CN106849327B

CN106849327B - Alternating current-direct current hybrid circuit breaker and control method

Info

Publication number: CN106849327B
Application number: CN201710044575.7A
Authority: CN
Inventors: 王云; 叶辰之; 李霄; 李福生; 杨建波; 曹碧颖
Original assignee: Shanghai Electric Group Corp
Current assignee: Shanghai Electric Group Corp
Priority date: 2017-01-19
Filing date: 2017-01-19
Publication date: 2020-03-17
Anticipated expiration: 2037-01-19
Also published as: CN106849327A

Abstract

The invention relates to the technical field of power electronics, in particular to an alternating current and direct current hybrid circuit breaker, which comprises: the high-speed mechanical switch is connected with the main loop and used for carrying out high-speed breaking on the main loop; a first diode, a second diode, a third diode and a fourth diode; a first thyristor, an inductor and a capacitor which are connected in series in sequence; the first thyristor is used for controlling the charging and discharging of the capacitor; one end of the capacitor, which is far away from the inductor, is high voltage so as to discharge through the high-speed mechanical switch and charge reversely; the energy absorption branch circuit is used for converting a first state into a second state when the received voltage is higher than a set value so as to reduce the current in the main loop to a safe current value; and a method of controlling the circuit breaker; the system conduction loss can be reduced, the thermal design difficulty of the solid-state circuit breaker is reduced, the possibility of mistaken touch of a controllable device is greatly reduced, the system reliability is improved, the system cost is reduced, and the action speed of the circuit breaker is accelerated.

Description

Alternating current-direct current hybrid circuit breaker and control method

Technical Field

The invention relates to the technical field of power electronics, in particular to an alternating current and direct current hybrid circuit breaker and a control method.

Background

In a direct current transmission and distribution system, when a short-circuit working condition occurs, because natural zero crossing points do not exist, the short-circuit current is more difficult to cut off compared with an alternating current system, if a mechanical switch is only used for directly drawing an arc to cut off the short-circuit current, on one hand, the breaking time is longer, the rising rate of the short-circuit current is fast, and when the breaking is finished, the short-circuit current is very large, so that other equipment in the system can be damaged; on the other hand, the mechanical switch continuously arcs in the breaking process, the damage to the contact is large, and the mechanical service life is shortened.

In a distributed microgrid system, when a fault occurs on a power grid side, the microgrid system needs to be capable of realizing rapid seamless switching of grid connection and grid disconnection, and the switching-off time of a traditional mechanical switch is usually more than 10ms, so that the requirement of seamless switching cannot be met.

In some occasions containing the critical load sensitive to the electric energy quality, when the short-circuit fault occurs to the original power supply system, the load is required to be quickly separated from the original power supply system and switched to a standby power supply system, in order to ensure that the electric energy quality can meet the requirement, the time requirement of the whole switching process is within 5-10 ms, and the requirement of quick switching of the double power supplies cannot be met only by a traditional mechanical switch.

Disclosure of Invention

In order to solve the problems, the invention provides an alternating current-direct current hybrid circuit breaker which is connected with a main loop; the method comprises the following steps:

the high-speed mechanical switch is connected with the main loop and used for carrying out high-speed breaking on the main loop when the main loop is short-circuited or power supply equipment is replaced;

the first diode and the second diode are reversely connected to form a first node, and two ends of the first diode and two ends of the second diode, which are far away from the first node, are connected to the high-speed mechanical switch;

the third diode and the fourth diode are butted to form a second node, and two ends of the third diode and two ends of the fourth diode, which are deviated from the second node, are connected to the high-speed mechanical switch in parallel;

a first thyristor, an inductor and a capacitor which are connected in series in sequence;

the conduction direction of the first thyristor faces the inductor and the capacitor and is used for controlling the charging and discharging of the capacitor;

one end of the first thyristor, which is far away from the inductor, is connected with the second node, and one end of the capacitor, which is far away from the inductor, is high-voltage and is connected with the first node so as to discharge and reversely charge in a loop where the first diode or the second diode is located through the high-speed mechanical switch;

the energy absorption branch circuit is connected with the high-speed mechanical switch in parallel and used for converting the received voltage into a second state from a first state when the received voltage is higher than a set value so as to reduce the current in the main loop to a safe current value.

