SU1524145A1 - Direct converter of m-phase voltage of one frequency into single-phase voltage of m-integer frequency - Google Patents

Abstract

The invention relates to power converter technology. The goal is to improve the quality of the output voltages and currents by reducing their non-sinusoidality. The device contains M pairs of anti-parallel-connected thyristors 1-2 M, which, together with the primary windings 9 of the transformer 10 connected to them, form sections interconnected according to the M-gon scheme. The output winding 11 is shunted by anti-parallel connected thyristors 7 and 8, controlled by the current and voltage information and the input of the filter 13. In one embodiment, the thyristors 7 and 8 can be connected in parallel with the additional winding 12. The filter 13 is designed as a series resonant LC circuit tuned to the reactivity of the load at the M-fold frequency. 1 hp f-ly. 10 il.

Description

The invention relates to electrical engineering, in particular, to converter technology, and can be used to obtain a single-phase voltage of increased frequency from a multi-phase network voltage.

The aim of the invention is to improve the quality of the output current and voltage of the converter by reducing their non-sinusondality, as well as improving the stability of the converter,

FIG. 1 shows a diagram of the proposed converter with shunt thyristors that is supplied from a multiphase network without a neutral wire; in fig. 2 is a block diagram of a control device for shunting thyristors of a converter; in fig. 3 and 4 are timing diagrams showing the voltage form and, “at the output of the converter (on shunt thyristors) at different, depending on the nature of the load of the converter and the angle unlock its oL thyristors, phase shifts between current and EMF phase (bde, and i,) and natural closure of shunt thyristors; in fig. 5 is a timing diagram when forcibly closing the shunt thyristors at the moment of passage of the edr voltage, through zero; in fig. 6 and 7 are time diagrams showing the operation of the converter at different phase shifts between the current and the EMF e, e. and e converter and operation of the current channel only; in fig. 8 - the same, when both the current channel and the voltage channel of the thyristor shunt control node of the converter are operating; in fig. 9 and 10 are a replacement circuit and a timing diagram illustrating the loss of stability of the converter in the absence of a time delay at the control node of the shunt thyristors, respectively.

The converter (fig.)) Contains m phases, each of which A, B, C, ... M has two main and parallel main thyristors 1 and 2, 3 and 4, 5 and 6, ..., 2m-1 and 2m, forming the main keys of alternating current. In addition, the converter includes two parallel-connected shunt thyristors 7 and 8, forming an additional AC key. Each of the main AC keys is connected in series with the transducer.

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g g

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The side winding 9 of the output transformer 10 of the converter and forms together with it its section. The converter sections are connected to a t-angle, whose vertices are the input terminals of the converter, intended for connection to the w-phase network.

An additional AC key (thyristors 7 and 8) is connected in parallel, either to the secondary winding 11 of the output transformer 10, or parallel to its additional winding 12 (shown by dotted lines). This is advisable, for example, in the case of KOI and the secondary voltage of the output transformer 11 is large, and shunt thyristors are available that are designed to operate at low voltages but high currents. The additional winding 12 is then calculated with a small output voltage, but a high current. In this case, the shunt thyristors are electromagnetically coupled to the converter circuit.

The load of the converter is connected in parallel to its secondary winding 1 through a series resonant LC filter 13, tuned with regard to its reactance at a T-fold frequency, i.e. working frequency converter.

The shunt thyristors 7 and 8 of the additional AC key are controlled by an additional control unit 14, whose input signals are the output signals of the instantaneous output current and voltage sensors of the converter, for example, current transformer 15 and voltage transformer 16 can be used. .

The shunt thyristor control unit 14 of the converter (Fig. 2) contains two zero-bodies 17 and 18, the inputs of which are connected to the outputs of the secondary windings of the current transformer 15 and voltage 16. The outputs of the zero-organs 17 and 18 of the current channel and voltage are respectively connected to the inputs of the two-input logic element OR 19, the output of which is connected to the element 20 of the time delay, and its output is connected to the input of the output shaper 21 control pulses of the shunt thyristors, the outputs of which

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they are connected to their control electrodes (Fig. 1). Control unit 14 removes control pulses of shunt thyristors with a delay relative to the current dropping to zero and voltage at the output of the converter. The zero-bodies of the control circuit work so that when dropping to zero and voltage at the output of the converter they form short on their outputs. voltage pulses. Typical analog or digital elements and nodes used in converter equipment can be used as a null organ, a delay element, and an output pulse generator.

