Method and system for evaluating lightning arresters of controllable commutated converters

Abstract

A method and system for evaluating a controllable phase-commutation converter arrester. In the method, a system electrical model is established by conducting power simulation based on a system model containing a controllable phase-commutation converter arrester to obtain the relationship between the current and voltage on the controllable phase-commutation converter arrester; the system electrical model is corrected based on the waveforms of normal operation and AC side short-circuit faults so that the system electrical model covers a variety of operating conditions and the waveforms borne by the controllable phase-commutation converter arrester are obtained; the energy value borne by the controllable phase-commutation converter arrester is calculated based on the extreme operating conditions and current-carrying capacity of the controllable phase-commutation converter arrester; a continuous pulse generator for evaluating the controllable phase-commutation converter arrester is established based on the waveform and energy value borne by the controllable phase-commutation converter arrester to simulate extreme operating conditions; and the quality, state, current-carrying capacity and repeated energy absorption capacity of the controllable phase-commutation converter arrester are evaluated based on the temperature rise of the controllable phase-commutation converter arrester.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage direct current commutation, and in particular to a method and system for evaluating a lightning arrester of a controllable commutation converter. Background Art

[0002] In high-voltage DC conversion, zinc oxide arresters have excellent nonlinear volt-ampere characteristics and exhibit insulating characteristics at low voltage. When the voltage reaches the arrester action voltage, the arrester resistance decreases, which has the function of reducing the overvoltage amplitude and preventing overvoltage from damaging the insulation system of electrical equipment. Arrester is widely used in power grid systems to ensure the safe operation of electrical equipment and power grid systems.

[0003] Zinc oxide arresters are widely used in power systems due to their advantages such as fast action, strong current-carrying capacity and small size to improve the lightning protection capability of transmission lines, mainly to deal with lightning strikes on transmission lines. However, the functions of the auxiliary branch IGBT arrester of the new controllable commutation converter are mainly the following two points: when a short circuit fault occurs on the AC side, the arrester establishes a commutation voltage to assist in commutation to avoid commutation failure; it acts as an energy-consuming resistor to absorb the power that the inverter station AC system cannot absorb. At this time, the arrester will be subjected to periodic continuous current pulses during the fault period. This working condition is different from the short-term lightning strike accidents under traditional transmission lines.

[0004] Zinc oxide resistors are formed by sintering and pressing. Microscopically, the nonlinear characteristics of zinc oxide come from the grain boundary layer, and the insulation characteristics come from the zinc oxide grains. When there are microcracks inside the resistor, or when the resistor is damp, the valve plate will be thermally aged, and the resistive leakage current flowing through the resistor will increase, resulting in increased thermal power consumption, which may eventually lead to thermal collapse of the arrester or even an explosion. The new controllable phase-changing converter auxiliary branch IGBT arrester may accumulate heat energy under the condition of short-circuit fault on the AC side. The thermal expansion caused by thermal stress may cause the valve plate to rupture and break, and even melt and perforate when the local temperature is too high.

[0005] In view of this, researchers have paid great attention to the detection of valve plates and have carried out a large number of targeted tests and studies. The existing detection methods for valve plates in converter stations are all based on the electrical quantities described in the GB / T 22389-2023 standard, mainly including heat dissipation characteristics test, residual pressure test, and large current impact tolerance test. These electrical quantities often use standard lightning waveforms as impact inputs, which do not meet the continuous current impact conditions borne by the auxiliary branch IGBT arrester. The auxiliary branch IGBT arrester affects the stability of the new controllable commutation converter, and the valve plates of the arrester need to be strictly screened and tested. Therefore, more detailed evaluation methods and processes are needed to solve the above problems.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0007] The present invention provides a method and system for evaluating a lightning arrester of a controllable commutation converter, which screens out lightning arresters that meet the standards by simulating the actual working conditions of a fully controlled device parallel lightning arrester in an auxiliary branch of a controllable commutation converter when the AC side is short-circuited, thereby ensuring the stable operation of an inverter station.

