RU23539U1 - SELF EXCITATION THREE PHASE INVERTER - Google Patents

Description

The utility model relates to the field of electrical engineering and can be used as a DC to three-phase sinusoidal current converter used in the auxiliary system of nuclear power plants and a low-power electric drive.

Known push-pull transistor inverter with self-excitation and transformer feedback, containing two transistors, a primary winding, a control winding and a secondary winding located on the toroidal core, while the primary winding and the control winding are divided into two equal parts connected in series 1. This inverter has npocTjoo electrical circuit, reliable in operation and has a high efficiency, however, it is single-phase, which limits its scope.

The closest in technical essence to the claimed utility model is a three-phase inverter with self-excitation for converting direct current into a three-phase sinusoidal current containing three single-phase self-excitation oscillators assembled according to a ring recalculation circuit, with each generator consisting of transistors and a transformer with primary windings , control windings and output winding, and the primary windings and control windings are divided into two equal parts, respectively, connected not sequentially 2, This inverter is characterized by the simplicity of the circuit and the relatively high quality of electricity, since the output voltage curve does not have a third or a multiple of three higher harmonics, but its efficiency is relatively low, since its magnetic system consists of three single-phase transformers.

The technical result of the utility model is to increase the SJP of a three-phase inverter with self-excitation.

The technical result is achieved in that in a three-phase inverter containing for each phase a single-phase inverter made according to a two-half-wave circuit with self-excitation and with the conclusion of the midpoint of the primary winding of the transformer, each of which includes two

a transistor and a magnetically coupled primary winding, consisting of two semi-windings, two positive feedback windings and a secondary winding, the windings of all three single-phase inverters are placed on a common magnetic circuit consisting of internal and external coaxial toroidal cores, said outer core is provided with grooves in which said windings are placed while the corresponding windings of single-phase inverters of all phases are shifted in space relative to each other by an angle a, located in the range 120 ° - (0.1 °) a 120 ° + (0.1 °).

In FIG. 1 shows a section through a composite magnetic circuit of an inverter. Figure 2 shows the circuit diagram of the inverter.

A three-phase inverter with self-excitation contains a composite magnetic circuit 1, which is made toroidal and consists of an external 2 and an internal 3 coaxial cores (figure 1). The inner core 3 is made in the form of a ring, and the outer core 2 is provided with grooves in which three groups of windings are stacked, each of which contains a primary winding 4, consisting of two half-windings 4-1 and 4-2, two positive feedback windings 5 and a secondary winding 6 (Fig. 2). In addition, the device contains three pairs of transistors 7 with combined emitters in each phase, with the first terminals of two series-connected primary semi-windings 4-1 and 4-2 of each group connected to the negative terminal of source 8, the second terminals connected to the collectors of the corresponding pair of transistors 7, the first conclusions of two series-connected windings 5-1 and 5-2 of positive reverse

the connections of each group are connected to the positive terminal of the source 8 connected to the combined emitters of each pair of transistors 7, the second leads to the bases of the said pair of transistors 7, the first leads of the secondary windings 6 of each group are connected to a star, and the second to terminals A, B and C for load connection. The designations of the elements in figure 2 are not fully entered, so as not to clutter the circuit. The primary windings 4, the positive feedback windings 5 and the secondary winding 6 of each group occupy one third of the total number of grooves of the outer core 2, which is determined by the formula:

where p is the number of pairs of poles of the composite magnetic circuit 1; w - the number of phases of the inverter; w 3; q is the number of grooves per pole and phase; q 1.

Due to the fact that the rational number of poles is 2p 2 or 2p 4, the number of grooves of the outer core 2 will be 6 or 12, while a larger number of grooves facilitates the use of steel of the composite magnetic core 1. The technology for making windings 4, 5 and 6 corresponds to the technology for manufacturing electrical windings AC machines, while the windings can be loop or wave depending on the magnitude of the voltage source and the operating voltage of the load. The parameters of the transistors 7 are identical in all phases. The numbers of turns of the windings 4-1 and 4-2, 5-1 and 5-2 in each group are selected from the conditions of the balance of amplitudes and phase balance of the oscillator, respectively, while the parameters of the arms of the oscillator are identical.

