A composite resonance type mechanical DC circuit breaker and its usage method

Abstract

The present invention discloses a composite resonant mechanical DC circuit breaker and a method for using the same, relating to the technical field of circuit breakers. The circuit breaker comprises a parallel main branch, an oscillation branch, and an energy-consuming branch; a main switch and an auxiliary oscillation switch are provided in series on the main branch; the auxiliary oscillation switch comprises four parallel auxiliary oscillation branches, a first lightning arrester is provided on the first auxiliary oscillation branch; an auxiliary switch is provided on the second auxiliary oscillation branch; a diode, an inductor, and a power electronic device are provided on the third auxiliary oscillation branch; the cathode of the diode is connected to the anode of the power electronic device, and the anode of the diode is connected to the cathode of the power electronic device; the power electronic device is also connected in series with the inductor; a capacitor is provided on the fourth auxiliary oscillation branch; an oscillation element is provided on the oscillation branch, and an energy-consuming element is provided on the energy-consuming branch. The present invention reduces the requirements for the continuous hard shutdown capability of the power electronic device, reduces the number of devices used, and further reduces costs.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit breakers, and in particular to a composite resonant mechanical DC circuit breaker and a method of using the same. Background Art

[0002] With rising carbon dioxide emissions and a surge in greenhouse gas emissions, climate change has become a global issue facing humanity. Renewable energy generation methods such as photovoltaic and wind power are growing rapidly, driving the upgrade of power systems towards an energy internet. Common distributed generation methods typically use direct current (DC) or rectified DC. However, integrating DC into the grid through inverters, coupled to existing AC systems, generates harmonics, reducing efficiency, impacting the correct operation of relay protection devices, and threatening system safety. Flexible DC transmission technology, with its advantages of low line losses, low cost, strong controllability, and high reliability, holds great promise for development. Furthermore, with the rapid development of power electronics technology, the number of DC loads has skyrocketed. This has enabled flexible DC distribution technology, with its advantages of high power efficiency and reliability, to play a significant role in the coordinated control of "source-grid-load" systems, attracting widespread attention.

[0003] Flexible DC systems have low impedance, a high rate of fault current rise, and rapid fault current diffusion after a fault occurs. Rapid and reliable fault isolation is a prerequisite for safe and stable DC system operation. However, DC systems lack the natural current zero crossing point found in AC systems, making interrupting DC fault currents difficult. The advent of DC circuit breakers provides a solution to this problem.

[0004] Existing DC circuit breakers, when used in high-voltage, high-capacity applications, still suffer from common issues such as high cost and large footprint. Relying on the capacitor voltage to continuously increase, thereby forcing the oscillating current amplitude to increase, allowing the mechanical switch to cross zero and extinguish the arc, can provide multiple zero-crossing points for the mechanical switch, increasing reliability while significantly reducing costs. However, current forced-resonance DC circuit breakers still require pre-charged capacitors and pre-charging devices, or power electronic components that require high frequency and multiple shutdown fault currents, hindering their further development to higher voltage and current levels. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite resonant mechanical DC circuit breaker and a method for using the same, so as to reduce the turn-on and turn-off losses of power electronic devices, lower the demand for continuous hard shutdown capability of power electronic devices, extend the service life of power electronic devices, reduce the number of power electronic devices used, and further save costs.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A composite resonant mechanical DC circuit breaker comprises a main branch, an oscillating branch and an energy-consuming branch, wherein the main branch, the oscillating branch and the energy-consuming branch are connected in parallel;

[0008] A main switch and an auxiliary oscillation switch are provided in series on the main branch; the auxiliary oscillation switch includes four auxiliary oscillation branches connected in parallel, namely a first auxiliary oscillation branch, a second auxiliary oscillation branch, a third auxiliary oscillation branch and a fourth auxiliary oscillation branch;

[0009] A first lightning arrester is provided on the first auxiliary oscillation branch;

[0010] An auxiliary switch is provided on the second auxiliary oscillation branch;

[0011] A diode, an inductor, and a power electronic device are provided on the third auxiliary oscillation branch; the cathode of the diode is connected to the anode of the power electronic device, and the anode of the diode is connected to the cathode of the power electronic device; the power electronic device is also connected in series with the inductor;

[0012] A capacitor is provided on the fourth auxiliary oscillation branch;

[0013] An oscillating element is provided on the oscillating branch, and an energy consuming element is provided on the energy consuming branch.