[0008] A method for evaluating a controlled commutation converter arrester comprises:

[0009] The system electrical model is established by conducting power simulation based on the system model containing the controllable commutation converter arrester, and the relationship between the current and voltage on the controllable commutation converter arrester is obtained;

[0010] The system electrical model is modified according to the waveforms of normal operation and AC side short-circuit faults, so that the system electrical model covers various working conditions and the waveforms that the controllable commutation converter arrester withstands are obtained;

[0011] According to the extreme working conditions and current carrying capacity of the controllable commutation converter arrester, calculate the energy value that the controllable commutation converter arrester can bear;

[0012] According to the waveform and energy value that the controllable commutation converter arrester is subjected to, a continuous pulse generator for evaluating the controllable commutation converter arrester is established to simulate extreme working conditions;

[0013] According to the temperature rise of the controllable commutation converter arrester, the quality, status, current carrying capacity and repeated energy absorption capacity of multiple pulses of the controllable commutation converter arrester are evaluated.

[0014] In the method for evaluating a controllable phase-commutation converter arrester, electrical modeling software is used to perform electrical modeling on the system in which the controllable phase-commutation converter arrester is located to establish a system electrical model, the model parameters are the same as the actual parameters, and the relationship between the current and voltage on the controllable phase-commutation converter arrester is obtained.

[0015] In the method for evaluating a controllable commutation converter arrester, the system electrical model includes a main branch and an auxiliary branch having a controllable commutation converter arrester. According to the waveform on the controllable commutation converter arrester during normal operation recorded by the recording software, the system electrical model of the switching process between the main branch and the auxiliary branch during normal operation is corrected. After the correction, the system electrical model covers all types of operating conditions, thereby obtaining the most extreme operating condition of the arrester. The continuous pulse generator generates a waveform identical to the current borne by the arrester under the most extreme operating condition to simulate the most extreme operating condition.

[0016] In the method for evaluating a controllable commutation converter arrester, the current carrying capacity of the controllable commutation converter arrester is greater than the maximum energy under the most extreme working condition, and a predetermined margin is reserved.

[0017] In the method for evaluating a controllable phase-commutated converter arrester, the fault model of the system electrical model when the AC side fails is corrected according to the waveforms of normal operation and AC side short circuit faults.

[0018] In the method for evaluating a controllable commutation converter arrester, the energy borne by the arrester is calculated based on the current and voltage waveforms of the arrester when the AC side fault occurs and the working time of the arrester, and then the energy value of the arrester is calculated based on a predetermined margin.

[0019] In the method for evaluating a controllable commutation converter arrester, the parameters of the continuous pulse generator are adjustable, and the parameters include pulse frequency, pulse amplitude, pulse width and duration.

[0020] In the method for evaluating a controllable commutation converter arrester, the quality, state, current carrying capacity and repeated energy absorption capacity of the controllable commutation converter arrester for multiple pulses are judged according to whether the controllable commutation converter arrester is damaged, thermally collapsed or thermally broken down, whether the temperature rise exceeds the tolerance value of the controllable commutation converter arrester, and whether the total absorbed energy exceeds the total current carrying capacity of the arrester.

[0021] In the method for evaluating a controllable commutation converter arrester, the highest amplitude in the actual waveform is used as the amplitude input of the continuous pulse generator, and the repetitive energy absorption capacity is the energy absorption capacity of the controllable commutation converter arrester for continuous repetitive current pulses.

[0022] A system for implementing a method for evaluating a controllably commutated converter arrester comprises,

[0023] A system simulation module, which establishes a system electrical model through power simulation, and a model correction module, which is connected to the system simulation module to correct the system electrical model according to the waveforms of normal operation and AC side short circuit faults.

[0024] An energy design module, which is connected to the model correction module to calculate the energy value that the controllable phase-commutation converter arrester is subjected to according to the most extreme working condition and current-carrying capacity of the controllable phase-commutation converter arrester; an impact test module, which is based on the waveform that the arrester is subjected to under the most extreme working condition; and a state evaluation module, which is connected to the impact test module to evaluate the quality, state, current-carrying capacity and repeated energy absorption capacity of the arrester for multiple pulses according to the temperature rise of the arrester.

[0025] In the system, the status evaluation module is an independent processor or a processor distributed on multiple network units.

[0026] Compared with the prior art, the present invention has the following advantages: the present invention calculates the energy design value of the lightning arrester by simulating and modeling the controllable phase-commutating converter power system; obtains the measured fault waveform through recording software and obtains the impulse current for the lightning arrester test; performs an impulse current test on the lightning arrester valve plate, measures the temperature rise value, and calculates the energy absorption value; determines whether the lightning arrester valve plate meets the requirements, and helps to screen the fully controlled device parallel lightning arrester of the auxiliary branch of the controllable phase-commutating converter that meets the requirements through a combination of simulation and testing, so as to ensure the stable operation of the controllable phase-commutating converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work. Moreover, the same reference numerals are used to represent the same components throughout the drawings.

