WO2020147572A1 - 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统 - Google Patents

混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统 Download PDF

Info

Publication number
WO2020147572A1
WO2020147572A1 PCT/CN2019/130085 CN2019130085W WO2020147572A1 WO 2020147572 A1 WO2020147572 A1 WO 2020147572A1 CN 2019130085 W CN2019130085 W CN 2019130085W WO 2020147572 A1 WO2020147572 A1 WO 2020147572A1
Authority
WO
WIPO (PCT)
Prior art keywords
fault
hybrid
circuit breaker
circuit
wavelet transform
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/CN2019/130085
Other languages
English (en)
French (fr)
Inventor
邹贵彬
张烁
魏秀燕
高厚磊
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Shandong University
Original Assignee
Shandong University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Shandong University filed Critical Shandong University
Publication of WO2020147572A1 publication Critical patent/WO2020147572A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/36—Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the invention relates to the technical field of line fault recovery of a flexible DC power grid, and in particular to an auxiliary circuit of a hybrid DC circuit breaker, a method and system for identifying fault properties of a multi-terminal flexible DC power grid.
  • the multi-terminal flexible DC grid based on overhead lines has outstanding advantages in large-scale clean energy generation and grid connection and large-capacity transmission. It is an important supplement to the AC grid and is currently under construction.
  • the Zhangbei project is a four-terminal flexible DC grid that transmits power through overhead lines.
  • the current fault isolation methods of flexible DC systems are mainly based on AC circuit breakers, fault self-clearing converters and DC circuit breakers.
  • the fault isolation scheme based on DC circuit breaker is considered to be the best solution to deal with multi-terminal DC grid DC line faults.
  • Hybrid DC circuit breaker is a relatively mature topology for engineering applications.
  • the DC circuit breaker used in Zhangbei project is 500kV Hybrid DC circuit breaker.
  • the AC overhead line in the AC system generally needs to be equipped with reclosing technology.
  • the method of reclosing the AC circuit breaker after a short delay after the fault can be used to clear the transient fault and shorten the power supply.
  • the recovery time greatly improves the reliability of power supply.
  • the probability of successful reclosing of overhead line reclosing in AC systems is 60% to 90%, and as the voltage level increases, the recombination power also increases substantially. Therefore, the reclosing technology can greatly improve the AC system's ability to respond to line faults, and the technology can also be applied to flexible DC grids that transmit electricity through overhead lines.
  • the reclosing technology also has certain disadvantages.
  • the circuit breaker may coincide with a permanent fault when it recloses, the power system will suffer two consecutive fault shocks in a short period of time, which will reduce the insulation of electrical equipment and reduce its service life.
  • the damage caused by continuous fault impact is far greater than the AC system. Therefore, in order to avoid coincidence in permanent faults and to provide a basis for DC circuit breaker whether to perform coincidence or not, it is of great significance to study the identification methods of fault properties suitable for flexible DC power grids.
  • the AC system mainly uses the recovery voltage generated by the coupling between the fault removal phase and the healthy phase to identify instantaneous and permanent faults. Since there is no coupling relationship between the pole lines after the fault removal of the flexible DC grid, this method is not applicable to the flexible DC system.
  • the present invention proposes an auxiliary circuit of a hybrid DC circuit breaker, a method and system for identifying fault properties of a multi-terminal flexible DC grid.
  • the auxiliary circuit of the hybrid DC circuit breaker injects characteristic signals into the DC line to achieve DC line failure. Nature discrimination.
  • the energy stored in the buffer capacitor of the IGBT sub-module after the hybrid DC circuit breaker cuts off the fault current can be used to determine the nature of the fault.
  • the additional cost of hardware is small, the control is simple, and it has permanent fault detection. Distance function. It is of great significance to improve the power supply reliability of DC overhead lines and avoid secondary shocks caused by overlapping permanent faults.
  • the auxiliary circuit is added to the Nc IGBT submodules on the side of the hybrid DC circuit breaker transfer branch close to the overhead line; the auxiliary circuit
  • the circuit includes: a thyristor, a resistor R g, and a fast mechanical switch.
  • the thyristor is respectively connected in series between the overhead line and the negative electrode of the buffer capacitor of the buffer circuit of the first IGBT submodule and between the buffer capacitors of the buffer circuits of two adjacent IGBT submodules.
  • the positive electrode of the buffer capacitor of the buffer circuit of the Ncth IGBT sub-module is connected in series with a resistance and a fast mechanical switch before being grounded; among them, Nc is the set value.
  • N c is taken as 10%-20% of the total number N of the transfer branch IGBT sub-modules.
  • a multi-terminal flexible DC grid fault identification system configured with a hybrid DC circuit breaker disclosed in one or more embodiments includes the above-mentioned auxiliary circuit of the hybrid DC circuit breaker, which will be stored in the converter branch IGBT sub-module The energy in the snubber capacitor of the snubber circuit is used as a characteristic signal injection source to detect the fault nature of the DC line.
  • the fault distance is calculated according to the obtained first and second wavelet transform modulus maximum sampling moments that satisfy the data validity condition.
  • wavelet transform modulus maximum that satisfies the data validity condition is specifically:
  • the setting value WTMM set is determined according to the maximum value of the wavelet transform modulus maximum value that can be caused by noise.
  • a multi-terminal flexible DC power grid fault identification system configured with a hybrid DC circuit breaker includes a server.
  • the server includes a memory, a processor, and is stored on the memory and can be stored on the processor.
  • a running computer program when the processor executes the program, the above-mentioned method for identifying the nature of a fault in a multi-terminal flexible DC power grid equipped with a hybrid DC circuit breaker is realized.
  • a computer-readable storage medium disclosed in one or more embodiments has a computer program stored thereon, and when the program is executed by a processor, the above-mentioned multi-terminal flexible DC power grid fault identification method configured with a hybrid DC circuit breaker is executed .
  • the fault identification method is based on the polarity of the current reflected wave, which has absolute selectivity
  • the principle of the identification method is simple and clear, the identification is accurate, easy to implement in engineering, the additional cost of auxiliary circuit is small, and the accuracy of permanent fault location can be achieved by increasing the sampling rate, which has high practical value.
  • Figure 1 is a schematic diagram of the structure of the hybrid DC circuit breaker in the first embodiment
  • FIG. 2 is a schematic diagram of the structure of a diode full-bridge IGBT sub-module in the first embodiment
  • FIG. 3 is a schematic diagram of the charging and discharging path of the buffer capacitor of the IGBT sub-module in the first embodiment
  • Figure 4 (a)-(b) are the transient current and voltage waveforms of each branch of the hybrid DC circuit breaker in the first embodiment
