Self-powered mechanical direct-current circuit breaker based on hybrid commutation and control method

Abstract

The invention belongs to the field of circuit breakers, and provides a self-powered mechanical direct-current circuit breaker based on hybrid commutation and a control method. The self-powered mechanical DC circuit breaker comprises a main channel branch, a commutation branch, an energy absorption branch and an intelligent driving control unit. The main channel branch is composed of a mechanical switch which is connected in series between a direct-current power supply and a load; the commutation branch is connected in parallel with two ends of the mechanical switch; the energy absorption branch is connected in parallel with the main channel branch and the commutation branch, and is used for absorbing the stored energy of the self-powered mechanical DC circuit breaker and establishing an insulation level in the breaking process of the mechanical switch, so as to achieve the thorough breaking of a fault current. And the intelligent driving control unit is configured to monitor the current change condition in the main channel branch, immediately send an opening signal to the mechanical switch when the current rise rate is greater than a set threshold value, take energy from the main channel branch in an induction manner, provide energy for the intelligent driving control unit and the commutation branch, and enable the commutation branch to be conducted.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of circuit breakers, and particularly relates to a self-powered mechanical DC circuit breaker based on hybrid commutation and a control method. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] A conventional hybrid DC circuit breaker (Hybrid DCCB) is usually composed of an ultra-fast mechanical switch (UFD), a normally-on solid-state switch (such as an IGBT string) and a metal oxide varistor (MOV). The conventional hybrid DC circuit breaker has the following disadvantages: (1) It relies on external power supply. The control system, driving circuit of the circuit breaker and the driving of the solid-state switch all need to rely on a stable and reliable external station power supply. When the hybrid DC circuit breaker is applied to a remote offshore wind power platform, the external power supply is costly, and once the power supply is lost, the circuit breaker as the core of protection will immediately fail, which will become a single point of failure for system safety. (2) The existing improvement scheme of the hybrid DC circuit breaker attempts to self-energy, but relies on the steady-state current of the DC line, the energy harvesting efficiency is low, and it cannot meet the requirement of fast driving in fault. SUMMARY

[0004] In order to solve the technical problems in the background art, the present application provides a self-powered mechanical DC circuit breaker based on hybrid commutation and a control method, which can significantly reduce or even eliminate the conduction loss of the circuit breaker in normal operation without relying on external power supply, while ensuring its ability to quickly and reliably break the DC fault current.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: The first aspect of the present application provides a self-powered mechanical DC circuit breaker based on hybrid commutation.

[0006] A self-powered mechanical DC circuit breaker based on hybrid commutation, comprising: a main channel branch, a commutation branch, an energy absorption branch and an intelligent driving control unit; The main channel branch is composed of a mechanical switch connected in series between a DC power supply and a load. The commutation branch is connected in parallel to both ends of the mechanical switch. In normal operation, the main channel branch is in a conduction state, and the commutation branch is in a complete off state. The energy absorption branch is connected in parallel to the main channel branch and the commutation branch, and is used to absorb the energy storage of the self-powered mechanical DC circuit breaker during the breaking process of the mechanical switch and establish an insulation level to achieve complete breaking of the fault current. The intelligent drive control unit is configured to monitor the current change in the main channel branch, judge whether the main channel branch has a fault, and if so, immediately send a tripping signal to the mechanical switch, and at the same time, inductively take energy from the main channel branch to provide energy for the intelligent drive control unit and the commutation branch, so that the commutation branch is turned on.

[0007] As an implementation form, the commutation branch is composed of a pre-charge capacitor and a commutation switch connected in series.

[0008] As an implementation form, the energy absorption branch is composed of a metal oxide voltage-dependent resistor.

[0009] As an implementation form, the intelligent drive control unit comprises an energy-taking inductive coil and an intelligent drive unit; the intelligent drive unit is used to control the on-off of the main channel branch and the commutation branch; and the energy-taking inductive coil is connected in series on the main channel branch.

[0010] The second aspect of the application provides a control method of a self-powered mechanical DC circuit breaker based on hybrid commutation.

