SU803088A1 - Thyratron frequency converter with direct coupling - Google Patents

Description

(54) VENTILATING CONVERTER OF FREQUENCY WITH IMMEDIATE - NON CONNECTION

one

The invention relates to static frequency converters of alternating current and can be used in electrical converters and in electric drive systems.

Known frequency converters 1, g with direct connection and natural switching of valves (picloconverters) are known, in which one half-wave of the output voltage produces a rectification, and the second half-wave - inverts the multi-phase convertible voltage by alternating switching groups of different groups of gates 1 and 2 Such converters are economical and have a relatively small installed capacity of power equipment, but they are characterized by the following pedostatki:

low output frequency, practically not exceeding 1 a half of the converted frequency, and difficulty in adjusting it without degrading the shape of the output voltage curve;

control complexity, especially with the so-called separate control of groups of creeps;

Significant distortions of the shape of the curve b; a sleek voltage.

To eliminate these drawbacks, both power and abrasive circuits must be complicated. For example, to increase the output voltage frequency, you have to significantly increase the number of phases or introduce elements of forced switching of valves or introduce resonant circuits, i.e., complicate power circuit. To improve the shape of the output voltage curve, it is difficult to control circuits, in particular, to control the converter according to the principle of a closed wake of the first systems.

Claims (3)

