RU2054786C1 - Single-phase-to-three-phase voltage changer - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: first lead of single-phase line is connected to third output lead (third phase of load). Common-core leg carries inductance coils wound one over other; wending height of all coils is equal. Capacitor and resistor form RC circuit. Other capacitor is inserted between second lead of single-phase line and starting lead of third inductance coil. Finishing lead of third inductance coil is connected to first phase of load. First lead of single-phase line is connected either through respective switch or directly across RC circuit and through the latter it is connected to starting lead of first inductance coil via other switch. Finishing lead of first inductance coil is connected to starting lead of second inductance coil and also through respective switch or directly across second phase of load. Finishing lead of second inductance coil is connected with second lead of single-phase line either through respective switch or across it, and also with capacitor; third capacitor may be connected in parallel to the latter either through respective switch or across it. Coil may have intermediate tap connected through switch to second lead of single-phase line. proposed joint arrangement of three inductance coils in space on common core leg reduces magnetic leakage between them and voltage unbalance in three-phase system. EFFECT: improved reliability and conversion efficiency; improved characteristics of three-phase system voltage across three-phase terminals of loads within narrow and broad working range. 3 cl, 4 dwg

Description

 The invention relates to electrical engineering and can be used to power three-phase motors and other three-phase consumers from single-phase networks, in particular utility (household).

Known converters of single-phase voltage to three-phase, containing two capacitors, a resistor and three inductors mounted on a common magnetic circuit, the second of which, directly or through a key, is connected to the second phase of the load by the beginning and end to the second terminal of the single-phase network, the first terminal of which is connected to the third phase load, either directly or through a key, is connected to the first terminal formed by the first capacitor and resistor of the RC circuit, which is connected by the second terminal to the beginning of the first inductor, hydrochloric end to the beginning of the second coil. The beginning of the third coil is connected to the second terminal of the single-phase network, and the end of the third coil to the second capacitor, which is connected to the first phase of the load by the other terminal [1]
Known converters of the type in question are characterized by a series connection of all three inductors. In this regard, the potential difference between the extreme terminals of the inductive element formed in this way is large and in certain load conditions there appear points with potentials relative to the neutral of the network and the converter housing that exceed the permissible value, especially with regard to household appliances. This reduces the reliability of these converters.

 The most important feature of the converters of this type is the creation of voltage drops on the elements of its electric circuit, which compensate for the distortion of the symmetry of the three-phase output voltage caused by changes in the current and load power.

 However, the known converters do not provide sufficiently complete compensation for distortion of the symmetry of the three-phase voltage system. The reason for this is primarily due to the fact that in known converters, the nature of the series installation of inductors on a common magnetic circuit and their winding leads to a certain mutual remoteness in space, causing a sufficiently large magnetic scattering. Therefore, in a three-phase system of output voltages, distortions of voltages modulo and phase appear, leading to symmetry breaking. Moreover, the degree of influence of magnetic scattering on the violation of the symmetry of the output three-phase voltage depends on the sequence of addition of the voltages on the capacitor and inductor, since the former at most real loads is greater than the latter. For known converters, a capacitor in one of the load phases is connected directly to the output after the inductance coil connected to it, which enhances the symmetry breaking of the output three-phase voltage of the converter caused by magnetic scattering.

 In addition, these circumstances narrow the operating range of the three-phase load, in which the known converter can be used, since the symmetry provided at its output at a certain fixed load is violated with an increase in load, the realized engine torque is reduced, which can lead to its stoppage and make it difficult to start . And vice versa, when the load on the motor shaft decreases, the symmetry is broken in such a way that in one or two phases of the motor the current rises sharply, the voltage rises above the nominal value, which can lead to engine failure. Such phenomena are possible, in particular, during the operation of the engine of the processing mechanism when the properties of the processed material change.

 Thus, the known converters have low reliability in operation and relatively low efficiency when used in a narrow range of three-phase load, while increasing this range, the reliability indicators of the converters are even more reduced.

 As a prototype, a solution [2] can be selected. All the described disadvantages are inherent in it.

 The aim of the invention is to increase the reliability and efficiency of the converter, as well as the quality (symmetry) of a three-phase voltage system at the terminals of three-phase power receivers both in a narrow and in a fairly wide operating range of a three-phase load.