[0011] A control method of a self-powered mechanical DC circuit breaker based on hybrid commutation, comprising: In the normal operation stage, only the main on-off branch works, and the commutation branch is completely turned off; When the intelligent drive control unit detects that the main channel branch has a fault, a tripping signal is immediately sent to the mechanical switch, and at the same time, inductively taking energy from the main channel branch provides energy for the intelligent drive control unit and the commutation branch, so that the commutation branch is turned on.

[0012] As an implementation form, the fault current on the main channel branch is divided into a transient stage and a steady state stage; if the fault current on the main channel branch enters the steady state stage, and inductively taking energy from the main channel branch cannot provide normal operation energy for the intelligent drive control unit and the commutation branch, a standby energy storage capacitor provides normal operation energy for the intelligent drive control unit and the commutation branch.

[0013] As an implementation form, when the intelligent drive control unit detects that the current amplitude of the main channel branch is greater than or equal to the maximum allowable value of the normal load current, a fault warning is triggered; and when the intelligent drive control unit detects that the current rising rate of the main channel branch is greater than or equal to the maximum rising rate of the current under normal working conditions, it is judged that the intelligent drive control unit detects that the main channel branch has a fault current.

[0014] In one implementation method, at the instant the contacts of the mechanical switch separate and generate an electric arc, the commutation branch is driven to conduct; the commutation branch and the electric arc of the mechanical switch form a reverse oscillating discharge circuit; the reverse current in the reverse oscillating discharge circuit and the fault current of the main channel branch are superimposed at the arc gap of the mechanical switch, forcibly canceling the arc current to zero quickly, realizing artificial zero crossing and arc extinguishing, and the mechanical switch completes the disconnection.

[0015] In one implementation, after the mechanical switch is disconnected, the fault current is entirely transferred to the converter branch to charge the pre-charge capacitor in the converter branch; when the voltage of the pre-charge capacitor rises to the operating threshold of the metal oxide varistor in the energy absorption branch, the metal oxide varistor is turned on, thus achieving complete disconnection of the fault current.

[0016] In one implementation, after the fault is cleared, the intelligent drive control unit detects that the voltage of the metal oxide varistor has dropped to a safe value and there is no fault current in the line. The intelligent drive control unit then controls the mechanical switch to close, and the self-powered mechanical DC circuit breaker resumes normal power supply and enters the normal operation stage.

[0017] The beneficial effects of this invention are: The self-powered mechanical DC circuit breaker based on hybrid converter of the present invention uses an intelligent drive control unit to monitor the current changes in the main channel branch and determine whether there is a fault in the main channel branch. When a fault exists in the main channel branch, it immediately sends a trip signal to the mechanical switch and simultaneously extracts energy from the main channel branch to provide energy to the intelligent drive control unit and the converter branch, so that the converter branch is turned on. This significantly reduces or even eliminates the conduction loss during normal operation of the circuit breaker without relying on an external power source, while ensuring that it has the ability to quickly and reliably interrupt DC fault current.

[0018] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a schematic diagram of a self-powered mechanical DC circuit breaker based on hybrid converter according to an embodiment of the present invention. Figure 2 This is a control principle diagram of a self-powered mechanical DC circuit breaker based on hybrid converter according to an embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] according to Figure 1 An embodiment of the present invention provides a self-powered mechanical DC circuit breaker based on hybrid converter, comprising: a main channel branch, a converter branch, an energy absorption branch, and an intelligent drive control unit; The main channel branch is composed of a mechanical switch UFD connected in series between the DC power supply and the load; the commutation branch is connected in parallel across the two ends of the mechanical switch; during normal operation, the main channel branch is in the conducting state and the commutation branch is in the completely off state. The energy absorption branch is connected in parallel with the main channel branch and the converter branch. It is used to absorb the stored energy of the self-powered mechanical DC circuit breaker and establish an insulation level during the mechanical switch disconnection process, so as to achieve complete disconnection of the fault current. The intelligent drive control unit is configured to: monitor the current change in the main channel branch, determine whether there is a fault in the main channel branch, and if so, immediately send a trip signal to the mechanical switch, and simultaneously extract energy from the main channel branch to provide energy to the intelligent drive control unit and the converter branch, so that the converter branch is turned on.