  • Figure 5 (a)-(b) are the transient current waveforms of the hybrid DC circuit breaker in the first embodiment and the second commutation process;
  • FIG. 6 is a schematic diagram of the auxiliary circuit structure of the hybrid DC circuit breaker in the first embodiment
  • FIG. 7 is a schematic diagram of the discharge path of the buffer capacitors of N c IGBT sub-modules in the second embodiment
  • Fig. 9 is a grid diagram of current traveling wave refracted reflection in the second embodiment.
  • Figure 10 is a flowchart of a method for identifying the nature of a fault in the second embodiment
  • Figure 11 is a simulation model of the dual-terminal MMC-HVDC system in the second embodiment
  • Figure 12 is a configuration diagram of a DC overhead line in the second embodiment
  • Figure 13(a)-(b) are respectively the DCCB1 transient current and wavelet transform modulus maximum waveform under permanent fault in the second embodiment
  • Figure 14(a)-(b) are respectively the DCCB1 transient current and wavelet transform modulus maximum waveform under transient fault in the second embodiment
  • Figure 15(a)-(b) are the identification results of the fault nature at different fault locations in the second embodiment
  • Figure 16(a)-(b) are respectively the DCCB1 transient current and wavelet transform modulus maximum waveform under the permanent inter-electrode short-circuit fault in the second embodiment;
  • Figures 17(a)-(b) respectively show the DCCB1 transient current and wavelet transform modulus maximum waveforms under permanent faults with different transition resistances in the second embodiment.
  • an auxiliary circuit of a hybrid DC circuit breaker is disclosed. As shown in FIG. 6, the auxiliary circuit is added to the Nc IGBT sub-modules on the side of the overhead line near the transfer branch of the hybrid DC circuit breaker.
  • the auxiliary circuit includes: a thyristor, a resistor Rg and a fast mechanical switch, the thyristor is respectively connected in series between the overhead line and the buffer capacitor negative electrode of the first IGBT sub-module buffer circuit and the buffer capacitors of two adjacent IGBT sub-module buffer circuits In between, the positive electrode of the buffer capacitor of the buffer circuit of the Nc-th IGBT sub-module is connected in series with a resistance and a fast mechanical switch before being grounded; where Nc is the set value.
  • the hybrid DC circuit breaker is composed of the main branch, the transfer branch and the metal oxide varistor (MOV), as shown in Figure 1.
  • the main branch routing is composed of IGBT-based load current switches (LCS) and ultra-high-speed mechanical switches in series, and LCS is mainly composed of IGBT sub-modules in series and parallel.
  • the transfer branch is composed of many IGBT sub-modules in series (usually hundreds in high-voltage and large-capacity application scenarios), and is divided into several groups, each group is connected with a MOV in parallel, and the MOV is used to absorb the residual energy in the fault circuit.
  • the IGBT sub-modules in the transfer branch mainly have IGBT full-bridge, diode full-bridge, co-emission, collector series and other structures.
  • R s represents the snubber resistance
  • C s represents the snubber capacitor
  • D s represents the diode.
  • the voltage on the snubber capacitor and the IGBT is mainly determined by the external circuit, and since the snubber capacitor has no discharge circuit when the IGBT is off, the voltage on the snubber capacitor can still maintain a high level when the external circuit voltage drops .
  • the IGBT is switched from the off state to the on state, the snubber capacitor in the snubber circuit will discharge through the snubber resistor.
  • the charging and discharging path of the diode full-bridge IGBT sub-module is shown in Figure 3.
  • the load current When the DC transmission system is operating normally, the load current all passes through the main branch of the hybrid DC circuit breaker. Since the main branch mainly contains mechanical switches and a small amount of IGBT sub-modules in the load current switch, the loss is small, usually 0.01% The delivery capacity.
  • the fault current is commutated from the main branch to the transfer branch by blocking the IGBT sub-module in the LCS, and the ultra-high-speed mechanical switch is disconnected when the fault current in the main branch weakens to the off-condition of the ultra-high-speed mechanical switch , At this time the fault current has all been commutated to the transfer branch.
  • the transfer branch IGBT sub-module starts to block the current, the current is commutated to the MOV branch, and the second commutation starts; the second commutation is completed at t 4 , and then the current is at The MOV begins to drop; the current drops to zero at t 5 , the hybrid DC circuit breaker is completed, and the fault current is cleared.
  • the first detailed commutation process in the time period t 1 -t 2 is that the fault current is firstly commutated from the main branch IGBT to the main branch snubber capacitor, and then from The snubber capacitor of the main branch commutates to the transfer branch IGBT.
  • the fault current is first commutated from the transfer branch IGBT to the transfer branch buffer capacitor, and then from the transfer branch buffer capacitor to the MOV.
  • the transient current waveform during the two commutation processes is shown in Figure 5.
  • the energy stored in the snubber capacitor has not disappeared. Therefore, by adding an auxiliary circuit, the energy of the snubber capacitor stored in the IGBT sub-module of the converter branch can be used as a characteristic signal injection source. Detect the nature of the fault in the DC line.
  • the auxiliary circuit of the hybrid DC circuit breaker for identifying the nature of the fault is shown in Figure 6.
  • the auxiliary circuit mainly includes a thyristor, a resistance R g and a fast mechanical switch.
  • the auxiliary circuit is added to the N c IGBT sub-modules near the line side of the transfer branch of the hybrid DC circuit breaker, where N c is recommended to be taken as 10%-20% of the total number N of the transfer branch IGBT sub-modules.
  • the number of N c can affect the intensity of the injected signal.
  • the auxiliary circuit includes a thyristor, a resistor R g and a fast mechanical switch.
  • the structure is shown in Figure 6;
  • trigger signals are first applied to all the thyristors in the auxiliary circuit, and then the fast mechanical switch in the auxiliary circuit is closed;
  • step (3) Perform wavelet transform on the current data collected in step (3) to calculate the first-scale wavelet transform modulus maximum; specifically:
  • a 0 (k) is the original signal
  • h 0 , h 1 are low-pass and high-pass filters respectively
  • a j (k), d j (k) are the j-th layer smoothing approximation coefficient and detail coefficient of the original signal , Respectively represent the signal components of frequency bands 0 ⁇ f s /2 j+1 and f s /2 j+1 ⁇ f s /2 j extracted from the original signal with sampling rate f s ;
  • Wavelet transform modulus maximum value d j (k n ) is defined as:
  • d j (k) is the smooth detail coefficient of the j-th layer of the original signal.
  • step (4) Perform a data validity check on the wavelet transform modulus maximum value obtained in step (4), and record the first and second wavelet transform modulus maximum value symbols and sampling times that meet the data validity conditions; specifically :
  • the setting value WTMM set is determined according to the maximum value of the wavelet transform modulus maximum value that can be caused by noise.
  • step (6) If step (6) is identified as a transient fault, turn on the fast mechanical switch in the auxiliary circuit and remove the trigger signal of the thyristor, and then the hybrid DC circuit breaker will reclose. If step (6) is identified as a permanent fault, the fast mechanical switch in the auxiliary circuit is opened and the trigger signal of the thyristor is removed, and the hybrid DC circuit breaker does not reclose. At the same time, the fault distance is calculated according to the first and second wavelet transform modulus maximum sampling moments obtained in step (5).
