A distributed energy grid-connected flexible consumption system based on intelligent fusion terminals

Abstract

The present invention belongs to the field of power equipment, and specifically relates to a distributed energy grid-connected flexible absorption system based on an intelligent fusion terminal. The system includes, in a top-down management order: a cloud master station, edge devices, and end devices. The end devices include an electric energy meter, an inverter, a distributed power generation unit, and an Internet of Things communication unit. The edge devices include a substation transformer, a centralized energy storage device, an intelligent fusion terminal, and a concentrator. The cloud master station is used to display the basic data of all equipment in the substation uploaded by the intelligent fusion terminal and the alarm information of the generated fault event according to the request of the power user; and respond to the power on / off instructions or power adjustment instructions issued by the power user to the inverter. The business functions performed by the system include: data collection and sharing, grid-connected anti-islanding effect protection, grid three-phase voltage balance adjustment, grid harmonic pollution monitoring, and energy storage adjustment. The present invention solves the problem that the existing power grid cannot effectively absorb the electric energy generated by the distributed power generation system.

Description

Technical Field

[0001] The present invention belongs to the field of electric power equipment, and in particular relates to a distributed energy grid-connected flexible consumption system based on an intelligent fusion terminal. Background Art

[0002] Distributed power generation systems refer to small-scale power generation systems built near user consumption sites. These systems primarily operate on a user-side basis, with surplus power being connected to the grid. Distributed power generation systems enable local generation, grid connection, conversion, and consumption. This not only effectively increases the power generation capacity of similarly sized power plants, but also effectively addresses power losses during voltage boosting and long-distance transportation. Conventional ground-based power stations offer the advantages of large capacity and abundant resources, but their insufficient consumption capacity and the extensive grid footprint significantly reduce their effectiveness. Distributed power stations effectively overcome these issues.

[0003] In China, the distributed power generation systems already in operation are primarily photovoltaic systems, including household photovoltaics, distributed industrial and commercial photovoltaics, and specialized regional photovoltaic projects. Distributed photovoltaic projects can alleviate the economic burden of electricity consumption for residents in impoverished areas, increase the utilization rate of clean energy, and achieve energy conservation and reduction. However, in current applications, most photovoltaic power generation is used for self-use and is rarely connected to the grid. This creates two independent networks for the photovoltaic power supply network and the low-voltage distribution substation. This situation prevents photovoltaic power generation from being integrated into the grid to absorb energy, generate data value, and further expand business opportunities. Consequently, the value of photovoltaic energy is not being maximized.

[0004] Most distributed generation systems, including household photovoltaic systems, suffer from low capacity, high volatility, widespread distribution, and high management costs. Low-voltage distribution substations lack data communication links with distributed photovoltaic systems, hindering access to the substations' operational status and basic data, complicating the management and maintenance of cross-regional power grids. Furthermore, grid-connected photovoltaic systems can have a range of impacts on the power system, such as voltage fluctuations, harmonic pollution, three-phase imbalance, and reduced power factor. Currently, there is a lack of effective methods to absorb and balance distributed photovoltaic power. Summary of the Invention

[0005] In order to solve the problem that the existing low-voltage power grid cannot effectively consume the electric energy generated by the distributed power generation system, the present invention provides a distributed energy grid-connected flexible consumption system based on an intelligent fusion terminal.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A distributed energy grid-connected flexible consumption system based on intelligent converged terminals manages substation equipment containing distributed renewable energy generation units, ensuring orderly bidirectional power flow in the distribution network, flexibly regulating power load distribution, and improving grid equipment utilization. This distributed energy grid-connected flexible consumption system comprises, in a top-down management order, a cloud master station, edge devices, and end devices.

[0008] The end devices include energy meters, inverters, distributed generation units, and IoT communication units. Energy meters collect energy usage information from power consumers on the marketing side. All energy meters within a substation communicate with a concentrator device via power carrier communication. The power generated by all distributed generation units within the substation is converted to AC power by inverters and then supplied to power consumers' loads or connected to the substation's low-voltage grid. Each inverter communicates with an intelligent converged terminal via the IoT communication unit.

[0009] Edge equipment includes substation transformers, centralized energy storage devices, intelligent fusion terminals, and concentrators. Substation transformers supply power to the low-voltage grid within the substation area. The centralized energy storage device is electrically connected to the low-voltage grid and is used to dynamically balance power when the substation transformer's power supply doesn't match the load's energy consumption, thereby absorbing the grid-connected power from distributed generation units. The intelligent fusion terminal collects inverter data, monitors fault status, and remotely controls the inverters. It also collects household meter data from the concentrator via RS485 or Ethernet interfaces. All collected basic data and fault alarm information are uploaded to the cloud master station.

