RU1770785C - Induction motor electromagnetic moment determining device - Google Patents

Abstract

SUMMARY OF THE INVENTION: the device comprises phase voltage sensors (1), phase current sensors (2), a multiplication unit (3), an induction motor (4), a magnetization current calculation unit (5), an aperiodic link (6). and a unit for calculating the current components of the current in the orthogonal coordinate system. (7). 1-5-7-6-3. 2-5-7-3, 2-7-3.2 ill. (L C VI 8 3 01

Description

The invention relates to electrical engineering and can be used in the development of high-quality control systems for variable-frequency asynchronous motors, as well as in those cases where it is required to measure the moment broken by an induction motor.

When determining the electromagnetic moment, the conditions were set: the moment is determined without the integration operation, since the latter leads to the accumulation of errors and the moment is determined without using the active resistance of the engine, since it changes significantly when the thermal state of the engine changes.

The electromagnetic moment of an induction motor is determined by a vector by the product of one of the following pairs of vectors: flux linkage of the rotor, stator, air gap, stator current and rotor current, the stator current vector (current sensors) is most simply determined. Below we will prove the possibility of determining the flux linkage of the rotor without the use of the integration operation, and therefore it is advisable to determine the torque of an induction motor by the expression

(li XVu),

where Zp is the number of pole pairs:

And is the stator current;

$ 2 rotor flux linkage;

Xm, X2 are the inductance in the magnetization circuit and rotor, respectively.

The classical method for determining the moment in a book (KP Kovach, I. Pay Transients in AC machines, state energy publishing house, 1963, M) according to the method described in this book, a device for measuring the moment (I. Rau and etc. An instrument for measuring the moment of an AC motor, there is a translation into Russian of the language No. Ts-29558.1974). In this device, the magnetic flux is determined by integration, and the motor torque is determined by the vector multiplication of the magnetic flux by the corresponding motor currents. However, this device has low stability over time and low accuracy when determining the torque at low frequencies. Indeed, the magnetic flux Φ is determined by the expression:

&} (U-L, R) dt,

where R is the stator resistance.

In order to ensure that the integrator readings correspond to the magnetic flux value, the integrator should calibrate the mode before measurements. Calibration consists in switching the integrator into adder mode and applying voltage through the voltage channel and current channel by changing the value of the resistor along the channel

0 voltages, ensure that the voltage at the output of the adder takes the maximum permissible value, then, by changing the value of the resistor along the current channel, they achieve that the voltage at the output 5 of the integrator is equal to zero. If we now put the adder into integration mode and apply signals proportional to voltage and current to the input, then at the output of the integrator we obtain the value of the magnetic flux.

However, with this determination method, the magnitude of the magnetic flux has low stability over time. This is due to the fact that the active resistance of the engine

5, depending on its mode, can vary significantly (1.2-1.8. Times), which will lead to imbalance. In steady state, the integrand will not be zero and will begin

0 integration process, which will lead to low stability of determining the moment in time.

An additional source of errors appears in frequency regulation, when it is required to determine the torque at lower frequencies. In this case, the component IR becomes comparable and the smallest changes in resistance caused by both temperature changes and nonlinearity of the magnetic circuits lead to errors in determining the moment, in the case of nonlinear dependences between voltage and current, scale factors along current channels change and voltage, calibration of the device, setting of scale factors is performed for one level of current and voltage, changing the modes at which the calibration was carried out leads to

0, a certain voltage appears at the input of the integrator, which, accumulating over time, leads to errors in determining the moment.

Thus, the described device is not

5 can be used as sensors in control systems, as it has a low time stability.

A device for measuring

electromagnetic torque of the electric motor (ed. St. No. 883675) published in

Byul, No. 43.1981)) this device allows to determine the electromagnetic moment of the motor from the rotor current and flux linkage of the air gap.

A disadvantage of this device is. that flux linkage is determined by means of a measuring winding located in the stator winding region, followed by signal integration. This requires disassembly and alteration of standard engines, which is undesirable. In addition, the integration operation reduces accuracy due to the departure of integer zeros.

A device is known for measuring the electromagnetic moment of an induction motor (ed. St. ISfe 976313, published in bull no 43, 1982). This device is closest to the proposed invention and therefore it is adopted as a prototype. This device by the stator current and stator flux linkage allows determining the electromagnetic moment of the motor. The device does have a simple block diagram, since the input signals of this device are stator current and stator flux linkage. However, the simplicity of the structure of this device is explained by the fact that the authors did not disclose the blocks that determine the flux linkage. As is known, flux linkage can be determined either by placing a Hall sensor in the gap of the electric motor, or a measuring winding, or using a special EMF measuring circuit (I.I. Epshtein Automated AC Electric Drive M., Energoizdat, 1982) with subsequent integration of this signal.

If this structural diagram is disclosed, the input units are determined by flux linkage, then the device adopted as a prototype will have low accuracy due to the integration operation.

The purpose of the invention is to improve accuracy.