The circuit breaker described above, wherein, still include:

the second thyristor and the third thyristor are in butt joint to form a third node, and the second thyristor and the third thyristor are deviated from two ends of the third node and connected to the high-speed mechanical switch in parallel and used for performing bidirectional rapid switching on the main loop after the high-speed mechanical switch is disconnected.

The circuit breaker, wherein the energy absorption branch comprises a lightning arrester.

The circuit breaker, wherein the energy absorption branch comprises a superconducting material with a positive temperature coefficient.

The circuit breaker described above, wherein, still include:

and the control module is respectively connected with the control ends of the first thyristor and the high-speed mechanical switch and is used for respectively controlling the on-off of the first thyristor and the high-speed mechanical switch.

The circuit breaker described above, wherein, still include:

the detection module is connected with the control module and used for detecting the current in the main loop and outputting the current to the control module;

and the control module respectively controls the on-off of the first thyristor and the high-speed mechanical switch according to the current in the main loop.

A control method of a breaker of an AC/DC hybrid type is applied to the breaker; the method comprises the following steps:

step S1, when the main loop is short-circuited or power supply equipment is replaced, the high-speed mechanical switch is adopted to carry out high-speed breaking on the main loop;

step S2, conducting the first thyristor during the operation of the high-speed mechanical switch, so that the capacitor discharges and reversely charges in the conducting direction of the first diode or the second diode through the high-speed mechanical switch;

step S3, keeping the reverse charging of the capacitor until the voltage received by the energy absorption branch is higher than the set value, and switching the energy absorption branch from the first state to the second state to reduce the current in the main loop to the safe current value.

The control method further includes:

step S4, the energy absorption branch continuously absorbs the current in the main loop until the current in the main loop decreases to 0 ampere.

Has the advantages that: the alternating current-direct current hybrid circuit breaker provided by the invention can avoid a solid device from being in a conducting state as much as possible when a system normally runs, reduces the conducting loss of the system and reduces the thermal design difficulty of the solid circuit breaker; by reducing the using number of the controllable devices, the possibility of mistaken touch of the controllable devices is greatly reduced, and the reliability of the system is improved; the system reliability can be improved, the system cost is reduced, and the action speed of the circuit breaker is accelerated.

Drawings

Fig. 1 is a schematic circuit diagram of an ac/dc hybrid circuit breaker according to an embodiment of the present invention;

fig. 2 is a timing diagram illustrating the control of the ac/dc hybrid circuit breaker according to an embodiment of the present invention;

fig. 3 is a flowchart illustrating steps of a method for controlling an ac/dc hybrid circuit breaker according to an embodiment of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

In a preferred embodiment, as shown in fig. 1, a hybrid ac/dc circuit breaker is proposed, which is connected to a main circuit (which may be connected to ports a and B in fig. 1, and the current direction of the main circuit may be from a to B or from B to a); the method can comprise the following steps:

the high-speed mechanical switch S is connected with the main loop and used for carrying out high-speed breaking on the main loop when the main loop is short-circuited or power supply equipment is replaced;

a first diode D1 and a second diode D2, the first diode D1 and the second diode D2 are reversely connected to form a first node, and two ends of the first diode D1 and the second diode D2 departing from the first node are connected to the high-speed mechanical switch S;

a third diode D3 and a fourth diode D4, the third diode D3 and the fourth diode D4 are connected in a butt joint manner to form a second node, and the two ends of the third diode D3 and the fourth diode D4 departing from the second node are connected to the high-speed mechanical switch S in parallel;

a first thyristor T, an inductor L and a capacitor C which are connected in series in sequence;

the conduction direction of the first thyristor T faces the inductor L and the capacitor C and is used for controlling the charging and discharging of the capacitor C;

one end of the first thyristor T, which is far away from the inductor L, is connected with the second node, and one end of the capacitor C, which is far away from the inductor L, is high-voltage and is connected with the first node so as to discharge and reversely charge in a loop in which the first diode D1 or the second diode D2 is positioned through the high-speed mechanical switch S;

the energy absorption branch MOV is connected in parallel with the high-speed mechanical switch S, and is configured to switch from a first state to a second state when the received voltage is higher than a predetermined value, so as to reduce the current in the main circuit to a safe current value.

The set value can be set according to the actual condition of the main loop; the first state may be a state in which the resistance of the energy absorbing shunt MOV is low, in which case the second state is a state in which the resistance of the energy absorbing shunt MOV is high; the safe current value may be a reduced current value, for example, a current of only several tens of milliamperes or several milliamperes.