[0025] In this embodiment of the invention, the main conducting branch is used to conduct load current under normal conditions. Because its conducting resistance is extremely small, its operating loss is extremely low.

[0026] In this embodiment of the invention, the converter branch is composed of a pre-charge capacitor C and a converter switch S connected in series. The converter branch is in a completely off state during normal operation, therefore there is no conduction loss.

[0027] In this embodiment of the invention, the energy absorption branch is composed of a metal oxide varistor (MOV). When the voltage across the MOV reaches a set value, the resistance drops sharply and the MOV begins to conduct and absorb energy.

[0028] In this embodiment of the invention, the intelligent drive control unit includes an energy harvesting induction coil (CT) and an intelligent drive unit; the intelligent drive unit is used to control the on / off state of the main channel branch and the converter branch; the energy harvesting induction coil is connected in series on the main channel branch.

[0029] Combination Figure 2 A control method for a self-powered mechanical DC circuit breaker based on hybrid converter according to an embodiment of the present invention includes: During normal operation, only the main branch circuit is operated, while the converter branch circuit is completely shut down. When the intelligent drive control unit detects a fault in the main channel branch, it immediately sends a trip signal to the mechanical switch and simultaneously draws energy from the main channel branch to provide power to the intelligent drive control unit and the converter branch, thus enabling the converter branch to conduct.

[0030] Specifically, during normal operation, only the main conduction branch operates, with extremely low on-resistance and almost no operating losses; the commutation branch (pre-charge capacitor C, commutation switch S, etc.) is completely off, with no additional conduction losses; the energy absorption branch (MOV: the voltage at which the resistance drops sharply and conduction begins to absorb energy when the voltage across the MOV reaches this value) is in the off state because the voltage across it has not reached the operating threshold. At this time, the system stably delivers load current through the UFD.

[0031] In practice, the fault current on the main channel branch is divided into a transient rise phase and a steady-state phase. If the fault current on the main channel branch enters the steady-state phase, and the energy extracted from the main channel branch is insufficient to provide the intelligent drive control unit and the converter branch with the energy for normal operation, the backup energy storage capacitor will provide the energy for normal operation of the intelligent drive control unit and the converter branch. This ensures the stability of the drive energy.

[0032] When the intelligent drive control unit detects that the current amplitude of the main channel branch is greater than or equal to the maximum allowable value of the normal load current (e.g., 1.2 times the rated load current), a fault warning is triggered; when the intelligent drive control unit detects that the current rise rate of the main channel branch is greater than or equal to the maximum current rise rate under normal operating conditions (e.g., dc / dt≤50A / μs), it is determined that the intelligent drive control unit has detected a fault current in the main channel branch.

[0033] For example, when a fault occurs (such as a short circuit), the current rise rate will sharply exceed the threshold, and the control unit will directly determine it as a fault without waiting for the amplitude to fully exceed the threshold, thus achieving a faster response. (If the scenario allows, the "current duration" can be used for judgment. For example, if the current exceeds the threshold and lasts for more than 10μs, transient interference can be eliminated, further improving the accuracy of the judgment.)

[0034] At the instant the contacts of the mechanical switch separate and generate an electric arc, the commutation branch is driven to conduct; the commutation branch and the electric arc of the mechanical switch form a reverse oscillating discharge circuit; the reverse current in the reverse oscillating discharge circuit and the fault current of the main channel branch are superimposed at the arc gap of the mechanical switch, forcibly canceling the arc current to zero quickly, realizing artificial zero crossing and arc extinguishing, and the mechanical switch completes the disconnection.

[0035] Specifically, at the instant the UFD contacts separate and generate an arc, the driving converter switch S is turned on; the pre-charge capacitor C forms a reverse oscillating discharge circuit through S and the arc of the UFD; the reverse current and the main fault current are superimposed at the arc gap of the UFD, forcibly canceling the arc current to zero quickly.