[0010] The cloud master station is used to display the basic data of all equipment in the substation area uploaded by the intelligent fusion terminal and the alarm information of the generated fault events according to the request of the power user; and respond to the power on / off instructions or power adjustment instructions issued by the power user to the inverter.

[0011] The business functions performed by the distributed energy grid-connected flexible consumption system based on intelligent fusion terminals include: data collection and sharing, grid-connected anti-islanding effect protection, grid three-phase voltage balance regulation, grid harmonic pollution monitoring and energy storage regulation.

[0012] As a further improvement of the present invention, in a distributed energy grid-connected flexible consumption system based on intelligent fusion terminals, the distributed power generation units include one or any combination of photovoltaic panels, solar thermal generator sets, wind turbines, tidal generators, and biomass power stations.

[0013] As a further improvement to the present invention, in data collection services, the basic data uploaded by the intelligent fusion terminal to the cloud master station includes energy consumption information of power users measured by electricity meters, as well as real-time data acquired from inverters using a timed polling method. Types of real-time data include: input power, grid voltage, grid current, active power, reactive power, power factor, grid frequency, efficiency, cumulative power generation, daily power generation, and meter device active power.

[0014] As a further improvement of the present invention, in the data collection and sharing service, the alarm information uploaded by the intelligent fusion terminal to the cloud master station is a status indicator used to reflect the real-time status of the inverter operation process. Alarm information types include: standby state, grid-connected state, fault shutdown state, power-limited shutdown state, shutdown state, communication connection failure state, grid feed state, overvoltage state, grid undervoltage state, grid overfrequency state, grid underfrequency state, output overcurrent state, active island state, and passive island state.

[0015] As a further improvement of the present invention, in the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided by the present invention, the grid-connected anti-islanding effect protection function is implemented by the following method:

[0016] (1) Each distributed power generation unit is equipped with an inverter with anti-islanding protection function. When any inverter detects that the current node has an islanding phenomenon, the inverter automatically disconnects from the grid within a specified time; then a corresponding islanding protection alarm status is generated and uploaded to the master station.

[0017] (2) When the system detects a power outage on any branch line within the distribution area, it sends a shutdown command to all inverters under the power outage line, so that the distributed generation units of the corresponding nodes are immediately disconnected from the grid.

[0018] (3) Receive the line maintenance request from the operation and maintenance personnel, and then according to the construction period of the line maintenance request, shut down the inverters of the distributed power generation units included in the maintenance line and disconnect them from the power grid within the corresponding period.

[0019] As a further improvement of the present invention, in the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided by the present invention, the grid three-phase voltage balance regulation function is used to overcome the problem of abnormal grid voltage increase caused by uneven grid power or excessive grid power. Among them, the three-phase imbalance problem caused by uneven grid power of distributed generation units is solved by adopting the following strategy:

[0020] According to the power generation capacity of different distributed power generation units, multiple distributed power generation units in the substation area are evenly connected to the three phases of the low-voltage power grid, and each distributed power generation unit is connected to the low-voltage power grid at multiple points.

[0021] As a further improvement of the present invention, the following power dynamic regulation method is used to control the problem of grid voltage increase caused by excessive grid-connected power of distributed power generation units:

[0022] S1: The cloud master station monitors the three-phase voltage of the power grid in real time.

[0023] S2: Determine whether the voltage value of each phase exceeds the preset rated value and lasts for more than 1 minute: if so, reduce the active power percentage of the inverter of all distributed generation units feeding power to the grid under the current phase line by 50%.

[0024] S3: Determine whether the voltage value on the corresponding phase line returns to normal after the active power is reduced:

[0025] (1) If yes, it is determined that the abnormal increase in grid voltage is caused by the grid connection of distributed generation units, and a corresponding alarm message is reported to the cloud master station.

[0026] (2) Otherwise, continue to reduce the active power percentage of the inverters of all distributed generation units feeding power to the grid under the current phase line by 50%.

[0027] S4: Determine whether the number of grid-connected power reductions of the distributed generation voltage on the phase line whose voltage value exceeds a preset rated value and lasts for more than 1 minute exceeds three times. If so, actively shut down all distributed generation units on the phase line that are feeding power to the grid.

[0028] S5: After power regulation and voltage reduction, when the voltage value on a phase line is lower than the rated value, the derating state of the inverters in the distributed power generation units is restored in turn.

[0029] As a further improvement of the present invention, during the implementation of the power dynamic regulation method, the state in which the voltage value on each phase line exceeds the preset rated value is evaluated as exceeding the default value by 7%; the state in which the voltage value on each phase line is lower than the preset rated value is evaluated as being lower than the default value by 1%.

