SU1734179A1 - Method of control over three-phase controlled valve converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control converters used in variable frequency drive systems. The aim of the invention is to improve the harmonic composition of the output voltage of the converter. The control method is to periodically switch the converter valves with a phase shift of 60 al. The associated control of the frequency and magnitude of the output voltage is carried out by continuously smoothly varying the duration of the main control signals at clock intervals of 60-120 and 240-300 al.grad. In contrast to the known, the duration of the clock subintervals, inside and in the middle of which form the main control signals over most of the adjustment range, is changed as a function of the output frequency according to a hyperbolic dependence. In the extreme 30-degree sections of the half-periods of the control signals, the converter valves generate additional control signals, the duration of which at each point of the frequency range is determined in accordance with the reduced tantsendental equation, including the number (frequency) of the eliminated harmonic of the spectrum, the number and duration the main control signals, the duration of the clock subintervals. 4 il. with co 4 i CHE

Description

The invention relates to electrical engineering and can be used in the control of converters used in variable frequency drive systems.

The algorithms of pulse-width control by three-phase voltage inverters are known, at which the duration of the control valve turn-on gates for the period of the output frequency is 120 or 150 electrical degrees.

However, the shape of the output voltage curve of the converter, to a large extent, depends on the parameters of the load, which makes it difficult to effectively use these algorithms when powering the electric motors.

There is also known a method of controlling a three-phase adjustable transducer, characterized by a constant stepwise variation of the duration of pauses between control pulses (signals)

and the control pulses themselves in the central regions of the clock intervals of 60-degree durations, which form the central part of the 180-degree conduction zones and the closed valve body. To maintain a constant ratio of the value of the half-period value of the output voltage of the converter to the frequency on the control subbands, where the regulation is carried out by varying the duration of the central pauses, the duration of the control signals varies depending on the values of the output frequency and the number of control pulses produced . Within the control zones, at which control pulses of variable durations are formed at the centers of the clock intervals, the duration of the pulses of the output voltage curve remains unchanged. At the same time, the control signals are formed in the middle of the clock subintervals, the beginning and the end of the first and the last of which are synchronized respectively with the beginning and the end of the corresponding clock interval.

The disadvantages of this control method include the fact that throughout the control range in the spectrum of the output voltage curve of the converter, there are significant parasitic harmonics, among which, in particular, the fifth harmonic component, which creates the highest braking torque for the asynchronous motor, is most undesirable. powered by the converter.

The purpose of the invention is to improve the harmonic composition of the output voltage of the converter;

The goal is achieved by the fact that, when controlled by this method, which provides N-fold coupled regulation of the frequency and magnitude of the output voltage of the converter, during which the main valves of different phases of the converter are periodically switched with a mutual phase shift of 60 electrons, while for each valve on the clock intervals of 60-120 al.grad, and on the clock intervals of 240-300 al.grad. form the main control signals, in accordance with which the valves are turned off and on, the number of these signals decreases with increasing output frequency F, and at the initial output frequency F0 each of these clock intervals is divided into N subintervals of duration

That is -Ј-p-jrr. inside and in the middle of each

of which form the above-mentioned valve control signals from the initial

N -1

Lo duration, and in the process

6 foNr

adjusting the output frequency in sections 60-90 and 240-270 el.grad. The formation of each i-ro main control signal, the beginning of the first of which is phased with the beginning of the clock interval, is performed by changing the output frequency of the converter from FO to FI. In this case, in the frequency range FH-I F0 P / (if Fii FJ), within each half of the clock intervals, i are formed by i main control signals with the duration

(-p p N). and in the range

Fi F each half clock intervals form on (i-1) main

a control signal of duration A, and the i-th main control signal is formed in the middle of the clock interval with duration A, and in sections 90-120 and 270-300 el.grad. the formation of control signals is carried out symmetrically. In contrast to the known method, for each valve in the extreme zones of the half-periods of the output voltage 0-30, 150-180, 180-210 and 330-360 el.grad. form additional control signals of duration y. the fronts closest to the boundaries of the half-periods are formed by shifting by Ј60 el.grad. Near to the middle half-periods of the front of the corresponding main control signals of duration A or Z. In the output frequency range FO - (N-1) Fo, the duration of the above-mentioned clock subintervals is varied in accordance with the ratio

t-, fo

6 F (N Fo + Fo - F)

A and A are found

ii-1

magnitudes

as

A

6 N Fo (2 i - 1)

1 -2 (l-1) r-i

one

6F j 6 N Fo (2 i - 1) the values of FJ and FJ are determined from the functional dependencies:

