Low-voltage distribution line load pre-balancing method based on user power consumption behavior prediction

Abstract

The invention provides a low-voltage distribution line load pre-balancing method based on user power consumption behavior prediction, and belongs to the technical field of power system dispatching. According to the method, a commutation control terminal is connected in parallel to the secondary side of a transformer to detect transformer area data, the three-phase unbalance degree and a commutation strategy are calculated, and a commutation command is sent to a commutation switch in a wireless communication mode; the phase-change switch is connected in parallel with a power grid feeder line in a three-phase four-wire system, is connected in series with a user through a zero line and a live line, collects electrical data of the user, uploads the electrical data to the phase-change control terminal, executes a phase-change instruction sent by the phase-change control terminal, and switches the user to a specified phase sequence. The method fully improves the operation safety, reliability and economical efficiency of the low-voltage power distribution network, has outstanding practical value, also provides a new thought for three-phase line load imbalance treatment research, and is very suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system dispatching, and specifically relates to a low-voltage distribution line load pre-balancing method based on user power consumption behavior prediction. Background Art

[0002] In low-voltage distribution networks, transformers transmit power to users through three-phase four-wire feeders. Single-phase loads account for the majority in the substation area (referring to the power supply area of ​​a distribution transformer), and the more developed the economy, the greater the proportion of single-phase users. The power consumption patterns of these loads are affected by multiple factors such as season, weather, and time, and have strong random characteristics, resulting in uneven distribution of three-phase power in the substation area, which in turn causes three-phase imbalance in the distribution network. In addition, with the rapid development of industrial production in recent years, factors such as the increase in nonlinear loads in the substation area, the increase in charging and discharging of electric vehicles, the access of distributed power generation to the grid, and the frequent start and stop of high-power equipment have exacerbated the three-phase imbalance problem in the low-voltage distribution network. Due to the incomplete consideration of early planning of some distribution substations, and the limitations of geographical location and economic costs, the three-phase imbalance problem has been ignored.

[0003] The three-phase four-wire power supply and distribution system has its unique advantages and has become the main distribution method for residential electricity. The problem of unbalanced load on three-phase lines has always existed since the beginning of the construction of the distribution network, but the relevant research on the management of unbalanced load on three-phase lines started late both at home and abroad. It was not until the rapid expansion of the scale of the power grid in the past 10 to 20 years that the unbalanced load on three-phase lines has become an unavoidable problem, and related research has gradually been taken seriously by research teams at home and abroad. According to the investigation, there are as many as 10 research groups in the US research institute that are studying issues such as power quality detection, unbalanced load management on three-phase lines, power supply and distribution loss control, and harmonic suppression. At present, the main methods for managing unbalanced load on three-phase lines are distribution network reconstruction, load compensation, and load commutation. Among them, the load commutation method is a method for managing three-phase imbalance from the source.

[0004] The load commutation method is to adjust the phase sequence of the single-phase load connected to the feeder through the phase-commutation device, and switch part of the load on the heavy-load phase to the light-load phase, so as to achieve the purpose of three-phase balance. The early load commutation method was manual commutation, and the switch was manually pulled according to the monitoring data and experience. It can indeed alleviate the three-phase imbalance problem to a certain extent in a short time, but it will cause power outages to users and the timeliness is poor. The development of power electronics technology has enabled automatic commutation devices to be designed to solve engineering problems. The load commutation method is a physical division and redistribution of the load. It has become the first choice of engineers because it can bring immediate treatment effects under severely unbalanced working conditions. Phase exchange can balance the unevenly distributed loads of each phase. However, the large-scale use of load commutation devices to treat three-phase imbalance still faces many challenges: the factors considered in the commutation strategy are not comprehensive and need to be optimized, and the short-term power outage problem at the moment of phase exchange needs to be solved urgently.

[0005] Many commutation strategies designed based on load commutation devices have been proposed. Some scholars have proposed that each factor in the commutation is abstracted as a mixed integer non-convex programming problem, and then an iterative algorithm is used to reduce the number of commutation device actions; a commutation strategy with the goal of minimizing the three-phase current imbalance is established, and the pigeon flock algorithm is used to solve the commutation scheme; a research institution has proposed an automatic balancing control commutation strategy for load imbalance, which has been verified in simulation; the commutation strategy studied above can effectively reduce the three-phase imbalance and reduce the number of commutations. However, these methods only consider the three-phase imbalance caused by electricity consumption, but ignore the impact of power transmission on the imbalance. The random phase selection of DG to inject current will aggravate the three-phase imbalance. Moreover, the above literature research only stays at the theoretical level of algorithm and simulation, and has not been implemented at the hardware level. Summary of the invention