[0028] In the attached picture:

[0029] Figure 1 This is a flow chart of a method for evaluating a fully controlled device parallel lightning arrester of an auxiliary branch of a controllable commutation converter according to a first embodiment;

[0030] Figure 2 This is a general view of the high voltage direct current power transmission system where the controllable commutation converter of the first embodiment is located;

[0031] Figure 3 This is a structural diagram of a single valve of a controllable phase-commutation converter according to Embodiment 1;

[0032] Figure 4 This is a topological diagram of the internal structure of the controllable phase-commutation converter valve in the first embodiment;

[0033] Figure 5 It is an actual waveform recording of the controllable commutation converter when the AC side fails in the first embodiment;

[0034] Figure 6 This is a wiring diagram of a continuous pulse generator test for evaluating a lightning arrester in Embodiment 1;

[0035] Figure 7 is a flow chart of Example 1 for determining whether a lightning arrester meets the standards;

[0036] Figure 8It is a module diagram of an evaluation system for a fully controlled device parallel lightning arrester of an auxiliary branch of a controllable commutation converter according to the second embodiment.

[0037] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0038] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0039] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0040] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0041] like Figures 1 to 8 As shown, the method for evaluating the arrester of a controllable commutation converter comprises the following steps:

[0042] The system electrical model is established by conducting power simulation based on the system model containing the controllable commutation converter arrester, and the relationship between the current and voltage on the controllable commutation converter arrester is obtained;

[0043] The system electrical model is modified according to the waveforms of normal operation and AC side short-circuit faults, so that the system electrical model covers various working conditions and the waveforms that the controllable commutation converter arrester withstands are obtained;

[0044] According to the extreme working conditions and current carrying capacity of the controllable commutation converter arrester, calculate the energy value that the controllable commutation converter arrester can bear;

[0045] According to the waveform and energy value that the controllable commutation converter arrester is subjected to, a continuous pulse generator for evaluating the controllable commutation converter arrester is established to simulate extreme working conditions;

[0046] According to the temperature rise of the controllable commutation converter arrester, the quality, status, current carrying capacity and repeated energy absorption capacity of multiple pulses of the controllable commutation converter arrester are evaluated.

[0047] In a preferred implementation of the method for evaluating a controllable phase-commutating converter arrester, electrical modeling software is used to perform electrical modeling on the system in which the controllable phase-commutating converter arrester is located to establish a system electrical model, and the model parameters are the same as the actual parameters to obtain the relationship between the current and voltage on the controllable phase-commutating converter arrester.

[0048] In a preferred embodiment of the method for evaluating a controllable phase-commutating converter arrester, the system electrical model includes a main branch and an auxiliary branch having a controllable phase-commutating converter arrester. According to the waveform on the controllable phase-commutating converter arrester during normal operation recorded by the recording software, the system electrical model of the switching process between the main branch and the auxiliary branch during normal operation is corrected. After the correction, the system electrical model covers all types of operating conditions, thereby obtaining the most extreme operating condition of the arrester. The continuous pulse generator generates a waveform identical to the current borne by the arrester under the most extreme operating condition to simulate the most extreme operating condition.

[0049] In a preferred implementation of the method for evaluating a controllable commutation converter arrester, the current carrying capacity of the controllable commutation converter arrester is greater than the maximum energy under the most extreme working condition, and a predetermined margin is reserved.

[0050] In a preferred implementation of the method for evaluating a controllable phase-commutated converter arrester, the fault model of the system electrical model when the AC side fails is corrected based on the waveforms of normal operation and AC side short circuit faults.

[0051] In a preferred implementation of the method for evaluating a controllable commutation converter arrester, the energy borne by the arrester is calculated based on the current and voltage waveforms of the controllable commutation converter arrester when an AC side fault occurs and the working time of the controllable commutation converter arrester, and then the energy value of the controllable commutation converter arrester is calculated based on a predetermined margin.

[0052] In a preferred embodiment of the method for evaluating a controllable commutation converter arrester, the parameters of the continuous pulse generator are adjustable, and the parameters include pulse frequency, pulse amplitude, pulse width and duration.

