Terminal power grid voltage deviation treatment method for load adaptive adjustment

Abstract

The invention provides a terminal power grid voltage deviation treatment method based on load adaptive adjustment, and belongs to the technical field of power grid operation management. According to the technical scheme, a terminal power grid voltage deviation treatment device with an energy storage unit and a four-quadrant converter device as cores is designed for solving the voltage problem of a power grid in an agricultural and pastoral area; a mature power electronic topological structure and an energy storage application scheme are adopted, each key node of an agricultural and pastoral area is connected in parallel, and an energy control strategy is optimized on the basis. The invention provides a new method for comprehensive treatment of terminal high-low voltage caused by seasonal load change of a power grid, and the method utilizes a micro energy storage system to adjust active power and reactive power in line transmission in real time, and stabilizes the terminal voltage of the power distribution network from a power root link. Normal node voltage is fully guaranteed, the power supply cost is reduced, and the power utilization requirements of users in a low-voltage transformer area are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid operation management, and specifically relates to a method for controlling voltage deviation of a terminal power grid with load adaptive regulation. Background Art

[0002] The economic operation, grid reliability and power quality of distribution networks in rural and pastoral areas have always been major research topics of concern to the power industry. With the widespread popularity of high-power loads such as charging piles and electric heating in rural and pastoral areas, the randomness and imbalance of distribution network operation have become more prominent, especially in the rural and pastoral areas of the northwest region. The power grid faces a series of unique and complex problems that urgently need in-depth research and solutions.

[0003] Specifically, the main problems faced by power grids in rural and pastoral areas include:

[0004] 1. Long power supply radius: The Northwest region, including Qinghai, is sparsely populated. The power supply radius of the power grid in the agricultural and pastoral areas is very long, which is much higher than the power supply radius required by the distribution transformer specifications. The voltage is low when electricity is in use, and high when not in use.

[0005] 2. Low power quality qualification rate: According to the statistical data of the user electricity information collection system, the power quality qualification rate of the distribution network in Qinghai Province is about 78%, and the power quality qualification rate of users in Haibei area is about 73%, which is lower than the provincial level. Distribution network transformation and investment are needed.

[0006] 3. Increased load and seasonal electricity consumption characteristics lead to difficulties in voltage regulation: With the increase in load in rural and pastoral areas and the characteristics of seasonal electricity consumption, the power distribution needs to be frequently adjusted and coordinated with the adjustment of the AVC system of the substation to meet the requirements of the voltage qualification range. Due to the characteristics of random load and seasonal electricity consumption, random heavy overload problems arise, and the capacity utilization rate of the substation area also decreases. It is worth studying how to carry out voltage management for the distribution network in rural and pastoral areas to better utilize the existing distribution network capacity in the substation area.

[0007] 4. New policy requirements: The new "Power Supply Business Rules" have put forward higher requirements on the quality of power supply, which increases the risk of electricity consumption complaints from users of distribution networks in rural and pastoral areas, and power supply companies face greater service pressure.

[0008] In recent years, scholars have conducted in-depth analysis on the load characteristics of power grids in agricultural and pastoral areas, and divided the load types into several categories, including residential electricity (such as daily lighting and household appliances), agricultural and animal husbandry production electricity (such as agricultural irrigation, greenhouses, breeding, agricultural and animal husbandry processing), and rural general industrial and commercial electricity (such as rural industry and commercial electricity). These studies have revealed that the load characteristics of power grids in agricultural and pastoral areas have the characteristics of large day and night changes, large annual peak-to-valley differences, and low power factors, and the characteristics of different types of loads are different.

[0009] In terms of voltage management, scholars have proposed a variety of technical and management improvement measures to address the problems of large voltage deviation at the end of the distribution network and low power quality qualification rate. At the technical level, these measures include reasonable selection of transformer capacity, increasing transmission voltage, optimizing grid configuration, adopting high-quality facilities, and increasing the application of reactive capacitor compensation. At the management level, they emphasize improving the loss reduction management system, strengthening electrician training and grid metering management. These measures are aimed at solving the voltage deviation problem at the root and improving grid operation efficiency and power supply reliability.