[0014] Optionally, the oscillation element includes an oscillation inductor and an oscillation capacitor connected in series.

[0015] Optionally, the energy-consuming element is a second lightning arrester.

[0016] Optionally, the power electronic device is an IGBT or an IEGT.

[0017] Optionally, an operating voltage of the first lightning arrester is different from an operating voltage of the second lightning arrester.

[0018] To achieve the above object, the present invention also provides the following technical solutions:

[0019] A method for using a composite resonant mechanical DC circuit breaker, comprising:

[0020] A composite resonant mechanical DC circuit breaker is installed in a DC system; in the composite resonant mechanical DC circuit breaker, a main switch and an auxiliary switch are in a closed state, power electronic components are in a closed state, and a first lightning arrester and energy-consuming components are not in operation;

[0021] When a fault occurs in the DC system, the main switch and the auxiliary switch are opened, and the power electronic device receives a first conduction instruction and is controlled to be turned on, so that the fault current in the DC system is transferred to the power electronic device;

[0022] When the power electronic device receives a shutdown instruction and shuts down, the fault current charges the capacitor, and when the voltage of the auxiliary oscillation branch reaches the operating voltage of the first lightning arrester, the first lightning arrester is activated, and the first lightning arrester oscillates with the oscillation branch to generate an oscillating current until the oscillating current reaches zero;

[0023] When the power electronic device receives the second conduction instruction to control conduction, the oscillating current oscillates in the reverse direction, and at the same time, the capacitor, the inductor and the power electronic device form an oscillation loop to oscillate, generating an auxiliary oscillating current;

[0024] When the oscillating current passes through zero again, the auxiliary oscillating current and the fault current cancel each other out, and the diode is turned on, so that the power electronic device is turned off when the voltage and current are both 0;

[0025] At the current moment, if the oscillating current does not cancel out the fault current, returning to the step where the power electronic device receives a shutdown instruction and shuts down;

[0026] At the current moment, if the oscillating current and the fault current cancel each other out, the main switch extinguishes the arc at zero crossing, and the fault current is transferred to the oscillating branch to charge the capacitor until the energy dissipation element is activated to transfer the fault current to the energy dissipation branch.

[0027] Optionally, the gate of the power electronic device is used to receive the first on-state instruction, the second on-state instruction and the off-state instruction.

[0028] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0029] The present invention discloses a composite resonant mechanical DC circuit breaker and a method for using the same, comprising a parallel main branch, an oscillation branch, and an energy-consuming branch. An oscillation element is provided on the oscillation branch, an energy-consuming element is provided on the energy-consuming branch, and a main switch and an auxiliary oscillation switch are provided in series on the main branch. The auxiliary oscillation switch comprises four parallel auxiliary oscillation branches, wherein a first lightning arrester is provided on the first auxiliary oscillation branch. Since the fault current in the DC system can be considered as a constant value, the first lightning arrester can be considered as a constant voltage source after being turned on, that is, the auxiliary oscillation switch appears to the outside as a constant voltage source; an auxiliary switch is provided on the second auxiliary oscillation branch. When the DC system is operating normally, the auxiliary switch conducts current, resulting in low conduction loss and no need for a large amount of water cooling equipment; a diode, an inductor, and a power electronic device are provided on the third auxiliary oscillation branch. Due to the introduction of the inductor and the capacitor, the power electronic device can be considered to be turned on with zero current during the turning-on process. The turn-on loss is extremely low, and zero voltage and zero current can be achieved during the shutdown process, and the shutdown loss is negligible. That is, the module reduces the demand for continuous hard shutdown capability of power electronic devices, greatly reduces the number of power electronic devices used, extends the service life of power electronic devices, and further saves costs. At the same time, the shutdown capability of the DC circuit breaker is not restricted by the shutdown capability of the device; in addition, the power electronic device is clamped by the first lightning arrester throughout the process and only withstands a very small voltage, which reduces the requirements for the device, saves costs, and does not require the device to be connected in series with a withstand voltage; a capacitor is set on the fourth auxiliary oscillation branch.