In a preferred embodiment, as shown in fig. 1, the method may further include:

a second thyristor T2 and a third thyristor T3, the second thyristor T2 and the third thyristor T3 are butted to form a third node, and the two ends of the second thyristor T2 and the third thyristor T3 departing from the third node are connected to the high-speed mechanical switch S in parallel, so as to perform bidirectional rapid switching on the main loop after the high-speed mechanical switch S is disconnected.

In a preferred embodiment, the MOV comprises an arrester.

In a preferred embodiment, the energy absorbing branch comprises a superconducting material with a positive temperature coefficient.

In a preferred embodiment, the method further comprises the following steps:

and the control module (not shown in the drawing) is respectively connected with the control ends of the first thyristor T and the high-speed mechanical switch S and is used for respectively controlling the on-off of the first thyristor T and the high-speed mechanical switch S.

In the above embodiment, preferably, the method may further include:

the detection module (not shown in the drawing) is connected with the control module and is used for detecting the current in the main loop and outputting the current to the control module;

and the control module respectively controls the on-off of the first thyristor T and the high-speed mechanical switch S according to the current in the main loop.

In particular, it can be seen in connection with fig. 2:

(1) when the system normally operates, the thyristor in the solid-state current conversion branch circuit is in a turn-off state, and the system current only flows through the high-speed mechanical switch S; during the normal operation of the system, the capacitor C in the solid-state commutation branch is charged to a set value through the charging loop.

(2) When the system has short-circuit fault, the working process and the control method are analyzed:

a) in the short-circuit detection stage td, the intelligent control unit performs short-circuit detection judgment, and assumes that the short-circuit current direction is from A to B. When the main loop current exceeds the preset action value Iset and the rising rate is within the set range for a period of time td, the short circuit detection unit judges that a short circuit occurs, triggers a short circuit protection mode and simultaneously sends a brake-separating action instruction signal to the high-speed mechanical switch S.

b) In the mechanical delay stage tm, after the high-speed mechanical switch S receives a brake opening instruction, the moving contact and the static contact of the high-speed repulsion mechanism start to separate after a certain mechanical delay time tm;

c) in the contact arcing stage tn, certain arc voltage is established between the moving contact and the fixed contact in the contact separation process to generate arc current, and after certain arcing time, an intelligent control unit issues an action instruction to the thyristor T;

d) in a solid-state commutation stage tc, an intelligent control unit issues a conduction instruction to a thyristor T of a forced commutation branch, a capacitor C discharges through a loop where a diode D2, a high-speed repulsion switch S, a diode D3, the thyristor T and an inductor L are located in sequence, and due to the fact that arc voltage between a moving contact and a static contact of a high-speed mechanical switch still exists, diodes D1 and D4 are cut off in a reverse direction, so that discharge current of the capacitor is totally opposite to original short-circuit current in the S to zero through the high-speed mechanical switch S, forced commutation of the high-speed mechanical switch is achieved, and when the current of the high-speed mechanical switch S is reduced to zero, the voltage;

e) in the medium recovery stage tz, after the high-speed mechanical switch S is completely disconnected, the arc voltage is zero, the condition that the diodes D1 and D4 are reversely cut off does not exist, the high-speed mechanical switch is forwardly conducted under the action of the capacitor voltage, the capacitor C continues to discharge, and the medium recovery time is provided for the high-speed mechanical switch in the medium recovery stage tz so as to prevent the high-speed mechanical switch from re-arcing under the action of the capacitor reverse voltage;

f) and in the LC current-limiting stage tr, after the capacitor is discharged, the capacitor C and the inductor L are connected in series to be connected into a main loop, the capacitor C is reversely charged at the moment, the current reaches a peak value and begins to decrease along with the increase of reverse voltage at two ends of the switch to source voltage, and the time used in the stage is the current-limiting time tr.

g) In a current conversion stage ti, when the voltages at the two ends of the capacitor C and the inductor L reach the action voltage of the piezoresistor or the positive temperature coefficient superconducting material, the impedance of the branch circuit is instantly reduced, the current of the solid-state forced current conversion branch circuit is gradually transferred to the energy absorption branch circuit, so that the current of the solid-state turn-off circuit is reduced, and the current of the piezoresistor or the positive temperature coefficient superconducting material is increased until the current of the main loop is completely transferred to the piezoresistor or the positive temperature coefficient superconducting material;

h) and in the energy absorption stage ta, when the current of the solid-state turn-off circuit is reduced to zero, the capacitor stops reverse charging, the voltage of the capacitor reaches the peak value, the current of the main loop completely flows through the energy absorption branch circuit, the current limiting circuit breaker absorbs the residual energy through the piezoresistor or the positive temperature coefficient superconducting material, finally the current of the main loop is reduced to zero under the action of the piezoresistor or the positive temperature coefficient superconducting material, and the current limiting circuit breaker finishes the whole process of current conversion turn-off.

