JPH036748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for an induction motor.

A conventional device of this type is shown in FIG.

In the figure, 1 is a DC power supply, 2 is a transistor,
An inverter main circuit that converts DC power into AC power is composed of capacitors, etc., 3 is an induction motor to be controlled, 4 is a speed detector such as a pilot generator, 5 is a control device for the induction motor 3, and is composed of the following: has been done. 6 is an operational amplifier that compares the reference speed ω _n ^* and the actual speed ω _n ; 7 is an operational amplifier 6
A circuit that generates _the primary reference current I ₁ ^* of the induction motor 3 from the output I 2 ^* , the actual speed ω _n , and the magnetic flux reference current I ₀ ;
8 is an operational amplifier that compares the primary reference current I ₁ ^* and the actual primary current I ₁ , and 9 is the voltage output from the actual primary current of the U phase and W phase.
10 is a base drive control circuit for a transistor in the inverter main circuit 2; 11 is a reference speed generation circuit; and 12 is a magnetic flux reference current generation circuit.

Next, the operation will be explained. When controlling the speed of the induction motor 3, a reference speed ω _n ^* is generated by the reference speed generation circuit 11, and the speed deviation between this reference speed ω _n ^* and the actual speed ω _n from the speed detector 4 is calculated by the operational amplifier 6. Amplify it by , and use it as the secondary reference current I ₂ ^* . The primary reference current I ₁ ^* is calculated and generated by the calculation circuit 7 from this secondary reference current I ₂ ^* , the magnetic flux reference current I ₀ and the actual speed ω _n . The deviation between this primary reference current I ₁ ^* and the actual primary current I ₁ is amplified by an operational amplifier 8 and is applied to a base drive control circuit 10 that controls transistor drive of the main circuit 2 . The base drive control circuit 10 controls the voltage generated by the main circuit 2 to control the speed of the induction motor 3.

Here, the calculation circuit 7 performs the following calculations based on each variable.

I ₁ ^* =√ ₂ ^*2 + ₀ ² sin {(ω _s + ω _n )t+} ... However, ω _s is the slip frequency corresponding to the torque of the induction motor 3, and the secondary reference current I ₂ ^* and the magnetic flux component From the reference current I ₀ , ω _s =K·I ₂ /I ₀ where K is a constant.

Also, is the phase difference between the magnetic flux reference current I ₀ and the actual primary current I ₁ , and is the phase difference between the secondary reference current I ₂ ^* and the magnetic flux reference current I ₀
It can be found from the formula = tan ^-1 I ₂ /I ₀ .

Conventional speed control devices for induction motors are configured to control using a primary reference current based on the speed frequency of the actual speed ω _{n .}
The problem was that disturbances caused problems in control stability.

This is because a ripple voltage is generated in the speed detector 4, so ω _n becomes a disturbance and affects the frequency component of the above equation, and as a result, the primary reference current I ₁ ^*
The control system became unstable and lost its stability.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and when the deviation between the reference speed and the actual speed of the induction motor is large, the primary reference current is calculated based on the speed frequency of the reference speed. It is an object of the present invention to provide a speed control device for an induction motor that can perform stable control.

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 2, 13 is an adder that adds the reference speed ω _n ^* and the secondary reference current I ₂ ^* , and 14 is the actual speed ω _n
an adder that adds coefficients to , 15 is a coefficient generator, 16
is a comparison circuit that compares the outputs of the adder 13 and the adder 14, and operates the output relay 17 when the output of the adder 14 is larger; 17 is an output relay that converts the speed input of the calculation circuit 7 into the actual speed _ω ^* to reference speed ω _n
Switch to 18 is a control circuit.

Next, the operation of the embodiment will be explained. The operation when controlling the speed of the induction motor 3 is similar to that of the conventional device, but the calculation circuit 7 calculates the primary reference current I ₁ ^* using the reference speed ω _n ^* instead of the actual speed ω _n ^*.
The difference is that it uses That is, the following arithmetic expression is obtained.