[0030] As a further improvement of the present invention, in the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided by the present invention, the control objectives of the grid harmonic pollution monitoring function are: the voltage total harmonic distortion rate limit is not higher than 5.0%, the odd harmonic content rate limit is 4.0%, and the even harmonic content rate limit is 2.0%. The grid harmonic pollution monitoring method adopted is as follows:

[0031] S01: The cloud master station monitors the voltage harmonic content rate of each phase in the power grid in real time;

[0032] S02: Determine whether the voltage harmonic content of each phase is higher than the limit and the duration reaches 1 minute. If so, actively shut down the inverters of all distributed generation units on the corresponding phase line that are feeding power to the grid;

[0033] S03: After the inverter of the distributed generation unit on a phase line is shut down, wait for 1 minute and determine again whether the harmonic content of the phase voltage is still higher than the limit: (1) If yes, no action is taken; (2) Otherwise, a corresponding harmonic limit-exceeding alarm message is reported to the cloud master station;

[0034] S04: After completing the judgment in the previous step, re-issue the restart command to the shut-down inverter; after restarting, when the voltage harmonic content rate on the corresponding phase line is lower than the limit, report the inverter harmonic limit recovery alarm information to the cloud master station.

[0035] 10. The distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal according to claim 9, characterized in that: in the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal, the energy storage regulation function is implemented by a centralized energy storage device, the centralized energy storage device is communicatively connected to the intelligent fusion terminal via an RS485 interface, and further receives control instructions issued by the intelligent fusion terminal; the intelligent fusion terminal is used to:

[0036] (1) Using centralized energy storage devices to improve the three-phase imbalance of the power grid: When the active power of the power grid fluctuates for a short time, the energy storage device is controlled to charge and discharge the active power, achieving the time and space shift of electric energy and balancing the operating state of the power grid;

[0037] (2) Using centralized energy storage devices to compensate for reactive power in the power grid: When the reactive power and reactive load in the power grid do not match, the energy storage device is used to control the charging and discharging of reactive power;

[0038] (3) Control the charging and discharging status of the centralized energy storage device according to the power changes of the distributed power generation units connected to the power grid: when the power grid is in a low-load state, the centralized energy storage device uses the low-voltage power grid to charge; when the power grid is in a high-load state, the centralized energy storage device feeds power to the low-voltage power grid.

[0039] The technical solution provided by the present invention has the following beneficial effects:

[0040] The present invention provides a distributed energy grid-connected flexible absorption system based on an intelligent fusion terminal, which can integrate all equipment and information within the power supply area through the intelligent fusion terminal, concentrator and Internet of Things communication device. The purpose is to dynamically manage different equipment in the overall system in real time. In the system, the intelligent fusion terminal serves as the center of the system, and monitors the power supply area in real time, quickly discovers and handles fault conditions in the power generation unit or power grid in the power supply area. This improves the management efficiency of the area and reduces the difficulty of management work in the area. The present invention can also connect the electricity generated by the photovoltaic power generation unit in the power supply area to the grid, realize on-site absorption of energy in the area, and reduce energy transmission losses.

[0041] The system provided by this invention can dynamically perceive the operating status of substation equipment and remotely interact with users through a cloud master station, enabling dynamic adjustment and remote management of substation equipment, thus facilitating the management and operation of cross-regional power grids. In particular, the system can not only effectively dissipate the grid-connected power generated within the substation, but also effectively address issues such as medium-voltage fluctuations, harmonic pollution, three-phase imbalance, and reduced power factor caused by the integration of distributed photovoltaic power generation, thereby ensuring the long-term stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0043] Figure 1 This is a system topology diagram of a distributed energy grid-connected flexible consumption system based on an intelligent fusion terminal provided in Example 1 of the present invention.

[0044] Figure 2 This is a flowchart of the steps of the power dynamic adjustment method provided in Example 1 of the present invention.

[0045] Figure 3 This is a flowchart of the steps of the power grid harmonic pollution monitoring method provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] Example 1

[0048] This embodiment provides a distributed energy grid-connected flexible absorption system based on intelligent fusion terminals. The system is used to manage substation equipment containing distributed new energy power generation units, realize the ordering of two-way power flow in the distribution network, flexibly regulate the distribution of power load, and improve the utilization rate of power grid equipment.

[0049] The distributed energy grid-connected flexible consumption system includes the following management order from top to bottom: cloud master station, edge device and terminal device. The topology of the system is as follows: Figure 1 shown.

[0050] Specifically, the end devices include energy meters, inverters, distributed generation units, and IoT communication units. The energy meters collect energy usage information from power users on the marketing side. All energy meters within a substation communicate with a concentrator device via power carrier communication. The electricity generated by all distributed generation units within the substation is converted into AC power by inverters and then supplied to power user loads or connected to the substation's low-voltage grid. Each inverter communicates with an intelligent converged terminal via the IoT communication unit.

