CN111600318B - Current detection method for realizing target three-phase unbalance - Google Patents
Current detection method for realizing target three-phase unbalance Download PDFInfo
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- CN111600318B CN111600318B CN201910736409.2A CN201910736409A CN111600318B CN 111600318 B CN111600318 B CN 111600318B CN 201910736409 A CN201910736409 A CN 201910736409A CN 111600318 B CN111600318 B CN 111600318B
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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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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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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
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Abstract
The application discloses a current detection method for realizing target three-phase unbalance, which comprises the steps of calculating the unbalance of load current of a power distribution area, and detecting zero sequence and negative sequence components, active components and reactive components thereof in the current by using an SDFT (fractional Fourier transform) and a symmetric component method under the condition that the unbalance does not reach the standard; judging whether the compensated zero-sequence component meets the requirement of unbalance degree or not by using a 'simulation compensation' mode, if so, carrying out binary operation on the zero-sequence current to obtain the minimum compensation current, and if not, judging the maximum capacity of the negative sequence capable of being compensated; if the maximum negative sequence capacity can meet the requirement of the degree of unbalance, carrying out dichotomy on the negative sequence current to obtain the minimum negative sequence compensation current, and otherwise, outputting according to the negative sequence current capacity; and superposing the obtained zero sequence current and the negative sequence current to obtain real-time compensation current.
Description
Technical Field
The invention relates to the field of electric energy quality of an electric power system, mainly aims at solving the problem of three-phase unbalanced current in a distribution network area, and carries out unbalanced current treatment on the principle that less equipment is used for outputting power and the service life of the equipment is prolonged.
Background
Because single-phase electric equipment is connected into the power distribution network, under the conditions of large load increase and decrease randomness, instability of seasonal power utilization and temporary power utilization, sensitivity of a small-capacity transformer area to load change, randomness of users in a public transformer area to use the electric equipment and the like, the power distribution network inevitably generates three-phase current imbalance.
The distribution network has unbalanced three-phase current, can produce great influence to transformer and user: the iron loss and the copper loss of the transformer are increased; hysteresis loss and eddy current loss are generated, and the service life of the transformer is influenced; a certain phase of the transformer may be overloaded or overloaded resulting in an imbalance of the three-phase supply voltages, which may thus lead to a malfunction of the consumer. Meanwhile, the national power grid company also issues related notifications aiming at three-phase unbalance of the power distribution area, and examines the unbalance degree of the three-phase current and the current of the zero line.
For three-phase unbalanced current, there are three governing schemes: 1. phase change switch type: the single-phase load is switched, three-phase imbalance is solved from the load side, but the installation workload is large; 2. capacitor type: the power capacitor is connected between the phase lines in a crossing mode, active power transfer is achieved, the installation is easy, but the compensation precision is low, and over compensation is easy; 3. power electronic type: the IGBT is used as a core, the three-phase current is accurately adjusted, and the IGBT is easy to install. In practical application, power supply companies and users mostly use power electronic equipment to treat unbalanced distribution areas of the power distribution network.
In the power electronic type equipment, the conventional unbalanced current treatment scheme is similar to a reactive compensation scheme, three-phase load current in a power distribution network is detected, unbalanced current components are calculated, the power electronic type treatment equipment is used for current compensation, under the condition of sufficient capacity, a transformer completely outputs only balanced current components, the same three-phase output is ensured, no current exists on a zero line, and therefore lower transformer loss is ensured, and the transformer is ensured to operate in a safe state. According to the relevant policies of the national power grid, the unbalance degree of the transformer area can reach the standard within 15%, and complete compensation of the unbalance current is not necessary from the viewpoint of assessment. Meanwhile, the unbalanced current is completely treated, so that the treatment equipment can emit more current. Because three phases output different forces, fully compensating unbalanced current easily causes a certain phase to output too much force for a long time, which may cause that the service life of the equipment is seriously influenced under the condition that the loss of the equipment is small in the other two phases and the loss of the other phase is large.
Disclosure of Invention
The invention aims to provide a current detection method for realizing target three-phase unbalance, which can reduce the output of treatment equipment as much as possible and ensure the relative balance of three-phase output on the premise of ensuring the small three-phase unbalance of a treatment distribution area, thereby prolonging the service life of the equipment. The method detects the unbalanced component of the load current in real time, calculates the required compensation current in real time and carries out three-phase unbalance treatment, and is suitable for the environment with fast load change.