[0006] The present invention aims to address the technical defects of the prior art and provide a low-voltage distribution line load pre-balancing method based on user power consumption behavior prediction to solve the technical problem that conventional load commutation schemes are difficult to achieve safe and reliable seamless commutation operation.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A load pre-balancing method for low-voltage distribution lines based on the prediction of user electricity consumption behavior, in which the phase-changing control terminal is connected in parallel to the secondary side of the transformer to detect the data of the substation, calculate the three-phase imbalance and the phase-changing strategy, and send the phase-changing command to the phase-changing switch through wireless communication; the phase-changing switch is connected in parallel with the grid feeder in a three-phase four-wire system, and is connected in series with the user through a neutral line and a live line. The phase-changing switch collects the user's electrical data and uploads it to the phase-changing control terminal, and executes the phase-changing command sent by the phase-changing control terminal to switch the user to the specified phase sequence.

[0009] Preferably, the commutation control terminal includes an MCU microcontroller module, a power module, a voltage measurement module, a current measurement module, a communication module, and a signal indication module, wherein the power module is electrically connected to the MCU microcontroller module, the voltage measurement module and the current measurement module are respectively communicatively connected to the MCU microcontroller module and send voltage information and current information to the MCU microcontroller module respectively, the MCU microcontroller module is communicatively connected to the signal indication module and sends an indication signal to the signal indication module, and the MCU microcontroller module communicates with the communication module in a bidirectional manner.

[0010] Preferably, the phase-changing switch performs system initialization and self-test in sequence after operation, uploads fault information when the self-test is abnormal, reads single-phase load electrical parameters when the self-test is normal, and then reads instantaneous current data when a phase-changing instruction is received, and executes the phase-changing circuit action when the phase-changing conditions are met.

[0011] Preferably, in the method, the relative measurement error of the input voltages of L1 and L2 of the same phase-changing switch is less than a certain threshold; and the relative error of current measurement between different phase-changing switches is less than a certain threshold.

[0012] Preferably, in this method, the phase switching time is less than 20 ms.

[0013] Preferably, the user power of the method is less than 100w when performing the commutation operation.

[0014] Preferably, the method targets the unbalanced load on the three-phase line caused by asymmetric load sizes and ignores the asymmetric load phases.

[0015] Preferably, the method evaluates the correlation of electricity users' electricity consumption behaviors by using a random matrix theory correlation analysis method. In the random matrix theory correlation analysis method, a load curve data set and an environmental factor data set are collected respectively, and then the random matrix correlation is determined by an augmented matrix method, the average spectrum radius is determined, and a correlation index is obtained.

[0016] As a preferred method, the method uses a discrete coefficient to calculate the three-phase current unbalance degree. In the calculation process, the discrete coefficient of the effective value of the three-phase current is used. Times represents the three-phase current unbalance:

[0017]

[0018] In the above formula, V s is the dispersion coefficient of the three-phase current.

[0019] Preferably, the following relationship is satisfied during the calculation process:

[0020]

[0021] From formula 2, we can get:

[0022]

[0023] In formula 3, I sum =I A +I B +I C , Substituting equation 3 into equation 1, we get the following equation 4:

[0024]

[0025] Among them, the three-phase current unbalance degree is the unbalanced current I N The percentage of the total current; the value range of the three-phase current unbalance is [0 1]. N =0, the three-phase current imbalance is zero, and the system is in a three-phase balanced state; when IN =I sum When , the three-phase current imbalance is 1, and the imbalance degree is the largest.

[0026] The present invention provides a method for pre-balancing the load of low-voltage distribution lines based on the prediction of user power consumption behavior. The method monitors and analyzes the current state or historical state of the distribution network to determine the most reasonable power phase for users who have not used electricity yet (power less than 100W) in the future, so as to switch the users to this phase in advance, so that when these users start to use electricity, it will always help reduce the unbalanced load of the three-phase line.

[0027] The present invention first combines the massive user electricity consumption data collected by the smart meter during the operation of the power grid and the background information of the power users obtained through the survey, and uses the power load curve clustering and the correlation analysis method based on the random matrix theory to analyze and study the power consumption behavior characteristics of the power users, so as to provide a reference for formulating a fine load pre-balancing strategy. On this basis, a set of low-voltage distribution line load pre-balancing strategies based on the phase-changing method is designed. Combined with the user's electricity consumption behavior characteristics, the phase-changing operation is completed before the user uses electricity, without the need for high-current phase-changing, thereby avoiding the phase-changing risk problem existing in the automatic phase-changing device.

