SU1757065A1 - Method of controlling bridge converter with width-code control - Google Patents

Abstract

The essence of the invention is related to controlling the frequency and magnitude of the output .2 voltage of a three-phase bridge converter according to an economical law that ensures a constant ratio of voltage to frequency, while smoothly changing the duration of the main and modulating control signals formed on the edge sections half-periods of control of clock intervals of 60-degree durations of the duration of the tact subintervals, inside and in the middle of which the synthesis uyuts modulating control signals when the control mode is proposed as a function of the values of the supply voltage of 2 n f- ly, 6 cl yl

Description

The invention relates to electrical engineering, namely to power converter technology, and can be used in controlling a rfa frequency converter based on voltage inverters that feed a variable frequency drive system.

Algorithms for 120- and 150-degree control of adjustable three-phase converters are known, which make it possible to form an output voltage AIN which is acceptable in terms of spectral composition, but does not ensure the independence of the shape of the output signal curve from the load parameters.

Also known is a 180-degree method of controlling a three-phase converter, which ensures the invariance of the shape of the output curve from the load. The method is based on modulating the extreme half-periods of the clock intervals with modulating control signals, the duration of which depends on the output voltage.

However, the direct application of the control method in systems of frequency-controlled asynchronous electric drives does not allow a smooth, unaccented change in the number of pulses in the output half-wave with associated frequency control and voltage (decrease in the number of pulses with increasing frequency)

The aim of the invention is to improve the quality of the converter control process due to the smooth, unaccented change in the shape of the output voltage curve.

When controlled by the method in which the main valves of different phases and groups of the converter are periodically turned on and off with mutual phase shifts of 60 e degree in the sequence + A C + B

V |

SL

h

About About SL

-A, + C, -B, in addition, for each valve form positive half-periods of conductivity and negative half-periods of the closed state, each of which consists of three clock intervals of 60-degree durations, at the extreme half-periods of clock intervals form modulating control signals (pulses) , the duration of which determines the value of the output voltage of the converter, in the process of N-fold coupled frequency control F and the voltage value according to the law of the ratio of the voltage value neither to the frequency at the nominal (minimum) supply voltage, the formation of these modulating control signals over the entire control range, starting from the initial frequency F0, is carried out in the middle of the clock intervals

Yeo

with duration t - –g. , the clock intervals are synchronized with the middle of the corresponding central clock subinterval (for odd N) or with the end and the beginning of the corresponding central clock subintervals (for odd N), while in the frequency ranges F F within the clock intervals they form I modulating control signals with a duration

/ 1, 1о

  F F0 E N the ranges F, F, F i at the extreme portions of the clock intervals form control signals with duration

, 1 (i-1) (i-2) Eo + Eo 12 FTRTET MIND

), on the frequency diagrams a, the survivability of the remaining (-2) -and control signals is determined in accordance with L1r;

addiction

1-1)

oJoTT

the values of the cut-off frequencies F i and FJ, which are transient from one control subband to

... -F0E (i-1) N

another is found as FI; /: -Lr p and

i (, i i; Co to

F0E (i-1) N

F

where the minimum (i-1) (i-2) & o-f-Eo on (nominal) and the current amplitude of the DC supply voltage converter are designated respectively as EO and E.

A set of relationships over the entire control range of interconnected current values of the output frequency of the converter, the value of the supply voltage and the number, duration and location of the control

The signals supplied to the converter valves characterize the new mode of the method.

FIG. 1 shows the power circuit

 a three-phase bridge converter, made on the basis of fully controllable keys; in fig. 2 shows timing charts explaining the proposed control method; Figures 3 and 4 show curves of changes in the magnitude of the correlating coefficient K; in fig. 5 is a block diagram of a converter control system; in fig. 6 - time diagrams explaining the principle of its functioning.

FIG. 2a built at the top

The timing diagram of the formation of the control signal at the + A gate of the anode group of the converter during the conduction half-period at the initial (minimum) output frequency Fo, below is the corresponding curve of the linear output voltage UAB. The value of the supply voltage of the inverter is considered to be nominal

(minimum) value of Eo. The fact that the frequency range of the associated frequency control and the value of the output voltage of the converter according to the law of the ratio of the magnitude

voltage to frequency is six ().

A characteristic feature of the basic 180-degree generation of control signals is that, as follows from the upper curve (Fig. 2), for each of the gates, each of the conduction half-periods and the closed state is broken by a sodium clock interval of 60-degree duration, and the formation of modulating control signals, opposite to the corresponding half-period, the duration of which is controlled by the value of the output voltage of the converter, is carried out within the extreme half-cycles of cycles s intervals.