  • step (6) the principle of identifying the nature of the fault is:
  • the fast mechanical switch is closed and the snubber capacitors of the N c IGBT sub-modules on the line side of the transfer branch are discharged to identify the nature of the fault.
  • the hybrid DC circuit breaker After the hybrid DC circuit breaker cuts off the fault current, after 200 milliseconds of fault point arcing time, a trigger signal is applied to the thyristor in the auxiliary circuit, and then the fast mechanical switch is closed. At this time, the DC bus voltage will be evenly distributed to the NN c IGBT sub-modules near the bus side in the transfer branch of the hybrid DC circuit breaker, so the voltage of the NN c IGBT sub-modules will rise to a new steady-state voltage.
  • N c U c and C s /N c are the equivalent voltage and equivalent snubber capacitance of N c IGBT sub-modules respectively, and Z c is the wave impedance of the DC line.
  • the on-state resistance of the thyristor is very Is small, so ignore it.
  • Closing the fast mechanical switch after the thyristor is triggered is equivalent to superimposing a step input with an amplitude of N c U c . Under the action of this step input, a current traveling wave propagating from the hybrid DC circuit breaker to the opposite end of the line will be generated.
  • the initial current traveling wave is as follows:
  • ⁇ I(s) and ⁇ i(t) are the frequency domain and time domain expressions of the initial current traveling wave, respectively.
  • the amplitude of the initial current traveling wave can be changed by changing the resistance of the resistor R g .
  • Figure 9 shows the refraction and reflection grid of the current traveling wave. Refraction and reflection occur when the current traveling wave propagates to the discontinuous wave impedance. Regardless of the line attenuation, the first reflected wave of the initial current traveling wave is as follows:
  • ⁇ is the reflection coefficient of the current traveling wave, which can be obtained by the following formula:
  • Z 2 is the equivalent characteristic impedance of the part where the current traveling wave will enter
  • Z c is the wave impedance of the line.
  • the first reflected wave of the initial current traveling wave detected by the relay is the reflected wave at the fault point. Since the reflection coefficient of the current traveling wave at the fault point is positive, the first reflection is The wave has the same polarity as the initial current traveling wave. Otherwise, the first reflected wave of the initial current traveling wave detected by the relay is the line opposite end reflection wave, and the line opposite end current traveling wave reflection coefficient is negative, so the first reflection wave has the opposite polarity to the initial current traveling wave.
  • step (7) when it is determined that a permanent fault has occurred, the fault distance calculation method is:
  • v is the propagation speed of the current traveling wave
  • t f is the detected initial current traveling wave moment
  • t s is the arrival time of the first reflected wave. If the DC line fault has disappeared after 200 milliseconds of dissociation time, t s is the arrival time of the reflected wave at the opposite end of the line, and l m is equal to the line length at this time. The arrival time of the reflected wave can be accurately obtained by the corresponding time of the wavelet transform modulus maximum.
  • the calculation accuracy of the above formula is related to the sampling rate. If the sampling rate is f, the maximum ranging error l error of the above formula is:
  • the present invention builds a ⁇ 500kV double-ended flexible straight system simulation model shown in FIG. 11 in the PSCAD/EMTDC software.
  • the converter station in Figure 11 has a symmetrical bipolar structure, and each converter station contains two MMCs.
  • the main parameters of the converter station are shown in Table 1.
  • the DC overhead line adopts a distributed frequency-dependent model, and its length is 262km, and its configuration is shown in Figure 12.
  • the main parameters of the hybrid DC circuit breaker are shown in Table 2.
  • the propagation speed of the current traveling wave can be obtained as 298.41 m/microsecond, and the wave impedance of the DC line is 325 ⁇ .
  • the sampling frequency of the DC circuit breaker port relay is 100kHz, so according to formula (7), the maximum error of fault location can be obtained as 1.492km.
  • N c is taken as 10% of the total number of IGBT sub-modules of the transfer branch, which is 30. Therefore, according to the schematic diagram of the auxiliary circuit structure shown in FIG. 6, the required number of thyristors is also 30.
  • the resistance R g is taken as 80 ⁇ .
  • WTMM set is set to 0.005.
  • the fault duration is 200 ms
  • the transition resistance is 50 ⁇ .
  • the identification of the nature of the fault starts 200 milliseconds after the hybrid DC circuit breaker cuts off the fault current.
  • the relevant waveforms are shown in Figure 14 (a) and Figure 14 (b).
  • the line fault is a transient fault
  • the fault nature is identified, the fault has disappeared.
  • the first reflected current traveling wave detected by the outlet relay of the DC circuit breaker is reflected by the opposite end of the line instead of the fault point.
  • the first and second wavelet transform modulus maxima that meet the data validity conditions have different signs. Therefore, the fault identification result is a transient fault.
  • the DC circuit breaker can be reclosed.
  • the influencing factors considered in this section are fault location, fault distance, and fault type.
  • a positive electrode disposed permanent ground fault on the dc line from the converter station S 1 to 26.2km (10% line length) of each interval, the transition resistance 50 ⁇ .
  • the identification of the nature of the fault starts 200 milliseconds after the DC circuit breaker cuts off the fault current.
  • the relevant waveforms are shown in Figure 15(a) and Figure 15(b).
  • the first and second wavelet transform modulus maxima that meet the data validity conditions are both negative, so the fault identification method determines that the fault is permanent malfunction.
  • the fault location result is 99.067km, and the error is only 0.033km.
  • the result is the same as the fault location result of the positive ground fault at the same fault location. Therefore, the fault type has almost no influence on the identification results of the fault nature identification method.
  • ⁇ is the reflection coefficient of the current traveling wave at the fault point, which can be approximately regarded as a constant.
  • the invention realizes the identification of the nature of the fault by arranging auxiliary circuits for the hybrid DC circuit breaker, and using the hybrid DC circuit breaker to cut off the fault current to transfer the energy stored in the buffer capacitor of the branch circuit.
  • First apply the trigger signal to the thyristor in the auxiliary circuit then close the fast mechanical switch, use the current data collected at the exit of the hybrid DC circuit breaker and perform wavelet transformation to obtain the first scale of the current traveling wave that satisfies the data validity condition.
  • One and the second wavelet transform modulus maximum value and then identify the instantaneous and permanent faults through its polarity, and calculate the fault distance of the permanent fault after the permanent fault is judged.
  • Simulation analysis shows that under various fault conditions, the present invention can correctly identify transient faults and permanent faults, with high sensitivity and strong reliability.
  • the invention can also realize permanent fault location, with small ranging error and high accuracy.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Locating Faults (AREA)
  • Driving Mechanisms And Operating Circuits Of Arc-Extinguishing High-Tension Switches (AREA)

