JP2626173B2 - Speed fluctuation suppression control method for induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a control method for suppressing speed fluctuation of an induction motor due to factors such as load fluctuation when performing variable speed control of an induction motor by a power converter such as an inverter device using a semiconductor switching element such as a thyristor or a transistor. About. In the drawings, the same reference numerals indicate the same or corresponding parts.

[Prior art]

FIG. 2 is a block diagram schematically showing the configuration of this type of speed control system of the induction motor. In the figure, 1 is a speed setter for giving a speed set value NS, 11 is an adder for obtaining a speed deviation 11a as a difference between the measured speed value NS and a detected value N of the rotation speed of the motor, and 2 is a speed setter for this speed deviation 11a. A so-called PI operation is performed on the deviation 11a so that the deviation
The speed controller 3 for outputting as a is a current converter for causing the induction motor to generate a torque τM proportional to the torque command 2a. In this example, the speed controller 3 comprises a so-called vector control type inverter device. τL is a load torque applied as a disturbance to the electric motor, 4 is an integrating circuit equivalently representing the electric motor mechanical system, and J is an integral time constant corresponding to a rotational inertia moment of the electric mechanical system. Reference numeral 13 denotes an adder for virtually calculating the difference between the motor generated torque τM and the load τL, which is the acceleration torque applied to the motor mechanical system 4, and N as the output of the motor mechanical system 4 is N , The speed detection value as the resulting rotational speed of the motor. Generally, in this type of motor, if the load torque τL changes in a step-like manner while the motor is rotating at a certain constant speed, the motor rotation speed N becomes dN / dt = (τM−τL) / J
To change. Thereafter, the rotation speed N is taken into the control device as a detected speed value, and a deviation amount 11a between the set value NS of the speed setting device 1 and the detected speed value N becomes an input to the speed control device 2. A torque command 2a as an adjustment amount according to the proportional gain K and the integration time T is output, and as a result, the function of changing the motor generated torque τM so that the detected speed value N matches the set speed value NS is performed. Will be FIG. 3 is a waveform diagram showing the movement of each part when the load torque τL is applied. At the time of applying and removing the load torque τL, it fluctuates by the motor rotation speed ΔN. The magnitude of ΔN is proportional to the proportional gain K and the integration time T of the speed controller 2.

[Problems to be solved by the invention]

As described above, in the conventional speed control device, the speed fluctuates when the load torque τL is applied. However, in a facility such as a rolling plant where a large number of motors are coupled through a load, the speed of one motor is reduced. If it fluctuates, extra torque will be applied to the material to be rolled, causing elongation, abrasion, etc., and it must be disposed of as a defective product.
There is a problem that leads to a decrease in product yield. Therefore, an object of the present invention is to provide a control method capable of promptly detecting a change in load torque of an induction motor and suppressing the amount of change in speed.

[Means for Solving the Problems]

In order to solve the above-mentioned problem, the method of the present invention is based on the following method: "The difference (speed deviation 11a, etc.) between the speed setting value (NS, etc.) of the induction motor and the detected speed value (N, etc.) A speed controller (2 or the like) that outputs a torque command (2a or the like) obtained by performing a PI operation, and a current converter (3 or the like) that generates a torque proportional to the torque command to the induction motor. In the speed control device, an estimated value (or the like) of the rotation speed of the induction motor when the load torque applied to the induction motor is ignored (via the mechanical system model 8 or the like) from the torque command is obtained. 6), an estimated decrease (6a or the like) in the rotational speed of the induction motor based on the load torque is determined as the difference between the estimated rotational speed and the detected speed value. Gain generator 7, etc. Gain equivalent) signal proportional to (load estimated torque , Etc.) (via the adder 9 or the like) as a compensation for the load torque.

[Operation]

A motor and mechanical system model is provided inside the control device, the load applied torque is directly estimated from the speed controller output signal and the detected speed value, and the result is added to the output of the speed controller to compensate for the speed. It is intended to suppress the speed fluctuation amount regardless of the response speed of the controller.

