SU587587A1 - Method of controlling squirrel-cage induction motor - Google Patents

Description

one

The invention relates to the field of electrical engineering / in particular to a controlled electric drive and can be applied in controlling the speed of the load.

There is a known method of controlling an asynchronous motor, which makes it possible to regulate the speed by changing the magnitude and frequency of the supply voltage. The disadvantage of this method is that it is impossible to ensure the rigidity of the mechanical characteristic is greater than that of the executive asynchronous motor,

A known method of controlling a short-circuited asynchronous motor, designed for drives with speed control load 2.

This method involves changing the magnitude and frequency of the stator motor currents according to the results of comparing the set and actual rotor speeds and makes it possible to obtain the rigidity of the mechanical characteristic of the drive more than the rigidity of the characteristic of the executive engine.

The disadvantage of this method is that it cannot provide significant rigidity of the mechanical characteristics of the drive due to the finite value of the gain in the stator current frequency shaping circuit.

In the proposed method, in order to increase the rigidity of the mechanical characteristics, the result of comparing the set and actual rotation frequencies of the motor rotor is converted into the frequency of the rotor currents corresponding to the stator current, the resulting frequency is sulled with the given rotation frequency and the stator current frequency is changed according to the result.

The invention is illustrated in the drawing, which shows a drive diagram with an asynchronous motor, constructed in accordance with the proposed method.

The drive contains a short-circuited asynchronous motor 1, differential 2, selsyn 3, tachogenerator 4, functional elements 5 and 6, converter voltage 7 to frequency, differential selsin 8, phase-sensitive rectifiers 9,10 and 11, current sources 12,13, 14 to power the engine 1,

The specified frequency and rotation of the rotor of the engine is the rotation frequency of the rosin of the selsynin 3 and is compared with the actual frequency of rotation of the Si-Sl-Asi

the rotor of the engine 1 by means of the differential 2. The resulting frequency g 51 is converted by means of a tachogenerator 4, powered by a voltage., B the voltage UoASlj which is fed to the inputs of elements 5 and b. Output voltages U. and Uq of elements 5 and b feed the two-phase rotor windings of the selsyn 3. The voltage But is also the input signal of the converter 7, which causes the selsyn 8 rotor with the frequency j to rotate. The voltages from the output of the selsyn 8 with the frequency and + I / are fed to the rectifiers 9-11, the output voltages of which are the signals of the reference -d current source 12-14. The reference voltage for the rectifiers 9-11 is the voltage and about. In the drive, the motor 1 is powered by currents whose magnitude is proportional to the square root of the sum of the squares of the voltages Uj and IQ. The signal Uj determines the magnetizing current, and the signal Uq the reduced current of the motor rotor. The frequency of the stator currents is formed as a sum of the frequencies and and Qg. Elements 5,6 and 7 form voltages Uj and UiD and frequency sij in accordance with the required mode of operation of the engine. For example, if a constant-flow motor operation is required, then element 5 performs a non-linear conversion of the UgA Si voltage to the Uj voltage; at any voltage at the input of the element 5 M. Element b linearly converts voltage UQASi into voltage Ifq, which linearly converts to frequency and 2, element 7. Voltage conversion factors Uq to stator current and frequency Sij are chosen for which the motor torque is a linear function of the voltage Un and, therefore if the voltage is required linearly and at the same time the minimum of losses in the motor is necessary, then the element 5 performs a linear conversion of the voltage B and the voltage Uj. In this case, the converter 7 operates as a nonlinear element, for which it holds for sigrtS2,5 slgKU.

In all cases, the conversion factors of elements 5,6,7 are chosen large enough and I can be considered, and and is the frequency of the rotor currents; the frequency of the stator currents is equal to an hour (from L to t iZjjT and the frequency is P, 5d. According to the proposed method, the frequency of the stator currents varies with frequency si. The actual frequency characteristics of the asynchronous motor.

Claims (1)

1.Bulgakov A.A. Frequency control of asynchronous electric motors. Science, 1966. pp.86-98. 2, Krivitsky S.O. and Einstein I.I. Dynamics of frequency-controlled electric drives with autonomous inverters, Energie, 1970, p.100-103.