SU955447A1 - Inverter - Google Patents

Description

(54) INVERTER

The invention relates to a converter technique and can be used in power and electric drive devices. Inverters with pulse transformers used to turn off thyristors 1 are known. These inverters have an increased weight, size, cost, and reduced efficiency due to the presence of switching capacitors and chokes, which is especially significant with high power and high frequency of the inverter; for the flow through the switching elements of currents exceeding the operating currents, and the application to these elements of significant connections in time intervals exceeding the thyristor off time at . DC-to-AC converters (inverters) are known, containing incompletely controlled power gates (thyristors) and a switching current transformer, the primary winding of which is connected in series to the AC output circuit of the converter, and equipped with fully controlled; the main valves, the current transformer is made with secondary windings according to the number of the main valves connected through the mentioned fully controlled - fans with power valves, and parallel to one of the the coil is connected to an additional two-pole fully controlled valve 2. These inverters have increased weight and dimensions and reduced efficiency due to the need to use fully controlled valves to pulse the entire load current of the inverter. The purpose of the invention is to improve the weight and size parameters and increase the efficiency of the inverter. The goal is achieved by the fact that in the inverter containing in each arm a main thyristor shunted by a reverse diode, the primary winding of the switching current transformer is connected to the inverter AC circuit, and two of the secondary fully controlled valves are connected to one of its secondary windings The windings of the mentioned switching current transformer are connected in series with the switching thyristors connected anti-parallel to the main thyristors.

In another modification of the inverter, diodes shunted by capacitors are connected in series with switching thyristors.

In the third modification of the inverter, the secondary windings of an additional pulse transformer are connected in series with the switching thyristors, the primary winding of which is connected to the input terminals through a fully controllable key.

In the fourth modification of the inverter, an additional power source is connected in series with the switching thyristors.

FIG. 1 shows the circuit diagram of the first modification of the inverter; in fig. 2 and 3 graphically illustrate his work; in fig. 4-6 are diagrams of other modifications of the inverter.

The inverter (Fig. 1) contains the main thyristors 1-4, reverse diodes, switching current transformer 9 with primary winding 10 and secondary windings 11-14 and current transformer 15 with primary winding 16 and secondary windings 17-20. Parallel to thyristor 1, connected in series are switching thyristor 21 and secondary winding 11, parallel to thyristors 2-4, respectively, switching thyristors 22-24 and secondary windings 12, 17 and 18. Primary windings 10 and 16 are included in the inverter AC circuit. Parallel to the secondary windings 13 and 19 of transformers 9 and 15, a two-pole switch is connected, consisting of a transistor 25 and diode bridges 26-29 and 30-33. The secondary windings 14 and 20 are connected via a diode bridge 34-37 and 38-41 to the source of supply voltage. (If there are midpoint points on windings 13, 14, 19 and 20, full-wave rectifiers can be used instead of bridges). At the output of the inverter, choke 42 (for stable operation of the inverter at idle) and a high harmonic filter 43 (if filtering of high harmonics is necessary) can be turned on. The polarities of switching on the transformer windings are shown in FIG. 1, dots. To the input of the inverter is connected a source of supply voltage of the polarity shown in Fig. 1, to the output of the inverter is connected a load.

The number of turns of the winding 11 (12 -, 17 or 18) is smaller (approximately 1.05-1.25 times) the number of turns of the winding 10 (16), the number of turns of the winding 14 (20) is less than the number of turns of the winding 11.

FIG. Figures 2 and 3 show diagrams of the current values of voltages and currents of the inverter. Bych - Inverter Output Voltage

(at points ab), - the output current of the inverter (to the drossel 42 and filter 43, if any). U | -1) 4 and U2i -Ujs are the control voltages (or currents) of thyristors 1-4, 21-24 and transistor 25 (formed by the inverter control system, not shown in Fig. 1), in, J, i. and 13 (i) are the currents through the respective windings. Currents through windings 11 and 12 at a given angle of shift of the output current of the inverter

relative to the output voltage is zero. The positive directions of the currents are shown in FIG. 1 arrows. U and U) 5 are the voltage forms on the windings of transformers 9 and 15, respectively (the polarity of the voltages on the windings 10 and 16 is positive

 shown in FIG. one).

The durability of the output voltage may vary by shifting the control voltages. The output current of inverter i, depending on the load of the inverter and filter 43, if it exists, can have almost any shape from almost rectangular to sinusoidal with an arbitrary phase shift relative to the output voltage. To eliminate sudden changes in the inverter output current in the switching intervals

5 thyristors, the filter 43 should start with the throttles, and if the filter 43 is absent and the inverter load is active or active-capacitive in nature, then a choke with a small inductance should be turned on.

FIG. 3 illustrates the switching off, for example, of the thyristor 1. The left column shows the turning off of the thyristor 1 at a positive value of the current 1 of the middle current - when the current ijyK passes through zero,

5 right - with a negative value of these

The thyristor I is turned off as follows.