FI FO x

y2iN-fl-VfilN. + (2I -l) (N + 3-il)

., 2N-2IN + 1 -V (2N-2IN + 1 + 4N (2 | -1) (N + I-2lT

over the output frequency range of the converter (N-1) Fo - NF0, the duration of the clock subintervals is defined as

t, p, and the formation of each of the 1st additional control signal is carried out by changing the output frequency from FO to Fi (N - 2i + 1) Fo (Fi Fi Ff). the duration of the additional control signals is determined in accordance with the functional dependence

g | А -% - в4 + СЈГС1

where K is the number of the suppressed higher harmonic;

L, ktg. CP k -t (+ i) -A,

A 4 sm sin sin - - L% 5 / i

D, K. kn

B 4 sin -o-sin -7, - cos

(| +1) + A. 2

for frequency bands Fi (N - 2i + 1) Fo F Fi, a

Kff

icti 2

C 4sin-sin-soi-cos - ;:, n kfi, (fr (25-02 l 1. To Ktf nЈ

42co5T5inkb

, / "

for frequency bands FM F FI

in also at

Fi F NF0 (npn i 2)

Sl. L .l Tl

 4 sin -7Г- sin -n- cos

K7G

cos K x

, n r. Kn. (-R-5-) - sin-s-sin

KT

Fig. 1 shows a simplified structure of a power section of a converter made on fully controlled thyristors; Fig. 2 shows timing diagrams illustrating the process of generating control signals for option N 5; Fig. 3 shows curves showing the course of change in the relative duration of the clock subintervals, as well as the locations of the fronts of the main and additional output pulses in the process of adjusting the transform; Fig. 4 is a generalized functional diagram of a control system implementing the proposed control method.

The time diagram, constructed in Fig. 2a, and the corresponding initial (minimum) output frequency of the Fo transducer, shows signals (pulses) of control Uy arriving at the + A cathode group of the three-phase inverter bridge circuit in the conducting state on the interval El 120 .grad and causing it to periodically lock on this interval. Below is the corresponding linear curve section.

output voltage converter uaB. In this case, the clock interval is 60-120 al. divided into 5 clock subintervals with the same duration T0, equal to 12 electrical degrees, inside and in the middle

each of which the main control impulses are formed

To th-g -; - 9.6 el. On clock

interval 240-300 el.grad. similarly, in the middle of the clock subintervals, they generate the main signals to turn on the valve. At the same time in the areas of 0-30 and 150-1 ai el.grad. zones of each valve and in the sections 180-210 and 330-360 el.grad. closed zones, additional control signals are generated.

An increase in the output frequency of the converter is accompanied by a corresponding decrease in the absolute value of the length of the clock intervals. At the same time when controlled by the described method in accordance with the ratio

t - varies by

6 F (N Fo + Fo - F) non-linear dependence of the absolute value of the duration of the clock subintervals up to the value of the frequency F (N-1) Fo. At the same time, over the entire adjustment range, the beginning of each clock interval is synchronized with the beginning of the corresponding first clock subinterval, and the end of the clock interval is synchronized with the end of the last clock subinterval. The formation of the main control pulses is performed in the middle of each clock subinterval, and the formation

Near the edges of the half-cycle, the fronts of the additional control signals are produced (shown by arrows in Fig. 2) by shifting by 60 electrical degrees. Near to the center of a half-cycle of the fronts of the corresponding main signals. The process of controlling the frequency of the output voltage of the inverter is accompanied in this case by a constant stepwise variation of the duration of the pauses between all control pulses, in that

the number of pauses, as well as the duration of the main control pulses themselves, in the central sections of the clock intervals, in the overlap zone of the middle clock subintervals,

formed symmetrically in each half of the corresponding clock intervals. At the same time, to maintain a constant ratio of the output voltage converter to frequency, on the control subbands, during which pauses are formed at the centers of the clock intervals, the duration of the main control signals varies depending on the output frequency values and the number of signals generated at each half of the clock intervals in accordance with the expression

I am 2-p (-p- fo n). On subranges

the adjustments at which control pulses of variable durations are formed in the centers of the clock intervals, the duration of the remaining main control signals also depends on the current values of the output frequency of the inverter and is determined from the ratio

I tg vi p / a 1 The limiting values of the frequencies Fr and FJ, passing from one of the mentioned control subbands to the other, are from the corresponding functional dependencies, including the parameters F0, N, i. In addition, on the upper frequency range with (N-1) Fo F NF0, the duration of the clock subintervals is defined as

t

12 F

in the middle of which up to

nominal frequencies are synthesized control signals with a duration of

111

I (r - N p). The duration of the additional control signals is determined over the entire control range in accordance with the functional dependence.

