CN112290517A - Flexible controller protection method based on power quantity - Google Patents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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Abstract
The method for protecting the flexible controller based on power quantity comprises the steps of detecting the currents of the positive electrode and the negative electrode of the rectifying side and the inverting side and the voltages of the line protection devices of the positive electrode circuit and the negative electrode circuit of the rectifying side and the inverting side, recording the sum of the direct current power of the positive electrode of the rectifying side and the direct current power of the negative electrode of the inverting side of the flexible controller as PKMThe sum of the DC power of the negative pole on the rectification side and the DC power of the positive pole on the inversion side is PMKDefinition of PKMAnd PMKIf the amplitude of the differential power exceeds the limit value, judging that a single-pole grounding fault or a double-pole short-circuit fault exists in a direct-current connecting line in the flexible controller; otherwise, no monopolar ground fault or bipolar short circuit fault is considered to occur. The invention can inhibit the influence caused by the fault in the fault clearing and fault crossing processes, and reduce the range of the fault influence, thereby improving the fault stability of the system; the self-adaptive power longitudinal differential protection method for self-adaptively setting the threshold value can be used for better protecting the whole systemThe fault type is clearly and quickly determined, and the safety of the current conversion equipment is ensured.
Description
Technical Field
The invention belongs to the technical field of electric power, relates to protection of a flexible controller in a flexible direct-current power distribution network system, and discloses a power quantity-based flexible controller protection method.
Background
The key equipment in the flexible direct current power distribution network system is a flexible controller, and the control strategy and the fault characteristics of the flexible controller are the basis of a control and protection scheme. Some control protection methods have been proposed for the fault of the flexible direct current power distribution network. However, due to the complex working state of the flexible controller, the complexity of control and protection is greatly increased, and the fault characteristics of the flexible controller are different from the fault characteristics of the existing components of the common direct current transmission system. Therefore, the control protection of the flexible controller requires special research and design. In the field of protection and control of direct current systems, domestic research mainly focuses on fault identification and isolation technology of voltage source type direct current transmission and distribution systems, and a protection method for a flexible controller is not mature.
References [1-2] propose flexible direct current transmission system control protection scheme configurations and related control protection strategies under direct current system faults. The fault treatment and isolation mainly depend on the regulation and control of a fixed mode of a direct current system, and certain flexibility is lacked. The size of the direct current controller, when a single feeder line and equipment have faults, the availability of the system is seriously reduced by means of locking or restarting the system. Moreover, the proposed protection scheme is based on a direct current transmission line and is not completely suitable for a flexible controller.
In order to achieve effective isolation of power distribution grid faults, references [3-4] propose fault handling techniques based on power distribution automation techniques. The combination of distribution network protection and automation technology provides a certain reference for the research of the control protection technology of the direct current system fault, and the combination of the direct current system protection and the control is a new idea for realizing the effective isolation of the direct current fault.
References [5-6] propose several methods of fault control and protection of flexible dc transmission lines that work effectively on the transmission line but have additional requirements on hardware equipment.
The methods are developed and analyzed for an alternating current system or a flexible direct current transmission line, and the equipment composition, the fault type and the like of the flexible controller are different from those of the alternating current system or the flexible direct current transmission line, so that the methods cannot be completely applicable.
Reference to the literature
[1] Zei New Red, Zhao Cheng Yong modular multilevel converter type high voltage direct current transmission system control protection system framework [ J ] power automation equipment, 2013,09: 157-.
[2] Liu Jian, Yu Yi Ling, Fan Chun Ju, yellow cover. Fault handling and protection technology comment [ J ] for flexible DC transmission line electric power system automation 2015,20: 158-.
[3] The method comprises the steps of beacon, slow administration, break-through, control protection strategy of direct-current side fault of a multi-terminal direct-current transmission system [ J ] power system automation, 2012,06:74-78.
