CN110797887B - Low-voltage area three-phase imbalance treatment self-decision control method - Google Patents
Low-voltage area three-phase imbalance treatment self-decision control method Download PDFInfo
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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
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- 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
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
Abstract
The invention discloses a self-decision control method for three-phase imbalance treatment of a low-voltage transformer area.A phase change switch locally decides whether phase change operation is needed or not, and does not depend on communication; firstly, calculating three-phase voltage unbalance degree and unbalanced voltage according to three-phase voltage data collected by a phase change switch, and triggering a phase change strategy when the number of continuous out-of-limit times of the three-phase voltage unbalance degree exceeds a limit value and the accumulated unbalanced voltage is out-of-limit; and then calculating the three-phase voltage value and the three-phase voltage unbalance degree after phase conversion according to the three-phase voltage, the load current, the line equivalent impedance and the current phase of the switch, and performing phase conversion operation if the three-phase voltage unbalance degree after phase conversion is obviously improved. The method not only can effectively reduce the three-phase unbalance of the head end of the station area, but also can reduce the three-phase unbalance of each branch line.
Description
Technical Field
The invention relates to a self-decision control method for three-phase imbalance management of a low-voltage transformer area, and belongs to the technical field of power system power grid.
Background
The problem of unbalanced three-phase load of the low-voltage distribution network exists for a long time in the process of power grid construction in China. Low-voltage distribution networks generally adopt a three-phase four-wire system power supply mode, and most users are single-phase loads or single-phase and three-phase mixed loads, so that single-phase loads in the distribution network are distributed among three phases in a serious unbalanced manner, and particularly, distribution systems for residential and commercial buildings are used. The three-phase load unbalance can cause the problems of overlarge zero line current, overhigh power grid loss, unbalanced three-phase voltage, low power grid voltage, low utilization rate of three-phase power equipment, high neutral line point position, endangered personal safety and the like.
In rural areas of China, the phenomenon of three-phase load unbalance in a power distribution network is common. The investigation shows that only nearly 10% of 100 distribution transformers in rural power network operation in a certain area are operated in a state of basically balanced three-phase load, the transformers which are operated in unbalanced three-phase load but not exceeding the regulated transformers account for 35%, and the transformers which are operated in severely unbalanced three-phase load account for 55%. In cities, the problem of unbalanced load three phases still exists, and the unbalanced load three phases have certain influence on the normal operation of the low-voltage distribution network, for example, the loss of a transformer and a circuit is increased, the working temperature of the normally operated transformer is increased, the actual available capacity of the transformer is reduced, the output three-phase voltage of the transformer is unbalanced, neutral point voltage offset is caused, and the electric equipment of a user can be burnt when the situation is serious. Therefore, the problem of low-voltage three-phase load unbalance should be paid attention to.
In order to reduce the power loss of the distribution area and improve the power quality of the distribution network, effective measures are necessary to treat or eliminate the low-voltage three-phase load unbalance. Besides improving planning and management level, conventional treatment measures for solving the problem of low-voltage three-phase imbalance at home and abroad mainly comprise: manual commutation, reactive compensation devices, automatic switching devices, etc.
(1) Manual phase change: the load is equally divided by adopting manual adjustment, the load is equally divided as much as possible by combining a history record under the condition of allowing conditions and according to real-time online monitoring data in a mode of manually adjusting wiring, and the three-phase load distribution control is enhanced. Aiming at the problem of three-phase unbalance brought by a distribution transformer, through statistical analysis of load data, phase sequences with heavy load and light load are subjected to phase modulation, so that the phase sequences are as close to three-phase balance as possible, but the single-phase electric equipment at a user side is lower in the same time rate, meanwhile, the electricity consumption condition of the user is greatly influenced by seasonal factors, and the electricity consumption of each month or each season of an electricity consumption client is often greatly different, so that the three-phase load of the distribution transformer is further unbalanced, and meanwhile, the adjustment effect is not ideal because of frequent interruption of the single-phase load.