[0030] In summary, compared to existing resonant DC circuit breakers, this invention eliminates the need for pre-charge capacitors and pre-charging devices. Furthermore, the power electronic devices employed can achieve zero-voltage and zero-current shutdown, resulting in negligible turn-on and turn-off losses, significantly extending the service life of the power electronic devices. Furthermore, the DC circuit breaker's shutoff capability is no longer constrained by the power electronic device's shutoff capability, significantly improving its breaking capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 Schematic diagram of the structure of the composite resonant mechanical DC circuit breaker of the present invention;

[0033] Figure 2 A schematic diagram of current during use of the composite resonant mechanical DC circuit breaker of the present invention;

[0034] Figure 3The timing of the DC circuit breaker breaking the fault current of the present invention is Figure 1 ;

[0035] Figure 4 The timing of the DC circuit breaker breaking the fault current of the present invention is Figure 2 .

[0036] Explanation of symbols:

[0037] 1-First lightning arrester, 2-Main branch, 3-Main switch, 4-Auxiliary switch, 5-Diode, 6-Inductor, 7-Power electronic device, 8-Capacitor, 9-Oscillation branch, 10-Energy consumption branch. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] The present invention proposes a composite resonant mechanical DC circuit breaker and its use method. This device combines the advantages of low cost and low loss of mechanical DC circuit breakers, while not requiring a pre-charging device. Furthermore, the power electronic devices employed can be switched on and off at zero voltage and zero current, resulting in minimal losses and reduced demand for continuous hard-shutdown capability. This significantly reduces the number of power electronic devices used, extending their service life and further saving costs. Furthermore, the DC circuit breaker's shutoff capability is not constrained by the device's shutoff capability, making it suitable for all voltage levels of flexible DC systems. Furthermore, this solution reduces the stress and junction temperature requirements for the power electronic devices, allowing for flexible selection of different device types based on actual needs. This further reduces economic costs while ensuring reliability, facilitating its further promotion and application.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown, the present invention provides a composite resonant mechanical DC circuit breaker, comprising a main branch 2, an oscillating branch 9 and an energy-consuming branch 10, wherein the main branch 2, the oscillating branch 9 and the energy-consuming branch 10 are connected in parallel. Figure 1As shown in the figure, the input end of the main branch 2 is connected to the input end of the oscillation branch 9 and the input end of the energy consumption branch 10 respectively, and the output end of the main branch 2 is connected to the output end of the oscillation branch 9, the output end of the energy consumption branch 10, and the output end of the auxiliary oscillation switch; the input end of the auxiliary oscillation switch is connected to the input end of the main switch 3 and the auxiliary switch 4.

[0042] The main branch 2 is provided with a main switch 3 and an auxiliary oscillation switch connected in series; the auxiliary oscillation switch includes four auxiliary oscillation branches connected in parallel, namely a first auxiliary oscillation branch, a second auxiliary oscillation branch, a third auxiliary oscillation branch and a fourth auxiliary oscillation branch.

