CN110829452A - Reactive current control method for reducing fault ride-through impact of alternating current-direct current hybrid power distribution network - Google Patents
Reactive current control method for reducing fault ride-through impact of alternating current-direct current hybrid power distribution network Download PDFInfo
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- CN110829452A CN110829452A CN201911113789.0A CN201911113789A CN110829452A CN 110829452 A CN110829452 A CN 110829452A CN 201911113789 A CN201911113789 A CN 201911113789A CN 110829452 A CN110829452 A CN 110829452A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
- H02J3/1857—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters wherein such bridge converter is a multilevel converter
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
The invention discloses a reactive current control method for reducing fault ride-through impact of an alternating-current and direct-current hybrid power distribution network, which provides an optimal given method for reactive control current with different function characteristics in a PET fault ride-through process according to a voltage drop factor and grid-connected point current, replaces the reactive current given value of a traditional low-voltage ride-through strategy with the optimized reactive current given value, better accords with the actual condition required by low-voltage ride-through, reduces the impact caused by state switching in the traditional low-voltage ride-through strategy, and improves the safety and reliability of a system.
Description
Technical Field
The invention relates to the technical field of Power Electronic Transformers (PET), in particular to a reactive current control method for reducing fault ride-through impact of an alternating-current and direct-current hybrid power distribution network.
Background
Power Electronic Transformers (PET) are a novel electric energy conversion device based on modern Power Electronic technology, and are widely applied to alternating current-direct current hybrid Power distribution networks to realize interconnection of various types of distributed Power supplies. Under the background of future energy internet and diversified load types, the popularization and application of the power electronic transformer can simplify the network structure and improve the power supply and distribution efficiency.
At present, researches on PET mainly focus on aspects of circuit topology, control strategies, novel power device application and the like, and few researches on fault current control strategies and low-voltage ride-through control strategies are carried out. The PET is a key device for realizing interconnection of various distributed power supplies in alternating current power grids and direct current power grids of different voltage levels, and faults on an alternating current side and a direct current side of the PET can have serious influence on safe and stable operation of the power grids and power supply reliability of users. Considering the sensitivity and the vulnerability of power electronic equipment, the PET is expected not to be disconnected immediately after the grid fails, and the fault ride-through control under low voltage is realized.
Disclosure of Invention
The technical purpose is as follows: in view of the above prior art, the present invention provides a reducerThe reactive current control method for fault ride-through impact of the small alternating current-direct current hybrid power distribution network is based on the voltage drop factor epsilon and the grid-connected point current INThe method adopts the reactive current set value after optimization of different functional characteristics to replace the traditional low-voltage ride-through strategy to replace INThe impact caused by state switching is reduced, and the safety and reliability of the system are improved.
The technical scheme is as follows: in order to achieve the technical purpose, the invention adopts the following technical scheme:
a reactive current control method for reducing fault ride-through impact of an alternating current-direct current hybrid power distribution network is characterized by comprising the following steps: detecting the voltage of the grid-connected point in real time to obtain a grid voltage drop factor representing the grid drop depth, and judging whether the grid operates normally before light according to the voltage drop factor: when the alternating current power grid normally operates, the power electronic transformer adopts an active power control strategy; when the alternating current power grid fails, the voltage amplitude of the power grid drops, the system needs to be switched to a reactive power control mode, the PET optimizes and adjusts the reactive current by adopting different functional characteristics in sections according to the voltage drop depth of the power grid and the current of a grid-connected point, the given value of the fault ride-through reactive reference current for reducing impact is obtained, and reactive support is provided for the power grid.
Preferably, the control method comprises the following operation steps:
s1, detecting voltage U of grid-connected point in real timeTAnd obtaining a power grid voltage drop factor epsilon:
wherein U isSFor voltage values, U, during steady operation of the gridTMeasuring a voltage real-time value of the power grid;
s2, carrying out sectional reactive current control on the PET according to the dropping factor epsilon:
when epsilon is less than or equal to 0.1, the system is in a normal operation state;
if epsilon is more than 0.8, the system is in serious failure, and the PET is locked at the moment;
when the epsilon is more than 0.1 and less than or equal to 0.8, determining a reference value of reactive current in fault ride-through control according to different fall factors epsilon:
in the formula: i.e. iq-refIs the component of the PET input stage current in the q-axis, INIs PET grid connection point current;
s3, synthesizing point-of-connection current INAnd optimizing a reactive control current I value in the PET fault ride-through process by adopting different function characteristics compared with the drop factor epsilon:
in the formula: k is an adjustment coefficient; h is a control parameter;
s4, replacing I in the formula (6) in the step S2 by the optimized reactive current set value obtained in the formula (7) in the step S3NObtaining a given value of the fault ride-through reactive reference current for reducing the impact:
preferably, the power electronic transformer adopts a mode of voltage-current double closed-loop control when the alternating current power grid is in normal operation.