[0051] In this embodiment of the distributed energy grid-connected flexible consumption system based on intelligent converged terminals, the system can effectively consume and utilize the electricity generated by different types of distributed generation units. Because the system does not restrict the type of distributed generation units, any one or more of conventional photovoltaic panels, solar thermal generators, wind turbines, tidal generators, and biomass power plants, as well as other promising new energy generation equipment in the future, such as geothermal power plants, can be installed on the system.

[0052] Edge equipment includes substation transformers, centralized energy storage devices, intelligent fusion terminals, and concentrators. Substation transformers supply power to the low-voltage grid within the substation area. The centralized energy storage device is electrically connected to the low-voltage grid and is used to dynamically balance power when the substation transformer's power supply doesn't match the load's energy consumption, thereby absorbing the grid-connected power from distributed generation units. The intelligent fusion terminal collects inverter data, monitors fault status, and remotely controls the inverters. It also collects household meter data from the concentrator via RS485 or Ethernet interfaces. All collected basic data and fault alarm information are uploaded to the cloud master station.

[0053] The cloud master station displays basic data for all equipment within the substation, uploaded by intelligent converged terminals, and generates fault alarms based on user requests. It also responds to power user commands for inverters to power on and off, or to adjust power levels. The cloud master station consists of a remotely deployed cloud server and can be categorized by function as either a distribution automation master station or a distribution IoT master station.

[0054] In the system provided in this embodiment, the intelligent fusion terminal is an information transfer station that realizes data and command interaction between the cloud master station, edge devices and terminal devices; at the same time, the intelligent fusion terminal itself is also an edge computing device that can perform simple processing on the collected data; thus, it serves as the control center of the system.

[0055] In the three-level architecture of this embodiment, the end devices are user-oriented and mainly include electricity meters, inverters, solar panels, and IoT communication units. The end devices are respectively connected to two different edge devices, intelligent fusion terminals, and concentrators. For example, the electricity meter communicates with the concentrator type I through a carrier, which belongs to the marketing business. The inverter converts between the carrier HPLC and RS485 channels through the IoT communication unit, and then communicates with the intelligent fusion terminal. The edge devices include intelligent fusion terminals deployed and installed near the transformer in the substation. The intelligent fusion terminals support functions such as data collection, fault event status monitoring, and remote control of the inverter. In addition, the intelligent fusion terminal can collect household meter data of the concentrator type I through the RS485 or Ethernet interface, realize data sharing for marketing and distribution, and monitor the basic data of the electricity meters consumed by residential users' photovoltaic power sources.

[0056] In this system, a centralized energy storage device can be installed on the transformer side. By adopting edge computing technology, the energy storage device can be used to absorb the power generated by photovoltaic grid-connected power and dynamically balance the healthy operation of the power grid system.

[0057] The intelligent fusion terminal can be connected to the distribution automation master station or the distribution Internet of Things master station according to project requirements. The basic data and alarm information of household photovoltaics can be uploaded to the cloud master station for display and reminders. Power users can remotely perform management operations such as power on / off and power adjustment on the photovoltaic inverter on the master station.

[0058] In this embodiment, the most simplified equipment deployment scheme of the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal in the household photovoltaic system is shown in Table 1 below:

[0059] Table 1: Equipment list of distributed energy grid-connected flexible consumption system based on intelligent fusion terminal

[0060] Serial number Device Name Specification quantity unit 1 Intelligent fusion terminal 220V / 380V, 5A 1 tower 2 Concentrator Type I 220V / 380V, 5(60)A 1 tower 3 Electricity meter 220V, 5(60)A several tower 4 IoT communication unit 220V several tower 5 Inverter 5kW / 30kW several tower 6 solar panels several piece 7 Centralized energy storage device 1 tower

[0061] The business functions performed by the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided in this embodiment include: data collection and sharing, grid-connected anti-islanding effect protection, grid three-phase voltage balance regulation, grid harmonic pollution monitoring and energy storage regulation, a total of five items.

[0062] 1. Data Collection Business

[0063] The real-time operating data of each device during the grid operation process is the basis for monitoring and evaluating whether the system and the grid are operating in a balanced manner. In this embodiment, the basic data uploaded by the intelligent fusion terminal to the cloud master station includes the energy consumption information of the power users measured by the electricity meter, and the real-time data obtained from the inverter using a timed polling method.

[0064] Specifically, the types of real-time data collected are shown in Table 2; they include: input power, grid voltage, grid current, active power, reactive power, power factor, grid frequency, efficiency, cumulative power generation, daily power generation, and meter equipment active power.