[0043] A first lightning arrester (MOV1) 1 is provided on the first auxiliary oscillation branch; since the fault current can be considered as a constant value, the first lightning arrester (MOV1) 1 can be considered as a constant voltage source after being turned on, that is, the auxiliary oscillation switch module appears to the outside as a constant voltage source. An auxiliary switch 4 is provided on the second auxiliary oscillation branch; when the DC system is operating normally, the auxiliary switch 4 conducts current, the conduction loss is low, and a large amount of water cooling equipment is not required. A diode (D) 5, an inductor (L1) 6 and a power electronic device (T) 7 are provided on the third auxiliary oscillation branch; the cathode of the diode (D) 5 is connected to the anode of the power electronic device (T) 7, and the anode of the diode (D) 5 is connected to the cathode of the power electronic device (T) 7; the power electronic device (T) 7 is also connected in series with the inductor (L1) 6; the inductor L1 includes a reactor and a stray inductance. A capacitor (C1) 8 is provided on the fourth auxiliary oscillation branch.

[0044] Due to the introduction of the inductor (L1) 6 and the capacitor (C1) 8, the power electronic device (T) 7 can be considered to be turned on with zero current during the turn-on process, with extremely low turn-on loss. During the turn-off process, zero voltage and zero current can be achieved, and the turn-off loss can be ignored. That is, this branch circuit setting realizes lossless turn-on and turn-off of the power electronic device, reduces the demand for the continuous hard turn-off capability of the power electronic device, greatly reduces the number of power electronic devices used, extends the service life of the power electronic device, further saves costs, and at the same time makes the turn-off capability of the DC circuit breaker not restricted by the turn-off capability of the device.

[0045] The power electronic device 7 is an IGBT or IEGT, which does not require multiple, high-frequency shutoff of fault currents, significantly reducing costs. The gates of the power electronic device 7 are all connected to a drive signal.

[0046] The oscillation branch is provided with an oscillation element, which includes an oscillation inductor L connected in series. osc and oscillation capacitor C osc . Oscillation inductance L oscThe energy dissipation branch is provided with an energy dissipation element, which is a second lightning arrester MOV2.

[0047] An operating voltage of the first lightning arrester is different from an operating voltage of the second lightning arrester.

[0048] Based on the above-mentioned composite resonant mechanical DC circuit breaker, the present invention further provides a method for using the composite resonant mechanical DC circuit breaker, comprising:

[0049] Step 100: Install a composite resonant mechanical DC circuit breaker in a DC system. At this point, the DC system is in normal operation and is in the on state. In the composite resonant mechanical DC circuit breaker, the main switch and auxiliary switch are in the closed state, the power electronic components are in the off state, and the first lightning arrester and energy-consuming elements are inactive.

[0050] Step 200: When a fault occurs in the DC system, the DC circuit breaker receives a system command or reaches a breaking current threshold, and initiates a breaking process. Specifically, the main switch and the auxiliary switch are opened, and the power electronic device receives a first conduction instruction and controls conduction until the auxiliary switch reaches a sufficient insulation distance. The fault current in the DC system is transferred to the power electronic device, as shown in FIG. Figure 2 shown.

[0051] Step 300: When the power electronic device receives a shutdown instruction and shuts down, the fault current i fault The capacitor is charged, and when the voltage of the auxiliary oscillation branch reaches the action voltage of the first lightning arrester, the first lightning arrester is actuated, and the first lightning arrester acts as a constant voltage source to oscillate with the oscillation branch, generating an oscillating current i osc until the oscillating current is zero.

[0052] Step 400: When the power electronic device receives a second turn-on instruction to control conduction, the oscillating current oscillates in the reverse direction. At the same time, the capacitor, the inductor and the power electronic device form an oscillation loop to oscillate, generating an auxiliary oscillating current i1.

[0053] Step 500: When the oscillating branch current i osc When the voltage and current cross zero again, the auxiliary oscillating current and the fault current cancel each other out, and the diode is turned on, so that the power electronic device is turned off when both the voltage and the current are zero.

[0054] Step 600: At the current moment, if the oscillating current does not cancel out the fault current, then return to the step where the power electronic device receives a shutdown instruction and shuts down, i.e., repeat the above steps until the oscillating current i osc Can be compared with the fault current i fault offset each other.