Preferably, the PET mainly comprises a preceding-stage AC/DC power conversion module and a subsequent-stage DC/DC power conversion module, wherein the preceding-stage AC/DC power conversion module adopts any one of an H-bridge cascaded multilevel converter, a modular multilevel converter MMC, or a hybrid module combination multilevel converter of a cascaded H-bridge + MMC structure; the post-stage DC/DC power conversion module adopts a bidirectional isolation type DC/DC converter (DAB).
Has the advantages that: due to the adoption of the technical scheme, the invention has the following technical effects:
the invention discloses a reactive current control method for reducing fault ride-through impact of an alternating current-direct current hybrid power distribution network, which is based on grid-connected point powerStream INAnd the drop factor epsilon, the fault ride-through reactive current setting optimized by the characteristics of different function curves is given, the actual situation required by low-voltage ride-through is better met, the process of switching different reactive current reference values by different drop factors is smoother, and the impact caused by the traditional low-voltage ride-through strategy is reduced.
Drawings
Fig. 1 is a schematic diagram of a PET-based alternating current and direct current hybrid distribution network.
Fig. 2 is a diagram illustrating the switching of the operation mode of PET.
Fig. 3 is a diagram of a fault-ride-through switching control architecture based on epsilon.
FIG. 4 shows the relationship between I and ε under different adjustment factors.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of an AC/DC hybrid distribution network based on PET shown in fig. 1, wherein the PET mainly comprises a front-stage AC/DC power conversion module and a rear-stage DC/DC power conversion module. The pre-stage AC/DC power conversion module is a core link of PET, and the link can be an H-bridge cascade multilevel converter, a modular multilevel converter MMC or a hybrid module combination multilevel converter with a cascade H-bridge + MMC structure. The post-stage DC/DC power conversion module adopts a bidirectional isolation type DC/DC converter (DAB). Through the interconnection and the coordination work of the two power conversion modules, the functions of interconnection of an alternating current-direct current power distribution network, distributed new energy access, conversion of different voltage grades and the like are realized.
As shown in a schematic diagram of switching the working control mode of the PET in fig. 2, when the ac power grid normally operates, the power electronic transformer adopts an active power control strategy, specifically, adopts voltage-current double closed-loop control; when the alternating current power grid fails, the voltage amplitude of the power grid drops, and the system needs to be switched to a reactive power control mode.
As shown in the structure diagram of epsilon-based fault ride-through switching control shown in fig. 3, when the power grid fails, the PET regulates reactive current in a segmented manner according to the voltage drop depth of the power grid, provides necessary reactive support for the power grid, and keeps the PET not to run off the power grid.
The voltage U of the grid-connected point is detected in real time based on the epsilon fault ride-through switching control structure chart shown in figure 3TTherefore, the power grid voltage drop factor is epsilon, and the PET is subjected to segmented reactive current control with different functional characteristics according to the drop factor epsilon
Wherein U isSFor the voltage at which the grid operates steadily, UTIs a real-time value of the network voltage.
Selecting a reactive current reference value in fault ride-through control according to different drop factors epsilon:
in the formula: i.e. iq-refIs the component of the PET input stage current on the q-axis; epsilon is a voltage sag factor; i isNIs PET grid connection point current. When epsilon is less than or equal to 0.1, the system is in a normal operation state; if epsilon is greater than 0.8, it indicates that the system is in serious failure, and the PET is locked.
The traditional low-voltage ride-through strategy directly adopts PET grid-connected point current INGiven as a fault ride-through reactive reference current. However, because of INThe current required by the low-voltage ride-through strategy is higher than that required by the actual low-voltage ride-through strategy, so that the input reactive reference current instruction is overhigh in value and generates impact.
Comprehensive grid connection point current INAnd a different function characteristic optimization given method of the reactive control current I in the PET fault ride-through process is provided with the dropping factor epsilon:
in the formula: k is an adjustment coefficient; h is a control parameter.
FIG. 4 shows the relationship between I and ε at different adjustment factors.