【Example】

FIG. 1 is a block diagram of a control system as an embodiment of the present invention and corresponds to FIG. 1 ~ 4,11,13
Are the same as those of the prior art described in FIG. The components added in the present invention are 6 to 9,12, of which 6 to 8,12 are internal models 10 for load torque estimation.
Is composed. That is, 6 is an adder for calculating a deviation 6a between the detected rotational speed N and the estimated internal speed (that is, a decrease in the estimated speed based on the application of the load torque τL) 6a is the deviation
Proportional to 6a as (G _M times) the value, load estimated torque The gain generator 9 calculates the load estimation torque. Is added to the torque command 2a as the output of the speed controller 2, and the load torque Is an adder that compensates for 12 is the load estimated torque from the added value of the adder 9 Is an adder for obtaining a torque command 2a-equivalent value by subtracting the same. 8 is a block called a mechanical system model, and is an integral element having a gain KC equal to the current converter 3 and a time constant J equal to the motor mechanical system 4, From the torque command 2a as an output of 12, an estimated speed value when no load torque τL (that is, no disturbance) exists is output. In other words, if the time constant J of the electric motor mechanical system 4 and the time constant J of the mechanical system model 8 in the internal model 10 are tuned to be the same, the amount of matching between the detected speed value N and the estimated speed value is obtained. Is the estimated load torque Corresponds to the actual load torque τL, and compensates for this, so that compensation independent of the response of the speed controller 2 is possible.

【The invention's effect】

According to the present invention, the speed deviation 11a as the difference between the speed set value NS of the induction motor and the detected speed value N is set to 0,
A speed controller 2 for an induction motor including a speed controller 2 for outputting a torque command 2a obtained by performing a PI operation on the deviation 11a, and a current converter 3 for causing the induction motor to generate a torque τM proportional to the torque command 2a. An estimated value of the rotational speed of the induction motor when the load torque τL applied to the induction motor is ignored from the torque command 2a via the mechanical system model 8 is obtained. And an estimated decrease 6a in the rotational speed of the induction motor based on the load torque τL as a difference between the estimated speed 6 and the detected speed N. The estimated decrease 6a is proportional to the estimated decrease 6a by the gain GM of the gain generator 7. Estimated load torque as signal Is added to the torque command 2a via the adder 9 as a compensation amount of the load torque. Therefore, when a small speed fluctuation occurs due to the application of the load torque, the load torque can be estimated and calculated almost at the same time, and the speed adjustment can be performed. Therefore, it is possible to control the generated torque of the electric motor required to maintain the speed regardless of the motor, and as a result, it is possible to suppress speed fluctuation.

[Brief description of the drawings]

FIG. 1 is a control block diagram as an embodiment of the present invention, FIG. 2 is a conventional control block diagram corresponding to FIG. 1, and FIG. 3 is a waveform diagram showing a response example when a load torque is applied in FIG. It is. 1: Speed setting unit, 2: Speed controller, 2a: Torque command, 3: Current converter, 4: Motor mechanical system, 6, 9, 11, 12, 13: Adder, 7: Gain generator, 6a: Estimated speed reduction, 8: mechanical model, 10:
Internal model for load torque estimation, NS: speed setting value, N: speed detection value,: speed estimation value, τM: motor generated torque, τL:
Load torque,

Claims (1)

(57) [Claims] 1. A speed controller for outputting a torque command obtained by performing a PI operation on a difference between a speed setting value and a speed detection value of an induction motor so as to make the difference zero, a torque proportional to the torque command. In the speed control device for an induction motor including a current converter that causes the induction motor to generate, an estimated value of a rotation speed of the induction motor when a load torque applied to the induction motor is ignored from the torque command, An estimated decrease in the rotational speed of the induction motor based on the load torque is calculated as a difference between the estimated rotational speed and the detected speed. A signal proportional to the estimated decrease in speed is used to compensate for the load torque. A speed fluctuation suppression control method for an induction motor, wherein the method is added to the torque command as a minute.