RU2374752C1 - Method for determining electromagnetic time constant of squirrel-cage rotor of asynchronous motor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in method for determining electromagnetic time constant of squirrel-cage rotor of asynchronous motor with rotor (ADKR), in order to determine current value of electromagnetic time constant of rotor, to the computing device there entered are design parametres of ADKR in the form of active resistance of stator winding and inductivity of magnetisation circuit, leakage coefficients of magnetic flows of stator and rotor in terms of stator current. During the process, there entered is information on the value of phase current and voltage and on phase displacement angle between voltage and current of stator winding. By means of computing device there determined is electromagnetic time constant of rotor by mathematical formula which is specified in application materials and which includes all the required parameters available for direct measurement in any ADKR mode.

EFFECT: providing economical and steady operation of variable-frequency electric drive on the basis of asynchronous motor with squirrel-cage rotor.

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Description

The invention relates to a variable frequency AC drive based on squirrel-cage induction motors (ADCR) and can be used in automatic control systems for traction electric motors of electric rolling stock, in marine propeller electric drives, rolling mill drives and other widely adjustable electric drives.

When operating a frequency-controlled ADCR, operational tracking of the rotor electromagnetic constant of the rotor time during operation is required in order to adjust the control algorithms to obtain the required functional characteristics of the asynchronous electric drive as a whole.

Direct measurement of the electromagnetic time constant of a squirrel-cage rotor is possible only when it is stationary. During operation, due to saturation and heating, the electromagnetic time constant of the rotor changes and, as a rule, is not exactly known. The change in the electromagnetic time constant of the rotor can reach 100% and lead to a breakdown of the control system. The uncertainty of this parameter leads to the need to adapt the control.

Known methods for identifying the electromagnetic time constant of a squirrel-cage rotor, including heuristic and strict ones (Zai LC, Demarko CL, Lipo T.A. Anaxtendid Kahman filter approach to motor time constant measurement in PWM induction drives // IEEE Trans.Industry Application, 1992. Vol .28, No. 1. P.96-104).

The principal disadvantages that impede the achievement of the technical result indicated below when using known methods include the fact that the known methods do not directly measure the parameter — the electromagnetic time constant of the rotor, but by identifying (identifying) the parameters through the control channel of the flux link vector having an external control loop voltage, and a torque control channel along the speed control loop having an external eyelid position control loop torus flux linkage of the rotor, which inevitably leads to errors in the control of ADCR.

The closest method of the same purpose to the claimed invention in terms of features is a method of controlling an induction motor with adaptation to a changing rotor time constant, in which the adaptive control concept with a reference model is used to find the identification algorithm, in which only the rotor equations of the induction motor are considered, moreover, The components of the magnetizing current of the rotor are taken as the vector of state variables, the stator currents are used as the input, and the mathematical engine model in the form of equations of currents and torque (C. Attaianese, A. Damiano, A. Perfetto. Control of an induction motor with adaptation to the changing electromagnetic constant of the rotor time. // Electrotechnics, 1996, No. 7. p.29-31).

The reasons that impede the achievement of the technical result indicated below when using the known method include the fact that the known method for implementing control of an induction motor uses adaptation to the changing electromagnetic time constant of the rotor model, rather than its direct determination, which also cannot ensure error-free control of the ADCR from -for the difficulty of ensuring the adequacy of the mathematical model, the complexity of the mathematical apparatus, requiring high-speed modeling tools.

The objective of the proposed method is to ensure economical and stable operation of a frequency-controlled electric drive based on asynchronous motors with a squirrel-cage rotor.

The problem is solved in that in the known method of controlling an induction motor, including measuring the rotor speed, stator phase current, stator phase voltage, stator magnetic field rotation speed, controlling the converter supplying the stator winding, setting operation modes using a computing device through a mathematical model control parameter, in which, to find the identification algorithm, the electromagnetic time constant of the short-circuited in real time in a mathematical model, the equations of the rotor are considered, differences are introduced, namely, to determine the current value of the electromagnetic constant time of the rotor, the design device additionally introduces the design parameters of the induction motor in the form of the active resistance of the stator winding and the inductance of the magnetization circuit, the magnetic scattering coefficients stator and rotor flows as a function of stator current; during operation, information is entered on the angle of the phase shift between voltage by the current and current of one of the phases of the stator winding, and the computing device determines the electromagnetic time constant of the rotor according to the mathematical formula, which includes all the parameters that are necessary and which are available for direct measurement in any operating mode of the engine

- модуль полного сопротивления фазы обмотки статораWhere

- stator winding phase impedance module

where U ₁ is the phase voltage; I ₁ - phase current;

φ is the angle of the phase shift between the phase current I ₁ and the phase voltage U ₁ ;

R ₁ is the active resistance of the stator winding;

ω _SK - the slip frequency of the rotor relative to the frequency of rotation of the magnetic field of the stator ω ₁

where ω ₂ is the rotor speed;

L _m is the inductance of the magnetization circuit;

σ ₁ and σ ₂ are the scattering coefficients of the magnetic fluxes of the stator and rotor, respectively.

The presented mathematical formula for the direct determination of the electromagnetic time constant of the rotor is obtained as follows.