[0055] Step 700: At the current moment, if the oscillating current and the fault current cancel each other out, the main switch extinguishes the arc at zero crossing, and the fault current is transferred to the oscillating branch to charge the capacitor until the energy-consuming element, that is, the second lightning arrester, is activated to transfer the fault current to the energy-consuming branch, and the second lightning arrester dissipates the remaining energy of the system.

[0056] Eventually, when the DC system current gradually decays to tens of mA, the DC circuit breaker clears and isolates the DC side fault. At this point, the DC system voltage is distributed across the oscillating branches according to the predetermined target.

[0057] The gate of the power electronic device is used to receive the first on-state instruction, the second on-state instruction and the off-state instruction.

[0058] like Figure 3 and Figure 4 As shown, the present invention also provides a specific process of interrupting the fault current of a DC circuit breaker, as follows:

[0059] 0-t0: the main switch 3 and the auxiliary switch 4 are in the closed state, conducting the system current, and the power electronic device 7 is in the off state.

[0060] t0-t1: A fault occurs in the DC system and the DC circuit breaker starts the breaking process.

[0061] t1-t2: the main switch 3 and the auxiliary switch 4 are disconnected, and the power electronic device 7 is turned on.

[0062] t2-t3: the auxiliary switch 4 reaches a sufficient insulation distance, and the fault current is transferred from the auxiliary switch 4 to the power electronic device 7.

[0063] t3-t4: The power electronic device 7 is shut down, and the fault current charges the capacitor 8, reaching the operating voltage of the first lightning arrester 1. The current transfers to the first lightning arrester, and the auxiliary oscillating switch voltage is clamped to the reference voltage of the first lightning arrester. It oscillates with the oscillation branch 9 as a constant voltage source until the oscillation current i osc Crossing zero, the first oscillation half-wave ends.

[0064] t4-t5: The power electronic device 7 is turned on, and the inductor 6 limits the current growth rate. The turn-on loss during the turn-on process is very small. After T is turned on, the oscillating current i osc In the reverse direction, the capacitor 8, the inductor 6 and the power electronic device 7 form an oscillation circuit to oscillate and generate an oscillating current i1. That is, three currents flow through the power electronic device 7 at the same time, namely the fault current i fault , oscillating current i osc and auxiliary oscillating current i1.

[0065] t5-t7: At t5, the auxiliary oscillating current i1 oscillates through zero, and the voltage of capacitor 8 oscillates in the reverse direction. i1 enters the negative half-wave oscillation process. At this time, i1 has a negative half-wave oscillation effect on i osc 、i fault Play a reverse canceling role, the current flows from left to right through the power electronic device 7 in the positive direction, when i1+i fault +i osc <0, diode 5 is turned on. fault +i osc When ≥0, the power electronic device 7 is turned on again. At time t6, the auxiliary oscillating current i1 passes through zero, and the voltage of the capacitor 8 is reversed again.

[0066] t7-t8: At t7, the auxiliary oscillating current i1 enters the negative half-wave oscillation process again. When i1+i fault +i osc When ≤ 0, diode 5 turns on again. When diode 5 reaches its maximum reverse conduction value, i.e., i1 reaches its maximum reverse value, T is controlled to turn off. Since diode 5 is in the on state at this time, no current flows through power electronic device 7. After turning off, power electronic device 7 only withstands the diode forward voltage drop, which is a very small value. Therefore, the turn-off loss of power electronic device 7 can be ignored. The oscillation period of i1 can be flexibly changed.

[0067] t8-t9: The power electronic device 7 is turned on and off repeatedly at a fixed frequency until time t9. During the off period of the power electronic device 7, the current of the main switch 1 crosses zero and the arc is extinguished. The fault current is transferred to the oscillation branch 9, which has an impact on the capacitor C. osc The charging is carried out until the operating voltage of the second lightning arrester 10 is reached, and the current is transferred to the energy consumption branch, and the second lightning arrester 10 consumes the remaining energy of the system.