[0036] After the mechanical switch is disconnected, the fault current is transferred to the converter branch to charge the pre-charge capacitor in the converter branch. When the voltage of the pre-charge capacitor rises to the action threshold of the metal oxide varistor in the energy absorption branch, the metal oxide varistor turns on, and finally the fault current is completely disconnected.

[0037] Specifically, when the metal oxide varistor is turned on, it absorbs the remaining energy stored in the system inductor on the one hand, and clamps the system voltage within a safe range on the other hand, preventing overvoltage damage to the equipment, and ultimately achieving complete interruption of fault current.

[0038] Once the fault is cleared, the intelligent drive control unit detects that the voltage of the metal oxide varistor has dropped to a safe value and there is no fault current in the line. The intelligent drive control unit then controls the mechanical switch to close, and the self-powered mechanical DC circuit breaker resumes normal power supply and enters the normal operation phase.

[0039] Energy is drawn from the main circuit through a rectifier circuit with boost function (considering that during normal operation, the main conduction branch is an ultra-fast mechanical switch UFD, whose conduction voltage drop is extremely low, and the rectifier circuit cannot obtain enough energy to charge the pre-charge capacitor, resulting in insufficient capacitor voltage and arc extinction failure during the next fault, so a boost module is needed to increase the energy extraction voltage) to replenish the pre-charge capacitor C until the voltage of the pre-charge capacitor C reaches the preset value; finally, the control unit is reset and returns to the real-time monitoring state, waiting for the next operation or fault response.

[0040] The fault clearing and judgment process is as follows: The intelligent drive control unit monitors the voltage across the MOV in real time. When the MOV voltage drops from the clamping value to "below the system rated voltage" and remains so for a period of time, it determines that the fault has been cleared (no residual energy needs to be absorbed). At the same time, it monitors the line current to confirm that the current has dropped to zero or the normal load level, thus avoiding operation with the fault during reset.

[0041] The process of restoring the main conduction when the UFD is closed is as follows: The intelligent drive control unit sends a closing signal to the UFD, and the UFD contacts close quickly, re-establishing the main channel circuit conduction path and starting to restore normal power supply through the UFD; at this time, the converter switch S remains open to avoid parallel conduction losses with the UFD.

[0042] The process of resetting and charging the pre-charge capacitor C is as follows: Because the UFD has an extremely low on-state voltage drop, the conventional rectifier circuit cannot draw power from the main channel circuit. Therefore, a "boost module" (such as a DC / DC boost circuit) needs to be activated to extract weak electrical energy from the UFD terminals and boost it to the preset charging voltage of the pre-charge capacitor C (such as 1.5 times the rated voltage of the system). The boosted electrical energy charges the pre-charge capacitor C through the rectifier circuit. The control unit monitors the voltage value of the pre-charge capacitor C in real time. When the voltage reaches the preset value, charging stops, and the pre-charge capacitor C enters the ready state to cope with the next fault.

[0043] The working process of the intelligent drive control unit and the converter switch reset is as follows: The intelligent drive control unit shuts down the discharge circuit of the energy storage capacitor, switches to "real-time monitoring mode", and restarts monitoring the amplitude and rate of rise of the line current. The converter switch S remains in the open state, and its drive circuit is de-energized (or in low-power standby) to avoid power loss; at the same time, the conduction trigger signal of the converter switch S is cleared to ensure that the control unit will trigger conduction only in the event of the next fault.

[0044] The reset verification process involves the intelligent drive control unit performing a self-check on the UFD closing status, the pre-charge capacitor C voltage value, and the line current status. If all parameters meet the normal operation requirements (UFD closing in place, C voltage meeting the standard, and line current normal), a "reset complete" signal is issued.