The invention provides a current detection method for realizing target three-phase unbalance, which comprises the following steps:
collecting three-phase power grid voltage and load current of a power distribution area, calculating the current unbalance of a corresponding algorithm according to the check standard of the national grid or the south grid on the unbalance, and judging whether compensation is needed or not; and if the unbalance degree of the load current is higher than the checking requirement, calculating the load rate, and judging whether the load rate is higher than a threshold value corresponding to starting unbalance compensation. And if the current power grid environment meets the conditions of the unbalance degree and the load rate, starting unbalance compensation.
Analyzing the three-phase power grid voltage by using a sliding Fourier transform algorithm or other phase-locking algorithms to obtain phases corresponding to the three-phase voltage; analyzing the three-phase load current by using a sliding Fourier transform algorithm to obtain a three-phase load current fundamental component result, solving positive sequence, negative sequence and zero sequence components of the three-phase load current fundamental component by using a symmetric component method according to the grid voltage phase information, and continuously solving active and reactive components of each sequence component; as the power grid company examines the zero-sequence current, the zero-sequence current component for preferentially compensating the load can be selected.
Judging the maximum zero-sequence current compensation quantity according to the factors such as the rated capacity of the equipment, the magnitude of the zero-sequence current on the load side and the like; judging whether the purely compensated zero-sequence current can meet the requirement of the degree of unbalance or not according to the load current and the compensated maximum negative-sequence current compensation value; if the unbalance degree requirement can be met by only compensating the zero-sequence current, the compensated zero-sequence current can be gradually reduced to meet the set unbalance degree, and if the unbalance degree requirement cannot be met by only compensating the zero-sequence current, whether the negative-sequence current can be continuously supplemented is judged; if the residual capacity continues to compensate the negative sequence current after compensating the zero sequence current, judging the residual capacity, and if the negative sequence current does not continue to be compensated without the residual capacity, not continuing to calculate; and under the condition that the residual capacity compensation negative sequence current exists, judging whether the residual capacity can completely compensate, if so, gradually reducing the current until the unbalance of the three-phase current reaches a set value, otherwise, compensating the full capacity, and finally, failing to reach the required unbalance.
Wherein, still include:
in the process of gradually approaching the current value, in order to lock the current magnitude as soon as possible, the current magnitude is judged by adopting a dichotomy, so that the judgment range of the current is exponentially reduced.
If harmonic current exists in the three-phase load current, the single-phase harmonic current effective value is calculated through the single-phase current effective value and the single-phase fundamental current effective value, and the harmonic current effective value always penetrates through the binary method in the process of solving the current, so that the method is also suitable for the environment with high harmonic content in the load current.
And a Fourier transform algorithm is adopted to correct the result obtained by the sliding Fourier transform, so that the compensation current detection error caused by accumulated error is avoided.
Further comprising:
in order to reduce the operation amount, the voltage fundamental wave components can be approximately considered to be balanced, the phase difference of the three-phase grid voltage fundamental wave components is an ideal phase difference, only the phase of the A-phase voltage is needed to be calculated, the other two-phase voltage phases are operated, and then the subsequent detection process is carried out.
In the process of gradually approaching the current value, in order to avoid the phenomenon of infinite times of binary operation, a current interval threshold value is set, when the current range is smaller than the threshold value in the binary operation process, the binary operation is stopped, and the current is used as the compensation current to be output.
In the process of gradually approaching the current value, in order to accelerate the locking process of the current value, a frequency limit value of binary operation is set, when the frequency of the binary operation exceeds the set frequency limit value, the binary operation is stopped, and the current is output as a compensation current.
The invention provides a current detection method for realizing target three-phase unbalance, which comprises the steps of judging whether a power grid environment meets a compensation condition, locking a phase of a single-phase power grid voltage, extracting a fundamental wave component of a three-phase load current, decomposing a positive sequence, a negative sequence and a zero sequence according to a symmetrical component method, detecting active power and reactive power of each sequence component according to the power grid voltage phase, compensating the zero sequence current or the zero sequence and the negative sequence current according to equipment capacity, and obtaining minimum compensation current meeting the set three-phase unbalance by using a dichotomy method.
