A low-voltage hybrid direct current circuit breaker tail current reliable commutation method and system

Abstract

The application discloses a low-voltage hybrid DC circuit breaker tail current reliable commutation method and system, and the method comprises the following steps: 1) a short-circuit fault is generated in a DC system, a mechanical circuit breaker senses the fault generation, opens contacts to generate an electric arc through an internal thermal magnetic release, and obtains a control system trigger signal; 2) the control system controls power electronic devices to be turned on through a fixed delay based on the trigger signal, and detects whether the power electronic devices are in an overcurrent state at the turning-on moment through a peripheral protection circuit; 3) when the power electronic devices are in the overcurrent state at the turning-on moment, the power electronic devices are forced to be turned off, and the step 2) is repeated; 4) when the power electronic devices are in a non-overcurrent state, current commutation is completed, the electric arc is extinguished, and the fault is cleared. The system comprises a signal acquisition module, a signal detection module, a first judgment module and a second judgment module. The application can be widely applied to multiple low-voltage hybrid DC circuit breaker products and has good applicability.

Description

Technical Field

[0001] The present invention belongs to the field of low-voltage power distribution, and in particular relates to a method and system for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker. Background Art

[0002] With the rapid development of low-voltage DC systems, such as photovoltaics, energy storage, and electric vehicles, efforts are underway to reduce power transmission losses by continuously increasing voltage levels. As voltage levels in the low-voltage sector gradually approach the 1500V upper limit specified by the IEC, demand is growing for miniaturized, easy-to-install, and fast-breaking protection equipment for low-voltage DC systems. As key protection devices in power systems, the reliability and high performance of circuit breakers are crucial for protecting DC systems. Compared to traditional AC systems, DC systems are more difficult to protect due to their lack of a natural zero crossing, low line impedance, and rapid rise in fault current. Therefore, research on interruption protection technologies for low-voltage DC systems is crucial for their development.

[0003] Circuit breakers can be categorized into mechanical, solid-state, and hybrid types based on their structure. Mechanical circuit breakers are the most mature, and based on their operating principles, they can be divided into thermal-magnetic and electronic types. Their arc extinguishing methods primarily involve adding arc-extinguishing grids, stretching the arc, and adding permanent magnets to achieve rapid arc extinguishing. However, with the development of DC systems, traditional arc extinguishing methods have become difficult to achieve rapid fault clearing, with arc extinguishing times typically measured in tens of milliseconds. The only way to meet the interruption requirements at high voltage levels is to continuously increase the volume of the arc extinguishing chamber, add gas-generating materials, and connect multiple stages in series. This places higher demands on their size and operational consistency. However, because they conduct current through metal contact, they offer low conduction losses, strong short-circuit current tolerance, and low cost. With the rapid development of semiconductor technology, solid-state circuit breakers, primarily based on power electronic devices, have garnered widespread attention. Solid-state circuit breakers utilize rapid detection and control modules to rapidly clear short-circuit currents, reducing fault-clearing time to microseconds. This solution is more reliable for DC systems with a high degree of power electronics. Under normal operating conditions, the rated current is conducted by the power electronic devices, which are then shut down in the event of a fault. While arc-free interruption can be achieved, conduction losses are greater, requiring higher requirements for heat dissipation structure design. While solid-state circuit breakers offer advantages such as long service life and fast interruption speed, they are currently only suitable for low-voltage (<100V) terminal protection due to limitations in device performance.

[0004] Hybrid interruption technology, developed by combining mechanical and solid-state circuit breakers, is considered a key development direction in the future low-voltage DC (low-voltage DC) field. This approach combines the advantages of low conduction losses of mechanical circuit breakers with the fast interruption speed of solid-state circuit breakers, while fully utilizing the current-limiting function of traditional circuit breakers. However, to further shorten interruption time, traditional hybrid circuit breakers require rapid conduction of power electronic devices at the initial arcing stage, enabling rapid commutation and arc extinguishing. However, in the low-voltage field, rapid commutation presents two key challenges: 1) if the contact spacing is too small, overvoltages caused by the power electronic devices during shutdown may lead to severe breakdown; and 2) conducting power electronic devices during the rising current stage requires higher device performance and quantity. These issues can be addressed by conducting power electronic devices at the later stage of arcing, but this method places high demands on the device conduction time. Ensuring reliable conduction and current commutation of power electronic devices under different mechanical breaker interruption conditions is a pressing issue for the further development of low-voltage hybrid DC circuit breakers, which is of great significance for promoting the development of low-voltage DC systems and improving the theory of low-voltage electrical appliances. Summary of the Invention

