RU2192088C1 - Single-phase-to-three-phase voltage changer - Google Patents

Abstract

FIELD: starting and controlling ac drives. SUBSTANCE: voltage changer has three-leg transformer with three secondary windings placed on respective legs and interconnected in star as well as two primary windings interconnected in series opposition and connected in series with supply mains; extreme legs are made of electric steels characterized in that ratio of specific magnetic reluctance to specific ohmic resistance of first extreme leg and ratio of specific magnetic reluctance to specific ohmic resistance of second leg are correlated by definite equation so that magnetic fluxes in extreme legs are relatively shifted 60 deg. apart. EFFECT: enhanced reliability of balanced voltages and stability of time characteristics. 2 dwg

Description

 The invention relates to electrical engineering and can be used to power three-phase electric motors from a single-phase mains.

 A known converter of single-phase voltage to multiphase / 1 /, in which a single-phase source creates magnetic flux in a branched magnetic circuit, the opposing magnetic flux is excited using additional secondary windings connected to the capacitors. As a result of the interaction of the main and opposing magnetic fluxes, a three-phase voltage is induced in the main secondary windings. In this case, the phase shift angle of the total magnetic flux is changed by successively counter-switching on the secondary secondary windings of different transformers and by changing the capacitance of the capacitors.

 The disadvantage of this converter is the complexity of its implementation and reduced reliability caused by the use of capacitors.

Also known is a single-phase to three-phase voltage converter / 2 /, adopted as a prototype, in which the opposing magnetic flux in one of the rods of a three-phase magnetic circuit is excited using a short-circuited winding, due to which magnetic fluxes are formed in the extreme rods of a three-rod transformer, phase-shifted 60 ^o , which in the middle rod are geometrically subtracted and form a third magnetic flux. Excited resulting magnetic fluxes induce in each of the three secondary windings located on the rods, electromotive forces forming a three-phase voltage system.

 The presence of a short-circuited winding in the converter leads to additional heating of the magnetic circuit, which degrades its magnetic characteristics and is a drawback.

 The objective of the present invention is to increase the reliability of creating a three-phase symmetrical voltage system with stable characteristics over time.

где

- удельные индуктивные магнитные сопротивления соответственно первого и второго крайнего стержней;

- удельные активные магнитные сопротивления соответственно первого и второго крайнего стержней.This problem is solved in that in a single-phase voltage to three-phase converter containing a three-rod transformer with three secondary windings located on each of the rods and interconnected according to the star pattern, and two primary windings located on the extreme rods and interconnected in series - counterclockwise and sequentially with the output for connecting the network, the outer rods are made of electrical steel, for which the ratio of specific inductive magnetic resistance Specific activity reluctance first end of the rod and the ratio of the specific inductive magnetic resistance to the specific activity of the magnetic resistance of the second rod connected extreme expression

Where

- specific inductive magnetic resistance, respectively, of the first and second extreme rods;

- specific active magnetic resistances, respectively, of the first and second extreme rods.

 The inventive converter of single-phase voltage to three-phase is illustrated by figure 1. Figure 2 shows a vector diagram of magnetomotive forces and magnetic flux, explaining the principle of operation of the Converter.

 The single-phase to three-phase voltage converter contains primary magnetizing windings 1, 2 located on the first 3 and second 4 extreme terminal of the magnetic circuit. On the middle rod 5, as well as on the extreme rods 3, 4, secondary windings 6, 7, 8 are placed, interconnected according to the star pattern. The primary windings are connected to each other sequentially in the opposite direction and sequentially with terminal 9 for connection to a single-phase network.

 The converter operates as follows.

(здесь в числителе индуктивное удельное магнитное сопротивление участка цепи, а в знаменателе активное удельное магнитное сопротивление). Так как у разных электротехнических сталей, из которых изготовлены крайние стержни, удельные магнитные сопротивления различны и подчиняются соотношению

то между МДС первой обмотки F₁ и соответствующим ему магнитным потоком φ₁ угол потерь в стали первого крайнего стержня будет отличаться от угла потерь между МДС F₂ и соответствующим магнитным потоком φ₂ второго крайнего стержня. Благодаря этому между магнитными потоками φ₁ и φ₂ в крайних стержнях преобразователя угол сдвига составит 60^o. В среднем стержне преобразователя возбуждается суммарный результирующий магнитный поток φ₃, который определится как:

Возбужденные магнитные потоки индуктируют во вторичных обмотках 6, 7, 8, размещенных на стержнях трансформатора, соответствующие ЭДС, которые по закону электромагнитной индукции

будут равны по модулю и иметь следующие фазовые сдвиги:

Для симметричной последовательности и чередования фаз необходимо изменить на 180^o фазу ЭДС E₁. Эту операцию можно выполнить изменением маркировки зажимов начала и конца вторичной обмотки 6, расположенной на первом стержне 3 магнитопровода (фиг.1), или изменением направления намотки данной обмотки по отношению к двум другим вторичным обмоткам.When flowing in the primary windings 1, 2 (FIG. 1) of alternating current in the extreme rods under the action of the corresponding magnetomotive forces (MDS), two magnetic fluxes φ ₁ and φ ₂ (FIG. 2) are excited. The phase shift between the MDS and the magnetic flux excited by it is determined by the ratio of the magnetic resistances in the magnetic circuit section. If the extreme sections of the magnetic circuit have the same cross section and the same length, then the loss angle can be determined through the ratio of specific magnetic resistances as

(here in the numerator the inductive specific magnetic resistance of the circuit section, and in the denominator the active specific magnetic resistance). Since the different electrical steels of which the extreme rods are made, the specific magnetic resistances are different and obey the relation

then between the MDF of the first winding F ₁ and the corresponding magnetic flux φ _{1, the} angle of loss in the steel of the first extreme bar will differ from the angle of loss between the MDF F ₂ and the corresponding magnetic flux φ _{2 of the} second extreme bar. Due to this, between the magnetic fluxes φ ₁ and φ ₂ in the extreme rods of the Converter, the shear angle will be 60 ^o . In the middle rod of the transducer, the total resulting magnetic flux φ ₃ , which is defined as:

The excited magnetic fluxes induce in the secondary windings 6, 7, 8, placed on the transformer rods, the corresponding EMF, which according to the law of electromagnetic induction

will be equal in magnitude and have the following phase shifts:

For a symmetric sequence and phase rotation, it is necessary to change the phase of the EMF E ₁ by 180 ^° . This operation can be performed by changing the marking of the clamps of the beginning and end of the secondary winding 6 located on the first core 3 of the magnetic circuit (Fig. 1), or by changing the direction of winding of this winding with respect to two other secondary windings.

 Using the specified Converter allows you to effectively use the dimension of a three-phase electric motor when it is powered from a single-phase network.

Sources of information
1. Copyright certificate 665376, N 02 M 5/14, 1979

 2. Patent of the Russian Federation 2047262, N 02 M 5/14, 1995

Claims (1)

A single-phase to three-phase voltage converter containing a three-rod transformer with three secondary windings located on each of the rods and interconnected according to the star pattern, and two primary windings located on the extreme rods and interconnected in series in the opposite direction and in series with the output for network connection, characterized in that the extreme rods are made of electrical steel, for which the ratio of specific inductive magnetic resistance to specific act the apparent magnetic resistance of the first extreme rod and the ratio of the specific inductive magnetic resistance to the specific active magnetic resistance of the second extreme rod are related by the expression

where ρ _X1 , ρ _X2 are the specific inductive magnetic resistances of the first and second extreme rods, respectively;
ρ _R1 , ρ _R2 are the specific active magnetic resistances of the first and second extreme rods, respectively.

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