SU1690143A1 - Method of conversion of dc current to three-phase ac current - Google Patents

Abstract

This invention relates to the field of power conversion technology. Its purpose is to reduce the vibroacoustic activity of the converted current electrical receivers. The method consists in converting the direct current into a three-phase alternating current by inverting the source direct voltage into an intermediate multi-phase alternating voltage of a rectangular shape, transforming this voltage on the main magnetic flux and vector summing the transformed multi-phase voltage into a three-phase voltage. The goal is achieved by the fact that, prior to inverting and transforming the voltages, the main multiphase magnetic flux is created in the form of a cosine distribution along the axis lying in the cross-sectional plane of the magnetic flux contour, and for a given cyclically repeated three-phase voltage, the magnetic flux distribution is uniformly pushed along axis so that the beginning of the cosinusoid reaches the end of the axis at the end of the three-phase voltage period, 3 sludge. with s

Description

The invention relates to electrical engineering, in particular, to ship electric power industry, and can be used to create DC-DC converters to three-phase AC and vice versa to power different AC electrical receivers from a DC source in electrical power systems on special marine vessels that require electrical receivers. and low noise operation transducers with limited installed equipment.

The purpose of the invention is to reduce the vibroacoustic activity of alternating current power consumers and transducers with a limited amount of

method of converting the necessary equipment.

FIG. 1 and 2 show examples of a device implementing the method; on 3 - the diagrams explaining the operation of the device.

A method for converting a direct current into a three-phase alternating current is as follows.

The input DC voltage is inverted into an intermediate multi-phase alternating voltage. After transforming it, the secondary multiphase voltage is vectorially summed to the output three-phase voltage, which is applied to the AC receivers.

Ltd

J

with

Inverting the input DC voltage is performed on the key elements assembled in a multiphase bridge circuit. The key elements in the device of FIG. 1 are controlled in such a way as to obtain a multiphase voltage in the form of a time sequence of alternating rectangular form of phase voltages one after the other, the sum of which is non-zero and converges at any instant to the instantaneous value of the input constant. tension

The transformation of the intermediate multiphase voltage and the vector summation of its secondary voltage to the output three-phase voltage is performed on a pre-formed main magnetic flux in the following order,

By pre-inverting the input DC voltage, a near-zero direct voltage source creates a magnetic flux in the form of a cosine distribution along the axis lying in the cross-section plane of the magnetic circuit. During a predetermined three-phase voltage output period, the magnetic flux distribution is uniformly pushed along the axis so that the cosine curve start reaches the end of the axis at the end of the three-phase voltage period. At least four electric circuits are coupled to the magnetic flux, to one of which an inverted multi-phase voltage is applied, and from the other three the output three-phase voltage is removed.

The formation of the main magnetic flux by the current of an external source is carried out with the help of an electric circuit magnetically coupled to the magnetic circuit so that when passing a constant current in the magnetic circuit, a spatially distributed magnetic flux is generated:

Ф0 К0 locos (10 + F)

(one)

where 10 -In -.- axis of magnetic flux distribution, rac:

c - initial conditions of the distribution curve;

I is a natural axis of length L in the cross-sectional plane of the magnetic circuit;

Co is the coupling coefficient of the flux linkage Ф0 with a current of 10.

By rebuilding the connections between the electric and magnetic circuits, the change in the initial conditions is set in time:

fl (ik t

(2)

In

where Sho - - - - is the rate of change of initial conditions in during a given period of time T of the output three-phase voltage.

The electric circuits of the multiphase and three-phase voltages are connected with the magnetic circuit so as to obtain the mutual induction induced from the main flux in the form of distributions along the axis on which the basic magnetic flux is distributed. For the electrical circuit of the multi-phase voltage, a flux link is obtained.

VW Who lo COS (10 + 0 - From), (3)

where trto is the flux linkage of mutual induction with respect to each m-phase of a multiphase voltage;

start of the distribution curve

a flux linkage for each m-phase from one number n of multiphase voltage phases alternating in time;

Who is the flux coupling ratio of Fto with a current of 10 for a multiphase voltage circuit.

For each of the three three-phase voltage circuits separately, flux couplings are obtained.

1rao Kao lo COS (1О + $);

# Îo Kyo lo cos (10 + d - 2 l: / 3); (4) Vco Kco lo cos (10 + $ - 4 L: / 3),

where ao Vfe ° is the flux linking of the mutual induction of the circuits a, b, from the three-phase voltage;

Kao Kio Kso - coupling coefficients for flux couplings from currents 10.

