RU109938U1 - FREQUENCY CONVERTER SLAVE BY A SINGLE-PHASE AC NETWORK FOR POWERING A SINGLE-PHASE ASYNCHRONOUS MOTOR - Google Patents

Abstract

 A frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor containing two pairs of semiconductor switches connected in parallel, the common outputs of one pair of semiconductor switches being used to connect the first stator winding of a single-phase asynchronous motor to the mains supply, common outputs another pair of semiconductor switches are used to connect to the mains supply a second stator winding of a single-phase asynchronous motor, characterized in I mean that transistors are used as semiconductor switches, passing current in both directions and designed to operate in key mode.

Description

The proposed utility model relates to frequency converters driven by a single-phase AC network, and can be used in a controlled AC electric drive for supplying a single-phase network of single-phase asynchronous motors.

A device is known for supplying a single-phase asynchronous motor from a single-phase network using a capacitor shift in the stator circuit, powered from a single-phase network of a single-phase asynchronous motor, in which, to obtain a rotating stator field, one winding of a single-phase asynchronous motor is connected to a single-phase network through a capacitor, and the other winding is directly to a single-phase network (IP Kopylov Electric machines. Textbook for high schools / IP Kopylov. - M.:

Higher School, 2006. - P.343, Fig. 3.96).

The main disadvantages of the described device for supplying a single-phase asynchronous motor from a single-phase network using a capacitor shift in the stator circuit are low reliability and increased dimensions due to the need to use paper capacitors of large capacity, as well as the inability to control the speed of rotation of a single-phase asynchronous motor.

The closest to the proposed utility model in technical essence and the achieved result (prototype) with speed control of the electric motor by changing the frequency of the supply network is a single-phase bridge low-frequency frequency converter driven by a single-phase network, containing two pairs of semiconductor switches connected to the supply network, forming bridge circuits rectification, two bridge rectification schemes in each pair, connected to each other in parallel. The common outputs of one pair of semiconductor switches are designed to connect the first stator winding of a single-phase asynchronous motor to the mains supply. The common outputs of another pair of semiconductor switches are designed to connect the second stator winding of a single-phase asynchronous motor to the mains supply. Sixteen thyristors were used as semiconductor switches (patent RU No. 2331153, IPC Н02Р 27/18 (2006.01)).

The main disadvantages of this single-phase bridge low-frequency frequency converter, driven by a single-phase network, are reduced reliability, increased cost and dimensions due to the use of a large number of thyristors, as well as the provision of regulation of the rotational speed of the electric motor only down from the nominal.

The proposed utility model solves the problem of improving reliability and efficiency, reducing the size, ensuring the regulation of the rotation speed of the motor above and below the nominal to expand the functionality of the device.

To solve the problem in a frequency converter driven by a single-phase AC network, to power a single-phase asynchronous motor containing two pairs of semiconductor switches connected in parallel with each other, the common outputs of one pair of semiconductor switches are designed to connect the first single-phase stator winding to the mains induction motor, the common outputs of another pair of semiconductor switches are designed to connect to the mains supply a second stator winding of a single-phase ac synchronous motor, according to a utility model, transistors are used as semiconductor switches, passing current in both directions and designed to operate in key mode.

Providing regulation of the motor rotation speed above and below the nominal, improving reliability and economy, reducing the size of the device due to the use of eight transistors as switching equipment, passing current in both directions and designed to operate in key mode, instead of using sixteen thyristors as semiconductor switches in the device selected as a prototype. The proposed frequency converter allows you to adjust the speed of the electric motor when the supplied frequency of the supply voltage to the motor changes above 50 Hz or lower, which makes it possible to adjust the motor speed both below the rated and above the rated speed, which expands its functionality.

