SU1144185A1 - Method of control of three-phase-to-m-phase direct frequency converter - Google Patents

Abstract

A METHOD FOR CONTROLLING A THREE-PHASE-M-PHASE DIRECT-FREQUENCY FREQUENCY CONVERTER, consisting of three-phase single-phase converters, made according to the main circuit on fully controlled two-way conductivity keys, which means that WF. The pulse control sequences are fully controlled with 1 key, shifted among themselves by / 3 for different keys of each of the three-phase-single-phase converters and for the same keys of different converters and made up of three intervals of setting the conductivity of the keys of Duration “/ 3” each, and during the first interval the conductivity is set unchanged, and during the second and third intervals shifted relative to the first by (G / 3 and f, respectively, they produce a modulation of the susceptibility by the high-precision method -frequency PWM control and mutual inversion pulses at these AND ntervapah, characterized in that, in order Decrease the 4 Sheni distortion supply Gety by reducing komutatsionnyh overpotential zheNII at its terminals, pmpulsy shirotno30 U1 pulsed control for each of the three phase-single-phase inverter is supplied with shift to the period.

Description

The invention relates to electrical engineering, in particular, to control systems of frequency converters with direct communication, and can be used in the construction of frequency converters for regulating AC drives. Methods are known for controlling frequency converters with direct communication using pulse-width regulation: (WID) output voltage. These methods of control are based on periodically connecting the load to linear or phase voltages of a three-phase mains supply using bridge or zero circuits on self-controlled keys with double-sided conductivity. To this end, for each of these keys, a multi-phase control circuit pulses, by changing the capacitance of these, change the output voltage of the converter lj and 2. A significant disadvantage of these methods is the adverse effect of the converter on the power supply network, the loss of power in the appearance of switching overvoltages and the intermittent nature of the input current. f The closest in technical essence to the present invention is a method of controlling a three-phase-phase-phase frequency converter with a direct connection consisting of m three-phase-single-phase converters made according to a bridge circuit on fully controlled two-way conductivity devices, which include that, to control these keys, they form pulse sequences that are shifted between themselves by x / 3 for different keys of each of the three-phase single-phase converters and by Zf / m for the keys of the same name Different transducers and made up of three intervals specifying the conductivity of 1G / 3 keys each, and during the first interval the conductivity is set constant and during the second and third intervals shifted relative to the first by 7/3 and IT, respectively, the module Conduction of conductivity P 5,1 according to the method of high-frequency WID and mutual inversion of pulses at these intervals. As a result of this control method, the output voltage of the converter is control-. It is controlled by introducing pauses during which each phase of the load is disconnected from the mains and shorted with the specified keys. It uses high frequency WID, i.e. during one cycle of operation of the converter, when the output voltage curve is formed from the same segment of the input voltage curve, the indicated load disconnection from the mains supply is performed several times. In addition, each shutdown is performed simultaneously. PT output phase converter t3. A disadvantage of the known control method is the deterioration of the input current curve with deep regulation, which leads to an increase in switching overvoltages in the network. The aim of the invention is to reduce power supply distortions during the SNR of the output voltage of the converter by reducing the switching overvoltages at its terminals. This goal is achieved by the fact that according to the method of controlling a three-phase-u-phased frequency converter with a direct connection consisting of m three-phase-single-phase converters made on bridges to a circuit on fully controllable keys with two-way conductivity, which means that to control the keys, pulse sequences are shifted between each other by 11/3 for different keys of each of the three-phase-single-phase converters and by 2 (/ fn for the same name for the different converters and with The left of the three intervals of the setting of the conductivity of keys with a duration of "/ 3 each, and during the first interval the conductivity is set unchanged, and during the second and third intervals shifted relative to the first Hait / 3 and I) Accordingly, the modulation of conductivity is made high-frequency WIDE and inverting pulses at these intervals-, the high-frequency SHIR pulses for each of the three-phase-single-phase converters. is shifted with a shift of 2c / gm1 to the period .. FIG. 1 shows a schematic diagram of three but moetovogo-phase frequency converter in FIG. 2 is a functional diagram of a control system implementing the proposed method; in fig .; 3 shows timing diagrams of control pulses of a power with keys, output voltage circuits constituting the input current consumed in phase A by a three-phase mains supply during operation of the phase with | converter, and the output current of phase A during operation of all phases of the converter according to the known method (for the sake of clarity, the active load is considered as an example); in fig. 4 - timing charts {tpulsov control with shorthand keys, diagrams of the output voltage and component of the input current consumed in phase A of the mains during phase b of the converter according to the proposed method; in fig. 5 shows timing diagrams of control pulses of power switches, output voltage plots and components of the input current consumed in phase A of the supply mains when the phase is operated from the converter according to the proposed method, and the resulting input current of phase A. The essence of the proposed control method consists of that when the output voltage is transformed by the conversion of the bodies, the disconnection of loads from the supply network is not performed simultaneously, as in the well-known method, when in the input phases the current consumed jumps to zero, but with a shift on, i.e. at each such disconnection, only one of the loads is disconnected, the rest continue to consume