 To achieve the goal, a single-phase to three-phase voltage converter contains two input terminals for connecting a single-phase supply network, three output terminals for connecting a three-phase load, an RC circuit from a series-connected resistor and a first capacitor, three mounted on a common magnetic circuit of the inductor, the second of which through the first switch, the beginning is connected to the output terminal for connecting the second phase of the load, the first input terminal is connected to the output terminal for connecting the third phase of the load ki, through the second key with the first output of the RC circuit, and through the third key with the beginning of the first inductor, the end connected to the beginning of the second inductor, the end of which through the fourth key is connected to the output terminal for connecting the second phase of the load, as well as the second capacitor, the second terminal of the RC circuit is connected to the beginning of the first inductor, the second capacitor is connected between the second terminal of the single-phase network and the beginning of the third inductor, the end of which is connected to the first phase of the load, the end of the second coil and inductance through the fifth switch is connected to the second input terminal; the windings of all inductors are arranged concentrically to each other on one rod of the common magnetic circuit and are wound one on top of the other with the same winding height.

 In addition, the converter can be equipped with a third capacitor, which can be connected in parallel with the second capacitor through an optional sixth key.

 The second inductor can be made with an additional intermediate terminal, which through an additionally entered seventh key can be connected to the second terminal of the single-phase network.

 In FIG. 1 schematic diagram of the proposed Converter; figure 2 the location of the inductors on the magnetic circuit, in section; figure 3 and 4 vector voltage diagrams.

 On the converter circuit (Fig. 1), in addition to digital designations of elements, letter designations of points or nodes are used for ease of description using equations and vector diagrams. Moreover, all points of the chain having the same potential have the same letter designation and are depicted by the corresponding point and letter on vector diagrams made in the form of topographic diagrams (see Figs. 3 and 4).

 The first output of a single-phase network 1 is indicated by the additional letter C, the second output of a single-phase network 2 by the letter N. At the inverter output there are three outputs for connecting a three-phase load: terminal 3, which corresponds to the first phase of the load and has the letter A, terminal 4 to the second phase B, terminal 5 the third phase C. Terminal 5 is connected to the first terminal of the single-phase network 1 and is therefore indicated by the same letter C.

 6,7,8, respectively, the first, second and third inductors are mounted on the rod 9 of the common magnetic circuit 10, and one is wound on top of the other and the winding height of all the coils is the same (see figure 2).

 The converter also contains a first capacitor 11, which in connection (point E) with a resistor 12 forms an RC circuit. A second capacitor 13 is connected between the second terminal 2 (N) of the single-phase network and the beginning (G) of the third inductor 8. If necessary, the converter may be equipped with a third capacitor 14. For switching, the device may have, for example, seven keys 15-21. It is possible to design the converter without keys, or with any other number of keys. It depends on the required breadth of the operating range of the three-phase load.

 The end of the third inductor 8 is connected to the first phase of the load 3, with both points indicated by the letter A. The first output of the single-phase network 1 through key 19 or directly connected to the first output of the RC circuit, the second output of which is connected to the beginning (F) of the first coil 6 inductance. In addition, the start F of the first coil 6 may be through the key 15 is additionally connected with the first output of the single-phase network 1.

 The end of the first coil 6 and the beginning of the second coil 7 are connected to a common point M, which is directly or through key 21 connected to the second phase B of the load 4. The end of the second coil 7 can also be connected to the second phase of the load through the key 20. The indicated end of the coil 7 is directly or through a key 16 it is connected to the second terminal 2 N of a single-phase network and has the same letter designation N. Moreover, this end of the coil 7 has a direct connection with a capacitor 13, in parallel with which a capacitor 14 can be connected via a key 17.

 To increase the voltage, the second coil 7 may have an additional intermediate terminal 22, which through the key 18 can be connected to the second terminal N of the single-phase network 2.

 Each combination of keys included gives a certain load level, which allows the converter to operate at a sufficiently high level of reliability in the required three-phase load power range.

 When compiling key closure programs, it should be borne in mind that under any of the options there should be no closure of keys 16 and 18, as well as 20 and 21 at the same time, so as not to short-circuit any of the coils.