Through the primary windings 10 and 16 of the current transformers 9 and 15 flows the load current. Through the secondary windings 13 and 19, shorted by an open transistor 25, flow countercurrents equal in amperages and reverse in direction to currents

5 primary windings. In the interval T (Fig. 3), the control voltages are removed from the thyristor 1 and from the transistor 25, and the control voltage is applied to the thyristor 22. Since in the current transformer the total current turns of the secondary windings are equal to

0, the values of and inverse to the sign of the ampere turns of the primary winding (with an accuracy of 0.5-3% depending on the transformer version), and the voltages on its windings are determined by external loads, then if the current in the winding 13 is interrupted by opening the transistor 25 in this interval T The equalizing current flows either through the winding 12 with the positive direction of the current of the winding 10 (Fig. 3, left column), or through the winding 14 with the negative direction of the current through the winding 10 (Fig. 3, right column). No current can flow through the winding 11 at this interval, since the uncoupling voltage is not applied to the thyristor 21. When the current through the winding 10 is positive, the equalizing countercurrent through the winding 12 closes through the open diode 5 and the thyristor 22 to the input voltage source of the inverter and the voltage across this winding at any current through it is almost equal to the voltage of this source (plus the voltage across the open thyristors 22 and diode 5) - the operation of the current transformer winding on the back-EMF. At the same time, the current through the winding 14 cannot flow, since the number of its turns is less than the number of turns of the winding 12 and the voltage across it is lower than the voltage on the winding 12, i.e. less than the input voltage of the inverter, and the current through the winding 14 and the diode bridge 34-37 can flow only if the voltage across it is greater than the input voltage. With a negative current direction through the winding 10, the current through the winding 12 and the thyristor 22 cannot flow in the opposite direction, and the equalizing countercurrent is closed through the winding 14 and the diode bridge 34-37 to the inverter input voltage source. With a positive direction of the current through the winding 10 at any value of this current, the winding 12 is greater than the current of the winding 10, since the amperages of these windings are equal and the number of turns of the winding 12 is less than the number of turns of the winding 10. The current through the left upper gate (thyristor 1 and diode 5 ), equal in the interval f of the difference in the currents of the windings 12 and 10, flows through diode 5, and the thyristor 1 is turned off by the reverse voltage removed from the open diode 5 in this interval. After the interval t ends (Fig. 3), the control voltage is removed from the thyristor 22 and the control voltages are supplied to the transistor 25 and to the thyristor 2. At this time, the output current of the inverter passes from the upper left valve (thyristor 1 and diode 5) to the lower left valve (thyristor 2 and diode 6), and the voltage of the output of the bridge varies abruptly. Similarly, the other inverter thyristors are turned off. In the inverter in FIG. 4, one or more diodes 46 and 47 connected in series in the thyristor off circuits 44 and 45, parallel to which a small capacitor 48 is turned on, and diodes 51 and 52 and a capacitor 53 included in the thyristor off circuits 49 and 50. 48 (53) is charged by the tripping current shown in FIG. 4 polarity up to a voltage equal to the direct voltage drop across the diodes 46, 47 and 51, 52. The number of series-connected diodes is chosen such that the total voltage across the diodes (capacitor 48 or 53) would be greater than the residual voltage The current transformer 58 windings 54-57. At the same time, after the end of time X, at which the shutdown current flows through the additional thyristor and the current transformer winding, the additional thyristor is turned off by the reverse voltage removed from the capacitor 48 or 53. For example, after The current of the thyristor 44 is turned off by the off loop: winding 54, thyristor 59, capacitor 48 and diodes 46 and 47 parallel to it, the voltage source feeding the inverter, and diode 60 — thyristor 59 is turned off by the voltage applied to it from capacitor 48 through diode 61 and a winding 54, the residual voltage on which is less than the voltage on the capacitor 48. Since the capacitor 48 is only recharged by the reverse current of the thyristors 59 and 62, its capacitance may be small. Similarly, thyristors 62, 63, and 64 are turned off after the time intervals for turning off thyristors 45, 49, and 50 are disconnected. Resistors 65 and 66 serve to prevent capacitors 48 and 53 from overcharging to reverse polarity with leakage currents of switched off thyristors 59, 62-64. A similar result can be achieved by including in the off-thyristor switching circuits of the secondary windings of a low-power pulse transformer, the primary winding of which is connected via an additional fully controlled switch and diode to the voltage source that supplies the inverter (Fig. 5). The inverter as shown in FIG. 5 contains a pulse transformer 67 with a primary winding 68 and secondary windings 69 and 70. The primary winding 68 through a transistor 71 is connected to a voltage source feeding the inverter. Transistor 71 operates in a pulsed mode and the inverter control system is open for short time intervals, immediately following the main intervals t, during which the main thyristors 72-75 are turned off. During the rest of the period, the transistor 71 is turned off. The inverter (Fig. 5) works as follows. When the current pulse passes during the main intervals T through one of the switching thyristors 76-79 and the winding 69 or 70, then through the diode 80, the winding 68 and the supply voltage source passes a countercurrent pulse equalizing the winding current 69i or 70. At the same time, the winding 68 The voltage is almost equal to the voltage of the power supply source. The polarities of the voltage on the windings 68-70 are shown in FIG. 5. The number of turns of the winding 69 or 70 is significantly less than the number of turns of the winding 68 and countercurrent through the winding 68 and the diode 80 is significantly less than the current through the windings 81-84 of the current transformer 85 and thyristors 76-79 in the intervals T.