[0005] Aiming at the problem of unreliable interruption in the late arcing stage of low-voltage hybrid DC circuit breakers, the present invention proposes a reliable commutation method and system for the tail current of low-voltage hybrid DC circuit breakers, providing a new idea for the development of low-voltage DC circuit breakers.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker comprises the following steps:

[0008] 1) When a short circuit occurs in the DC system, the mechanical circuit breaker senses the fault, opens the contacts through the internal thermal magnetic release to generate an arc, and obtains the control system trigger signal;

[0009] 2) The control system controls the power electronic device to turn on after a fixed delay based on the trigger signal, and works through the peripheral protection circuit to detect whether the power electronic device is in an overcurrent state when it is turned on;

[0010] 3) When the power electronic device is in an overcurrent state at the time of conduction, the power electronic device is forced to shut down and step 2) is repeated;

[0011] 4) When the power electronic device is in a non-overcurrent state, the current is commutated, the arc is extinguished, and the fault is cleared.

[0012] A further improvement of the present invention is that the specific implementation method of step 1) is as follows: the mechanical circuit breaker adopts a molded case circuit breaker. When a short circuit fault occurs, the internal thermal magnetic release senses the fault and drives the mechanism to open the metal contacts, an arc is generated between the contacts, and the fault current continues to decrease under the action of arc current limiting.

[0013] A further improvement of the present invention is that the specific implementation method of step 2) is as follows: when the arc voltage is detected to exceed the threshold, the control unit starts to control the delay, and the delay is until the current decreases to control the power electronic device to turn on, and the peripheral desat protection circuit works, and the voltage at both ends of the device is detected to determine whether it is in an overcurrent state.

[0014] A further improvement of the present invention is that the specific implementation method of step 3) is as follows: the peripheral desat circuit detects the voltage across the power electronic device and compares it with the threshold voltage. When in an overcurrent state, the voltage across the two ends exceeds the threshold voltage, forcing the driver chip to lock and control the power electronics to shut down. Subsequently, the driver chip is reset under the action of the control unit, and after a fixed delay, the IGBT is driven to turn on again. The desat circuit again detects whether the power electronic device is in an overcurrent state. If it is in an overcurrent state, this step is repeated.

[0015] A further improvement of the present invention is that the specific implementation method of step 4) is as follows: when the power electronic device is in a non-overcurrent state, the voltage across the device is less than the threshold voltage, the peripheral desat protection circuit does not work, the power electronic device is successfully turned on, the fault current is commutated to the power electronic device through the mechanical circuit breaker, and after a programmed delay, the power electronic device is turned off, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

[0016] A low-voltage hybrid DC circuit breaker tail current reliable commutation system, comprising:

[0017] The signal acquisition module is used to generate an arc when a short-circuit fault occurs in the DC system. The mechanical circuit breaker senses the fault and opens the contacts through the internal thermal magnetic release to generate an arc and obtain the control system trigger signal.

[0018] The signal detection module is used to control the power electronic device to turn on after a fixed delay based on the trigger signal, and detect whether the power electronic device is in an overcurrent state when it is turned on through the peripheral protection circuit;

[0019] The first judgment module is used to force the power electronic device to shut down and repeat the signal detection module when the power electronic device is in an overcurrent state at the time of conduction;

[0020] The second judgment module is used to complete the current commutation and clear the arc extinguishing fault when the power electronic device is in a non-overcurrent state.

[0021] A further improvement of the present invention is that in the signal acquisition module, the mechanical circuit breaker adopts a molded case circuit breaker. When a short circuit fault occurs, the internal thermal magnetic release senses the fault and drives the mechanism to open the metal contacts, an arc is generated between the contacts, and the fault current continues to decrease under the action of arc current limiting.

[0022] A further improvement of the present invention is that in the signal detection module, when the arc voltage is detected to exceed the threshold, the control unit starts to control the delay, and the delay is until the current decreases to control the power electronic device to turn on, and the peripheral desat protection circuit works, and the voltage at both ends of the device is detected to determine whether it is in an overcurrent state.

