CN111525517B - Method and system for suppressing overvoltage of converter valve submodule - Google Patents
Method and system for suppressing overvoltage of converter valve submodule Download PDFInfo
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- 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
- H02H7/10—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 for converters; for rectifiers
- H02H7/12—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 for converters; for rectifiers for static converters or rectifiers
- H02H7/122—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 for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
- H02H7/1225—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 for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters responsive to internal faults, e.g. shoot-through
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Abstract
The invention relates to a method and a system for inhibiting overvoltage of a converter valve submodule, wherein the method comprises the steps of calculating the dynamic variance of the direct-current port voltage of a converter valve in the current sampling period and the previous sampling period; judging whether serious faults occur or not according to the dynamic variance; and if serious faults occur, starting the shutdown protection of the converter station. According to the system, a serious fault judgment module is added in a control protection system of the converter valve, energy stored in a capacitor of a submodule is reduced by quickly cutting off a continuous charging loop of the submodule under the serious fault, and the overvoltage level of the submodule is effectively reduced on the basis, so that the safety margin of an offshore wind power system is improved.
Description
Technical Field
The invention relates to the technical field of new energy and electric power engineering, in particular to a method and a system for inhibiting overvoltage of a converter valve submodule.
Background
With the increasing energy problem, the development and utilization of new clean energy has become a hot issue in the world. With the continuous progress of science and technology, the offshore wind power generation capacity is continuously expanded, and the development of offshore wind power plants has important significance for solving the energy crisis. Offshore wind power grid-connected operation becomes the most effective mode for large-scale utilization of wind energy, and direct-current power transmission is suitable for large-capacity and long-distance electric energy transmission and is widely applied to offshore wind farms. With the increasing requirements of transmission distance and transmission capacity, direct current transmission plays an important role in the development and utilization of offshore wind farms. Compared with conventional direct current transmission and direct current transmission based on a two-level voltage source type converter and a three-level voltage source type converter, the offshore wind power flexible direct current access system based on the modular multilevel converter is more suitable for a long-distance and large-scale offshore wind power access system.
Along with continuous operation of onshore flexible direct-current transmission engineering, the modular multilevel converter technology is gradually mature, but the offshore converter station has the characteristics of high maintenance cost, long period, high difficulty and the like, so the design of the converter station is always a key technology in a high-capacity offshore wind power flexible direct-current transmission system, and a plurality of problems exist at present. The safety and the stability of the flexible direct-current transmission converter valve determine the reliability of the whole flexible direct-current sending-out system. The submodule based on the half-bridge or full-bridge topology is the minimum unit for the operation of the flexible-straight converter valve, and the stability and safety characteristics of the submodule determine the operation state of the whole flexible-straight output system. Due to the limitation of the self characteristics of the fully-controlled power electronic device, the relatively high overvoltage level and the relatively low safety margin of the flexible-direct converter valve sub-module in the fault process are always key factors influencing the safe operation of the system. For an offshore wind power soft and direct sending-out system, the overvoltage problem of the converter valve submodule is more severe.
At present, no offshore platform engineering example for an offshore wind power soft direct-sending system exists domestically, the effect of suppressing the overvoltage level of the converter valve submodule from the angles of one-time complete set design, insulation fit design, device voltage grade improvement and the like is limited, and the economical efficiency and the engineering practicability are poor.
Disclosure of Invention
The invention aims to provide a method and a system for inhibiting overvoltage of a converter valve submodule, which are used for reducing energy stored in a submodule capacitor by quickly cutting off a continuous charging loop of the submodule under serious fault, effectively reducing the overvoltage level of the submodule on the basis, so as to improve the safety margin of an offshore wind power system, and have very low technical cost of engineering realization and better economy.
In order to solve the above problem, one aspect of the present invention provides a method for suppressing an overvoltage of a converter valve submodule, where the method includes: calculating the dynamic variance of the voltage of the direct current port of the converter valve in the current sampling period and the previous sampling period;
judging whether serious faults occur according to the dynamic variance;
and if serious faults occur, starting the converter station to stop the protection, and if not, not acting.