The method can detect current signal components in real time, obtain real-time compensation current values in a 'simulation compensation' mode, has the advantages of high tracking speed, small detection operand and the like, can adapt to a power grid environment with large load harmonic current, and finally achieves the effects of small current output of management equipment, long service time and capability of meeting the requirement of the imbalance degree of a transformer area.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a flow chart of an overall detection process provided by an embodiment of the present invention;
FIG. 2 is a flow chart of a key process of current detection according to an embodiment of the present invention;
FIG. 3 is a flow chart of a current approximation process provided by an embodiment of the present invention;
FIG. 4 is a diagram illustrating a process for detecting components of each sequence of current according to an embodiment of the present invention;
fig. 5 is a flowchart of a remaining capacity detection process according to an embodiment of the present invention;
fig. 6 is a simulation result of compensating current for only compensating zero sequence current according to an embodiment of the present invention;
FIG. 7 is a simulation result of compensating currents for compensating zero-sequence and negative-sequence currents according to an embodiment of the present invention;
FIG. 8 is a simulation result of the compensation current that cannot reach the imbalance level setting due to capacity limitation according to the embodiment of the present invention;
fig. 9 is a simulation result of the compensation current when the unbalanced current is fully compensated according to the embodiment of the present invention.
Detailed Description
The core of the invention is to provide a current detection method for realizing the target three-phase unbalance degree, which has high real-time performance, small operand and high tracking speed, is suitable for a power grid environment with more harmonic current and can eliminate accumulated errors caused by interference and iterative operation.
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Fig. 2 is a flowchart of a critical process of current detection according to an embodiment of the present invention, where the method includes:
step 1, collecting three-phase load current, calculating the unbalance degree of the current load side according to the power grid standard, and judging whether unbalance compensation is needed;
and if the actual unbalance degree is higher than the target unbalance degree value and the current station area load rate is higher than the set load rate threshold, performing a subsequent detection process, otherwise, not performing unbalance compensation.
Step 2, calculating a grid voltage phase, calculating a load current fundamental wave component, solving positive sequence, negative sequence and zero sequence components of the load current, further solving active and reactive components of the negative sequence and the zero sequence of the load current, and solving harmonic current content;
the SDFT algorithm is used for solving the power grid voltage phase and the load current fundamental wave component, and the SDFT operation formula is as follows:
n is the number of sampling points in one cycle.
According to the formula of the calculation,determining the voltage phase of an A-phase network
The phase of the BC phase voltage is->
Method for calculating fundamental component RMS of three-phase load current I ＝abs(I n+1 )，/>
According to a symmetrical component method, positive sequence, negative sequence and zero sequence contents of three-phase current are obtained, and then active and reactive components of the negative sequence and the zero sequence of the three-phase current are obtained according to the voltage phase of a power grid and serve as sources of subsequent residual capacity solving.
Wherein, each formula is as follows:
symmetrical component method
The negative sequence and the zero sequence of the three-phase current are respectively as follows:
and by combining the voltage phase of the power grid, the included angles between the negative sequence and zero sequence components of the three-phase current and the voltage of the power grid are respectively as follows:
the active and reactive components of the negative sequence and the zero sequence of the three phases are respectively:
the three-phase harmonic effective value is:
step 3, judging the zero-sequence current capacity, and solving the zero-sequence current demand by utilizing a dichotomy;
judging the maximum zero-sequence current which can be sent out according to the capacity of the equipment and the maximum zero-sequence current which can be sent out by the equipment, judging whether the maximum zero-sequence current can meet the requirement of unbalance degree by using a simulation compensation mode, and (1) if the unbalance degree after the simulation compensation is lower than the unbalance degree set value at the moment, carrying out dichotomy on the zero-sequence current, solving the minimum zero-sequence current which can meet the unbalance degree, and not carrying out subsequent operation; (2) if the unbalance degree after the analog compensation is higher than the unbalance degree set value, performing subsequent operation;
and when the length of the current interval in the binary operation process is smaller than the interval threshold or the number of binary operations reaches the set number, stopping current detection, and outputting the current result.
Step 4, if the condition (2) is met, judging the residual capacity, and calculating the demand of the negative sequence current by using a dichotomy;
(1) if the zero sequence current requirement exceeds the rated capacity of the equipment in the last step, the residual capacity is 0; (2) otherwise, according to the active and reactive components of the zero sequence and the negative sequence, the maximum compensated negative sequence current is judged;
if the condition (2) is met, the maximum negative sequence current proportion is obtained, if the negative sequence full compensation does not exceed the set rated capacity, the proportion is 1, otherwise, the current proportion is solved by using a unitary quadratic function mode;
if the maximum compensatable negative sequence current of the analog compensation is not enough to enable the current unbalance degree to meet the requirement, the negative sequence current is output according to the maximum compensatable value; otherwise, carrying out dichotomy operation on the maximum compensatable negative sequence current to obtain the minimum current demand meeting the set unbalance degree, wherein the negative sequence current dichotomy operation mode is the same as the zero sequence current dichotomy operation mode.
