SU1720132A1 - Method of control valve-type three-phase converter - Google Patents

Abstract

The invention relates to power converter technology. The aim of the invention is to improve the spectral composition of the output voltage of the converter in the process of wide-range coupled frequency and voltage control. The control method is based on a universal 180-degree asymmetrical control algorithm for a three-phase composite inverter, in which the main sequence of control (modulating) signals is formed asymmetrically to the half-period center inside the average on the half-periods of the clock intervals of 60-degree durations. Due to the variation in step-by-step variations in the durations of the median at the clock intervals of the control pulses and the pauses between them, the process of regulating the converter is accompanied by a smooth unaccented change in the number of pulses in the output wave half-waveform. Simultaneously with the formation of the main sequence of control signals over the entire control range inside the extreme sections of the control zones, whose duration is close to 30 al. Degrees, additional control signals are formed, the locations of the front edges of which are close to the edges of the half-periods of the fronts of the corresponding main edges. control signals, and the duration of additional signals is in a nonlinear dependence on the duration of the main Sive output pulses, 5 Il. H go about w go

Description

The invention relates to electrical engineering and can be used to control converters based on autonomous voltage inverters that are part of variable frequency electric drive systems.

Pulse-width control algorithms for three-phase inverters are known.

voltages at which the total duration of the switching-on impulse valves is 120 or 150 electrical degrees.

However, the shape of the output voltage curve of the converter, in this case, to a large extent depends on the load parameters, which makes it difficult to effectively use the above algorithms when

power supply of varying loads of motor type.

A method of controlling autonomous three-phase voltage inverters with asymmetrical 180-degree control, which is invariant to the load parameters, is also known, whereby the total duration of the switching-on control signals to each of the six gates of the three-phase inverter circuit of the inverter during the output frequency period is 180 el. hail, while for each main valve during one half period from 0 to 180 el. degrees, a conduction interval is created, during the other half period - from 180 to 360 el.grad. - create a closed state interval, clock intervals of conductivity from 60 to 120 al. and the closed state from 240 to 360 e-hail is divided into an integer number of segments of equal duration, in the right-hand faucet of the part of each of which form respectively the main signals of locking and turning on the valves (3). At the same time, in the process of coupled frequency control and the output voltage of the inverter, the number of these main signals gradually decreases with increasing output frequency until these signals completely disappear at the nominal output frequency of the converter. In the case of an N-fold range of the associated frequency control and the half-period average value of the output voltage at the initial (minimum) output frequency of the converter Fo, the number of said control signals within the clock intervals is N, and their duration is defined as

1 N -1

LO o-

6F0N2

However, the spectrum of such forms of output voltage throughout the entire control range contains parasitic harmonic components of considerable amplitude.

One of the drawbacks of the control method is the fact that the transition from one control band to another, accompanied by a change in the number of pulses in the half-wave of the inverter output curve, is made in steps, due to a sharp discrete change in the duration of the output pulses and their temporal position. This is accompanied with noticeable jumps in the magnitudes of the effective value of the output voltage of the converter and the amplitudes of the harmonics of its spectrum and adversely affects the course

electromagnetic processes in the converter and the load.

The aim of the invention is to improve the harmonic composition of the output voltage of the converter in the process of a smooth, shock-free transition from one control band to another.

The goal is achieved by the fact that, when controlled by this method, providing N-fold coupled frequency control and output voltage of the converter, when the valves of different three-phase bridge converters are periodically turned on and off with a mutual phase shift of 60 el. each valve for one half period from 0 to 180 el.grad. form the conduction band, during the other half period from 180 to 360 el.grad. form a zone of the closed state, within the clock intervals of conduction from 60 to 120 al. and clock intervals of the closed state of the valves from 240 to 300 el.grad. respectively, turn off and turn on the valves (control signals), the number of which is consistently reduced with increasing output frequency of the converter, and, at the initial output frequency F0, the clock intervals are divided into .N intervals with

with a duration equal to „r k,, in the extreme N

the right side of each of which, over the entire adjustment range, forms control signals with an initial duration of N -1

by size

that fo l 2

 in the range of 6F0N2

Fo duration

the clock subintervals t are kept constant and equal to t, the beginning of each first and the end of each last clock sub-interval is synchronized with the beginning and end of the corresponding clock interval, the formation of every 1 st from the end to the middle of the clock interval of the control signal of (each (M) th from the beginning of the clock signal interval) is carried out when the output frequency of the converter varies from F0 2 (1 -1) N

