SU1372551A1 - Three-phase inverter - Google Patents

Abstract

The invention relates to the field of converter technology and can be used in power supply systems, electric drive and automation to convert a constant voltage into a three-phase quasi-sinusoidal. noe. The goal is to improve the shape of the output voltage curve, reducing weight and size. The inverter contains two three-phase bridges, one of which is made on dc keys, and the other on ac keys, and a control unit. The inputs of the bridges are connected to the buses of two sources, the voltage values of which are 1: 2, with the source with a lower voltage level being connected to the second bridge. The bridge outputs are directly connected to the output terminals of the inverter. The two opposite source buses are interconnected via a controlled dc switch. Using the keys of the bridges in the interval of each stage, the sources are connected in series and the output terminals of the inverter are connected to the three source terminals. As a result of the operation of the inverter, a three-phase five-step voltage is generated at its output. 3 il. with (L with KJ

Description

The invention relates to electrical engineering and can be used in secondary power supply and electric drive systems to convert a DC voltage to a three-phase AC voltage.

The purpose of the invention is to improve the shape of the output voltage curve and reduce mass and dimensions.

Figure 1 shows the circuit diagram of the power section of a three-phase inverter; Fig. 2 is a schematic diagram of the control system; on fig.Z diagrams on the principle of operation of the inverter.

The power part of the inverter contains two three-phase bridges, one of which is made on the keys 1-6 permanent

1628, at the outputs of which pulse sequences 49-61 are formed, which, after being amplified by block 29, arrive at the control inputs of the keys 1-13. As a result of the operation of the inverter in the phase of the load connected by a star, a voltage 62 is formed, the amplitudes of the steps of which with the first one are equal to U / 3, and, 4U / 3, 5U / 3, 2U, respectively. To obtain voltage with the indicated voltage amplitudes, the power sources of the bridges must be equal to U and 2U. The half period of the inverter output voltage can be divided into nine equal intervals.

In the first interval, the keys 1,5,7 and 12 are closed (diagrams 49, 53, 55

current, for example, transistors, shuntiro 20 and 60). In this case, with the help of keys 1 of the baths with return diodes, the other bridge is fulfilled on the keys 7-12 of alternating current. The opposite input terminals of the bridges are connected via a dc key 13, a bypass return-25 2U of the first source, through keys 5

and 7 power supplies are connected in series. Through closed keys 1 and 5, voltage is applied to the inverter outputs A and B

35

diode. The DC inputs of the first and second bridges are connected to the terminals for connecting DC sources with voltages of 2U and, respectively, and the current outputs of the bridges are directly connected to the outputs of the inverter.

The converter control unit (Fig. 2) comprises a master oscillator 14, the output of which is connected to the input of the pulse distributor 15. The outputs of the latter are connected via logic elements OR 16-28 and the block 29 of buffer amplifiers with the control inputs of the keys 1-13, and the numbers of the outputs of the block 29 correspond to the numbers of the keys to which they are connected.

The diagrams (fig.Z) represent the pulse forms at the outputs of the following elements: 30 — master oscillator 14; 31-48 - dispenser 15 pulses; 49-61 - elements OR 16-28 (key control pulses 1-13, respectively); 62 - inverter (output phase voltage U).

Three-phase inverter works as follows.

The master oscillator 14 generates

and 12 to cables C and B - the sum of the voltage sources, equal to 3U, to the terminals C and A through the keys 12 and 1 - the voltage of the second source. In this case, the phase voltages on the load connected by a star are equal to:

and,

and.

    2u-u and, 3 of 3 UAB: 3i-2u 5U 3 C 4U

,)

40

and, - (U, - Ug.