 From the condition of minimizing the structural mass of the converter, the most appropriate key closure options can be recommended. They are shown in the following table.

и

для этой ступени, когда замкнуты ключи 16,19,21 при разомкнутых остальных (первая строка вышеприведенной таблицы):

Ik₂x_LI₁-Ix

I+Ik $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ x_LI +Ik₁k₂x_LI exp (-j60^°), (1)

(R-Ix

+ Ik₁x_L)I₁+(R-Ix

+ Ik $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ x_L)I exp (-I60^°)+Ik₁k₂x₂I (2)
где R активное сопротивление резистора;
х_с1 емкостное сопротивление первого конденсатора;
х_с2 емкостное сопротивление второго конденсатора;
х_L индуктивное сопротивление системы из первой и второй катушек индуктивности;
I ток первой фазы трехфазной нагрузки, протекающий, начиная с точки А, через второй конденсатор, третью и вторую катушки индуктивности;
I₁ ток, потребляемый из однофазной сети, направленный от точки 2 N к токе 1 С;
k₁ коэффициент трансформации между первой катушкой и системой, состоящей из первой и второй катушек;
k₂ коэффициент трансформации между системой, состоящей из второй и третьей катушек, и системой, состоящей из первой и второй катушек.The process of operation of the converter can be considered at any fixed stage, i.e. on a specific combination of keys included. The first stage is especially characteristic in that, at an arbitrarily small load, full symmetry of the three-phase voltage system at the converter output is ensured. To illustrate the above, we compose the voltage equations

and

for this stage, when the keys 16,19,21 are closed with the rest open (the first row of the above table):

Ik ₂ x _L I ₁ -Ix

I + Ik $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ x _L I + Ik ₁ k ₂ x _L I exp (-j60 ^° ), (1)

(R-Ix

+ Ik ₁ x _L ) I ₁ + (R-Ix

+ Ik $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ x _L ) I exp (-I60 ^° ) + Ik ₁ k ₂ x ₂ I (2)
where R is the resistor resistance;
x _s1 capacitance of the first capacitor;
x _c2 capacitance of the second capacitor;
x _L inductance of the system of the first and second inductors;
I the current of the first phase of the three-phase load, flowing, starting from point A, through the second capacitor, the third and second inductors;
I ₁ current consumed from a single-phase network, directed from point 2 N to current 1 C;
k ₁ the transformation coefficient between the first coil and the system consisting of the first and second coils;
k _{2 is} the transformation coefficient between the system consisting of the second and third coils and the system consisting of the first and second coils.

 Those terms in equations (1) and (2) that correspond to mutual induction stresses contain, as factors, the products of the indicated transformation coefficients.

It is known from theory that a three-phase symmetric system is characterized by a combination of three complex quantities: three equal in magnitude and argument of the load resistance, three equal in absolute value of the linear voltages, the phase shift between them is 120 ^° , so that on the topographic diagram they form an equilateral ABC triangle (see. figure 3), and three equal in absolute value and shifted together in phase current, also by 120 ^about . Therefore, when solving the system of equations (1), (2), one should set either the voltage symmetry or the current symmetry. Then, if, when solving, the unknown of these quantities also turns out to be symmetric, the parameters of the converter satisfy the symmetry conditions of the output voltages.

In this case, we set the system of load currents and determine the system of voltages. Therefore, in the equations (1), (2), in addition to the currents I ₁ and I, contain current Iehr ^(-60 °), the direction of which is selected from the point C to the load that the direction of all three bypass circuits within the converter circuit had the same right to left. Moreover, in a symmetric system of driving currents, the current directed from point C lags in phase by 60 ^° from the current directed to point A, which is reflected in equations (1), (2).