[0065] Table 2: Real-time data collected by intelligent fusion terminals

[0066]

[0067] In data collection and sharing services, the alarm information uploaded by the intelligent convergence terminal to the cloud master station is a status indicator that reflects the real-time status of the inverter's operation. Table 3 shows the uploaded alarm information. Alarm types include: standby state, grid-connected state, fault shutdown state, power-limited shutdown state, shutdown state, communication connection failure state, grid feed state, overvoltage state, grid undervoltage state, grid overfrequency state, grid underfrequency state, output overcurrent state, active islanding state, and passive islanding state.

[0068] Table 3: Alarm information table reported by intelligent fusion terminal

[0069]

[0070] 2. Grid-connected anti-islanding effect protection function

[0071] When photovoltaic power generation units are operating normally, the inverter transmits excess power to the grid. However, if the low-voltage grid experiences a power outage due to a fault and the inverter fails to detect the outage and continues to transmit power, the photovoltaic modules themselves become an independent power supply system, a phenomenon known as the "islanding effect."

[0072] Islanding can impact the entire power grid and user equipment. When an islanding event occurs, the grid cannot regulate the inverter's output voltage and frequency, potentially leading to overvoltage, undervoltage, overfrequency, or underfrequency, which can damage user equipment and pose a threat to maintenance personnel.

[0073] To eliminate the hazards caused by the islanding effect, multiple protection measures are required. This embodiment uses the following method to achieve comprehensive grid-connected anti-islanding effect protection:

[0074] (1) Each distributed power generation unit is equipped with an inverter with anti-islanding protection function. When any inverter detects that the current node has an islanding phenomenon, the inverter automatically disconnects from the grid within a specified time; then a corresponding islanding protection alarm status is generated and uploaded to the master station.

[0075] (2) When the system detects a power outage on any branch line within the distribution area, it sends a shutdown command to all inverters under the power outage line, so that the distributed generation units of the corresponding nodes are immediately disconnected from the grid.

[0076] (3) Receive the line maintenance request from the operation and maintenance personnel, and then according to the construction period of the line maintenance request, shut down the inverters of the distributed power generation units included in the maintenance line and disconnect them from the power grid within the corresponding period.

[0077] 3. Voltage balance adjustment function

[0078] Grid-connected photovoltaic power generation may cause the voltage of the grid to increase, which will lead to imbalance in the three-phase voltage of the grid and may also cause the user's equipment to malfunction or be damaged. In the power supply area of ​​distributed photovoltaic power generation grid-connected, the main causes of grid voltage increase are the following two situations:

[0079] 1. Connecting multiple inverters to the same phase of the grid can easily lead to grid voltage imbalance and voltage increase. This situation can be easily resolved through management measures.

[0080] 2. The installed capacity of distributed photovoltaic power generation in the same substation is too large, and the grid load consumption capacity is insufficient. Since the electricity generated by the photovoltaic system cannot be consumed nearby and cannot be transmitted over long distances, it will obviously lead to an increase in the grid voltage.

[0081] The conventional and most effective solution for both of these situations is to reduce the capacity of household PV installations and increase the capacity of substation transformers. However, the PV capacity of individual users is selected based on their own electricity consumption, and the grid cannot control this. The disadvantage of increasing transformer capacity is the high investment cost. Increasing distributed PV capacity should reduce transformer capacity, but increasing transformer capacity clearly violates the principles of substation construction.

[0082] Therefore, in the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided in this embodiment, the following strategy is adopted to solve the three-phase imbalance problem caused by the uneven grid-connected power of distributed power generation units: according to the power generation power of different distributed power generation units, multiple distributed power generation units in the substation are evenly connected to the three phases of the low-voltage power grid, and each distributed power generation unit is connected to the low-voltage power grid at multiple points.

[0083] To solve the problem of grid voltage increase caused by excessive grid-connected power of distributed generation units, the following methods are adopted: Figure 2 The power dynamic adjustment method is controlled, which specifically includes the following steps:

[0084] S1: The cloud master station monitors the three-phase voltage of the power grid in real time.

[0085] S2: Determine whether the voltage value of each phase exceeds the preset rated value and lasts for more than 1 minute: if so, reduce the active power percentage of the inverter of all distributed generation units feeding power to the grid under the current phase line by 50%.

[0086] S3: Determine whether the voltage value on the corresponding phase line returns to normal after the active power is reduced:

[0087] (1) If yes, it is determined that the abnormal increase in grid voltage is caused by the grid connection of distributed generation units, and a corresponding alarm message is reported to the cloud master station.

[0088] (2) Otherwise, continue to reduce the active power percentage of the inverters of all distributed generation units feeding power to the grid under the current phase line by 50%.