current. Therefore, the maximum change in the input current at each instant of tripping is reduced, for example, for a three-phase-three-phase converter approximately by a factor of three. As a result, switching overvoltages at the input terminals of the supply network are reduced. Consider the implementation of the proposed control method by example. converter circuits and control systems for them (fig. 1-5). The frequency converter (Fig. 1) contains fully controlled keys 1a-6q, 1b-6b, 1c-6c with double-sided conductivity, connected in three-phase bridge circuits with loads Tyg, 7b and 7c and input phases A, B, C of the supply network. In the functional diagram (Fig. 2a), the first alternator 8 is connected to a scaling circuit 9, the second master oscillator 10 is connected to a phase-shifting device 11, the outlets 12-14 of which are connected to the inputs of inverting circuits 15-17, respectively. The recirculation circuit outputs 1823 9, the outputs 12-1D of the phase shifter And, and the outputs 24-26 of the inverters 15-17 are fed to a logic unit 27 consisting of the same logic cells 28-45. The device of one of such logic cells 28 is shown in FIG. 2S. The logical element AND 46 (Fig. 2b) is connected to the output 19 of the counting circuit 9 and the output 12 of the phase shifter 11, the logical element I47 on the input of the output 21 of the counting circuit 9 and the output 24 of the inverter 15, the logical element OR 48 - on the input with outputs 49 and 50 elements And 46 and 47 and, with output 18 of the counting circuit 8 At the output of the logic element OR 48, the control pulses of the power keys 1q, 1b, 3c (Fig. 1) are generated by a known method and the power control pulses of the key 101 by the proposed method (Fig. 3). At the outputs of logic cells 29-33, control pulses are generated for the rest of the eyes by a known method and 2o-6q keys according to the proposed method (Fig. 3). At the output of logic cells 34-39, power control pulses 1b-6b are formed, the outputs of logic cells 40-45 are the pulses controlling the power switches 1c-6c according to the proposed method (Figs. 4 and 5). The key and load numbers in FIG. 1 correspond to the numbers of the outputs of the circuits in FIG. 2 and timing numbers in FIG. 3-5 Consider the operation of the converter and its control circuit. The first task generator 8 (Fig. 2) generates pulses with a frequency of 61), of which in the crossover circuit 9 six sequences of impulse-j ow duration / 3 are formed, following with. S.114 control frequency i | and shifted one relative to another. The second generator 10 generates length-adjustable frequency pulses Oi can be built as a sawtooth generator and a comparator, where the sawtooth voltage is compared with a predetermined level. The pulses from the output of the generator 10 enter the phase-shifting device 11 and are divided therein into three channels according to the number of phases of the converter, in each of which they are shifted by 27/3 one relative to the other. As a phase shifter 11, for example, three sawtooth voltage generators can be used, synchronized by pulses from compressors, at the inputs of which the sawtooth voltage from generator 10 and constant voltages at the amplitudes of one third are compared. sawtooth voltage. Then, the sawtooth voltages shifted in this way by 2 | G / 3 relative to the other are compared at the inputs of other comparators with a constant voltage, the level of which determines the specified adjustable pulse frequency to. As one of these three sawtooth generators, generator 10 can be used with its comparator. The pulses from the outputs 12-14 of the phase-shifting device 11. Enter the inverting circuit 15-17, respectively. The pulses from the output 12 of the phase-shifting device 11, the output 24 of the inverter 15 and the outputs 18-23 of the counting circuit 9 are fed to the inputs of the logic cells 28-33 of the logic unit 27 in the respective combinations, as shown in FIG. 2. As a result of logical transformations, in the cells 28-33 at their outputs, the control signals are generated using keys 1 (5-6a, shown in time diagrams (Fig. 3). In accordance with the key operation algorithm, the output voltage of phase a The converter has the form shown in plot 1 (Fig. 3). Plot 51a shows the form of the input current consumed in phase A of the mains during the operation of the converter phase A. The pulses formed at the outputs of logic cells 2833 are used also for control of the power switches of phases b and c of the converter. The pulses from the input cell of cell 28 are supplied to control keys IQ, 2b and 3c, from the output of cell 29 to control keys, 3b, 1c, etc. according to a cyclic algorithm. output voltage, and correspondingly, and w pulses of current in the load coincide in time for all phases of the converter. The input current of phase A, equal to the sum of the components consumed at the input during the operation of each phase of the converter, is shown in plot 51; (Fig. 3). As can be seen from the plot, it is clearly pronounced intermittent and leads, as already noted, to distortions in the supply network. The control of the converter according to the proposed method is carried out as follows. The pulses from the output 13 of the phase-shifting device 11, the output 25 of the inverter 16 and the outputs 18-23 of the counting circuit 9 are supplied in appropriate combinations to the inputs of logic cells 34-39 (Fig. 2), which realize the same logic function, observed for phase Q. At the outputs of the cells 34–39, control signals are generated with bipolar keys 1b – 6b, shown in time diagrams (Fig. 4). The Nazfure 7b (Fig. 4) shows the shape of the output voltage, and the plot 51b shows the shape of the input current consumed in phase A of the mains during the operation of phase b of the converter. In contrast to the known method, the voltage and current pulses here do not coincide in time with the corresponding phase Q pulses and are shifted relative to them by 21/3. The sequence of generating pulses for controlling the power switches of the phase from the converter is similar. The pulses from the output 14 of the phase-shifting device 11, the output 26 of the inverter 17 and the outputs 18-23 of the counting circuit 9 are fed to the inputs of logic cells 40-45, the outputs of which form control pulses with keys 1c-6c shown in the time diagrams (Fig . five). Plots 7c and 51o show the shape of the output voltage and the shape of the input current consumed in phase A of the mains, when the phase is operating from the converter.

