Electric energy quality optimization method and system after high-proportion distributed power supply is connected to power distribution network

Abstract

The invention relates to an electric energy quality optimization method and system after a high-proportion distributed power supply accesses a power distribution network. The method comprises the following steps: determining an influence coverage range of a first inverter according to an access position of the first inverter; acquiring a second inverter which exists in the influence coverage range and is accessed to the power grid; when the number of the second inverters is larger than or equal to one, the correlation influence degree of the first inverter and the second inverters is calculated, and an influence degree numerical value is obtained; and selecting an access mode of the first inverter according to the influence degree value, wherein the access mode comprises introduction of virtual impedance, droop control and starting of an electric reactor. According to the electric energy quality optimization method and system after the high-proportion distributed power supply is connected to the power distribution network, the proper processing scheme is selected through dynamic evaluation of the access position, the stability of the power distribution network after the distributed power supply is connected to the power distribution network can be effectively improved, and then the quality of electric energy provided by the power distribution network can be stable.

Description

Technical Field

[0001] This invention relates to the field of power grid safety management technology, and in particular to a method and system for optimizing power quality after a high proportion of distributed power sources are connected to the distribution network. Background Technology

[0002] The large-scale integration of distributed power sources into medium and low voltage distribution networks and the increased penetration of photovoltaic power have introduced various random disturbances into traditional and active distribution networks, severely damaging the power quality of the system and causing serious problems such as harmonic pollution, unstable power supply voltage, and imbalance between three-phase voltage and reactive power.

[0003] The quality of the current injected into the grid is a significant concern. International standards specify the connection methods between PV inverters and the grid and limit the harmonic content of the injected current. Inverter grid connection is prohibited if the harmonic injection content exceeds the limit. Therefore, numerous control algorithms have been proposed, including repetitive controllers, integrators in rotating coordinate systems, and resonant integrators, and LCL filters are used to prevent grid pollution from switching harmonics.

[0004] Another challenge is that parallel inverters are coupled due to grid impedance, and these couplings affect each other. Furthermore, inverter current can circulate through the parallel inverters without being injected into the grid. Ideally, the grid impedance should be zero, eliminating coupling. However, in reality, resonant behavior has been detected in many PV power sources or power plants, causing currents to exceed grid connection standards and leading to equipment damage. Summary of the Invention

[0005] This invention provides a method and system for optimizing power quality after a high proportion of distributed power sources are connected to the distribution network. By dynamically evaluating the connection location to select a suitable processing scheme, the stability of the distribution network after the distributed power sources are connected to the distribution network can be effectively improved, thereby ensuring stable power quality provided by the distribution network.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for optimizing power quality after a high proportion of distributed power sources are connected to a distribution network, comprising:

[0008] In response to the access request of the first inverter, determine the access location of the first inverter;

[0009] The impact coverage of the first inverter is determined based on its connection location.

[0010] The system identifies any second inverters already connected to the power grid within the affected coverage area. The number of second inverters may be zero, one, or more.

[0011] When the number of second inverters is greater than or equal to one, calculate the correlation influence between the first inverter and the second inverter to obtain the influence value;

[0012] The connection method of the first inverter is selected based on the impact value. The connection methods include introducing virtual impedance, droop control, and enabling the reactor.

[0013] In one possible implementation of the first aspect, before determining the influence coverage of the first inverter based on its connection location, the method further includes:

[0014] Calculate the short-circuit capacity at the location where the first inverter is connected;

[0015] Calculate the ratio of short-circuit capacity to the current power supplied to the first inverter;

[0016] The first inverter is allowed to connect based on the ratio. When the ratio is greater than the first set value, the first inverter is allowed to connect. When the ratio is less than the second set value, the first inverter is not allowed to connect. When the ratio is greater than or equal to the second set value and less than or equal to the first set value, the coverage area of ​​the first inverter is determined based on the connection location of the first inverter.

[0017] In one possible implementation of the first aspect, determining the coverage area of ​​the first inverter based on its connection location includes:

[0018] Calculate the power flow changes in the distribution network after the virtual first inverter is connected;

[0019] In the power distribution network, identify the nodes associated with the access location of the first inverter; the number of nodes is multiple.

[0020] Calculate the voltage drop of a node; when the voltage drop of a node is greater than or equal to the allowable value, the node is marked as an affected node.

[0021] The impact coverage of the first inverter is constructed using the impact nodes.

