RU2192707C2 - Three-phase switching unit - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: switching unit that may be alternatively made as contactless design version and that is distinguished by more complete voltage transmission to load has power thyristor in each phase being handled (A, B, C) whose cathode is connected to anode of power diode; additional diode whose cathode is connected to anode of power thyristor, the latter being connected in its turn through its cathode to output bus of switching unit and through anode, to cathode of power diode and to terminal for connecting supply mains phase A (B, C); first, second, and third diodes whose cathodes are connected through threshold elements, which are in series opposition to them, to gate electrodes of power thyristors of each phase and through anodes for first and third phases, to first leads of current-limiting resistors and through control switch for second phase, to first lead of current-limiting resistor whose second lead is connected to preceding (first) phase A, second leads of current-limiting resistors of first and third phases A and C being connected to output buses of third and second phases, respectively; fourth, fifth, and sixth diodes connected through their cathodes to anodes of respective power thyristors and through anodes, to first leads of current-limiting resistors. EFFECT: reduced current through control switch; reduced internal noise of switching unit in closed position. 1 dwg

Description

 The invention relates to a pulse technique and can be used to turn on and off a three-phase load.

 A thyristor AC output device (1) is known that contains two counter-parallel connected thyristors, a diode is connected in series with each of them, and a bias voltage source is connected to the connection points of the thyristors and diodes through a current-limiting resistor.

 The disadvantages of this device are the complexity of the control circuit, requiring an auxiliary DC power source, its applicability only for single-phase load.

 Known contactless switch of three-phase circuits (2), containing an actuator made on counter-parallel connected thyristors and diodes, two transformers, a control unit on counter-connected diodes and a transistor and diode-resistor chains, and the transformers are made three-phase, the primary windings of one of them connected in a triangle and connected to the input of the switch, the secondary windings are connected in a star and connected to the beginnings of the primary windings of another three-phase transformer, the ends of which are connected are connected to common points of the on-board diodes of the control unit, the end of the secondary winding of phase A of the second three-phase transformer is connected through a diode-resistor circuit to the control electrode of the thyristor phase C of the actuator, similarly the end of the secondary winding of phase B is connected to the control electrode of the thyristor phase A, end the secondary winding of phase C is connected to the control electrode of the thyristor phase B, and the beginning of these windings are connected to the output of the switch.

 The disadvantage of this switch is the complexity of the control circuit due to the presence of two three-phase transformers and a control unit, heat losses in the control transitions of power thyristors, the need to use a relatively high-current control key, since the total current of the power control transitions flows through it (taking into account the transformation coefficient of the second three-phase transformer) thyristors. All this reduces the reliability of the device.

 A thyristor switch (3) is also known, which contains a power thyristor and a power diode in each switched phase, in which the connection point of the power diode anode to the power thyristor cathode is connected to the phase input bus, and the connection point of the power diode cathode and the power thyristor anode is connected to the output bus , the first, second and third diodes, the cathodes of which are connected to the control electrodes of the power thyristors of each phase, respectively, and the anodes to the first output of the control key, the fourth, fifth and sixth diodes, the first, second, third cut sources and a zener diode, and the zener diode is connected by an anode to the second output of the control key, and by the cathode to the anodes of the fourth, fifth and sixth diodes and the first output of the first, second and third resistors, the connection point of the cathode of the fourth diode with the second output of the first resistor is connected to the output terminal of the first phase, the connection point of the cathode of the fifth diode and the second output of the second resistor to the output terminal of the second phase, the connection point of the cathode of the sixth diode and the second output of the third resistor to the output terminal of the third phase.

что влечет за собой появление в нагрузке отсечки напряжения в 30 эл. град.The drawback of the switch, with all the simplicity of its control circuit, is the lag of the leading edge of the control pulse from the anode voltage of the thyristor of this phase by an angle

which entails the appearance in the load of a cut-off voltage of 30 el. hail.

 The closest to the proposed technical essence and the achieved effect is a three-phase thyristor switch (4) (prototype), containing counter-parallel connected controlled and uncontrolled valves in each phase and a control unit made in the form of a three-phase diode rectifier, the output of which is through a control key, resistors and diodes are connected to the control electrodes of the valves, and the control unit is equipped with threshold elements and additional elements included in the circuit of the control electrodes of the valves diodes shunting the transition control electrode-anode of the valves.