[0023] A further improvement of the present invention is that, in the first judgment module, the peripheral desat circuit works to detect the voltage across the power electronic device and compares it with the threshold voltage. When in an overcurrent state, the voltage across the two ends exceeds the threshold voltage, forcing the driver chip to lock and control the power electronics to shut down. Subsequently, the driver chip is reset under the action of the control unit, and after a fixed delay, the IGBT is driven to turn on again. The desat circuit again detects whether the power electronic device is in an overcurrent state, and repeats when it is in an overcurrent state.

[0024] A further improvement of the present invention is that, in the second judgment module, when the power electronic device is in a non-overcurrent state, the voltage across the device is less than the threshold voltage, the peripheral desat protection circuit does not work, the power electronic device is successfully turned on, the fault current is commutated to the power electronic device through the mechanical circuit breaker, and after a programmed delay, the power electronic device is turned off, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

[0025] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0026] The present invention provides a low-voltage hybrid DC circuit breaker tail current reliable commutation circuit structure based on a traditional molded case circuit breaker, which realizes autonomous detection and tripping of fault current, and solves the problem of complex circuit structure and control strategy design of hybrid circuit breakers. The present invention adopts a method of controlling the conduction of power electronic devices in the arc current drop stage, which solves the problem of long arcing time, reduces arc release energy, and prolongs the overall service life of the circuit breaker on the one hand, and solves the problem of heavy breakdown caused by commutation in the early stage of arcing and the high cost of power electronic devices on the other hand, and effectively reduces the risk of electrical fire accidents caused by circuit breaker failure. The present invention uses a desaturation detection circuit to periodically control the conduction of power electronic devices, thereby maximizing the current-carrying capacity of power electronic devices without adding an external detection module, solving the problem of reliable interruption of fault currents under different working conditions, and meeting the low-cost and miniaturized design requirements of hybrid circuit breakers.

[0027] In summary, the hybrid circuit breaker of the present invention has good scalability, can be widely applied to various types of molded case circuit breakers, has good applicability, and includes a single-chip microcomputer control part, which can provide better functional expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the tail current commutation principle diagram of the low-voltage hybrid DC circuit breaker.

[0029] Figure 2a This is the normal working condition diagram;

[0030] Figure 2b It is a short circuit fault diagram;

[0031] Figure 2c This is the overcurrent detection diagram;

[0032] Figure 2d This is the overcurrent protection diagram;

[0033] Figure 2e is the current transfer diagram;

[0034] Figure 2f It is the energy consumption stage diagram;

[0035] Figure 2g This is the fault clearance diagram;

[0036] Figure 3 This is a schematic diagram of the drive control timing.

[0037] Figure 4 This is an operation flow chart of the commutation method.

[0038] Figure 5 This is a structural block diagram of a low-voltage hybrid DC circuit breaker tail current reliable commutation system according to the present invention. DETAILED DESCRIPTION

[0039] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0040] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0041] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0042] It should be further understood that the term "and / or" as used herein in the specification and in the claims, if any, means any one of the associated listed items, as well as all possible combinations of the associated listed items.

[0043] The various structural diagrams according to the disclosed embodiments of the present application are shown in the accompanying drawings. These diagrams are not drawn to scale, in which certain details are exaggerated for clarity and others omitted. The shapes and relative sizes of the various regions, layers, and elements illustrated in the figures are exemplary only and can vary in actual implementation depending on, for example, manufacturing techniques and tolerances, and design choices. The skilled person can design alternative regions / layers with different shapes, sizes, relative positions according to actual needs.

[0044] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0045] The low-voltage hybrid DC circuit breaker tail current reliable commutation method disclosed by the present application mainly aims to realize the rapid clearing of fault current in a low-voltage DC system, thereby protecting the safe and reliable use of electricity.

[0046] Another purpose of the low-voltage hybrid DC circuit breaker tail current reliable commutation method disclosed by the present application is to provide an arc burning late breaking strategy different from the traditional hybrid circuit breaker, to solve the problem of heavy breakdown and high cost of power electronic devices caused by arc burning early breaking.

[0047] Another purpose of the low-voltage hybrid DC circuit breaker tail current reliable commutation method disclosed by the present application is to provide a circuit topology structure different from the traditional hybrid circuit breaker.