[0022] In one possible implementation of the first aspect, when constructing the influence coverage of the first inverter using influence nodes, any two influence nodes are connected by line segments to obtain a connection network, and the maximum outer edge of the connection network is taken as the influence coverage of the first inverter.

[0023] In one possible implementation of the first aspect, after obtaining the coverage area, the sensitive nodes within the coverage area are obtained and the allowable voltage drop of the sensitive nodes is calculated;

[0024] When the allowable voltage drop of a sensitive node is less than the voltage drop of the node, the first inverter is connected to the distribution network using a tiered connection method.

[0025] When the allowable voltage drop of a sensitive node is greater than or equal to the voltage drop of the node, the first inverter is allowed to be directly connected to the distribution network.

[0026] In one possible implementation of the first aspect, calculating the degree of correlation between the first inverter and the second inverter includes calculating the ratio of the equivalent coupling impedance to the inverter output impedance.

[0027] In one possible implementation of the first aspect, when calculating the ratio of the equivalent coupling impedance to the inverter output impedance, it is necessary to determine the active frequency range of the first inverter.

[0028] After determining the active frequency range of the first inverter, calculate the ratio of the equivalent coupling impedance to the inverter output impedance at each active frequency value.

[0029] When the ratio of the equivalent coupling impedance to the inverter output impedance is always less than or equal to 1, the correlation influence between the first inverter and the second inverter is zero.

[0030] When there is at least one active frequency value such that the ratio of the equivalent coupling impedance to the inverter output impedance is always greater than 1, the correlation influence between the first inverter and the second inverter is the total number of active frequency values.

[0031] Secondly, the present invention provides a power quality optimization device for a high proportion of distributed power sources connected to a distribution network, comprising:

[0032] A location determination unit is used to determine the access location of the first inverter in response to the access request of the first inverter;

[0033] The range determination unit is used to determine the influence coverage range of the first inverter based on the connection location of the first inverter.

[0034] The first processing unit is used to acquire the second inverters that are already connected to the power grid within the affected coverage area. The number of the second inverters is zero, one, or more.

[0035] The second processing unit is used to calculate the correlation influence between the first inverter and the second inverter when the number of second inverters is greater than or equal to one, and obtain the influence value.

[0036] The access processing unit is used to select the access method of the first inverter based on the influence value. The access methods include introducing virtual impedance, droop control, and enabling the reactor.

[0037] Thirdly, the present invention provides a power quality optimization system for a high proportion of distributed power sources connected to a distribution network, the system comprising:

[0038] One or more memories for storing instructions; and

[0039] One or more processors are configured to retrieve and execute the instructions from the memory to perform the methods described in the first aspect and any possible implementation thereof.

[0040] Fourthly, the present invention provides a computer-readable storage medium comprising:

[0041] The program, when run by a processor, is executed as described in the first aspect and any possible implementation thereof.

[0042] Fifthly, the present invention provides a computer program product, including program instructions that, when the program instructions are run by a computing device, execute the method described in the first aspect and any possible implementation thereof.

[0043] In a sixth aspect, the present invention provides a chip system including a processor for implementing the functions involved in the foregoing aspects, such as generating, receiving, transmitting, or processing data and / or information involved in the foregoing methods.

[0044] This chip system can consist of chips or include chips and other discrete components.

[0045] In one possible design, the chip system also includes a memory for storing necessary program instructions and data. The processor and the memory can be decoupled and located on different devices, connected via wired or wireless means, or the processor and the memory can be coupled to the same device. Attached Figure Description

[0046] Figure 1 This is a schematic flowchart of the steps of a power quality optimization method provided by the present invention.

[0047] Figure 2 This is a schematic diagram of an access location provided by the present invention.

[0048] Figure 3 This is a schematic diagram of the distribution of influencing nodes provided by the present invention.

[0049] Figure 4 This is a schematic diagram illustrating the influence coverage of a first inverter constructed using influence nodes, as provided by the present invention. Detailed Implementation

[0050] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings.

[0051] This invention discloses a power quality optimization method for a high proportion of distributed power sources connected to the distribution network. Please refer to [link / reference]. Figure 1 In some examples, the power quality optimization method disclosed in this invention after a high proportion of distributed power sources are connected to the distribution network includes the following steps:

[0052] S101, in response to the access request of the first inverter, determine the access location of the first inverter;

[0053] S102, determine the influence coverage range of the first inverter based on the connection location of the first inverter;

[0054] S103, obtain the second inverters that are already connected to the grid within the affected coverage area, the number of which may be zero, one, or more;

[0055] S104, When the number of second inverters is greater than or equal to one, calculate the correlation influence between the first inverter and the second inverter, and obtain the influence value;

[0056] S105, select the connection method of the first inverter according to the influence value. The connection methods include introducing virtual impedance, droop control and enabling reactor.