[0028] The present invention fully improves the safety, reliability and economy of low-voltage distribution network operation, has outstanding practical value, provides new ideas for the research on three-phase line load imbalance control, and is very suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the circuit model diagram of the three-phase four-wire power supply system.

[0030] Figure 2 This is the simulation model diagram of the daily system.

[0031] Figure 3 This is a diagram of the commutation device and user load model.

[0032] Figure 4 This is the model diagram of the commutation device.

[0033] Figure 5 This is the overall framework diagram of the intelligent monitoring device.

[0034] Figure 6 This is the program flow chart of the commutation device. DETAILED DESCRIPTION

[0035] The specific embodiments of the present invention will be described in detail below. In order to avoid too much unnecessary details, the well-known structures or functions will not be described in detail in the following examples. The approximate language used in the following examples can be used for quantitative expression, indicating that the quantity can be allowed to have a certain change without changing the basic function. Unless otherwise defined, the technical and scientific terms used in the following examples have the same meaning as those generally understood by those skilled in the art to which the present invention belongs.

[0036] my country's low-voltage power supply and distribution system adopts the TN-C three-phase four-wire system, while the user load is mostly single-phase load, the user load power is uncertain, and the power consumption time is uncertain, resulting in unequal loads on the three-phase line, causing unbalanced loads on the three-phase line. In the low-voltage power supply and distribution system, the three-phase power supply is generally symmetrical, so the imbalance of the three-phase line is mainly caused by the asymmetry of the phase and size of the three-phase load, among which the asymmetry of the load size accounts for the main part. Therefore, the present invention mainly studies the problem of unbalanced load on the three-phase line caused by the asymmetry of the load size, and ignores the part of the asymmetry of the load phase.

[0037] Figure 1 It is a circuit model of a three-phase four-wire power supply system. Taking node N as the reference node, the voltage between N′ and N can be easily obtained by the node voltage method:

[0038]

[0039] In formula (1), In actual situations, it is generally believed that the three-phase power supply is symmetrical, that is, there are:

[0040]

[0041] Therefore, when the loads of each phase are symmetrical, that is, Z A =Z B =Z C When the load current of each phase is equal, Neutral current At this time, the system is in a three-phase balanced state; when the loads of each phase are unequal, that is, Z A ≠Z B ≠Z C , the load currents of each phase are not equal, Generally not zero, neutral current At this time, the system is in a three-phase unbalanced state, and the current on the neutral line is Will be in Z N A voltage drop is generated on the three-phase load, which in turn affects the load voltage of each phase, resulting in an unbalanced three-phase voltage.

[0042] Reasonable calculation of the three-phase line load imbalance is very important for evaluating the three-phase line load imbalance. The calculation methods given in the "Distribution Network Operation and Maintenance Regulations" (Q / GDW 1519-2014) standard and the IEEE Std 1159 standard are similar, but they both have defects. First, the relationship between the three-phase current imbalance and the neutral line current is not taken into account, and the neutral line current is also an important indicator for measuring the degree of three-phase imbalance; second, when the total three-phase load changes, the imbalance between the two times is meaningless to compare. Similarly, the imbalance between two substations with different total loads is also meaningless to compare, which is not convenient for testing the governance effect. To solve this problem, the present invention proposes a method for calculating the three-phase current imbalance using a discrete coefficient.

[0043] The coefficient of dispersion, also known as the coefficient of variation, is a commonly used statistical indicator in statistics. It is a relative statistic that measures the degree of dispersion of data. Its advantage is that it can compare the degree of dispersion of different sample data, regardless of the total number of samples. The larger the coefficient of dispersion, the greater the degree of dispersion of the data, and the smaller the coefficient of dispersion, the smaller the degree of dispersion of the data. Here, the present invention uses the coefficient of dispersion to calculate the unbalance of the three-phase current. Specifically, the coefficient of dispersion of the effective value of the three-phase current is used. times to express the three-phase current unbalance, that is

[0044]

[0045] In the above formula, V s is the discrete coefficient of the three-phase current. Based on the above definition, there is also the following relationship:

[0046]

[0047] Simplifying formula (4) we can get:

[0048]

[0049] In formula (5), I sum =I A +I B +I C , further substituting formula (5) into formula (3) we can get:

[0050]

[0051] It can be seen from formula (6) that under this definition, the three-phase current unbalance can also be calculated by the ratio of the neutral line current to the sum of the three-phase currents. Its physical meaning is clear, that is, the unbalanced current (I N ) is a percentage of the total current. The value range of the three-phase current unbalance is [0 1]. N=0, the three-phase current imbalance is zero, and the system is in a three-phase balanced state; when I N =I sum When the three-phase current imbalance is 1, the imbalance is the largest. At this time, one phase should be loaded while the other two phases are unloaded.