Consider the operation of the proposed converter in various modes using the example of a three-phase converter.

To simplify the time diagrams of the converter operation, the following assumptions are made that slightly affect the qualitative analysis of the processes in them: the active and inductive network impedances are zero, the switching of the thyristors occurs instantaneously, the ideal resonant LC filter is set at the output of the converter the output voltage of the converter, taking into account the load reactance, the time of switching the thyristors and the action of the delay element 20 is zero.

The latter assumption is based on the fact that the operation time of the delay element 20 is short (0.1-0.2 mS) and practically does not affect the nature of the working processes in the converter.

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When considering the operation modes of the converter, the following conventions are used: units, e., - EMF applied to the phases A, B and C of the converter, respectively; ift, ig, ij. - currents in phases A, B and C of the converter, respectively; U is the voltage at the output of the converter (on shunt thyristors); ) - current in shunt thyristors; L C, 1 C - respectively, the voltage and load current of the converter; 2 p / 3-r (n + l) ir - the unlocking angle of the main thyristors of the converter, n "0,1,2,.,.; , and, - voltage pulses applied to the control electrodes of the shunt thyristors, respectively, along the voltage channel and

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current from the shunt control unit

thyristors.

The analysis of the converter operation at different angles of unlocking the phase thyristors can be reduced to the consideration of two general cases, characterized by the ratio between the moments of dropping to zero phase current and the corresponding phase emf of the converter. In the first case, the unlocking angle of the thyristors of the sections is such that the phase current drops to zero earlier than the corresponding phase emf, in the second this occurs after the fall to zero phase phase emf.

In the first case, timing diagrams showing the curves of units, 1d, and, are shown in FIG. 3, the full timing diagrams of the converter in this mode are shown in FIG. 6. As can be seen from them, the load current iu is assembled from the plots in which the phase and shunt thyristors alternately work, the numbers of which (Fig. 1) are shown in the diagram inside the shaded areas. Consider this process, starting, for example, from time t, when, under the action of a control pulse from the main thyristor control system, the thyristor 6 is turned on in phase C of the converter. At time tj, this thyristor, when current passes in phase C through zero, is turned off in a natural way. At the same time, under the action of the control pulses of the oscillations, and the pulses generated by the current and voltage channels in this case appear at the same moment of time), a shunt thyristor 7 is turned on, through which the current flows until due to the energy stored in the reactive elements of the filter 13 and the load on the converter. At time t, the pvd action of the control pulse from the system controlled by the main thyristors turns on the thyristor 3 in the phase B of the converter, which in the switching process turns off the shunting thyristor

7. At time t, the thyristor 3 is turned off in a natural way and under the action of the shunt thyristor control unit, the thyristor turns on

8. Next, the process is repeated cyclically with the thyristors of the other sections.

As can be seen from the diagram of the loading current (Fig. 6), it is continuous and close to sinusoidal with a good-quality LC filter 13.

Consider the operation of the converter in the second case, i.e. when the current drops to zero after the corresponding phase emf.

At first, this mode of operation of the converter is considered when only the current channel is working in its shunt thyristor control unit, and the main thyristors of the section do not have control pulses at the output of the voltage channel (for example, if the voltage channel malfunctions or is deliberately turned off). As can be seen from the diagrams of this mode (Fig. 7), there are regions of different polarities of the voltage U in the interval of repetition of the structure of the converter circuit. The mapping of the diagram in FIG. 7 with diagrams of the operation of the converter in the previously discussed first case (Fig. 6) shows that the order of operation of the thyristors is the same here, the main thyristors are turned off in a natural way and the converter remains operable. However, it is not always advisable to use this mode due to a decrease in the amplitude of the voltage tripled at the load and a decrease in the zone of stable operation of the converter according to the angle of control of the section thyristors.

Let us now consider, with reference to the second case, such a mode of operation of the converter, when in its control module of shunt thyristors both the current channel and the voltage channel are operating (Figs. 5 and 8),

At time t, (Fig. 8), the impulse from the main thyristor control system turns on the thyristor 6, which runs until time t. At time t, the thyristor 8 is turned on by a pulse from the voltage channel of the shunt thyristor control unit, turning off the main thyristor 6 during the switching process.

