Reliable conversion method and system for tail current of low-voltage hybrid direct-current circuit breaker

Abstract

The invention discloses a reliable conversion method and system for tail current of a low-voltage hybrid direct-current circuit breaker, and the method comprises the steps: 1), enabling a direct-current system to generate a short-circuit fault, enabling a mechanical circuit breaker to sense the fault, opening a contact through an internal thermomagnetic release to generate an electric arc, and obtaining a control system trigger signal; (2) the control system controls the power electronic device to be switched on through fixed time delay on the basis of the trigger signal, and detects whether the power electronic device is in an overcurrent state or not at the switching-on moment through work of a peripheral protection circuit; (3) when the power electronic device is in an over-current state at the conduction moment, the power electronic device is forcibly turned off, and the step (2) is repeated; and 4) when the power electronic device is in a non-overcurrent state, current commutation is completed, and an arc extinguishing fault is eliminated. The system comprises a signal acquisition module, a signal detection module, a first judgment module and a second judgment module. The method can be widely applied to multi-low-voltage hybrid direct-current circuit breaker products and has good applicability.

Description

Technical Field

[0001] The 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, people are continuously increasing the voltage level to reduce the power transmission loss. The voltage level in the low-voltage field is gradually increasing and approaching the 1500V upper limit specified by the IEC. Therefore, the protection equipment of the low-voltage DC system is required to be miniaturized, easy to install, and fast to open. As a key protection device in the power system, the circuit breaker has an important role in the protection of the DC system due to its reliability and high performance. Compared with the traditional AC system, the DC system lacks a natural zero-crossing point, and the line impedance is small and the fault current rises quickly, making it more difficult to protect. Therefore, the research on the breaking protection technology of the low-voltage DC system is of great significance to its development.

[0003] Circuit breakers can be divided into mechanical circuit breakers, solid-state circuit breakers, and hybrid circuit breakers according to their different structures. Among them, mechanical circuit breakers are the most mature. According to the different operating principles of the mechanism, they can be divided into thermal magnetic circuit breakers and electronic circuit breakers. The arc extinguishing method mainly achieves rapid arc extinguishing by adding arc extinguishing grids, stretching arcs, and adding permanent magnets. However, with the development of DC systems, traditional arc extinguishing methods are difficult to achieve rapid fault clearance. The arc extinguishing time is usually tens of milliseconds. Only by continuously increasing the volume of the arc extinguishing chamber, increasing gas-producing materials, and multi-stage series connection can the breaking requirements under high voltage levels be met, which puts forward higher requirements on its volume and operation consistency. However, since it conducts current through metal contact, it has the characteristics of small conduction loss, strong short-term short-circuit current tolerance, and low cost. With the rapid development of semiconductor technology, solid-state circuit breakers based on power electronic devices have received extensive attention. Solid-state circuit breakers use fast detection modules and control modules to quickly clear short-circuit currents, and the fault clearing time can be shortened to microseconds. This solution is more reliable for highly power-electronic DC systems. Under normal operating conditions, the rated current is conducted by power electronic devices, and the device is shut down when a fault occurs. Therefore, although arc-free breaking can be achieved, the conduction loss is greater, and the requirements for heat dissipation structure design are higher. It has the advantages of long service life and fast breaking speed, but is limited by the performance of the device itself. Solid-state circuit breakers are currently only suitable for low-voltage (<100V) terminal protection occasions.

[0004] The hybrid breaking technology developed by combining mechanical circuit breakers and solid-state circuit breakers is considered to be one of the important development directions in the future low-voltage DC field. This solution has the advantages of low conduction loss of mechanical circuit breakers and fast breaking speed of solid-state circuit breakers while making full use of the current limiting function of traditional circuit breakers. However, in order to further shorten the breaking time, traditional hybrid circuit breakers need to quickly turn on power electronic devices at the beginning of arcing to complete rapid commutation and arc extinguishing. However, in the low-voltage field, there are two key problems in rapid commutation: 1) The contact opening distance is too small, and the overvoltage of power electronic devices may cause heavy breakdown when they are turned off; 2) Turning on power electronic devices in the current rising stage requires higher device performance and quantity. The above problems can be solved by turning on power electronic devices in the late arcing stage. However, this method has a high demand for the time when the devices are turned on. How to achieve reliable conduction and current commutation of power electronic devices under different mechanical circuit breaker breaking conditions is an urgent problem to be solved for the further development of low-voltage hybrid DC circuit breakers, which is of great significance to promoting the development of low-voltage DC systems and improving low-voltage electrical appliance theory. Summary of the invention

[0005] Aiming at the problem of unreliable breaking in the late arcing stage of a low-voltage hybrid DC circuit breaker, the present invention proposes a reliable commutation method and system for the tail current of a low-voltage hybrid DC circuit breaker, 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 solution:

[0007] A reliable commutation method for 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 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 detects again whether the power electronic device is in an overcurrent state, and repeats this step when it is in an overcurrent state.