Abstract

一种混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统，所述辅助电路添加在混合式直流断路器转移支路靠近架空线路侧的Nc个IGBT子模块上；所述辅助电路包括：晶闸管、电阻R g以及快速机械开关，所述晶闸管分别串联在架空线路与第一个IGBT子模块缓冲电路的缓冲电容负极之间以及相邻两个IGBT子模块缓冲电路的缓冲电容之间，第Nc个IGBT子模块缓冲电路的缓冲电容正极依次串联电阻和快速机械开关后接地；其中，Nc为设定值。利用混合式直流断路器辅助电路实现特征信号的注入从而识别瞬时性以及永久性故障，并且可以实现永久性故障的故障测距。

Description

混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统 技术领域
本发明涉及柔性直流电网线路故障恢复技术领域，尤其涉及混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统。
背景技术
本部分的陈述仅仅是提供了与本发明相关的背景技术信息，不必然构成在先技术。
随着直流断路器的发展以及现代电网对于运行灵活性的要求，基于架空线路的多端柔性直流电网在大型清洁能源发电并网、大容量输电方面优势突出，是交流电网的重要补充，目前在建的张北工程便是通过架空线路输电的四端柔性直流电网。
发明人发现，相比于直流电缆，架空线由于暴露在空气中因此故障概率较高。据统计，电力系统中的大部分故障均发生在架空线。目前柔性直流系统的故障隔离方法主要为基于交流断路器，故障自清除换流器以及直流断路器的方法。基于直流断路器的故障隔离方案被认为是处理多端直流电网直流线路故障的最佳方案，而混合式直流断路器是目前工程应用较为成熟的拓扑，张北工程所采用的直流断路器便是500kV混合式直流断路器。
由于架空线故障大多为瞬时性故障，因此在交流系统中交流架空线一般要配置重合闸技术，利用故障后经短暂延时再重合交流断路器的方法可以实现瞬时性故障的清除，缩短了供电恢复时间，极大的提高了供电可靠性。据统计，交流系统中架空线重合闸重合成功的概率为60％～90％，并且随着电压等级的提高，重合成功率也大幅增加。因此，重合闸技术可以极大地提高交流系统对于线路故障的应对能力，并且该技术可同样的应用于通过架空线输电的柔性直流电网。但是，重合闸技术也存在一定的缺点。由于断路器重合时可能重合于永久性故障，此时会导致电力系统在较短的时间内连续遭受两次故障冲击，会降低电气设备绝缘、减少其使用寿命。对于柔性直流电网来说，由于柔性直流电网的低阻抗特性以及电力电子器件的脆弱性，连续遭受故障冲击带来的危害要远大于交流系统。因此，为避免重合于永久性故障，为直流断路器是否进行重合提供依据，研究适用于柔性直流电网的故障性质识别方法具有重要意义。
目前交流系统主要利用故障切除相与健全相之间由于耦合作用而产生的恢复电压进行瞬时性与永久性故障的识别。由于柔性直流电网故障切除后极线之间并无耦合关系，因此该方法对于柔性直流系统不适用。
发明内容
为了解决上述问题，本发明提出了一种混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统，通过混合式直流断路器辅助电路向直流线路注入特征信号从而实现直流线路故障性质判别。通过在混合式直流断路器中增加辅助电路，利用混合式直流断路器切断故障电流后IGBT子模块缓冲电容中储存的能量实现故障性质判别，硬件附加成本小，控制简单，并且具有永久性故障测距功能。对提高直流架空线路的供电可靠性和避免重合于永久性故障导致的二次冲击具有重要意义。
为了实现上述目的，本发明采用如下技术方案：
在一个或多个实施方式中公开的一种混合式直流断路器的辅助电路，所述辅助电路添加在混合式直流断路器转移支路靠近架空线路侧的Nc个IGBT子模块上；所述辅助电路包括：晶闸管、电阻R g以及快速机械开关，所述晶闸管分别串联在架空线路与第一个IGBT子模块缓冲电路的缓冲电容负极之间以及相邻两个IGBT子模块缓冲电路的缓冲电容之间，第Nc个IGBT子模块缓冲电路的缓冲电容正极依次串联电阻和快速机械开关后接地；其中，Nc为设定值。
进一步地，所述N c取为转移支路IGBT子模块总数N的10％-20％。
在一个或多个实施方式中公开的一种配置混合式直流断路器的多端柔性直流电网故障性质识别系统，包括上述的混合式直流断路器的辅助电路，将储存在换流支路IGBT子模块缓冲电路的缓冲电容中的能量作为特征信号注入源，检测直流线路的故障性质。
在一个或多个实施方式中公开的一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，该方法基于上述的辅助电路，具体包括：
混合式直流断路器切除故障电流后，经过设定时间的故障点电弧去游离时间，为辅助电路中所有的晶闸管施加触发信号，闭合辅助电路中的快速机械开关；
实时采集混合式直流断路器线路侧的电流数据；
对采集到的电流数据进行小波变换，计算第一尺度小波变换模极大值；
对得到的小波变换模极大值进行数据有效性检验，记录第一个以及第二个满足数据有效性条件的小波变换模极大值的符号和采样时刻；
建立故障性质识别判据，利用计算得到的小波变换模极大值符号进行瞬时性故障与永久性故障的识别。
进一步地，如果识别为瞬时性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，混合式直流断路器进行重合闸；如果识别为永久性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，混合式直流断路器不再进行重合。
进一步地，根据获得的第一个以及第二个满足数据有效性条件的小波变换模极大值采样时刻计算故障距离。
进一步地，所述满足数据有效性条件的小波变换模极大值具体为：
设定整定值WTMM set，取小波变换模极大值的绝对值大于所述整定值的数据为满足数据有效性条件的小波变换模极大值；
其中，整定值WTMM set根据噪声所能引起的小波变换模极大值的最大值确定。
进一步地，建立故障性质识别判据，具体为：
定义第一尺度满足数据有效性条件的第一个以及第二个小波变换模极大值为WTMM f、WTMM s，若满足：
WTMM f·WTMM s>0；
则判定为永久性故障，否则判定为瞬时性故障。
在一个或多个实施方式中公开的一种配置混合式直流断路器的多端柔性直流电网故障性质识别系统，包括服务器，所述服务器包括存储器、处理器及存储在存储器上并可在处理器上运行的计算机程序，所述处理器执行所述程序时实现上述的配置混合式直流断路器的多端柔性直流电网故障性质识别方法。
在一个或多个实施方式中公开的一种计算机可读存储介质，其上存储有计算机程序，该程序被处理器执行时执行上述的配置混合式直流断路器的多端柔性直流电网故障性质识别方法。
与现有技术相比，本发明的有益效果是：
(1)利用混合式直流断路器辅助电路实现特征信号的注入从而识别瞬时性以及永久性故障，并且可以实现永久性故障的故障测距；
(2)在各种故障初始条件下可靠、快速地识别瞬时性以及永久性故障，过渡电阻、故障位置、故障类型等因素对故障性质识别结果几乎没有影响，可靠性、灵敏性高；
(3)故障性质识别方法通过电流反射波的极性进行识别，具有绝对的选择性；
(4)识别方法原理简单、清楚，识别准确，易于工程实现，辅助电路附加成本小，且永久性故障测距的精度可通过提高采样率实现，具有较高的实用价值。
附图说明
构成本申请的一部分的说明书附图用来提供对本申请的进一步理解，本申请的示例性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。
图1为实施例一中混合式直流断路器结构示意图；
图2为实施例一中二极管全桥式IGBT子模块结构示意图；
图3为实施例一中IGBT子模块缓冲电容充放电路径示意图；
图4(a)-(b)分别为实施例一中混合式直流断路器暂态各支路电流和电压波形；
图5(a)-(b)分别为实施例一中混合式直流断路器第一次以及第二次换流过程暂态电流波形；
图6为实施例一中混合式直流断路器辅助电路结构示意图；
图7为实施例二中N c个IGBT子模块缓冲电容放电路径示意图；
图8为实施例二中N c个IGBT子模块缓冲电容放电过程等效电路；
图9为实施例二中电流行波折反射网格图；
图10为实施例二中故障性质识别方法流程图；
图11为实施例二中双端MMC-HVDC系统仿真模型；
图12为实施例二中直流架空线配置图；
图13(a)-(b)分别为实施例二中永久性故障下DCCB1暂态电流以及小波变换模极大值波形；
图14(a)-(b)分别为实施例二中瞬时性故障下DCCB1暂态电流以及小波变换模极大值波形；