The proposed utility model is illustrated in the drawing, where Fig. 1 shows a circuit diagram of the proposed frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor; figure 2 is a vector diagram of a circular rotating field of the stator of the engine, consisting of four fixed positions of the magnetic flux; figure 3 - phase-by-phase change in magnetic flux in the stator windings at a frequency in accordance with the vector diagram depicted in figure 2; figure 4 - the direction of the magnetic flux and the flowing current along the stator windings of the motor in accordance with the vector diagram depicted in figure 2; figure 5 is a vector diagram of a circular rotating field of the stator of the motor, consisting of four fixed positions of the magnetic flux, while turning on two windings of the stator of the motor; figure 6 - phase-by-phase change in magnetic flux in the stator windings at a frequency in accordance with the vector diagram depicted in figure 5; in Fig.7 - the direction of the magnetic flux and the flowing current through the windings of the stator of the motor in accordance with the vector diagram depicted in Fig.5; on Fig is a vector diagram of a circular rotating field of the stator of the motor, consisting of eight fixed positions of the magnetic flux; figure 9 - phase-by-phase change in magnetic flux in the stator windings f at a frequency in accordance with the vector diagram depicted in Fig; figure 10 - the direction of the magnetic flux and the flowing current along the stator windings of the motor in accordance with the vector diagram shown in Fig; figure 11 - phase-by-phase change in magnetic flux in the stator windings at a frequency freg = f _NETWORK in accordance with the vector diagram shown in figure 2; in Fig.12 - the direction of the magnetic flux and the flowing current along the stator windings of the motor in accordance with the vector diagram depicted in Fig.2; in Fig.13 - phase-by-phase change in the magnetic flux in the stator windings at a frequency freg = 2f _NETWORK in accordance with the vector diagram shown in Fig.2; in Fig.14 - the direction of the magnetic flux and the flowing current along the stator windings of the motor in accordance with the vector diagram depicted in Fig.2.

In addition, the drawing shows the following:

- f - phase;

- 0 - zero;

- C1-C4 - conclusions of the stator windings of a single-phase asynchronous motor;

- VT1-VT8-transistors operating in key mode;

- I, II, III, IV, V, VI, VII, VIII - sequential fixed positions of the magnetic flux vector of the circular rotating field of the stator of a single-phase asynchronous motor;

- straight lines with arrows - the direction of the magnetic flux vector of the circular rotating field of the stator of a single-phase asynchronous motor;

- Uset = f (t) - change in the supply voltage of the AC network in time;

- straight lines with arrows along the stator windings of a single-phase asynchronous motor - the direction of magnetic flux and current in the stator windings.

- VT1, VT2, VT3, VT4, VT5, VT6, VT7, VT8 - openable transistors for both windings of a single-phase asynchronous motor at each moment of time to ensure rotation of the stator field.

A frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor contains two pairs of semiconductor switching keys connected in parallel with each other. As semiconductor switches, transistors are used that transmit current in both directions and are designed to operate in key mode. The common outputs of one pair of semiconductor switches are designed to connect the first stator winding of a single-phase asynchronous motor to the mains supply. The common outputs of another pair of semiconductor switches are designed to connect the second stator winding of a single-phase asynchronous motor to the mains supply.

An example of a frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor. In the first pair of semiconductor switches, the emitter of the first transistor 1 (VT1) is connected to the phase of the supply network, and the emitter of the second transistor 2 (VT2) is connected to zero of the supply network. The collector of the first transistor 1 (VT1) and the collector of the second transistor 2 (VT2) are combined into a common output and are designed to connect to the first terminal 3 (C1) of the first stator winding of a single-phase asynchronous motor. The emitter of the third transistor 4 (VT3) is connected to the phase of the mains, and the emitter of the fourth transistor 5 (VT4) is connected to zero of the mains. The collector of the third transistor 4 (VT3) and the collector of the fourth transistor 5 (VT4) are combined by a common terminal and are designed to connect to the second terminal 6 (C2) of the first stator winding of a single-phase asynchronous motor. Transistors 1 (VT1) and 2 (VT2) are connected to each other in parallel; transistors 4 (VT3) and 5 (VT4) are also connected in parallel with each other.