= X_L

R;
X

= 2/

R. (3)
Подставляя параметры (3) в уравнения (1), (2), решаем систему относительно

:

I

KI₁- I

RI+ I

RI + I

RI exp (-I60^°);

R-I

R + I

R

I₁+

R-I

R + I

R

I exp(-I60^°)I

RI
После математических упрощающих выкладок получим:

=

RI₁ exp (I90^°)+

RI (4)
U_BC=

RI₁ exp (-I30^°)+

RI exp (- I120^°) (5)
При делении уравнения (4) на (5) токи и сопротивления сокращаются, получаем условие симметрии трехфазного напряжения на выходе преобразователя независимо от тока нагрузки:

:

= exp (-I120^°) (6)
Полученное решение исходит из абсолютной магнитной связи между тремя катушками. Практически при предложенном расположении катушек на магнитопроводе (см. фиг.2) степень магнитной связи достигает 0,99, т.е. рассеяние и погрешность решения (6) не превышают 1% чем можно пренебречь.Recommended parameters of the converter circuit, at which voltage symmetry will be ensured:
K ₁ = K ₂ = 2/3;
X

= X _L

R;
X

= 2 /

R. (3)
Substituting parameters (3) into equations (1), (2), we solve the system with respect to

:

I

KI ₁ - I

RI + I

RI + I

RI exp (-I60 ^° );

Ri

R + I

R

I ₁ +

Ri

R + I

R

I exp (-I60 ^° ) I

Ri
After mathematical simplifying calculations we get:

=

RI ₁ exp (I90 ^° ) +

RI (4)
U _BC =

RI ₁ exp (-I30 ^° ) +

RI exp (- I120 ^° ) (5)
When dividing equation (4) by (5), the currents and resistances are reduced, we obtain the symmetry condition for the three-phase voltage at the converter output, regardless of the load current:

:

= exp (-I120 ^° ) (6)
The resulting solution comes from the absolute magnetic coupling between the three coils. In practice, with the proposed arrangement of coils on the magnetic circuit (see Fig. 2), the degree of magnetic coupling reaches 0.99, i.e. scattering and error of solution (6) do not exceed 1% than can be neglected.

A special case of the considered mode corresponds to a vector topographic stress diagram shown by solid lines in Fig. 3. Used lettering eliminates additional explanation. For comparison, the diagram in dashed lines shows the same prototype converter mode, which is characterized by a sufficiently large magnetic scattering caused by the spatial distance of the inductance coils from each other. Therefore, here the voltage on the third coil NG modulo and phase deviates by some noticeable angle from the straight line FN corresponding to the voltage of the first and second coils. This shift gives the main share in the resulting displacement of point A ¹ on the diagram and the transformation of triangle A ² BC into non-equilibrium. In addition, the relative position of the second capacitor and the third coil relative to the first phase of the load gives the prototype, in the presence of the indicated scattering, an additional quite noticeable phase shift of the G ¹ A vectors. This is due to the fact that in the operating modes of the converter with an active-inductive load (which include engines) vector capacitor voltage (NG in this case, as in the prototype a ^{1 1} G) significantly more vector third coil voltage (in our case, the AG, and the prototype NG ¹⁾ and other than the proposed solution, pos edovatelnostyu summation voltages vectors (first U _s, and then U _L3). Even if there was scattering (if it remained significant in the proposed transducer), its influence on the position of point A ¹ (in our solution T.A) would be more significant, since the vector G ¹ A ¹ is already deposited from the point G ¹ shifted as a result of scattering . In addition, in the prototype, the potential of the point G between the second capacitor and the third coil is outside the acceptable range relative to the potential of the point of the network C.

Solution (6) indicates the symmetry of voltages at any load current, but does not contain information about the module (actual value) of the three-phase voltage. Physically, it decreases with increasing load current, and its minimum acceptable level practically limits the power of the converter in the first stage under consideration. According to the norms, the output voltage should not be less than 95% of the mains voltage. To determine the maximum allowable load current under this condition, replace the product RI ₁ by the single-phase network voltage U _NC in equation (4) and express the load current through the current I ₁ consumed from the network, giving it the most unfavorable argument -45 ^о , at which the output voltage falls most steeply, and introducing a coefficient modulo n.