[0010] In addition, with the rapid development of renewable energy technology, scholars are also actively exploring voltage management methods after photovoltaics are connected to the distribution network. Some studies have attempted to build a new energy network in rural areas with abundant photovoltaics using low-voltage direct current distribution and use, analyzing its advantages in terms of safety, power supply reliability and economy, and exploring key technical issues in actual operation.

[0011] However, although the existing technology has made some progress in load analysis and voltage management of rural power grids, a unified and efficient method for high and low voltage management at the end of the distribution network has not yet been formed. In particular, the problems of large terminal voltage deviation and low power quality qualification rate caused by seasonal changes in rural power grids still require further in-depth research and technological innovation. Summary of the invention

[0012] The technical problem to be solved by the present invention is: how to develop a unified and efficient method for managing high and low voltages at the end of the distribution network in view of the large terminal voltage deviation and low power quality qualification rate caused by seasonal changes in the power grid in agricultural and pastoral areas.

[0013] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0014] A method for controlling terminal grid voltage deviation with load adaptive regulation, the method connects a terminal grid voltage deviation control device to a node of a grid in parallel; the terminal grid voltage deviation control device comprises a control system module, a communication module, a rectifier-inverter module, and an energy storage battery module, wherein the energy storage battery module is electrically connected to the rectifier-inverter module, the rectifier-inverter module is connected to the grid, the control system module is respectively communicated with the rectifier-inverter module and the energy storage battery module, and the communication module is communicated with the control system module.

[0015] Preferably, the rectifier inverter module is connected to the 220V / 380V distribution network upward, and is connected to the energy storage battery downward. The rectifier inverter module is provided with an interface for accessing the DC power supply and the load. The control system module is respectively connected to the energy storage battery and the rectifier inverter module through communication lines. The control system module communicates wirelessly with the remote monitoring platform through the 4G network.

[0016] Preferably, the interface is connected to a photovoltaic system, a wind power system or an electric vehicle.

[0017] Preferably, in this method, when the system voltage is higher than a first threshold, the terminal grid voltage deviation management device performs energy storage and power compensation; when the system voltage is lower than a second threshold, the terminal grid voltage deviation management device compensates the system for active and reactive power.

[0018] Preferably, the system voltage is higher than the first threshold value during the night time of the rural power grid, 9 to 11 am, or 3 to 5 pm.

[0019] Preferably, in the method, a micro energy storage system is used to adjust the active power and reactive power in line transmission in real time.

[0020] Preferably, when the voltage at the end of the distribution network is lower than a certain value, the micro energy storage system acts as a power source to provide reactive power and active power to the end of the distribution network; when the load change exceeds a certain value, the power difference between the two is provided by the micro energy storage system, and at the same time the micro energy storage system outputs a certain reactive power to improve the power factor of the grid; when the voltage at the end of the distribution network is higher than a certain value, the micro energy storage system acts as a load, consumes part of the active power and reactive power, and stores the excess electric energy that causes the high voltage.

[0021] Preferably, the micro energy storage system includes a battery, an inverter, a controller, and a line impedance, wherein the battery is electrically connected to the inverter, the inverter is connected to the power grid through a power line, has a line impedance on the power line, has several user terminals connected in parallel on the power line, and the controller is connected to the inverter through a signal line.

[0022] Preferably, the converter is a four-quadrant converter.

[0023] Preferably, the micro energy storage system changes the conductor cross-section-power factor influence factor k by changing the power factor, and changes the line voltage drop by changing the line transmission power S, thereby stabilizing the terminal voltage.

