BG109571A - Method and device for regulating the speed of a two-phase induction motor with a quasi-resonance single-phase cycloconvertor - Google Patents

Abstract

The invention relates to a method and device for regulating the speed of a two-phase induction motor with a quasi-resonance single-phase cycloconvertor intended for reaching low and superlow speeds. The method for reaching low and superlow speeds consists in immediate conversion of the single-phase supply voltage into a two-phase system of lower frequency voltages, such conversion being realized under resonance conditions of the voltages of the single-phase supply voltage frequency, regardless of the frequency of the two-phase induction motor. The device for realizing the method represents two identical quasi-resonance single-phase to three-phase cycloconvertor embodied according to a single-phase bridge circuit with four triacs (1.1 - 1.4). To the central points of the bridge circuits there are connected the stator windings (2) of the two-phase induction motor (3), while to one of the two arms, through an inductive coil (4) and a capacitor (5) connected in series, and the other arm, supply is performed from a source of single-phase supply voltage (6).

Description

METHOD AND DEVICE FOR REGULATING THE SPEED OF A TWO-PHASE ASYNCHRONOUS MOTOR WITH A QUASI RESONANCE ONE-PHASE CYCLON CONVERTER

Technical field

A method and device for controlling the speed of a two-phase asynchronous motor with a quasi-resonant single-phase two-phase converter is used in machines and mechanisms requiring low and super low speeds, in domestic appliances, as well as on-board electric motors used in airplanes and ships with current sources .

BACKGROUND OF THE INVENTION

A known frequency method for controlling the speed of a two-phase induction motor. The method is that the frequency and voltage regulation, as well as the ratio between them, is performed in the transistor inverter itself. By changing the pulse fill factor by pulse width modulation (PWM), it changes

L.

the voltage amplitude applied to the motor, and by changing the pulse width the frequency changes.

The device according to the known method consists of two transistor inverters made in single phase bridge circuit with four transistors in each of them. The terminals of the two windings are included in the middle points of the bridge circuits, and a constant non-adjustable voltage is applied to the two arms of the bridge circuits.

The disadvantages of the known method are the presence of a DC link, which does not allow the return of energy from the motor to the grid, and hence the inability to perform generator (brake) modes.

Double conversion and the associated losses are also a drawback of the device.

There is also a method whereby a direct frequency conversion is carried out by means of a so-called single-phase two-phase cycloconverter. In order to obtain the desired mechanical characteristics, regulation is performed by two parameters - by the number of half-waves of the single-phase supply voltage superimposed on the positive and negative half-waves of the synthesized from the cycloconverter voltage and at the phase angle of the valve opening.

The presence of a pulse-phase impulse control system is a major drawback of the method. The device implementing the method is characterized by all the negatives of the phase control, such as low torque, efficiency and power factor, and the presence of interruptible current modes.

Technical nature

The aim of the invention is to achieve a cyclic exchange of the electromagnetic energy accumulated in the inductors of the motor windings and of an inductive coil, with the electrostatic energy accumulated in an additional included capacitor, this exchange being carried out at the frequency of a single-phase power supply, inside the device itself

The aim is to create a method in which the direct conversion of the frequency to a lower one, by superimposing a certain number of half-waves from a single-phase supply voltage into the positive and negative half-waves of the synthesized voltage, is performed at

the presence of a resonant mode of voltages with a frequency equal to or close to the frequency of the single-phase supply voltage, independent of the frequency synthesized by the device and supplied to the motor windings.

To achieve this, a device consisting of two completely identical quasi-resonant single-phase cycloconverters has been created, so their device and operation in the following explanations will only refer to one of them.

The device of the quasi-resonant single-phase two-phase cycloconverter is made according to a single-phase bridge circuit of four triacs. A single motor coil is connected to the two middle points of the bridge circuit, and a single-phase supply voltage is applied to one of the two bridge circuits, through a series capacitor and an inductor coil and the other arm. The role of the capacitor is to resonate the reactive energy stored in the device itself, without this energy being taken from the outside. The role of the inductive coil is to reduce the impedance of the resonant circuit by approximating or equalizing the natural frequency of the circuit with the frequency of the single-phase supply voltage and also to exert a smoothing effect on the current flowing through it. The capacitor, the inductor coil, one of the windings of the motor and the source of the single-phase supply voltage are involved in the resonant circuit.

The advantages of the method are that the conversion of the frequency to a lower one occurs in the presence of a resonant mode of voltage, with a frequency equal to or close to the frequency of the source of the single-phase supply voltage, regardless of the frequency synthesized by the device.

The advantages of the device implementing the method of the power factor is close to one, the current flowing through the windings of the induction motor has a continuous character, which determines high torque and high efficiency, does not emit harmonics, enables operation in generator modes. Since the two quasi-resonant single-phase cycloconverters are exactly the same, the rotating electromagnetic field in the motor at low speeds is circular rather than elliptical.

Description of the attached figures

Figure 1 is a schematic diagram of the device without the control portion not within the scope of the present invention.

Examples of implementation

The method is applied in the system: two-phase asynchronous motor-two exactly the same quasi-resonant single-phase two-phase converter, powered by a single-phase power supply.

The device of the quasi-resonant single-phase two-phase cycloconverter is made according to a single-phase bridge circuit of four triacs 1.1-1.4. A coil 2 of the two-phase induction motor 3 is connected to the two middle points of the bridge circuit, and power is supplied to one of the two arms of the bridge circuit via a series-inductive coil 4 and a capacitor 5 and the other arm. .

Use of the invention

With the supply of a single-phase supply voltage, two of the valves opposite to the two arms of the bridge circuit, eg valves 1.1 and 1.2, are simultaneously released. this is

always performs at the beginning of each positive or negative half-wave of the single-phase supply voltage. The valves act as a switch that switches coil 2 at the beginning of each change of the single-phase supply voltage polarity in such a way that, through the inductive coil 4 and capacitor 5, the current changes direction at the beginning of each half-phase of the single-phase supply voltage, and winding 2 of the two-phase induction motor 3 changes the direction of the dream "N" times less, where "N" is the number of half-waves and a single-phase supply voltage superimposed within the positive and negative half-waves of the synthesized w device voltage of lower frequency. . The winding 2 of the two-phase induction motor 3, together with the inductive coil 4 of the capacitor 5 and the source of the single-phase supply voltage 6, form a sequential resonant circuit with natural frequency equal to or close to the frequency of the single-phase supply voltage independent of the frequency synthesized by the device of the engine.

Attachment: 1 figure.

References:

1. Griko VM, Static converters on the carrier frequency, Zh. 1970's Electrical Engineering.

2. FiragoB. I., Thyristornme Cyclo-Converter, Science and Technology,

Minsk, 1973.

Claims (2)

Claims 1. A method for controlling the speed of a two-phase asynchronous motor with a quasi-resonant single-phase two-phase cycloconverter based on the direct conversion of a single-phase supply voltage to a two-phase system of voltages, characterized in that the direct conversion of the frequency into a lower frequency occurs voltages, at the frequency of the single-phase supply voltage, regardless of the frequency supplied to the motor windings. A device for controlling the speed of a two-phase asynchronous motor with a quasi-resonant single-phase two-phase cycloconverter, characterized in that it contains two completely identical quasi-resonant single-phase two-phase cycloconverters, executed in a single-phase bridge circuit of four triacs (1.1-1.4) circuit includes windings (2) of the two-phase induction motor (3), and a source is connected to the two arms of the bridge circuit through series-connected inductive coil (4) and capacitor (5) and the other arm single-phase power supply (6).