltage having an effective voltage proportional to the DC input voltage is generated.

On the other hand, in the voltage control system, the frequency command f * is input to the voltage command generator 15 and the AC output voltage / output frequency ratio (hereinafter abbreviated as V / f) becomes substantially constant according to the frequency command f *. to output a voltage command V _R as. The output of the DC transformer 10 connected to both ends of the capacitor 4 is input to the voltage detection circuit 23 which is a proportional coefficient multiplier, and the voltage detection circuit 2
The DC voltage feedback V _F is obtained as the output of No. 3, and the output of the subtractor 16 with the voltage command V _R as the positive input and the DC voltage feedback V _F as the negative input is input to the proportional integrator 17. (Here, the proportional gain K1 and the integral gain K2 of the proportional integrator 17 are positive values.) The output of the proportional integrator 17 is obtained by amplifying the deviation between the voltage command V _R and the DC voltage feedback V _F. As a current command I _R
Connect to the positive input terminal of. The current transformer 9 detects the three-phase AC current flowing in the connection line between the three-phase AC power supply 1 and the three-phase AC input terminal of the converter 2, and the current detection circuit 19 rectifies and smoothes the output of the current transformer 9. A direct current value corresponding to the effective value of the three-phase alternating current is obtained and is used as the input current feedback I _F. The input current feedback I _F is connected to the negative input terminal of the subtractor 18, and the output of the subtractor 18 is input to the proportional integrator 20. (Here, the proportional gain K3 of the proportional integrator 20 is
The integral gain K4 is a positive value. ) The output of the proportional integrator 20 is input to the inverse cosine converter 21, and the output of the inverse cosine converter 21 is input to the converter control device 22 as the control phase angle command of the thyristor forming the converter 2. The converter control device 22 controls the thyristor switch forming the converter 2 based on the control phase angle command of the thyristor, and generates a voltage waveform having a DC average voltage proportional to the output of the proportional integrator 20 at the DC output terminal of the converter 2. Let

In the operation when the DC voltage feedback V _F of this voltage control system is lower than the voltage command V _R , the output of the subtractor 16 becomes a positive value and the output of the proportional integrator 17, that is, the current command I _R increases. Do it. When the current command I _R becomes larger than the input current feedback I _F , the output of the subtractor 18 becomes a positive value, the output of the proportional integrator 20 increases, and the DC output terminal voltage of the converter 2 increases. On the other hand, in the operation when the DC voltage feedback V _F is higher than the voltage command V _R , the output of the subtractor 16 becomes a negative value and the output of the proportional integrator 17, that is, the current command I _R decreases.
If the current command I _R becomes smaller than the input current feedback I _F , the output of the subtractor 18 becomes a negative value, the output of the proportional integrator 20 decreases, and the DC output terminal voltage of the converter 2 drops. In this way, the voltage of the capacitor 4 is controlled by the operation of this voltage control system so as to match the value proportional to the voltage command V _R.

With the above configuration, the DC input voltage of the inverter 5 is normally controlled by the voltage control system of the converter 2 so that the DC input voltage of the inverter 5 becomes a voltage proportional to the output frequency of the inverter 5. Therefore, the AC output voltage of the inverter 5 is controlled. Inverter 5
The output voltage is proportional to the output frequency of V
It becomes a constant variable voltage variable frequency converter and the induction motor is controlled at a variable speed according to the speed command.

Further, while the converter and the inverter are stopped, the induced voltage of the induction motor 7 is detected by the AC transformer 24, and this output is input to the frequency detector 25 to restart the operation as the output. Get the speed command when.

The present invention is applied to the coefficient-added square calculator 27 and the switch 28 (the portion surrounded by the dotted line in FIG. 1).

In the present invention, the load of the electric motor is such that the torque increases with the square of the speed like a pump.
When a speed command is input to the coefficient squared computing unit 27, a current command value required to maintain the speed when the operation is restarted can be obtained as the output. The current command value required to maintain the speed at the time of restarting this operation is input to the switch 28, and is set as the output of the integrator of the proportional integrator 17 while it is stopped. This operation can be easily performed by software processing by a recent microcomputer.

According to FIG. 1, since the output of the proportional integrator when the operation is restarted is given a value necessary for maintaining the speed in advance, the delay in the response of the proportional integrator 17, mainly due to the integrator, occurs. The current that is shortened and required to maintain the speed is injected only with a response delay of the proportional integrator 20 for current control (generally 1/10 or less of the response characteristic of the proportional integrator 17 for voltage control). Therefore, the speed response characteristic of the induction motor 7 is improved. Further, due to the cooperation with the load, the speed response characteristic can be easily improved even when the response characteristic of the proportional integrator 17 for voltage control cannot be increased.

FIG. 2 shows a second embodiment of the present invention. Figure 1
Is different from the one-time differentiator 29, the coefficient unit 30, and the adder 3
This is the point where 1 is added. The purpose of adding these control elements is to correct the output of the coefficient-based square calculator 27 only for the current command at a constant speed, not for acceleration / deceleration. .