And 5, obtaining the compensated zero sequence current and the compensated negative sequence current according to the mode, and combining the phases of the zero sequence current and the negative sequence current to output the current compensation current.
The embodiments are mainly described with reference to the differences from the other embodiments, and the same portions in the embodiments may be referred to one another.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or the like. While the foregoing description has generally described various example compositions and steps in terms of their functionality, the manner in which such functionality is implemented should not be construed as exceeding the scope of the invention.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (7)
1. A current detection method for realizing target three-phase unbalance is characterized in that the method detects the current unbalance of a distribution transformer area, detects unbalanced components of current, and detects the minimum compensation current for realizing the target unbalance in an analog compensation mode, and comprises the following specific steps:
1) Collecting three-phase load current, calculating three-phase unbalance according to a power grid standard, and judging whether a compensation starting condition is met or not according to the load unbalance and a load rate;
2) If the starting compensation condition is met, the zero-sequence current is compensated preferentially, and whether the compensated zero-sequence current meets the requirement of the unbalance degree is judged in a 'simulation compensation' mode:
if the requirements are met, reducing and compensating the zero-sequence current by a dichotomy; if the unbalance degree requirement is not met, performing the subsequent steps;
3) Calculating the residual capacity of the negative sequence current, namely the maximum value of the negative sequence current which can be compensated;
through the mode of "simulation compensation", judge whether the negative sequence current maximum value that can compensate satisfies the degree of unbalance requirement:
if the requirements are met, the negative sequence current is continuously reduced and compensated by a dichotomy; if the unbalance degree requirement is not met, the compensation negative sequence current is completely used for compensation;
4) And calculating to obtain a final compensation current result according to the compensation zero sequence current and the compensation negative sequence current obtained in the step.
2. The method as claimed in claim 1, wherein the SDFT algorithm is used to obtain the phase of the grid voltage and the fundamental component of the load current, the symmetric component method is used to obtain the negative sequence component and the zero sequence component of the load current, and the grid voltage phase information is combined to obtain the active and reactive components of the corresponding components for the subsequent residual capacity calculation process.
3. The method as claimed in claim 1, wherein a dichotomy interval threshold and a dichotomy number limit are set, and in the dichotomy process, when the current interval is smaller than the set interval threshold or the dichotomy number reaches the number limit, the operation is stopped.
4. The method as claimed in claim 1, wherein the harmonic effective value is obtained from the current effective value and the fundamental component in an environment with a large harmonic current, and is used in a subsequent analog compensation process.
5. The current detection method for achieving the target three-phase imbalance degree according to claim 1, wherein the specific step of calculating the negative-sequence current residual capacity in the step 3) is as follows: and judging whether the three-phase load current exceeds the output current limit value or not during the negative sequence current full compensation according to the proportion of zero sequence current compensation and the active and reactive component sizes of the negative sequence current, and solving the negative sequence current proportion by using a unitary quadratic equation solution mode if the three-phase load current exceeds the output current limit value so as to obtain the maximum value of the negative sequence current capable of being compensated.
6. The method as claimed in claim 2, wherein the DFT operation is performed intermittently to correct the result of the SDFT algorithm, thereby preventing the current detection error caused by the accumulated error.
7. The method as claimed in claim 1, wherein the load current component is detected in real time, the compensation current reference is obtained in real time, and a good tracking effect can be achieved in a power grid environment with fast current fluctuation.
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| CN112531695B (en) * | 2020-11-27 | 2022-09-06 | 国网湖南省电力有限公司 | Electric energy quality branch self-adaptive compensation method and system |
| CN112946374B (en) * | 2021-01-27 | 2024-03-19 | 华北电力大学 | Three-phase unbalance detection method and device based on convolution window function |
| CN113098005B (en) * | 2021-04-09 | 2022-07-01 | 广东电网有限责任公司广州供电局 | Orderly power utilization monitoring method and device and distribution side monitoring equipment |
| CN114113774B (en) * | 2021-11-19 | 2023-12-19 | 国网辽宁省电力有限公司鞍山供电公司 | State analysis method of distribution transformer based on zero line current data |
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