) (21-3) 4-1 p Rich when changing the output frequency from F0 to 2 (I - 1) N

to fi fo

Fi fo

inside

2 (I -1) (2i -1) - 1 each clock subinterval forms a control signal with a duration of

6 (2 | 1-1) - () priP p -F |

I -

inside (1-1) - and the right and (1-2) - and left-hand clock sub-intervals from the middle of the half-period form control signals with the duration A 12PcM (G-1) (21-1) in the extreme right part of the interval located between these sub-intervals, form a control signal with a duration of

A-fl-p-12F0N (l-1) in dia

N

Frequency band - - F0 - NF0 The duration of the clock intervals is changed in accordance with the dependence r

the right extreme part of which form the main control signals with a duration of 1/11

I -..- and

by the value of A

on all

 “0” has a control range for each main valve within the 0-30 interval,

(V)

WITH

(150) -180. 180-210, and () I UU. I JW f. IV, t l)

- 360 el.grad. synthesize additional pauses and conduction segments (additional control signals), while the locations of the fronts 1 closest to the boundaries of the first 1s to the account of additional control signals at intervals of 0-30, 180-210 electrons, determine

accordingly as

60 fSl) and 180.

№11e „, glad

0) i

-) - 180i (330-F0N at intervals

(ABOUT

-) - 360 el.grad.

The fronts closest to the boundaries of the half-periods are formed by shifting by 60 degrees. towards the front of the half-periods near the middle of the edges of the corresponding main control signals of the same name with duration A. In addition, the duration of the additional control signals is determined from the functional dependence

for K (.t-A), where the numerical value of the coefficients K at each point of the control range is determined using the curve constructed in FIG.

Figure 1 shows the simplified structure of the power circuits of a three-phase single-bridge converter made on fully controlled valves; 2 are timing diagrams illustrating the process of performing the techniques.

ten

15

20

25

thirty

35

40

45

50

the proposed control method: in FIG. 3 - the curve of the dependence of the value of the coefficient K on the relative output frequency; Figures 4 and 5 are functional diagrams of a control system implementing this method and diagrams explaining the algorithm of its operation.

The timing diagrams presented in Fig. 2 correspond to the variant of the associated frequency control and the output voltage of the converter in the five-fold range (N 5). Fig. 2a shows cyclograms of the control signals Uy of the valves + A and + B of the converter at the initial output frequency F at the half-period of the output frequency and the corresponding curve of the linear output voltage of the converter UAB. The entire central clock interval of 60-degree duration is divided into five sub-intervals of a long time.

stew T T0

12 el. each,

6F0N shown in figure 2 and arcs.

In the right extreme part of each subinterval, at the indicated time interval of the conduction band of the valve -A, the main gate valves are formed.

N - 1. , 2

control with duration

6 fo n

 9.6 el. The moments of the formation of the blocking valves of the pulses in Fig. 2 correspond to the zero level of the signals, and the conductive state of the valves corresponds to the positive value of the signals Uy. Similar to the formation of the main locking signals in the interval 60-120 al. at a clock interval of 240-300 al. degrees, the main including valves of control signals Uy are synthesized.

