RU2370876C1 - Device for capacitor-free start of three-phase electric motor from single-phase grid - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: invention is related to the field of electric engineering and may be used in electric drive to supply to asynchronous three-phase electric motors. In start device stator windings of asynchronous motor are connected as per delta circuit and are connected to single-phase grid via semiconductor switch. As semiconductor switch intended for shorting of one of motor stator windings with connection of stator windings according to delta circuit, they use antiparallel connected dynistors. One common outlet of dynistors is connected to outlets of electric motor windings, one of which with its one outlet is connected to zero of single-phase grid, and with other outlet - to phase of single-phase grid, and the other winding is connected to zero of single-phase grid. The other common outlet of dynistors is connected to outlets of windings, one of which is connected to zero of single-phase grid, and the other one - to phase of single-phase grid.

EFFECT: higher reliability and efficiency and reduced dimensions.

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Description

The invention relates to devices for starting three-phase asynchronous electric motors from a single-phase network and can be used in an electric drive to power asynchronous three-phase electric motors, the stator windings of which are connected according to the "triangle" scheme.

A device for the capacitor start of a three-phase electric motor from a single-phase network, containing a capacitor and inductance. The capacitor and inductance have a common output, which is designed to connect to the outputs of the windings, one of which is connected to the zero of the single-phase network, and the other is connected to the phase of the single-phase network. The other output of the capacitor is connected to the phase of the single-phase network and is designed to connect to the outputs of the windings, one of which is connected to the zero of the single-phase network. The other inductance output is connected to the zero of the single-phase network and the outputs of the windings, one of which is connected to the phase of the single-phase network. The motor windings are connected in the form of a triangle (S. Biryukov. Three phases - Without loss of power / S. Biryukov // Radio. - M., 2000. - No. 7. - P.37, Fig. 1).

The main disadvantages of the described device for the capacitor starting of a three-phase electric motor from a single-phase network are increased dimensions, due to the need to use paper capacitors of large capacity and inductances, as well as low reliability due to the presence of capacitors and inductances in the circuit.

The closest to the proposed invention in terms of technical nature and the achieved result (prototype) is a device for non-capacitive start of a three-phase electric motor from a single-phase network, containing a semiconductor key for shorting and a control system for this key, when connecting the stator windings according to the "triangle" circuit, connected in parallel to one winding. One output of the semiconductor switch is connected to the outputs of the windings, with one of the windings connected by one output to zero of the single-phase network, and the other output to the phase of the single-phase network, and the other winding connected only to the phase of the single-phase network. The second output of the semiconductor switch is connected to the outputs of the windings, one of which is connected to the zero of the single-phase network, and the other to the phase of the single-phase network. The control system for this semiconductor key consists of a diode bridge and two thyristors connected by cathodes in the opposite direction to one of the diagonals of the bridge. The common cathode point of these thyristors is connected to the minus of the other diagonal of the bridge. (Golik V. Device for starting three-phase motors / V. Golik // Radio. - M., 1996. - No. 6. - P.39, Fig. 1, 3).

The main disadvantages of this device for capacitor-free starting of a three-phase electric motor from a single-phase network are reduced reliability, large dimensions and high cost due to the use of a complex control system for starting and introducing a large number of elements such as a diode bridge, a zener diode, two transistors, two thyristors.

The present invention solves the problem of improving reliability and efficiency, as well as reducing the dimensions of the device of the capacitor-free start-up of a three-phase electric motor from a single-phase network.

To solve this problem, in a device for capacitorless starting of a three-phase electric motor from a single-phase network, containing a semiconductor key, designed to short-circuit one of the stator windings of the motor when connecting the stator windings according to the "triangle" scheme, according to the invention, counter-parallel connected dinistors are used as semiconductor switches, and one common output of the dynistors is designed to connect to the outputs of the motor windings, one of which is connected to one output it is connected to the zero phase of the single-phase network, and the other output is connected to the phase of the single-phase network, and the other winding is connected to the zero of the single-phase network, the other common output of the dynistors is designed to connect to the outputs of the windings, one of which is connected to the zero of the single-phase network, and the other to the phase of the single-phase network.

The increase in reliability and economy, as well as the decrease in the size of the device for the capacitor-less starting of a three-phase electric motor from a single-phase network, is due to the use of counter-parallel connected dinistors as a semiconductor key, which do not require an additional control system for opening and closing them.

The invention is illustrated by drawings, where figure 1 shows a circuit diagram of the proposed device of the capacitor-free start-up of a three-phase electric motor from a single-phase network; figure 2 shows a vector diagram of rotation, consisting of four fixed positions of the magnetic flux of the stator field; figure 3 shows the phase-wise change in magnetic flux in the stator windings in accordance with the vector diagram shown in figure 2.

In addition, the drawings show the following:

- Ф - phase;

- 0 - zero;

- A, B, C - stator windings of the electric motor;

- VT1-VT2 - dinistors;

- I, II, III, IV - sequential fixed positions of the magnetic flux vector of a circular rotating field of the stator of an induction motor;

- arcuate lines with an arrow - the direction of rotation of the stator magnetic field;

- U network = f (t) - change in supply voltage over time.

The device for capacitor-free starting of a three-phase electric motor from a single-phase network contains a semiconductor switch, which is used as counter-parallel connected dinistors 1 (VT1) and 2 (VT2). One common output of the dynistors 1 and 2 is designed to connect to the outputs of the stator windings of the electric motor, one of which, winding A, is connected to the single-phase network zero by one output, and the single-phase network phase is the other output, and the other winding, B winding, is connected to zero single phase network. Another common output of the dynistors 1 and 2 is for connecting to the outputs of the windings, one of which, winding B, is connected to the zero of the single-phase network, and the other, winding C, to the phase of the single-phase network. Stator windings A, B, C of the electric motor are connected according to the "triangle" scheme.

The operation of the device of the capacitorless start of a three-phase electric motor from a single-phase network is as follows. With the passage of the positive half-wave of the supply voltage, first the current passes through all three windings A, B, C of the electric motor (figure 3). The first position of the stator magnetic field vector is formed. When the threshold value of the supply voltage is reached, the dinistor 1 (VT1) opens. The winding B is shorted and the second position of the stator magnetic field vector is formed. With the passage of the negative half-wave of the supply voltage, first the current passes through all three windings A, B, C of the electric motor. A third position of the stator magnetic field vector is formed. When the threshold value of the supply voltage is reached, the dinistor 2 (VT2) opens. The fourth position of the stator magnetic field vector is formed. The stator field is ellipsoidal, spatial, and changes in time.

Thus, reliability and economy are increased, as well as the dimensions of the device for non-capacitor starting of a three-phase electric motor from a single-phase network are reduced in the absence of the use of a complex control system for starting a three-phase electric motor.

Claims (1)

A device for capacitorless starting of a three-phase electric motor from a single-phase network, containing a semiconductor switch, designed to short-circuit one of the stator windings of the motor when connecting the stator windings according to the "triangle" scheme, characterized in that counter-parallel connected dynistors are used as a semiconductor switch, with one common output dynistors is designed to connect to the outputs of the motor windings, one of which is connected to the zero of a single-phase network by one output, and others the other output is connected to the zero of the single-phase network, the other common output of the dynistors is designed to connect to the outputs of the windings, one of which is connected to the zero of the single-phase network, and the other to the phase of the single-phase network.

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