After termination and intervals t, the transistor 71 is turned on by the control system during the time intervals noted above. During these intervals, the voltage on the windings of the transformer 67 has the same sign and almost the same value as in the intervals T, but the winding 68 turns out to be connected to the supply voltage not through the diode 80, but through the transistor 71. The windings 68 and 69 in these intervals exceed the residual voltages on the windings 81-84 of the current transformer 85, shorted by transistor 86. The difference in these voltages switches the switching thyristors 76 to 79. The operating current of the transistor 71 is equal to the sum of the reverse current of the switchable current ister 7679, reduced in the transformer 67 ratio, and the no-load current of the winding 68 of this transformer. After turning off the transistor 71, the no-load current of the winding 68 is clamped through the diode 87 and the zener diode 88, linearly decreasing to zero.

From the point of view of obtaining the maximum efficiency of the inverter and the best weight and size parameters, the inverter according to the scheme in FIG. 1 it is expedient to use at the input voltage of the inverter up to 24-27 V, the inverter as shown in FIG. 5 - from 24-27 V to several hundred volts, the inverter according to the scheme in FIG. 4- over several hundred volts.

If an additional voltage supply is used in the power supply system (for example, the inverter is powered by a battery and there is a backup battery), then this source can be used as a source included in the thyristor deactivation circuits. The circuit of such an inverter is shown in FIG. 6. Turning off, for example, the thyristor 89 in this inverter is as follows. In the shutdown interval of this thyristor, the shutdown current passes through the circuit of the switching off winding 90 of the current transformer 91, the thyristor 92, an additional source of supply voltage — a backup battery 93, a diode 94 and a small capacitor 95 connected in parallel with it, a diode 96. During the interval T the thyristor 89 is turned off by the reverse voltage of the diode 96. In this case, the capacitor 95 is charged to a voltage of 0.9-1.5 V shown in FIG. 6 polarity, the capacitor 97 is charged as shown in FIG. 6 polarity up to a voltage equal to the difference between the voltage of the backup and running batteries, plus the voltage on the capacitor 95 (note that the voltage of the unloaded backup battery, recharged by the thyristors off current, is higher than the voltage loaded

battery). After the interval I has ended and the thyristor 98 or diode 99 is turned on, thyristor 92 is turned off by the circuit: thyristor 92, capacitor 97, thyristor 98 or diode 99, winding 90. In this circuit, the voltage on the capacitor 97 is greater than the sum of the residual voltage on the winding 90 and to diode 99. The capacitor 97 (95) is small because it is only discharged by the reverse current of the thyristor 92 that is turned off and the reverse leakage current of the thyristor 100. Instead of capacitors 95 and 97, there may be included resistors. At the same time, the thyristor 92 is turned off through both of these resistors by the difference of the reserve and working batteries voltage minus the voltage on the open diode 99 and the residual voltage on the winding 90. If the backup battery 93 is at a considerable distance from the inverter, then it is parallel to its points connections to the inverter it is necessary to turn on a small capacitor.

Similarly to single-phase inverters, multiphase, in particular, three-phase inverters with transformerless and transformer-free output, as well as step-sinusoidal voltage inverters consisting of a number of single-phase inverters can be made. A current transformer and a two-pole switch are made common to all the power thyristors of such inverters.

In high power inverters, for power supply, for example, radio transmitters, other incompletely controlled gates, such as thyratrons or mercury gates, can be used instead of thyristors, and vacuum tubes instead of key transistors.

The technical and economic efficiency of the proposed invention is to reduce the weight, size, cost of inverters and increase their efficiency by reducing the weight, size, cost of the thyristor switching system, reducing power loss.

Claims (4)

1. An inverter containing a main thyristor in each arm, shunted by a reverse diode, the primary winding of the switching current transformer being included in the AC circuit of the inverter, and two-pole fully controlled valves are connected to one of its secondary windings, characterized in that in order to improve energy performance and reduce the mass and dimensions of the inverter, other secondary windings of the mentioned switching current transformer are connected in series with the switching thyristors, 9 connected anti-parallel to the main thyristors. 2. The inverter according to claim 1, characterized in that diodes connected by capacitors are connected in series with the switching thyristors. 3. The inverter according to claim 1, characterized in that the secondary windings of an additional pulse transformer, the primary winding of which is connected to the input terminals via a fully controllable switch, are connected in series with the switching thyristors. ten 4. An inverter according to claim 1, characterized in that an additional power source is included in series with the switching thyristors. Information sources, taken into account in the examination 1. Glazenko, T. A. Semiconductor converters in electric drives of direct current. L., “Energie, 1973, p. 264-265, fig. 4-44 and 4-45. 2. USSR author's certificate No. 838967, cl. H 02 M 7/515, 09/20/79 (prototype). R R g Г ГП R g R 72 15 U. 25 iJuiiUs fig.Z