Simultaneously with the main control signals, inside the extreme sections of the conduction bands and the closed state of the gates, additional control signals are generated, the initial number of which for the variant is three. As shown in Fig. 2a, the locations of the i-x fronts closest to the boundary of the half-periods in the account of additional signals in sections 0-30 and 180210 el.grad. are like

gp N

five

180

, 60FQ-1)

, - .. el.grad., that when analy N

This variant for the first half period at the frequency F0 gives the values: 0; 9.6 and

(ABOUT

19.2 El. On sites (150 And

-) - 180

(ABOUT

and (330) - 360 el. marked

the fronts of the additional signals are formed by shifting by - 60 degrees of the respective corresponding main control signals. The duration of the additional control signals at the initial frequency F0 is as follows: K (t-A) K (r0 -Ao) 0.31 (12-9.6) 0.81 e.h.grad, where the value 31 is chosen as the frequency F0 in accordance with the curve constructed in FIG. 3 for a point

Wow

U

exit N

 0.2.

Fl f

1) (2I -1) + 1

n + 1

-75-for odd n and

The frequency and magnitude of the output voltage of the converter for the asymmetric control method under consideration are controlled by a constant, smooth variation in the pause durations between the main control signals and the main control signals themselves in the areas adjacent to the centers of the clock intervals, followed by a change in the duration of the additional signals according to non-linear dependence . Frequency range of work

converter from frequency F0 to -th- F0

it is broken down into subranges. The boundaries of these subbands are the output frequency values, defined as F, F0 2 (| D () () + GI

2 (I-1) N

 where

2TG

Fi1 Fi. I I + 1 for even n, where n is the number

generated basic control signals within clock intervals. Within the marked subranges, transducer adjustment is performed by two reference algorithms. On the control subbands, at which Fi F i + i, inside (at the extreme right part) of all clock sub-intervals, the beginning of the first and the end of the last of which are synchronized respectively with the beginning and end of the clock interval, the main control signals with duration

I T (C1-1) - (T - PTA) The frequency change (duration of the clock interval) is produced by changing the duration of the clock nearest to it on the left side to the center of the clock interval.

0

five

five

0

0

five

0

five

five

0

The pulse curve of the linear output voltage of the converter corresponds to the central pause between control signals, which at the time the output frequency reaches the FI value, decreases to zero at the interval 60-120 °.

In the frequency ranges FI F, inside the (1-1) - and the right and (I-2) - and the left from the middle of the half-cycle of the clock subintervals, the control signals are formed with a constant duration of definite, 4 (i - 1) 2 - 1

my as I am --T2F0N (I-1) (21-1) In the extreme right part of the interval located between the specified sublots, the main control signal of an adjustable length, „1 2 (i-1) (2i-3) + 1 A - A, .- 1-,

by changing which the output frequency of the converter is adjusted. A decrease in the value of A to zero is observed at the boundary frequencies F | ..B range of high output frequencies of the N converter at NF0 F -n-Fo duration

Each of the two subintervals, g, is defined as t 1ggs for each clock subinterval; in its extreme right part, one main control signal is formed with a length of 1 .1

by the value of A

T2f

-. At the edge of IZrW

In this case, the control zones are formed by one additional control signal.

Throughout the entire operating range of the converter, the transition from one control subband to another is performed by the unstressed method, by smoothly varying the duration of the respective control signals and the pauses between them. The described control mode thus provides practical constancy in the ratio of the first harmonic of the output voltage of the converter to the frequency when the latter varies over a wide range, as well as a significant improvement in the harmonic composition of the output voltage at each point of the control range.

In the case of the analyzed variant of the associated control of the frequency and magnitude of the output voltage of the converter in the range of an odd number of times () on the first subrange of control, the change (increase) in the frequency (reduction of the period) of the output

the signal is produced by reducing the duration shown in Fig. 2, and by the left central arrow on the clock interval of the main trigger pulse. The duration of the shut-off valves of the main control signals changes in accordance with the functional condition1 (11

B (2 - 1) (T TSGT

-ttg marked process

% JU I go Go Go

continues until the output frequency of the 2Q-1) N converter is reached

depending

cheni rz 20

 2 (1-1) (2I -1) -1 FO, at which the length of ukamostI

6T

120Ro

increase in frequency

20

and decreases from zero value F3l

13

nineteen

the main switching pulse is reduced to zero.