This goal is achieved by the fact that a magnetization current calculation unit, an aperiodic link and a current component of the current are calculated in the orthogonal coordinate system connected to the rotor, the first output of which is connected through the aperiodic link to the first input of the multiplication unit, and the second, respectively to the second input of the multiplication unit, while the phase voltage sensors are connected to the first input of the magnetization current calculation unit, the output of which is connected to the first input of the unit

calculating the current components of the current in the orthogonal coordinate system associated with the rotor, the second input of which is connected to the phase current sensors and

the second input of the magnetization current calculation unit.

The mentioned essential features distinguish the claimed solution from the prototype and therefore it meets the criterion of novelty. Significant features in the present invention provide new unexpected properties that can significantly improve the accuracy of measurement,

In FIG. 1 shows a functional diagram of a device; in FIG. 2 is a vector diagram of an induction motor.

A device for determining the electromagnetic moment of an induction motor includes phase voltage sensors 1, phase current sensors 2, a multiplication unit 3 and an induction motor 4. Into the device for determining the electromagnetic moment of an induction motor are introduced

unit for calculating the magnetization current 5. an aperiodic link 6 and a unit for calculating the current components of the current in the orthogonal coordinate system associated with stream 7. Moreover, the output of the phase sensors

voltage 1 is connected to the first input of the magnetization current calculation unit 5, the output of which is connected to the first input of the current component component calculation unit 7 in the orthogonal coordinate system;

connected to the rotor, and the second input of block 7 is connected to the phase current sensors 2 and to the second input of the magnetization current calculation unit 5. The first output of the current component determination unit 7 is

the aperiodic link b is connected to the first input of the multiplication block 4, and the second output of block 7 is connected to the second input of the multiplication block 4 directly. In addition, the current component determination unit 7

has a third control output, which is connected to the third control input of the multiplication unit 4. All blocks, except the magnetization current detection unit 5 and the current component detection unit 7, are standard computer units. Blocks 5 and 7 are described in ed. No. 1372579 published in bull. Mg 5, 1988.

In FIG. 2 is a vector diagram of an induction motor for torque

the time when the projection of the resultant current vector onto the flux linkage axis of the rotor pk2 is equal to the projection of the magnetization current on this axis. The value of the resulting current vector is determined by the magnitude of the currents

A, B, C, and the magnitude of the magnetization current is determined by the reactive power and reactive parameters of the motor (ed. St. No. 1372579).

Thus, for the point in time when the projection of the stator current onto the rotor flux linkage axis is equal to the projection of the magnetization current onto this axis, it is possible to determine the angles a and / 3, a. consequently, the electromagnetic moment of the engine. Determining the projection of the stator current in the coordinate system of the rotor flux linkage and substituting them into expression (1), taking into account that there is a link with an aperiodic transfer function between the current component ha d and the rotor flux linkage, we obtain;

wf, Vu (p) Xm. W (p) ii2d (p) Tr + 1

where Tr W Lr, Rr is electromagnetic noKr

the time constant of the rotor, the inductance of the rotor and the resistance of the rotor, respectively.

Substituting the value of ipz (p) from expression (3) in (1), we obtain

 If J-4 {Iic ° s "J3) jI, smW.B)

. "VfafaJtsL i

The device operates as follows. When the asynchronous motor 3 is operating, the voltage (via voltage sensors 1) and current (via current sensors 2) are supplied to the magnetization current calculation unit 5, in which the magnetization current is determined from the signals of current sensors 2 and voltage 1. A signal proportional to the magnetization current is supplied to the first input of the current component determination unit 7, the second input of which receives a signal from the output of the current sensors 2. In the current component determination unit 7, projections of the stator current on the Cartesian coordinate axes associated with flux linkage are determined rotor, and a point in time is determined when the stator current vector occupies the position shown in the vector diagram (Fig. 2). In this case, a signal proportional to the had component appears at the first output of the component component determination unit for current 7 by

the second output is a control pulse.

A signal proportional to h2 q is input directly to the multiplication unit, and a signal proportional to ii2 d is input to the multiplication unit 4 through the aperiodic link b. When a pulse appears at the third output of block 7, signals proportional to h2 d and Н2 q.

are multiplied according to expression (4), which ensures the appearance of a signal proportional to the moment at the output of the multiplication unit.

The economic effect is achieved in

by increasing the stability and accuracy of determining the moment, since this does not use the integration operation. In addition, at low frequencies with deep control, an irregular rotation of the induction motor is observed. To eliminate uneven rotation, an additional control loop is introduced into the control system using a torque sensor. The considered device has stable characteristics over time and therefore can be used as a torque sensor, which contributes to the creation of high-quality control systems

Claims (1)

The claims A device for detecting the electromagnetic moment of an induction motor. comprising phase current sensors, phase voltage sensors and a multiplication unit, characterized in that. in order to increase accuracy, a magnetization current calculator, an aperiodic link, and a current component of the current in the orthogonal coordinate system connected to the rotor are introduced into it, the first output of which is connected through the aperiodic link to the first input of the multiplication unit, and the second, respectively, to the second input of the multiplication unit, while the phase voltage sensors are connected to the first input of the magnetization current calculation unit, the output of which is connected to the first the input of the current component calculation unit in an orthogonal coordinate system connected to the rotor, the second input of which is connected to the phase current sensors and to the second input of the current calculation unit magnetization. Thebes. 2