[0048] In the actual use process of the present application, the low-voltage hybrid DC circuit breaker tail current reliable commutation method adopts the following steps:

[0049] As Figure 1The tail current reliable commutation topology of the low-voltage hybrid DC circuit breaker shown in the figure, when the hybrid circuit breaker is closed, the mechanical circuit breaker is closed, and the rated current of the system is conducted through the mechanical circuit breaker. Since the mechanical switch is connected by metal contacts, its conduction loss can be approximately ignored; when the system is overloaded or short-circuited, the current rises rapidly, the thermal magnetic tripping mechanism of the mechanical circuit breaker is activated, and the metal contacts of the mechanical circuit breaker are opened under the action of the mechanism, and an arc is generated between the contacts. Under the action of the arc current limiting, the current continues to decrease, and then the power electronic devices in the commutation unit are turned on for a short time. When the current exceeds this limit, the power electronic devices When the device is at its maximum on-current, it is in an overcurrent state. At this time, the desaturation detection circuit is activated, forcing the driver chip to shut down the power electronic device. After a delayed reset, the power electronic device tries to turn on again. At this time, due to the arc, the current continues to decrease. When the current is lower than the maximum on-current of the device, the commutation is completed. Under the action of the arc voltage, the current is commutated to the branch where the power electronic device is located. After the power electronic device is turned off, the energy-consuming branch in the commutation unit becomes a low-resistance state under the action of overvoltage, and the fault current is commutated to this branch. Finally, the line energy is dissipated through this branch, and the fault is completely cleared.

[0050] The structure of the low voltage DC hybrid circuit breaker is as follows Figure 1The topology is composed of a molded case circuit breaker (MCCB) K, a metal oxide varistor (MOV) MOV, and an insulated gate bipolar transistor (IGBT) S1 in parallel. The structure has a positive side A and a negative side B. The desaturation detection circuit is composed of a diode D1, a resistor R2, a capacitor C1, a voltage stabilizing tube D2, an operational amplifier, a current source, and a metal-oxide-semiconductor field-effect transistor (MOSFET) S2. The current source, the operational amplifier, and the S2 are integrated in a driving chip. The cathode of the diode D1 is connected to the collector of the S1, and the anode is connected to the resistor R2. The other end of the resistor R2 is connected to the cathode of the voltage stabilizing tube D2. The capacitor C1 is connected in parallel to the voltage stabilizing tube, and the cathode of the voltage stabilizing tube D2 is connected to the positive input terminal of the operational amplifier. The molded case circuit breaker M is used to conduct the rated current under normal conditions, and the conduction loss can be approximately ignored. When a fault occurs, the metal contact of the branch opens the arc, and the fault current rises slowly under the arc current limiting effect. The S1 is used to bear the fault current for a short time. When the branch is turned on, the current quickly changes from the main current branch to the branch under the arc voltage, thereby completing the rapid arc extinction. The desaturation detection circuit is used to detect whether the device S1 is in an overcurrent state. When the current is too large at the time of current commutation, the S1 is in an overcurrent state, the desaturation detection circuit acts to forcibly turn off the S1, and the driving chip is self-locked until a reset signal is received from the control chip. Then, the driving chip works again to try to turn on the S1. The energy consumption branch is used to consume the stored energy in the line. Under normal conditions, the branch is in a high resistance state. When the commutation branch is turned off, the branch becomes a low resistance state under the action of overvoltage, the fault current commutates to the branch, and the stored energy in the line is dissipated through the branch.

[0051] In combination Figure 1 , FIG. 2, the working process of the proposed low-voltage hybrid DC circuit breaker tail current reliable commutation method is specifically described taking a short circuit fault as an example.

[0052] Under normal conditions, the mechanical circuit breaker K is closed, and the system rated current is conducted through the branch where the mechanical circuit breaker K is located. Since it is a metal contact, the conduction loss of the branch under rated conditions can be ignored.

[0053] When an overload or short circuit fault occurs, the thermal magnetic release mechanism in the mechanical circuit breaker K acts due to heating and electromagnetic force, thereby driving the metal contact of the mechanical circuit breaker K to open, generating an arc between the contacts, and the arc voltage gradually rises as the contact opens. At the same time, the fault current rises at a reduced speed or even slowly under the action of arc voltage.