(2) Reactive power compensation device: reactive compensation is carried out aiming at the unbalance problem, and is a main measure for treating the three-phase unbalance problem in various countries in the world at present, and the reactive compensation device is adopted for carrying out reactive compensation, so that the power factor of the system can be greatly improved, the loss of a circuit and a transformer can be reduced, and the stability of the system can be increased. Currently, a static reactive compensator, an active filter and the like are commonly adopted as important devices for reactive compensation internationally. In an actual power system, three-phase unbalance and reactive power often occur at the same time, so that the reactive power compensation and three-phase unbalance inhibition function can be achieved simultaneously by improving a control algorithm on the basis of the traditional power electronic SVC or SVG reactive power compensation function. However, the device is often arranged on the low-voltage side of the distribution transformer for centralized compensation, and although the power quality of the outlet voltage and the current of the transformer can be well adjusted to improve the running state of the transformer, the problem of unbalanced three-phase load of a low-voltage line is not fundamentally solved, and the problems of high line loss and voltage quality of end loads still exist.
(3) An automatic switching device: the scheme for adjusting the three-phase unbalanced current by the phase change switching device has the advantages that the intelligent logic judgment is adopted to automatically select the power supply phase, the unbalance of the three-phase load is automatically adjusted, the loss of electric energy in the transmission process is reduced, the problem of low voltage at the tail end of a line is effectively solved, the utilization rate of the electric energy is improved to the maximum extent, and the reliability of power supply of a power grid is enhanced; the disadvantage is that the power factor of the power supply line is limited to increase, the overall investment cost of the equipment is high, and the overall reconstruction of facilities is difficult.
At present, the three-phase unbalanced load change-over switch needs to be controlled by a control terminal to give a remote control command so as to finish the change-over work of the phase change. A main control terminal is generally arranged at the head end of the low-voltage side of a transformer area, a plurality of phase change switches are arranged on branch lines, and the phase change switches are controlled by the main control terminal to adjust three-phase unbalance, but the mode has higher requirements on communication conditions. The communication modes of the station area mainly include two modes: micropower wireless and carrier communication. Both modes of communication face engineering difficulties. The micro-power wireless communication encounters shielding, which can lead to communication failure or instability. The carrier communication is interfered by power electronic equipment such as SVG or APF, and in a station area in an economically developed area, the communication interference is caused due to complex load distribution.
The invention researches a three-phase imbalance treatment mode which is not dependent on communication, adopts a self-decision built-in control strategy, performs strategy optimization and treatment on the basis of the existing load change-over switch, upgrades the load change-over switch into intelligent load change-over switch equipment, and can finish three-phase imbalance treatment within a local area range even if communication is interrupted.
Disclosure of Invention
Aiming at the limitation of the load regulation mode of the existing phase change switch, the invention provides a method for regulating the phase-to-phase load imbalance state by collecting and calculating the deviation of the voltage at each branch line, relying on the phase change switch equipment and not depending on communication to form a localized self-decision type control strategy.
The technical solution of the invention is as follows: a self-decision control method for three-phase imbalance treatment of a low-voltage transformer area comprises the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and performing data rationality verification;
s2: calculating the voltage unbalance degree and the accumulated unbalanced voltage, and judging whether to trigger a commutation strategy according to the voltage unbalance degree and the accumulated unbalanced voltage;
s3: if the current phase is the maximum voltage phase, not performing phase change operation, returning to S1, otherwise entering S4;
s4: pre-estimating a voltage change value after phase change and a three-phase imbalance treatment effect;
s5: calculating the execution delay time of the commutation command according to the imbalance degree beta of the three-phase voltage before commutation and the imbalance degree improvement value delta beta of the voltage after commutation;
s6: and updating the load phase-change out-phase and load phase-change phase line equivalent impedance table after the phase change is executed.
