SU1377997A1 - Apparatus for measuring angular speed of d.c.el motor - Google Patents

Abstract

The invention relates to electrical engineering and can be used in direct current drives. The aim of the invention is to improve accuracy. The device contains a voltage relay, the coil 6 of which is connected to the terminals of the motor winding 1. Block 5 compensating for the reaction of switching currents is made in the form of a functional converter, whose characteristic is reversing the magnetization curve of the electric motor in the range of the reaction of switching currents. In this device, the difference between the corrected magnitude of the voltage on the motor and the voltage drop in its core circuit is entered as a feedback signal over the frequency of rotation. 3 il. L

Description

WITH

-si

one

so; about M

Phie. one

The invention relates to electrical engineering, namely, electric direct current drives with feedback on the frequency of rotation of electric motors, mainly with unregulated excitation flow.

The purpose of the invention is to improve the accuracy of the device.

Fig, 1 shows a functional diagram of the device; Fig. 2 shows the magnetization curve of an electric motor; on fig.Z - the characteristic of the functional converter.

A device for determining the frequency of rotation of a DC motor 1 (i | mr, l) contains sensors 2 voltage and a sensor 3, the outputs of which are connected respectively to cyMMHpyromeNfy and reading the inputs of the comparison unit 4, as well as block 5 for switching reaction performance currents, the input of which is connected to the current sensor 3 is a core, and the output to the summing input of the comparison unit 4, performed as a functional converter, the characteristic of which is inverse to the magnetization curve of the electric motor in the range of the switch reaction Ion currents, as well as a voltage relay, the coil 6 of which is connected to the terminals of the motor winding, and its closing contact 7 is connected to the power supply circuit of the functional converter. The output of the comparator unit 4 is connected to the input of the rotational speed controller 8, to which the output of the speed limiter is also connected (signal oz,) and the output of the rotational frequency controller 8 is connected to the input of the current regulator of the slave control system (not shown)

When determining the frequency of rotation of an electric motor using a tachometer bridge, the dependence is realized

E G-Fbe and - IR,

(ABOUT

where Cg is constructively constant; P - voltage on the engine; , 1 - motor current; R is the resistance of the root chain

Electric motor, hence the rotational speed

„And - IR, (2)

- SeF

tfe ,, the frequency of rotation of an electric motor at a constant excitation flow is proportional to its emf,

At the same time, for electric motors of direct current, especially for uncompensated machines, the main field of the machine changes under the influence of its switching reaction field, demagnetizing the main flux of the machine (engine) during accelerated switching, which the machine is usually tuned to,

The demagnetized action of the switching current reaction field is also characteristic of compensated machines, where the usual core reaction does not appear at all.

It is known that the ampere-turns of the switching current reaction field are determined from the ratio

AWp 0.12 - 0.2-AS-b

to

(3)

25

thirty

35

0

five

0

where AS is the linear load of the machine; bj, is the width of the commutation zone

The magnitude of the linear load of the AS machine and the width of its switching zone b are determined according to the manufacturers of the machines and lie respectively within (100-600 A-CT / cm) and (4-7 cm)

With a nominal load of the machine, the demagnetizing effect of the switching reaction field (in amperes) can reach 10-15% of the magnetizing force of the main pole winding, and in the flow for a full magnetic system, it can weaken the flow to 5-10%. the unsaturated magnetic system and double operating overloads of the electric motor, the main field of the machine is reduced by up to 40% or more due to the action of the switching current reaction.

When the motor goes over, for example, in the deceleration mode to the generating mode, with the same accelerated switching, the main field is magnetized, which is insignificant for a saturated magnetic system,

In view of the demagnetizing effect of the switching current reaction field, the rotation frequency

03

(four)

and - IR

WITH()

where dF is the decrease in the excitation flux determined by the magnetization curve of the machine, due to the demagnetizing ampere-turns of the switching current reaction, calculated from the relation (3) Fig2.3.

Consequently, to obtain a more accurate value of the motor's frequency of rotation measured by the value of its motor, it is necessary to correct the value of its excitation flux which is unchanged by the value of lF, depending on the demagnetizing ampere-turns of the switching current, and the load current of the machine.

The device works as follows.

At an ideal idle speed of the electric motor 1, the output voltages of the current sensor 3 and block 5 are equal to zero, and the rotational speed of the electric motor is proportional to the value of the voltage supplied to the electric motor.

We believe that the load on the motor shaft 1 appeared, and the block 5 was not involved

In this case, the voltage at the output of sensor 2, the voltage is algebraically summed with the value of the voltage at the output of current sensor 3, proportional to the voltage drop IR in the motor circuit

If the reaction of the switching currents were absent and the magnetic flux of the machine at the load on the motor shaft remained unchanged, the motor emf value and proportional to the voltage value at the output of the comparison unit 4 would display the rotation frequency of the motor.

However, due to the effect of the switching current of the switching current of the electric motor 1, its magnetic flux decreases, as a result of which the rotation frequency of the electric motor increases and the EMF remains unchanged (as in the case of the usual regulation of the rotation frequency by changing the excitation flow of the electric motor)

Consequently, when the block 5 is not activated, the measurement of the frequency of rotation of the electric motor 1 according to its EMF is inaccurate, increased

five

0 5

About 5

about

five

about

five

due to the weakening of the motor flow

When block 5 is put into operation, simultaneously with an increase in the load of the electric motor 1 and a corresponding decrease in its excitation flow, the output of block 5 appears a voltage proportional to the increment of the emf of the engine and corresponding to the increment (decrease) of its excitation flow (fig.2). As a result, the total value of the signal at the input of the comparator unit 4 increases to a value proportional to maintaining the rotational speed of the electric motor at such a level as if the reaction of the switching currents did not act.

Consequently, at the output of the comparator unit 4, the voltage also increases,

Since the output of the comparator unit 4 is connected to the input of the regulator 8 as a feedback signal, and the driving signal at the input of the regulator 8 is assumed to be unchanged, the resulting signal at the output of the regulator 8 is reduced by an amount that compensates for the increase in the frequency of rotation of the electric motor due to demagnetizing action switching current reactions.

In addition, the output signal of the block 5 can be fed in opposite with the master signal to the input of the speed regulator 8. In this case, the output of block 5 is not connected to the input of block 4 of comparison.

If a manual motor field attenuation mode is provided, then the parameters of the functional converter 5 can be adjusted accordingly, for example, the characteristic of its nonlinearity can be changed (no adjustment is shown).

If the motor of the electric motor 1 is energetically and schematically provided, then to eliminate the error introduced in this mode, due to the effect of the functional converter, a voltage relay is provided, the setting for triggering which on the inverter and turning on the power supply of the functional converter 5 is determined by the voltage value on an electric motor that is superior in stand-down mode

Fn

F,

pw

Av / res

FIG. 2

-4W

II

II 7

11, |.

Iav / ptrrv

Figz

Claims (1)

Claim A device for determining the rotational speed of a DC motor, comprising a voltage sensor-15 and a current sensor, the outputs of which are connected respectively to the summing and subtracting inputs of the comparison unit, as well as the compensation unit. action of the reaction of switching currents, the input of which is connected to the armature current sensor, and the output to the summing input of the comparison unit, characterized in that, in order to improve accuracy, a voltage relay is introduced into it, and the compensation unit for the action of the response of switching currents is made in the form of a functional a converter whose characteristic is the inverse of the magnetization curve of the electric motor in the area of switching currents, while the voltage relay coil is connected to the terminals of the armature winding of the electric motor, and it closes, first contact is included in a functional power converter circuit. FIG. 2 Fig δ