RU151766U1 - SINGLE-PHASE THREE-PHASE BROADBAND TRANSISTOR FREQUENCY CONVERTER LED BY A SINGLE-PHASE NETWORK - Google Patents

Abstract

A single-phase-three-phase broadband transistor frequency converter driven by a single-phase network containing three rectification circuits, the middle point of each of the three circuits is connected to the corresponding beginning of one of the stator windings of a three-phase asynchronous motor, the ends of the windings of which are connected to a star, and a single-phase supply is used as the mains AC network, characterized in that in each of the rectification schemes used two field-effect transistors.

Description

The proposed utility model relates to broadband frequency converters driven by a single-phase network, and can be used in an electric drive to control the speed of asynchronous three-phase and synchronous motors.

Known three-phase low-frequency semiconductor frequency converter, driven by a three-phase network, formed of three three-phase zero thyristor rectifiers, outputs connected to the inputs of three stator windings included in the star. Moreover, the zero point of the power source is connected to the zero point of a three-phase asynchronous motor (Bernstein I.Ya. Thyristor frequency converters without a DC link / I.Ya. Bernstein. - M: Energy, 1968. - P. 42, Fig. 2-10a .).

The main disadvantages of this low-frequency semiconductor frequency converter driven by a three-phase network are the lack of the possibility of direct use in a single-phase network and a violation of the operation mode of the induction motor and its characteristics due to the supply of a unidirectional rectified voltage to the stator windings.

The closest to the proposed utility model in terms of technical nature and the achieved result (prototype) is a single-phase-three-phase low-frequency frequency converter driven by a network containing semiconductor valves connected to the mains, connected by three zero anti-parallel rectification circuits. The midpoint of each of the three circuits is connected to the corresponding beginning of one of the stator windings of a three-phase asynchronous motor. The ends of the stator windings of the electric motor are connected to a star. As a power supply network, a single-phase AC power supply network was used. Zero anti-parallel rectification circuits made on semiconductor valves are designed to provide the possibility of changing the direction of rotation of the stator field magnetic flux vector. Semiconductor valves are assembled on thyristors (patent RU 88227, IPC H02P 21/10 (2006.01)).

The main disadvantages of the described low-frequency frequency conversion device driven by the network are the inability to control the frequency of the voltage supplied to the stator windings of the electric motor in a wide range, the complicated control circuit of the valves due to the need to take into account the polarity of the supply voltage, as well as the increased cost and low reliability due to the use a large number of semiconductor valves in zero anti-parallel rectification schemes.

The proposed utility model solves the problem of providing the possibility of regulating the voltage supplied to the stator windings of the electric motor in a wide range, simplifying the valve control system, as well as reducing cost and increasing reliability.

To solve the problem in a single-phase-three-phase broadband transistor frequency converter driven by a single-phase network containing three rectification circuits, the middle point of each of the three circuits is connected to the corresponding beginning of one of the stator windings of a three-phase asynchronous motor, the ends of the windings of which are connected to a star, and as the supply network used a single-phase AC supply network, according to the utility model, two field-effect transistors were used in each of the rectification schemes.

Providing the ability to control the voltage supplied to the stator windings of the electric motor in a wide range, simplifying the valve control system, reducing cost and increasing reliability are due to the use of two field-effect transistors in each of the three rectification schemes, each of which can pass current in the forward and reverse directions without taking into account the polarity of the applied voltage.

The proposed utility model is illustrated in the drawing, where in FIG. 1 shows a circuit diagram of the proposed single-phase three-phase broadband transistor frequency converter driven by a single-phase network; in FIG. 2 is a vector diagram of rotation consisting of three fixed positions of the magnetic flux of a stator field; in FIG. 3 is a vector rotation diagram of a stator field consisting of four fixed positions of the magnetic flux; in FIG. 4 is a vector rotation diagram of a stator field consisting of six fixed positions of the magnetic flux; in FIG. 5 shows a phase-wise change in magnetic flux in the stator windings in accordance with the vector diagram depicted in FIG. 2; in FIG. 6 shows the direction of the magnetic flux and the current flowing through the stator windings in accordance with the vector diagram shown in FIG. 2; in FIG. 7 shows a phase-wise change in magnetic flux in the stator windings in accordance with the vector diagram depicted in FIG. 3; in FIG. 8 shows the direction of the magnetic flux and the current flowing through the stator windings in accordance with the vector diagram depicted in FIG. 3; in FIG. 9 shows a phase-wise change in magnetic flux in the stator windings in accordance with the vector diagram depicted in FIG. four; in FIG. 10 - direction of the magnetic flux and the flowing current along the stator windings, in accordance with the vector diagram depicted in FIG. four; in FIG. 11 is a phase-wise change in magnetic flux in the stator windings in accordance with the vector diagram depicted in FIG. 2, when the engine is operating at an increased frequency; in FIG. 12 is the direction of the magnetic flux and the flowing current along the stator windings in accordance with the vector diagram depicted in FIG. 4, when the engine is operating at high frequency. In addition, the drawing shows the following:

- f - phase;

- 0 - zero;

- C1-C3 - the beginning of the stator windings;

- VT1-VT6 - field effect transistors;

- I, II, III, IV, V, VI - consecutive fixed positions of the magnetic flux of the stator;

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

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

- straight lines with arrows - directions of the magnetic flux and current in the stator windings of the motor.

A single-phase - three-phase broadband transistor frequency converter driven by a single-phase network contains three rectification schemes. As a power supply network, a single-phase AC power supply network was used. In each of the zero rectification schemes, two field-effect transistors are used.