图15(a)-(b)分别为实施例二中不同故障位置下故障性质识别结果；
图16(a)-(b)分别为实施例二中永久性极间短路故障下DCCB1暂态电流以及小波变换模极大值波形；
图17(a)-(b)分别为实施例二中不同过渡电阻永久性故障下DCCB1暂态电流以及小波变换模极大值波形。
具体实施方式
应该指出，以下详细说明都是示例性的，旨在对本申请提供进一步的说明。除非另有指明，本发明使用的所有技术和科学术语具有与本申请所属技术领域的普通技术人员通常理解的相同含义。
需要注意的是，这里所使用的术语仅是为了描述具体实施方式，而非意图限制根据本申请的示例性实施方式。如在这里所使用的，除非上下文另外明确指出，否则单数形式也意图包括复数形式，此外，还应当理解的是，当在本说明书中使用术语“包含”和/或“包括”时，其指明存在特征、步骤、操作、器件、组件和/或它们的组合。
实施例一
在一个或多个实施方式中公开了一种混合式直流断路器的辅助电路，如图6所示，辅助电路添加在混合式直流断路器转移支路靠近架空线路侧的Nc个IGBT子模块上；辅助电路包括：晶闸管、电阻Rg以及快速机械开关，所述晶闸管分别串联在架空线路与第一个IGBT子模块缓冲电路的缓冲电容负极之间以及相邻两个IGBT子模块缓冲电路的缓冲电容之间，第Nc个IGBT子模块缓冲电路的缓冲电容正极依次串联电阻和快速机械开关后接地；其中，Nc为设定值。
混合式直流断路器由主支路、转移支路以及金属氧化物压敏电阻(MOV)三部分组成，如图1所示。主支路由基于IGBT的负载电流开关(LCS)以及超高速机械开关串联构成，LCS主要由IGBT子模块相互串并联构成。转移支路由许多IGBT子模块串联构成(在高压、大容量应用场景下通常为数百个)，并且被划分为几组，每组并联有一个MOV，MOV用来吸收故障回路中的残存能量。转移支路中的IGBT子模块主要有IGBT全桥型、二极管全桥型、共发射、集电极串联型等结构，这几种结构都是组合利用了IGBT电流转移能力以及电容电流缓冲能力实现断路器内部成功换流。由于二极管全桥型成本较低，因此在高压大容量场合多采用二极管全桥型IGBT子模块，其结构如图2所示。
图2中R s表示缓冲电阻，C s表示缓冲电容，D s表示二极管，上述三种元件共同构成了IGBT子模块中的缓冲电路。当IGBT由开通转为关断状态时，IGBT中流过的电流转移到子模块缓冲电容，缓冲电容通过二极管进行充电，在此过程中缓冲电阻被二极管短路。当充电过程结束后缓冲电容以及IGBT上的电压主要由外部电路决定，并且由于在IGBT关断状态下缓冲电容没有放电回路，因此当外部电路电压降低时缓冲电容上的电压仍然能保持较高水平。当IGBT由关断状态切换为导通状态时，缓冲电路中缓冲电容会通过缓冲电阻进行放电。二极管全桥型IGBT子模块充放电路径如图3所示。
当直流输电系统正常运行时，负荷电流全部通过混合式直流断路器的主支路，由于主支路主要包含机械开关以及负载电流开关中少量的IGBT子模块，因此损耗较小，通常为0.01％的输送容量。当故障发生后，通过闭锁LCS中的IGBT子模块将故障电流由主支路换流至转移支路，待主支路中故障电流减弱到超高速机械开关关断条件时断开超高速机械开关，此时故障电流已经全部换流至转移支路。之后闭锁转移支路的IGBT子模块，将故障电流换流至MOV支路，通过MOV消耗掉储存在直流电抗器以及故障回路中的残存能量，从而将故障电流切断。混合式直流断路器分断故障电流时断路器各支路中的电流(i main表示主支路电流，i transfer表示换流支路中的电流，i MOV表示MOV中的电流)以及电压如图4所示。
图4中，t 0时刻发生故障，主支路电流快速上升；t 1时刻流过主支路的故障电流达到最大 可关断电流或者直流断路器接收到跳闸信号，LCS中的IGBT闭锁，故障电流开始换流至转移支路，第一次换流过程开始；t 2时刻第一次换流完成，超高速机械开关开始启动分闸；t 3时刻超高速机械开关分闸完成，此时故障电流已全部换流至转移支路，此时转移支路IGBT子模块开始闭锁电流，电流换流至MOV支路，开始第二次换流；t 4时刻第二次换流完成，之后电流在MOV中开始下降；t 5时刻电流下降至零，混合式直流断路器动作完成，故障电流被清除。
以上过程中，由于IGBT子模块缓冲电容的存在，t 1-t 2时间段内的第一次详细换流过程是故障电流首先由主支路IGBT换流至主支路缓冲电容，之后再由主支路缓冲电容换流至转移支路IGBT。同样，在t 3-t 4时间段进行的第二次换流过程中，故障电流首先由转移支路IGBT换流至转移支路缓冲电容，之后再由转移支路缓冲电容换流至MOV。两次换流过程中暂态电流波形如图5所示。
当混合式直流断路器动作完成后，缓冲电容储存的能量并没有消失，因此通过增加辅助电路，将储存在换流支路IGBT子模块中的缓冲电容的能量作为特征信号注入源，可以用来检测直流线路的故障性质。
用于故障性质识别的混合式直流断路器辅助电路如图6所示，辅助电路主要包括晶闸管、电阻R g以及快速机械开关。辅助电路添加在混合式直流断路器转移支路靠近线路侧的N c个IGBT子模块上，此处N c推荐取为转移支路IGBT子模块总数N的10％-20％。N c的个数能够影响到注入信号的强度大小。
实施例二
基于实施例一中所述的辅助电路，提出一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法及其应用，如图10所示，包括以下步骤：
(1)为混合式直流断路器配置辅助电路，辅助电路包括晶闸管、电阻R g以及快速机械开关，其结构如图6所示；
(2)混合式直流断路器切除故障电流后，经过200毫秒的故障点电弧去游离时间，首先为辅助电路中所有的晶闸管施加触发信号，而后闭合辅助电路中的快速机械开关；
(3)实时采集混合式直流断路器线路侧的电流数据；
(4)将步骤(3)采集到的电流数据进行小波变换，计算第一尺度小波变换模极大值；具体为：
Figure PCTCN2019130085-appb-000001
式中，a 0(k)为原始信号，h 0、h 1分别为低通和高通滤波器；a j(k)、d j(k)为原信号的第j层平滑逼近系数和细节系数，分别代表从采样率为f s的原始信号中提取的频段0～f s/2 j+1和f s/2 j+1～f s/2 j的信号分量；
小波变换模极大值d j(k n)定义为：|d j(k n)|≥|d j(k)|；
其中，d j(k)为原信号的第j层平滑细节系数。
(5)对步骤(4)得到的小波变换模极大值进行数据有效性检验，记录第一个以及第二个满足数据有效性条件的小波变换模极大值的符号和采样时刻；具体为：
设定整定值WTMM set，取小波变换模极大值的绝对值大于所述整定值的数据为有效数据；
式中，整定值WTMM set根据噪声所能引起的小波变换模极大值的最大值确定。
(6)建立故障性质识别判据，利用步骤(5)计算得到的小波变换模极大值符号进行瞬时性故障与永久性故障的识别；
定义第一尺度满足数据有效性条件的第一个以及第二个小波变换模极大值为WTMM f、WTMM s，若满足
WTMM f·WTMM s>0；
则判定为永久性故障，否则判定为瞬时性故障。
(7)若步骤(6)识别为瞬时性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，之后混合式直流断路器进行重合闸。若步骤(6)识别为永久性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，混合式直流断路器不再进行重合。同时，根据步骤(5)获得的第一个及第二个小波变换模极大值采样时刻计算故障距离。
步骤(6)中，故障性质识别原理为：
利用晶闸管施加触发信号后快速机械开关闭合导致转移支路中线路侧N c个IGBT子模块缓冲电容放电为直流线路注入的电流行波的极性识别故障性质。
在混合式直流断路器切断故障电流后，经过200毫秒的故障点电弧去游离时间，对辅助电路中的晶闸管施加触发信号，随后闭合快速机械开关。此时，直流母线电压会平均分配到混合式直流断路器转移支路中靠近母线侧的N-N c个IGBT子模块上，因此N-N c个IGBT子模块的电压会上升到一个新的稳态电压。对于转移支路中靠近线路侧的N c个IGBT子模块，当快速机械开关闭合时，N c个IGBT子模块的缓冲电容会通过晶闸管、电阻R g以及快速机械开关对线路放电，放电路径如图7所示，放电过程的等效电路如图8所示。图8中，N cU c和C s/N c分别是N c个IGBT子模块的等效电压和等效缓冲电容，Z c是直流线路的波阻抗，晶闸管的通 态电阻由于阻值很小，因此将其忽略。