According to one embodiment of the invention, the dynamic variance is calculated by:
wherein, Ft1And Ft2Dynamic variances of the direct current port voltage in the previous sampling period and the current sampling period are respectively; a. thei1And Ai2Respectively enabling signals of a counter in a previous sampling period and a counter in a current sampling period; u shapedct1And Udct2The DC port voltages in the previous sampling period and the current sampling period are respectively; u shapedcNIs rated DC port voltage, C is rated DC port voltage UdcNIs not critical.
According to one embodiment of the invention, the counter enable signal AiIs determined asThe following:
if the DC port voltage is less than the first voltage threshold (CxU)dcN) Then A isiWhen the value is equal to 0, the result output of the counter is zero;
if the DC port voltage is greater than the first voltage threshold (C U)dcN) Then A isiThe counter starts counting at 1.
According to an embodiment of the present invention, the determining whether a serious fault occurs according to the dynamic variance includes:
comparing said Ft1And said Ft2The method comprises the following steps: if Ft1Is greater than or equal to Ft2If CP is equal to 1, the counter is in zero clearing state, the result of counter is NtIs zero. If Ft1Less than Ft2And A isiWhen CP is equal to 0, the counter starts counting, and the counting result is output as Nt；
Compare counter result NtAnd a second threshold value NDThe comparison result is output as UP, which includes:
if N is presenttGreater than or equal to NDIf the UP is equal to 1, judging that the converter valve has serious faults; if N is presenttLess than NDAnd if the UP is equal to 0, judging that the converter valve has no serious fault.
According to one embodiment of the invention said initiating converter station shutdown protection comprises: locking the converter valve; and simultaneously disconnecting the converter valve alternating-current side breaker.
In another aspect, the present invention provides a converter valve sub-module overvoltage suppression system, including:
a dynamic variance calculation module for calculating the dynamic variance F of the DC port voltage of the converter valve in the previous sampling periodt1And the dynamic variance F of the current sampling periodt2Dynamic variance of the sampling period and the counter enable signal AiThe converter valve direct current port voltage, the converter valve rated direct current port voltage and the non-serious fault overvoltage multiple of the rated direct current port voltage are related;
the serious fault judgment module is used for judging whether a serious fault occurs according to the dynamic variance;
and the protection module is used for performing protection operation according to the judgment result of the serious fault judgment module, starting the converter station to stop protection if the serious fault occurs, and otherwise, not acting.
According to an embodiment of the invention, the converter further comprises a counter enable module for comparing the dc port voltage of the converter valve with a first voltage threshold, and if the dc port voltage is less than the first voltage threshold, the counter enable signal a is generatediWhen the value is equal to 0, the result output of the counter is zero; if the DC port voltage is greater than the first voltage threshold, then AiThe counter starts counting as 1.
According to one embodiment of the invention, the dynamic variance is calculated by:
wherein, Ft1And Ft2Dynamic variances of the DC port voltage in the previous sampling period and the current sampling period are respectively; a. thei1And Ai2Respectively enabling signals of a counter in a previous sampling period and a counter in a current sampling period; u shapedct1And Udct2The DC port voltages in the previous sampling period and the current sampling period are respectively; u shapedcNIs rated DC port voltage, C is rated DC port voltage UdcNIs not critical.
According to an embodiment of the present invention, the catastrophic failure determination module includes:
a first comparison module for comparing the Ft1And said Ft2To obtain a comparison result CP: if Ft1Greater than or equal to Ft2If CP is 1; if Ft1Less than Ft2If CP is 0;
a counter for outputting a counting result N according to the CPt: if CP is equal to 1, the counter is in zero state, and the result N of the countertIs zero; if CP is equal to 0, and the counter is setCan signal AiWhen the counting result is equal to 1, the counter starts to count, and the counting result output of the counter is Nt；
A second comparison module for comparing the NtAnd a second threshold value NDOf the comparison result UP: if N is presenttGreater than or equal to NDIf UP is 1; if N is presenttLess than NDIf UP is 0;
a judging module, configured to judge whether the converter valve has a serious fault according to the UP: if UP is 1, judging that a serious fault occurs; if UP is 0, it is determined that no serious failure has occurred.