[0024] The present invention provides a method for controlling voltage deviations of terminal power grids with load adaptive regulation. This technical solution aims at the voltage problems existing in power grids in rural and pastoral areas, and designs a terminal power grid voltage deviation control device with energy storage units and four-quadrant converters as the core; it adopts mature power electronic topology and energy storage application solutions, and connects to key nodes in rural and pastoral areas in parallel, and optimizes the energy control strategy on this basis. The present invention proposes a new method for comprehensive control of high and low voltages at the terminal due to seasonal load changes in the power grid. The method uses a micro-energy storage system to adjust the active power and reactive power in line transmission in real time, and stabilizes the terminal voltage of the distribution network from the fundamental power link. The present invention fully ensures the normal node voltage, reduces the power supply cost, and meets the electricity demand of users in low-voltage areas.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Improve voltage stability: Through the application of micro energy storage technology, rapid voltage adjustment and compensation can be achieved at the end of the power grid, effectively improving the voltage deviation problem and improving the voltage stability of the power grid.

[0027] 2. Improve power quality: Micro energy storage devices can smooth out random fluctuations in the power grid, reduce power quality problems such as voltage fluctuations and flicker, and improve the overall power quality of the power grid.

[0028] 3. Optimize resource allocation: Through reasonable control strategies, micro energy storage devices can make full use of the temporal and spatial complementarity of loads, optimize resource allocation, and improve the capacity utilization rate of the substation.

[0029] 4. Reduce the financial pressure of network transformation: The application of micro energy storage technology can reduce the dependence on grid hardware facilities, reduce the capital investment in grid transformation and upgrading, and alleviate the financial pressure of network transformation in rural and pastoral areas.

[0030] 5. Improve service level: By improving the power quality and power supply reliability of the power grid, the complaint rate of users in rural and pastoral areas can be reduced, the service level of power supply companies can be improved, and the social responsibility and image of power supply companies can be enhanced.

[0031] In summary, the present invention not only helps to solve the problems of voltage deviation and power quality faced by power grids in agricultural and pastoral areas, but also can promote the development and application of renewable energy and promote the sustainable development of the agricultural and pastoral economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of the terminal power grid voltage deviation management device in the present invention.

[0033] Figure 2 It is a structural schematic diagram of the micro energy storage system in the present invention.

[0034] Figure 3 This is a working flow chart of the micro energy storage system in the present invention. 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] A method for controlling terminal grid voltage deviation with load adaptive regulation, the method connects a terminal grid voltage deviation control device to a node of a grid in parallel; the terminal grid voltage deviation control device comprises a control system module, a communication module, a rectifier-inverter module, and an energy storage battery module, wherein the energy storage battery module is electrically connected to the rectifier-inverter module, the rectifier-inverter module is connected to the grid, the control system module is respectively communicated with the rectifier-inverter module and the energy storage battery module, and the communication module is communicated with the control system module.

[0037] Among them, the rectifier inverter module is connected to the 220V / 380V distribution network upward, and the rectifier inverter module is connected to the energy storage battery downward. The rectifier inverter module is provided with an interface for accessing the DC power supply and the load. The control system module is connected to the energy storage battery and the rectifier inverter module respectively through the communication line, and the control system module communicates wirelessly with the remote monitoring platform through the 4G network. The interface is connected to the photovoltaic system, the wind power system or the electric vehicle. When the system voltage is higher than the first threshold, the terminal grid voltage deviation management device performs energy storage and power replenishment. When the system voltage is lower than the second threshold, the terminal grid voltage deviation management device compensates the system for active and reactive power. When the system voltage is higher than the first threshold, it is the time period of the agricultural grid at night, 9 to 11 in the morning or 3 to 5 in the afternoon.

[0038] In this method, a micro energy storage system is used to adjust the active power and reactive power in line transmission in real time. When the voltage at the end of the distribution network is lower than a certain value, the micro energy storage system acts as a power source to provide reactive power and active power to the end of the distribution network; when the load change exceeds a certain value, the power difference between the two is provided by the micro energy storage system, and the micro energy storage system outputs a certain reactive power to improve the power factor of the power grid; when the voltage at the end of the distribution network is higher than a certain value, the micro energy storage system acts as a load, consumes a part of the active power and reactive power, and stores the excess electric energy that causes high voltage. The micro energy storage system includes a battery, a converter, a controller, and a line impedance, wherein the battery is electrically connected to the converter, the converter is connected to the power grid through a power line, has a line impedance on the power line, and has several user terminals connected in parallel on the power line, and the controller is connected to the converter through a signal line. The converter is a four-quadrant converter. The micro energy storage system changes the conductor cross-section-power factor influence factor k by changing the power factor, and changes the line voltage drop by changing the line transmission power S, thereby stabilizing the terminal voltage.