[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, the power electronic device is turned off after a program delay, 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 for the DC system to generate a short-circuit fault, the mechanical circuit breaker to sense the fault, open the contacts through the internal thermal magnetic release to generate an arc, and obtain the control system trigger signal;

[0018] A signal detection module is used to control the power electronic device to be turned on after a fixed delay based on the trigger signal, and to 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 be turned 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 drive chip to lock and control the power electronics to shut down. Subsequently, the drive 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.

[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, the power electronic device is turned off after a program delay, 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 reliable current commutation circuit structure of the tail current of a low-voltage hybrid DC circuit breaker based on a traditional molded case circuit breaker, 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 initial stage of arcing and the high cost of power electronic devices on the other hand, effectively reducing 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 schematic diagram of the current commutation principle of the tail of the low-voltage hybrid DC circuit breaker.

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

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

[0031] Figure 2c It is the over-current 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 a fault clearance diagram;

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

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

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

[0039] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0040] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

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

[0042] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0043] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

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

[0045] The invention discloses a reliable commutation method for tail current of a low-voltage hybrid DC circuit breaker, the main purpose of which is to realize rapid clearing of fault current in a low-voltage DC system, thereby protecting the system from safe and reliable power consumption.

[0046] The present invention discloses a reliable commutation method for tail current of a low-voltage hybrid DC circuit breaker. Another purpose of the present invention is to provide a late arc breaking strategy different from that of traditional hybrid circuit breakers, so as to solve the problems of heavy breakdown caused by early arc breaking and excessive cost of power electronic devices.

[0047] The present invention discloses a reliable commutation method for tail current of a low-voltage hybrid DC circuit breaker, and another purpose thereof is to provide a circuit topology structure different from that of a traditional hybrid circuit breaker.

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

[0049] like 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 system rated current 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 point, the power electronic devices When the device is at its maximum on-current, the device 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 1As shown. The topology is composed of a molded case circuit breaker (MCCB) K, an energy-consuming device metal oxide varistor (MOV) MOV, and an insulated gate bipolar transistor (IGBT) S1 in parallel. The A side of the structure is the positive electrode and the B side is the negative electrode. The desaturation detection circuit is composed of a diode D1, a resistor R2, a capacitor C1, a voltage regulator D2, an operational amplifier, a current source, and a metal oxide semiconductor field effect transistor (MOSFET) S2. The current source, operational amplifier, and S2 are integrated inside the driver chip. The cathode of the diode D1 is connected to the collector of 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 regulator D2. The capacitor C1 is connected in parallel with the voltage regulator, and the cathode of the voltage regulator D2 is connected to the positive input terminal of the operational amplifier. Molded case circuit breaker M is used to conduct rated current under normal working conditions, and its conduction loss can be approximately ignored. When a fault occurs, the metal contact of this branch opens and an arc is generated. Under the action of arc current limiting, the fault current rises slowly; S1 is used to bear the fault current for a short time. When this branch is turned on, the current quickly switches from the main current branch to this branch under the action of arc voltage, thereby completing the rapid arc extinguishing; 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 commutation moment and S1 is in an overcurrent state, the desaturation detection circuit acts to force the driver chip to turn off S1, and the driver chip self-locks until it receives the reset signal provided by the control chip, and the driver chip works again to try to turn on S1. The energy consumption branch is used to consume the energy stored in the line. Under normal working conditions, this branch is in a high-impedance state. When the commutation branch is turned off, the branch becomes a low-impedance state under the action of overvoltage. The fault current switches to this branch, and the energy stored in the line is finally dissipated through this branch.

[0051] Combination Figure 1 2. Taking short-circuit fault as an example, the working process of the proposed reliable commutation method of tail current of low-voltage hybrid DC circuit breaker is specifically explained.