[0089] S4: Determine whether the number of grid-connected power reductions of the distributed generation voltage on the phase line whose voltage value exceeds a preset rated value and lasts for more than 1 minute exceeds three times. If so, actively shut down all distributed generation units on the phase line that are feeding power to the grid.

[0090] S5: After power regulation and voltage reduction, when the voltage value on a phase line is lower than the rated value, the derating state of the inverters in the distributed power generation units is restored in turn.

[0091] During the implementation of the above-mentioned power dynamic regulation method, the state where the voltage value on each phase line exceeds the preset rated value is evaluated by exceeding the default value by 7%; the state where the voltage value on each phase line is lower than the preset rated value is evaluated by being lower than the default value by 1%.

[0092] 4. Grid harmonic pollution monitoring

[0093] Harmonics may be generated during power grid operation. Harmonics can reduce the efficiency of electricity production, transmission, and utilization, cause electrical equipment to overheat, generate vibration and noise, and degrade insulation, shortening service life and even leading to failure or burnout. Harmonics can cause localized parallel or series resonance in the power system, amplifying harmonic content and damaging equipment such as capacitors. Harmonics can also cause malfunctions in relay protection and automatic devices, disrupting energy metering. Externally, harmonics can severely interfere with communications and electronic equipment.

[0094] Harmonics in the power grid primarily originate from connected nonlinear loads and power electronics. Grid-connected inverters are a major source of harmonics. On the inverter output side, a bridge circuit typically consists of fully controlled devices such as IGBTs controlled by SPWM waves. The output voltage is a rectangular modulated wave containing a sinusoidal signal, and the output current is a sinusoidal sawtooth wave.

[0095] As the capacity and number of grid-connected inverters continue to increase, the power grid is facing a huge challenge, placing high demands on inverter harmonic suppression. Whether grid-connected inverters are effectively controlling harmonic content requires technical means to conduct research and monitoring.

[0096] In the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal provided in this embodiment, the control objectives of the grid harmonic pollution monitoring function are: the voltage total harmonic distortion rate limit is not higher than 5.0%, the odd harmonic content rate limit is 4.0%, and the even harmonic content rate limit is 2.0%; the grid harmonic pollution monitoring method used is as follows: Figure 3 As shown, the specific steps include:

[0097] S01: The cloud master station monitors the voltage harmonic content rate of each phase in the power grid in real time;

[0098] S02: Determine whether the voltage harmonic content of each phase is higher than the limit and the duration reaches 1 minute. If so, actively shut down the inverters of all distributed generation units on the corresponding phase line that are feeding power to the grid;

[0099] S03: After the inverter of the distributed generation unit on a phase line is shut down, wait for 1 minute and determine again whether the harmonic content of the phase voltage is still higher than the limit: (1) If yes, no action is taken; (2) Otherwise, a corresponding harmonic limit-exceeding alarm message is reported to the cloud master station;

[0100] S04: After completing the judgment in the previous step, re-issue the restart command to the shut-down inverter; after restarting, when the voltage harmonic content rate on the corresponding phase line is lower than the limit, report the inverter harmonic limit recovery alarm information to the cloud master station.

[0101] 5. Energy storage adjustment function

[0102] Existing household photovoltaic systems lack local energy storage modules. PV power units generate electricity for their own use during the day, with any excess energy connected to the grid. However, the integration of large numbers of distributed photovoltaic systems into the grid can have significant impacts on the grid. For example, peak nighttime electricity demand can easily lead to problems such as overloaded distribution transformers, low voltage, and three-phase imbalance. Existing power grids typically improve the operation of distribution substations by installing voltage-scaling and balancing devices, expanding and upgrading transformers, or constructing and renovating new facilities. These approaches offer limited solutions, require long implementation cycles, and offer poor returns on grid investment.

[0103] As an emerging solution, energy storage is developing rapidly and its cost is constantly decreasing. It can provide functions such as peak shaving and valley filling, voltage compensation, and play a role in improving power quality.

[0104] The centralized energy storage device provided by this solution can communicate with the intelligent fusion terminal via RS485 data. The intelligent fusion terminal controls the power charging and discharging, and grid connection and disconnection of the centralized energy storage device. Its main business functions are as follows:

[0105] 1. Improve three-phase imbalance. Distribution substations utilize a three-phase, four-wire wiring system. Single-phase and nonlinear loads continue to grow, leading to frequent imbalances in three-phase active power within the substations. This directly increases line losses and makes substation operations uneconomical. In this situation, energy storage devices are controlled to charge and discharge active power, achieving spatial and temporal shifting of electrical energy and peak-shaving and valley-filling for short-term load fluctuations.