[0039] Aiming at the voltage problem existing in the power grid in agricultural and pastoral areas, the present invention adopts the parallel type agricultural and pastoral area load adaptive adjustment terminal power grid voltage deviation management device with energy storage unit and four-quadrant converter as the core, adopts mature power electronic topology structure and energy storage application scheme, and connects to each key node of agricultural and pastoral area in parallel. Through the optimal energy control strategy, the microgrid power supply technology is improved to ensure the normal node voltage, reduce the power supply cost, and meet the power demand of users in low-voltage area. In addition, the device retains the DC bus interface to provide conditions for the local consumption of new energy such as photovoltaic and wind power, and solve the problems of power shortage and power restriction existing in the current agricultural power grid.

[0040] The structure of the terminal grid voltage deviation control device is as follows: Figure 1 As shown. The rectifier inverter function module is connected to the 220V / 380V distribution network upward and to the energy storage battery downward. The rectifier inverter module also provides an expansion interface for accessing DC power sources and loads such as photovoltaic, wind power and electric vehicles. The control system dedicated module is connected to the energy storage battery and the rectifier inverter function module through a wired communication medium, and realizes information interconnection with the remote monitoring platform through wireless 4G communication. Energy storage and power replenishment are carried out during the night of the rural power grid and the periods of light load and high voltage during the period of new energy law such as 9-11 am and 3-5 pm; when the load side power consumption increases and the system voltage is low, the device automatically compensates the system for active and reactive power to achieve the purpose of raising the terminal power voltage and realizing stable power consumption for residents. The device can effectively solve the power quality problems such as low voltage and frequent and large-scale voltage fluctuations that are common in remote power grids in remote agricultural and pastoral areas.

[0041] In the high-voltage transmission system, the value of the line resistance R is much smaller than the value of the line reactance X, and the product of the line reactance X and the reactive power Q in the transmission power has the main impact on the line voltage loss. As the voltage level gradually decreases, the ratio R / X of the resistance component R to the reactance component X will gradually increase, and there will even be a situation where the resistance component R is greater than the reactance component X. Therefore, it is different from the high-voltage transmission system. In the medium and low voltage distribution system with lower voltage levels, the line resistance R plays a more important role in affecting the voltage loss and cannot be directly ignored. The product of the active power in the transmission power and the line resistance R occupies an important position in affecting the voltage loss. If you want to achieve the high and low voltage management of the line terminals of the medium and low voltage distribution network, only taking reactive compensation measures cannot effectively adjust the terminal voltage. The influence of the resistance component R and the active power P parameters should also be fully considered.

[0042] At present, the main means to solve the high voltage problem of distribution network are: (1) Management and control of power factor. This method does not require investment. Starting from the power factor, the conductor cross-section, which is a power factor influencing factor, is changed. The effect is good, but the reactive power of the load is not considered; (2) Installing inductive reactive compensation devices, such as shunt reactors, etc. This method changes the conductor cross-section by changing the reactance component X in the line parameters, which is a power factor influencing factor and can effectively suppress overvoltage, but switching and maintenance are not very convenient, and under certain conditions, line losses will increase. (3) Automatic on-load voltage regulation of distribution transformers can perform bidirectional regulation well, with a wide voltage regulation range, strong load bearing capacity, and relatively ideal voltage stabilization effect. However, it requires real-time adjustment and frequent operation, which increases maintenance costs.