At the same time, over the entire control range, the modulating control signals are synthesized in the midpoints of the clock sub-intervals having a duration of

Yeo

1 6 F Fo N

functionally dependent on the current value of the supply voltage E, into which the clock intervals are divided. In this case, the midpoints of clock intervals are continuously synchronized with the midpoint of the corresponding central clock subinterval (for an odd N index value) or with the end and beginning of the corresponding two central clock subintervals (for even N, the time diagrams in Fig. 2 correspond to this variant). )

As shown by the arrows (Fig. 2), the process of adjusting the output frequency of the converter when controlled by the method is carried out in two stages by successive smooth transition from one mode to another and vice versa. In the first (conditionally) control mode, to which the forms of the control signals and the linear output voltage correspond (Fig. 2a, b, e), the main control signals are formed at the extreme parts of the clock sub-intervals, and the duration I of all the modulating control signals, the number which inside the clock intervals is i, is determined according to the ratio

1 1 (1 Eo h

 F7E7JJ

In this case, the output frequency of the converter is controlled (increased), as shown by arrows, by changing (decreasing) the duration of the extreme basic control signals, which is accompanied by an identical decrease in the extreme and central output pulses in the half-wave of the linear output voltage. The upper boundaries of such modes are observed at frequencies F0E (-1) N

Gr-1) to -Eo

F

on extreme impulses reduced to close to zero values

The second control mode (Fig. 26, d) is characterized by the formation on the edges of the clock intervals of the modulating control signals with the duration

J0-1) (i-2) Eo + EO

12 F12 (1-1)

BUT

and the duration of the remaining (I-2) - and modulating control signals in this case determined by Eo (.- 2)

how am I doing

Top

 E (T-1JN the border of this mode for each specific i are the frequencies

F - .. f.oNEji-1)

F | - (i-1) (i-2J + i; An index value i identical to the number of modulating control signals generated within the clock intervals, while successively decreasing from the maximum value occurring at the initial output frequency (FIG. 2a for and, also in Fig. 26, further for the signals shown in Fig. 2c, d and i 2 in Fig. 2e),

on which

five

0

Fulfillment of the above ratios over the entire adjustment range realizes at the same time the ratio of the output voltage of the converter to the frequency - and thus provides one of the most economical laws for regulating asynchronous electric motors supplied from the converters of the considered class,

For a particular analyzed mode (,) with increasing frequency of the converter, the first boundary frequency is F F0 (I-1) N F0 -5 - 6 30 r 6 f-Tf-T 5-6-1 29 0- Formation of the output curve, such as built in FIG. 26, implemented in a range of

FO -5-6 30 21

frequency band F 6-Fe

   OU p

 tt go

5 T

4-5 + 1 Further in the range of output frequencies F 6-F 4 Fo-36 18 s.

 -don - ut F0, the output voltage form corresponds to the curve of fig 2b, moreover, in the frequency subband F 4-F4

1R

Fo voltage form is modified

0

five

0

to curve, type built on fig. 2g

On the next frequency subband (Fig. 2p), as the frequency increases, the clock centers are interested in, in the middle of which the modulating control signals (two control signals,) are generated.

11 1 duration I-t (-c.)

Ј, Rc

each, successively shifted to the boundaries of the clock intervals, so that, as shown by the arrows, the duration of the output pulses, which are extreme at half a period, decreases, decreasing to close to zero values simultaneously with

F0E N

I at frequency F 2Es

(in case of

0

five

F), which corresponds to the upper limit of the range of the associated control of the magnitude and frequency of the voltage. The output voltage of the converter is maximal and is formed from a sequence of 120-degree different pulses without pauses.

At the stage of regulating the converter from F4 to F 2 for even N, the half-wave linear output voltage is formed from five output pulses up to the upper (nominal) output frequency, which leads to additional loss of communication in the range of high output frequencies of the converter Therefore, even N From the energy point of view, it is advisable, starting from frequency F, to carry out synchronous

Theo

shift of the modulating signals to the centers of the clock intervals until they merge into a single central modulating

F0E N

F signal

2 her

The coordinates of the centers Ci and Cr, as well as Cs and C4 of the modulating control signals within each positive half-period in the frequency range from F 4 to F, vary in accordance with the functional dependence

C1 () e hail;

C2 (7575E0F

) el.grad;

N h F0 Сз (+ Ю5) el.grad;

75FE0

 C4 (195 -,

) el.grad,

N F0E

Within the clock intervals of 180-240 and 300-360 el.grad, the formation of the modulating control cischs is carried out symmetrically. In the output frequency range F-F 2, the duration A of the synthesized e centers of the specified intervals of the modulating control signals varies all the response 1 1Eo

wines with dependence l - zrtr to p m s

To improve the harmonic composition of the output voltage of the converter, the compensation principle can be used, consisting, as shown by the dotted line (Fig. 2), in forming a sequence of additional pulses, the harmonics of which are out of phase with the corresponding parasitic harmonic components of the main Array of output pulses and contributes to the most reduction (compensation) of the parasitic harmonic amplitudes in the resulting output curve. At the same time, in order to reduce the amplitudes of parasitic harmonics that are close to the main one, it is expedient to control the whole range of regulation in the range of output frequencies of E N Fo E N expander - -g- - -р--