[4] High thickness epitaxy, pointless music, Li Shang Zheng, Qi protecting delay peak, Wangzhou, Multi-agent based intelligent feeder automation self-healing control [ J ] high voltage technology, 2013,05: 1218-.
[5] Korea, xulingbao converter station control/direct current protection system and valve interface design [ J ] high voltage technology, 2005,02:48-49.
[6] Fierce week, heading, forest satellite, Wenqui, Zuiping left, flexible direct current power grid direct current line fault active current limiting control [ J ] power grid technology, 2018,42(07):2062 + 2072.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the prior art mainly aims at the line protection of a flexible direct current power distribution network, the electrical structure of the direct current power distribution network is different from that of a flexible controller, the traditional line protection method cannot be directly applied to device protection, and the prior art lacks an effective protection method for a flexible controller device in the flexible direct current power distribution network.
The technical scheme of the invention is as follows: the method for protecting the flexible controller based on power quantity comprises the steps of detecting the currents of the positive electrode and the negative electrode of the rectifying side and the inverting side and the voltages of the line protection devices of the positive electrode circuit and the negative electrode circuit of the rectifying side and the inverting side, recording the sum of the direct current power of the positive electrode of the rectifying side and the direct current power of the negative electrode of the inverting side of the flexible controller as PKMThe sum of the DC power of the negative pole at the rectification side and the DC power of the positive pole at the inversion side of the flexible controller is PMKDefinition of PKMAnd PMKIf the amplitude of the differential power exceeds a set threshold value, judging that a single-pole grounding fault or a double-pole short-circuit fault exists in a direct-current connecting line in the flexible controller; otherwise, no unipolar ground fault or bipolar short circuit fault is considered to occur; and performing protection action on the flexible controller according to the judgment result.
Further, when the direct current connecting line in the flexible controller is judged to have faults, the high-frequency component is attenuated through the sliding average filtering processing, the low-frequency component of the electric quantity is extracted, and the filtered power P is obtainedKMAnd PMKHas different positive and negative combinations under different fault types on the direct current side of the flexible controller, if the P after filteringKMIs a negative value, PMKIf the positive values are positive values and the amplitudes exceed the threshold value, the occurrence of positive grounding faults of the direct current line of the system is judged; if the filtered PKMIs a positive value, PMKIf the values are negative values and the amplitudes exceed the threshold value, the occurrence of negative earth faults of the direct current line of the system is judged; if the filtered PKMAnd PMKIf the positive values are positive values and the amplitude exceeds the threshold value, the bipolar short circuit fault of the direct current line of the system is judged.
The invention has the following beneficial effects:
(1) the method for protecting the flexible controller selects the typical electrical quantity in the flexible controller, does not need to add extra electrical measurement equipment, has the advantages of small calculated quantity and high calculation efficiency, and can realize the functional coordination among all levels of protection by reasonably configuring the fault criterion setting value and the action time according to the working state and the transmitted power of the actual flexible controller, wherein the setting value is the threshold value PsetThe action time refers to the delay of the start of the protection. Therefore, in the fault removal and fault ride-through processes, the influence caused by the fault is inhibited, the fault influence range is reduced, and the fault stability of the system is improved.
(2) The invention provides the self-adaptive power pilot differential protection method of the self-adaptive setting threshold value according to the running state of the flexible controller, can more clearly and quickly determine the fault type, simplifies the work of a maintainer for checking a circuit, can quickly identify and isolate the fault, and ensures the safety of the converter equipment.
Drawings
FIG. 1 is a schematic diagram of a flexible controller.
FIG. 2 is a schematic diagram of the protection method of the present invention.
Detailed Description
Aiming at the novel flexible controller MMC, as shown in figure 1, the novel flexible controller is a single device, the internal circuit is extremely short, the traveling wave of the circuit can be ignored, and the power high-frequency characteristic of the MMC converter is different from that of the traditional two-level VSC, so that the high-frequency power correlation pilot protection and the traveling wave direction pilot protection in the prior art are not suitable. Meanwhile, at different working condition switching moments, the mutation rate of direct current and voltage is also large, and the direct current and voltage cannot be used as a fault judgment basis. The invention provides the differential protection based on the power quantity in consideration of the problems that the operating conditions of the flexible controller are variable and the conventional current protection has difficulty in setting, and simultaneously, the flexible controller has small volume and short transmission distance of differential protection signals, so that the quick action performance of the protection can be well met.