The invention has the advantages that:
1) The self-decision control strategy algorithm is embedded in the phase change switch, so that the problems of information loss and the like caused by difficult communication construction or unstable communication of a transformer area can be avoided, and the bottleneck of three-phase imbalance treatment by data communication between the distribution transformer terminal equipment or the centralized control switch and the branch phase change equipment is fundamentally broken through;
2) According to data acquisition and analysis of the three-phase voltage at the user side, low-voltage three-phase unbalance self-decision control can be realized, so that not only is the three-phase current unbalance degree at the head end of the transformer area reduced, but also the three-phase current unbalance degree of the branch line is effectively reduced.
Drawings
FIG. 1 is a schematic diagram of a three-phase imbalance governance self-decision control system for a low-voltage transformer area.
FIG. 2 is an algorithm flow chart of a low-voltage area three-phase imbalance remediation decision control method.
Detailed Description
A self-decision control method for three-phase imbalance treatment of a low-voltage transformer area specifically comprises the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and performing data rationality check, namely checking whether the measured electric quantity is in a reasonable range or not, and checking whether data are dead data or not;
s2: calculating the voltage unbalance degree and the accumulated unbalanced voltage, and judging whether to trigger a commutation strategy according to the voltage unbalance degree and the accumulated unbalanced voltage; step S2 includes steps S21, S22 and S23:
s21: calculating three-phase voltage unbalance beta:
wherein max (u a ,u b ,u c ) For the maximum value of the three-phase voltage, min (u a ,u b ,u c ) Is the minimum value of three-phase voltage.
S22: calculating a three-phase average voltage u av Phase a unbalanced voltage deltau a Phase B imbalance voltage Deltau b Unbalanced C-phase voltage Deltau c ：
u av ＝(ua+ub+uc)/3
Δu a ＝u a -u av
Δu b ＝u b -u av
Δu c ＝u c- u av
Wherein u is a For the A-phase voltage, deltau b For B-phase voltage, deltau c Is the C phase voltage;
the unbalanced voltages of each phase measured each time are respectively accumulated to obtain the accumulated unbalanced voltage Deltau of each phase a_sum 、Δu b_sum And Deltau c_sum ：
Δu a_sum ＝∑Δu ai
Δu b_sum ＝∑Δu bi
Δu c_sum ＝∑Δu ci
S23: when the out-of-limit times of the voltage unbalance degree reach the limit value and the accumulated unbalanced voltage value reaches the limit value, entering a commutation strategy; s3: if the current phase is the maximum voltage phase, not performing phase change operation, returning to S1, otherwise entering S4;
s4: the voltage change value after commutation and the commutation treatment effect are estimated, and the method comprises the following two steps of S41 and S42:
s41: calculating load phase-out voltage u 'after phase change' out And load transfer phase voltage u' in ：
u′ out ＝u out +i×Z out
u′ in ＝u in +i×Z in
Wherein u is out To change the load to output the phase voltage, u in For switching the load to the phase voltage before switching, i is the load current, Z out To transfer the equivalent impedance of the same line for the load, Z in Equivalent impedance for load transfer to the same line;
s42: calculated u 'according to S41' out And u' in And calculating the imbalance degree beta 'of the three-phase voltage after the phase conversion according to the voltage value of the other phase, if the imbalance degree is improved by the value delta beta=beta-beta' > delta beta lim Then the phase change operation is carried out, delta beta lim The threshold is improved for voltage imbalance.
S5: calculating the commutation command execution delay time delta t according to the three-phase voltage unbalance beta before commutation and the voltage unbalance improvement value delta beta after commutation:
wherein T is 1 And T 2 The reference delay time corresponding to the unbalance degree and the reference delay time corresponding to the unbalance degree improvement are respectively obtained; s6: judging whether a commutation condition is met, locking equipment for a period of time after a commutation command is executed, updating a load phase-out and load phase-in equivalent impedance table, and storing voltage and equivalent impedance before commutation:
in the formula, u' out The voltage is measured by the phase change for the load after phase change, u out To transfer out the phase measurement voltage for the phase change preload, u' in To transfer into the phasor voltage after the phase change, u in For the commutation-before-commutation phase-inversion voltage measurement, i is the load current.