[0068] The present invention can complete the matching of oscillation frequency during parameter design in the design process of the composite resonant mechanical DC circuit breaker. During the actual oscillation process, it is only necessary to send on / off signals to the power electronic device 7 at a fixed frequency, and the control logic is convenient and simple.

[0069] In summary, the present invention has the advantages of low conduction loss, no need for water cooling equipment in the main branch, low cost, small footprint, ability to create multiple zero-crossing points for the mechanical switch, and high breaking reliability.

[0070] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0071] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A composite resonant mechanical DC circuit breaker, characterized in that: It includes a main branch, an oscillating branch and an energy-consuming branch, and the main branch, the oscillating branch and the energy-consuming branch are connected in parallel; A main switch and an auxiliary oscillation switch are provided in series on the main branch; the auxiliary oscillation switch includes four auxiliary oscillation branches connected in parallel, namely a first auxiliary oscillation branch, a second auxiliary oscillation branch, a third auxiliary oscillation branch and a fourth auxiliary oscillation branch; A first lightning arrester is provided on the first auxiliary oscillation branch; An auxiliary switch is provided on the second auxiliary oscillation branch; A diode, an inductor, and a power electronic device are provided on the third auxiliary oscillation branch; the cathode of the diode is connected to the anode of the power electronic device, and the anode of the diode is connected to the cathode of the power electronic device; the power electronic device is also connected in series with the inductor; A capacitor is provided on the fourth auxiliary oscillation branch; An oscillating element is provided on the oscillating branch, and an energy consuming element is provided on the energy consuming branch.

2. The composite resonant mechanical DC circuit breaker according to claim 1, characterized in that: The oscillating element includes an oscillating inductor and an oscillating capacitor connected in series.

3. The composite resonant mechanical DC circuit breaker according to claim 1, characterized in that: The energy-consuming element is a second lightning arrester.

4. The composite resonant mechanical DC circuit breaker according to claim 1, characterized in that: The power electronic device is an IGBT or an IEGT.

5. The composite resonant mechanical DC circuit breaker according to claim 3, characterized in that: An operating voltage of the first lightning arrester is different from an operating voltage of the second lightning arrester.

6. A method for using a composite resonant mechanical DC circuit breaker, characterized in that: include: The composite resonant mechanical DC circuit breaker according to any one of claims 1 to 5 is arranged in a DC system; In the composite resonant mechanical DC circuit breaker, the main switch and the auxiliary switch are in the closed state, the power electronic device is in the off state, and the first lightning arrester and the energy-consuming element are not in operation; When a fault occurs in the DC system, the main switch and the auxiliary switch are opened, and the power electronic device receives a first conduction instruction and is controlled to be turned on, so that the fault current in the DC system is transferred to the power electronic device; When the power electronic device receives a shutdown instruction and shuts down, the fault current charges the capacitor, and when the voltage of the auxiliary oscillation branch reaches the operating voltage of the first lightning arrester, the first lightning arrester is activated, and the first lightning arrester oscillates with the oscillation branch to generate an oscillating current until the oscillating current reaches zero; When the power electronic device receives the second conduction instruction to control conduction, the oscillating current oscillates in the reverse direction, and at the same time, the capacitor, the inductor and the power electronic device form an oscillation loop to oscillate, generating an auxiliary oscillating current; When the oscillating current passes through zero again, the auxiliary oscillating current and the fault current cancel each other out, and the diode is turned on, so that the power electronic device is turned off when the voltage and current are both 0; At the current moment, if the oscillating current does not cancel out the fault current, returning to the step where the power electronic device receives a shutdown instruction and shuts down; At the current moment, if the oscillating current and the fault current cancel each other out, the main switch extinguishes the arc at zero crossing, and the fault current is transferred to the oscillating branch to charge the capacitor until the energy dissipation element is activated to transfer the fault current to the energy dissipation branch.

7. The method for using the composite resonant mechanical DC circuit breaker according to claim 6, characterized in that: The gate of the power electronic device is used to receive the first on-state instruction, the second on-state instruction, and the off-state instruction.

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