According to one embodiment of the invention, the protection module starts the shutdown protection of the converter station comprises: shutting off the converter valve; and simultaneously disconnecting the converter valve alternating-current side breaker.
The invention reduces the energy stored in the capacitor of the sub-module by quickly cutting off the continuous charging circuit of the sub-module under serious faults, and effectively reduces the overvoltage level of the sub-module on the basis, thereby improving the safety margin of the offshore wind power system.
The technical scheme of the invention has the following beneficial technical effects:
firstly, a fault judgment module is used for carrying out criterion design, so that a serious fault which can cause overvoltage of a submodule can be effectively judged, and meanwhile, the fault judgment module cannot be triggered in the operating modes of non-serious faults, fault ride-through and the like, so that the integral reliability and stability of the operation of the converter valve are guaranteed;
secondly, the dynamic variance of the voltage of the direct current port of the converter valve is used as a fault criterion, so that the fault identification can be completely and accurately carried out, and the accuracy of equipment fault troubleshooting is improved;
and thirdly, the original control and protection system is perfected, no cost is increased, and the economy is better.
Drawings
FIG. 1 is a schematic diagram of a power transmission mode of an offshore wind power soft direct-sending system;
FIG. 2 is a circuit schematic diagram of a process for generating an overvoltage in a modular multilevel submodule of a land-based converter station in a fault;
FIG. 3 is a circuit schematic diagram of an overvoltage generation process for the modular multilevel sub-module of the offshore converter station under fault;
FIG. 4 is a flow chart of a method for suppressing overvoltage of a submodule of a converter valve according to an embodiment of the invention;
fig. 5 is a schematic diagram of a critical fault criterion circuit based on dynamic variance of dc port voltage of a modular multilevel converter according to an embodiment of the present invention;
FIG. 6 is a flow chart of a converter valve submodule overvoltage suppression method based on a severe fault criterion according to an embodiment of the invention;
fig. 7 is a block diagram of an overvoltage suppression system of a sub-module of a converter valve according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the accompanying drawings in combination with the embodiments. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The invention provides a method and a system for suppressing overvoltage of a converter valve submodule, wherein the scheme for suppressing the overvoltage of the submodule is that a serious fault criterion module is added in a control and protection system of a modular multilevel converter, when the fault is obtained by the serious fault criterion module after the fault occurs and belongs to the fault causing serious overvoltage of the converter valve submodule, the functional signal UP output of the serious fault criterion module is 1, the emergency shutting down protection (TAD) of a pole control system is directly triggered, the modular multilevel converter is shut down, and meanwhile, a breaker on the alternating current side performs opening operation; when the UP output is 0, the function is not enabled. The method does not increase the area of a primary system and an offshore platform, and has very low technical cost of engineering realization and better economy.
The converter valve submodule overvoltage suppression scheme takes a serious fault criterion UP as a judgment condition for emergency locking shutdown of the modular multilevel converter. According toDesigning a fault criterion UP capable of identifying serious faults causing the overvoltage of the sub-modules according to the operation and fault characteristics of a system, wherein the UP is based on the voltage U of a direct current port of the modular multilevel converterdcAnd (3) judging a serious fault of the dynamic variance, and when the serious fault exceeds a protection fixed value, starting UP, and quickly locking the modular multilevel converter and simultaneously connecting the breaker on the alternating current side of the transformer for opening. The overvoltage suppression scheme for the converter valve submodule used for the offshore wind power flexible and direct sending-out system provided by the invention has the advantages that the overvoltage level of the converter valve submodule is effectively suppressed mainly by judging the serious fault causing the submodule overvoltage in advance and quickly cutting off the continuous charging loop of the submodule, and the reliability of an offshore wind power system can be remarkably improved through the scheme.