[0057] Overall, the technical solution disclosed in this invention is achieved by accessing a location, such as... Figure 2 As shown, the scope of influence is determined, and then a second inverter that exists within the scope of influence is searched. When the second inverter exists, the correlation influence between the first inverter and the second inverter is calculated, and then the access method of the first inverter is selected according to the influence value.

[0058] The specific details of the access method are as follows:

[0059] Virtual impedance: A virtual impedance element is actively introduced into the inverter control algorithm. Through virtual impedance, the influence of the actual grid impedance can be offset or weakened, making the system behave more like it is connected to a strong grid (low impedance), thereby decoupling the correlation between inverters.

[0060] Droop control: Simulating the power-frequency characteristics of a traditional synchronous generator, this method allows the inverter to adjust active and reactive power based on frequency and voltage deviations. It is a "wireless" control method based on local measurements, enabling automatic power distribution and enhancing system stability to a certain extent, and naturally exhibiting robustness against impedance coupling.

[0061] Enabling a reactor: Connecting an inductor in series at the inverter output can increase the total output impedance, change the system's impedance ratio, and move it away from the region that is prone to resonance.

[0062] When choosing between these three methods, virtual impedance is selected when the influence value is small, droop control is selected when the influence value increases, and reactor activation is selected when the influence value continues to increase. This can be summarized as the influence value corresponding to three stages, and each stage corresponds to one method.

[0063] Before determining the coverage area of ​​the first inverter based on its connection location, the following steps were added:

[0064] Calculate the short-circuit capacity at the location where the first inverter is connected;

[0065] Calculate the ratio of short-circuit capacity to the current power supplied to the first inverter;

[0066] The first inverter is allowed to connect based on the ratio. When the ratio is greater than the first set value, the first inverter is allowed to connect. When the ratio is less than the second set value, the first inverter is not allowed to connect. When the ratio is greater than or equal to the second set value and less than or equal to the first set value, the coverage area of ​​the first inverter is determined based on the connection location of the first inverter.

[0067] These preliminary steps will produce three results: allowing the first inverter to connect, disallowing the first inverter to connect, and determining the impact coverage of the first inverter based on its connection location. Specifically, allowing the first inverter to connect means that the first inverter can be directly connected, disallowing the first inverter to connect means that the first inverter is not allowed to connect because it will cause instability in the power distribution network. Determining the impact coverage of the first inverter based on its connection location means that it is necessary to decide whether to allow the first inverter to connect based on the impact coverage.

[0068] The specific method for determining the impact coverage of the first inverter based on its connection location is as follows:

[0069] Calculate the power flow changes in the distribution network after the virtual first inverter is connected;

[0070] In the power distribution network, determine the node associated with the access location of the first inverter, such as... Figure 3 As shown, there are multiple nodes;

[0071] Calculate the voltage drop of a node; when the voltage drop of a node is greater than or equal to the allowable value, the node is marked as an affected node.

[0072] The impact coverage of the first inverter is constructed using the impact nodes. Figure 4As shown by the dashed line.

[0073] In some possible implementations, when constructing the influence coverage of the first inverter using influence nodes, any two influence nodes are connected by line segments to obtain a connection network, and the maximum outer edge of the connection network is taken as the influence coverage of the first inverter.

[0074] In some cases, after obtaining the affected coverage area, the sensitive nodes within the affected coverage area are identified, and the allowable voltage drop of the sensitive nodes is calculated.

[0075] When the allowable voltage drop of a sensitive node is less than the voltage drop of the node, the first inverter is connected to the distribution network using a tiered connection method.

[0076] When the allowable voltage drop of a sensitive node is greater than or equal to the voltage drop of the node, the first inverter is allowed to be directly connected to the distribution network.

[0077] In some possible implementations, calculating the correlation between the first and second inverters involves calculating the ratio of the equivalent coupling impedance to the inverter output impedance, as follows:

[0078] When calculating the ratio of the equivalent coupling impedance to the inverter output impedance, it is necessary to determine the active frequency range of the first inverter.