[0054] At this time the drive chip output drive voltage, the insulated gate bipolar transistor S1 starts to conduct, while the drive chip internal current source I cc Charging the capacitor C1, at this time the voltage on the capacitor C1 is:

[0055] V C = V R + V D + V CE (1)

[0056] In the formula, V C is the voltage of capacitor C1, V R is the voltage of resistor R2, V D is the voltage drop of diode D1, V CE is the on-state voltage drop of IGBT.

[0057] When the current is too large and exceeds the maximum allowable current of the device, with the insulated gate bipolar transistor S1 conducting, the device is in an overcurrent state, at this time the desaturation detection circuit starts to work, the collector-emitter voltage gradually rises, and the voltage of capacitor C1 also rises, when the voltage of capacitor C1 is greater than the internal set value V th of the drive voltage, the operational amplifier outputs V fault signal, at this time the drive chip is turned off, the output drive voltage is reduced, and the insulated gate bipolar transistor S1 is forced to turn off.

[0058] After the drive chip is turned off, the control unit receives the fault signal, and at the same time, with the arc continuing to burn, the arc current gradually decreases, after a fixed delay, the control unit outputs a reset signal and a conduction signal, the drive chip is reset again and turned on, and the above overcurrent detection process is repeated.

[0059] When the current gradually decreases to below the maximum allowable current of the insulated gate bipolar transistor S1, the insulated gate bipolar transistor S1 is no longer in an overcurrent state, at this time it is normally turned on, and the current is forced to commutate to the insulated gate bipolar transistor S1 under the action of the arc voltage, when the current is completely commutated, the arc between the contacts is extinguished.

[0060] When the insulated gate bipolar transistor S1 is turned on for a short time and then turned off, due to the existence of parasitic inductance in the circuit, a large overvoltage is generated across the insulated gate bipolar transistor S1, which will cause the device to break down if no protective measures are taken, therefore a metal oxide varistor MOV is added to protect it, which is in a high resistance state at low voltage, and rapidly changes to a low resistance state when the voltage exceeds its clamping voltage, at the same time the voltage remains almost stable, therefore when the insulated gate bipolar transistor S1 is turned off under overvoltage conditions, the MOV-containing energy dissipation branch is turned on, the current commutates to this branch, and finally the energy of the circuit is dissipated in the form of heat through this branch, and the fault is cleared.

[0061] Example 1

[0062] The present invention provides a method for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker, comprising the following steps:

[0063] 1) When a short circuit occurs in the DC system, the mechanical circuit breaker senses the fault, opens the contacts through the internal thermal magnetic release to generate an arc, and obtains the control system trigger signal;

[0064] 2) The control system controls the power electronic device to turn on after a fixed delay based on the trigger signal, and works through the peripheral protection circuit to detect whether the power electronic device is in an overcurrent state when it is turned on;

[0065] 3) When the power electronic device is in an overcurrent state at the time of conduction, the power electronic device is forced to shut down and step 2) is repeated;

[0066] 4) When the power electronic device is in a non-overcurrent state, the current is commutated, the arc is extinguished, and the fault is cleared.

[0067] In this embodiment, the specific implementation method of step 1) is as follows: the mechanical circuit breaker adopts a molded case circuit breaker. When a short circuit fault occurs, the internal thermal magnetic release senses the fault and drives the mechanism to open the metal contacts, an arc is generated between the contacts, and the fault current continues to decrease under the action of arc current limiting.

[0068] In this embodiment, the specific implementation method of step 2) is as follows: when the arc voltage is detected to exceed the threshold, the control unit starts to control the delay, and the delay is until the current decreases to control the power electronic device to turn on, and the peripheral desat protection circuit works, and determines whether it is in an overcurrent state by detecting the voltage across the device.

[0069] In this embodiment, the specific implementation method of step 3) is as follows: the peripheral desat circuit works to detect the voltage across the power electronic device and compares it with the threshold voltage. When it is in an overcurrent state, the voltage across the two ends exceeds the threshold voltage, forcing the driver chip to lock and control the power electronics to shut down. Subsequently, the driver chip is reset under the action of the control unit, and after a fixed delay, the IGBT is driven to turn on again. The desat circuit again detects whether the power electronic device is in an overcurrent state. If it is in an overcurrent state, this step is repeated.