 A disadvantage of the known switch is the need to use a relatively high-current control switch, since the total current of the thyristor control transitions flows through it, a relatively high level of switching noise, since in addition to a control pulse of sufficient steepness and amplitude, a certain anode voltage amplitude is also required at which, through it starts to flow on current. All this reduces the reliability of the device, leads to the appearance of internal noise of the device in the on state.

 When creating the invention, the problem was solved to increase reliability, reduce the level of switching noise in the switched on state of the switch, and more fully transfer the mains voltage to the load.

 A significant difference of the proposed switch is that in a three-phase switch, containing in each switched phase a power thyristor connected by a cathode to the anode of the power diode, the first, second and third diodes connected by cathodes through threshold elements connected in opposite direction with the control power thyristor electrodes of each phase, and anodes for the first and third phases with the first terminals of the limiting resistors, the fourth, fifth and sixth diodes connected by cathodes to the anode correspond power thyristor, and the anodes with the first outputs of the phase limiting resistors, and a control key, an additional diode is connected to the power circuit of each phase, connected by a cathode to the anode of the power thyristor, which, in turn, is connected by a cathode to the output bus of the switch, and the anode with the cathode of the power diode and the terminal for connecting the network phase, the anode of the second diode of the second phase is connected via the control key to the first output of the limiting resistor connected to the input bus of the previous - first - phase, the second output s limiting resistors of the first and third phases are connected to the output buses third and second phases, respectively.

 The essence of the proposed technical solution lies in the development of a switch, in which a substantially reduced current flows through the control key, moreover, a pulsed current of one of the thyristors (power thyristors of other phases are turned on after turning on the corresponding thyristor of the previous phase); The inclusion of power thyristors occurs before the appearance of a positive potential on their anodes, which significantly reduces the level of switching noise in the on state and allows you to more fully transfer the mains voltage to the load.

 The drawing shows a schematic diagram of a device.

 The switch contains in each switched phase A (B, C) a power thyristor 1 (2, 3) connected by a cathode to the anode of a power diode 4 (5, 6), an additional diode 7 (8, 9) connected by a cathode to the anode of a power thyristor 1 (2, 3), connected, in turn, by the cathode to the output bus 10 (11, 12) of the switch, and the anode - with the cathode of the power diode 4 (5, 6) and a terminal for connecting phase A (B, C) of the network; the first 13, second 14 and third 15 diodes connected by cathodes through threshold elements 16, 17, 18, connected in opposite-sequence with the control electrodes of the power thyristors of each phase, and the anodes for the first and third phases with the first terminals of the limiting resistors 19, 20, and - for the second phase - through the control key 21 - with the first output of the limiting resistor 22 connected to the previous output - the first - phase A, the second outputs of the limiting resistors 19, 20 of the first (A) and third (C) phases are connected respectively to the output the bottom tires 12, 11 of the third and second phases, respectively; the fourth 23, fifth 24 and sixth 25 diodes connected by cathodes to the anode of the corresponding power thyristor 1, 2, 3, and by the anodes to the first terminals of the limiting resistors 19, 22 and 20.

 The switch operates as follows.

по цепи фаза А, ограничительный резистор 22, управляющий ключ 21, второй диод 14, пороговый элемент 17, управляющий переход силового тиристора 2, силовой диод 5, фаза В протекает ток, открывающий тиристор 2, после его открывания по цепи фаза А, ограничительный резистор 22, пятый диод 24, силовой тиристор 2, силовой диод 5, фаза В течет ток (до

), минуя цепь, состоящую из управляющего ключа 21, второго диода 14, порогового элемента 17 и управляющего перехода тиристора. В момент времени

когда потенциал фазы В становится положительным, в нагрузке появляется ток, текущий по цепи фаза В, дополнительный диод 8, силовой тиристор 2, нагрузка, силовой диод 6, фаза С (при этом по цепи фаза А, ограничительный резистор 22, пятый диод 24, дополнительный диод 8, смещенный током нагрузки в прямом направлении, фаза В протекает ток, также минующий цепь управляющего перехода тиристора 2, до момента времени