[0052] The three-phase current imbalance defined by formula (6) can not only accurately reflect the three-phase imbalance situation, but also reflect the relationship between the neutral line current and the total current, and can also establish the relationship between the three-phase current imbalance and the unbalanced line loss. It has excellent characteristics. Therefore, this calculation method will be used in the subsequent pre-balancing system phase change strategy design of the present invention.

[0053] At present, the phase-changing devices based on the load phase-changing method still find it difficult to achieve safe and reliable seamless phase-changing, and the phase-changing risk always exists. The fundamental reason is that they all adopt real-time balancing solutions, that is, when the device determines that the imbalance exceeds the standard, it immediately performs phase-changing operations on some users who are using electricity. At this time, the user current is often large, and phase-changing is very difficult. In the context of the long-term difficulty in breaking through the bottleneck of phase-changing technology, the present invention proposes a pre-balancing solution, which monitors and analyzes the current state or historical state of the distribution network, and determines the most reasonable power phase for users who are not using electricity (power less than 100W) in the future, thereby switching users to this phase in advance, so that when these users start to use electricity, it always helps to reduce the load imbalance of the three-phase line.

[0054] (1) Overall solution

[0055] The pre-balancing system first formulates a corresponding commutation strategy based on the user's behavior characteristics. It has two working modes: current commutation mode (using a current commutation strategy based on) and voltage commutation mode (using a voltage commutation strategy). In order to measure the user's voltage and current and perform commutation operations, the pre-balancing system has a commutation device installed on the user side; when the pre-balancing system works in the current commutation mode, the system must perform a comprehensive calculation of the current data of all commutation devices in the substation area to obtain the optimal commutation solution, so the pre-balancing system includes a centralized control center (hereinafter referred to as the "centralized control center"); when the pre-balancing system works in the voltage commutation mode, since the voltage of each power node is the result of the joint action of all power loads under the distribution network, each commutation device can make a commutation decision based on its own measured voltage to obtain its own optimal commutation solution, without the need to concentrate the voltage data of all commutation devices for analysis. In order to facilitate the monitoring of the overall three-phase imbalance of the distribution network and timely obtain the three-phase imbalance control effect of the pre-balancing system, an intelligent control device is installed at the JP cabinet under the transformer.

[0056] The phase-changing control terminal (PSCT) is connected in parallel to the secondary side of the transformer to detect the data of the substation, calculate the three-phase imbalance and the phase-changing strategy, and send the phase-changing command to the phase-changing switch (PSS) through wireless communication. The PSS is connected in parallel with the grid feeder in a three-phase four-wire system, and is connected in series with the user through a neutral line and a live line. The PSS is responsible for collecting the user's electrical data and uploading it to the PSCT, and executing the phase-changing instructions sent by the PSCT to accurately switch the user to the specified phase sequence. If phase A in the substation is overloaded, phase B is average, and phase C is lightly loaded, the PSCT sends a phase-changing instruction to a PSS installed on phase A, and switches part of the load on phase A to be powered by phase C, which can alleviate the three-phase imbalance.

[0057] (2) System design principles

[0058] The design of the pre-balance system follows the following principles:

[0059] 1) The relative error of voltage and current measurement should be as small as possible. The relative measurement error of L1 and L2 input voltages of the same commutation device should be as small as possible; the relative error of current measurement between different devices should be as small as possible.

[0060] 2) The switching time should be as short as possible. A large number of studies have shown that a voltage interruption within 20ms during the switching process will not have much impact on household appliances. Therefore, in order not to affect the normal power consumption of users, the switching time should be shortened as much as possible.

[0061] 3) Avoid interphase short circuit during commutation. There is no large current commutation in the pre-balanced system, so there is no need for a complex commutation structure. The simpler the commutation structure, the higher its safety and stability.

[0062] 4) The commutation strategy gives the optimal commutation plan. The optimal commutation plan reduces the number of commutations as much as possible, reduces the impact of commutation operations on the distribution network, and prolongs the service life of the commutation device while ensuring the three-phase unbalance effect.

[0063] 5) Software and hardware are easy to maintain and expand. Modular and hierarchical design is adopted when designing system software and hardware to improve system development efficiency and ensure system maintainability and easy expandability.