In the next subinterval of control, the duration A of all the main control signals, with the exception of the central one, remains unchanged and is equal to R1lp g / and the duration of the central main control signal is determined from the functional dependence

On the next subband of the converter, observed in the frequency range from Pz -yj- F0 to Fa 2F0 and

characterized by a decremented index value i (), the frequency is controlled, as in the first sub-band, by decreasing down to zero the length of the left central main switching valve shown in FIG. 26 by synchronous change (decrease) of the duration of the switching-off main signals management The number of additional control signals is two.

A further change of the main control signal left from the center of the clock interval is made in accordance with the dependence

12 + 111

I

6T

at

 FO 6 F 20 Fo

constant duration of the second signal, -j

equal to K pR ° D ° lies to my

The timeframe for achieving the F - FO value,

Starting with the specified frequency F-F 0 and

up to the nominal output frequency of the NF0 converter, within the clock intervals, two clock subintervals are formed equal to the duration, which is defined as r –tttr / in the right-hand part of which

main control signals are synthesized with decreasing frequency

the duration of I .TRTG

thirty

35

40

reaching zero at the rated output frequency of the converter.

The number of additional control signals generated within the extreme 20 thirty-degree segments of the control zones, in the process of regulation, gradually decreases from a value equal to

N NICK, N

-d-for odd N and-y for even N,

25 to one additional impulse formed in the zone of increased output

frequency converter with F F0

(figv). The curve of the values of the correlating coefficient K constructed in FIG. 3, which connects the duration of the additional control signals with the duration of the main pulse array of the output curve of the converter, shows its essentially nonlinear character. The relationship between the current values of the output frequency F and that plotted in Fig. 3 on the abscissa axis is determined by the relative value of the output voltage of the converters from the ratio-p-jq-

So, at the nominal frequency of the converter NF0 (U out 1) for all modes

45 value K 0,2, respectively, in relative units, the duration of additional control impulses -. at the same time (and additional pulses of the output voltage curve)

50 for K (Mr.I) 6 el.grad.

The principle of construction of vertical type control systems that implement the described control method as applied to the variant will be considered on the example of a device, the functional diagram of which is shown in Fig. 4. The oscillator clock pulses 1, to the input of which an analog signal is received, sets the frequency Ur, forms at its first output a sequence of short pulses, the frequency of which throughout the entire control range is 12 times higher than the output frequency of the inverter variable voltage 2 synchronizes its operation, so that at the output of generator 2 a symmetrical sawtooth voltage sweeps six times as compared to the output of the frequency inverter. The reference voltage source 3 is connected to the positive inputs of adders 4-6, to the other inputs of which a signal comes from the output of the integrator 7. The output of the functional converter 8 is connected to the inputs of the multiplying unit 9, the other input of which is connected to the output of the integrator 7. The output signal multiplier 9 is fed to the inputs of adders 10 and 11, also connected to the outputs of adders 4 and 5.

The output of the sweep generator 2 is associated with the first inputs of the comparators 12-17, the second inputs of which receive signals from the adders 4-6 and 10-11, respectively. The outputs of all comparators include forming circuits, consisting, as shown in relation to comparators 13 and 15, of logical inverters 18 and 20 and differentiators (differentiating circuits 1922, forming short unipolar pulses at times of equality of signals at the inputs of comparators 12-17, which through clauses 25-27 are sequentially received at the inputs of counting triggers 28-30 and cause their periodic triggers. Signals (pulses) from node 19 and from the second output of clock generator 1, the pulse frequency from which 6 times exceeds the output frequency of the transducer, through the disjunctor 23 is fed to the input of the four-bit register 24. The outputs of the flip-flops 28-30 are connected to the information inputs of the logical distributor of control pulses 31, the output of the trigger 28 is also connected to the input of the unit determining the total duration of the output pulses 32. At the input of the unit 32, a capacitor 33 is switched on, which selects a constant component of the pulse sequence p of the trigger output 28.