晶闸管触发后闭合快速机械开关相当于叠加一个幅值为N cU c的阶跃输入。在此阶跃输入的作用下，将产生由混合式直流断路器向线路对端传播的电流行波。初始电流行波如下式所示：
Figure PCTCN2019130085-appb-000002
Figure PCTCN2019130085-appb-000003
式中，ΔI(s)和Δi(t)分别为初始电流行波的频域和时域表达式。通过改变电阻R g的阻值可以改变初始电流行波的幅值。
电流行波传播过程中的折反射网格图如图9所示。电流行波传播到波阻抗不连续处会发生折反射。不考虑线路衰减，初始电流行波的第一个反射波如下式所示：
ΔI r＝ΓΔI     (3)
式中，Г为电流行波的反射系数，可以通过下式得到：
Figure PCTCN2019130085-appb-000004
式中，Z 2为电流行波将要进入部分的等效特征阻抗，Z c为线路的波阻抗。
假设故障点处过渡电阻为R f，则故障点处的电流行波反射系数Г f为：
Figure PCTCN2019130085-appb-000005
由上式可以看出，无论过渡电阻为何值，Z 2均小于Z c。因此，故障点电流行波的反射系数Г f总大于零。
对于线路对端的电流行波反射系数Г t，由于直流线路被隔离，即线路对端开路，此时Z 2为无穷大，因此对端线路端口的电流行波反射系数Г t近似为-1。
根据以上分析，可以得出结论：
快速机械开关闭合后，若直流断路器线路侧检测到的初始电流行波与初始电流行波的第一个反射波极性相同，则说明故障仍然存在于线路上，否则说明故障已经消失。因为若闭合快速机械开关时故障仍然存在，则继电器检测到的初始电流行波的第一个反射波为故障点反射波，由于故障点处的电流行波反射系数为正，因此第一个反射波与初始电流行波的极性相 同。否则继电器检测到的初始电流行波的第一个反射波为线路对端反射波，线路对端电流行波反射系数为负，因此第一个反射波与初始电流行波的极性相反。
因此，基于以上结论可以判断直流线路上发生的故障为瞬时性故障还是永久性故障。
步骤(7)中，当判定发生永久性故障时，故障距离计算方法为：
由图9可以看出，故障距离可以利用下式计算：
Figure PCTCN2019130085-appb-000006
式中，v是电流行波的传播速度，t f是检测到的初始电流行波时刻，t s是第一个反射波的到达时间。如果经过200毫秒的去游离时间后直流线路故障已经消失，则t s为线路对端的反射波的到达时刻，此时l m等于线路长度。反射波的到达时间可以通过小波变换模极大值的对应时刻精确获得。
上式的计算精度与采样率有关，如果采样率为f，则上式的最大测距误差l error为：
Figure PCTCN2019130085-appb-000007
利用PSCAD构建双端MMC-HVDC柔性直流系统仿真模型，对所提故障性质识别方法进行仿真验证：
1)建立模型
本发明依据张北柔性直流示范工程的相关参数，在PSCAD/EMTDC软件中搭建了如图11所示的±500kV双端柔直系统仿真模型。图11中换流站为对称双极结构，每个换流站包含两个MMC，换流站的主要参数示于表1。仿真模型中直流架空线采用分布依频模型，其长度为262km，其配置如图12所示。
表1换流站主要参数
Figure PCTCN2019130085-appb-000008
混合式直流断路器的主要参数示于表2。根据PSCAD/EMTDC软件的线路参数程序，可以得到电流行波的传播速度为298.41米/微秒，直流线路的波阻抗为325Ω。直流断路器端口继电器的采样频率为100kHz，因此根据式(7)可得故障测距的最大误差为1.492km。在仿真模型中，N c取为转移支路IGBT子模块总数的10％，即30。因此根据图6所示的辅助电路结构示意图可知，晶闸管的需求数量同样为30个。为了将直流断路器出口故障的初始电流行波幅值限制在1kA以内，电阻R g取为80Ω。
表2混合式直流断路器主要参数
Figure PCTCN2019130085-appb-000009
由于瞬时性故障持续时间通常小于200毫秒，因此在DCCB中断故障电流后，故障性质识别在200毫秒时启动。为避免噪声干扰，WTMM set设置为0.005。
2)永久性故障仿真
在距离换流站S 1100km处设置永久性正极接地故障，过渡电阻为50Ω。故障性质识别在混合式直流断路器切除故障电流后的200毫秒开始进行，检测到的电流及其小波变换模极大值如图13(a)-(b)所示。
由图13(a)和图13(b)可知，第一个以及第二个满足数据有效性条件的小波变换模极大值均为负极性，因此判断该故障为永久性故障，此时直流断路器不再进行重合。此外，经计算得到的故障距离为99.967km，与实际故障距离误差仅为0.033km。
3)瞬时性故障仿真
在距离换流站S 1100km处设置瞬时性正极接地故障，故障持续时间为200毫秒，过渡电阻为50Ω。故障性质识别在混合式直流断路器切除故障电流后的200毫秒开始进行，相关波形如图14(a)和图14(b)所示。
由于线路故障为瞬时性故障，因此当进行故障性质识别时，故障已经消失，直流断路器出口继电器检测到的第一个反射电流行波是由线路对端反射而非故障点反射。如图14(a)和图14(b)所示，满足数据有效性条件的第一个和第二个小波变换模极大值具有不同的符号，因此，故障性质识别结果为瞬时性故障，直流断路器可以进行重合。
4)影响因素分析
本部分考虑的影响因素为故障位置、故障距离以及故障类型等。
A.不同故障位置。在直流线路上距离换流站S 1以26.2km(10％线路长度)为间隔分别设置永久性正极接地故障，过渡电阻为50Ω。故障性质识别于直流断路器切断故障电流后200毫秒开始，相关波形如图15(a)和图15(b)所示。
由图15(a)和图15(b)可知，第一个和第二个满足数据有效性条件的小波变换模极大值具有相同的符号，因此判定线路上发生的故障为永久性故障，因此故障性质识别结果正确，并且故障测距的最大误差为0.3％，能够满足工程需要。因此，故障位置不会影响故障性质识别方法的判别结果。
B.不同故障类型。在距离换流站S 1100km处设置永久性极间短路故障，故障电阻为50Ω。故障性质识别在混合式直流断路器切除故障电流后的200毫秒开始进行，结果如图16(a)和图16(b)所示。
如图16(a)和图16(b)所示，第一个及第二个满足数据有效性条件的小波变换模极大值均为负，因此故障性质识别方法判定发生的故障为永久性故障。故障测距结果为99.067km，误差仅为0.033km，该结果与相同故障位置发生的正极接地故障的故障测距结果相同。因此，故障类型对于故障性质识别方法的判别结果几乎没有影响。
C.不同过渡电阻。在距离换流站S 1100km处设置永久性正极接地故障，过渡电阻分别为0.01Ω、50Ω、250Ω以及500Ω。故障性质识别结果如图17(a)和图17(b)所示。
由图17(a)和图17(b)可知，改变过渡电阻并不会影响反射波的极性以及到达时间，仅会影响电流行波的幅值。但是，即使过渡电阻高达500Ω，故障性质识别方法依然能够准确判别故障性质以及计算故障距离。
D.其他影响因素。根据式(1)可以得到，初始电流行波各个频率分量的幅值|ΔI(jω)|为：
Figure PCTCN2019130085-appb-000010
因此，在不考虑线路衰减的情况下，初始电流行波在故障点的反射波各个频率分量的幅值|ΔI r(jω)|为：
Figure PCTCN2019130085-appb-000011
式中Г为故障点处电流行波反射系数，可以近似看作一个常数。
由式(9)可以看出，故障点反射波各个频率分量的幅值|ΔI r(jω)|可以通过增大缓冲电容C s以及采用的IGBT子模块的个数N c来提高，从而增加故障性质识别方法的灵敏度。
本发明通过为混合式直流断路器配置辅助电路，利用混合式直流断路器切断故障电流后转移支路部分缓冲电容储存的能量实现故障性质识别。先将触发信号施加在辅助电路中的晶闸管，之后闭合快速机械开关，利用混合式直流断路器出口处采集的电流数据并进行小波变换，求得电流行波第一尺度满足数据有效性条件的第一个以及第二个小波变换模极大值，之后通过其极性识别瞬时性以及永久性故障，并且在判别为永久性故障后计算永久性故障的故障距离。仿真分析表明，在各种故障条件下，本发明均能正确识别瞬时性故障与永久性故障，灵敏度高，可靠性强。另外，该发明还可以实现永久性故障测距，测距误差小、精度高。
上述虽然结合附图对本发明的具体实施方式进行了描述，但并非对本发明保护范围的限制，所属领域技术人员应该明白，在本发明的技术方案的基础上，本领域技术人员不需要付出创造性劳动即可做出的各种修改或变形仍在本发明的保护范围以内。