I ₁ ^* =√ ₂ ^*2 + ₀ ² sin {(ω _s + ω _n ^* ) t +}... However, the value obtained by adding the reference speed ω _n ^* and the secondary reference current I ₂ ^* to the adder 13, and the addition The comparator circuit 16 compares the value obtained by adding the slip limit value to the actual speed ω _n in the comparator 14, and the adder 1 adds the slip limit value to the actual speed ω _n .
When the value of 4 is larger than the value of the other adder 13, the output relay 17 is operated and the primary reference current I ₁ ^*
is performed using the above formula, but the value of adder 14 is
If the value is smaller than 3, the formula used in the conventional device is used. Therefore, output relay 17 does not operate.

In other words, when the deviation between the reference speed ω _n ^* and the actual speed ω _n of the induction motor 3 is greater than a predetermined value, it is determined that the actual speed ω _n includes a disturbance, and the calculation circuit 7 calculates I ₁ ^* = √
I ₂ ^*2 + I ₀ ² sin {(ω _s + ω _n ^* ) t+}, and if the deviation is less than a predetermined value, the calculation circuit 7 determines that the disturbance included in the actual speed ω _n can be ignored. I ₁ ^* = √
Perform I _{2 *2} + I ₀ ² sin {(ω _s + ω _n )t+}.

Note that the actual speed ω _n is added to the amplitude component of the primary reference current I ₁ ^* .
Although the secondary reference current I ₂ ^* is included as a parameter, the disturbance of the actual speed ω _n that affects around this time can be ignored.

Therefore, during steady state, the influence of the ripple voltage of the speed detector 4 is reduced and the stability of the control system is improved.

Furthermore, by using the coefficient generator 15 in the predetermined value that is determined by the comparison circuit 16, there is an effect that the slip limit value can be taken into account.

In addition, in the above embodiment, the case of transistor drive control of the inverter main circuit was explained.
Even when applied to other main circuit electric switches, the same effects as in the above embodiment can be obtained. Furthermore, it goes without saying that similar effects can be achieved in other frequency conversion devices such as cycloconverters.

As described above, according to the present invention, when the deviation between the reference speed and the actual speed of the induction motor exceeds a predetermined value, the primary reference current is calculated based on the speed frequency of the reference speed. This has the effect of providing a highly stable induction motor speed control device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional speed control device for an induction motor, and FIG. 2 is a block diagram showing a speed control device for an induction motor according to an embodiment of the present invention. In the figure, 3 is an induction motor, 4 is a speed detector, 6 is an operational amplifier, 7 is an operational circuit, 8 and 9 are operational amplifiers, 10 is a base drive control circuit, and 11
12 is a reference speed generation circuit, 12 is a magnetic flux reference current generation circuit, 13 and 14 are adders, 15 is a coefficient generator,
16 is a comparison circuit, 17 is an output relay, and 18 is a control device. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first operational amplifier that outputs a secondary reference current by comparing the actual speed of the induction motor detected by the speed detector and the reference speed output from the reference speed generation circuit, and a first operational amplifier that outputs a secondary reference current by comparing the actual speed of the induction motor detected by the speed detector, and the A first adder that adds the reference speed, a second adder that adds the actual speed and the coefficient output from the coefficient generator, and an output of the first adder and the second adder. a comparison circuit that compares the outputs and outputs an output when the latter output is larger than the former output; a relay that receives the output of the comparison circuit and switches the supply path for the actual speed to the supply path for the reference speed; and the secondary reference. a calculation circuit that calculates and generates a primary reference current using the current, the above-mentioned actual speed or the above-mentioned reference speed, and the magnetic flux reference current output from the magnetic flux reference current generation circuit; A speed control device for an induction motor, comprising: a second operational amplifier that amplifies a deviation from the current; and a signal output circuit that outputs a speed control signal for the induction motor based on the output of the second operational amplifier.