The voltage of the capacitor 33 goes further to the divider 34, in which it is divided by the analog signal of setting the output frequency UF, with the result that the output of the block 32 at the appropriate scale produces a voltage proportional to the total duration of the output pulses over a half-period. This signal is fed to the negative input of the integrator 7, the positive input of which is connected to the constant voltage source 35. The outputs of the register 24 are connected to the clock inputs of the distributor 31.

Figure 5 presents time diagrams explaining the operating principle of the control system. The signal indices in FIG. 5 correspond to the numbering of the nodes and blocks of the system shown in FIG. 4. The amplitude of the sweep signal U2 of the generator 2 decreases in proportion to the output frequency of the converter and is permanently detected by an amplitude sensor 36, the output of which is fed to the first input of the circuit 37, the second input of which is connected to the constant voltage source 38. Selection of the voltage of sources 3 and 38 produced in accordance with the conditions:

U2max N

J 3

- x- U2.

- -i2max

N

2 3

U2

Max

where 112max is the maximum amplitude of the U2 signal, observed at the initial output frequency of the converter. The magnitude of the 11z signal determines the duration of the clock subintervals on the lower frequency subband. The amplitude of the signal at the output of the integrator 7 is proportional to the duration of the main output pulses of the output voltage curve. Simultaneously with the formation of the main array of output pulses using signals generated by the outputs of the flip-flops 29 and 30, additional pulses are generated, the duration of which at each point of the control range is determined by the size of the output signal taken from the output of the multiplication unit 9, to the first input of which from block 7 signal comes

O) proportional to the value (mA), and

the second receives a signal from the functional converter 8, which is connected to the input signal with the UF reference signal and forms an analog signal at its output on the appropriate scale, the value of which is proportional to the value of the coupling coefficient K.

The outputs of the adders 4-6, in accordance with the diagram of their connection, synthesize signals that determine the moments of the formation of the fronts of the main pulses of the output voltage curve of the converter. The internal feedback loop of the system, including nodes and blocks 28, 32-34 and 7, provides for the entire adjustment range the formation of a correction signal, which is fed to the inputs of adders 4-6 and automatically maintains the constant volt-second constant, according to the static principle. the area of the output pulses at half time in the process of changing the output frequency. In this case, the implementation of the functional dependencies between the duration of the control signals, their temporal position and the values of the output frequency of the converter, presented in the first part of the description, is performed automatically, from one control subband to another, observed at the boundary frequencies of the RS and FI, and also with the help of a key 39, controlled by a command from the output of the comparison circuit 37, the transition from low-frequency to high-frequency control takes place, often From 2 FO.

By virtue of the inclusion of a four-bit register 24, the input of which is connected to the output of the comparator 13 through the differentiator 19, the required asymmetry of the formation of control signals is provided. The digitized states of the output bits Q, Oz, Q2, QI of register 24 in the output frequency period are respectively recorded as: 1000, 1001, 0010, 0011, 0000, 0001. 1010, 1011, 1100, 1101, 1110, 1111. The logical functions implemented by the distributor 24 and coming in the form of control signals to the inverter valves are, thus, as follows.

-A Q4Q3Q2Q1U29 + CMQaCteQi +

+ CMQaCteChUaO + Q4d3Q2QlU29 + + Q2U28 + Q3U28 + Q4CHU29 +

+ ШШШШЬЬаэ + CUQ1 from,

+ B CUQ2QlU29 + CUQ2Q1 + + OzSSHSShzO + Q3Q2Q1U29 + Q2U28 + + 5 Q2U28 + CUQlU29 +

+ Q4Q3Q2CHU29 + Q4QiU3o; + C CteQzQlLteo + QsQ2Qi +

, + Q4Q2QlU30 + Q / lQ2QlU29 + Q.U28 + + Q3U26 + Q4Q3QtU29 +

5 + Q4Q2QiU29 + Q4Q2Ghll30

Thus, the proposed method of controlling a three-phase valve converter based on an inverter with a voltage of 0, in which a smooth, unstressed transition from one control band to another is achieved over the entire range of associated frequency control and output voltage.