For a detailed description of the technical solutions of the present invention, reference will be made to the following description with reference to the accompanying drawings.
Fig. 1 shows a power transmission mode of an offshore wind power flexible direct-output system.
The typical offshore wind power flexible direct-transmission system comprises an offshore wind farm, an alternating current collecting system, an alternating current booster station, an offshore converter station, a direct current transmission system and an onshore converter station, wherein equipment such as a converter valve of the offshore converter station is located on an offshore platform.
Each wind power station collects power through an offshore wind power collection system, and the collection system generally adopts an alternating current collection mode. Collecting the power of each offshore wind farm to a booster station through a multi-loop alternating current submarine cable, wherein the power of the offshore wind farm is represented as Pwind。
And after the booster station finishes the collection of power and the voltage change, the alternating current power is transmitted to the offshore flexible direct current converter station through the alternating current submarine cable. Conversion of AC power to DC power P by offshore flexible DC converter stationdcTransmitting power to the onshore flexible direct current converter station through the direct current submarine cable; the land-based converter station converts the dc power to ac power and transmits it to the local grid.
Due to the factors of high cost of an offshore platform, high fault rate of a direct current submarine cable, high price and the like, the symmetrical monopole modular multilevel topological structure is more suitable for being adopted by an offshore wind power output system. By adopting the system scheme, the areas of the convertor station equipment and the offshore platform can be effectively reduced, and the system has better economy.
According to the characteristics of the modular multilevel converter, four-quadrant operation control can be realized in the operation process. Two-terminal modular multilevel converter pass pair P1、Q1、P2And Q2The control of (c) enables the transmission of power.
The power relationship of the sending-side converter is as follows:
in the above formula, US1For the voltage amplitude, U, of the AC system of the offshore converter stationMMC1Outputting voltage amplitude value X for AC side of modular multilevel converter of offshore converter station1Connecting impedances, delta, for offshore converter station systems1And the phase angle difference between the voltage of the alternating current system of the offshore converter station and the output voltage of the alternating current side of the modular multilevel converter. The soft direct current converter adopts a vector control mode, and a control system consists of an inner loop current controller and an outer loop power controller.
During operation, the angle delta can be adjusted1Sum voltage amplitude UMMC1The control of (2) realizes the four-quadrant operation of the converter. Modular multilevel converter of offshore converter station mainly outputs voltage U to alternating current side of modular multilevel converterMMC1And controlling to provide a stable alternating voltage for the operation of the wind power plant so as to realize the output of power.
Modular multilevel converter pair U caused when fault occurs in offshore converter station or offshore alternating current systemMMC1If the wind power plant is out of control or the control capability is reduced, the power transmitted to the modular multilevel converter by the wind power plant is reduced, and the power transmitted by the direct current system is reduced.
The power relationship of the inverter at the other end is as follows:
in the above formula, US2The voltage amplitude of the alternating current system of the land-based converter station is determined by a local power grid. U shapeMMC2For the output voltage amplitude, X, of the AC side of a modular multilevel converter of a land converter station2Connecting impedances for the onshore converter station system. Delta. for the preparation of a coating2The phase angle difference between the output voltage at the alternating current side of the modular multilevel converter of the onshore converter station and the voltage of an alternating current system is obtained.
In operation, when the onshore converter station or the onshore alternating current system fails, the modular multilevel converter pair U is causedMMC2Out of control or reduced control capability, resulting in a point-to-point transmission power P2Causing a surplus of power in the straightening system.
Due to factors such as communication delay, low fan control rate and the like, surplus power in the flexible-straight system causes overvoltage of converter valve sub-modules of converter stations at two ends. The process of converter valve sub-module overvoltage generation is explained below with reference to fig. 2 and 3.
