RU2423775C1 - Asynchronous ac converter-fed motor - Google Patents

Abstract

FIELD: electricity. ^ SUBSTANCE: asynchronous ac converter-fed motor with supply from DC source comprises an m-phase winding with even quantity of phases installed on a stator. All phase windings are arranged with a middle lead connected to one terminal of the supply source. End leads of n winding are connected to the second terminal of the supply source by means of controlled key elements, where n = 1, 3, 5, etc., at the same time end leads of (n + 1) winding are connected to the specified leads of n winding via diodes connected in accord relative to current in according sections of n winding. There is a capacitor connected in parallel to each section of (n + 1) winding. ^ EFFECT: simplified design by simplification of a circuit of an asynchronous motor connection to a DC source, increased reliability of this motor by reduction in quantity of switching key elements. ^ 3 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of electrical engineering and may find application in devices with battery power or power from a DC network.

State of the art

Asynchronous motors belong to AC machines and are most often used in electric drives using a three-phase or single-phase AC network as a power source. The rotation of the rotor is ensured by the rotating magnetic field of the stator, the conditions for the creation of which are phase-shifted alternating current supplied to the stator windings, and the location of the stator windings with an offset in space relative to each other.

Unlike DC motors, induction motors (AM) are characterized by such valuable qualities as reliability, contactless design (lack of a brush-collector mechanism), low cost and ease of maintenance, which makes them attractive for use in DC drives.

Known electric drive devices powered by a direct current source, made on the basis of an asynchronous electric motor (see patent RU 2193814, IPC: Н02Р 21/00, publ. November 27, 2002, patent SU 949767, IPC: Н02Р 742, op. 07.08. 82 g., Patent SU 1246322, op. 07.23.86 g., Patent SU 1582327, IPC: H02P 763, op. 30.07.90). In all known solutions, the induction motor is connected to the power source through an autonomous inverter, the input of which is supplied with a constant voltage, and the alternating current received at the inverter output with a given number of phases and parameters is supplied to the phase windings of the stator of the induction motor. As a disadvantage of all the mentioned devices, their complexity can be noted.

A stand-alone inverter can be made in the form of a switching device containing semiconductor key elements (valves), which provide alternating connection of the phase windings of the AM to a power source. Partially or fully controllable semiconductor switches are used as such gates: thyristors and transistors. A known power scheme for the stator winding of an induction motor from a thyristor frequency converter (see book. Electric rolling stock with asynchronous traction motors, N.A. Rotanov. M.: Transport, 1991, pp. 14-15, or patent SU 1781805, IPC: Н02М 7/48, op. 15.12.92 g.). Observing a certain sequence of opening of the thyristors and providing switching current in them, they receive a rotating MDS stator winding, necessary to create an electromagnetic moment. To ensure the normal operation of the circuit, an induction energy storage device is placed at the input of the converter.

Known DC valve electric drive containing an induction motor with a multiphase winding and a semiconductor switch made by a multiphase bridge circuit connected between a current source and phase stator windings (see patent SU 1775808, IPC: Н02К 29/00, op. 15.11.92 g .).

Known asynchronous valve machine containing a rotor, a stator with a three-phase winding connected to a star and connected to the output of a bridge autonomous inverter, implemented on fully controlled key elements - transistors (patent SU 1046863, IPC: Н02К 29/02, op. 07.10.83 g .). An additional three-phase winding is placed on the stator, providing the possibility of direct control of the valves, however, the presence of an additional winding does not provide engine starting, and for this additional elements are added to the circuit.

The main drawback of all of the above-mentioned valve actuators is the presence of a large number of switching elements - two or more for each phase of the motor, which negatively affects the reliability of its operation.

As the closest analogue for the proposed solution adopted the above valve actuator patent SU No. 1775808, IPC: Н02К 29/00, op. 11/15/92

Common signs with the claimed device are the following:

- the presence of an induction motor with an m-phase stator winding,

- power to the induction motor from a direct current source,

- the presence of fully controllable key elements that provide the connection of the phase stator windings to the power source.

Disclosure of invention

The task of the invention is to simplify the connection of an induction motor to a constant current source and increase the reliability of its operation by reducing the number of switching key elements per phase of the motor.

The problem is solved in that in an asynchronous induction motor powered by a direct current source containing an m-phase stator winding connected to the power source through fully controllable key elements, according to the claimed invention, an even number of phase windings made with an average terminal are placed on the stator, the middle terminals of all phase windings are connected to one terminal of the power source, and the terminal leads are connected to the second terminal of the power source through the mentioned key elements n-th winding, where n = 1, 3, 5, etc., while the terminal leads of the (n + 1) -th winding are connected to the terminal leads of the n-th winding through diodes connected according to the current in the corresponding sections of the n-th winding, and in parallel to each section of the (n + 1) -th winding, a capacitor is included.

A fundamentally different, in comparison with the prototype, phase-winding connection scheme made it possible to exclude the current inverter from the power supply circuit of the induction motor as a separate device and halve the number of switching elements per phase of the motor.

The operation of the inventive asynchronous electric motor is based on the phenomenon of mutual induction induced in the section of the adjacent (n + 1) -th phase winding when the power supply circuit of the corresponding section of the nth phase winding is opened, which is illustrated by specific examples of the device implementation given below.

The stator windings work in pairs, and therefore the number of phase windings on the stator must be even, i.e. m = 2, 4, 6, .. In other words, an induction motor made according to the claimed solution can be two-phase, four-phase, etc.

The inventive connection diagram of an induction motor to a constant current source provides the creation of a starting torque of rotation on the rotor, its untwisting and further work without the use of any additional elements.

Brief Description of the Drawings

The claimed solution is illustrated by drawings, where

Figure 1 shows a diagram of an induction valve motor with a two-phase stator winding.

Figure 2 shows the temporal graphical dependence of the current on the phases of the motor.

Figure 3 shows a diagram of an induction valve motor with a four-phase stator winding.

The implementation of the invention

In the general case, the stator winding is m-phase, where m is an even number - 2, 4, 6, etc. For simplicity of explanation, we call the nth winding, where n = 1, 3, 5, etc. - the main, and the adjacent (n + 1) -th winding - auxiliary. With which winding the countdown starts - it does not matter, the numbering is entered conditionally, for clarity of explanation.

Each phase stator winding is made with an average terminal and consists of two isolated sections with the same number of turns. The middle output represents the end of the winding of the first phase section and the beginning of its second section. The middle terminals of all phases are connected to one terminal of the constant emf source (for example, to positive). Phase windings are connected in pairs in such a way that the terminal leads of the n-th winding, where n is a natural number 1, 3, 5, etc., are connected to the second (negative) terminal of the power source through controlled key elements, which use transistors . The terminal leads of its adjacent (n + 1) -th winding are connected to the terminal terminals of the corresponding n-th winding through diodes connected in accordance with the current in the corresponding sections of the n-th winding.

Figure 1 shows a diagram of a two-phase induction valve motor made according to the claimed invention. An asynchronous valve motor (see figure 1) contains a rotor 1 and a stator 2 with the main L ₁ L ₂ and auxiliary L ₃ L ₄ phase windings shifted in space by 90 electrical degrees. Each winding is made with an average output, i.e. consists of two identical sections L ₁ and L ₂ , L ₃ and L ₄ . The middle phase leads are connected to the positive terminal of the power supply.

The terminal leads of sections L ₁ and L _{2 are} connected to the negative terminal of a direct current source (constant EMF) through electronic switches K ₁ and K ₂ made in the form of transistors controlled by a control circuit (not shown).

The terminal leads of sections L ₃ and L _{4 are} connected to the terminal terminals of sections L ₁ and L ₂ through diodes D ₁ and D ₂ , connected in such a way that the anode of the corresponding diode is connected to the corresponding terminal terminal of the main winding (L ₁ or L ₂ ), and cathode - to the corresponding output section of the auxiliary winding (L ₃ or L ₄ ).