As you know, the total power consumed by an induction motor is the sum of the total reactive power losses, the active power losses in the stator winding and the total power transmitted to the rotor by means of a magnetic field in the gap of the motor, and can be described by the equation

where P _Σ is the total power consumed by the engine;

Z ₁ = R ₁ + jω ₁ L ₁ - resistance of the stator winding,

where L ₁ is the leakage inductance of the stator winding;

P _a - active power;

P _b - reactive power;

Ω _ck - relative slip frequency of the rotor

where R ₂ is the active resistance of the rotor winding;

where L ₂ is the rotor scattering inductance equal to L _m σ ₂ = L ₂ .

From (4) we can write

or

, а

, запишемGiven that

, but

write

or

Dividing (13) by (11), we obtain

According to the definition of Ω _ck = ω _ck T _R , then the electromagnetic constant of the rotor time is determined from the measurement result, as

Expression (15) includes the parameters that are necessary and available for measurement under any operating engine mode, i.e. current I ₁ , voltage U ₁ at the input of the phase winding and the angle of the phase shift between them φ, the rotational speed of the stator magnetic field ω ₁ and the rotor slip frequency ω _sk relative to the rotational speed of the stator magnetic field ω ₁ , as well as design parameters: stator winding resistance R ₁ ; the inductance of the magnetization circuit L _m and the scattering coefficients of the magnetic fluxes of the stator and rotor σ ₁ and σ ₂ .

This method is implemented using the device represented by the block diagram in the drawing.

An inverter 2, powered by a power transformer, a phase current sensor 3, a phase voltage sensor 4, a phase angle angle sensor between phase current and phase voltage 5 through sensors 3 and 4 is connected to the stator winding of the induction motor 1 through a speed sensor 6 Sensors are connected to the computing device 7: phase current 3, phase voltage 4, phase angle between the current and phase voltage of the stator 5 and speed 6. The computing device 7 is structurally made integral with the system unit control 8, which is connected to the mode dial 9.

The method for determining the electromagnetic time constant of an ADCR rotor is carried out as follows: the design parameters of an induction motor are introduced into the computing device 7: active resistance R ₁ , magnetization inductance L _m , stator magnetic flux scattering coefficient σ ₁ and rotor σ ₂ as a function of stator current; then, when the electric drive is operating, information is supplied to the computing device from the sensor 3 about the current strength I ₁ and the frequency of rotation of the stator magnetic field ω ₁ , from the sensor 4 about the magnitude of the phase voltage U ₁ , from the sensor 5 about the magnitude of the phase shift angle φ between the phase current and the phase voltage, from the sensor 6 about the rotor speed ω ₂ and the computing device 7 determine the electromagnetic time constant of the rotor in accordance with the mathematical model according to the formula (1)

and submit information to the control system 8, which, combining this information with information from the mode dial 9, controls the inverter 2, which feeds the induction motor.

When measuring at ω ₂ = 0, it is necessary that ω ₁ = ω _ck , and in order to reduce the power consumed by the motor in the mode ω ₂ = 0 and, accordingly, undesirable rotor overheating during measurement, the supply voltage of the stator winding should be as low as possible.

As a result of the above interactions, the electromagnetic time constant of the squirrel-cage rotor is directly determined and, by its magnitude, the asynchronous motor is controlled.

Claims (1)

METHOD FOR DETERMINING THE ELECTROMAGNETIC time constant ROTOR shortcircuited asynchronous motor, comprises measuring SPEED ROTOR, PHASE CURRENT stator phase voltages of the stator SPEED stator magnetic field, controlling converter, feeds stator coil TASK MODE OPERATION WITH COMPUTER DEVICES THROUGH MATHEMATICAL MODEL PARAMETER CONTROL DISTINCTING THAT IN THE COMPUTER DEVICE ADDITIONALLY ADD CONSTRUCTION PARAMETERS OF THE ASYNCHRONOUS MOTOR AS A VIEW The active resistance of the stator winding and inductive circuit magnetization scattering coefficient of the magnetic flux of stator and rotor in function of the current stator DURING WORK to enter information about the angle of the phase shift between voltage and current of one phase of the stator winding, and the computing device determines Electromagnetic rotor time on mathematical FORMULA IN WHICH ALL PARAMETERS ARE AVAILABLE FOR DIRECT MEASUREMENT AT ANY MODE OF THE OPERATING ENGINE:

,
WHERE

- MODULE FOR FULL RESISTANCE OF STATOR WINDING PHASE, EQUAL

;
WHERE U ₁ - PHASE VOLTAGE;
I ₁ - PHASE CURRENT;
φ is the PHASE SHIFT ANGLE BETWEEN the PHASE CURRENT I ₁ and the PHASE VOLTAGE U ₁ ;
R ₁ - ACTIVE RESISTANCE OF STATOR WINDING;
ω _SK - ROTOR SLIDING FREQUENCY REGARDING THE ROTATION FREQUENCY OF THE STATOR MAGNETIC FIELD ω ₁ ;
ω _SK = ω ₁ -ω ₂ ;
WHERE: ω ₂ - ROTOR ROTATION;
L _M - Inductance of the magnetization circuit;
σ ₁ and σ ₂ - SCATTERING FUNCTIONS OF MAGNETIC FLOWS OF STATOR AND ROTOR, APPROXIMATELY.

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