The principle of the pilot protection scheme of the flexible controller based on the power quantity is explained below.
First, the characteristics of the dc line current and the dc line voltage are analyzed. As shown in fig. 1, which is a schematic diagram of a flexible controller, the direct-current side faults of the flexible controller are divided into two types, namely a single-pole ground fault and a double-pole short-circuit fault. In FIG. 1, iKpAnd iMpFor the current flowing through the mounting of the rectifier-side positive line and the inverter-side positive line protection device, iKnAnd iMnFor the current flowing through the corresponding negative line protection device mounting, uKpAnd uMpFor the voltage at the mounting of the positive line protection devices on the rectifying side and the inverting side, uKnAnd uMnThe voltage at the installation position of the rectification side and the inversion side negative electrode line protection device. The voltage and current reference directions are as indicated by the arrows in the figure. For simplification, in the embodiment of the present invention, when processing the voltage and the current, the values converted from the per unit value are uniformly used for calculation. Protection methods commonly described in the disciplines of power systems broadly include methods of fault determination, selection, and removal. The protection method comprises the selection of electrical one-time detection measurement, the construction of protection criterion, the setting principle of protection setting value and the faultAnd judging the method, wherein the protection action is used as a switch to trip.
Based on the analysis of the flexible controller, the invention integrates the voltage quantity and the current quantity of the direct current line, and the power of the protection installation position of the flexible controller is set as P ═ ui, wherein u and i are the voltage and the current of the protection installation position of the direct current line respectively. The values of the available DC power P under various fault conditions are shown in Table 1, where Udc、IdcIndicating the rated voltage and current values of the direct current line.
TABLE 1 DC POWER TAKE-OFF TABLE
From table 1, the sum of the dc powers of the different polar lines of the inverters at the two ends, that is, the sum of the dc power of the positive pole at the rectification side of the flexible controller and the dc power of the negative pole at the inversion side, and the sum of the dc power of the negative pole at the rectification side of the flexible controller and the dc power of the positive pole at the inversion station, is zero when the flexible controller is in normal steady-state operation and has an ac side fault, and is not zero when there is a monopolar ground fault and a bipolar short circuit fault. The sum of the positive direct current power and the negative direct current power of the inversion side of the flexible controller is recorded as PKMThe sum of the DC power of the negative electrode of the flexible controller and the DC power of the positive electrode of the inversion side is PMKDefinition of PKMAnd PMKFor differential power, the formula is defined as:
if the differential power amplitude is not zero, judging that a single-pole ground fault or a double-pole short circuit fault exists in a direct-current connecting line in the flexible controller; otherwise, no unipolar ground fault or bipolar short circuit fault is considered to occur; and performing protection action on the flexible controller according to the judgment result. Considering that the distributed capacitance of the direct current line has certain influence on the electrical quantity characteristic when the system is in fault and mainly influences the high-frequency component of the electrical quantity, the invention adopts the sliding average filter to attenuate the high-frequency component in the protection, extracts the low-frequency component of the electrical quantity and is used for correcting the analysis result obtained by neglecting the distributed capacitance of the direct current line.
Differential power PKMAnd PMKThe output after the filtering process of the moving average is
PKMAnd PMKIs a time variable, PKM_f(k) And PMK_f(k) Representing the filtered PKMAnd PMKAnd generating data in a past time period T of the current time k, wherein the time period T is a sampling period, and N is the number of sampling points of the sampling period. In order to filter out high frequency components quickly and effectively, T is preferably 3ms, namely for each sampling moment k, N sampling points within 3ms before the moment k are used for calculating corresponding PKM_f(k) And PMK_f(k) Each sample point corresponds to a time instant in the sampling period.