In the second pair of semiconductor switches, the emitter of the fifth transistor 7 (VT5) is connected to the phase of the supply network, and the emitter of the sixth transistor 8 (VT6) is connected to zero of the supply network. The collector of the fifth transistor 7 (VT5) and the collector of the sixth transistor 8 (VT6) are combined into a common output and are designed to connect to the first terminal 9 (C3) of the second stator winding of a single-phase asynchronous motor. The emitter of the seventh transistor 10 (VT7) is connected to the phase of the mains, and the emitter of the eighth transistor 11 (VT8) is connected to zero of the mains. The collector of the seventh transistor 10 (VT7) and the collector of the eighth transistor 11 (VT8) are combined and are designed to connect to the second terminal 12 (C4) of the second stator winding of a single-phase asynchronous motor. Transistors 7 (VT5) and 8 (VT6) are connected in parallel with each other; transistors 10 (VT7) and 11 (VT8) are also connected in parallel with each other.

Thus, in the first pair, transistors 1 (VT1), 2 (VT2), 4 (VT3), 5 (VT4) are used as semiconductor switches, which pass current in both directions and are designed to operate in key mode, and in the second pair in As the semiconductor switches used transistors 7 (VT5), 8 (VT6), 10 (VT7), 11 (VT8), transmitting current in both directions and designed to operate in key mode.

Using a frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor, it is possible to carry out vector control of a single-phase asynchronous electric motor, creating several types of rotating stator fields: passing four consecutive fixed positions of the magnetic flux vector of a circular rotating field while simultaneously turning on one winding of the motor stator ( see figure 2), four consecutive fixed positions of the magnetic flux vector of the circles nth rotating field with the simultaneous inclusion of two windings of the motor stator (see Fig. 5), and eight (see Fig. 8) consecutive fixed positions of the magnetic flux vector of the circular rotating field of the stator of the motor.

Vector control of a single-phase asynchronous motor through four consecutive fixed positions of the stator field magnetic flux vector for one revolution of the motor while simultaneously turning on one stator winding is as follows.

To ensure rotation of the magnetic flux vector of the circular rotating field of the stator of a single-phase asynchronous motor in accordance with the vector diagram shown in figure 2, the directions of the currents flowing in the stator windings in the sequence I-II-III-IV are shown in figure 4 . Control pulses on the base of transistors operating in the key mode must be submitted in the following order:

- in the positive half-cycle of the supply voltage and network 1 (VT1), 5 (VT4); - I fixed position of the stator field magnetic flux vector;

- in the negative half-cycle of the supply voltage 8 (VT6), 10 (VT7) - II fixed position of the stator field magnetic flux vector;

- in the next positive half-cycle of the supply voltage 4 (VT3), 2 (VT2) - III fixed position of the stator field magnetic flux vector;

- in the next negative half-cycle of the supply voltage 11 (VT8), 7 (VT5) - IV fixed position of the stator field magnetic flux vector.

With the above-described transistor turn-on sequences, this frequency converter driven by a single-phase AC network to power a single-phase asynchronous motor allows the motor to operate at a frequency .

Vector control of a single-phase asynchronous motor through the passage of four consecutive fixed positions of the stator field magnetic flux vector for one revolution of the motor while simultaneously turning on two windings of the motor stator is carried out as follows.

To ensure rotation of the magnetic flux vector of the circular rotating field of the stator of a single-phase asynchronous motor in accordance with the vector diagram shown in figure 5, the directions of the currents flowing in the stator windings in the sequence I-II-III-IV are shown in Fig.7 . The control pulses on the transistors must be submitted in the following order:

- in the positive half-cycle of the supply voltage 1 (VT1), 5 (VT4), 7 (VT5), 11 (VT8) - I fixed position of the stator field magnetic flux vector;

- in the negative half-cycle of the supply voltage 2 (VT2), 4 (VT3), 11 (VT8), 7 (VT5) - II fixed position of the stator field magnetic flux vector;

- in the positive half-cycle of the supply voltage 4 (VT3), 2 (VT2), 10 (VT7), 8 (VT6) - III fixed position of the stator field magnetic flux vector;

- in the negative half-period of the supply voltage 5 (VT4), 1 (VT1), 8 (VT6), 10 (VT7) - IV fixed position of the stator field magnetic flux vector.

