SU771821A1 - Frequency converter with quasisingle-band modulation - Google Patents

Description

one

The invention relates to a converter technique and can be used in cases where higher voltage quality is required, regulation or stabilization of electrical parameters — voltage and frequency — with great accuracy under restrictions on the mass-dimensional parameters of the device that implements these functions.

Devices are known that convert one frequency to another and regulate the magnitude of the converted output voltage. These are frequency converters with DC link 1 and frequency converters with direct communication 2, 3. Frequency converters of the first type contain a rectifier (controlled or unmanaged), input terminals connected to the mains, and output terminals to power buses inverter. The disadvantages of such an IF structure are the comparatively low quality of the converted voltage (typical harmonic voltage coefficient is about 0.3), as well as circuit complexity or degraded mass-dimensional parameters in those

cases where the exchange of reactive and active load power with the network is carried out.

The second type IF (with direct connection), performed on thyristors with natural commutation, for example, using bridge 5 circuit 4, providing among the known solutions of this type the best quality of the output voltage (with harmonics also not more than 0.3) has limited functionality, since they do not allow obtaining bo frequencies, 1 less than 10 (0.25-0.3) fi (where fi is the mains voltage frequency), and also have a rather complicated control system.

The second type of IF (with direct connection), performed on thyristors with artificial switching, as opposed to IF

15 with natural commutation, they allow to obtain frequencies higher than the frequency of the mains supply; however, their circuits are characterized by a relatively large value of the voltage harmonic coefficient (0.31).

In addition, the inverter of the first and second type

20 made on thyristors with artificial switching, have increased weight and dimensions (due to the presence of an artificial switching unit).

The closest technical solution to the proposed one is a frequency converter 5, containing three single-phase inverter bridges made on controlled keys with double-sided conductivity, and a control unit including a master oscillator, a main pulse distributor and an amplifier-breaker node, connected to outputs control inputs of single-phase inverter bridge switches. The power inputs of the inverter bridges form the output pins of the converter for connecting it to a three-phase network.

In order to match the voltage levels of the supply network and the consumer, output transformers are installed at the output of the inverter bridges, the secondary windings of which are interconnected in series to form the output terminals of the converter.

The disadvantages of such a converter include the low quality of its output voltage.

The aim of the invention is to improve the quality of the output voltage by reducing its harmonic coefficient.

To achieve this goal, the converter, which contains single-phase inverter bridges connected to the t-phase network and executed on controlled switches with double-sided conductivity, which together with the output transformers, and the control unit, including the master oscillator, are the main pulse distributor and an amplifier-decoupling node, with outputs connected to the control inputs of single-phase inverter bridge switches, in accordance with the invention, the secondary winding of the transformer is each The transforming cell is made with tapes connected together with the other end of the secondary winding of the transformer via additionally inserted controlled keys with two-sided conductivity to a common point that forms another output terminal of the transforming cell. The control unit is equipped with a trigger and two additional pulse distributors, the output of the master oscillator is connected to the input of one of the additional pulse distributors and the trigger input, and the inverse and direct trigger outputs are connected respectively to the inputs of the main and other additional pulse distributors.

FIG. 1 is a schematic diagram of the power section of the converter; in fig. 2 converter control circuit; in fig. 3 shows timing diagrams explaining the generation of control signals supplied to the inputs of the double-ended transducer keys of FIG. one ; in fig. 4 shows timing diagrams of the formation of the output voltage of the converter; in fig. 5 shows the dependence of the harmonic coefficient of the output voltage of the converter on the number of keys N in each inverter cell.

Consider a converter with m 3.

The proposed converter (Fig. 1) contains three single-phase inverter bridges 1-3, made on controlled switches 4-15 with two-sided conductivity. The power inputs 16-19 of the inverter bridges form the terminals of the frequency converter for connecting it to a three-phase network. Power outputs 20-25 of the inverter bridges are connected to the primary windings 26-28 of transformers 29-31. The secondary winding of each transformer is made with taps 32-34 connected together with one end 35-37 of the secondary winding of the transformer via additionally inserted control keys 38-43 with double-sided conductivity to common points 44-46, which form one of the output outputs of the transforming cell . The second output terminal of each conversion cell is formed by the other ends 47-49 of the respective secondary windings of the transformers. The output pins of the transducer cells are interconnected in series to form the output pins of the transducer.

The control unit 50 comprises a master oscillator 51, a trigger 52, a main 53, two additional pulse distributor 54, 55, and a booster unit 56.

The output of master oscillator 51 is connected to the input of the additional pulse distributor 55 and to the input of the trigger 52, and the inverse and direct outputs of the trigger are connected respectively to the inputs of the main 53 and additional 54 pulse distributors. The outputs of the pulse distributors 53-55 are connected to the control inputs of the keys 4-15, 38-43 of the frequency converter via the amplifier section 56. The output voltage of the converter is explained by time diagrams (see Fig. 3). Accepted designations:

TI - clock pulses at the output of the master oscillator 51;

TI (, TIG - pulses at the inverse and direct outputs of trigger 52;

and 4-Ui5 are control signals supplied to the inputs of the keys with double-sided conductivity of single-phase i interlocking bridges 1-3;

and 38 and 43 are control signals provided to the inputs of additional switches 38-43 with two-sided conductivity.