Fig. 2 shows a submodule overvoltage generation process in a modular multilevel converter of a land converter station under a fault.
The deduction shows that the working condition causing severe overvoltage of the converter valve sub-module of the offshore wind power soft direct-sending system is mainly that the onshore converter station fails to generate power surplus in the system. As shown in fig. 2, when the onshore converter station fails, surplus power exists in the flexible direct current transmission system, and the surplus power causes surplus energy of the onshore converter station, and further causes the voltage of the sub-module to increase.
As shown in fig. 2, the upper arm submodule passes through the positive pole UPGLAnti-parallel diode and valve side alternating current system uvForming upper bridge arm submodule UsmupThe charging circuit of (1).
The lower bridge arm passes through the anode UNGLAnti-parallel diode and valve side alternating current system uvForm a lower bridge arm sub-die UsmdownThe charging circuit of (1).
After the onshore converter station fails, the relationship between the submodule voltage and the surplus power is as follows:
in the above formula, wΔTo surplus power PΔResulting surplus energy; u shapesm1The voltage value of the submodule in the steady-state operation process is determined by the direct-current port voltage of the modular multilevel converter and the number of the bridge arm submodules, and the value is a constant in the normal operation process; csmIs the sub-module capacitance value.
By converting the above equation, the relationship between the voltage increase of the sub-modules of the land-based converter station is as follows:
as can be seen from the above equation, when there is surplus power in the onshore converter station, the surplus power will convert the energy into electric field energy, and be discharged or stored in the sub-module capacitor. The larger the surplus energy is, the more the submodule voltage increase is caused.
When the voltage of the sub-module increases, the voltage U of the DC port of the onshore converter station is causeddcLAnd the voltage of the sub-modules of the offshore converter station is further increased. The generation process of sub-module overvoltage in the modular multilevel converter of the offshore converter station is described below with reference to fig. 3.
Fig. 3 shows a sub-module overvoltage generation process of a modular multilevel converter of a subsea converter station under a fault.
DC port voltage U of onshore converter stationdcLThe increase can cause the port voltage U of the offshore converter stationdcHIn UdcHIn the increasing process, the direct current system charges the neutron module of the modular multilevel converter of the offshore converter station.
As shown in fig. 3, the upper arm submodule passes through the positive pole UPGAnti-parallel diode and valve side alternating current system uvForming an upper bridge arm submodule UsmupThe charging circuit of (1).
The lower bridge arm passes through the anode UNGAnti-parallel diode and valve side alternating current system uvForming a lower bridge arm submodule UsmdownThe charging loop of the converter station finally causes the voltage of the submodules in the offshore converter station to increase.
From the above analysis, it can be known that, for the occurrence of the overvoltage of the sub-module in the converter station in the offshore wind power soft and direct output system, the surplus power of the system mainly results in that the surplus power stores energy in the sub-module capacitor through the charging loop, which causes the generation of the overvoltage of the sub-module.
The invention provides a method for suppressing overvoltage of a converter valve submodule as shown in fig. 4, which comprises the following steps:
step S100, calculating the dynamic variance of the voltage of the direct current port of the converter valve in the current sampling period and the previous sampling period;
step S200, judging whether serious faults occur according to the dynamic variance;
and step S300, if serious faults occur, starting the converter station to stop the protection, and if not, stopping the operation.
In step S100, the sampling period of the valve control system is T, and the dc port voltage U of each sampling period is compared with the dc port voltage U of the valve control systemdct2And the DC port voltage U of the last sampling perioddct1And respectively performing dynamic variance calculation:
in the above formula, Ai1And Ai2The counter enable signals in the previous sampling period and the current sampling period are respectively. Ft1And Ft2The dynamic variances of the dc port voltage in the previous sampling period and the current sampling period, respectively. U shapedcNIs rated DC port voltage, C is rated DC port voltage UdcNIs not critical.