(3) When a system needs to switch power supplies for sensitive loads, in some occasions where key loads are sensitive to power supply quality, when the system has short-circuit faults, the loads need to be separated from an original power supply system and switched to a standby power supply seamlessly, and normal operation of key electric equipment is guaranteed. Therefore, when the intelligent control unit detects that a short-circuit fault occurs in the system and the fast breaker quickly cuts off the load from the original power supply system, the intelligent control unit sends an action command to the thyristors T1 and T2, if the energy is from A to B, the thyristor T1 and the diode D2 are conducted, and if the energy is from B to A, the thyristor T2 and the diode D1 are conducted, so that the fast switch-on is completed, and the load is switched to the standby power supply; and then the high-speed mechanical switch is switched on, and the current is transferred to the high-speed mechanical switch from the solid-state current conversion branch circuit due to the low resistance after the mechanical switch is switched on.

In addition to the above-mentioned ac/dc hybrid circuit breaker, in a preferred embodiment, the present invention further provides a control method for an ac/dc hybrid circuit breaker, which can be applied to the circuit breaker in any one of the above embodiments; as shown in fig. 3, may include:

step S1, when the main loop is short-circuited or power supply equipment is replaced, a high-speed mechanical switch S is adopted to carry out high-speed breaking on the main loop;

step S2, conducting the first thyristor during the high-speed mechanical switch operation S to make the capacitor C discharge and reversely charge in the conducting direction of the first diode D1 or the second diode D2 through the high-speed mechanical switch S;

in step S3, the reverse charging of the capacitor C is maintained until the voltage received by the energy absorption branch MOV is higher than the set value, and the energy absorption branch MOV is switched from the first state to the second state to reduce the current in the main circuit to the safe current value.

In the above embodiment, preferably, the method may further include:

in step S4, the energy absorption branch continuously absorbs the current in the main circuit until the current in the main circuit decreases to 0 ampere.

The MOV of the energy absorption branch circuit reduces the current in the main circuit to 0 ampere, which should not be regarded as only 0 ampere, because the process of absorbing the electric energy is a dynamic process changing with time, the current in the main circuit can be reduced to 0 ampere or reduced to nearly 0 ampere, but the current in the main circuit can be completely absorbed in general.

In conclusion, the alternating current-direct current hybrid circuit breaker provided by the invention can avoid the solid-state device from being in a conducting state as much as possible when the system normally operates, so that the conducting loss of the system is reduced, and the thermal design difficulty of the solid-state circuit breaker is reduced; by reducing the using number of the controllable devices, the possibility of mistaken touch of the controllable devices is greatly reduced, and the reliability of the system is improved; the system reliability can be improved, the system cost is reduced, and the action speed of the circuit breaker is accelerated.

While the specification concludes with claims defining exemplary embodiments of particular structures for practicing the invention, it is believed that other modifications will be made in the spirit of the invention. While the above invention sets forth presently preferred embodiments, these are not intended as limitations.

Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. Therefore, the appended claims should be construed to cover all such variations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. An AC/DC hybrid circuit breaker is connected with a main loop; it is characterized by comprising:

the energy absorption branch circuit is connected with the high-speed mechanical switch in parallel and used for converting the received voltage into a second state from a first state when the received voltage is higher than a set value so as to reduce the current in the main loop to a safe current value;

further comprising:

2. The circuit breaker of claim 1, wherein said energy absorbing branch comprises a surge arrester.

3. The circuit breaker according to claim 1, characterized in that said energy absorption branch comprises a superconducting material with a positive temperature coefficient.

4. The circuit breaker of claim 1, further comprising:

5. The circuit breaker of claim 4, further comprising:

6. A control method of an AC/DC hybrid circuit breaker is applied to the circuit breaker of any one of claims 1 to 5; it is characterized by comprising:

7. The control method according to claim 6, characterized by further comprising: