阅读说明：本技术 自然换流型混合式直流断路器及直流系统的电流关断方法 (Natural commutation type hybrid direct current circuit breaker and current turn-off method of direct current system ) 是由 余占清 曾嵘 黄瑜珑 屈鲁 周雁南 陈政宇 甘之正 于 2020-03-10 设计创作，主要内容包括：本发明提供一种自然换流型混合式直流断路器及直流系统的电流关断方法,所述自然换流型混合式直流断路器由主通流支路、转移支路和能量吸收支路组成,所述主通流支路、转移支路和能量吸收支路并联连接；所述主通流支路由真空间隙快速机械开关和气体间隙快速机械开关串联组成。本发明的自然换流型混合式直流断路器具有通态损耗近零、支持重合闸和电流差异化、换流可靠、可控性强、体积紧凑、占地面积小、成本低等特点。(The invention provides a natural current conversion type hybrid direct current circuit breaker and a current turn-off method of a direct current system, wherein the natural current conversion type hybrid direct current circuit breaker consists of a main current branch, a transfer branch and an energy absorption branch, and the main current branch, the transfer branch and the energy absorption branch are connected in parallel; the main through-flow branch is formed by connecting a vacuum gap quick mechanical switch and a gas gap quick mechanical switch in series. The natural current conversion type hybrid direct current circuit breaker has the characteristics of nearly zero on-state loss, support of reclosing and current differentiation, reliable current conversion, strong controllability, compact size, small occupied area, low cost and the like.)

1. A natural current conversion type hybrid direct current circuit breaker is characterized in that the natural current conversion type hybrid direct current circuit breaker is composed of a main current through branch, a transfer branch and an energy absorption branch,

wherein the content of the first and second substances,

the main through-flow branch, the transfer branch and the energy absorption branch are connected in parallel;

the main through-flow branch is formed by connecting a vacuum gap quick mechanical switch and a gas gap quick mechanical switch in series.

2. The naturally commutating hybrid DC breaker of claim 1,

the gas gap fast mechanical switch is SF₆Gap fast mechanical switch.

3. The naturally commutating hybrid DC breaker of claim 1,

the energy absorption branch is composed of a metal oxide piezoresistor.

4. A naturally commutating hybrid DC breaker according to any of claims 1-3,

the transfer branch is formed by connecting bidirectional solid-state switches in series.

5. A naturally commutating hybrid DC breaker according to claim 4,

the bidirectional solid-state switch is a modular bidirectional solid-state switch.

6. A naturally commutating hybrid DC breaker according to claim 4,

the bidirectional solid-state switch is an anti-series connection structure bidirectional solid-state switch, a full-bridge structure bidirectional solid-state switch or a diode bridge structure bidirectional solid-state switch.

7. A method for turning off current of a dc system, wherein the method for turning off current is performed by using the natural commutation type hybrid dc circuit breaker of any one of claims 1 to 6.

8. The method as claimed in claim 7, wherein when the dc system is in an obstacle, the method issues a switch-off command to the natural commutation type hybrid dc circuit breaker to control the vacuum gap fast mechanical switch and the gas gap fast mechanical switch to switch off.

9. The current turn-off method of the dc system according to claim 8, wherein the switching-off actions of the vacuum gap fast mechanical switch and the gas gap fast mechanical switch are performed such that: 1. transferring the fault current to a transfer branch; 2. after the contacts of the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch are quenched, the contact gaps of the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch bear transient recovery voltage of the direct current system, and then a turn-off instruction is sent to the natural current conversion type hybrid direct current circuit breaker to control the bidirectional solid-state switch in the transfer branch to be turned off.

Technical Field

The invention belongs to the field of direct current circuit breakers, one of key devices of a direct current power grid, and particularly relates to a natural commutation type hybrid direct current circuit breaker and a current turn-off method of a direct current system.

Background

With the continuous development of distributed energy and the increase of the types of power loads, the direct current power grid has obvious advantages in the aspects of large-capacity power transmission, distributed energy access, provision of reactive compensation of an alternating current system and the like

The flexible direct-current power grid has more complex and various system main wiring structures and operation modes, so that the direct-current system has multiple fault modes, fast fault development and wide influence range. Therefore, a fault isolation technology of the flexible direct current power grid is urgently needed to ensure safe and reliable operation of the flexible direct current power grid. The direct current breaker is the most ideal choice for realizing direct current fault isolation in the direct current transmission and distribution system. The dc circuit breaker is mainly classified into a solid-state dc circuit breaker, a mechanical dc circuit breaker, and a hybrid dc circuit breaker according to a difference in topology. Due to the quick on-off characteristic of the solid-state dc circuit breaker and the low loss characteristic of the mechanical dc circuit breaker, the hybrid dc circuit breaker becomes one of the main development directions of the high voltage dc circuit breaker.

At present, domestic and foreign scholars develop extensive researches around the aspects of a novel topological structure, a high-reliability current conversion mode, an operation control strategy, a type test method and the like of a hybrid direct-current circuit breaker for a direct-current power grid or a direct-current power transmission and distribution system, and carry out primary application in a flexible direct-current power grid demonstration project.

The existing hybrid circuit breaker is mainly of the forced commutation type.

Fig. 1 shows a typical topology of a forced commutation type hybrid dc circuit breaker. As can be seen from fig. 1, the forced commutation type hybrid dc circuit breaker includes a main branch, a transfer branch and an energy absorption branch. The main branch circuit is formed by connecting a quick mechanical switch and a full-bridge module in series; the transfer branch is formed by connecting full bridge modules in series; the energy absorbing branch is formed by MOV; each full-bridge module may be an IGBT full-bridge module or a diode full-bridge module. Under the steady-state operation working condition of the direct-current system, the main branch is conducted, the system runs load current in a steady state, the on-state impedance of the main branch is low, and the generated loss is negligible; at the time T1 after the direct current system breaks down, the direct current breaker receives a system breaking command, and the full-bridge module of the main branch is locked to force the current to be transferred to the transfer branch. At a time T2 after the time T1, the main through-current branch current is switched off after zero crossing until it generates enough open distance to withstand the transient-state breaking voltage, and the transfer branch full-bridge module is locked to force the current to be transferred to the energy consumption branch. The MOV overvoltage protection action suppresses the switching overvoltage while dissipating the stored energy of the system inductive element until the fault current crosses zero.

However, the current forced commutation type hybrid dc circuit breaker still has the problems of large volume, high cost, need of providing heat dissipation equipment, no consideration of current parameter differentiation, poor reliability and controllability, and the like.

Disclosure of Invention

In view of the above problems, the present invention provides a natural commutation type hybrid dc circuit breaker and a current turn-off method for a dc system.

The natural flow changing type mixed DC breaker provided by the invention consists of a main through-current branch, a transfer branch and an energy absorption branch,

wherein the content of the first and second substances,

the main through-flow branch, the transfer branch and the energy absorption branch are connected in parallel;

the main through-flow branch is formed by connecting a vacuum gap quick mechanical switch and a gas gap quick mechanical switch in series.

Further, in the present invention,

the gas gap fast mechanical switch is SF₆Gap fast mechanical switch.

Further, in the present invention,

the energy absorption branch is composed of a metal oxide piezoresistor.

Further, in the present invention,

the transfer branch is formed by connecting bidirectional solid-state switches in series.

Further, the method can be used for preparing a novel material

The bidirectional solid-state switch is a modular bidirectional solid-state switch.

Further, the method can be used for preparing a novel material

The bidirectional solid-state switch is an anti-series connection structure bidirectional solid-state switch, a full-bridge structure bidirectional solid-state switch or a diode bridge structure bidirectional solid-state switch.

The invention also provides a current turn-off method of the direct current system, and the current turn-off method adopts the natural commutation type hybrid direct current breaker to turn off the current.

Further, in the present invention,

and when the direct current system is in obstacle, a brake opening instruction is sent to the natural current conversion type hybrid direct current circuit breaker to control the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch to be opened.

Further, in the present invention,

through the opening action of the vacuum gap quick mechanical switch and the gas gap quick mechanical switch, the following steps are carried out: 1. transferring the fault current to a transfer branch; 2. after the contacts of the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch are quenched, the contact gaps of the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch bear transient recovery voltage of the direct current system, and then a turn-off instruction is sent to the natural current conversion type hybrid direct current circuit breaker to control the bidirectional solid-state switch in the transfer branch to be turned off.

The natural commutation type hybrid direct current circuit breaker has the characteristics of low loss, support of reclosing and current differentiation, strong controllability and reliability, small occupied area, reliable commutation, compact volume, low cost and the like. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 shows a topology of a forced commutation type hybrid dc circuit breaker of the prior art;

fig. 2 shows a topology of a natural commutation type hybrid dc circuit breaker according to the present invention;

fig. 3a shows a bidirectional solid-state switch module with an anti-series connection structure in the natural commutation type hybrid dc circuit breaker according to the present invention;

fig. 3b shows a full-bridge bidirectional solid-state switch module in the natural commutation type hybrid dc circuit breaker according to the present invention;

fig. 3c shows a diode bridge structure bidirectional solid-state switch module in the natural commutation type hybrid dc circuit breaker according to the present invention;

fig. 4 shows an operation sequence of the natural commutation type hybrid dc circuit breaker according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 2 shows a topology of the natural commutation type hybrid dc circuit breaker according to the present invention. As can be seen from fig. 2, the natural commutation type hybrid dc circuit breaker of the present invention includes: the device comprises a main through-flow branch, a transfer branch and an energy absorption branch, wherein the main through-flow branch, the transfer branch and the energy absorption branch are connected in parallel.

The main through-flow branch is formed by connecting a vacuum gap quick mechanical switch and a gas gap quick mechanical switch in series, wherein the gas gap quick mechanical switch is preferably SF₆A gap fast mechanical switch; the transfer branch is formed by connecting bidirectional solid-state switches in series; the energy absorption branch consists of a Metal Oxide Varistor (MOV).

The main through-flow branch is formed by connecting mechanical switches in series without special heat dissipation equipment, so that the on-state loss of the natural current conversion type hybrid direct-current circuit breaker is nearly zero; the bidirectional solid-state switch in the transfer branch can be designed in a modularized mode, so that multi-current-grade series products can be formed, current parameter differentiation selection according to the requirements of the converter station is supported, and the technical and economic performance of equipment can be improved to the maximum extent.

The bidirectional solid-state switch may be an anti-series structure, a full-bridge structure, or a diode bridge structure as shown in fig. 3a, 3b, and 3c, respectively.

As can be seen from fig. 3a, the anti-series bidirectional solid-state switch is composed of two diodes D1 and D2 and two fully-controlled devices S1 and S2. The cathode of D1 is connected with the anode of S1, and the anode of D1 is connected with the cathode of S1; the cathode of D2 is connected with the anode of S2, and the anode of D2 is connected with the cathode of S2; the cathode of S1 is connected to the cathode of S2. The cathode of D1 is used as the input (or output) of the anti-series-structure bidirectional solid-state switch, and the cathode of D2 is used as the output (or input) of the anti-series-structure bidirectional solid-state switch.

As can be seen from fig. 3b, the full-bridge bidirectional solid-state switch comprises: the circuit comprises a capacitor C, four diodes D3, D4, D5 and D6 and four fully-controlled devices S3, S4, S5 and S6. The anode of D3 is connected with the cathode of S3 and one electrode of C, the cathode of D3 is connected with the anode of S3, the cathode of S4 and the anode of D4, and the cathode of D4 is connected with the anode of S4 and the other electrode of C; the anode of D5 was connected to the cathode of S5 and the cathode of S3, the cathode of D5 was connected to the anode of S5, the cathode of S6 and the anode of D6, and the cathode of D6 was connected to the anode of S6 and the anode of S4. The cathode of the D3 is used as the input (or output) end of the full-bridge bidirectional solid-state switch, and the cathode of the D5 is used as the output (or input) end of the full-bridge bidirectional solid-state switch.

As can be seen from fig. 3c, the diode bridge bidirectional solid-state switch is composed of five diodes D7, D8, D9, D10 and D11 and a fully-controlled device S7. The cathode of D7 is connected with the cathode of D9, the cathode of D11 and the anode of S7, and the anode of D7 is connected with the cathode of D8; the anode of D9 is connected with the cathode of D10, the anode of D10 is connected with the anode of D11, the anode of D8 and the cathode of S7, and D11 is connected with S7 in anti-parallel. The anode of D7 is used as the input (or output) of the diode bridge structure bidirectional solid-state switch, and the anode of D9 is used as the output (or input) of the diode bridge structure bidirectional solid-state switch.

The fully-controlled devices in fig. 3a, 3b and 3c may be fully-controlled power electronic devices such as thyristors, Insulated Gate Bipolar Transistors (IGBTs), Integrated Gate Commutated Thyristors (IGCTs), and Gate Injection Enhanced transistors (IEGTs). When the fully controlled device is an IGBT, the anode of the fully controlled device should be the collector and the cathode should be the emitter.

As can be seen from the above description, the transfer branch is mainly composed of a power electronic switch, and thus the natural commutation type hybrid dc circuit breaker of the present invention can implement a fast reclosing using the power electronic switch of the transfer branch. The specific process of the rapid reclosing switch is as follows: when the control protection system of the direct current system judges that the direct current system has a fault and is cleared, sending a conduction instruction to the power electronic switch of the transfer branch, wherein the system current flows through the transfer branch, and if the direct current system has a fault, immediately turning off the power electronic switch; and if no fault exists at the moment, sending a closing instruction to the quick mechanical switch of the main through-flow branch, and turning off the power electronic switch after the system current passes through the main through-flow branch.

The invention relates to a natural commutation type hybrid direct current breaker for a direct current system, which is characterized in that: 1. conducting normal current of a direct current system by using the main through-current branch; 2. short-time loading and switching-off of fault current of the direct current system by using the transfer branch, and establishing transient recovery voltage by using the transfer branch; 3. the energy absorption branch is used for restraining the transient recovery voltage and absorbing the energy stored by a direct current circuit and a current-limiting reactance connected with the natural current conversion type hybrid direct current circuit breaker. The current conversion mode of the natural current conversion type hybrid direct current circuit breaker is 'natural current conversion', namely the sum of the arc voltages of the vacuum gap quick mechanical switch and the gas gap quick mechanical switch is larger than the conduction voltage drop of the transfer branch circuit, so that the fault current is 'natural' transferred to the transfer branch circuit from the main through-flow branch circuit.

Based on the principle, the current turn-off method of the direct current system comprises the following steps: when a direct current system adopting the natural commutation type hybrid direct current breaker of the invention has faults (the fault forms are various, such as single-pole earth fault at the direct current system side, interelectrode short-circuit fault and the like), a brake-separating instruction is sent out by a direct current system control protection system, the natural commutation type hybrid direct current breaker receives the brake-separating instruction and then simultaneously brakes a vacuum gap quick mechanical switch and an air gap quick mechanical switch, when contacts of the vacuum gap quick mechanical switch and the air gap quick mechanical switch are both separated by a certain distance, a bidirectional solid-state switch module in a transfer branch is conducted, fault current (namely current flowing through a direct current circuit in the direct current system after the direct current system has the fault) is forced to be transferred from a main through-flow branch to the transfer branch, and when the current of the quick mechanical switch crosses zero, the contacts are quenched; and then, the vacuum gap rapid mechanical switch and the gas gap rapid mechanical switch contact continue to perform the opening movement, after the expected bearing voltage value (the maximum voltage value which can be borne) of the contact gap of the rapid mechanical switch is not lower than the transient recovery voltage of the direct current system, the direct current system control protection system sends out a switching-off instruction to switch off the bidirectional solid-state switch in the transfer branch, so that the fault current is transferred to the energy absorption branch, the voltage between the ends of the direct current breaker is limited by the energy absorption branch, and meanwhile, the fault current gradually drops to zero.