Those. the first positive is formed, the fourth is negative and the third is positive the phase of the phase voltages and., and

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In the second interval, the keys I, 3, 8, and 13 are closed. At the same time, via key 13, the sources are connected in series, but with different, different polar tires. Through the keys I, 8 and 3, 8 to the outputs A, B and C, B respectively, the sum of the source voltages is applied, equal to Zi. Via keys 1 and 3, outputs C and A are short-circuited, as a result, the linear voltages become equal to Zi, Zi, O and phase

50

pulse sequence 30, ko-55 U, 2U, U, i.e. The generator is fed to the input of the 18-channel second positive, nth distributor 15 pulses. Weekend and second positive

signals 31-48 of the distributor 15 and the phase voltage of U, Ug, U.

pulses are summed by the elements of the ILIN (the following intervals are the work of the in (60). In this case, using the keys 1 2U of the first source, through the keys 5

and 7 power supplies are connected in series. Through the closed switches 1 and 5, the output voltage of the inverter A and B is applied to the inverter.

and 12 to cables C and B - the sum of the voltage sources, equal to 3U, to the terminals C and A through the keys 12 and 1 - the voltage of the second source. In this case, the phase voltages on the load connected by a star are equal to:

and,

and.

    2u-u and, 3 of 3 UAB: 3i-2u 5U 3 C 4U

,)

and, - (U, - Ug.

Those. the first positive is formed, the fourth is negative and the third is positive the phase of the phase voltages and., and

 at

Il

In the second interval, the keys I, 3, 8, and 13 are closed. In this case, via key 13, the sources are connected in series, but with different, different polar tires. Through the keys I, 8 and 3, 8 to the outputs A, B and C, B respectively, the sum of the source voltages is applied, equal to Zi. Via keys 1 and 3, outputs C and A are short-circuited, as a result, the linear voltages become equal to Zi, Zi, O and phase

The rotation occurs similarly to that described in accordance with diagrams 30-61.

Connecting any branch of the circuit with the help of controlled keys with double-sided conductivity provides the possibility of current flow in two directions and the constant potential difference of the phases during each interval. This causes the inverter to work at any load power factor with a constant output voltage curve.

The preloaded three-phase inverter has a better eruptive output voltage curve (five-step Cr harmonic coefficient of 11.9% instead of a three-step curve of Cr 15.2%) by about 20% less weight and size due to the replacement single bridge ac keys to dc keys.

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Invention Formula). and

A three-phase inverter containing two three-phase bridges, the first of which is made on AC switches, DC bridges of the bridges are connected to terminals for connecting two power sources, and AC outputs of both bridges are directly connected to the outputs of the inverter, and a control unit that is different By the fact that in order for the plotter to shape the output voltage curve, reduce the mass and dimensions, the second bridge is executed on controlled DC switches shunted by the return diodes one time The named terminals for connecting the power sources are interconnected via a controlled DC switch, shunted by a return diode, the voltage values of the power sources are interconnected as 1: 2, and the inputs of the first bridge are connected to the terminals for connecting the power source with a lower level tension

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Claims (1)

SUMMARY OF THE INVENTION A three-phase inverter containing two three-phase bridges, the first of which is made with alternating current switches, the DC input terminals of the bridges are connected to the terminals for connecting two power supplies, and the AC outputs of both bridges are directly connected to the output terminals of the inverter, and the control unit, o characterized in that, in order to improve the shape of the output voltage curve, reduce weight and dimensions, the second bridge is made on controlled DC keys, shunted by return diodes, one opposite terminals for connecting power sources are interconnected via a controlled DC switch, shunted by a return diode, the voltage values of the power sources are 1: 2, and the input terminals of the first 25 bridge are connected to the terminals for connecting a power source with a lower level voltage. the vertically occurs as described in accordance with the diagrams 30-61. 5 Connecting any branch of the circuit using controlled keys with two-sided conductivity provides the possibility of passing current in two directions and the constancy of the difference in phase potentials during each interval. This causes the inverter to operate at any load power factor with an unchanged shape of the output voltage curve 15. The proposed three-phase inverter has a better output voltage curve than the known one (a five-stage with a harmonic coefficient K _g = 11.9% instead of a three-stage curve with K _g = 15.2%), which has approximately 20% less mass and dimensions due to replacing the AC keys of one bridge with DC keys. * —I ”..... ~ ι Fig!