Claims (10)

  1. 一种混合式直流断路器的辅助电路，其特征在于，所述辅助电路添加在混合式直流断路器转移支路靠近架空线路侧的Nc个IGBT子模块上；所述辅助电路包括：晶闸管、电阻R g以及快速机械开关，所述晶闸管分别串联在架空线路与第一个IGBT子模块缓冲电路的缓冲电容负极之间以及相邻两个IGBT子模块缓冲电路的缓冲电容之间，第Nc个IGBT子模块缓冲电路的缓冲电容正极依次串联电阻Rg和快速机械开关后接地；其中，Nc为设定值。
  2. 如权利要求1所述的一种混合式直流断路器的辅助电路，其特征在于，所述N c取为转移支路IGBT子模块总数N的10％-20％。
  3. 一种配置混合式直流断路器的多端柔性直流电网故障性质识别系统，其特征在于，包括权利要求1-2任一项所述的混合式直流断路器的辅助电路，将储存在转移支路IGBT子模块缓冲电路的缓冲电容中的能量作为特征信号注入源，检测直流线路的故障性质。
  4. 一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，该方法基于权利要求1-2任一项所述的辅助电路，具体包括：
    混合式直流断路器切除故障电流后，经过设定时间的故障点电弧去游离时间，为辅助电路中所有的晶闸管施加触发信号，闭合辅助电路中的快速机械开关；
    实时采集混合式直流断路器线路侧的电流数据；
    对采集到的电流数据进行小波变换，计算第一尺度小波变换模极大值；
    对得到的小波变换模极大值进行数据有效性检验，记录第一个以及第二个满足数据有效性条件的小波变换模极大值的符号和采样时刻；
    建立故障性质识别判据，利用计算得到的小波变换模极大值符号进行瞬时性故障与永久性故障的识别。
  5. 如权利要求4所述的一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，如果识别为瞬时性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，混合式直流断路器进行重合闸；如果识别为永久性故障，则打开辅助电路中的快速机械开关并去除晶闸管的触发信号，混合式直流断路器不再进行重合。
  6. 如权利要求4所述的一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，根据获得的第一个以及第二个满足数据有效性条件的小波变换模极大值采样时刻计算故障距离。
  7. 如权利要求4所述的一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，所述满足数据有效性条件的小波变换模极大值具体为：
    设定整定值WTMM set，取小波变换模极大值的绝对值大于所述整定值的数据为满足数据 有效性条件的小波变换模极大值；
    其中，整定值WTMM set根据噪声所能引起的小波变换模极大值的最大值确定。
  8. 如权利要求4所述的一种配置混合式直流断路器的多端柔性直流电网故障性质识别方法，其特征在于，建立故障性质识别判据，具体为：
    定义第一尺度满足数据有效性条件的第一个以及第二个小波变换模极大值为WTMM f、WTMM s，若满足：
    WTMM f·WTMM s>0；
    则判定为永久性故障，否则判定为瞬时性故障。
  9. 一种配置混合式直流断路器的多端柔性直流电网故障性质识别系统，其特征在于，包括服务器，所述服务器包括存储器、处理器及存储在存储器上并可在处理器上运行的计算机程序，所述处理器执行所述程序时实现权利要求4-8任一项所述的配置混合式直流断路器的多端柔性直流电网故障性质识别方法。
  10. 一种计算机可读存储介质，其上存储有计算机程序，其特征在于，该程序被处理器执行时执行权利要求4-8任一项所述的配置混合式直流断路器的多端柔性直流电网故障性质识别方法。
PCT/CN2019/130085 2018-12-24 2019-12-30 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统 Ceased WO2020147572A1 (zh)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CN201811581663 2018-12-24
CN201910045238.9 2019-01-17
CN201910045238.9A CN109713653B (zh) 2018-12-24 2019-01-17 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统

Publications (1)

Publication Number Publication Date
WO2020147572A1 true WO2020147572A1 (zh) 2020-07-23

Family

ID=66261552

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2019/130085 Ceased WO2020147572A1 (zh) 2018-12-24 2019-12-30 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统

Country Status (2)

Country Link
CN (1) CN109713653B (zh)
WO (1) WO2020147572A1 (zh)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114498546A (zh) * 2021-12-28 2022-05-13 清华大学 一种混合双重桥式直流断路器拓扑电路及其控制方法
US11791617B2 (en) 2018-12-27 2023-10-17 Supergrid Institute Current cut-off device for high-voltage direct current with capacitive buffer circuit, and control method
US11798763B2 (en) 2019-03-22 2023-10-24 Supergrid Institute Current cut-off device for high-voltage direct current with resonator and switching
CN117013817A (zh) * 2022-04-28 2023-11-07 清华大学 一种可关断换流器的缓冲均压电路及换流器拓扑结构
US11824346B2 (en) 2018-12-27 2023-11-21 Supergrid Institute Current cut-off device for high-voltage direct current with adaptive oscillatory circuit, and control method
US11867771B2 (en) 2021-02-10 2024-01-09 Infineon Technologies Ag Methods and devices for detecting an electrical arc
CN121123915A (zh) * 2025-11-10 2025-12-12 昆明理工大学 基于构网型pcs信号注入的风电场送出线路三相自适应重合闸方法