When the operation is restarted, the speed was being reduced due to the load resistance or the like as described above, but the acceleration / deceleration changes due to the constant speed command or acceleration. If the acceleration / deceleration changes, the output of the one-time differentiator 29 becomes a value proportional to the acceleration / deceleration.
The output of the one-time differentiator 29 is converted into an additional current component mainly determined by the inertia coefficient of the load, and added by the adder 31 to the current command at a constant speed. As a result, the accuracy of the output of the adder 31 is improved as compared with the case of only the coefficient squared calculator 27, and the effect of shortening the response delay of the proportional integrator 17 is greater than that of the method of FIG.

FIG. 3 shows a third embodiment of the present invention. Figure 1
2 is different from the coefficient squared calculator 27 and the switch 28.
Was a control element that worked only when was stopped,
Instead of them, a double differentiator 32, a coefficient unit 33, and an adder 34 are added. The purpose of adding these control elements is to obtain the same effect with respect to the change (acceleration / deceleration) of the speed command at the normal time. If there is a change in "change in speed command (acceleration / deceleration)" (change in acceleration / deceleration), 2
The output of the time differentiator 32 outputs a value corresponding to the amount of change in acceleration / deceleration when the change in acceleration / deceleration occurs. This is converted by the coefficient unit 33 into an additional current amount mainly determined by the inertia coefficient of the load, and added by the adder 34 to the integrator output preparation value of the proportional integrator 17. The integrator output preparation value is a result calculated by the integrator according to its input signal (output of the subtractor 16), and can be easily used in software processing by a recent microcomputer. As a result, the integrator of the voltage control proportional integrator 17 is set to an appropriate value according to the change in acceleration / deceleration even in the normal time, and the speed response characteristic can be improved.

FIG. 4 shows a fourth embodiment of the present invention. This embodiment is the second embodiment (FIG. 2) and the third embodiment (FIG. 3).
Are connected by a switch 35, and naturally have the characteristics of both.

In the above description, the induction motor connected to the voltage type inverter is used as the variable speed controlled motor load connected to the controllable voltage source, but the DC motor is driven at the variable speed by the voltage source. The same effect can be obtained when doing. Also, the same effect is obtained when the voltage control unit is configured by a first-order delay calculator instead of the integrator.

[0023]

According to the present invention, when a rapid change in the torque of the electric motor is required such as when the operation is restarted or when the speed command is changed, even if the response of the voltage control unit is slow, it is easy. With the addition of various functions, the required electric power can be quickly supplied, which is very effective in improving the speed response characteristics of the electric motor.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a block diagram of a third embodiment of the present invention.

FIG. 4 is a block diagram of a fourth embodiment of the present invention.

FIG. 5 is a timing chart of conventional control.

[Explanation of symbols]

1 ... Constant frequency AC voltage source, 2 ... Converter, 3 ... Inductor, 4 ... Capacitor, 5 ... Inverter, 7 ... Induction motor, 8 ... Load, 11 ... Speed command device, 13 ... Frequency command generator, 14 ... Inverter control Device, 15 ... Voltage command generator, 17 ... Proportional integrator, 27 ... Coefficient squaring calculator, 2
9 ... 1-time differentiator, 32 ... 2-time differentiator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noboru Azusa 5-2-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Omika factory

Claims (5)

[Claims] 1. A voltage source having an output end connected to a variable speed controlled motor load, a voltage detector for detecting an output voltage of the voltage source, a command value of the output voltage and an output of the voltage detector. A first subtractor that calculates a difference, a voltage control unit that receives the output of the first subtractor as an input and includes an integral element or a first-order lag element in its transfer function, and detects an input or output current of the voltage source A current detector, a second subtractor that calculates the difference between the output of the voltage control unit and the output of the current detector, a current control unit that receives the output of the second subtractor, and the current control In the control device of the variable speed drive system, which comprises the voltage source control unit that variably controls the output voltage of the voltage source with the output of the unit as the input, the input of the voltage source from the operation command signal of the electric motor including the speed command value and the load characteristic. Or corresponding to the required value of output current That the current command calculation portion for calculating a value provided, the control device of the variable speed drive system and sets the output of the current calculation unit as the output value of the integrator or a first-order lag element in the voltage control unit. 2. A method according to claim 1, wherein a value corresponding to a required value of an input or output current of the voltage source is calculated as a method of calculating a speed command of a variable speed controlled motor and a timing at a time when an operation mode changes. A control device for a variable speed drive system that calculates from a signal and a load characteristic. 3. A speed command of a variable speed controlled motor and a first-order differential coefficient of the speed command as a method of calculating a value corresponding to a required value of an input or output current of the voltage source. And a control device for a variable speed drive system that is calculated from a timing signal and a load characteristic at the time when the operation mode changes. 4. The method according to claim 1, wherein a value corresponding to a required value of the input or output current of the voltage source is calculated from a second-order differential coefficient of a speed command of a variable speed controlled motor and a load characteristic. A control device for a variable speed drive system adapted to perform calculation. 5. The method according to claim 1, wherein a value corresponding to a required value of the input or output current of the voltage source is calculated from the second-order differential coefficient of the speed command of the variable speed controlled motor and the load characteristic. A control device for a variable speed drive system, wherein the obtained value is added to the integral value of the integrator of the voltage control unit at that time for calculation.