[0053] In a preferred implementation of the method for evaluating a controllable phase-commutation converter arrester, the quality, state, current-carrying capacity and repeated energy absorption capacity of the controllable phase-commutation converter arrester for multiple pulses are judged based on whether the controllable phase-commutation converter arrester is damaged, thermally collapsed, or thermally broken down, whether the temperature rise exceeds the tolerance value of the controllable phase-commutation converter arrester, and whether the total absorbed energy exceeds the total current-carrying capacity of the arrester.

[0054] In a preferred embodiment of the method for evaluating a controllable commutation converter arrester, the highest amplitude in the actual oscillogram is used as the amplitude input of the continuous pulse generator, and the repetitive energy absorption capacity is the energy absorption capacity of the controllable commutation converter arrester for continuous repetitive current pulses.

[0055] A system for implementing a method for evaluating a controllably commutated converter arrester comprises,

[0056] System simulation module, whose power simulation establishes the system electrical model and obtains the relationship between the current and voltage on the arrester of the controllable commutation converter;

[0057] A model correction module, which is connected to the system simulation module to correct the system electrical model according to the waveforms of normal operation and AC side short circuit fault, so that the model covers various working conditions;

[0058] An energy design module, which is connected to the model correction module to calculate the energy value that the controllable phase-commutation converter arrester is subjected to according to the most extreme working condition and current carrying capacity of the controllable phase-commutation converter arrester;

[0059] The impulse test module establishes a continuous pulse generator for evaluating the arrester to simulate the most extreme working conditions based on the waveform that the arrester is subjected to under the most extreme working conditions;

[0060] The state assessment module is connected to the impulse test module to assess the quality, state, current carrying capacity and repeated energy absorption capacity of the arrester for multiple pulses according to the temperature rise of the arrester.

[0061] In a preferred embodiment of the system, the controllable commutation converter arrester comprises a zinc oxide arrester.

[0062] In one embodiment, embodiment 1 provides a method for evaluating a fully controlled device parallel lightning arrester of an auxiliary branch of a controllable phase-commutated converter, which aims to generate the most extreme operating condition of the lightning arrester by establishing a corrected electrical model, and simulate the extreme operating condition by controlling a continuous pulse generating device, thereby realizing the testing of lightning arrester samples, screening samples that meet the requirements, and improving the stability of the transmission system.

[0063] Reference Figure 1As shown, a method for evaluating a fully controlled device parallel lightning arrester of an auxiliary branch of a controllable commutation converter comprises the following steps:

[0064] S1: Conduct power simulation based on the system model, establish the system electrical model, and obtain the general laws of current and voltage on the lightning arrester.

[0065] S2: Modify the system electrical model based on the waveforms of normal operation and AC side short-circuit faults to make the model cover various working conditions.

[0066] S2 specifically includes: Waveform recording example Figure 5 shown.

[0067] S3: Based on the most extreme working condition of the arrester and taking into account the current carrying capacity, calculate the energy value that the arrester can withstand.

[0068] S3 specifically includes: the current carrying capacity of the lightning arrester must be greater than the maximum energy under the most extreme working conditions, and a certain margin must be left.

[0069] S4: According to the waveform and energy design value that the arrester is subjected to, a continuous pulse generator for evaluating the arrester is established to simulate extreme working conditions.

[0070] S4 specifically includes: the continuous pulse generator is controlled by a control system, and the parameters are adjustable, including pulse frequency, pulse amplitude, pulse width, duration, etc.

[0071] S5: Based on the temperature rise of the arrester, evaluate the arrester's quality, status, current-carrying capacity, and repeated energy absorption capacity for multiple pulses.

[0072] S5 specifically includes: Based on the temperature rise of the lightning arrester, combined with national standards and various standards, as well as the electrical model, evaluate whether the quality, state, current-carrying capacity and repeated energy absorption capacity of multiple pulses of the lightning arrester meet the requirements of the electrical model.

[0073] Figure 2 This is a general view of the high voltage direct current transmission system where the controllable commutation converter of the first embodiment is located.

[0074] The transmission side includes a power generation section 100 and an AC filter 110 .

[0075] The AC power transmission line transmits the three-phase AC power generated by the power generation unit 100 to the transmission-side converter transformer 120 .

[0076] The AC filter 110 removes the remaining frequency components except the frequency component used by the converter transformer 120 from the transmitted three-phase AC power.