5 allows, due to the formation of additional compensating pulses, to improve the harmonic composition of the output voltage due to the complete elimination from the spectrum over the entire range of adjustment of the fifth

0 harmonic component and a significant decrease in the amplitude of the seventh harmonic.

These closest to the main harmonic create maximum braking

5 moment of asynchronous motors powered by converters, their exclusion makes it possible to significantly reduce losses in the converter system and the load and to improve the quality of the control process in

0 whole.

Claims (1)

The invention The method of controlling a three-phase valve converter, which consists in the fact that in the process of M-fold 5 adjusting the frequency and output voltage values, the valves of different phases of the converter are periodically turned on and off with a mutual phase shift of 60 degrees., While for each valve for one half-period from 0 to 180 degrees, a conduction band is formed, during the other half period from 180 to 360 al., form a zone of the closed state, within the clock intervals 5 conductivities from 60 to 120 el.grad, and clock intervals of the closed state of the valves from 240 to 300 el.grad. form. signals with the corresponding control zone; 0 which are consistently reduced with increasing output frequency F of the converter, and at the initial output frequency F0 within the clock intervals form N subintervals of the same for all 5 duration adjustment range, 1 equal to G0  the end of each of k6F0N on the entire range of control form the control signals from the beginning-jN-1 Noah duration / C -g-, 6 fo n characterized in that, in order to improve the harmonic composition of the output voltage of the converter, in the process of smooth unstressed transition from one control band to another, in the frequency range F0 - (N / 2) F0, the duration of the clock subintervals is constant and equal to r0, the beginning of each the first and the end of each last clock sub-slot are synchronized with the beginning and the end of the corresponding clock interval, the formation of every 1 st from the end to the middle of the clock interval of the control signal This (each (1-1) -th from the beginning of the clock interval of the signal) is performed when the output frequency of the converter is changed from F0 to 2 (- 1) N - s 3 h + and with Rg fo 2 (1 -1) (2i changes the output frequency from F0 to FI 2 (. I - 1) N  SG inside each ° T (-l) (2i -1) -1 th clock subscript, a control signal with a duration of A 6 (2i1-1) (G T5Tg) with RFF inside (1-1) -x right and (i-1) -x left from the middle of the half-cycle of clock subintervals form control signals with a length ,, 4 (i-1) 2 - one A 12 F0 M (I) in the extreme right part of the interval located between the specified intervals, a control signal with a duration of 0 five 0 five 0 BUT 1 2 (i -1) (2i -3) + 1 :, - A., in dia. frequency zone N / 2 F0 - NF0, the duration of the clock subintervals change in according to the dependence of t - - tu-p-in the right extreme parts of which form the main control signals with a duration of A 1/12 (1 / F - 1 / FoN), and for the entire control range for each main valve within the 0-30, (150 -A {1) / 2 intervals - 180, 180-210 and (330 - AG) / 2) - -360 el.grad. generate additional control signals, while the location of the fronts of the 1st near the borders of the half-periods of the 1st in the account of additional control signals at intervals of 0-30 and 180-210 al.grad. defined respectively as 60 0 F0 -1-1 Gup 60 F (l -1) ig m (1 NP 4-- --J- cm gpdp N FoLN fo el.grad .. At intervals (150 - А (1) / 2) - 180 and. (330 - ti jf / 2} - 360 el.grad. the fronts closest to the boundaries of the half-periods are formed by shifting by 60 el. hail, in the direction of ahead of the half-periods of the fronts close to the middle of the corresponding corresponding main control signals with the duration A h, while the duration of the additional control signals is found from the functional (ABOUT the dependences y – K (m – A), where the numerical value of the coefficient K at each point of the control range is determined using the curve constructed in FIG. ) ъ f (} with 1 .thirty  iJ ul M l // j  + GP G1G-1 GP G ° P P -I G . fciЈ L L1 ". JLJULJULJULJULJUbLJ I.M-t ± f3E ± 1 etp PG A.PPPPPPPP south tsv ° " Lee L 3 EZ L1 tgt 0.050.060.08 0.1 0.2 Fig. 3 0.4 0.6 0.8 1.0 LH I