A three-phase inverter with self-excitation works as follows. When voltage appears on the positive and negative terminals of the source, one of the three pairs of transistors 7 comes into operation, while one of the transistors will open more than the other, and under the influence of the difference of the collector currents a magnetic field arises, the intensity of which saturates the composite magnetic circuit 1. When magnetization occurs

Z 2 p m q,

external and internal cores 2 and 3, a magnetic flux is formed in them, crossing the turns of the windings of each group, so the corresponding EMF will appear in the windings 4, 5 and 6. For the EMF generator under consideration, the positive feedback windings 5-1 and 5-2 are directed so that the open transistor of pair 7 opens even more, while the closed transistor closes completely, which will lead to even more magnetization of the cores 2 and 3 and even more increasing EMF of windings 5-1 and 5-2 of positive feedback. This process proceeds like an avalanche, and when the open transistor is fully saturated, it starts to close, and the previously completely closed transistor of pair 7 starts to open, which leads to the magnetization of cores 2 and 3 in the lower part of the hysteresis loop, while the EMF of windings 4, 5 and 6 changes its direction. The flow of the magnetic flux through the composite magnetic circuit 1 during operation of any of the oscillators creates the conditions for the inclusion of the next oscillator, etc., that is, in this circuit there is a circular rotating magnetic field (CMF). The main magnetic flux KVMP provides the creation in the secondary winding of the EMF, the value of which is equal to

where f is the switching frequency of the transistors of pair 7; W2 is the number of turns of the secondary winding 6; F is the amplitude of the magnetic flux KVMP; The co-winding coefficient of the secondary winding 6. Due to the fact that the oscillators and their transistors 7 operate in the key mode, the output of the secondary winding 6 has the shape of a voltage curve in the form of an incomplete triangle, in which there is no third and all multiples of three harmonics. The conditions for the formation of 1CVMP in this model are:

Er 4.44 fw20 cob, the equality of the phase shifts of the primary windings 4 and

control windings 5 of each group in the corner space in

equality of phase shifts of difference collector

currents of each pair in time angle of 120 °;

equality of magnetomotive forces of each group

FI F2 l2,

where FI, FI, FS are magnetomotive forces;

1 b b - differential collector currents of pairs of transistors 7; Wi, W2, W3 - the number of turns of the primary windings 4 of each group or generator.

If necessary, synchronization of the switching frequency of the pairs of transistors 7 can be carried out by applying to any of the control windings 5-1 or 5-2 a control signal from the master oscillator.

Thus, the implementation of a composite magnetic circuit common to all oscillators and toroidal in shape can significantly increase the efficiency of the inverter and eliminate the asymmetry of the output voltage. Calculations show that the efficiency of the prototype containing three magnetic cores is 0.95 0.95 O, 95 0.85, and the 1SPD of the proposed three-phase inverter is 0.95, that is, the efficiency increases by 11%.

Sources taken into account:

1 Power supply for communication devices. Ed. O.A. Domoratsky, M :, Radio and communications, 1981, p. 150, fig. 6.8.

2 Romash E.M. Sources of secondary power supply of electronic equipment, M :, Radio and communication, 1981, p. 171, Fig. 829 a, b.

Claims (1)

A three-phase inverter with self-excitation, containing for each phase a single-phase inverter made according to a half-wave circuit with self-excitation and with the conclusion of the midpoint of the primary winding of the transformer, each of which includes two transistors and a magnetically coupled primary winding, consisting of two half-windings, two positive feedback windings and a secondary winding, characterized in that the windings of all three single-phase inverters are placed on a common magnetic circuit, consisting of internal and external coaxial toroidal core, the outer core is provided with grooves in which the indicated windings are located, while the corresponding windings of single-phase inverters of all phases are shifted in space relative to each other by an angle α located in the range 120 ^• - (0,1 ^• ) = 120 = 120 ^• + (0,1 ^• ).