[0043] The measures to deal with the low voltage problem include: (1) Optimizing the grid structure. This method reduces the line transmission distance L and can improve the power quality in a larger area, but it requires a certain amount of investment. (2) Reactive power compensation, such as parallel passive capacitors. This method changes the conductor cross-section - the power factor influencing factor by changing the reactance component X in the line parameters, which can achieve reactive power balance and improve reactive power voltage levels. However, there is no systematic capacity evaluation standard and the equipment switching and maintenance are difficult, so it is difficult to apply to power grids with many nodes and complex structures; installing active power electronic devices such as SVG. This method reduces the line transmission power S and can achieve dynamic and smooth regulation of inductive and capacitive reactive power, but the equipment maintenance is more difficult and the reliability is not high. (3) Automatic on-load voltage regulation of distribution transformers can perform bidirectional regulation well, has a wide voltage regulation range, strong load bearing capacity, and a relatively ideal voltage stabilization effect. However, it requires real-time adjustment and frequent operation, which increases maintenance costs.

[0044] The above solutions and means can regulate the voltage to a certain extent, but they do not fundamentally solve the problem of seasonal fluctuations in the terminal power grid, or a single measure cannot simultaneously solve the voltage fluctuation problem caused by seasonal changes. Therefore, the voltage fluctuation problem of the low-voltage distribution network urgently needs new management ideas. The management of the voltage at the end of the low-voltage distribution network line can automatically adapt to the voltage fluctuation problem caused by seasonal load changes.

[0045] Based on the analysis of the actual architecture of the Northwest Power Grid, the load changes greatly with seasonal changes in suburban areas, agricultural and pastoral areas, etc. where the power grid is weak, and the voltage changes greatly accordingly. The present invention proposes a new technology for comprehensive management of high and low voltages at the end due to seasonal load changes in the power grid. The method uses a micro-energy storage system to adjust the active power and reactive power in line transmission in real time, and stabilizes the voltage at the end of the distribution network from the fundamental power link. When the line parameters do not change and the micro-energy storage system is not connected, the voltage Us at the end of the distribution network will change with the change of load. Connecting the micro-energy storage system can stabilize the voltage at the end of the distribution network. When low voltage appears at the end of the distribution network, the micro-energy storage system is equivalent to a power source, and it is necessary to provide reactive and active support to the end of the distribution network, reduce the active and reactive energy absorbed by the load from the distribution network line, thereby reducing the network loss voltage and increasing the terminal voltage. That is, at this time, the current flowing into the connection point of the power grid remains unchanged, the power P flowing into the connection point of the power grid remains unchanged, and the power provided to the user by the power grid does not change. When the load changes significantly, the power difference between the two is provided by the micro energy storage system. At the same time, in order to compensate for the reactive power of the terminal line, the micro energy storage system also outputs a certain amount of reactive power to improve the power factor of the power grid. When high voltage appears at the end of the distribution network, the situation is just the opposite. The micro energy storage system is equivalent to the load. It will absorb part of the active and reactive power, and store the excess electric energy that causes high voltage, reducing the current flowing from the power grid to the user load. When the load impedance does not change, the voltage at the connection point between the user end and the power grid is reduced. At this time, the power flowing into the connection point of the power grid remains unchanged, but the power provided by the power grid to the user is reduced due to the absorption of the micro energy storage system. Although this increases a certain network loss voltage drop, the micro energy storage system ensures the safe operation of the power grid and users, saves energy, and can also improve the power factor of the power grid, and still has certain economic benefits. The structure and working process of the micro energy storage system are as follows. Figure 2 , Figure 3 shown.

[0046] When the line length L and the transmission voltage Y remain unchanged, the parameters that affect the line voltage drop are only the line transmission power S and the conductor cross-section-power factor influence factor k. Different from the conventional method of changing the line parameters (line resistance per unit length r and line reactance per unit length x) to change the conductor cross-section-power factor influence factor k and then change the line voltage drop, the micro energy storage system changes the conductor cross-section-power factor influence factor k by changing the power factor, and changes the line transmission power S to comprehensively change the line voltage drop, ultimately achieving the purpose of stabilizing the terminal voltage.