[0077] The transmission side converter transformer unit 120 includes a transformer 121a, 121b for the positive pole and transformers 122a, 122b for the negative pole. The transmission side LCC rectifier includes an LCC rectifier 130 for generating positive direct current and an LCC rectifier 131 for generating negative direct current. The LCC positive rectifier 130 includes a three-phase valve bridge corresponding to the transformers 121a, 121b for the positive pole. The LCC negative rectifier 131 includes a three-phase valve bridge corresponding to the transformers 122a, 122b for the negative pole.

[0078] When two LCC rectifiers 130 are used for the positive pole, the positive direct current with 12 pulses can be generated by using the alternating current. Here, the transformer 121a adopts a double star connection method, and the transformer 121b adopts a star-delta connection method.

[0079] The more the number of positive LCC rectifiers is, the more the number of pulses of the positive DC power increases, and the more the filter price can be reduced.

[0080] When two LCC rectifiers 131 are used for the negative pole, the alternating current can be used to generate a negative direct current with 12 pulses. Here, the transformer 122a adopts a double star connection method, and the transformer 122b adopts a star-delta connection method.

[0081] The more negative LCC rectifiers there are, the more the number of pulses of negative DC increases, and the more the filter price can be reduced.

[0082] The DC transmission line 140 includes a transmission-side positive smoothing reactor 141, a transmission-side positive DC filter 142, a transmission-side negative smoothing reactor 146, a transmission-side negative DC filter 147, a positive DC power transmission line 143, a negative DC power transmission line 148, a user-side positive DC filter 144, a user-side positive smoothing reactor 145, a user-side negative DC filter 149, and a user-side negative smoothing reactor 1410.

[0083] The transmission-side positive smoothing reactor 141 suppresses the positive DC ripple output by the positive LCC rectifier 130 , so that the output DC is close to the ideal DC.

[0084] The transmission-side positive DC filter 142 includes an inductor L1 and a capacitor C1 , and performs DC filtering on the positive DC power output by the positive LCC rectifier 130 .

[0085] The positive DC power transmission line 143 is a DC line for transmitting positive DC power, and the ground line can be used as a current feedback path. At least one switch can be arranged on the DC line.

[0086] The user-side positive DC filter 144 includes an inductor L2 and a capacitor C2 , and performs DC filtering on the positive DC power transmitted via the positive DC power transmission line 143 .

[0087] The user-side positive smoothing reactor 145 suppresses the positive direct current transmitted by the positive direct current transmission line 143, so that the output direct current is close to the ideal direct current.

[0088] The transmission-side negative smoothing reactor 146 suppresses the negative DC ripple output by the negative LCC rectifier 131 , making the output DC close to the ideal DC.

[0089] The transmission-side negative DC filter 147 includes an inductor L3 and a capacitor C3 , and performs DC filtering on the negative DC power output by the negative LCC rectifier 131 .

[0090] The negative DC power transmission line 148 is a DC line for transmitting negative DC power, and a ground line may be used as a current feedback path. At least one switch may be arranged on the DC line.

[0091] The user-side negative DC filter 149 includes an inductor L4 and a capacitor C4 , and performs DC filtering on the negative DC power transmitted via the negative DC power transmission line 148 .

[0092] The user-side negative smoothing reactor 1410 suppresses the negative DC power transmitted by the negative DC power transmission line 148 , so that the output DC is close to the ideal DC.

[0093] The user-side converter transformer unit 160 includes a transformer 161a, 161b for the positive pole and transformers 162a, 162b for the negative pole. The user-side CLCC inverter includes a CLCC inverter 150 for inverting positive DC power and a CLCC inverter 151 for inverting negative DC power. The CLCC positive inverter 150 includes a three-phase valve bridge corresponding to the positive converter transformers 161a, 161b. The CLCC negative inverter 151 includes a three-phase valve bridge corresponding to the transformers 162a, 162b for the negative pole.

[0094] When two CLCC inverters 150 are used for the positive pole, the direct current can be used to generate the positive alternating current with 12 pulses. Here, the transformer 161a adopts a double star connection method, and the transformer 161b adopts a star-delta connection method.

[0095] The more positive CLCC inverters there are, the more the number of positive AC pulses increases, and the more the filter price can be reduced.

[0096] When two CLCC inverters 151 are used for the negative pole, the direct current can be used to generate the negative alternating current with 12 pulses. Here, the transformer 162a adopts a double star connection method, and the transformer 162b adopts a star-delta connection method.