-e-t - continued & o

ability of clock subintervals t to take

1 equal to t-gp-g

In order to form a sequence of additional output pulses, the duration must change (Fig. 2) by the indicated value, the duration of the corresponding modulating signals of the control located in the vicinity of; verge tsmtuluperiodov half

five

0

five

0

five

0

five

0

five

at the same time from the ratio of U o

na clock intervals. At the same time, the duration of the control signals located inside the conduction half-cycles is increased by the value of y, and the duration of the modulating control signals inside the closed state semi-cycles is reduced by the indicated value. The marked change in the duration of the modulating control signals is carried out in both cases by a corresponding shift of the edges furthest to the boundaries of the half-periods of the corresponding control signals.

The value of y at each point of the control range is chosen in accordance with the functional dependence K (r - I), where the numerical value of the coupling coefficient K is chosen for the corresponding value of the relative / output voltage U out of the family of universal curves constructed for the corresponding values of E / Eo for even N (Fig. 3) and odd J (Fig. 4). The relationship between the current values of the output frequency F and the delayed (Fig. 3 and 4) on the x-axis relative magnitude of the output voltage of the inverter U py is determined

FE

TS The number of additional output pulses in the output half-wave successively gradually decreases with increasing output frequency of the converter. The choice of the value of y according to the indicated algorithm at the same time provides for the entire range of regulation the complete elimination from the spectrum of the output voltage curve of the transforming harmonic component, which in the process of operation creates the maximum braking torque of the asynchronous motor fed from the converters and which is most undesirable . The amplitude of the seventh harmonic component also decreases noticeably.

The principle of operation of control systems that implement the control method will be considered on the example of the functional diagram of the device (Fig. 5) and the time diagrams of its operation (Fig. 6). The output frequency setting unit 1 is connected to a generator of 2 clock pulses, the frequency of which for the entire adjustment range is 12 times higher than the output frequency of the converter. The generator 2 is connected by its output to a sweep-saw voltage generator 3 and a three-digit register 4. A supply voltage amplitude sensor 5 is connected to

the positive input of the two-input integrator 6 and through the matching amplifier 7 to the inputs of the adders 8-12

The number of specified adders in the general case is equal to the maximum number of modeling control signals generated within each clock interval at the initial output frequency of the converter at the maximum amplitude E of the supply voltage converter. The other inputs of the adders 8-12 receive signals from the output of the integrator 6 and the source 13 of the reference voltage. The outputs of the adders 8-12 are connected to the control pulse shaping unit 14, which sequentially compares the signals from the outputs of the adders 8-12 with the sweep voltage Uz of the generator 3 and produces short command pulses at the instants of equality of these signals, which sequentially arrive through the disjunctor to the counting trigger included in block 14, the output of block 14 is connected to the input of block 15 for determining the total duration of the output pulses and to the information input of the logical distributor 16 control pulse excitation

The operation of the system is based on the vertical principle of control. The clock generator 2 synchronizes the operation of the sweep generator 3 (Fig. 6) due to the corresponding setpoint the minimum (zero) value of the sweep signal Us over the entire control range is observed in the middle of the clock intervals, and the maximum of the clock intervals Us signal amplitude smoothly decreases with increasing output frequency, and the slope remains unchanged, whereby the number of pulses in the output half-wave smoothly decreases.

The voltage at the output of sensor 4 decreases in proportion to the increase in voltage E, while the transfer coefficient of sensor 5 is adjusted so as to ensure that

, Jpp U5Q-N-.

where Dam is the maximum amplitude of the sitel of the generator 3 sweep, observed at the initial frequency F0

The transmission coefficient of the amplifier 7 in this case in the case of odd N is equal to two. The amplitude of the signal 1H2 of the source 13 selects j Uso with from the ratio Ui3 - r. At the input of block 15, a capacitor 17 is switched on, which separates the fixed component of the sequence of pulse signals from the output of block 14 The voltage from the capacitor 17 goes to divider 18, in which division is performed the signal to the signal of the task Ui, as a result of which the output of the block 15 generates a voltage proportional to the total duration of the output pulses over a half period, which is fed further to the negative input of the integrator 6

In this case, the internal feedback loop of the system, including nodes 5, 6, 14 and

15, provides a continuous, high-precision, astatically-based, generation of a correction signal at the inputs of adders 8-12 and automatically maintaining the constancy of the total volt-second area of output pulses over the entire control range, thereby automatically providing a control method with constant value ratio voltage to specified frequency

The states of the outputs Oz Q2 Qi register 4 on the period of the output frequency are sequentially recorded as 100,001,000, 101,

110, 111. 100 The logical equations characterizing the operation of the distributor of control pulses, thus have the following form (with reference to control signals for the valves of the anode group)

+ A -QiQ3 + QiQ2UM + QiQ3Ui4 (

+ B QiQ2Q3 + QiQ3Ui4 + QiQ2Ui4 + QiQ2Ui4 +

+ QiCbUi4, „.