[0045] This embodiment utilizes an intelligent drive control unit to monitor current changes in the main channel branch and determine whether a fault exists in the main channel branch. When a fault exists in the main channel branch, a trip signal is immediately sent to the mechanical switch. At the same time, energy is extracted from the main channel branch to provide power to the intelligent drive control unit and the converter branch, enabling the converter branch to conduct. This significantly reduces or even eliminates the conduction loss of the circuit breaker during normal operation without relying on an external power source, while ensuring its ability to quickly and reliably interrupt DC fault current.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-powered mechanical DC circuit breaker based on hybrid converter, characterized in that, include: Main channel branch, converter branch, energy absorption branch and intelligent drive control unit; The main channel branch is a mechanical switch connected in series between the DC power supply and the load; the commutation branch is connected in parallel across the two ends of the mechanical switch; during normal operation, the main channel branch is in the conducting state and the commutation branch is in the completely off state. The energy absorption branch is connected in parallel with the main channel branch and the converter branch. It is used to absorb the stored energy of the self-powered mechanical DC circuit breaker and establish an insulation level during the mechanical switch disconnection process, so as to achieve complete disconnection of the fault current. The intelligent drive control unit is configured to: monitor the current change in the main channel branch, determine whether there is a fault in the main channel branch, and if so, immediately send a trip signal to the mechanical switch, and simultaneously extract energy from the main channel branch to provide energy to the intelligent drive control unit and the converter branch, so that the converter branch is turned on.

2. The self-powered mechanical DC circuit breaker based on hybrid converter as described in claim 1, characterized in that, The converter branch consists of a pre-charged capacitor and a converter switch connected in series.

3. The self-powered mechanical DC circuit breaker based on hybrid converter as described in claim 1, characterized in that, The energy absorption branch is composed of metal oxide varistors.

4. The self-powered mechanical DC circuit breaker based on hybrid converter as described in claim 1, characterized in that, The intelligent drive control unit includes an energy harvesting induction coil and an intelligent drive unit; the intelligent drive unit is used to control the on / off state of the main channel branch and the converter branch; the energy harvesting induction coil is connected in series on the main channel branch.

5. A control method for a self-powered mechanical DC circuit breaker based on hybrid converter as described in any one of claims 1-4, characterized in that, include: During normal operation, only the main branch circuit is operated, while the converter branch circuit is completely shut down. When the intelligent drive control unit detects a fault in the main channel branch, it immediately sends a trip signal to the mechanical switch and simultaneously draws energy from the main channel branch to provide power to the intelligent drive control unit and the converter branch, thus enabling the converter branch to conduct.

6. The control method as described in claim 5, characterized in that, The fault current on the main channel branch is divided into a transient rise phase and a steady state phase. If the fault current on the main channel branch enters the steady state phase, and the energy extracted from the main channel branch cannot provide the energy for the intelligent drive control unit and the converter branch to operate normally, the backup energy storage capacitor will provide the energy for the intelligent drive control unit and the converter branch to operate normally.

7. The control method as described in claim 5, characterized in that, When the intelligent drive control unit detects that the current amplitude of the main channel branch is greater than or equal to the maximum allowable value of the normal load current, it triggers a fault warning; when the intelligent drive control unit detects that the current rise rate of the main channel branch is greater than or equal to the maximum current rise rate under normal operating conditions, it determines that the intelligent drive control unit has detected a fault current in the main channel branch.

8. The control method as described in claim 5, characterized in that, At the instant the contacts of the mechanical switch separate and generate an electric arc, the commutation branch is driven to conduct; the commutation branch and the electric arc of the mechanical switch form a reverse oscillating discharge circuit; the reverse current in the reverse oscillating discharge circuit and the fault current of the main channel branch are superimposed at the arc gap of the mechanical switch, forcibly canceling the arc current to zero quickly, realizing artificial zero crossing and arc extinguishing, and the mechanical switch completes the disconnection.

9. The control method as described in claim 5, characterized in that, After the mechanical switch is disconnected, the fault current is transferred to the converter branch to charge the pre-charge capacitor in the converter branch. When the voltage of the pre-charge capacitor rises to the action threshold of the metal oxide varistor in the energy absorption branch, the metal oxide varistor turns on, and finally the fault current is completely disconnected.

10. The control method as described in claim 5, characterized in that, Once the fault is cleared, the intelligent drive control unit detects that the voltage of the metal oxide varistor has dropped to a safe value and there is no fault current in the line. The intelligent drive control unit then controls the mechanical switch to close, and the self-powered mechanical DC circuit breaker resumes normal power supply and enters the normal operation phase.

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