[0097] The more negative CLCC inverters there are, the more the number of negative AC pulses increases, and the more the filter price can be reduced.

[0098] The user-side AC power unit includes an AC power filter 170 and an AC power transmission line.

[0099] The AC filter 170 removes the remaining frequency components of the AC power generated by the user-side CLCC inverter 150 except for the frequency components used by the user unit 180 .

[0100] Figure 3 This is a structural diagram of a single valve of a controllable phase-commutating converter according to Embodiment 1.

[0101] The converter bridge consists of 6 bridge arms, namely VT1, VT2, VT3, VT4, VT5, and VT6. The three new controllable phase-changing converter valves (VT1, VT3, and VT5) whose cathodes are connected together are called a common cathode group; the three new controllable phase-changing converter valves (VT4, VT6, and VT2) whose anodes are connected together are called a common anode group.

[0102] The common anode group is turned on in the positive half cycle of the power supply, and the forward current flows through the secondary winding of the transformer. The common cathode group is turned on in the negative half cycle of the power supply, and the reverse current flows through the secondary winding of the transformer.

[0103] The bridge arms are numbered according to the order in which they are turned on, so the order in which the bridge arms are turned on is VT1, VT2, VT3, VT4, VT5, and VT6.

[0104] Figure 4 This is a topological diagram of the internal structure of the controllable phase-commutation converter valve in Example 1.

[0105] The single valve of the controlled commutation converter (CLCC) consists of a main branch and an auxiliary branch. The main branch includes a thyristor Thy1 and an insulated gate bipolar transistor IGBT2; the auxiliary branch includes an insulated gate bipolar transistor IGBT3 and its parallel lightning arrester MOV3 and a thyristor Thy4.

[0106] During normal operation, the first stage is the main branch current flow stage, Thy1, IGBT2 and IGBT3 are triggered to conduct at the same time, and the main branch current flows at this time. This stage has the same working mechanism as the LCC.

[0107] After the main branch is turned on for a certain period of time, the commutation between the bridge arms begins. During the commutation of the bridge arm, IGBT2 is turned off and the current begins to transfer to the auxiliary branch. After the commutation is completed, the current in the main branch passes through zero, Thy1 is subjected to reverse pressure, and enters the blocking recovery period. After the bridge arm completes natural commutation, IGBT3 is turned off with zero current, and the entire bridge arm restores its blocking capability.

[0108] After the main branch IGBT2 is turned off, the auxiliary branch remains in the on state for a period of time, and the IGBT2 turn-off voltage is reversely applied to the thyristor Thy1 to provide it with a recovery voltage to ensure that the thyristor is reliably turned off.

[0109] When an AC side fault occurs, the CLCC operates in forced commutation mode.

[0110] Since the bridge arm current cannot complete natural commutation, the main branch current is transferred to the auxiliary branch during commutation; after the main thyristor valve is turned off at zero crossing, the auxiliary branch current is transferred to MOV3 to enhance the commutation voltage and avoid commutation failure.

[0111] The maximum peak current of the auxiliary branch is twice the rated current. Considering the commutation time of the main and auxiliary branches and the recovery time of the main branch thyristor, the current conduction time generally does not exceed 1ms.

[0112] Figure 5 This is an actual waveform recording of the controllable commutation converter when an AC side fault occurs in the first embodiment.

[0113] Figure 5 Middle Figure A, Figure 5 Middle Figure B, Figure 5 The three figures in Figure C show the three-phase voltage on the AC side, the A-phase current, the B-phase current and the arrester-bearing current of the three-phase current on the valve side.

[0114] like Figure 5 As shown in Figure A, a single-phase ground short circuit fault of phase A on the AC side occurred at relative time 0ms, and the fault was cleared at 52.3ms.

[0115] like Figure 5 As shown in Figure B, the enlarged part shows the current change of the two phases during the phase switching process of phase A and phase B on the valve side. The phase switching process starts at 18.2ms and ends at 19.0ms.

[0116] Since the short-circuit fault on the AC side is phase A, the phase-changing process between phases A and B on the valve side is forced commutation, and a lightning arrester is required to establish a commutation voltage to assist the commutation.

[0117] like Figure 5As shown in Figure C, the arrester is subjected to current pulses before the commutation process. Taking the first pulse as an example, it starts at 16.6ms with an amplitude of 1.224kA and ends at 18.1ms with an amplitude of 0.934kA. The pulse duration is 1.5ms, and the time interval between each pulse is 20ms. Therefore, a pulse occurs in each cycle, which is consistent with the system frequency of 50Hz.