+ C QiQ2 + QiQ3Ui4 + QiQ2Ui4.

To form additional output pulses that correct the spectral composition of the output voltage into the system, as shown by the dotted lines.

(FIG. 5) for a variant of an additional channel, a functional converter 19 can be entered that implements one of the input-output characteristics constructed in FIGS. 3 and 4, the adder 20 comparator 21 and the trigger 22 connected by its output to the additional information input of the distributor 16 Register 4 in this case should be four-bit

Claims (2)

Thus, the control method allows to significantly improve the quality of the three-phase converter control process for an electric drive due to a smooth, step-by-step unaccented transition from one control zone to another, followed by a change in the number of pulses in the output half-wave and carried out on the principle of width-width modulation (width-coded control), at which the duration of the modulating and main control signals generated at the edges of the clock intervals over the entire control range are identified (coded) according to certain dependencies with the durations of the main array of control signals. This makes it possible to reduce the spikes of instantaneous values of gok in the power circuits of the converter and the load and to increase the reliability of the functioning of the converting systems under consideration. Claim 1. Method of controlling a bridge converter with a width-code control, which consists in the fact that the main valves of different phases and groups of the converter are periodically turned on and off, with a mutual phase shift of 60 e. degrees in the sequence + A, -C, -B, -A, + C, -B, and for each valve they form positive conduction half-periods and negative half-periods of the closed state, each of which consists of three clock intervals of sixty tigradusnyh durations the extreme at half periods of clock intervals are formed by modulating control signals, the duration of which determines the value of the output voltage of the converter, characterized in that, in order to ensure a smooth unaccented change in the shape of the curve, you one voltage of the converter in the process of N-fold coupled frequency control F and voltage value according to the law of the constant ratio of voltage value to frequency at nominal (minimum) supply voltage, the formation of these modulating control signals over the entire control range, starting from the initial FO frequencies are performed in mid-stroke sub-intervals with a duration of Yeo g - -err - icr with the middle mentioned D fc th N clock intervals are synchronized with the middle of the corresponding central clock sub-interval with odd N or with the end and the beginning of the corresponding center clock intervals with even N, while in the frequency ranges F i F; j F c-2 within the clock intervals form i modulating control signals WITH DIFFERENCE I TJ-J (t; -grm). on the frequency bands F i F} F i, in the extreme parts of the clock intervals form control signals of the duration Ai 1 (1-1) (1-2) E0 + Eo 0 five 0 five 0 five 0 to be found as and f where eo and 12 F12 F0E (1-1) N and the duration of the remaining (i-2) control signals is determined in accordance with the dependence of I p mut-TTE on the values of the limiting frequencies F i and F i, which are transitional from one control subband to the other, PT TETH-EO . FoE (l-1) N (i-1) fRZ7Eo TE0 E is the minimum (nominal) and current amplitude of the DC supply voltage converter. 2. The method according to claim 1, characterized in that in the output frequency range of pre, .Fo E N FQ E N the educator -dr-- -p-- the duration of r clock intervals take 1 equal to r 3 The method according to claim 2, characterized in that, in order to improve the spectral composition of the output voltage of the converter, throughout the entire control range, the duration is located at the half of the clock intervals of the modulating control signals located near the edges of the half-periods, and the duration control signals on the conduction half-periods and reduce the indicated duration on the closed half-periods by a corresponding shift to the above half-periods The fronts of the corresponding modulating control signals, and the value of y at each point of the control range is chosen according to the functional dependence of K (r-Z), where the numerical value of the coefficient K is chosen from the family of curves constructed in FIG. 3 for even N and in FIG. 4 for odd N, and ttMt nb - p gk n rt - ( five P n n - g and Yu 1 yy yyyy - y I- 1Sh P -.P ...-- P P CHAMP: sir L: t G-PLP d, -, .. m-.   П Н about 1c I; 1e, s ls ;one; % flfc I --O.Ui IT II R II 6 / 2QQi | fj fQ ° t; 3 j wag 2 ° : W, ;one; ij Hj4iS® 0.1 02 02 And & r - -jrjL GP Sp in- + 0 -0 0.8 1 U W - c - ttЈ,   7 ГЈ 1-1-Y1411- OB 0.8 / /, 2W about y   &} - № - ..