Based on the differential power after the moving average filtering process, the DC side fault criterion can be expressed as
|PKM_f|＞Pset&|PMK_f|＞Pset
In the formula: psetIn order to set a threshold value, the value is related to the output power of the flexible controller in the previous period, and is set to be 0.05-0.1P according to the working state of the flexible controllerRated value。
Power PKMAnd PMKThe direct current side of the flexible controller has obviously different positive and negative combinations under different fault types. If the filtered PKMIs a negative value, PMKIf the positive value is positive, the positive grounding fault of the system direct current line can be judged; if the filtered PKMIs a positive value, PMKIf the value is a negative value, the negative earth fault of the direct current line of the system can be judged; if the filtered PKMAnd PMKIf both are positive values, thenThe bipolar short-circuit fault of the system direct-current line can be judged. Thus, the fault type identification criterion can be expressed as
When the flexible controller normally operates in a steady state and the AC side fails
When the positive pole of the flexible controller is in ground fault
When the negative pole of the flexible controller is in ground fault
When the flexible controller has bipolar short circuit fault, the flexible controller is controlled
And if the fault types are judged to be the three faults, the protection unit executes protection action after the set delay time. The matching relation exists between all levels of protection in the flexible direct current power distribution network, and the protection is realized through the time delay of different levels of protection.
The protection method is used for protecting the interior of the device of the flexible controller. The sudden power change is the change rate of the power quantity in unit time, and the large sudden power change exists when the working condition of the flexible controller is switched and the fault occurs, so the scheme directly according to the power change in the prior art cannot be applied to the occasion of the invention. The power difference of the invention is a double-end quantity, and the electric quantities at two ends are different, so that the protection misoperation caused by normal power change can be avoided. In addition, the prior art also has a scheme of protecting by using a current voltage protection setting value, but the scheme is specific to a certain fixed working condition, if the working condition is changeable, the setting needs to be reset, and on the use occasion of the flexible controller, the site generally does not have the condition of real-time setting. The power longitudinal differential protection method constructed according to the power quantity of the flexible controller does not need additional electric appliance measurement and setting equipment, has small calculated quantity and high adaptability, and can accurately and timely judge the state of the flexible controller, thereby realizing the protection of the flexible controller.
In summary, the invention uses differential power to construct the protection principle of the dc connection line in the flexible controller, when the ac side fails, the dc side failure criterion is not satisfied, and the protection does not act; when the direct current side has a fault, the direct current side fault criterion is established, and then fault type identification is carried out through the fault type identification criterion, so that the protection acts correctly. The invention passes P based on the amount of powersetAnd the design of protection action delay realizes the self-adaptive protection of the flexible controller, and the logic block diagram of the self-adaptive power pilot differential protection is shown in fig. 2.
Claims (7)
1. The method for protecting the flexible controller based on power quantity is characterized by detecting the currents of the positive and negative electrodes at the rectifying side and the inverting side and the voltages at the installation positions of the line protection devices of the positive and negative electrode circuits at the rectifying side and the inverting side, and recording the sum of the direct current power of the positive electrode at the rectifying side and the direct current power of the negative electrode at the inverting side of the flexible controller as PKMThe sum of the DC power of the negative pole at the rectification side and the DC power of the positive pole at the inversion side of the flexible controller is PMKDefinition of PKMAnd PMKIf the amplitude of the differential power exceeds a set threshold value, judging that a single-pole grounding fault or a double-pole short-circuit fault exists in a direct-current connecting line in the flexible controller; otherwise, no unipolar ground fault or bipolar short circuit fault is considered to occur; and performing protection action on the flexible controller according to the judgment result.
