SU879724A1 - Frequency-controllable electric drive - Google Patents

Description

The invention relates to electrical engineering, in particular to variable frequency drives, and can be used in various industries of the textile, metalworking, metallurgical and other industries. A highly dynamic electric drive with an asynchronous short-circuited motor 1 is known, which contains a frequency converter with an autonomous current inverter, coordinate transducers, vector analyzers, a task shaping unit, blocks, multiplications and differentiations, controllers (speed, flow, current) and sensors (speeds , flow, current). A disadvantage of this device is the presence of Hall sensors in the air gap of an electric motor, which complicates the assembly process, increases the accuracy requirements for processing a number of parts and assemblies of an electric motor, and reduces the reliability of the electric drive as a whole. A disadvantage of this device is also the presence on the motor shaft of the speed sensor, which reduces reliability and limits the scope of application of the device. The closest to the proposed electric drive according to the technical essence is the device for controlling the speed of the asynchronous motor 2, which contains an asynchronous motor, the stator windings of which are connected to a frequency converter consisting of a series-connected stand-alone inverter, a smoothing drossel, a controlled rectifier with a discharge control system devices, to the control input of which the output is connected, the current regulator connected with one of the inputs to the current sensor, the other to one from the outputs of the coordinate converter, connected by the second output to the control system INBEPTOjioM, and one of the inputs to the output of the control unit of the coordinate converters, another input to the output of the flow coupling regulator, the third input to the output of the frequency regulator, one of whose inputs and the flux linkage torus is connected to the job node; regulator; second coordinate transducer; the EMF sensor of the asynchronous electric motor and the differentiating inertial element, one of the inputs of the second coordinate converter is connected to the output of the EMF sensor, the second input is connected to the output of the control unit of the coordinate converters, and the output is connected to one of the inputs of the actuator whose second input is connected. There is a differentiating inertial link with the input of the flux linkage regulator, the output of the regulator is connected to the input of the control unit of the coordinate transducers and to the second input of the mentioned frequency regulator. .

The disadvantages of this device are low reliability and energy performance. The decrease in the reliability of the device is due to unstable operation (at high rates of flow coupling change) is proportional to. and differential flow controller required for the implementation of high-quality flow control of an asynchronous motor with flow control loop without feedback over flow coupling. As a consequence, the device has inherent low energy indicators associated with a certain limitation in the possibility of quality control of the flow linkage for the realization of optimal energy modes of operation of an electric motor,

The purpose of the invention is to improve the energy performance, reliability and expansion of the field of application of the device,

The goal is achieved by the fact that a clock-controlled electric drive containing a stator current shaping unit of an induction motor connected by one input to the output of a frequency regulator, in which one input is connected to one of the outputs of the reference node, the other input to the frequency sensor, and EMF sensor, additionally introduced a two-zone control unit and an adder, with a two-zone control unit. One of the inputs is connected to the EMF sensor, and the other input is connected to the second output of the task unit connected by the third output to one of the BX The adder OJ30B, whose input is connected to the second input of the stator current shaping device, and the second input to the output of the dual-zone control unit.

The drawing shows the functional diagram of the frequency-controlled electric drive.

The electric drive contains an asynchronous electric motor 1 / whose stator windings are connected to a stator current formation unit 2 connected by one whisk to the output of frequency regulator 3, in which one input is connected to one of the outputs of node 4 of the task, and the other input to sensor 5, the sensor .6 EMF, node

7 two-zone control is the accumulator 8, and the node 7 of the two-zone control is connected to one of the inputs to the EMF sensor 6, and another to the second output of the task 4, connected by the third input to one of the inputs of the adder 8, the output of which is connected to the second input of the stator forming unit 2 current, and the second input - with the output of node 7 of the two-zone control.

The device works as follows.

At the output of the dual-zone control unit 7, an -Al signal is generated of the following form:

oh if

X

-U1 h-ULi (d -1 it od if E E,

jU

whereE, E - respectively signals

set EMF and feedback on the electromotive force of the electric motor.