[0106] 2. Achieve reactive power compensation. The balance between the reactive power generated by reactive power sources in the grid, the reactive load, and the reactive losses in the grid directly affects the voltage. When the distribution network experiences a reactive power shortage, low voltage or increased losses will occur, which is also one of the main factors affecting the quality of distribution power supply. Low voltage on distribution network lines is often caused by voltage drops due to short-term load increases. In this case, installing traditional capacitors cannot solve the problem. Reactive power compensation can be achieved by controlling the charging and discharging of reactive power in energy storage devices.

[0107] 3. Peak load shaving and valley loading. During the day, distributed photovoltaic grid-connected systems output a large amount of power to the grid. When the grid's absorption capacity is insufficient, the energy storage device can be treated as a large load and controlled for charging. This consumes the grid-connected power and effectively reduces overvoltage issues caused by grid connection. During peak nighttime electricity consumption, the energy storage device is controlled to output power to the grid, thereby alleviating the operating pressure on the grid.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A distributed energy grid-connected flexible consumption system based on intelligent fusion terminals, characterized by: It is used to manage substation equipment containing distributed renewable energy power generation units, realize the orderly bidirectional flow of distribution network, flexibly control the distribution of power load, and improve the utilization rate of power grid equipment; The distributed energy grid-connected flexible consumption system includes, in a top-down management order, a cloud master station, edge devices, and end devices; The terminal device includes an energy meter, an inverter, a distributed generation unit, and an Internet of Things communication unit; the energy meter is used to collect energy consumption information of power users on the marketing side, and all energy meters in the substation area are connected to a concentrator device via power carrier communication; the electricity generated by all distributed generation units in the substation area is converted into AC power by the inverter, and then used by the load of the power user or connected to the low-voltage power grid in the substation area; each inverter is connected to an intelligent fusion terminal via the Internet of Things communication unit; The edge equipment includes: a substation transformer, a centralized energy storage device, an intelligent fusion terminal and a concentrator; the substation transformer is used to power the low-voltage power grid within the substation area; the centralized energy storage device is electrically connected to the low-voltage power grid, and the centralized energy storage device is used to perform dynamic balancing adjustment when the power supply of the substation transformer does not match the load energy consumption, thereby absorbing the power of the distributed power generation unit connected to the grid; the intelligent fusion terminal is used to collect data, monitor the status of fault events and remotely control the inverter; and collect household meter data obtained by the concentrator through the RS485 or Ethernet interface; at the same time, all the collected basic data and fault event alarm information are uploaded to the cloud master station; The cloud master station is used to display the basic data of all devices in the substation area uploaded by the intelligent fusion terminal and the alarm information of the generated fault events according to the request of the power user; and respond to the power on / off command or power adjustment command issued by the power user to the inverter; The business functions performed by the distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal include: data collection and sharing, grid-connected anti-islanding effect protection, grid three-phase voltage balance regulation, grid harmonic pollution monitoring and energy storage regulation; The three-phase voltage balancing and regulation function of the power grid is used to overcome the problem of abnormal grid voltage increase caused by uneven grid power or excessive grid power. Among them, the following power dynamic regulation method is used to control the problem of grid voltage increase caused by excessive grid power of distributed generation units: S1: The cloud master station monitors the three-phase voltage of the power grid in real time; S2: Determine whether the voltage value of each phase exceeds the preset rated value and the duration exceeds 1 minute: if so, reduce the active power percentage of the inverter of all distributed generation units feeding power to the grid under the current phase line by 50%; S3: Determine whether the voltage value on the corresponding phase line returns to normal after the active power is reduced: (1) If yes, it is determined that the abnormal increase in grid voltage is caused by the grid connection of distributed generation units, and a corresponding alarm message is reported to the cloud master station; (2) Otherwise, continue to derate the active power percentage of the inverters of all distributed generation units feeding into the grid under the current phase line by 50%; S4: Determine whether the number of grid-connected power reductions of the distributed generation voltage on the phase line whose voltage value exceeds the preset rated value and lasts for more than 1 minute exceeds three times. If so, actively shut down all distributed generation units feeding power to the grid under the phase line; S5: After power regulation and voltage reduction, when the voltage value on a phase line is lower than the rated value, the derating state of the inverters in the distributed power generation units is restored in turn.

2. The distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal according to claim 1 is characterized by: In the distributed energy grid-connected flexible consumption system based on intelligent fusion terminals, the distributed power generation units include one or any combination of photovoltaic panels, solar thermal generator sets, wind turbines, tidal generators, and biomass power stations.

3. The distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal according to claim 2 is characterized by: In the data collection business, the basic data uploaded by the intelligent fusion terminal to the cloud master station includes the energy consumption information of the power users measured by the electricity meter and the real-time data obtained from the inverter using the timed polling method; Real-time data types include: input power, grid voltage, grid current, active power, reactive power, power factor, grid frequency, efficiency, cumulative power generation, daily power generation, and meter equipment active power.