Referring to fig. 4, when the change of the current of the dc system is first seen, the dc system fails at time t1, the fast mechanical switch starts to open, the contact of the fast mechanical switch is opened at a certain distance at time t2, the fault current of the bidirectional solid-state switch module in the conduction transfer branch starts to be transferred from the main current branch to the transfer branch, the fault current is completely transferred to the transfer branch at time t3, the bidirectional solid-state switch in the transfer branch is turned off at time t4, the fault current starts to be transferred to the energy absorption branch, and the fault current is completely transferred to the energy consumption branch at time t5, so that the natural current-exchanging hybrid dc circuit breaker consumes energy from time t 4. From the time t1 when the direct current system fails, the system current continuously increases to a time t5 and then starts to decrease along with the increase of the energy consumption branch current to the maximum value Ip until a time t6, the system current reaches 0, and the energy consumption process of the natural current conversion type hybrid direct current circuit breaker is finished. And the break voltage of the circuit breaker is rapidly increased from 0 to the transient peak voltage Up at the time t8 at the time t7 when the transfer branch current is about to reach the maximum value, then the break voltage is gradually reduced, the break voltage is reduced to the MOV residual voltage Uc at the time t9, then the break voltage is further reduced, and the direct-current line voltage Udc in the direct-current system is reduced at the time t10 when the system current is about to reach 0.

The natural flow changing type hybrid direct current circuit breaker utilizes the arc voltage sum of a main flow branch formed by serially connecting a vacuum gap quick mechanical switch and an air gap quick mechanical switch to be larger than the conduction voltage drop of a transfer branch, so that fault current is transferred to the transfer branch from the main flow branch naturally, the natural flow changing type hybrid direct current circuit breaker is different from L C resonant type mechanical direct current circuit breaker in that the mechanical switch in the mechanical switch needs the assistance of a L C resonant branch to complete the transfer of the current, and the forced flow changing type hybrid direct current circuit breaker in that the current is forced to realize the transfer through a full bridge module to complete the function of the circuit breaker, so the natural flow changing type hybrid direct current circuit breaker provided by the application is a novel hybrid direct current circuit breaker.

Compared with the L C resonant mechanical DC circuit breaker and the forced commutation type hybrid DC circuit breaker, the natural commutation type hybrid DC circuit breaker of the invention also has the following advantages:

(1) small occupied area and low manufacturing cost. Compared with the scheme of the forced commutation type hybrid direct current breaker (such as an ABB breaker, a union institute auxiliary switch forced commutation type hybrid direct current breaker and a coupling negative pressure forced commutation type hybrid direct current breaker), the natural commutation type hybrid direct current breaker reduces forced commutation components, and further can reduce the volume and the manufacturing cost of the direct current breaker.

(2) The reliability is high. Compared with a mechanical circuit breaker, the natural commutation type hybrid direct current circuit breaker has short arcing time, so that the natural commutation type hybrid direct current circuit breaker has the advantages of prolonged service life and improved reliability; compared with a forced current conversion type hybrid direct current circuit breaker, the natural current conversion type hybrid direct current circuit breaker utilizes the fact that the sum of the arc voltages of the vacuum gap quick mechanical switch and the gas gap quick mechanical switch is larger than the conduction voltage drop of the transfer branch circuit, so that fault current is transferred to the transfer branch circuit from the main through-current branch circuit 'naturally', and the current conversion reliability is high.

(3) The controllability is strong. Compared with the existing mixed direct current circuit breaker, the natural current changing type mixed direct current circuit breaker has the advantages of simple current changing process, high reliability of the turn-off current of power electronic devices, definite turn-off time under different currents, strong control capability of the transient energy of the system and easy matching with the control protection of a direct current system.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.