[0118] like Figure 5 As shown in Figure C, although the fault was removed at 52.3ms, the system has not yet recovered and the voltage of phase A on the AC side is insufficient. Therefore, the lightning arrester is still subjected to current-assisted commutation at around 55ms, but the amplitude is significantly lower than during the fault duration, indicating that the voltage of phase A is recovering.

[0119] like Figure 5 As shown in Figure C, although the three current pulse amplitudes in this example are different, in actual testing, the state where all pulse amplitudes are at the maximum value should be considered to simulate the most extreme working condition.

[0120] Figure 6 This is a wiring diagram of a continuous pulse generator test for evaluating a lightning arrester in Example 1.

[0121] The continuous pulse control system controls the continuous pulse generator to simulate the most extreme working conditions of the lightning arrester. The control parameters include pulse frequency, pulse amplitude, pulse width, duration, etc.

[0122] Control Parameters Reference Figure 5 Recording data, pulse frequency is within the range of 50Hz±0.5Hz, pulse amplitude range is 0kA-2.5kA, pulse width range is 0.5ms-2.0ms, and the maximum duration should be at least greater than 800ms (40 cycles).

[0123] The continuous pulse generator is composed of multiple independent impulse current discharge circuits and can meet the control requirements of the control system.

[0124] The arrester sample is an actual arrester sample or a thermal proportional unit of an actual arrester used in a new controllable commutation converter, simulating the temperature rise or damage of the arrester under the most extreme working conditions;

[0125] Rogowski coil is used to measure the current and voltage waveforms after the impact.

[0126] The temperature measuring device transmits the temperature of the arrester after the test to the data processing module through the temperature sensor.

[0127] The data processing module calculates the energy absorbed by the arrester based on the temperature of the arrester, compares it with the energy of the current under the most extreme working condition of the arrester obtained by simulation, and determines whether the arrester meets the requirements.

[0128] Figure 7 This is a flow chart of Example 1 for determining whether a lightning arrester meets the standards.

[0129] After continuous impact, check whether the lightning arrester is damaged. If so, the lightning arrester is unqualified. If not, the energy absorbed by the lightning arrester is calculated through the data processing module. If it exceeds the energy design value, it does not meet the requirements. If it is within the energy design value range, it meets the requirements.

[0130] Figure 8 It is a module diagram of an evaluation system for a fully controlled device parallel lightning arrester of an auxiliary branch of a controllable commutation converter according to the second embodiment.

[0131] S110 is a system simulation module.

[0132] The system simulation module performs power simulation based on the system model, establishes the system electrical model, and obtains the general laws of current and voltage on the lightning arrester.

[0133] S120 is a model correction module.

[0134] The model correction module corrects the system electrical model according to the recording diagrams of normal operation and AC side short-circuit fault, so that the model covers various working conditions;

[0135] S130 is the energy design module.

[0136] The energy design module calculates the energy value that the arrester can withstand based on the most extreme working conditions of the arrester and taking into account the current carrying capacity.

[0137] S140 is the impact test module.

[0138] The impulse test module establishes a continuous pulse generator for evaluating the arrester based on the waveform and energy design value that the arrester is subjected to, simulating extreme working conditions.

[0139] S150 is a status assessment module.

[0140] According to the temperature rise of the lightning arrester, evaluate the quality, status, current-carrying capacity and repeated energy absorption capacity of the lightning arrester for multiple pulses.

[0141] In the system, the status evaluation module is an independent processor or a processor distributed on multiple network units.

[0142] In several embodiments provided by the present invention, it should be understood that the disclosed method can be implemented as a corresponding functional unit, a processor or even a system, wherein the various parts of the system can be located in one place or distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, each functional unit can be integrated in a processing unit, or each unit can exist separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention is essentially or partly contributed to the prior art or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a smart phone, a personal digital assistant, a wearable device, a laptop, a tablet computer) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage media include: USB flash drives, read-only memories (ROM), random access memories (RAM), mobile hard disks, magnetic disks or optical disks, and other media that can store program codes.

[0143] The method and system provided by the present invention are helpful to improve the safety, reliability and economy of high-voltage direct current transmission system, reduce the commutation failure caused by arrester failure, and effectively guarantee the power demand of users. With the continuous development and innovation of related technologies, the detection and management level of the new controllable commutation converter auxiliary branch fully controlled device parallel arrester will continue to improve, providing solid technical support for the safe and stable operation of transmission lines.