The idle current set value optimized by different function characteristics replaces the traditionLow voltage ride through strategy instead of INObtaining the given of the fault ride-through reactive reference current for reducing the impact:
according to the grid-connected point current INAnd the drop factor epsilon, the fault ride-through reactive current setting with different curve characteristics is given, the actual conditions required by low-voltage ride-through are better met, the process of switching different reactive current reference values by different drop factors is smoother, and the impact caused by the traditional low-voltage ride-through strategy is reduced.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (4)
1. A reactive current control method for reducing fault ride-through impact of an alternating current-direct current hybrid power distribution network is characterized by comprising the following steps: detecting the voltage of the grid-connected point in real time to obtain a grid voltage drop factor representing the grid drop depth, and judging whether the grid operates normally before light according to the voltage drop factor: when the alternating current power grid normally operates, the power electronic transformer adopts an active power control strategy; when the alternating current power grid fails, the voltage amplitude of the power grid drops, the system needs to be switched to a reactive power control mode, the PET optimizes and adjusts the reactive current in sections by adopting different functional characteristics according to the voltage drop depth of the power grid and the current of a grid-connected point, the given value of the fault ride-through reactive reference current for reducing impact is obtained, and reactive support is provided for the power grid.
2. The reactive current control method for reducing fault-ride-through impact of the alternating current-direct current hybrid power distribution network according to claim 1, characterized by comprising the following operation steps:
s1, detecting voltage U of grid-connected point in real timeTAnd obtaining a power grid voltage drop factor epsilon:
wherein U isSFor voltage values, U, during steady operation of the gridTMeasuring a voltage real-time value of the power grid;
s2, carrying out sectional reactive current control on the PET according to the dropping factor epsilon:
when epsilon is less than or equal to 0.1, the system is in a normal operation state;
if epsilon is more than 0.8, the system is in serious failure, and the PET is locked at the moment;
when the epsilon is more than 0.1 and less than or equal to 0.8, determining a reference value of reactive current in fault ride-through control according to different fall factors epsilon:
in the formula: i.e. iq-refIs the component of the PET input stage current in the q-axis, INIs PET grid connection point current;
s3, synthesizing point-of-connection current INAnd optimizing a reactive control current I value in the PET fault ride-through process by adopting different function characteristics compared with the drop factor epsilon:
in the formula: k is an adjustment coefficient; h is a control parameter;
s4, replacing I in the formula (6) in the step S2 by the optimized reactive current set value in the formula (7) in the step S3NObtaining a given value of the fault ride-through reactive reference current capable of reducing impact:
3. the reactive current control method for reducing fault ride-through impact of the alternating current-direct current hybrid power distribution network according to claim 1, characterized by comprising the following steps of: when the alternating current power grid normally operates, the power electronic transformer adopts a voltage and current double closed-loop control mode.
4. The reactive current control method for reducing fault ride-through impact of the alternating current-direct current hybrid power distribution network according to claim 1, characterized by comprising the following steps of: the PET mainly comprises a front-stage AC/DC power conversion module and a rear-stage DC/DC power conversion module, wherein the front-stage AC/DC power conversion module adopts any one of an H-bridge cascaded multilevel converter, a modular multilevel converter MMC or a hybrid module combined multilevel converter of a cascaded H-bridge + MMC structure; the post-stage DC/DC power conversion module adopts a bidirectional isolation type DC/DC converter (DAB).
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| CN111555328A (en) * | 2020-06-05 | 2020-08-18 | 南京工程学院 | Intelligent state judgment and mode switching method for high-voltage direct-hanging energy storage system |
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| EP3462559A1 (en) * | 2017-09-28 | 2019-04-03 | Vestas Wind Systems A/S | Low voltage fault ride through method for wind power plants |
| CN110311381A (en) * | 2019-07-03 | 2019-10-08 | 国网江苏省电力有限公司电力科学研究院 | A kind of alternating current-direct current mixing grid power electronic transformer passing through DC Line Fault |
| CN110323781A (en) * | 2019-07-03 | 2019-10-11 | 国网江苏省电力有限公司电力科学研究院 | A kind of low voltage traversing control method of modular multilevel electric power electric transformer |
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| EP3462559A1 (en) * | 2017-09-28 | 2019-04-03 | Vestas Wind Systems A/S | Low voltage fault ride through method for wind power plants |
| CN110311381A (en) * | 2019-07-03 | 2019-10-08 | 国网江苏省电力有限公司电力科学研究院 | A kind of alternating current-direct current mixing grid power electronic transformer passing through DC Line Fault |
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