. С появлением на аноде силового тиристора 2 положительной полуволны напряжение по цепи фаза В, дополнительный диод 8, силовой тиристор 2, ограничительный резистор 20, третий диод 15, пороговый элемент 18, управляющий переход силового тиристора 3, силовой диод 6 начинает протекать ток, открывающий тиристор 3, далее происходят процессы, аналогичные с процессами в фазе В (включение силового тиристора 1 происходит с появлением положительной полуволны напряжения на аноде силового тиристора 3 в фазе С).In the initial state, the control switch 21 is open, the control transition of the power thyristor 2 is disconnected, the thyristor 2 is closed, the control transitions of the power thyristors 1 and 3 are also disconnected, the thyristors are closed, and there is no current in the load circuit. When the control key 21 is closed, for example, at a time

phase A circuit, limiting resistor 22, control key 21, second diode 14, threshold element 17, power thyristor 2 control transition, power diode 5, phase B current flows, opening thyristor 2, after it opens phase A circuit, limiting resistor 22, fifth diode 24, power thyristor 2, power diode 5, phase B current flows (up to

), bypassing the circuit consisting of a control key 21, a second diode 14, a threshold element 17 and a control transition of the thyristor. At time

when the potential of phase B becomes positive, a current appears in the load, current flowing through the phase B circuit, additional diode 8, power thyristor 2, load, power diode 6, phase C (in this case, phase A along the circuit, limiting resistor 22, fifth diode 24, additional diode 8, biased by the load current in the forward direction, phase B flows current, also bypassing the control transition circuit of thyristor 2, up to the point in time

. With the appearance of a positive half-wave at the anode of power thyristor 2, the phase B voltage, an additional diode 8, power thyristor 2, a limiting resistor 20, a third diode 15, a threshold element 18, a control transition of the power thyristor 3, a power diode 6 starts to flow current, opening the thyristor 3, then processes similar to those in phase B occur (power thyristor 1 is turned on with the appearance of a positive voltage half-wave at the anode of power thyristor 3 in phase C).

 Thus, the inclusion of power thyristors 1, 2, 3 occurs earlier than the appearance of a positive potential on their anodes, which avoids switching interference at each next load connection to the network, additional diodes 7, 8, 9 allow this operation.

 To turn off the device, the control key 21 opens, thyristor 2 closes and then thyristors 3 and 1, respectively.

 Compared with the prototype, the claimed three-phase switch has a significantly lower current flowing through the control key, the ability to implement it in a non-contact version, a more complete transfer of the mains voltage to the load, which increased the reliability of the switch and reduced the internal noise of the switch in the on state.

Sources of information
1. USSR author's certificate 485561, N 03 K 17/56, 1976

 2. Copyright certificate of the USSR 673667, N 03 K 17/56, 1979

 3. RF patent 2020742, N 03 K 17/72, 1992

 4. Copyright certificate of the USSR 760329, N 02 M 1/08, 1980 (prototype).

Claims (1)

 A three-phase switch containing in the power circuit of each switched phase a power thyristor connected by a cathode to the anode of the power diode, first, second and third diodes of the first, second and third phases, respectively, connected by cathodes through the corresponding threshold elements connected in opposing series with the control power thyristor electrodes of the corresponding phase, and anodes for the first and third phases with the first terminals of the limiting resistors; the fourth, fifth and sixth diodes of the first, second and third phases, respectively, connected by the cathodes to the anodes of the corresponding power thyristors, and by the anodes to the first terminals of the limiting resistors of the first, second and third phases, respectively, and a control key, characterized in that in the power circuit In each phase, an additional diode is introduced, connected by the cathode to the anode of the corresponding power thyristor, connected by the cathode to the output bus of the corresponding phase, and by the anode to the cathode of the corresponding power diode and a terminal for connecting For the corresponding phase of the network, the anode of the second diode of the second phase is connected through the control key to the first output of the second phase limiting resistor connected to the terminal for connecting the first phase of the network, the second terminals of the first and third phase limiting resistors are connected to the output buses of the third and second phases, respectively .