At time t, the thyristor 8 is turned off in a natural way and the pulse of the current channel of the control unit of the shunt thyristors turns on the thyristor 7, which at time t, turns off during the switching process when the section is turned on

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thyristor 3 system control sectional thyristors. During the next switching at time tg, when the shunt thyristor 7 is turned on by a voltage pulse U, the main / section thyristor 3 is turned on. The thyristor 7 is turned off in a natural way at time tg. At the same time, a shunt thyristor 8 is turned on with a pulse Ui. Then the process is cyclically repeated with the participation of other main thyristors.

Thus, in the second case considered, the converter is operational and outputs a current close to sinusoidal to the load.

The absence of the time delay of the pulses L of the CL and in the thyristor shunt control unit 14 may lead to a short circuit in the converter. This can be shown by observing his work, for example, at time t (Fig. 6). The replacement circuit of the converter for this moment is shown in FIG. 9, and a timing diagram showing the occurrence of a short circuit current in FIG. 10. From the diagram of FIG. 9 that when simultaneously the main 2 and the shunting 7 thyristors are simultaneously open, a short circuit in phase A of the converter appears in the converter circuit. Such a situation can be with the use of main (sectional) thyristors with a long turn-off time and with a premature (until the phase current of the converter drops to zero) the control pulse is applied to the control electrode of the shunt thyristor 7. Indeed, when the current decreases to the setting level IUCT the zero-organ of the current control channel of the shunt thyristors, at its output appears impulse voltage ccr. This pulse appears somewhat earlier than the current decay i. to zero and if it is fed without delay to the control electrode of the shunt thyristor 7, then when the sectional thyristor 2 is on, a short circuit with current of 1 c appears in the converter circuit. In the presence of a time delay element, a short circuit does not occur if the delay time t d, is longer than the turn-off time of the sectional thyristor t gy by the time it takes for the zero-organ to respond to the 91524

the time of decay to zero phase current 1d, i.e. when t ,, + t o.

Thus, the use of the proposed technical solution makes it possible to improve the quality of the output parameters of the direct converter of the t-phase voltage at a single-phase t-multiple frequency and to increase the stability of its operation in a wide range of loads.

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Claims (2)

1. Direct converter of t-phase voltage of one frequency into single-phase t-multiple frequency, containing m sections, each of which is made in the form of series-connected main switch of alternating current from counter-parallel connected thyristors and primary phase winding t- phase output transformer, and the sections are connected to a closed t-angle, whose vertices form the input terminals for connecting them to the g-phase network, the output terminals are formed by the output filter connected to the secondary winding mentioned transformer, as well as a pulse-phase control system synchronized with the network, designed to form and cyclically feed the keys of control pulses in the range of unlocking angles (n + l) i (where, 1,2, ... when counting from the beginning of the positive half-wave of a linear network voltage, attached to the city section, about t - 0 1A5 10 distinguished by the fact that, in order to improve the quality of the output current and voltage by reducing their non-sinusoidality, as well as improving the stability of the converter, it is equipped with an additional AC key in the form of two anti-parallel connected shunt thyristors connected either parallel to the secondary winding of the output transformer of the converter, or parallel to the additional winding of the same transformer, and the control unit of this key, which provides the formation and supply to it of impulses with a delay in relation to the moments of decay to zero output current, for the duration of the longer wrenching time of the main switches of the alternating current, and the filter is completed in the form of a series (resonant LC circuit tuned to the t-fold frequency . 2. Converter according to claim 1, t - characterized by the fact that the control unit with an additional AC key is made in the form of sensors of instantaneous values of the output current and voltage of the converter, the outputs of which through the zero-organs are connected to the inputs of the two-input OR element, and the latter through the element of the time delay and the output driver of control pulses is connected to the output terminals of the said block. Manage U4ynmupy u4uf u. / pyris tori s. P 20 )9 0 Tj about f8 sixteen four FI.2 P. . X ish . L / Have Fiel / /;  / V / .five fljc. G. L / C j w ( 5 /: h 5 / J 1X 1X HRP I / I I I sv / j  . 17 Wjx , fCA Th / UTG Vy. to .k h to TO. /one /one v . h  .5J7 / J I / , 2Jfli 41 th / 3.  14 l r / "... IX U IX KM II M II II II I A 2Jf / fM A / jx- / g Fig.8 Fie.9