The criterion for causing a serious overvoltage fault in the submodule, i.e. step S200, is explained in detail below with reference to fig. 5.
Fig. 5 is a schematic diagram of a critical fault criterion circuit based on the dynamic variance of the dc port voltage of the modular multilevel converter.
In the sub-module charging process after the fault occurs, the voltage of the direct current port can be increased along with the fault. The more serious the fault is, the more surplus energy is, the more the voltage of the sub-modules is increased, and the more the voltage of the direct current port of the modular multilevel converter is increased.
Under the stable operation state and partial fault working condition, the voltage U of the direct current port of the converter station at two endsdcLAnd UdcHSubstantially a certain value or a limited fluctuation range. Obtaining a direct current port voltage protection fixed value (C multiplied by U) after carrying out a large amount of analysis and simulation demonstration on the systemdcN) I.e. the first voltage threshold and the count constant NDWherein C is rated DC port voltage UdcNThe non-serious fault overvoltage multiple of (2) is generally between 1.15 and 1.25. As shown in FIG. 5, the DC port voltage enters the control and protection system through the sampling system, and the enable signal of the counter is AiIf the DC port voltage is less than the protection constant value, AiThe counter is not started, and the counting result output is zero. If the DC port voltage is greater than the protection constant value, AiThe counter starts up as 1, and has a counting function.
Then F is mixedt1And Ft2The comparison is performed and the output result CP of the comparator is taken as a clear signal of the counter. When F ist1Is greater than or equal to Ft2When CP is equal to 1, the counter is in zero clearing state, counting result NtIs zero and less than NDThe catastrophic failure criterion output UP is 0.
When F is presentt1Is less than Ft2When CP is equal to 0, the counter has counting function, when the signal A is enabledi2When the counting is 1, the counting is started, and the counting output result is Nt(ii) a When N is presenttGreater than NDMeanwhile, the serious fault criterion output result UP is 1.
And performing overvoltage suppression operation on the converter valve sub-module according to a fault criterion UP which can cause serious faults of the converter valve sub-module overvoltage as an action command. The sub-module overvoltage suppression scheme is described below in conjunction with fig. 6.
Fig. 6 illustrates a converter valve sub-module overvoltage suppression scheme based on a critical fault criterion.
As shown in fig. 6, after the occurrence of the fault, it is determined whether the fault causes a serious overvoltage in the sub-module according to UP. According to the graph shown in fig. 5, when the onshore converter station has a serious fault, the flexible-straight system generates relatively large surplus power, and the port voltage U of the converter stations at two ends is modular and multi-leveldcWill continuously increase in a period of time, the port voltage UdcThe dynamic variance protection of (d) will trigger quickly, starting the rapid shutdown protection TAD. The continuous charging time of the submodules of the converter stations at two ends is greatly reduced, and the overvoltage level of the submodules is effectively reduced.
And when UP is 1, immediately starting the shutdown protection TAD of the converter station, issuing a switching-off command to an alternating-current side circuit breaker of the converter station, and simultaneously issuing a locking command to the modular multilevel converter. Due to the fact that the switching-off time of the alternating-current circuit breaker is long, the blocking of the modular multilevel converter is already completed in the switching-off process of the alternating-current circuit breaker.
When UP is 0, it is indicated that the system needs to perform fault ride-through, or faults of the system cannot cause serious sub-module overvoltage phenomenon to the converter valve, and the control and protection system performs judgment and operation according to a conventional processing mode.
Another aspect of the present invention provides a system for suppressing an overvoltage of a converter valve submodule, as shown in fig. 7, including: a dynamic variance calculation module for calculating the dynamic variance F of the DC port voltage of the converter valve in the previous sampling periodt1And the dynamic variance F of the current sampling periodt2The dynamic variance of the sampling period and the counter enable signal AiThe converter valve direct current port voltage, the converter valve rated direct current port voltage and the non-serious fault overvoltage multiple of the rated direct current port voltage are related;
the serious fault judging module is used for judging whether a serious fault occurs according to the dynamic variance;
and the protection module is used for performing protection operation according to the judgment result of the serious fault judgment module, starting the converter station to perform shutdown protection if a serious fault occurs, and otherwise, stopping the operation.