Accepted in FIG. 4 designations:

Claims (5)

UAB, UEC, UCA - linear voltages of a three-phase network supplied to inputs 16-19 of the frequency converter (if there is a neutral wire, phase voltages can be supplied to the converter inputs instead of linear ones); , I yJi are equivalent algorithms for switching keys of single-phase inverter bridges 1-3,,. HJr Chyu-V “,; H 13, 5; Un ,, lJuj, T / C j-voltage on the primary windings of 26-28 transformers 29-31; lUzcA - voltage at the outputs of the transforming cells; the shape of the output voltage of the converter. The operation of the converter is due to the operation of one conversion cell. When power is connected to the control unit and the power section of the converter and the closing of the keys 4, 5 of the inverter bridge 1, the primary winding 26 of the transformer 29 is short-circuited (to-t interval in Fig. 4). In the voltage UuiHa of the primary winding 26, a pause is formed in this case, and the additional key 30 with bilateral conductivity remains closed at this moment, which ensures the passage of reactive current. When the keys 5, 6 of the inverter bridge 1 are locked on the winding 26, a positive voltage pulse Yc is generated (interval ti-taHa in Fig. 4). The polarity of the transformer windings is such that when the key 39 is closed, the first step of the positive half-wave of the voltage is formed at the output of the conversion cell. The closure of the key 39 form the second voltage level Uj, d (interval). The further formation of the voltage of the voltage and of the voltage, i.e., occurs similarly in accordance with the timing diagrams shown in FIG. 3, 4. The output voltage of the converter U2 is obtained as a result of summing up the output voltages of the conversion cells ig.dv, Uj.bc. By using the control unit's Complication, you can build a converter with output voltage control Ug. Regulation can be made in each of the power units of the inverter cells: in inverter bridges (due to the phase shift of the key management signals of one rack of the inverter bridge relative to the key management signals of the other rack) in transformers (due to biasing) and additional keys with two-sided conductivity (by choosing the appropriate algorithm for their control). With the aim of simplifying the control system, it is more rational to regulate the voltage in the inverter bridges. By switching over taps on the secondary side of the transformers, pulse-amplitude modulation of the voltages produced on the primary windings is carried out. A reasonable number of additional controllable keys with double-sided conductivity (N), which are additionally input into each conversion cell, is selected in each specific case depending on the requirement for distortion of the output voltage of the converter. The dependence of the harmonic ratio of the output voltage of the converter on the number of keys additionally introduced into each transformation cell, which allows the selection of the number N, is shown in FIG. 5. In the well-known solution, taken as a prototype, the harmonic coefficient of the converter voltage is 0.3. In the proposed converter, as follows from FIG. 5, with the number of keys N equal to two, Kg (s) 0.16. With four additional controllable keys in each cell transforming cell, the harmonic ratio of the output voltage of the converter can be reduced to 0.067. Since the converter consists of parallel-connected conversion channels, it is easy to increase the power of the converter. So, with power up to ten kilovolt-amperes, transistors can be used to build a frequency converter and, consequently, its mass-dimensional parameters can be significantly improved (due to the absence of switching blocks). It should also be noted that such a solution allows obtaining frequencies both greater and lower than the frequency of the mains voltage. At the same time, + fM, where fi is the voltage frequency of the network (see Fig. 4); f m is the modulation frequency (determines the switching algorithm for the additionally input controlled keys with double-ended conductivity); f j is the frequency of the output voltage of the converter. Thus, the proposed converter can be used, for example, to create devices that provide precise stabilization of the mains frequency (at a given level), as well as for a frequency-controlled electric drive. Claims A frequency converter with quasi-single-sided modulation, containing single-phase inverter bridges connected to a b-phase network and executed on controlled keys with double-sided conductivity, which together with the output transformers form one end of the corresponding secondary windings of the transformer connected by its primary winding to the output of the corresponding bridge, and the outputs of the cells are connected in series and o The output pins of the frequency converter, as well as the control unit, including the master oscillator, the main pulse distributor and the amplifier-breakout node, are output, connected to the control inputs of single-phase inverter bridge switches, in order to improve the quality of the output voltage by reducing its harmonic coefficient, the secondary winding of the transformer of each transforming cell is made with tapes connected together with the other end of the secondary winding of the transformer Through additionally introduced controlled keys with double-sided conductance to a common point, which forms another output terminal of the conversion cell, and the control unit is equipped with a trigger and two additional pulse distributors, the output of the master oscillator is connected to the input of one of the additional pulse distributors and to the trigger input, and the inverse and direct outputs of the trigger are connected, respectively, with the input of the main and other additional pulse distributors. Sources of information taken into account in the examination 1. USSR author's certificate number 238656, cl. H 02 M 5/27, publ. 10.03.69. 2. USSR author's certificate number 309435, cl. H 02 M 5/27, publ. 07.09.71 3. USSR author's certificate No. 325671, class, N 02 M 5/27, publ. 01/07/72. 4. USSR author's certificate number 169663, cl. H 02 M 5/27, publ. 03.17.65. 5.Sb. “Devices of converter equipment, vol. 2, Kiev, “Naukova Dumka, 1969, p. 110 (prototype). V, TH sh , % u v 2 HI G ... fl r "j j kKr (2)