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

[0053] When an overload or short circuit fault occurs, the thermal magnetic tripping mechanism inside the mechanical circuit breaker K is activated due to heat and electromagnetic force, thereby driving the metal contacts of the mechanical circuit breaker K to open, generating an arc between the contacts. The arc voltage gradually increases as the contacts open, and at the same time, the fault current increases at a slower rate or even slowly decreases under the action of the arc voltage.

[0054] At this time, the driver chip outputs the driving voltage, the insulated gate bipolar transistor S1 starts to conduct, and the internal current source I cc Charge capacitor C1. The voltage on capacitor C1 is:

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

[0056] Where 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 the IGBT.

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

[0058] When the driver chip is turned off, the control unit receives a fault signal. As the arc continues to burn, the arc current gradually decreases. After a fixed delay, the control unit outputs a reset signal and a turn-on signal. The driver chip is reset and turned on again, 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 and is normally turned on. 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 line, a large overvoltage is generated at both ends of the insulated gate bipolar transistor S1. If no protective measures are taken, the device will break down. Therefore, a metal oxide varistor MOV is added to protect it. At low voltage, MOV is in a high-resistance state. When the voltage exceeds its clamping voltage, it quickly changes to a low-resistance state, and the voltage remains almost stable. Therefore, when the insulated gate bipolar transistor S1 is turned off, the energy consumption branch where the MOV is located is turned on under overvoltage conditions, and the current is commutated to this branch. Finally, the line energy is dissipated in the form of heat through this branch, and the fault is cleared.

[0061] Example 1

[0062] The present invention provides a reliable commutation method for 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 releaser 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 detects 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 detects whether the power electronic device is in an overcurrent state again, and repeats this step when it is in an overcurrent state.

[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, 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.

[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 for the DC system to generate a short-circuit fault, the mechanical circuit breaker to sense the fault, open the contacts through the internal thermal magnetic release to generate an arc, and obtain the control system trigger signal;

[0074] A signal detection module is used to control the power electronic device to be turned on after a fixed delay based on the trigger signal, and to 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] In conjunction with FIGS. 2 to 4 , the working process of the low-voltage hybrid DC circuit breaker tail current reliable commutation method is specifically described, and 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 of the circuit breaker and side B being the negative pole of the circuit breaker. 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 release mechanism of the mechanical circuit breaker K is activated, the contacts are separated by the mechanism, an arc is generated, and the current in the main current branch reaches a peak value and begins to slowly decrease under the action of the arc voltage. 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 drive voltage V g At this time, S1 starts to conduct. The internal current source of the driver chip charges the capacitor C1 on the one hand, and discharges through the capacitor R1 and the 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 the capacitor C1 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 after a delay inside the driver chip, the FLT signal is output, corresponding to Figure 2d At time t3, the microcontroller output reaches the preset value and then drops to zero.

[0083] Stage 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, stage 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 Therefore, 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 the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0088] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A reliable commutation method for 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 through the internal thermal magnetic release to generate an arc, and obtains the control system trigger signal; 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; 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; 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 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.

3. 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 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 drops 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.

4. 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 3) is as follows: the peripheral desat circuit detects 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 detects again whether the power electronic device is in an overcurrent state, and repeats this step when it is in an overcurrent state.

5. 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 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 the power electronic device is turned off after a program delay, and the fault current is commutated to the energy consumption branch to complete energy dissipation, and finally the fault is cleared.

6. A low voltage hybrid DC circuit breaker tail current reliable commutation system, characterized in that: include: The signal acquisition module is used for the DC system to generate a short-circuit fault, the mechanical circuit breaker to sense the fault, open the contacts through the internal thermal magnetic release to generate an arc, and obtain the control system trigger signal; A signal detection module is used to control the power electronic device to be turned on after a fixed delay based on the trigger signal, and to detect whether the power electronic device is in an overcurrent state when it is turned on through the peripheral protection circuit; 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.

7. A low voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 6, 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.

8. A low voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 6, characterized in 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 delays to the current drop stage 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 at both ends of the device.

9. A low voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 6, characterized in 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 detects again whether the power electronic device is in an overcurrent state, and repeats when it is in an overcurrent state.

10. A low voltage hybrid DC circuit breaker tail current reliable commutation system according to claim 6, 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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