[0079] After determining the active frequency range of the first inverter, calculate the ratio of the equivalent coupling impedance to the inverter output impedance at each active frequency value.

[0080] When the ratio of the equivalent coupling impedance to the inverter output impedance is always less than or equal to 1, the correlation influence between the first inverter and the second inverter is zero.

[0081] When there is at least one active frequency value such that the ratio of the equivalent coupling impedance to the inverter output impedance is always greater than 1, the correlation influence between the first inverter and the second inverter is the total number of active frequency values.

[0082] This invention also provides a power quality optimization device for high-proportion distributed power sources connected to the distribution network, comprising:

[0083] A location determination unit is used to determine the access location of the first inverter in response to the access request of the first inverter;

[0084] The range determination unit is used to determine the influence coverage range of the first inverter based on the connection location of the first inverter.

[0085] The first processing unit is used to acquire the second inverters that are already connected to the power grid within the affected coverage area. The number of the second inverters is zero, one, or more.

[0086] The second processing unit is used to calculate the correlation influence between the first inverter and the second inverter when the number of second inverters is greater than or equal to one, and obtain the influence value.

[0087] The access processing unit is used to select the access method of the first inverter based on the influence value. The access methods include introducing virtual impedance, droop control, and enabling the reactor.

[0088] In one example, the unit in any of the above devices may be one or more integrated circuits configured to implement the above methods, such as one or more application-specific integrated circuits (ASICs), or one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs), or a combination of at least two of these integrated circuit forms.

[0089] For example, when the units in the device can be implemented through a processing element scheduler, the processing element can be a general-purpose processor, such as a central processing unit (CPU) or other processor capable of calling programs. Alternatively, these units can be integrated together to form a system-on-a-chip (SOC).

[0090] In this invention, various objects such as messages / information / devices / network elements / systems / devices / actions / operations / processes / concepts may be named. It is understood that these specific names do not constitute a limitation on the relevant objects. The names may be changed depending on the scenario, context, or usage habits. The understanding of the technical meaning of the technical terms in this invention should be mainly determined from their functions and technical effects embodied / performed in the technical solution.

[0091] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0092] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0093] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0094] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0095] It should also be understood that in the various embodiments of the present invention, "first," "second," etc., are merely used to indicate that multiple objects are different. For example, a first time window and a second time window are only used to indicate different time windows, and should not have any effect on the time window itself. The aforementioned "first," "second," etc., should not impose any limitations on the embodiments of the present invention.

[0096] It should also be understood that, in the various embodiments of the present invention, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions between different embodiments are consistent and can be referenced by each other, and the technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

[0097] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a computer-readable storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned computer-readable storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0098] This invention also provides a power quality optimization system for a high proportion of distributed power sources connected to the distribution network, the system comprising:

[0099] One or more memories for storing instructions; and

[0100] One or more processors are configured to retrieve and execute the instructions from the memory, performing the methods described above.

[0101] The present invention also provides a computer program product including instructions that, when executed, cause the terminal device and the network device to perform operations corresponding to the methods described above.

[0102] The present invention also provides a chip system including a processor for implementing the functions involved in the above description, such as generating, receiving, transmitting, or processing the data and / or information involved in the above methods.

[0103] This chip system can consist of chips or include chips and other discrete components.

[0104] The processor mentioned above can be a CPU, a microprocessor, an ASIC, or one or more integrated circuits that execute a program to control the method of transmitting the feedback information described above.

[0105] In one possible design, the chip system also includes a memory for storing necessary program instructions and data. The processor and the memory can be decoupled and located on different devices, connected via wired or wireless means to support the chip system in implementing the various functions described in the above embodiments. Alternatively, the processor and the memory can also be coupled to the same device.

[0106] Optionally, the computer instructions are stored in memory.

[0107] Optionally, the memory can be a storage unit within the chip, such as a register or cache. Alternatively, the memory can be a storage unit located outside the chip within the terminal, such as a ROM or other types of static storage devices that can store static information and instructions, such as RAM.

[0108] It is understood that the memory in this invention can be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory.

[0109] Non-volatile memory can be ROM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory.

[0110] Volatile memory can be RAM, which is used as an external cache. There are many different types of RAM, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link dynamic random access memory (SLDRAM), and direct memory bus random access memory.