With the above-mentioned transistor turn-on sequences, this frequency converter driven by a single-phase AC network to power a single-phase asynchronous motor allows the motor to operate at a frequency .

Vector control of a single-phase asynchronous motor through the passage of eight consecutive fixed positions of the magnetic flux vector of the circular rotary field of the stator per engine revolution is as follows.

To ensure the rotation of the magnetic flux vector of the circular rotating field of the stator of a single-phase induction motor in accordance with the vector diagram shown in Fig. 8, and the directions of the currents flowing in the stator windings in the sequence I-II-III-IV-V-VI-VII-VIII shown in figure 10. The control pulses on the transistors must be submitted in the following order:

- in the positive half-cycle of the supply voltage 1 (VT1), 5 (VT4), 7 (VT5), 11 (VT8); - I fixed position of the stator field magnetic flux vector;

- in the negative half-cycle of the supply voltage 2 (VT2), 4 (VT3) - II a fixed position of the stator field magnetic flux vector;

- in the positive half-cycle of the supply voltage 1 (VT1), 5 (VT4), 8 (VT6), 10 (VT7) - III fixed position of the stator field magnetic flux vector;

- in the negative half-cycle of the supply voltage 7 (VT5), 11 (VT8) - IV fixed position of the stator field magnetic flux vector;

- in the positive half-cycle of the supply voltage 4 (VT3), 2 (VT2), 10 (VT7), 8 (VT6) - V fixed position of the stator field magnetic flux vector;

- in the negative half-period of the supply voltage 1 (VT1), 5 (VT4) - VI fixed position of the stator field magnetic flux vector;

- in the positive half-cycle of the supply voltage 4 (VT3), 2 (VT2), 7 (VT5), 11 (VT8) - VII fixed position of the stator field magnetic flux vector;

- in the negative half-cycle of the supply voltage 8 (VT6), 10 (VT7) - VIII, the fixed position of the stator field magnetic flux vector.

With the above-mentioned transistor turn-on sequences, this frequency converter driven by a single-phase alternating current network to power f a single-phase asynchronous motor allows the motor to operate at a frequency .

By adjusting the moment of supply of the control signal to the base of the transistors, it is possible to operate the electric motor at nominal or at an increased frequency of the supply voltage to the motor, and, consequently, control the speed of the motor. So, by adjusting the moment the transistors are turned on, it is possible to ensure the rotation of the magnetic flux vector of the circular rotating field of the stator of a single-phase asynchronous motor in accordance with the vector diagram shown in figure 2, in the sequence I-II-III-IV at an adjustable frequency that ensures rotation of the motor at nominal speed, as shown in Fig.11, the directions of the currents flowing in the stator windings are shown in Fig.12. On Fig shows the phase-by-phase change in the magnetic flux in the stator windings at an increased frequency of the supply voltage to the motor, the directions of the currents flowing in the stator windings in this mode are shown in Fig. 14.

Thus, with the above-described transistor turn-on sequences, this frequency converter driven by a single-phase AC network to power a single-phase asynchronous motor allows the motor to operate at a frequency above and below the frequency of the mains.

The proposed utility model has advantages over known similar technical solutions due to the possibility of using engine speed control above and below the nominal, higher reliability and economy, as well as small dimensions.

Claims (1)

A frequency converter driven by a single-phase AC network for supplying a single-phase asynchronous motor containing two pairs of semiconductor switches connected in parallel, the common outputs of one pair of semiconductor switches being used to connect the first stator winding of a single-phase asynchronous motor to the mains supply, common outputs another pair of semiconductor switches are used to connect to the mains supply a second stator winding of a single-phase asynchronous motor, characterized in I mean that transistors are used as semiconductor switches, passing current in both directions and designed to operate in key mode.