SU1737685A1 - Method of conversion of constant voltage into quasi- sinusoidal stepped one - Google Patents

Abstract

Use: Conversion of DC voltage to quasi-sinusoidal step-alternating voltage for secondary power supply and electric drive systems. The essence of the invention: the converter that implements the proposed method consists of several cells. The rectangular output voltages generated in each cell are mutually shifted by the same angle y. To adjust the output voltage in each such voltage, pulses of opposite polarity of increased frequency and adjustable duration are formed. At the same time, these pulses are formed in one half of the L / 2 cells at the initial 2/3 of each half-period - on the final 2/3 of each half period. The resulting output cell voltages are summarized in a common contour. 5 il. (Ls

Description

The invention relates to the field of converters of technology and can be used to build sources of secondary power supply of a centralized type with a low-frequency output of high power in cases where coordination is required, with galvanic isolation, input and output voltage levels, improved quality of converted electrical energy, manufacturability and acceptable weight and size indicators of the secondary source.

A known method for converting a constant voltage into a quasi-sinusoidal one, in which an even number of equal amplitude alternating square-wave alternating pulses are formed, is set equal in magnitude and sign

phase shift for all pulses and sum them. In accordance with this method, at certain intervals, the frequency of the pulses is increased compared with the output frequency.

The disadvantage of this method is limited functionality due to the inability to control the quasi-sinusoidal voltage.

The closest to this is the method of converting a constant voltage into a quasi-sinusoidal stepwise method, according to which an even number of galvanically developed equal in form variables with a frequency F of voltages having the form of a square wave is sequentially shifted from the constant voltage

4 CO XI O 00

ate

angle each other and sum them up. The angle y is given from the condition of multiplicity l / 3 to this angle.

The disadvantage of this method is also the limitation of its functionality associated with the inability to control the output voltage.

The purpose of the invention is to expand the functionality by adjusting the output voltage in magnitude.

The goal is achieved by the fact that in the method of transforming a constant voltage into a quasi-sinusoidal stepwise method, in which an even number L of electrically developed equal in amplitude variables with a frequency F voltage is formed from a constant voltage, they are successively shifted by an angle y relative to each other and summed, and the angle y is set from the condition of multiplicity / 3 to this angle, in half-waves of each of L specified voltages within m adjustable intervals of duration a and vary with frequency f 3mF polarity In these voltages, the opposite, and in the first half of the L / 2 voltage, frequency F, forming the first group, adjustable intervals are introduced at intervals of

respectively

 l

K - (- y-) and

four

K (- - 2), and in each of the L / 2 ostal

frequency voltages F. forming the second group, adjustable intervals

2, entered at intervals

K- () and

five

K (-), where K is the number of the output period.

the voltage is measured from the beginning of the first half-wave of each voltage, and the said intervals a of the first voltage frequency group F are shifted by an angle / 2 at the frequency f with respect to the intervals of the second voltage group.

FIG. 1 and FIG. For b, presents time diagrams that explain the proposed method for the case: angle y / 9. m 3; in fig. 2 - the power part of the Converter that implements the proposed method; in fig. 4 is a block diagram of a converter control system; in fig. 5 - timing diagrams explaining the algorithm of the converter operation.

The essence of the proposed method is as follows.

An even number L is formed, galvanically mapped of the same amplitude.

-

ten

15

20

25

thirty

35

40

45

50

55

variables with frequency F voltages having, for example, the shape of a meander. They are successively shifted relative to each other by an angle y, and the angle y is determined from the condition of brevity of the angle / 3 to this angle y. For the case of L 6, the indicated voltages are shown in FIG. 1 and 3 (Itei-Uae). In the half-waves of each of the L specified voltages within m, the duration intervals a are adjustable by duration. the polarity of these voltages is reversed with the frequency f 3mF to the opposite (m 3 in the example). In the first half of the L / 2 voltage frequency F, forming the first group, adjustable intervals are introduced at intervals of K (–t, –– I) and K (--- –2 I), respectively;

the house of the remaining L / 2 voltages forming the second group, adjustable intervals are introduced at intervals

K - () and K - (- where K is the number of the output voltage period. The indicated intervals are measured from the beginning of the first half-wave of each voltage, and the said intervals in the first voltage frequency group F with respect to the intervals a. The voltages are shifted by an angle of / 2 at frequency F. The resulting sequences of alternating pulses (U21-U26) are summarized in a common contour, thereby forming the output voltage U2 curve of a quasi-sinusoidal shape (Fig. 1 and 3).

One of the particular variants of the method implementation can be the converter in FIG. 2. It is made in the form of six power busbars of inverter cells 1-6 connected in buses according to a zero-point circuit with a transformer output. The secondary windings 7-12 of transformers 13-18 are connected in series to form the summing circuit of the output voltages of the inverter cells connected to the output terminals of the converter.