In addition, by passing currents through electric circuits, self-induction flux couplings are obtained. For a multi-phase voltage circuit

Vmd Kmd Id COS (I0 - From). (5)

where ipmd is the self-induction flux chain relative to the multiphase voltage m-phase;

Kmd coupling ratio flux 1 / Jmd with DC Id IN CONTOUR

Phase voltage.

For three-phase electric circuits

 - Ka la cos I;

Vb Кь 1ь cos (lo - 2/3); (6) KC lccos (10-4l; / 3),

where t / k is the Vc flux linkage of the self-induction of the circuits, a, b, c, c of the three-phase voltage;

Qa and Kc are the coupling coefficients of coupling to the phase currents la, Ib, Ic.

As a result of changes in the timing of mutual coupling in electrical circuits, emf is induced. As the first time derivative of flux couplings, a multiphase EMF is obtained in a multiphase voltage circuit:

Hundred Who lo Sin ((o + 0 - w). (7)

In the three-phase voltage circuits, a three-phase EMF is obtained:

eao - Kao lo (DO sin (fo + $);

eo Kboio sin (fo +, - 2 7G / 3); (eight)

eco Kco lo sin (63 + f - 4/3).

An inverted multiphase voltage is compared with the obtained multi-phase EMF, and a three-phase EMF is applied as an output three-phase voltage to AC receivers.

The goal of the invention is achieved by electromagnetic balancing the input DC current in a multiphase voltage circuit with a three-phase output current in a three-phase voltage circuit. Electromagnetic equilibrium of various kinds of currents is provided as follows.

By controlling the key elements in the multiphase bridge circuit, the inverted multiphase voltage is brought to the multiphase EMF induced from the main magnetic flux so that on the timing diagram each of the alternating phase axes of the phase voltages is located symmetrically on both sides of

amplitude of the corresponding phase emf. Moreover, such a total number of p phases is preliminarily chosen for multiphase voltage and multiphase emf at which, due to the short duration of the phase voltage rectangles, the instantaneous phase emf values in the corresponding time segments differ little from the amplitude values of B

as a result, alternating time sections and in time as a whole on the DC side receive DC current with small pulsations:

 Ud - e Gax

that

Rd

(9)

where Ud, Id are input constant voltage

and current;

Max

emo1 - phase EMFs in temporary areas in the vicinity of their amplitudes;

Rd is the resistance of alternating current power consumers brought to the multiphase voltage loop,

The direct current flowing in the multiphase voltage circuit creates a coupling of self-induction according to expression (5). This flux linkage is balanced by flux linkage of the self-induction from the active component of the output three-phase current.

After substitution of three-phase current values into expression (6)

la 1maxS05 (#,);

1 1 Max 8 (3-p-2/3): (10)

Ic max cos (fy - p 4 7G / 3),

where Laicc is the amplitude of the three-phase current;

(p is the angle characterizing the ratio of the active and reactive components in the three-phase current,

and the subsequent summation of the phase values obtain the resulting flux linkage of self-induction from the three-phase current

3

Vb.b.c | KalMaKcCOs (t0-) (11)

or after decomposing the two angles by the cosine formula in the form of two components:

% b, with V d - V; q

(12)

where 1 / d - 2 Ka max COS (L $) COS f) is the coupling of the active component of the three-phase current; (13)

Vq 2 Ka max Sin (1 $ 9) Sin Ј - FLOW coupling from the reactive component of the three-phase current (14)

Comparison of expression (5) for linking from input DC to expression (13) for linking from the active component of three-phase current shows that to balance them, the necessary condition is:

Kmd d 2 Ka max COS p; (15)

.(sixteen)

Equality (15) is satisfied by adjusting the magnitude of the shock in expression (9) for the input DC current Id. The regulation of 1max is carried out by changing the magnitude of the current lo from a third-party source in the electric circuit to form the main magnetic flux according to expression (1). The second equality (16) is maintained within the permissible limits of deviations of 9t from the current values of 9 by choosing the total number of phases for multiphase voltage and multiphase emf. In this case, the error, divided on both sides of the amplitudes of alternating phase EMF, does not exceed the value:

A device for converting direct current into three-phase alternating current contains a transformer 1 connected via a multiphase inverter 2 input constant voltage to the main source 3 of direct current and through a thyristor switch 4 to an external source of direct current with near-zero voltage.