I

+

n exp (-I 45^°)

Переходя затем к модулям и подставляя условие U_АВ=0,95 U_NС, получим n= 0,33, или максимально допустимый ток нагрузки
I=0,33I₄ (7)
Значением (7) определена максимальная мощность преобразователя на первой ступени и численное значение сопротивлений (3). Следовательно, если ток нагрузки превышает треть тока однофазной сети, следует переходить на другое положение ключей согласно приведенной выше таблице.Then
U _AB = U

I

+

n exp (-I 45 ^° )

Moving then to the modules and substituting the condition U _AB = 0.95 U _NС , we obtain n = 0.33, or the maximum allowable load current
I = 0.33 I ₄ (7)
The value (7) determines the maximum power of the converter in the first stage and the numerical value of the resistances (3). Therefore, if the load current exceeds a third of the current of a single-phase network, you should switch to a different position of the keys according to the table above.

= I

RI₃=

, а другое линейное напряжение на выходе преобразователя

= I

RI₃- I

RI + I

RI, (8) где I ток однофазной сети на третьей ступени, причем
I₃= I₁:

Подставляя условие (6) в уравнение (8), после преобразований получим отношение модулей токов нагрузки и сети при аргументе тока нагрузки -45^о:
I=2,3I₃=1,33I₁.For example, for the third stage, as can be seen from the key closure table,

= I

RI ₃ =

and another line voltage at the output of the converter

= I

RI ₃ - I

RI + I

RI, (8) where I is the current of the single-phase network in the third stage, and
I ₃ = I ₁ :

Substituting condition (6) into equation (8), after transformations, we obtain the ratio of the modules of the load currents and the network with a load current argument of -45 ^о :
I = 2.3I ₃ = 1.33I ₁ .

 Comparing the result with (7), we can conclude that the power of the third stage is 4 times greater than the first, i.e. the considered combination of key closure extends the operating range of the converter by 4 times. A vector topographic stress diagram for this case is shown in FIG. 4.

 At the fourth stage, intermediate terminal 22 (see Fig. 1) of the second inductor is used, which allows increasing the voltage at the three-phase output with a significant increase in the load current, for example, when starting the motors, or at a reduced voltage of the supply single-phase network.

 As can be seen from relations (3), the active, capacitive and inductive resistances of the converter elements are interconnected by a proportional relationship, and in relation to the calculated power of the converter is inversely proportional. For example, for a 1.5 kW inverter with a rated voltage of 220 V and a frequency of 50 Hz, each capacitor has a capacitance of 20 μF, a resistor resistance of 65 Ohms, the inductance between the beginning of the first coil F and the end of the second coil N is 120 Ohms. The indicated value of the inductive resistance is provided constructively by selecting the thickness of the gaskets in the non-magnetic gap of the magnetic circuit.

 In FIG. 2 shows a tape magnetic circuit with the best location of the non-magnetic gap, providing the smallest magnetic scattering between the coils.

 Thus, the proposed converter provides a higher level of reliability, efficiency and quality (symmetry) of a three-phase voltage system both in a narrow and in a fairly wide operating range of a three-phase load.

Claims (3)

 1. A SINGLE-PHASE VOLTAGE CONVERTER IN THREE-PHASE, containing two input terminals for connecting a single-phase supply network, three output terminals for connecting a three-phase load, an RC circuit from a series-connected resistor and a first capacitor, three installed on a common magnetic circuit of the inductor, the second of which through the first the key is connected to the output terminal for connecting the second phase of the load, the first input terminal is connected to the output terminal for connecting the third phase of the load, through the second key - with the first output of the RC circuit, and through the third key - with the beginning of the first inductor, the end connected to the beginning of the second inductor, the end of which through the fourth key is connected to the output terminal for connecting the second phase of the load, and a second capacitor, characterized in that the second terminal of the RC circuit is connected to the beginning of the first inductor, the second capacitor is connected between the end of the second inductor and the beginning of the third inductor, the end of which is connected to the output terminal for connecting the first phase of the load, with the end of the second inductor through an additionally introduced fifth key connected to the second input terminal, and the windings of all inductors are concentrically one another on one rod of the common magnetic circuit and wound one on top of the other with the same winding height.  2. The Converter according to claim 1, characterized in that it is additionally equipped with a third capacitor, which is connected through an additional sixth key in parallel with the second capacitor.  3. The Converter according to claim 1, characterized in that the second inductor is made with an additional intermediate terminal, which is connected through an additional seventh key to the second input terminal.

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