SU1621135A1 - Ac electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in following drives for wide-range control of the frequency of rotation of an asynchronous motor with frequency control when powered from an adjustable source of variable frequency and amplitude voltage. The aim of the invention is to increase the dynamic accuracy of the electric drive by increasing the accuracy of stabilizing the flow coupling in all quadrants of the mechanical characteristic and simplifying the tuning. This goal is achieved by the fact that an electric drive containing an asynchronous motor 1, functional converters 5, b, respectively, realizing the dependence of the control voltage on the stator current frequency when the engine is idling and the dependence of the additional control voltage on slip, is introduced realizes the dependence of the stator current frequency on the slip. This makes it possible to represent a complex dependence for the voltage amplitude as a superposition of three simple functions in realization. This simplifies tuning and increases dynamic accuracy. Expressions of implemented dependencies are given. 2 silt SO From about

Description

43

The invention relates to electrical engineering, namely to a control electric drive, and can be used in following drives for wide-range control of the frequency of rotation of an asynchronous motor with frequency control when powered from an adjustable source of variable frequency voltage and amplitude.

The aim of the invention is to increase the dynamic accuracy by increasing the accuracy of stabilizing the flux linkage in all quadrants of the mechanical characteristic and simplifying the tuning.

Figure 1 shows the functional diagram of the AC drive; Fig. 2 shows the stress versus frequency and slip dependencies.

The AC drive contains an asynchronous motor 1 (Fig. 1), a torque sensor 2, a sensor 3 for the rotation speed of the motor shaft 1, a first adder A, a first functional converter 5 that regulates the dependence of the control voltage on the current frequency the stator when the engine is idling, the second functional converter 6, which implements in the stabilization mode of the engine's motor coupling, the dependence of the additional control voltage on the slip and connected by the input with the output of the setpoint generator 2, the second adder 7, connected by inputs to the outputs of functional converters 5, 6, the voltage source 8 regulated in frequency and amplitude, connected by control inputs to the outputs of adders 4, 7, and the outputs to the stator windings of an asynchronous motor 1 .

A third functional converter 9 is implemented in the AC drive, realizing the dependence of the stator current frequency offset on the slip and connected to the output of the torque setting device 2, and the third adder 10 connected to the output of the functional converter 9 and the output of the adder 4, and the output to the functional input converter 5.

Functional converters 5, 6, 9 implement respectively dependencies

U1 (a) s) - frtg) 2 + (a iplj2 -.

U2 () RslsOr) x / h

(wl) lsOr) Aws (ftjr)

g l

ten

Rsls (QJr)) s (). ls (ojr) l

at

where Ui, U2, Aros are the signals at the outputs of the corresponding transducers;

Is, ty s are the moduli of the current and current splicing vectors;

los, is the current and flux linkage module of the stator when the engine is idling;

o) 3, - frequency of the stator current and how

wives

Expressions for U2 (coz) and (o) d) can be represented as

II2 (a,) K "M11 ± ЈШ,

Ao () Re ieilSuMix,

(Vs)

where lxs, IYS, if -ipfy are the components of the current and stator flux linkage vectors in the rotating rectangular coordinate system X, Y, connected by the X axis with one of the vectors for the drive realization: the flux linkage of the stator s, the flux linkage of the i / fr rotor, magnetic

flow p in the air gap of the engine.

The modules of the current and flux linkages of the stator and their components in axes X, Y are uniquely determined by known expressions depending on the parameters of the motor and the chosen mode of stabilizing flux linkage. The stator current and flux linkages when the engine is idling are determined under the condition

W o 0.

A specific feature of the electric drive under consideration is that the known complex functional dependences for the amplitude of the voltage of an induction motor on frequency and slip are implemented as a superposition of the three functions Ui (ws), Ua (wg) () using the appropriate functional transducers. This possibility follows from the graphic-analytical method for determining the indicated functions, according to which for any DC motor-drive device selected for realization, the engine is calculated and plotted in the USl plane.

CDS is a family of parametric characteristics U (w5, m) in which engine slip is taken as a parameter

w 0, w G1, ..., etc., and as an argument, the frequency o) s. As follows from figure 2, all

The parametric characteristics U (o) s, a)) have almost the same dependence with respect to the new coordinate system, combined with the vertices (minimum points) of these characteristics, including the idling characteristic U (ws, o), which is shifted depending on slip t relative to the origin of frequency

the value of D ms (a)) and amplitude by the value of U2 (wf). For a set of all possible slip values, w is plotted graphically in the plane UaftA, the function 1) 2 () is realized by the functional converter 6, and in the plane & ws (a) r}

function (), realizable by functional converter 9. Functions

Ui (ftJs), is an equation of the voltage amplitude characteristic versus frequency at zero motor slip and a coordinate system aligned with the top of this characteristic.