[0047] Therefore, on the basis of line optimization and when reactive power regulation has little effect, the micro energy storage system can take advantage of the controllable advantages of both active and reactive power. Compared with reactive power regulation methods such as SVG and TCR, it has the advantage of a wide voltage regulation range.

[0048] By analyzing the topological structure of the micro energy storage system, the control strategy of the new solution for the micro energy storage system to manage the high and low voltage at the end of the distribution network is improved. The charge and discharge control of the micro energy storage device is explained through the boost / buck step-up and step-down circuit and the corresponding control, which closely matches the output of the battery and optimizes the capacity configuration of the energy storage device from an optimization perspective to ensure the economic, effective and stable operation of the micro energy storage system. Finally, the grid-connected control of the micro energy storage system to manage the terminal voltage fluctuation problem is introduced in detail, and how the grid-connected technology controls and stabilizes the terminal voltage amplitude and phase (or active component and reactive component) is deeply analyzed. The parameter selection scheme of the current inner loop and the voltage outer loop in the controller design, as well as the corresponding following performance and anti-interference performance are given, so as to finally achieve the purpose of effectively managing the voltage fluctuation problem at the end of the distribution network.

[0049] 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 method for controlling voltage deviation of a terminal power grid with load adaptive regulation, characterized in that: The method connects a terminal grid voltage deviation management device to a node of a grid in parallel; the terminal grid voltage deviation management device includes a control system module, a communication module, a rectifier inverter module, and an energy storage battery module, wherein the energy storage battery module is electrically connected to the rectifier inverter module, the rectifier inverter module is connected to the grid, the control system module is respectively communicated with the rectifier inverter module and the energy storage battery module, and the communication module is communicated with the control system module.

2. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 1 is characterized in that: The rectifier inverter module is connected to the 220V / 380V distribution network upward, and is connected to the energy storage battery downward. The rectifier inverter module is provided with interfaces for accessing the DC power supply and the load. The control system module is connected to the energy storage battery and the rectifier inverter module respectively through communication lines. The control system module communicates wirelessly with the remote monitoring platform through the 4G network.

3. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 2 is characterized in that: The interface is connected to a photovoltaic system, a wind power system or an electric vehicle.

4. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 1 is characterized in that: In this method, when the system voltage is higher than a first threshold, the terminal grid voltage deviation management device performs energy storage and power replenishment; when the system voltage is lower than a second threshold, the terminal grid voltage deviation management device compensates the system for active and reactive power.

5. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 4 is characterized in that: When the system voltage is higher than the first threshold, it is during the night time of the rural power grid, 9 to 11 am, or 3 to 5 pm.

6. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 1 is characterized in that: In this method, a micro energy storage system is used to adjust the active power and reactive power in line transmission in real time.

7. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 6 is characterized in that: When the voltage at the end of the distribution network is lower than a certain value, the micro energy storage system acts as a power source to provide reactive power and active power to the end of the distribution network; when the load change exceeds a certain value, the power difference between the two is provided by the micro energy storage system, and the micro energy storage system outputs a certain amount of reactive power to improve the power factor of the power grid; when the voltage at the end of the distribution network is higher than a certain value, the micro energy storage system acts as a load, consumes part of the active power and reactive power, and stores the excess electric energy that causes high voltage.

8. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 6 is characterized in that: The micro energy storage system includes a battery, an inverter, a controller, and a line impedance, wherein the battery is electrically connected to the inverter, the inverter is connected to the power grid through a power line, there is a line impedance on the power line, a plurality of user terminals are connected in parallel on the power line, and the controller is connected to the inverter through a signal line.

9. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 8 is characterized in that: The converter is a four-quadrant converter.

10. The method for controlling voltage deviation of the terminal power grid with load adaptive regulation according to claim 6, characterized in that: The micro energy storage system changes the conductor cross-section-power factor influence factor k by changing the power factor, and changes the line voltage drop by changing the line transmission power S, thereby stabilizing the terminal voltage.

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