SU1539952A1 - Ac electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in asynchronous electric drives of hoisting-and-transport machines. The aim of the invention is to expand the range of rotational frequencies in which the dependence of the stiffness of the mechanical characteristics does not depend on the magnitude of the load to increase reliability by reducing the inrush moment. The AC drive contains induction elements 2 and a thyristor switch 3 connected to the rotor circuit of the induction motor 1. The feedback signal is the sum of the voltage across the motor rotor and the voltage drop across the induction element 2. The reference block 9 forms three voltages that compared with the feedback signal on one of the comparison blocks 10-12. Depending on the ratio of the feedback signal and the setting voltage, thyristors 4-6 of the switch are controlled. In this case, one of the thyristors operates in a pulse-key mode, while the others are on or off. 2 Il.

Description

The invention relates to electrical engineering and can be used in asynchronous electric drives of hoisting-and-transport machines.

The purpose of the invention is to expand the range of rotational frequencies in which the rigidity of the mechanical characteristic does not depend on the magnitude of the load, and to increase reliability by reducing the torque spikes

FIG. 1 is a block diagram of an AC drive; in fig. 2 - mechanical characteristics.

The variable-frequency drive contains an induction motor 1 with a phase rotor, three induction elements 2, switch 3 made on k-b thyristors interconnected, for example, in a triangle (thyristors can be connected in a bridge circuit). Some of the terminals of the inductive elements are connected to the terminals of the respective phases of the rotor winding of the induction motor 1, and the other terminals of the induction elements are connected to the connection points of thyristors 4-6. The control electrodes of the thyristors k-6 are connected to the outputs of the corresponding drivers 7 of the control pulses, the terminals of the phases of the rotor winding are connected to one input of the adder 8, the second input of which is connected to the terminals

ABOUT

From this equation (3) in order

induction elements 2. The drive also contains block 9 of task c, so that the signal at the output of the adder is three outputs, blocks 10-12 comparisons, the first inputs of which are connected to the output of the adder 8, and the second input of each comparison block is connected to the corresponding input of block 9 tasks 4d Outputs Comparison units connected

It is directly proportional to the EMF of the rotor.

(four)

Chzch, ge kzz

r we4

Here

+

z ... .- + X2

respectively to the inputs of the formers 7.

FIG. 2, the following designations are introduced: 13 — mechanical characteristic of the electric motor 1 when all three thyristors are turned on; 14 - the characteristic when turning on two thyristors; 15 - characteristic when turning on one thyristor; 16 is the value of the task, 17 is the shutdown level of the comparison unit 10; 18 - the level of its inclusion; 19 —the value of the task; 20 — the level of shutdown of the comparison device 11; 21 - the level of its inclusion; 22 - the value of the task; 23 — level of shutdown of comparison unit 12; 2k - the level of its inclusion.

The drive works as follows.

Unit 9 of the task generates three voltages of the task U,, U, and moreover, and U.

A signal proportional to the rotor voltage is taken from the rotor winding:

k (Up lgs1 (Et - IpZg), (I)

where kf is a constant coefficient; Up is the linear voltage of the rotor winding;

E - phase EMF of the rotor; 1p - rotor current; Z. - phase impedance

rotor.

A signal proportional to the voltage drop across the IC phase is removed from the induction resistance (IC):

 U “c u c.

(2)

de t u

k2 j "c

Z

is

constant coefficient; the voltage across the phase winding of the induction resistance;

impedance of the phase of the IC "signal at the output of the adder

U k, Up + k2lb ,, c - 1 „2E f 41 zwc. (3)

ABOUT

From this equation (3) in order

To be a signal at the output of the adder

so that the signal at the output of the adder was

It is directly proportional to the EMF of the rotor.

(four)

Chzch, ge kzz

r we4

would sig

Here

so that the signal at the output of the adder was

+

z ... .- + X2

Lp is v-cs –m where Rp is “the active resistance of the rotor of the engine;

X „Р

reactive resistance of the rotor when the motor slides;

is “with

0

five

- active and reactive impedances of the IC, which are nonlinear functions of slip and rotor current. Due to the fact that both Z ,, and Z depend on the slip of the electric motor, the equality of and) is strictly fulfilled only at the same speed. But since the dependences of 2E and 2IS on the slip are of the same nature — as the slip decreases, both Zg and Z decrease,

This approximate equality between the right and left sides of equation (4) is maintained regardless of the speed value. Therefore, the signal at the output of the adder is proportional to the EMF of the rotor in a wide range of speeds and loads, and, consequently, the rigidity of the mechanical characteristics varies slightly.

When motor 1 is turned on in the network, the signal of the adder 8 is greater than any of the reference voltages produced by block 9. Blocks 10-12 comparisons are triggered, and all three thyristors 4-6 and switch 3 turn on. The motor accelerates according to characteristic 13 with increasing rotor EMF speed and the signal of the adder U is reduced. When the signal reaches the level 17, the comparison device 10 is activated and the thyristor 4 is turned off. If the operating point lies between the characteristics 13 and 14, then the thyristors 5 and 6 are constantly on, and the thyristor 4 is turned on when the speed decreases under the action of the load torque to level 16 and off when the speed increases to level 17 provides an average response of 16. If the operating point lies to the left of characteristic 14, then the motor accelerates after the thyristor 4 is turned off. When the speed reaches level 20, the comparison device 11 is triggered and the thyristor 5 is turned off. In case the operating point lies between characteristics 14 and 15, the thyristor 6 Constantly on, thyristor 5, turned on and off, provides characteristic 19, while electromagnetic moment throws are limited by characteristic 14. If the operating point is to the left of characteristic 15, then thyristors 4 and 5 are turned off, and thyristor 6, the operation is pulsed -key mode, provides an average response of 22, while the moment throws are limited by the response of 16.

i i

Thus, the use of a voltage on an induction element as a signal proportional to

39952

6

to that

ten

15

current, leads to the fact that the feedback signal remains proportional to the rotor EMF, regardless of the rotational speed and load of the engine, which means almost constant rigidity of performance. The introduction of an additional two blocks of comparison and two pulse formers makes it possible to control the thyristors of the switches separately and, consequently, reduce the electromagnetic torque of the motor.

Claims (1)

Invention Formula 0 five 0 0 An AC drive containing an asynchronous motor with a phase rotor, three inductive elements, each of which is connected to the output of the corresponding phase of the rotor winding of the induction motor by a single terminal; driver of control pulses with three inputs and three outputs, each of which is connected to the control input of one of the thyristors of the switch, an adder, one input to It is connected to the terminals of the phases of the rotor winding, and the output is connected to one input of the comparison unit, another input connected to the output of the reference block, characterized in that, in order to expand the range of the rotational speed, in which the rigidity of the mechanical characteristic does not depend on the load torque, and increase reliability by reducing the inrush moment, the leads of the induction elements are provided with clips for connecting to the second input of the adder, and 5 task block — two outputs and two comparison blocks are entered, the first inputs of which are connected to the output of the adder, the second input of each input comparison block to one of the additional outputs of the reference block, and the outputs of the comparison blocks are connected to the inputs of the control pulse former. 5 i / J Ala