The converter valve further comprises a counter enabling module used for comparing the voltage of the direct current port of the converter valve with a first voltage threshold value, and if the voltage of the direct current port is smaller than the first voltage threshold value, a counter enabling signal AiWhen the value is equal to 0, the result output of the counter is zero; if the DC port voltage is greater than the first voltage threshold, then AiThe counter starts counting as 1.
Further, the serious fault determination module includes:
a first comparing module for comparing Ft1And said Ft2Obtaining a comparison result CP: if Ft1Is greater than or equal to Ft2If CP is 1; if Ft1Less than Ft2If CP is 0;
a counter for outputting a counting result N according to the CPt: if CP is equal to 1, the counter is in zero clearing state, and the result N of the countertIs zero; if CP is equal to 0, and the counter enables signal AiWhen the counting result is equal to 1, the counter starts to count, and the counting result output of the counter is Nt；
A second comparison module for comparing the NtAnd a second threshold value NDTo obtain a comparison result UP: if N is presenttIs greater than or equal to NDIf UP is 1; if N is presenttLess than NDIf UP is 0;
a judging module, configured to judge whether the converter valve has a serious fault according to the UP: if UP is 1, judging that a serious fault occurs; if UP is 0, it is determined that no catastrophic failure has occurred.
Further, the protection module starts the shutdown protection of the converter station and comprises: shutting off the converter valve; and simultaneously disconnecting the converter valve AC side breaker.
The invention provides a scheme for inhibiting overvoltage of a converter valve submodule aiming at the characteristics of an offshore wind soft direct-sending system, the scheme is mainly used for judging serious faults which cause serious submodule overvoltage and threaten equipment safety, and the protection function can not be triggered in a normal operation state and when the faults which do not cause the submodule serious overvoltage occur.
After the scheme for suppressing the overvoltage of the converter valve submodule of the offshore wind power soft and direct sending-out system is adopted, the voltage stress level of the submodule of the modular multilevel converter can be effectively reduced, the safety of equipment and the system is improved, and the design of the converter valve is convenient. In addition, no primary equipment and measuring equipment are added in the implementation process of the scheme, the implementation process is simple, and the method has better economy in the actual operation of the converter station.
Firstly, a fault judgment module is used for carrying out criterion design, so that a serious fault which can cause overvoltage of a submodule can be effectively judged, and meanwhile, the fault judgment module cannot be triggered in the operating modes of non-serious faults, fault ride-through and the like, so that the integral reliability and stability of the operation of the converter valve are guaranteed;
secondly, the dynamic variance of the voltage of the direct current port of the converter valve is used as a fault criterion, so that the fault identification can be completely and accurately carried out, and the accuracy of equipment fault troubleshooting is improved;
and thirdly, the original control and protection system is perfected, no cost is increased, and the economy is better.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modifications, equivalents, improvements and the like which are made without departing from the spirit and scope of the present invention shall be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundary of the appended claims, or the equivalents of such scope and boundary.
Claims (8)
1. A method for suppressing an overvoltage in a converter valve submodule, the method comprising:
calculating the dynamic variance of the voltage of the direct-current port of the converter valve in the current sampling period and the previous sampling period; the dynamic variance is calculated by:
wherein, Ft1And Ft2Dynamic variances of the direct current port voltage in the previous sampling period and the current sampling period are respectively; a. thei1And Ai2Respectively enabling signals of a counter in a previous sampling period and a counter in a current sampling period; u shapedct1And Udct2The DC port voltages in the previous sampling period and the current sampling period are respectively; u shapedcNIs rated DC port voltage, C is rated DC port voltage UdcNNon-critical fault overvoltage multiples of (1);
judging whether serious faults occur according to the dynamic variance;
and if a serious fault occurs, starting the shutdown protection of the converter station, otherwise, not acting.