Transformer 1 is made on the toroidal ribbon core of the magnetic conductor with one primary winding 6 and three secondary windings 7-9. The core has, in particular, thirty-six holes, separating equidistant rods of the magnetic circuit. Each winding 6-9 consists of two parallel-connected coils laid on diametrically opposite sides of the core of the magnetic circuit. The coils of windings 6-9 are formed by winding around rods

each coil consists of eighteen elementary turns, each turn covers fifteen rods, each subsequent turn is shifted by

one rod in the direction of winding, the last turn of one coil is connected to the first turn of the second coil, and vice versa

The primary winding 6 is provided with taps from turns of one and the other of its coils,

which are connected to the outputs of the inverter 2 and the switch 4. The secondary windings 7-9 are three-phase windings connected in a star and connected to three-phase electrical receivers (not shown). The secondary winding 7 is made similar to the primary winding 6 with the exception of taps. The secondary winding 8 is made similarly to the winding 7 and is positioned relative to it with a shift in the direction of winding by twelve rods of the magnetic core core. The secondary winding 9 is made similarly to the winding 8 with a shift relative to it also by twelve rods of the core of the magnetic circuit.

Inverter 2 voltage is made on thyristors on the pavement, in particular, a thirty-six-phase circuit. The first eighteen phases of the inverter 2 are connected to the tapes of one coil of the winding 6, and the second to the tapes of its other coil. Inverter 2 is provided with a conduction angle of 10 al. Degrees, for each arm of its bridge.

Switch 4 is made on thyristors with forced capacitive commutation as well as a thirty-six-phase bridge circuit with an angle of conduction on each arm of the bridge 10 electrical degrees.

A device for converting a direct current into a three-phase alternating current operates as follows.

Through the switch 4, the source 5 is connected to the initial pair of taps of the primary winding 6 and the main flow distribution of the transformer magnetic core 1 is approximated to a cosine. sum, the resulting flow distribution F0.

Switching taps of winding 6 using switch 4 causes the flow distribution Ф0 to move along the axis

distribution I.

Due to the electromagnetic inertia, the movement of the distribution of the flux Fo in the areas between the switchings of the taps of the winding 6 becomes smooth. Frequency

switchings are set in proportion to the number of taps and the frequency of the output three-phase voltage.

The moving distribution of the main flow Fo induces a multiphase EMF in the primary winding 6 and a three-phase EMF in the secondary windings 7-9 of the transformer 1. Multiphase EMF balances the inverted multiphase voltage at the output of the voltage inverter 2. The three-phase EMF creates a three-phase current in the electrical receivers.

The flux coupling from the three-phase current flowing through the secondary windings 7–9 is balanced by the two coupling components of the primary winding 6. The first flux coupling component of the winding 6 from the current of the main source 3 balances the flux coupling created by the active component of the three-phase current of the windings 7-9, the second component of the winding source 3. the other side source 5 is generated by the reactive component of the same current of power receivers.

Electromagnetic balancing of the input DC current with the output three-phase current of the AC electrical receivers through the formation of the main magnetic flux due to a third-party direct current source with a near-zero voltage allows

sides of the converter and, thus, reduce the vibroacoustic activity of the AC electric receivers, as well as the equipment conversion method.

Claims (1)

The Invention A method for converting a direct current into a three-phase alternating current by inverting a source direct voltage into an intermediate multi-phase alternating voltage of a rectangular shape, transforming this voltage on a main multi-phase magnetic flux, vector summing the transformed multi-phase voltage into a three-phase voltage, which differs in the three-phase magnetic current that distinguishes a three-phase magnetic flux, which is the vector summation of the transformed multiphase voltage into a three-phase voltage, which differs in the three-phase magnetic current, which is different from the vector summation of the transformed multi-phase voltage to a three-phase voltage, which differs in the three-phase magnetic current, which is characterized by the vector summation of the transformed multi-phase voltage into a three-phase voltage, which differs in the three-phase magnetic current, which is different from the vector summation of the transformed multi-phase voltage to a three-phase voltage, which differs in the three-phase magnetic current, which is characterized by the vector summation of the transformed multi-phase voltage to a three-phase voltage, which differs in the three-phase magnetic current, which is different from the vector summation of the transformed multiphase voltage to three-phase voltage, which differs in the three-phase magnetic current that differs from that, in order to reduce the vibroacoustic activity of transformed current electrical receivers, before inverting and transforming Voltage of the on-line multiphase magnetic flux is created in the form of a cosine distribution along the axis lying in the cross-sectional plane of the magnetic flux contour, and during a predetermined cyclically repeated three-phase voltage period the magnetic flux distribution is uniformly pushed along the axis so that the cosine wave begins to end axis at the end of the three-phase voltage period. FIG. / Rig 2 .d