4. The distributed energy grid-connected flexible consumption system based on the intelligent fusion terminal according to claim 3 is characterized by: In the data collection and sharing service, the alarm information uploaded by the intelligent fusion terminal to the cloud master station is a status flag used to reflect the real-time status of the inverter operation process; The types of alarm information include: standby state, grid-connected state, fault shutdown state, power-limited shutdown state, shutdown state, communication connection failure state, grid feed state, overvoltage state, grid undervoltage state, grid overfrequency state, grid underfrequency state, output overcurrent state, active island state, and passive island state.

5. The distributed energy grid-connected flexible consumption system based on intelligent fusion terminal according to claim 4 is characterized by: The grid-connected anti-islanding protection function in the distributed energy grid-connected flexible consumption system based on intelligent fusion terminals is implemented using the following method: (1) Each distributed power generation unit is equipped with an inverter with anti-islanding protection function. When any inverter detects that the current node has an islanding phenomenon, the inverter automatically disconnects from the grid within a specified time; then a corresponding islanding protection alarm status is generated and uploaded to the master station; (2) When the system detects a power outage on any branch line within the distribution area, it sends a shutdown command to all inverters under the power outage line, so that the distributed generation units of the corresponding nodes are immediately disconnected from the grid; (3) Receive the line maintenance request from the operation and maintenance personnel, and then according to the construction period of the line maintenance request, shut down the inverters of the distributed power generation units included in the maintenance line and disconnect them from the power grid within the corresponding period.

6. The distributed energy grid-connected flexible consumption system based on intelligent fusion terminal according to claim 5 is characterized by: The following strategies are used to solve the three-phase imbalance problem caused by uneven grid-connected power of distributed generation units: According to the power generation capacity of different distributed power generation units, multiple distributed power generation units in the substation area are evenly connected to the three phases of the low-voltage power grid, and each distributed power generation unit is connected to the low-voltage power grid at multiple points.

7. The distributed energy grid-connected flexible consumption system based on intelligent fusion terminal according to claim 1 is characterized by: During the implementation of the power dynamic regulation method, the state where the voltage value on each phase line exceeds the preset rated value is evaluated by exceeding the default value by 7%; the state where the voltage value on each phase line is lower than the preset rated value is evaluated by being lower than the default value by 1%.

8. The distributed energy grid-connected flexible consumption system based on intelligent fusion terminal according to claim 1 is characterized by: The control objectives of the grid harmonic pollution monitoring function in the distributed energy grid-connected flexible consumption system based on intelligent fusion terminals are: the voltage total harmonic distortion rate limit is no higher than 5.0%, the odd harmonic content limit is 4.0%, and the even harmonic content limit is 2.0%. The grid harmonic pollution monitoring method used is as follows: S01: The cloud master station monitors the voltage harmonic content rate of each phase in the power grid in real time; S02: Determine whether the voltage harmonic content of each phase is higher than the limit and the duration reaches 1 minute. If so, actively shut down the inverters of all distributed generation units on the corresponding phase line that are feeding power to the grid; S03: After the inverter of the distributed generation unit on a phase line is shut down, wait for 1 minute and determine again whether the harmonic content of the phase voltage is still higher than the limit: (1) If yes, no action is taken; (2) Otherwise, a corresponding harmonic limit-exceeding alarm message is reported to the cloud master station; S04: After completing the judgment in the previous step, re-issue the restart command to the shut-down inverter; after restarting, when the voltage harmonic content rate on the corresponding phase line is lower than the limit, report the inverter harmonic limit recovery alarm information to the cloud master station.

9. The distributed energy grid-connected flexible consumption system based on intelligent fusion terminal according to claim 8, characterized in that: In a distributed energy grid-connected flexible consumption system based on an intelligent fusion terminal, the energy storage regulation function is implemented by a centralized energy storage device. The centralized energy storage device is connected to the intelligent fusion terminal via an RS485 interface and receives control instructions from the intelligent fusion terminal. The intelligent fusion terminal is used to: (1) Using centralized energy storage devices to improve the three-phase imbalance of the power grid: When the active power of the power grid fluctuates for a short time, the energy storage device is controlled to charge and discharge the active power, achieving the time and space shift of electric energy and balancing the operating state of the power grid; (2) Using centralized energy storage devices to compensate for reactive power in the power grid: When the reactive power and reactive load in the power grid do not match, the energy storage device is used to control the charging and discharging of reactive power; (3) Control the charging and discharging status of the centralized energy storage device according to the power changes of the distributed power generation units connected to the power grid: when the power grid is in a low-load state, the centralized energy storage device uses the low-voltage power grid to charge; when the power grid is in a high-load state, the centralized energy storage device feeds power to the low-voltage power grid.

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