} -j arctg

(B + C) 2 (B + C)

A 4sin-sin-K (-y-A) B 4sin-cos ± Alsin; С 4 sin 1ф- sin cos cos К X

HCG-T «in K7G - KG

X (- "- J-sinsin

When determining the first (or initial) value of the cutoff frequency, it should be taken into account that it depends on the value of the number N (it is even or odd). So, at an even value of N, the first boundary frequency will be FI (where i N / 2), in this case in the range F0 F of the RGU,

eleven (

 -up- {. p- -yy-p- J, and when N is an odd, the first frequency will be the frequency of FI

(where i

N + 1

2-), since the corresponding

the value of Fi 1 is less than F0 and therefore does not make sense. Therefore, for the considered variant, on the first sub-band of adjustment of the output frequency of the converter, the adjustment process is carried out by successively changing the duration of the control pulse (arrows in Fig. 2a) centrally on the clock interval produced by i 3 according to the relation:

, "H - 1

I -.TP 1) G 6NF0 (2i-l)

down to the frequency

Rs Fo X

45

21 + 1 -V (2IN +1) - NC2I-1) {N + 3-2I) 2

where K is the number of suppressed higher harmonics, for the frequency subbands FT (- 2i + 1) WG;

. . Kt (i-rt.). h. ft 4snn-Ј-ggSin

K "li-4 Ktfc .- fri A l. K

-COS

k X A (ft 1C

About 4 sin -Ј s.n -Ј- cos -cos k -

k7 rfr (2.-04 i k. k1G. to Tecaeie, nK i - r-jJe.n1-S, nTS.nr,

Iit

for frequency bands Fi F FI, a also for FI F NF0 (rfle i 2):

0

five

where N 5, i 3.

Substituting the indicated values, we determine the value of the first cut-off frequency Pz 1.71 FO. Determined in accordance with the specified method, the duration of X additional control signals at frequencies F0 and Pz, they are respectively 0.62 and 1.88 ehgrad. (see the dependence plotted in FIG. 3, expressed in electrical degrees, y versus the output frequency, calculated for the variant of eliminating the fifth harmonic (K 5).

When the output frequency of the converter reaches the limit value

RZ the duration of the central on the clock interval of the main control pulse is reduced to zero.

In the next relatively short adjustment range, the change in the output frequency of the converter is accompanied by a successive change in the length of the pause between the main control pulses central to the clock interval, the duration of the main control pulses themselves, the number of which within each half of the clock intervals is two (i 2), changes (decreases with frequency) according to dependency

111

I 2 i (rk with) carried out

by two-way modulation of the edges of the control signals located in the middle of the corresponding clock subintervals. Here, after the frequency limit Pi (N - 2i + 1) of Fo 2F0 is close to Pz, the number of additional control signals decreases from two to one. The duration of the clock subintervals continues to decrease sequentially. The upper frequency limit of this subband is the frequency

X 2N-aiN + l + V (2N-2IN + iy + 4N (2 | -lKN + 1 -TlL; jjf

The next subinterval control observed in the frequency range

F -rim g, -frJjLl XM-M J -Д.5 (And - 1 I5 +3 -O ",", Fo

characterized by a consistent change in the duration of the central control signal on the half-period I

ill 2 (i - 1) Fo, L 6FL NF0 + Fo-FJ

6 N Fo (2 i -1)

 1 M 2 Fo .1 f

6 F 6 Fo -F 90 Fo

The sequence diagram of the formation of the control signals at the frequency Fa F Fa is depicted in FIG.

At F Fa, two main control signals (i 1) are formed within the clock intervals, as well as in the extreme zones, by one additional signal. The upper limit of the specified control subrange is observed at the nominal rate of 5.

the input frequency of the converter F NF0. The specified subrange is divided into two parts: after the output frequency reaches the value F (N - 1) F0 4F0 and 5 to the frequency NF0, the relative duration of the clock subintervals t is fixed at the level t 12 F 30el, degrees,

in the middle of which the main control pulses are formed with successively decreasing duration

i

12 F N Fo

Thus, along with a sequential change in the number of main pulses in the half-wave of the output curve of the inverter, carried out by smooth continuous variation of the shape of the output voltage curve and providing