The control system (FIG. 4) comprises a serially connected master oscillator 19 with a forward 20 and inverse 21 outputs and a shift register 22 having L outputs with information 23 and clock 24 inputs. In addition, the control system contains a frequency divider 25 with a division factor of 9 connected between the direct output 20 of the master oscillator 19 and the information input 23 of the shift register 22, which is connected to the inverse output 21 of the master oscillator 19 by the clock input. Outputs

the register 22 is connected to the inputs of the logic unit 27 directly, and the direct output 20 of the master oscillator 19 is connected via a pulse width modulator 26. The outputs of logic unit 27 are associated with the control inputs of the keys of the inverter cells.

The converter operation algorithm, which provides for adjusting the output voltage by magnitude, is explained in the timing diagram of FIG. 5. The indices used at voltages reflect the belonging to their respective node or point of the circuit: 11 (cr) is the signal (voltage) at the direct output 20 of the master oscillator 19; and (d) - the output signal of the splitter 25 frequencies Upi-U (p6) - output signals of the register 22;

V; 1 (1) V1 1 (1) signals applied to the control inputs of the power switches of the first inverter cell 1;

U21-U26-voltages generated in the secondary windings 7-12 of transformers 13-18;

U2 is the output voltage of the converter.

Consider the operation of the converter using the example of the formation of a voltage U2 with the number of stages N 3 (Fig. 5). The master oscillator 19 generates paraphase clock signals on the forward and inverse outputs. From the output 20 of the master oscillator, the pulses U (3r) are fed to the input of the frequency divider 25, from the output of which the pulses with a frequency 9 times less than the clock frequency are fed to the information input 23 of the register 22 and the input of the modulator 26 of the pulse width. At the outputs of the P1-P6 register, a sequence of rectangular pulses U (pi) -U (p6) is formed, with the phase shift between the pulses being y.

The signals from the output of the shift register 22 and the pulse width modulators 26, after corresponding logical processing in logic unit 27, arrive after preamplification and galvanic isolation to the control inputs of the transistors of the inverter cells 1-6 (Fig. 2). Switching the keys in accordance with the control signals supplied to their control inputs ensures that inverter cells 1–6 are formed at the outputs, as well as primary and secondary windings 7–12 of transformers 13–18 of U21 – U26 voltages (Fig. 1. 3, 5 ). The quasi-sinusoidal voltage 1) 2 at the output of the converter is obtained by summing in the output circuit from the series-connected secondary windings 7-12 of the transformers 13-18 of the voltages U21-U26.

In the half-waves of each of the U21-U26 voltages within m adjustable duration intervals a, with the frequency f 3mF, the polarity of these voltages is reversed. In each of the three voltages that make up the first group, these intervals are introduced at intervals, respectively.

proper

.

33

of the three remaining voltages forming the second group, the intervals are entered on

with intervals and lk-.

Possible modifications of the proposed method. For example, when the front of the first of the reverse polarity pulses of the first group of voltages is formed at the beginning

Ptg

gap (Fig. Over), and the front is first j

pulse of the reverse polarity of the second group of voltages is fixed at

from 1 / 6mF from the beginning of the gap 0-.

In another case (Fig. 1), the front of the last pulse of the first voltage group is fixed at 1 / 6mF from the end of the gap

4 n Q, and the front of the last pulse

reverse polarity of the second group of voltages is fixed at the end of the gap

tg 5I

l 3.

5 In the third case (Fig. 36), the fronts of the first and last pulses of the reverse polarity of the first voltage group are fixed, respectively, at the beginning and end of the said intervals, and the middle of the first pulse of the reverse polarity of the second voltage group is fixed at the point

1 / 6mF from the beginning of the interval 0--.

J

Thus, at even L summed voltages, using two-pole pulse-width regulation (WID) of each of the voltages, with the appropriate arrangement of the adjusting pulses m in the half-waves of each voltage, one can realize uni-polar WID of the resulting voltage U2.

The proposed method can be applied not only with square waveforms such as square wave, but also with more complex waveforms.

Claims (1)

The invention The method of converting a constant voltage into a quasi-sinusoidal stepwise method, in which an even number L of electrically developed equal in amplitude variables with a frequency F voltage is formed from a constant voltage, successively shifted them by an angle relative to each other and summed, and the angle The condition of the multiplicity of the angle n / 3 is set to this angle, y, which is different in that, in order to extend the functionality by ensuring the resulting voltage is adjustable in magnitude, in the half-waves of each of the L specified voltages within m adjustable length intervals a, the polarity of these voltages is reversed with a frequency f 3mF, and in the first half of L / 2 the voltage voltages F constituting the first group, adjustable intervals are introduced at intervals of K (-y -) and K (Fr - 2 n), respectively and in each of the L / 2 remaining voltages of the frequency F, forming the second group, adjustable intervals are introduced at intervals K (0 0 and K (l ---), where the number of the resulting voltage period, and the indicated intervals are counted from the beginning the first half-wave of each voltage, and the aforementioned intervals in the first group of frequency voltages F with respect to the intervals a of the second group of stresses is shifted by an angle n II at a frequency f. Fig 2