[0064] (3) Simulation research

[0065] The present invention uses simulink to build a simulation model of the station area. Figure 2 For the experimental simulation model, the resistance in the circuit is 0.1 ohm to simulate the circuit resistance. Figure 3 The connection method between the phase-changing device and the user is shown. The user load is implemented with a variable resistor so that the load can be dynamically connected or disconnected during the simulation. The load power connected to each phase-changing device is between 1-3kW and is randomly initialized during the simulation. Figure 4 It is a commutation device model that uses two ideal switches to achieve commutation operation.

[0066] (4) Hardware transformation

[0067] The intelligent monitoring device (PSCT) is designed using a modular design method. It is mainly composed of six modules: MCU microcontroller module, power module, voltage measurement module, current measurement module, communication module, and signal indication module. The structural block diagram is shown in the figure. Figure 5 shown.

[0068] The phase switching device (PSS) is mainly an improvement on the software of the existing device, which enables it to have a self-judgment function. Once it receives a command sent by the phase switching control terminal and the phase switching conditions are met, it will immediately execute the phase switching action. Figure 6 shown.

[0069] (5) System testing and network verification

[0070] In order to verify the effectiveness of the system and the feasibility of the method, a test platform is built in the distribution network laboratory to test the actual engineering performance of the phase-changing control terminal and the phase-changing switch. After completing the test in the experimental environment, a typical pilot project will be selected for grid-connected trial operation.

[0071] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-voltage distribution line load pre-balancing method based on user power consumption behavior prediction, characterized in that: The method connects the phase-changing control terminal in parallel with the secondary side of the transformer to detect the data of the substation, calculates the three-phase imbalance and the phase-changing strategy, and sends the phase-changing command to the phase-changing switch through wireless communication; the phase-changing switch is connected in parallel with the grid feeder in a three-phase four-wire system, and is connected in series with the user through a neutral line and a live line. The phase-changing switch collects the user's electrical data and uploads it to the phase-changing control terminal, and executes the phase-changing command sent by the phase-changing control terminal to switch the user to the specified phase sequence.

2. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1 is characterized in that: The commutation control terminal includes an MCU microcontroller module, a power module, a voltage measurement module, a current measurement module, a communication module, and a signal indication module, wherein the power module is electrically connected to the MCU microcontroller module, the voltage measurement module and the current measurement module are respectively connected to the MCU microcontroller module in communication and send voltage information and current information to the MCU microcontroller module respectively, the MCU microcontroller module is connected to the signal indication module in communication and sends an indication signal to the signal indication module, and the MCU microcontroller module communicates with the communication module in a bidirectional manner.

3. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: After the phase-changing switch is in operation, the system initialization and self-check are performed in sequence. When the self-check is abnormal, the fault information is uploaded. When the self-check is normal, the single-phase load electrical parameters are read. Then, when the phase-changing instruction is received, the instantaneous current data is read. When the phase-changing conditions are met, the phase-changing circuit action is executed.

4. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: In this method, the relative measurement error of the input voltages of L1 and L2 of the same phase-changing switch is less than a certain threshold; and the relative error of current measurement between different phase-changing switches is less than a certain threshold.

5. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: In this method, the commutation switching time is less than 20ms.

6. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: The method uses less than 100W of user power when performing commutation operation.

7. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: This method targets the unbalanced load on the three-phase line caused by asymmetric load sizes and ignores the asymmetric load phase.

8. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: The method evaluates the correlation of power consumption behavior of power users by using a random matrix theory correlation analysis method. In the random matrix theory correlation analysis method, a load curve data set and an environmental factor data set are collected respectively, and then the random matrix correlation is determined by an augmented matrix method, the average spectrum radius is determined, and the correlation index is obtained.

9. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 1, characterized in that: This method uses the discrete coefficient to calculate the three-phase current unbalance. In this calculation process, the discrete coefficient of the effective value of the three-phase current is used. Times represents the three-phase current unbalance: In the above formula, V s is the dispersion coefficient of the three-phase current.

10. The method for pre-balancing load of low-voltage distribution lines based on prediction of user power consumption behavior according to claim 9, characterized in that: The following relationship is satisfied during this calculation process: From formula 2, we can get: In formula 3, I sum =I A +I B +I C , Substituting equation 3 into equation 1, we get the following equation 4: Among them, the three-phase current unbalance degree is the unbalanced current I N The percentage of the total current; the value range of the three-phase current unbalance is [0 1]. N =θ, the three-phase current imbalance is zero, and the system is in a three-phase balanced state; when I N =I sum When , the three-phase current imbalance is 1, and the imbalance degree is the largest.

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