0 unstressed transition from one control band to another, in the extreme parts of the output curve up to the upper part of the frequency range additional pulses are formed, the number of which also gradually decreases with increasing frequency up to one pulse per quarter period and the parameters of which contribute to compensating the amplitudes of unwanted spurious harmonics of the sequence main output pulses. In this case, the current parameters of all pulses are selected from the condition of ensuring the total volt-second area of the half-wave over the entire range of constancy control

5 is the output curve of the inverter, which is identical to the almost linear change in the first (main) harmonic of the output voltage with a change in the output frequency, corresponding to the most economical law of controlling an asynchronous electric drive. The calculated for Fig. 3 for the option N 5, the duration values for the additional control signals are determined

5 from the condition of complete suppression of the fifth harmonic component (K 5), as being in antiphase with the main harmonic, which creates the maximum braking torque of the electric motor and is therefore the most undesirable. An analysis of the course of change of values of y shows, in particular, that the maximum values of y and, accordingly, the longest duration of additional signals (shown by the dotted line in Fig. 3 with reference to variant N 5) is observed at the boundary frequencies FI, and the smallest values of the indicated value - at frequencies FI.

five

0

0

A generalized functional diagram of the converter control system, performed according to the vertical principle and implementing the described method, is shown in FIG. 4. At the output of the frequency setting unit 1, a signal Ui is generated, the value of which is directly proportional to the value of the output frequency of the converter, which provides 2 clock pulses and functional converters 3 and 4 to the generator inputs. In this case, the functional converter 3 contains N output channels. The frequency of the clock pulses of the generator 2 determines the frequency of the output signal of the generator 5 of a developing sawtooth voltage balanced on both sides, which, in this case, is six times higher in the control range than the output frequency of the inverter. The magnitude of the signals at the outputs of the functional converter 3 over the entire control range is proportional to the current values of the temporal positions of the edges of the respective main control signals at half the clock intervals (upper time diagram in Fig. 2a). The value of the output signal of the functional converter 4 at each point of the control range is proportional to the absolute value of the durations of the additional control signals, the frequency dependence of which for option N 5 is constructed in FIG. The marked values of a and y are tentatively determined by calculation from the above ratios characterizing the mode of implementation of the control method under consideration, Relative, expressed in el. Degrees, the angles of a-O5 are plotted in FIG.

The signals from the output of the functional converter 4 are fed to the inputs of adders 6 and 7, the other inputs of which receive signals from the even outputs of the functional converter 3, with the help of which the formation of even fronts ag and OA is formed. The outputs of block 3 and adders 6 and 7 are connected (figure 4) with the corresponding inputs of blocks for forming the main 8 and additional 9 control pulses, to which the sweep voltage Us of the generator 5 also arrives. At moments of equal voltage Us the output signal of nodes 3 6 and 7 inside blocks 8 and 9 are produced (shown by the dotted line in Fig. 2a), commands for forming the fronts of control (and output) pulses, which, as shown with reference to the structure of block 9, are in the form of short pulses from the comparator nodes 10 and 11 through disjunctor 12 n arrive at the input of the counting trigger 13, and from its output in the form of a sequence of pulses with a duration of Y, the information input of the logical distributor of control pulses 14. Similarly, the other information input of the distributor 14 receives a sequence of pulses whose duration is equivalent to the current duration of the main array of output pulses . The clock input of the distributor 14 is connected to the four-bit register channels 15. Digitized states of the outputs 04, 0.3, 02, 0.1 of which are recorded on the output frequency period as 1000.1001, 0010, 0011, 0000, 0001, 1010, 1011, 1100 , 1101, 1110,1111 .... The logical functions implemented by the distributor 14 and received in the form of control pulses to the corresponding inverter valves have the following form:

-A Q4Q3Q2QiU 9 + Q4.Q3Q2Q1 + Oz0201 +

+ Q3Q2Q1U9 + Q.4Q2U8 + Q3Q2U8 +

+ Q4Q.3Q2Q1U9 + Q.4Q2QiU9;

B j} 4Q.2QlU9 + Q.4Q2Q1 + Q3Q2Q1 +

tQsCteQiUg + Q4Q2U8 + Q4Q3Q2Us + Q4QiUg + + Q3Q2QiU9;

С ОССштоэ + ОзИ201 +, 040.201 + + Q4Q2Q1U9 + Q4Q2U8 + Q3Q2U8 + Q.4Q2CH Ug + + Q4Q2QiUg.