It is to be understood that the above examples of the present invention are provided by way of illustration only and not by way of limitation of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (1)
1. A self-decision control method for three-phase imbalance treatment of a low-voltage transformer area is characterized by comprising the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and performing data rationality verification;
s2: calculating the voltage unbalance degree and the accumulated unbalanced voltage, and judging whether to trigger a commutation strategy according to the voltage unbalance degree and the accumulated unbalanced voltage:
s21: calculating three-phase voltage unbalance beta:
wherein max (u a ，u b ，u c ) For the maximum value of the three-phase voltage, min (u a ，u b ，u c ) Is the minimum value of three-phase voltage;
s22: calculating a three-phase average voltage u av Phase a unbalanced voltage deltau a Phase B imbalance voltage Deltau b Unbalanced C-phase voltage Deltau c ：
u av ＝(ua+ub+uc)/3
Δu a ＝u a -u av
Δu b ＝u b -u av
Δu c ＝u c -u av
Wherein u is a For the A-phase voltage, deltau b For B-phase voltage, deltau c Is the C phase voltage;
the unbalanced voltages of each phase measured each time are respectively accumulated to obtain the accumulated unbalanced voltage Deltau of each phase a_sum 、Δu b_sum And Deltau c_sum ：
Δu a_sum ＝∑Δu ai
Δu b_sum ＝∑Δu bi
Δu c_sum ＝∑Δu ci
S23: when the out-of-limit times of the voltage unbalance degree reach the limit value and the accumulated unbalanced voltage value reaches the limit value, entering a commutation strategy;
s3: if the current phase is the maximum voltage phase, not performing phase change operation, returning to S1, otherwise entering S4;
s4: pre-estimating a voltage change value after phase change and a three-phase imbalance treatment effect:
s41: calculating load phase-out voltage u 'after phase change' out And load transfer phase voltage u' in ：
u′ out ＝u out +i×Z out
u′ in ＝u in +i×Z in
Wherein u is out To change the load to output the phase voltage, u in For switching the load to the phase voltage before switching, i is the load current, Z out To transfer the equivalent impedance of the same line for the load, Z in Equivalent impedance for load transfer to the same line;
s42: according toS41 calculated u' out And u' in And calculating the imbalance degree beta 'of the three-phase voltage after the phase conversion according to the voltage value of the other phase, if the imbalance degree is improved by the value delta beta=beta-beta' > delta beta lim Then the phase change operation is carried out, delta beta lim Improving a threshold for voltage imbalance;
s5: calculating the commutation command execution delay time delta t according to the three-phase voltage unbalance beta before commutation and the voltage unbalance improvement value delta beta after commutation:
wherein T is 1 And T 2 The reference delay time corresponding to the unbalance degree and the reference delay time corresponding to the unbalance degree improvement are respectively obtained;
s6: updating the load phase-change output and load phase-change input line equivalent impedance table after the phase change is executed:
s61: commutation operation execution conditions: the command execution time is reached and the switch is not locked;
s62: updating line impedance information:
in the formula, u' out The voltage is measured by the phase change for the load after phase change, u out To transfer out the phase measurement voltage for the commutation preload, u i ′ n To transfer into the phasor voltage after the phase change, u in For the phase inversion before phase inversion, the phase measurement voltage is converted, i is the load current;
and writing the equivalent impedance value and the voltage before commutation into a database for the next estimated voltage after commutation.
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| CN113890067A (en) * | 2021-09-10 | 2022-01-04 | 三峡大学 | Three-phase unbalance treatment method based on combination of STATCOM and commutation switch |
| CN114243733A (en) * | 2021-12-08 | 2022-03-25 | 国网福建省电力有限公司晋江市供电公司 | Three-phase voltage unbalance treatment device and method based on voltage dynamic compensation |
| CN117117910B (en) * | 2023-10-25 | 2024-01-16 | 成都汉度科技有限公司 | Automatic three-phase unbalance adjustment method for transformer area |
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