[0070] In this embodiment, the specific implementation method of step 4) is as follows: when the power electronic device is in a non-overcurrent state, the voltage across the device is less than the threshold voltage, the peripheral desat protection circuit does not work, the power electronic device is successfully turned on, the fault current is commutated to the power electronic device through the mechanical circuit breaker, and after a programmed delay, the power electronic device is turned off, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

[0071] Example 2

[0072] like Figure 5 As shown, the present invention provides a low-voltage hybrid DC circuit breaker tail current reliable commutation system, comprising:

[0073] The signal acquisition module is used to generate an arc when a short-circuit fault occurs in the DC system. The mechanical circuit breaker senses the fault and opens the contacts through the internal thermal magnetic release to generate an arc and obtain the control system trigger signal.

[0074] The signal detection module is used to control the power electronic device to turn on after a fixed delay based on the trigger signal, and detect whether the power electronic device is in an overcurrent state when it is turned on through the peripheral protection circuit;

[0075] The first judgment module is used to force the power electronic device to shut down and repeat the signal detection module when the power electronic device is in an overcurrent state at the time of conduction;

[0076] The second judgment module is used to complete the current commutation and clear the arc extinguishing fault when the power electronic device is in a non-overcurrent state.

[0077] Example 3

[0078] 2 to 4 , the working process of the low-voltage hybrid DC circuit breaker tail current reliable commutation method is described in detail. The specific working process is described as follows:

[0079] Phase 1: The circuit breaker is initially in the closed state, with side A being the positive pole and side B being the negative pole. Figure 2a At this time, the system is in normal working state, the rated current is conducted through the mechanical circuit breaker K, and the conduction loss of the circuit breaker can be approximately ignored.

[0080] Phase 2: The thermal magnetic tripping mechanism of the mechanical circuit breaker K is activated, the contacts are separated under the action of the mechanism, an arc is generated, and the current in the main flow branch reaches a peak under the action of the arc voltage and begins to slowly decrease. Figure 2b .

[0081] Phase 3: At t1, the MCU starts to work and outputs the conduction signal OUT, the driver chip starts to work and outputs the driving voltage V g At this time, S1 starts to conduct, and the internal current source of the driver chip charges the capacitor C1 on the one hand, and discharges through the capacitor R1 and diode D1 on the other hand. The current begins to reverse under the action of the arc voltage. When the current is too large, the voltage across S1 gradually increases, and then the voltage V c Gradually increases, corresponding to Figure 2c .

[0082] Phase 4: At t2, the voltage of capacitor C1 rises rapidly, diode D1 is turned off, and Vc Greater than the internal preset voltage V of the driver chip th When the operational amplifier outputs a voltage signal V fault , while driving the chip output voltage V g When the current drops to zero, S1 is turned off and the driver chip outputs the FLT signal after a delay inside the driver chip. Figure 2d At time t3, the MCU output reaches the preset value and then drops to zero.

[0083] Phase 5: At t4, the MCU outputs the RST signal and the driver chip is reset. At t5, the MCU outputs a pulse signal again to try to turn on S1. When the current is too large, Phase 3 is repeated.

[0084] Phase 6: At t6, S1 is turned on. At this time, the current has dropped below the maximum allowable current of the device, so the current can be completely reversed, V c Increased, but less than V th , so the driver chip will not be turned off, the arc between the contacts is extinguished, the arc extinguishing medium between the contacts begins to recover, and the mechanical circuit breaker K is completely disconnected. Figure 2e .

[0085] Phase 7: S1 is turned off at t7. Under the action of overvoltage, the energy consumption branch where the MOV is located is turned on. At this time, the fault current is commutated to this branch, corresponding to Figure 2f At this time, the driver chip no longer works, the current in the energy consumption branch drops linearly to zero, and the fault is cleared.

[0086] Stage 8: The DC system fault is completely cleared, the circuit breaker no longer works, and the corresponding Figure 2g .

[0087] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all points of view, the embodiments should be regarded as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and range of equivalents of the claims are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0088] Furthermore, it should be understood that although the specification is described in terms of embodiments, each of which contains only one independent technical solution, the specification is described in this way only for the sake of clarity, and the skilled person should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that the skilled person can understand. The above is only to illustrate the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made on the basis of the technical solutions according to the technical idea of the present application falls within the protection scope of the claims of the present application.