Thus, the proposed control method allows one to significantly improve the harmonic composition of the output voltage of three-phase transducers, both by increasing the number of output pulses generated in a half-wave by the average and increased output frequency ranges, which is achieved by continuous nonlinear modulation clock intervals, and due to the formation of additional pulses in the output curve, the duration and

whose temporal positions vary according to the formulated non-linear dependencies, which ensure the complete elimination (compensation) from the inverter output voltage spectrum of the most undesirable parasitic harmonic components. At the same time, in the process of adjustment, a smooth unaccented transition from one subband to another is provided. The improved quality of the output voltage of the converter and

Claims (1)

the regulation process favorably affects the nature of the processes occurring in the load, which makes it possible to reduce losses and reduce the amplitude of current pulsations and torque of asynchronous electric motors. The invention The method of controlling a three-phase adjustable valve converter with N-fold coupled frequency and output voltage control is that the valves of the different phases of the valve converter are periodically switched with a mutual phase shift of 60 electrons, for each valve clock intervals from 60 to 120 el.grad. and at clock intervals from 240 to 300 el.grad. form the main control signals, according to which the valves are turned off and on, the number of these signals decreases with an increase in the output frequency F, and at the initial output frequency F0 each of the specified intervals is divided into N subintervals one the duration of 6Fo N inside and in the middle of each of which form the above-mentioned basic valve control signals from the initial Yao duration - and in the process 6 F0Nr adjusting the output frequency in sections 60-90 el.grad. and 240-270 el.grad. The formation of each 1st main control signal synthesized in the middle of the corresponding clock subinterval, the beginning of the first of which is phased with the beginning of the clock interval, is performed by changing the output frequency of the converter from Fo to FI, while in the frequency range FH-I F Fi ( Fi In Ff-FI + I), within each half of the clock intervals, form i basic control signals for a duration of 1 1 I'm here 12 i VF F0N and but in the range FI F FI at each half of the clock intervals form on (i-1) main a control signal of duration I, the main control signal is formed in the middle of a clock interval with a duration of D, and in sections 90-120 electrical degrees. and 270-300 el.grad. the formation of the main control signals is carried out symmetrically with respect to the middle of the half-period of the output voltage, characterized in that, in order to improve the harmonic composition of the output voltage of the converter for each valve in extreme zones of half-periods of output voltage 0-30,150-180,180-210 and 330-360 el.grad. form additional control signals of duration y, the fronts of which are close to the borders of the half-periods are formed by shifting by эл60 e.h. near to the middle half-periods of the edges of the corresponding main control signals of duration A or H1, and in the output frequency range F0 - (N-1) F0 the duration of the above clock subintervals is changed in accordance with Fo with a ratio of t g s / m s -i About GM GM Go t Go - G) the values of I1 and I, are found as ii r1 .. Tt N Fo (2 I - 1) A () T 6F0N (2I-1) the values FI and FI are determined from the functional dependencies x 2IN + 1 - / {2IN + l) i- “NCll-l) (N +3 - 21) c t - e v FI Fo X  IN - 2IN +1 + V (2N - 2IN + 1T + N (2I - t) N + 1 - 2 |) in the output frequency range of the (N-1) FO-NFo converter, the duration of the clock subintervals is defined as t - „p, and the formation of each i-ro additional control signal is carried out when the output frequency is changed from Fo to (N - 21 + 1) Fo (Fi FI). the duration of the additional control signals is determined in accordance with the functional dependence x. where K is the number of the output voltage of the highest harmonic to be excluded from the spectrum, for the frequency subbands Fi + i F F W and for FI F Fo N (for i 2) “... Ј,%., -four . "V,. „T (t, 5ll 6.tt.n-e. ,,“ - j “e-i-i j -. . kЈ1. to k / s-; Јi Sin-jeos-SovkMt --- k7 to -sinrjsin-j-, "T For frequency subbands, FI F $ Fj „,. kUi-0. k№-fc; - Vl. A - 4 s.n - -smg5in - „A. K "(t-i Kt-t-.. B sm-2-cc so  . K-X1, kg, Ј C-4s, ni: e.r, TcoeTcosK (-g-T) iff. rfiu; -i) C -x -i. to-g KiT. a teco5-g9.nK --- --- J5m - 5, .iy) four silt J P. JZj & i: go ILJJULn П П П П П Jl В Д ... "," M, "frЦ-Ц M-fr Mn. fl ft . Jljil in n, r 3fO mraurnmrj on fe. ) ( g, 1  , KG JZj & i: go in n, r 3fO on Fiel