In the first rectification circuit 1, the midpoint 2 of the field effect transistors 3 (VT1) and 4 (VT2) is connected to the beginning 5 (C1) of the stator winding of the electric motor. In the second rectification circuit 6, the midpoint 7 of the field effect transistors 8 (VT3) and 9 (VT4) is connected to the beginning 10 (C2) of the stator motor winding. In the third rectification circuit 11, the midpoint 12 of the field effect transistors 13 (VT5) and 14 (VT6) is connected to the beginning 15 (C3) of the stator motor winding. The ends of the stator windings with the beginnings 5, 10, 15 (C1, C2 and C3) of the electric motor are connected to a star.

Single-phase - three-phase broadband transistor frequency converter, driven by a single-phase network, operates as follows.

Initially, a voltage was applied to the gates of the transistors 3, 4, 8, 9, 13, 14 (VT1-VT6), which creates an electric field to close the transistors. Vector-algorithmic control is carried out by removing voltage from the gates of transistors in a certain sequence.

In order to ensure rotation of the stator field in accordance with the vector diagram shown in FIG. 2, it is necessary to carry out the removal of voltage from the gates of transistors 3, 4, 8, 9, 13, 14 (VT1-VT6) in the following sequence:

simultaneously VT2, VT3, VT5 - I position of the stator field vector, then

simultaneously VT2, VT3, VT6 - II position of the stator field vector, then

simultaneously VT1, VT3, VT6 - III position of the stator field vector, then

simultaneously VT1, VT4, VT6 - I position of the stator field vector, then

simultaneously VT1, VT4, VT5 - II position of the stator field vector, then

simultaneously VT2, VT4, VT5 - III position of the stator field vector.

With the passage of the next positive half-wave of the supply voltage, the opening sequence of the transistors is repeated.

With the above-described sequences of switching on transistors, that is, removing voltage from the corresponding gates, this single-phase - three-phase broadband transistor frequency converter driven by a single-phase network allows the motor to operate at a frequency f of the _network / 1.5.

In order to ensure rotation of the stator field in accordance with the vector diagram shown in FIG. 3, it is necessary to carry out the removal of voltage from the gates of transistors 3, 4, 8, 9, 13, 14 (VT1-VT6) in the following sequence:

simultaneously VT2, VT5 - I position of the stator field vector, then

simultaneously VT2, VT3, VT6 - II position of the stator field vector, then

simultaneously VT1, VT6 - III position of the stator field vector, then

simultaneously V1, V4, VT5 - IV position of the stator field vector.

With the passage of the next positive half-wave of the supply voltage, the opening sequence of the transistors is repeated.

.With the above-described transistor switching sequences, this single-phase - three-phase broadband transistor frequency converter driven by a single-phase network allows the motor to operate at a frequency

.

In order to ensure rotation of the stator field in accordance with the vector diagram shown in FIG. 4, it is necessary to carry out the removal of voltage from the gates of transistors 3, 4, 8, 9, 13, 14 (VT1-VT6) in the following sequence:

simultaneously VT2, VT3, VT5 - I position of the stator field vector, then

simultaneously VT1, VT3, VT6 - II position of the stator field vector, then

simultaneously VT1, VT4, VT5 - III position of the stator field vector, then

simultaneously VT2, VT3, VT5 - IV position of the stator field vector, then

simultaneously VT1, VT3, VT6 - V position of the stator field vector, then

simultaneously VT1, VT4, VT5 - VI position of the stator field vector.

With the passage of the next positive half-wave of the supply voltage, the opening sequence of the transistors is repeated.

With the above-described transistor switching sequences, this single-phase - three-phase broadband transistor frequency converter driven by a single-phase network allows the motor to operate at a frequency f of the _network .

In order to ensure operation of the engine at a _network frequency 2f in accordance with the vector diagram shown in FIG. 2, it is necessary to carry out the removal of voltage from the gates of transistors 3, 4, 8, 9, 13, 14 (VT1-VT6) in the following sequence:

simultaneously VT2, VT3, UT5 - I position of the stator field vector, then

simultaneously VT1, VT5, VT4 - II position of the stator field vector, then

simultaneously VT1, VT3, VT6 - III position of the stator field vector, then

simultaneously VT1, VT4, VT6 - I position of the stator field vector, then

simultaneously VT2, VT3, VT6 - II position of the stator field vector, then

simultaneously VT2, VT4, VT5 - III position of the stator field vector.

With the passage of the next positive half-wave of the supply voltage, the opening sequence of the transistors is repeated.

Based on the analysis of the diagrams, the relationship between the frequency of the voltage supplying the motor and the parameters of the converter is as follows:

where f _with - the frequency of the mains

n is the number of half-periods per revolution of the magnetic field of the motor stator;

a - the number of half-cycles in one position of the engine. Thus, the proposed single-phase-three-phase broadband transistor frequency converter driven by a single-phase network has advantages over the known ones due to the possibility of controlling the voltage supplied to the stator windings of the electric motor in a wide range, simplifying the valve control system, as well as reducing cost and increasing reliability.

Claims (1)

A single-phase-three-phase broadband transistor frequency converter driven by a single-phase network containing three rectification circuits, the middle point of each of the three circuits is connected to the corresponding beginning of one of the stator windings of a three-phase asynchronous motor, the ends of the windings of which are connected to a star, and a single-phase supply is used as the mains AC network, characterized in that in each of the rectification schemes used two field-effect transistors.

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