The voltage and current pulses are shifted by 21G / 3 due to the corresponding pulses in other phases.

The resulting input current consumed in phase A of the mains during operation of all phases of the converter is shown in junction 51 (Fig. 5). It has a less pronounced intermittent nature than limestone.

method due to the fact that the pauses in the output voltages of the converter are separated in time one relative to another. Therefore, the time-pulses of the currents consumed in the input phases of the transducer do not coincide. As a result, overvoltages at the power supply terminals are reduced, the probability of failure of the power switches is reduced, and the requirements for key protection elements against overvoltages are reduced. In addition, input-. Noah current is easier to filter.

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Claims (1)

METHOD FOR CONTROL OF THREE-PHASE-m-PHASE DIRECT FREQUENCY CONVERTER, consisting of, m three-phase-single-phase converters, made according to the bridge circuit on fully controllable keys with two-side conductivity, consisting in the fact that they form-. pulse control sequences of fully controlled keys shifted between each other by Τ '/ 3 for different keys of each of the three-phase single-phase converters and by 2V / m for the keys of the same name with different converters and made up of three intervals of setting the key conductivity of 7/3 each, and during the first interval, the conductivity is set unchanged from ¹ variable, and during the second and third intervals shifted relative to the first by 7/3 and 7, respectively, the conductivity is modulated by the high-precision method pulse-width pulse-width regulation and mutual inversion of pulses at these intervals, characterized in that, in order to reduce the distortion of the supply network by reducing switching overvoltages at its terminals, pulse-width regulation pulses for each of the three-phase single-phase converters are fed with a shift of 27 / t to the period. Jll44185 I>