Claims

1. A method for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker, characterized in that: The following steps are involved: 1) When a short circuit occurs in the DC system, the mechanical circuit breaker senses the fault, opens the contacts via the internal thermal-magnetic release to generate an arc, and obtains a trigger signal from the control system; 2) The control system controls the power electronic device to turn on after a fixed delay based on the trigger signal, and detects whether the power electronic device is in an overcurrent state when it is turned on through the peripheral protection circuit. When the arc voltage exceeds the threshold, the control unit starts to control the delay, and controls the power electronic device to turn on when the current decreases. The peripheral desat protection circuit works and determines whether it is in an overcurrent state by detecting the voltage across the device. 3) When the power electronic device is in an overcurrent state during the on-time, the power electronic device is forced to shut down and step 2 is repeated); 4) When the power electronic device is in a non-overcurrent state, the current is commutated, the arc is extinguished, and the fault is cleared.

2. A reliable commutation method for tail current of a low-voltage hybrid DC circuit breaker according to claim 1, characterized in that: The specific implementation method of step 1) is as follows: The mechanical circuit breaker uses a molded case circuit breaker. When a short circuit fault occurs, the internal thermal magnetic release senses the fault and drives the mechanism to open the metal contacts, generating an arc between the contacts. Under the action of arc current limiting, the fault current continues to decrease.

3. The method for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker according to claim 1, characterized in that: The specific implementation method of step 3) is as follows: the peripheral desat circuit detects the voltage across the power electronic device and compares it with the threshold voltage. When in an overcurrent state, the voltage across the two ends exceeds the threshold voltage, forcing the driver chip to lock and control the power electronics to shut down. Subsequently, the driver chip is reset under the action of the control unit, and after a fixed delay, the IGBT is driven to turn on again. The desat circuit again detects whether the power electronic device is in an overcurrent state. If it is in an overcurrent state, this step is repeated.

4. The method for reliable commutation of tail current of a low-voltage hybrid DC circuit breaker according to claim 1, characterized in that: The specific implementation method of step 4) is as follows: when the power electronic device is in a non-overcurrent state, the voltage across the device is less than the threshold voltage, the peripheral desat protection circuit does not work, the power electronic device is successfully turned on, and the fault current is commutated to the power electronic device through the mechanical circuit breaker. After a programmed delay, the power electronic device is turned off, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

5. A low-voltage hybrid DC circuit breaker tail current reliable commutation system, characterized in that: include: The signal acquisition module is used to detect a short-circuit fault in the DC system. The mechanical circuit breaker senses the fault, opens the contacts through the internal thermal magnetic release to generate an arc, and obtains the control system trigger signal. The signal detection module is used to control the power electronic device to turn on after a fixed delay based on the trigger signal, and detect whether the power electronic device is in an overcurrent state when it is turned on through the peripheral protection circuit. When the arc voltage exceeds the threshold, the control unit starts to control the delay, and controls the power electronic device to turn on when the current decreases. The peripheral desat protection circuit works and determines whether it is in an overcurrent state by detecting the voltage across the device. The first judgment module is used to force the power electronic device to shut down and repeat the signal detection module when the power electronic device is in an overcurrent state at the time of conduction; The second judgment module is used to complete the current commutation and clear the arc extinguishing fault when the power electronic device is in a non-overcurrent state.

6. The low-voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 5, characterized in that: In the signal acquisition module, the mechanical circuit breaker uses a molded case circuit breaker. When a short circuit fault occurs, the internal thermal magnetic release senses the fault and drives the mechanism to open the metal contacts. An arc is generated between the contacts, and the fault current continues to decrease under the action of arc current limiting.

7. The low-voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 5, characterized in that: In the first judgment module, the peripheral desat circuit works to detect the voltage at both ends of the power electronic device and compares it with the threshold voltage. When it is in an overcurrent state, the voltage at both ends exceeds the threshold voltage, forcing the driver chip to lock and control the power electronics to shut down. Then the driver chip is reset under the action of the control unit, and after a fixed delay, the IGBT is driven to turn on again. The desat circuit detects again whether the power electronic device is in an overcurrent state, and repeats when it is in an overcurrent state.

8. The low-voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 5, characterized in that: In the second judgment module, when the power electronic device is in a non-overcurrent state, the voltage across the device is less than the threshold voltage, the peripheral desat protection circuit does not work, the power electronic device is successfully turned on, and the fault current is commutated to the power electronic device through the mechanical circuit breaker. After a program delay, the power electronic device is turned off, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

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