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109713653B (zh) * 2018-12-24 2019-12-06 山东大学 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统
CN110333439B (zh) * 2019-06-06 2025-09-16 全球能源互联网研究院有限公司 直流断路器闭环开通关断子模块试验设备
CN110460028A (zh) * 2019-07-30 2019-11-15 中电普瑞科技有限公司 一种限制电网短路故障电流的装置及方法
CN110768221A (zh) * 2019-10-22 2020-02-07 华中科技大学 一种架空柔直电网自适应重合闸方法
CN111142044B (zh) * 2020-02-05 2022-03-18 东南大学 一种具备短路故障能量吸收能力的直流线路故障二次检测装置
CN112103925A (zh) * 2020-07-24 2020-12-18 西安交通大学 一种多端口混合式直流断路器及控制方法
CN113437731B (zh) * 2021-07-14 2023-03-14 东北林业大学 一种基于高速机械开关的限流型混合直流断路器
CN113659541B (zh) * 2021-07-23 2022-09-09 华中科技大学 基于波形相似度匹配的多端直流电网重合闸方法及系统
CN113625122A (zh) * 2021-08-23 2021-11-09 全球能源互联网研究院有限公司 一种伪双极柔性直流系统故障性质识别方法
CN113991619B (zh) * 2021-10-12 2024-06-28 平高集团有限公司 一种直流断路器用电流转移电路以及电流转移装置
CN116231598A (zh) * 2021-12-06 2023-06-06 国网浙江省电力有限公司电力科学研究院 判别直流线路故障的方法、电子设备和计算机程序产品

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140347897A1 (en) * 2013-05-24 2014-11-27 Eaton Corporation High voltage direct current transmission and distribution system
CN104753044A (zh) * 2015-03-27 2015-07-01 中国西电电气股份有限公司 一种混合式全固态高压直流断路器拓扑结构
CN106026048A (zh) * 2016-07-15 2016-10-12 浙江大学 一种基于就地检测就地保护的直流电网故障处理策略
CN106786707A (zh) * 2015-11-23 2017-05-31 国网智能电网研究院 一种基于混合拓扑换流器的柔直系统直流故障恢复方法
CN109119977A (zh) * 2018-09-20 2019-01-01 山东大学 基于单端电压的多端柔性直流电网直流线路快速保护方法及系统
CN109713653A (zh) * 2018-12-24 2019-05-03 山东大学 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140347897A1 (en) * 2013-05-24 2014-11-27 Eaton Corporation High voltage direct current transmission and distribution system
CN104753044A (zh) * 2015-03-27 2015-07-01 中国西电电气股份有限公司 一种混合式全固态高压直流断路器拓扑结构
CN106786707A (zh) * 2015-11-23 2017-05-31 国网智能电网研究院 一种基于混合拓扑换流器的柔直系统直流故障恢复方法
CN106026048A (zh) * 2016-07-15 2016-10-12 浙江大学 一种基于就地检测就地保护的直流电网故障处理策略
CN109119977A (zh) * 2018-09-20 2019-01-01 山东大学 基于单端电压的多端柔性直流电网直流线路快速保护方法及系统
CN109713653A (zh) * 2018-12-24 2019-05-03 山东大学 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11791617B2 (en) 2018-12-27 2023-10-17 Supergrid Institute Current cut-off device for high-voltage direct current with capacitive buffer circuit, and control method
US11824346B2 (en) 2018-12-27 2023-11-21 Supergrid Institute Current cut-off device for high-voltage direct current with adaptive oscillatory circuit, and control method
US11798763B2 (en) 2019-03-22 2023-10-24 Supergrid Institute Current cut-off device for high-voltage direct current with resonator and switching
US11867771B2 (en) 2021-02-10 2024-01-09 Infineon Technologies Ag Methods and devices for detecting an electrical arc
CN114498546A (zh) * 2021-12-28 2022-05-13 清华大学 一种混合双重桥式直流断路器拓扑电路及其控制方法
CN114498546B (zh) * 2021-12-28 2023-01-20 清华大学 一种混合双重桥式直流断路器拓扑电路及其控制方法
CN117013817A (zh) * 2022-04-28 2023-11-07 清华大学 一种可关断换流器的缓冲均压电路及换流器拓扑结构
CN121123915A (zh) * 2025-11-10 2025-12-12 昆明理工大学 基于构网型pcs信号注入的风电场送出线路三相自适应重合闸方法

Also Published As

Publication number Publication date
CN109713653A (zh) 2019-05-03
CN109713653B (zh) 2019-12-06

Similar Documents

Publication Publication Date Title
CN109713653B (zh) 混合式直流断路器的辅助电路、多端柔性直流电网故障性质识别方法及系统
CN109119977B (zh) 基于单端电压的多端柔性直流电网直流线路快速保护方法及系统
CN110021912B (zh) 基于混合式直流断路器的多端柔性直流电网自适应重合闸方法
CN108988303B (zh) 利用断路器注入脉冲信号的mmc-hvdc直流线路自适应重合闸方法
Zhang et al. A non-unit boundary protection of DC line for MMC-MTDC grids
CN109217267B (zh) 基于限流电感电压极性的多端柔性直流电网纵联保护方法及系统
CN108512201A (zh) 一种多端柔性直流电网直流线路快速保护方法及系统
CN110350496B (zh) 一种多端柔性直流电网故障限流方法及装置
CN111969552B (zh) 一种适用于直流断路器重合闸方法
CN108551161A (zh) 利用换流器主动注入和行波耦合的直流线路故障保护方法
CN106026048B (zh) 一种基于就地检测就地保护的直流电网故障处理策略
CN106468752B (zh) 集成故障定位的固态断路器rcd缓冲电路及故障定位方法
CN110797847A (zh) 一种基于电流微分状态量的双端直流配电网分布式区域保护方法
CN108832605A (zh) 识别混合双端直流输电线路区内、外故障的纵联保护方法
CN108808636B (zh) 一种基于传递熵的多端直流输电线路保护方法
CN109217270B (zh) 一种直流线路分段式定时限过流保护方法与装置
CN115425623A (zh) 一种基于暂态电流比值的多端柔性直流输电线路纵联保护方法
CN109038516B (zh) 一种用于直流配电网线路的加速保护方法
CN115360678A (zh) 具备自适应重合闸能力的混合式直流断路器及故障清除判别方法
CN110768221A (zh) 一种架空柔直电网自适应重合闸方法
CN107863759A (zh) 一种基于机械开关的串入电容型直流断路器及其直流故障处理策略
Guo et al. An adaptive reclosing strategy for high-voltage DC grids with mechanical DC circuit breakers
CN212277918U (zh) 一种多端口混合式直流断路器
CN109994989A (zh) 一种基于直流断路器的柔性直流电网的保护方法及系统
Guo et al. A nonunit two-stage protection scheme for DC transmission lines in high-voltage DC grids

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19910639

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19910639

Country of ref document: EP

Kind code of ref document: A1

32PN Ep: public notification in the ep bulletin as address of the adressee cannot be established

Free format text: NOTING OF LOSS OF RIGHTS PURSUANT TO RULE 112(1) EPC (EPO FORM 1205A DATED 04/02/2022)