The connection of the diodes must always be consistent with the connection of the phase windings to the power source. If you change the polarity of the connection of the phase windings of the motor to the power source shown in the example, it will also be necessary to reverse the inclusion of diodes.

In parallel to sections L ₃ and L _{4 of the} auxiliary winding, capacitors C ₁ and C _{2 are} connected.

The device operates as follows.

Key K ₁ is closed, key K _{2 is} open. Under the influence of electromotive force power source section L ₁ primary winding current increases to a certain value, the main winding magnetic energy accumulates ω _L1 = L · I ₁ ^2/2.

Open the key K ₁ . Under the influence of the self-induction EMF of the section L _{1 of the} main winding, the diode D ₁ opens, and the stored energy ω _L1 creates a current in the auxiliary winding circuit L ₃ , while the presence of a capacitor C ₂ in the circuit reduces the overvoltage on the circuit elements at the moment of opening of the key K ₁ and prevent its undesirable consequences.

The magnetic field in section L ₁ decreases, and in section L ₃ - increases. The decrease in the magnetic field of the main winding in combination with the increasing field of the auxiliary winding creates a displacement of the magnetic field vector in the stator of the motor from the pole of the main winding to the pole of the auxiliary, which captures the rotor and creates a torque on the rotor.

The second section L _{2 of the} main winding is connected to the power source (close the key K ₂ , the key K _{1 is} open). After a specified time, the control circuit opens the key K ₂ , and the process is repeated, but already for the circuit elements L ₂ D ₂ C ₁ L ₄ .

The torque appears again on the rotor, and the rotor receives a second “push”, and the rotational moment on the rotor is directed in the same direction as in the first stage.

Due to the proposed scheme of connecting phase windings, their implementation with an average output, and the fact that the sections of each phase winding are connected to the power source in turn, during each subsequent cycle the stator iron is magnetized, without going into saturation.

The pulsations of a rotating magnetic field are smoothed out due to the inertia of the rotor of the induction motor, and the latter quickly unwinds.

Thus, the proposed scheme for switching on an induction motor provides both starting torque and further operation of the motor.

The modern base of semiconductor and microprocessor devices allows you to implement the necessary key switching control circuit. So, in the current model of the claimed engine, the control circuit was built on the basis of the Atmega8515L microcontroller, which controls, using the IR2110L driver, a pair of IGBT transistors IRG4PH50. As diodes of the DLC chain, diodes HFA16TA120 are used.

By changing the switching period of the keys K ₁ and K ₂ you can adjust the frequency of rotation of the motor rotor. What was also confirmed in the experimental model of the engine, made according to the scheme shown in figure 1. Figure 2 shows the temporary graphical dependence of the current on the phases of the motor.

It is possible to increase the reliability of the engine by placing on the stator two or three of the above circuits, while distributing the windings in the stator space, and the pulses controlling the keys - in time. Connection of phase windings can be carried out both to one and to different power sources.

Figure 3 shows a diagram of a four-phase motor made according to the claimed invention. Switching the keys of the phase windings L ₁ L ₂ and L ₅ L _{6 is} separated in time, which made it possible to realize a four-phase motor of increased reliability.

If one part of the circuit (a pair of phase windings) fails, the engine will continue to work.

Claims (1)

An asynchronous inboard motor powered by a DC source, containing an m-phase stator winding connected to a power source through fully controllable key elements, characterized in that the stator has an even number of phase windings made with an average terminal, the middle terminals of all phase windings are connected to one terminal of the power source, and to the second terminal of the power source through the controlled key elements connected to the terminal leads of the nth winding, where n = 1, 3, 5, etc., while the terminal leads rows (n + 1) -th coil terminals connected to said n-th winding through diodes included according respect to the current in the respective sections n-th coil, and parallel to each section (n + 1) th switched capacitor winding.

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