2. The method of claim 1, wherein the counter enable signal AiThe following were determined:
if the DC port voltage is not greater than the first voltage threshold (CxU)dcN) Then A isiWhen the counter value is equal to 0, the counter result output is zero;
if the DC port voltage is greater than the first voltage threshold (C U)dcN) Then A isiThe counter starts counting at 1.
3. The method of claim 2, wherein said determining whether a catastrophic failure has occurred based on said dynamic variance comprises:
comparing said Ft1And said Ft2The method comprises the following steps: if Ft1Greater than or equal to Ft2If CP is equal to 1, the counter is in the zero clearing state, and the counter result N is obtainedtIs zero; if Ft1Is less than Ft2If CP is equal to 0, and AiWhen the counter counts 1, the counter starts counting, and the result of the counter is Nt；
Comparison counter nodeFruit NtAnd a second threshold value NDThe comparison result is output as UP, which includes:
if N is presenttIs greater than or equal to NDIf the UP is equal to 1, judging that the converter valve has serious faults; if N is presenttLess than NDAnd if the UP is equal to 0, judging that the converter valve has no serious fault.
4. A method according to any of claims 1-3, characterized in that said initiating converter station shutdown protection comprises: locking the converter valve; and simultaneously disconnecting the converter valve AC side breaker.
5. A converter valve sub-module overvoltage suppression system, characterized in that the system comprises:
a dynamic variance calculation module for calculating the dynamic variance F of the DC port voltage of the converter valve in the previous sampling periodt1And the dynamic variance F of the current sampling periodt2The dynamic variance is calculated by:
wherein, Ft1And Ft2Dynamic variances of the DC port voltage in the previous sampling period and the current sampling period are respectively; a. thei1And Ai2Respectively enabling signals of a counter in a previous sampling period and a counter in a current sampling period; u shapedct1And Udct2The DC port voltages in the previous sampling period and the current sampling period are respectively; u shapedcNIs rated DC port voltage, C is rated DC port voltage UdcNNon-critical fault overvoltage multiples of (1);
the serious fault judgment module is used for judging whether a serious fault occurs according to the dynamic variance;
and the protection module is used for performing protection operation according to the judgment result of the serious fault judgment module, starting the converter station to perform shutdown protection if a serious fault occurs, and otherwise, stopping the operation.
6. The system of claim 5, further comprising a counter enable module configured to compare the DC port voltage of the converter valve to a first voltage threshold, wherein the counter enable signal A is asserted if the DC port voltage is less than the first voltage thresholdiWhen the value is equal to 0, the result output of the counter is zero; if the DC port voltage is greater than the first voltage threshold, then AiThe counter starts counting as 1.
7. The system of claim 5, wherein the critical failure determination module comprises:
a first comparing module for comparing Ft1And said Ft2To obtain a comparison result CP: if Ft1Is greater than or equal to Ft2If CP is 1; if Ft1Less than Ft2If CP is 0;
a counter for outputting a counting result N according to the CPt: if CP is equal to 1, the counter is in zero state, and the result N of the countertIs zero; if CP is equal to 0, and the counter enables signal AiWhen the counting result is equal to 1, the counter starts to count, and the counting result output of the counter is Nt；
A second comparison module for comparing the NtAnd a second threshold value NDTo obtain a comparison result UP: if N is presenttGreater than or equal to NDIf UP is equal to 1; if N is presenttLess than NDIf UP is 0;
a judging module, configured to judge whether the converter valve has a serious fault according to the UP: if UP is 1, judging that a serious fault occurs; if UP is 0, it is determined that no serious failure has occurred.
8. The system according to any one of claims 5-7, wherein said protection module initiating converter station shutdown protection comprises: shutting off the converter valve; and simultaneously disconnecting the converter valve AC side breaker.
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