Also known is a valve converter with direct connection, containing on 1 1 in each phase of a multiphase voltage source transformers with primary windings located on them, connected to the source phases, secondary, connected in series, and control and control windings h, i each of which included a pair. —1.1 the voltage of the corresponding winding is controlled 3. The disadvantages of this converter are: a low output voltage frequency, a much lower frequency of the power supply direct voltage, since each half-wave of the output voltage of the folded half-wave of the phase voltage supply zheny; complexity of power and control circuits; distorting the shape of the output voltage curve, consisting of sinusoidal supply voltage; possibility of only single-phase output, which limits the possibilities of application. The aim of the invention is to increase the frequency control range and simplify the device. This goal is achieved by the fact that in a gate-mounted frequency converter with a direct connection containing transformers connected to each phase of a multiphase voltage source with primary windings located on them connected to the source phases, secondary, connected in series, and control windings, and controlled valves , each of which is connected in parallel with the corresponding control winding, the control electrodes of all the gates are combined. FIG. 1 shows a diagram of the proposed converter; in fig. 2 - circuit currents; in fig. 3 shows the magnetic fluxes of the transformers of the circuit of FIG. one; in fig. 4 and 5 are diagrams of the proposed converter (various variants). The converter (Fig. 1) contains eight identical controlled transformers connected to an eight-phase source with a zero wire (marked "O) of the supply sinusoidal voltage of the angular frequency. The primary winding 1 of each transformer is connected in series with load 2 to one phase of the supply voltage. The secondary windings 3 of all transformers are connected in series to form the output winding of the HH converter. Each transformer also contains a control winding 4 closed by a controllable valve (thyristor) 5. The control winding circuits can be connected (Fig. 1) or galvanically uncoupled. The control electrodes of all valves 5 are combined and the source of control pulses is connected to the common points of the quince. The resistances of loads 2 are much smaller than the inductive resistances of windings 1, if the cores of the transformers are not saturated, and they are much larger than them, if the cores are saturated. The magnetization curves of the cores are close to rectangular. If there is a constant voltage between the terminals of the quince, sufficient opening of the thyristors, self-saturation of all transformers occurs. In this case, the voltage drop across their windings is insignificant, and the sinusoidal currents i, shown in FIG. 2 thin sinusoidal lines. In the absence of a control signal at the quince terminals, all thyristors are locked, almost all source voltage is applied to windings 1, and a small magnetization current flows through loads 2 and the magnetic fluxes Φ of eight transformers change sinusoidally, as shown in FIG. 3 thin sinusoidal lines. The maximum magnetic flux Φ of the unsaturated transformer is chosen to be slightly less than the saturation flux (see Fig. 3). Consider the operation of eight transformer-valve circuits, when the control signal is simultaneously applied to the thyristor control electrodes in the interval from W1 Out / 7. The interval during which the control signal is applied is shown in the lower part for clarity (Fig. 3 ) rectangle with light circles. The moment It / of supplying the control signal for the thyristor of the first circuit falls into that half-period when the thyristor can conduct. Since the voltage drop on the conducting thyristor and the active resistance of the winding 4 is insignificant, after switching on the thyristor at the time l, the magnetic flux practically ceases to change (Fig. 3, dash-dotted line). The constant value of the flux is preserved until the end of the half period tut rG, when the anode voltage of the thyristor changes sign and it ceases to conduct. From this point on, the magnetic flux increases, when (and t (j-l) 19- reaches the saturation value Fu and stops changing until the end of the period uj t 2. Then the flux decreases, by the time a, reaches the initial value, and the process repeats During two intervals 3j u) t jr and 19 u) t, when the magnetic flux does not change and the voltage drop across the winding 1 is insignificant, a current flows through the load 2 of the first circuit (Fig. 2, dash-dash line). The magnetic flux of the second transformer (Fig. 3, dotted line), at the moment l - is equal to the saturation flux Фf. The second thyristor may turn on at the time W t when its anode voltage becomes positive. From this point on, the flux can be changed to a very small value, for example, from c to F, corresponding to the voltage drop on the conducting thyristor and the active resistance of the winding 4, i.e. it remains almost unchanged until time tJJT, when the anode voltage the thyristor changes the sign and it ceases to conduct. The core of the transformer is again saturated, and the process is stopped. Since during the entire period the magnetic flux of the second transformer remains almost unchanged and the inductance of its primary winding is insignificant, a continuous sinusoidal current flows through the load 2 of the second circuit (dotted line in Fig. 2). In the third, fourth, and fifth circuits, the thyristors do not have time to turn on during the supply of the control signal (their anode voltage is negative). Therefore, the magnetic fluxes of the third, fourth, and fifth transformers vary sinusoidally, and the currents in the respective loads 2 are absent. The magnetic flux of the string transformer is shown in FIG. 3 line "two dashes - dot (.). Since the thyristor is turned on at the very end of its conductive half-period, the magnetic flux of the conductor transformer does not change and only a short interval of 3-sh1 flows through its load 2. The second is the same interval when the core is saturated, separated from the first by s, that is, the interval. The magnetic flux of the seventh transformer is shown in FIG. 3 small-dotted line. From the moment l. it does not change until w t changes the sign of the voltage and then increases. The arrival (fi + d.) Of the IS core is saturated, the flow remains unchanged until the end of the half period t 3 -, after which it decreases, and the process repeats. The current of load 2 of the seventh circuit flows in two intervals, when the flow does not change, namely 3 and 19 with t O (Fig. 2, a small dotted line). The process in the eighth chain proceeds similarly - the dotted lines in FIG. 2 and 3; the magnetic flux does not change to the inlet 2 of the eighth circuit, a current flows in the intervals w t 3 and 19 and t 7. The sum of the magnetic fluxes of all transformers is the flux linkage of the H – H winding, which determines the voltage at its terminals (Fig. 3, 6, a solid line with bright circles. The flux linkage contains a constant component, due to the presence of valves, and a variable component. If the duration of the control signal is increased, for example, to the interval (Fig. 3, at the bottom of the corner with blackened circles), work of all chains except the three The third thyristor can turn on at the beginning of the half-period of its conductivity, 4O t, therefore the magnetic flux of the third transformer, like the second, will not practically change, and a sinusoidal current will flow through its primary winding. in this case, curve 7 (flat line with black circles) is shown. If the duration of the control signal is increased to the interval 3 u) t 7y (Fig. 3, below the rectangle with crosses), then the fourth thyristor will turn on, and the magnetic flux of the fourth transformer will also stop changing. The corresponding winding flux linking curve is HH - line 8 with crosses. From a comparison of curves b, 7, and 8 it can be seen that the duration of the control pulse, equal to about a quarter of the period, is optimal, since the variable component of the output flux coupling of the output winding is at the same time the best shape and most relevant to the constant component. As can be seen from curves 6-8, the variable flux component of the output winding has a minimum at the time of supplying the control signal and a maximum located at ji. Therefore, by changing the moment of the signal within the period, it is possible to smoothly change the phase of the voltage at the terminals H – H. Thus, the converter (Fig. 1) can operate with a phase shifter, ensuring smooth voltage phase control at terminals H – H within 360. If the control signal supply time changes its position from period to period of the power frequency i.e. if the signal frequency is not equal to the power frequency, then the voltage frequency at the terminals H – H is equal to the signal frequency. Since the frequency of the output voltage is equal to the signal frequency, and the power to the load comes from the power source, the converter is a power amplifier. The current in the neutral wire — the sum of the currents of the primary windings of the transformers — is shown in FIG. 2, curve 9 for the duration of the control signal 3 u) t 7 and curve 10 for the duration of the signal 3. The frequency and phase of the main harmonic of this current are determined by the moments of the supply of the control signal, so the load can also be included in the neutral wire. As loads 2, it is convenient to use multi-phase windings of electric masins, for example, asynchronous motors. When the phase windings of the machine are energized by currents i (Fig. 2), the resulting magnetizing force is a traveling wave, the position and speed of which are determined by the moments of supplying the control signal. Consequently, the converter (Fig. I) allows frequency control of the AC drive speed with a single control signal. Thus, the transducer (Fig. 1) can be used to power both multiphase and single phase loads. The operation of the converter (FIG. 1) is considered for simplicity when powered from an eight-phase source. Obviously, its operation does not change at the power supply from a four-phase source, if half of the transformers change the mutual direction of windings 1 and 4. It is known that a transformer in a magnet-valve amplifier can be replaced by an autotransformer, if a small DC component is acceptable. through consistently included load. FIG. 4 shows the autotransformer circuit of the proposed converter, in which there are no control windings. If, to improve the shape of the output voltage curve, the number of phases of the circuit must be greater than the number of phases of the supply voltage, then the primary windings of the transformers can be connected in series to form a converter of the number of phases. FIG. Figure 5 shows a converter circuit, which also contains an array of controlled transformers, but is powered from a two-phase source. Each transformer contains the primary windings 11 and 12. The number of turns of the windings 11 are distributed but the cores are sinusoidal, and the windings 12 are cosine-shaped. When connecting successively connected windings II to the first phase L -.X of the power supply two-phase voltage, and windings 12 to the second phase B-U and in the absence of a control signal at the quince terminals, the voltage of the secondary windings 3 form a symmetrical eight-phase system , i.e., their sum at the output terminals H - H is zero. When a control signal is applied to terminals a. in the work scheme. 5, the principle is not different from the operation of the circuit of FIG. 1. Thus, this device provides frequency control both downwards and upwards with respect to the frequency of the power supply, and is simpler than the prototino.m, since it contains 1I1l one transformer and one gate per phase. The proposed device is functionally universal, since it can supply both single phase and multiphase loads at the same time and can be connected to power sources with different number of phases while maintaining the number of phases of the circuit and, accordingly, the shape of the output voltage curve. Claims of a Directly Coupled Frequency Converter, containing transformers included in each phase of a multiphase source, voltage transformers located on them primary windings connected to the source phases, secondary connected in series and control windings, and controlled. which napa is included. correspondently to the control winding, characterized in that, with an increase in the frequency control and control range, the control electrodes of all the valves MBT United. Sources of information taken into account in the examination 1. Patent USA.4. No. 3368136, cl. 321-7, 1975. 2. Patent SSh.L, .Vo 3803478, cl. 321-7, 1975. 3..Hvtorskoe certificate of the USSR but; A2182446 / 24-07. cl. H 02 .M 5 16, Vk L9 1975.% 7ГJf f f Jf f f 7f 2 Fig. H 2fr FIG. five