[0144] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and instructive, rather than restrictive. A person of ordinary skill in the art can also make many forms under the guidance of this specification and without departing from the scope of protection of the claims of the present invention, all of which belong to the protection of the present invention.

Claims

1. A method for evaluating a lightning arrester of a controllable commutation converter, characterized in that: The steps include: Conduct power simulation based on the system model containing the controllable commutation converter arrester to establish the system electrical model, and obtain the relationship between the current and voltage on the controllable commutation converter arrester; modify the system electrical model based on the waveforms of normal operation and AC side short-circuit faults, so that the system electrical model covers a variety of working conditions and obtains the waveforms that the controllable commutation converter arrester is subjected to; According to the extreme working conditions and current carrying capacity of the controllable commutation converter arrester, calculate the energy value that the controllable commutation converter arrester can bear; According to the waveform and energy value that the controllable commutation converter lightning arrester is borne by, a continuous pulse generator for evaluating the controllable commutation converter lightning arrester is established to simulate extreme working conditions. According to the temperature rise of the controllable commutation converter lightning arrester, the quality, state, current carrying capacity and repeated energy absorption capacity of multiple pulses of the controllable commutation converter lightning arrester are evaluated.

2. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The electrical modeling software is used to perform electrical modeling on the system where the controllable commutation converter arrester is located to establish the system electrical model. The model parameters are the same as the actual parameters, and the relationship between the current and voltage on the controllable commutation converter arrester is obtained.

3. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The system electrical model includes a main branch and an auxiliary branch with a controllable commutation converter arrester. According to the waveform on the controllable commutation converter arrester during normal operation recorded by the recording software, the system electrical model of the switching process between the main branch and the auxiliary branch during normal operation is corrected. After the correction, the system electrical model covers all types of operating conditions, thereby deriving the most extreme operating condition of the arrester. The continuous pulse generator generates a waveform identical to the current that the arrester withstands under the most extreme operating condition to simulate the most extreme operating condition.

4. A method for evaluating a controllable commutation converter arrester according to claim 3, characterized in that: The current carrying capacity of the controllable commutation converter arrester is greater than the maximum energy under the most extreme working condition, and a predetermined margin is reserved.

5. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: According to the waveforms of normal operation and AC side short circuit fault, the fault model of the system electrical model when the AC side fails is corrected.

6. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The energy borne by the arrester is calculated based on the current and voltage waveforms of the arrester when the AC side fails and the working time of the arrester, and then the energy value of the arrester is calculated based on the predetermined margin.

7. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The parameters of the continuous pulse generator are adjustable, including pulse frequency, pulse amplitude, pulse width and duration.

8. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The quality, state, current carrying capacity and repeated energy absorption capacity of the controlled commutation converter arrester can be judged based on whether the controlled commutation converter arrester is damaged, thermally collapsed, or thermally broken down, whether the temperature rise exceeds the tolerance value of the controlled commutation converter arrester, and whether the total absorbed energy exceeds the total current carrying capacity of the arrester.

9. A method for evaluating a controllable commutation converter arrester according to claim 1, characterized in that: The highest amplitude in the actual oscillogram is used as the amplitude input of the continuous pulse generator, and the repetitive energy absorption capacity is the absorption capacity of the controllable commutation converter arrester for the energy of continuous repetitive current pulses.

10. A system for implementing the method for evaluating a controllable commutation converter arrester according to any one of claims 1 to 9, characterized in that: These include, A system simulation module, which establishes a system electrical model through power simulation, and a model correction module, which is connected to the system simulation module to correct the system electrical model according to the waveforms of normal operation and AC side short circuit faults. An energy design module, which is connected to the model correction module to calculate the energy value that the controllable phase-commutation converter arrester is subjected to according to the most extreme working condition and current-carrying capacity of the controllable phase-commutation converter arrester; an impact test module, which is based on the waveform that the arrester is subjected to under the most extreme working condition; and a state evaluation module, which is connected to the impact test module to evaluate the quality, state, current-carrying capacity and repeated energy absorption capacity of the arrester for multiple pulses according to the temperature rise of the arrester.

11. The system according to claim 10, characterized in that The status evaluation module is a processor that is independent or distributed to multiple network elements.

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