An exemplary view of the functions is given in FIG. 1 in the designations of the respective functional transducers. As a result of their approximation by piece-line dependencies, the transducers can be implemented in circuit form as a device for allocating a module with a dead zone {function Ui (ws), 1) 2 (o) d) and

amplifier limiter (function D s s (w)).

The AC drive works as follows.

Proportional slip signal

WG, from the output of the setpoint 2, is fed to the input of the adder 4, where it is summed with a signal proportional to the rotational speed of the shaft of the engine 1, coming from the output of the rotational speed sensor 3. From the output of the adder 4, a signal proportional to the frequency ft) s is fed to the input at the frequency of the voltage source 8 which is adjustable in frequency and amplitude. From the output of the setting device 2 of the moment the signal is proportional to the slip w, comes

ten

15

0

five

0

five

0

five

0

five

also to the input of the function converter 9, which calculates the frequency offset signal Aws (wr). From the output of the functional Converter 9, the signal is fed to the input of the adder 10, the second input of which from the output of the adder 4 receives a signal proportional to the specified frequency w5. From the output of the adder 10 signal

(+ D. (Wg)) is fed to the input of the functional converter 5, which calculates the voltage Ui (w5) depending on the frequency, taking into account its displacement by the value of (a) d). From the output of the setpoint generator 2, a signal proportional to the slip is fed to the input of the functional converter b, which produces a signal proportional to the magnitude of the displacement along

amplitude 1) 2 (mg). From the output of the functional converter 6, the signal is fed to the input of the adder 7, the second input of which receives a signal from the output of the functional converter 5. Due to this, the amplitude shift in

plane Ui sh5 idle characteristics

the move ui (). From the output of the adder 7, a signal proportional to the amplitude of the motor voltage is input to the amplitude of the frequency and amplitude adjustable voltage source 8 connected by the outputs to the stator windings of the induction motor 1. The adjustment of the functional converter 5 for a specific engine is carried out in idling mode. The adjustment of the functional converter 9 by adjusting its transmission coefficient is performed in the acceleration and deceleration modes of the drive, ensuring that the current amplitude is equal in the acceleration mode at the corresponding speed and the amplitude of the current in the deceleration mode. The adjustment of the functional converter 6 in the mode of constant magnetic flux is carried out by adjusting its transmission coefficient to ensure that the amplitudes of the motor current are equal throughout the acceleration and deceleration part.

In the electric drive, a high accuracy of stabilization of the engine for the implementation of any flow coupling in all quadrants of the mechanical characteristic, including at low frequencies of rotation, is provided, simplicity of execution and adjustment of the functional converters for a specific engine, due to which, in comparison with the known solution, increases dynamic accuracy

Claims (1)

AC drive comprising an asynchronous motor with a short-circuited rotor, a torque generator, a motor shaft speed sensor, a first adder connected by inputs to the torque master output and a frequency sensor output, the first function converter for implementing the control voltage dependence on frequency of the stator current when the engine is idling, the second functional converter for implementing the dependence of the additional control voltage on the slip and a second adder connected by an input to an output of a torque master, connected by inputs to the outputs of the first and second function converters, a voltage source controlled by frequency and amplitude, connected by control inputs to the outputs of the first and second adders, and outputs to the asynchronous stator windings engine, characterized in that, in order to increase the dynamic accuracy by increasing the accuracy of stabilizing the flux linkage in all quadrants of the mechanical characteristic and simplifying the tuning, The third functional converter for implementing the dependence of the frequency offset of the stator current on the slip, connected by an input to the output of the torque converter, and a third adder, connected by inputs to the output of the third functional converter and the output of the first adder, and the output to the first functional converter, while the first, second and third functional converters implement, respectively, dependencies Ui (ws) V (RslS) + (S) zB S I S  K I oh, U2 () RslsOr) x L ), | SOr) AftjsOr) 20 - Rsls (QJr) (ftJr). I8 () ys where Ui, 1) 2, are the signals at the outputs of the corresponding transducers; Rs - stator resistance; los, V ° stator current-coupling and current-linkage modules when the engine is idling: thirty a) s, - stator current and slip frequency; | S,;, S I, are the modules of the current vector and stator flux linkage. U (wf, Offset characteristic, ni, h , IKU / / h  /