When the actuator is operating in the first zone, the frequency of the CCF below or equal to the nominal f (, (), the inequality Е Е is satisfied and the output signal -L 7 of the two-zone control is zero. As a result, the output signal i of the adder 8 arriving at one of the block inputs 2 stator current formations, equal to the nominal specification of the reactive projection of the current, specified by the assignment node 4. This ensures the nominal value of the flux linkage Ч Fn of the electric motor in the first zone of operation of the electric drive.

In the second zone of operation of the drive, the frequency is higher than the nominal

(Year) where the inequality B is violated, since E fg) fn and the output signal - A-iJi of node 7 of the two-zone control, other than zero, 9 affects the magnitude of the output signal -nn i of the adder 8, which determines the value of the projection of the reactive current in block 2. stator current formation. As a result of this, the magnitude of the flow build-up of the electric motor is changed, and the control of the magnitude of the flux linkage V by the two-zone control unit 7 is carried out in such a way that equality is restored and maintained: E cons.t.

Obviously, when the frequency is changed, the EMF constant mode of the electric motor is achieved due to the inversely proportional law of change in the flux linkage-s-f / UUo While maintaining the EMF constant law by the node 7 of the two-zone control over the entire change range

frequency and at a constant value of the projection i of the active current of the electric motor, specified in this case from the node 4 of the task, the operating mode of the electric drive is achieved at constant power, since the mechanical power on the shaft of the electric motor is:

Rdleh - E Chz const

at E, i and const, where id is the projection of the stator current of the electric motor. In this case, when increasing (decreasing) the moment // from the load on the motor shaft according to the basic equation of the electric drive: I ...

J (l ® C- COOT6 Ot

electromagnetic moment, motor and load moment, W - angular velocity is rotating. electric motor; I is the reduced moment of inertia of the drive; the angular velocity of rotation of the motor and the angular frequency iV u + p decrease (increase);

 %

. - absolute slip;

Hum is the active resistance of the motor rotor (stator current), specified by the stator current formation unit 2. In the mode of constant emf of an electric motor, with a decrease (increase) in the angular frequency of 1 l of stator current, the magnitude of the coupling of the electric motor varies inversely, and hence the electromagnetic moment of the electric motor changes: JU 4 and with id const.

The new steady-state values of the angular frequency lA.t of the stator current and the angular velocity U; motor rotations correspond to restoring the equality of moments fJt / (AsDan's technical solution allows to increase energy performance, reliability, speed, as well as expand the range of application for mechanisms requiring control law at constant power.

The energy indices increase due to the introduction of a two-zone speed control unit providing a constant EMF of the electric motor, namely, below the nominal frequency, the constant coupling of the electric motor is provided, and above the nominal frequency the constant electromotive force is applied. Thus, a decrease in electrical, loss of electric motor operation mode is achieved, which is close to the optimal electromotive loss.) And the frequency converter's voltage utilization ratio increases.

Improving the reliability of the electric drive is ensured by performing regulation of the electric motor by means of an EMF control loop made according to the principle of deviation, with, in contrast to unstable excitation control in a known device, carried out by means of an open loop link control loop.

An increase in the speed of the electric drive is achieved by providing the maximum possible excitation of an induction motor in the case of a control law with a constant emf under real limitation

5 of the output voltage of the converter, which makes it possible to generate the maximum electromagnetic moment of the electric motor at a given current value.

0 The extension of the field of application of the electric drive to the area of mechanisms operating at constant power is achieved by providing the constant mode of the EMF of the electric motor at a constant setting of the active current of the electric motor.

This electric drive can find wide application on the mechanisms of milk, for example, in the metallurgical, chemical, textile industry.,

Claims (2)

1. The patent of Germany 2144422, 0 кл. H 07 P 5/28, 1978. 2. USSR author's certificate  according to application no. 2682788, cl. H 02 R 7/42 07.24.79.