[0111] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for optimizing power quality after a high proportion of distributed power sources are connected to a distribution network, characterized in that, include: In response to the access request of the first inverter, determine the access location of the first inverter; The impact coverage of the first inverter is determined based on its connection location. The system identifies any second inverters already connected to the power grid within the affected coverage area. The number of second inverters may be zero, one, or more. When the number of second inverters is greater than or equal to one, calculate the correlation influence between the first inverter and the second inverter to obtain the influence value; The connection method of the first inverter is selected based on the impact value. The connection methods include introducing virtual impedance, droop control, and enabling the reactor.

2. The power quality optimization method for high-proportion distributed power sources connected to the distribution network according to claim 1, characterized in that, Before determining the coverage area of ​​the first inverter based on its connection location, the process also includes: Calculate the short-circuit capacity at the location where the first inverter is connected; Calculate the ratio of short-circuit capacity to the current power supplied to the first inverter; The first inverter is allowed to connect based on the ratio. When the ratio is greater than the first set value, the first inverter is allowed to connect. When the ratio is less than the second set value, the first inverter is not allowed to connect. When the ratio is greater than or equal to the second set value and less than or equal to the first set value, the coverage area of ​​the first inverter is determined based on the connection location of the first inverter.

3. The power quality optimization method for high-proportion distributed power sources connected to the distribution network according to claim 2, characterized in that, The influence coverage area of ​​the first inverter, determined based on its connection location, includes: Calculate the power flow changes in the distribution network after the virtual first inverter is connected; In the power distribution network, identify the nodes associated with the access location of the first inverter; the number of nodes is multiple. Calculate the voltage drop of a node; when the voltage drop of a node is greater than or equal to the allowable value, the node is marked as an affected node. The impact coverage of the first inverter is constructed using the impact nodes.

4. The power quality optimization method for a high proportion of distributed power sources connected to the distribution network according to claim 3, characterized in that, When constructing the influence coverage of the first inverter using influence nodes, any two influence nodes are connected by line segments to obtain a connection network, and the maximum outer edge of the connection network is taken as the influence coverage of the first inverter.

5. The power quality optimization method after a high proportion of distributed power sources are connected to the distribution network according to claim 3 or 4, characterized in that, After obtaining the affected coverage area, identify the sensitive nodes within the affected coverage area and calculate the allowable voltage drop value for the sensitive nodes; When the allowable voltage drop of a sensitive node is less than the voltage drop of the node, the first inverter is connected to the distribution network using a tiered connection method. When the allowable voltage drop of a sensitive node is greater than or equal to the voltage drop of the node, the first inverter is allowed to be directly connected to the distribution network.

6. The power quality optimization method for high-proportion distributed power sources connected to the distribution network according to claim 1, characterized in that, Calculating the correlation between the first inverter and the second inverter involves calculating the ratio of the equivalent coupling impedance to the inverter output impedance.

7. The power quality optimization method for a high proportion of distributed power sources connected to the distribution network according to claim 6, characterized in that, When calculating the ratio of the equivalent coupling impedance to the inverter output impedance, it is necessary to determine the active frequency range of the first inverter. After determining the active frequency range of the first inverter, calculate the ratio of the equivalent coupling impedance to the inverter output impedance at each active frequency value. When the ratio of the equivalent coupling impedance to the inverter output impedance is always less than or equal to 1, the correlation influence between the first inverter and the second inverter is zero. When there is at least one active frequency value such that the ratio of the equivalent coupling impedance to the inverter output impedance is always greater than 1, the correlation influence between the first inverter and the second inverter is the total number of active frequency values.

8. A power quality optimization device for a high proportion of distributed power sources connected to a distribution network, characterized in that, include: A location determination unit is used to determine the access location of the first inverter in response to the access request of the first inverter; The range determination unit is used to determine the influence coverage range of the first inverter based on the connection location of the first inverter. The first processing unit is used to acquire the second inverters that are already connected to the power grid within the affected coverage area. The number of the second inverters is zero, one, or more. The second processing unit is used to calculate the correlation influence between the first inverter and the second inverter when the number of second inverters is greater than or equal to one, and obtain the influence value. The access processing unit is used to select the access method of the first inverter based on the influence value. The access methods include introducing virtual impedance, droop control, and enabling the reactor.

9. A power quality optimization system for a high proportion of distributed power sources connected to a distribution network, characterized in that, The system includes: One or more memories for storing instructions; and One or more processors are configured to retrieve and execute the instructions from the memory to perform the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes: The program, when run by the processor, executes the method as described in any one of claims 1 to 7.

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