2. The method of claim 1, wherein the flexible controller protection based on power amount is based on a power amountIs provided with iKpAnd iMpFor the current flowing through the installation of the rectifier-side and inverter-side positive line protection devices, iKnAnd iMnFor the current flowing through the corresponding negative line protection device mounting, uKpAnd uMpFor the voltage at the mounting of the positive line protection devices on the rectifying side and the inverting side, uKnAnd uMnFor the voltage at the installation position of the rectification side and the inversion side negative pole line protection device, the differential power is defined as
3. The method for protecting a flexible controller based on power quantity as claimed in claim 1 or 2, wherein when it is judged that the dc link in the flexible controller has a fault, the high frequency component is attenuated by the moving average filtering process, the low frequency component of the electrical quantity is extracted, and the filtered power P is obtainedKMAnd PMKHas different positive and negative combinations under different fault types on the direct current side of the flexible controller, if the P after filteringKMIs a negative value, PMKIf the positive values are positive values and the amplitudes exceed the threshold value, the occurrence of positive grounding faults of the direct current line of the system is judged; if the filtered PKMIs a positive value, PMKIf the values are negative values and the amplitudes exceed the threshold value, the occurrence of negative earth faults of the direct current line of the system is judged; if the filtered PKMAnd PMKIf the positive values are positive values and the amplitude exceeds the threshold value, the bipolar short circuit fault of the direct current line of the system is judged.
4. The method of claim 3, wherein the differential power P is a power valueKMAnd PMKThrough the moving average filtering process, the filtered output is:
PKMand PMKIs a time variable, PKM_f(k) And PMK_f(k) Representing the filtered PKMAnd PMKGenerating data in a past time period T of the current time k, wherein the time period T is a sampling period, and N is the number of sampling points of the sampling period;
the dc side fault criterion is expressed as
|PKM_f|＞Pset&|PMK_f|＞Pset
PsetThe set threshold value is determined according to the working state of the flexible controller and is set to be 0.05-0.1PRated value。
5. The power amount based flexible controller protection method as claimed in claim 4, wherein the period T is 3 ms.
6. The flexible power flow based controller protection method as claimed in claim 4, wherein the identification criteria for fault type based on the filtered output is expressed as:
7. the method as claimed in claim 1, wherein the dc link in the flexible controller corresponds to the differential power in the following relationship:
during normal steady state operation of the flexible controller and fault on the alternating current side,
when the positive pole of the flexible controller is in ground fault,
Udc、Idcindicates the rated voltage and current values of the direct current line,
when the negative pole of the flexible controller is in ground fault,
when the flexible controller has a bipolar short circuit fault,
and if the fault types are judged to be the three faults, the protection unit executes protection action after the set delay time.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114204525A (en) * | 2021-11-10 | 2022-03-18 | 华中科技大学 | Pilot protection method for direct-current transmission line and application thereof |
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| CN102130441A (en) * | 2011-03-16 | 2011-07-20 | 中国电力科学研究院 | Protection configuration method of flexible direct-current (DC) transmission system of modular multiple-level converter |
| CN108777483A (en) * | 2018-05-31 | 2018-11-09 | 国网浙江省电力有限公司电力科学研究院 | Load based on flexible multimode switch turns for strategy online |
| CN111398851A (en) * | 2020-03-30 | 2020-07-10 | 云南电网有限责任公司电力科学研究院 | MMC-HVDC direct current transmission line fault detection method |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102130441A (en) * | 2011-03-16 | 2011-07-20 | 中国电力科学研究院 | Protection configuration method of flexible direct-current (DC) transmission system of modular multiple-level converter |
| CN108777483A (en) * | 2018-05-31 | 2018-11-09 | 国网浙江省电力有限公司电力科学研究院 | Load based on flexible multimode switch turns for strategy online |
| CN111398851A (en) * | 2020-03-30 | 2020-07-10 | 云南电网有限责任公司电力科学研究院 | MMC-HVDC direct current transmission line fault detection method |
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| CN114204525A (en) * | 2021-11-10 | 2022-03-18 | 华中科技大学 | Pilot protection method for direct-current transmission line and application thereof |
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