Three-phase imbalance treatment method and system for distributed photovoltaic and distribution area adjustable resources

Abstract

A method and system for managing three-phase imbalance in distributed photovoltaic (PV) and adjustable resources in distribution networks utilizes a power allocation algorithm. First, the reactive power output of the first group of distributed PV devices is determined based on an upper limit for the three-phase imbalance. The current three-phase imbalance is then calculated based on this output. Next, the reactive power output of the reactive power regulating equipment is determined based on this current imbalance. Finally, the current three-phase imbalance is corrected by summing the reactive power outputs of the reactive power regulating equipment and the first group of distributed PV devices. If the corrected imbalance exceeds the limit, the above steps are repeated to determine the reactive power output of the second group of distributed PV devices and the reactive power regulating equipment, until the three-phase imbalance is less than or equal to the limit. This invention solves the problems of untimely and inaccurate three-phase imbalance regulation in distribution networks with distributed PV integration.

Description

Technical Field

[0001] This invention belongs to the field of power system power quality technology, specifically, it relates to a method and system for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations. Background Technology

[0002] To alleviate resource shortages and environmental pollution caused by traditional thermal power generation, reduce greenhouse gas emissions, and develop clean energy, a large number of distributed photovoltaic (PV) devices have been connected to the power distribution network, gradually transforming the traditional power distribution network system into an active power distribution system. However, due to the intermittent and random nature of distributed PV power output, the variations in its output power exacerbate the three-phase voltage imbalance problem in the power distribution network.

[0003] As the penetration rate of distributed photovoltaic (PV) power increases, its probabilistic power output affects the power flow of grid-connected phases, thus influencing node voltages. Changes in the voltage at the beginning of the grid-connected phases exacerbate three-phase voltage imbalances. Current technologies address three-phase imbalances through load commutation or reactive power compensation. However, frequent load commutation places high demands on the switching devices and carries the risk of load outages. Reactive power compensation devices cannot handle the capacitive reactive power issues associated with nonlinear loads. These methods are no longer suitable for increasingly complex distribution lines with ever-higher power quality requirements. Therefore, improvements to the mitigation methods are needed to adapt to changes in distribution network structures and power quality demands.

[0004] A comprehensive control device, a low-voltage distribution network, and a multi-stage voltage regulation method at the end of a low-voltage distribution network line (CN115102207A) are disclosed. This method distributes three-phase power and voltage at the end of a low-voltage distribution network line, employing a combination of various regulation methods (AC / DC energy storage conversion modules, inductors, and / or capacitors) to achieve flexible voltage control and address three-phase imbalance at the end of the low-voltage distribution network line. A reactive power coordination control method for distributed photovoltaic inverters and capacitor banks (CN105) is also disclosed. 811424B) determines the reactive power borne by the capacitor bank and photovoltaic inverter respectively; it determines the reactive power output command of the photovoltaic inverter, the current actual active power generated by each photovoltaic inverter, and the AC side voltage value, modifies the reactive power output command, and issues it to each photovoltaic inverter; the capacitor bank monitors the power factor at the user's incoming line in real time according to the connection time, connection capacity, disconnection time, and disconnection capacity, calculates the reactive power deficit, and distributes the reactive power deficit proportionally to each photovoltaic inverter according to the current active power generated by the photovoltaic inverter. However, the existing technology does not fully utilize the characteristic that changes in the output power of distributed photovoltaics can change the voltage at the beginning of the line. Therefore, when performing three-phase imbalance adjustment in distribution network areas with distributed photovoltaic access, there are problems of untimely and inaccurate adjustment. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and system for managing three-phase imbalance in distributed photovoltaic (PV) and adjustable distribution network resources. It fully utilizes the characteristic that variations in the output power of distributed PV can alter the voltage at the beginning of the line. A power allocation algorithm is used to determine the relationship between the three-phase imbalance degree and the output value of the capacitor bank, as well as the relationship between the three-phase imbalance degree and the variation in the output value of distributed PV. This enables the management of three-phase imbalance in distribution network areas connected to distributed PV, solving the problems of untimely and inaccurate three-phase imbalance adjustment in these areas.

[0006] The present invention adopts the following technical solution.

[0007] This invention proposes a method for managing three-phase imbalance in distributed photovoltaic systems and adjustable resources in transformer substations, comprising:

[0008] Step 1: Establish equivalent models of lines, transformers, and reactive power regulation equipment within the distribution area; based on these models, obtain the distribution area's operational data.

[0009] Step 2: Calculate the three-phase imbalance based on the transformer area operation data; use the three-phase imbalance to determine the reactive power output of the reactive power regulation equipment and the reactive power output of the distributed photovoltaic equipment respectively;

[0010] Step 3: Extract the maximum and minimum values ​​of active power output of distributed photovoltaic equipment and the maximum and minimum values ​​of user load from the historical longitudinal data of the transformer area; determine the upper limit of three-phase imbalance based on the minimum value of distributed photovoltaic equipment output and the maximum value of user load.

[0011] Step 4: First, determine the reactive power output of the first group of distributed photovoltaic (PV) devices based on the upper limit of the three-phase imbalance. Calculate the current three-phase imbalance based on the reactive power output of the first group of PV devices. Determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulating equipment in the transformer area and the reactive power output of the first group of PV devices. If the corrected current three-phase imbalance is greater than the limit, repeat the above steps to determine the reactive power output of the second group of PV devices and the reactive power regulating equipment, until the three-phase imbalance is less than or equal to the limit.

[0012] Preferably, in step 1, the equivalent model of the line ignores the ground admittance of the π-type circuit, and the equivalent model of the transformer adopts the Γ-type circuit model of the distribution transformer.

[0013] The operating data of the transformer area includes, but is not limited to: active power, reactive power, voltage, and other data of users or equipment.

[0014] Preferably, step 2 includes:

[0015] Step 2.1, when addressing three-phase imbalance by adjusting the reactive power output of the reactive power regulation equipment and distributed photovoltaic equipment within the transformer substation, the adjustment of reactive power output needs to be based on the substation operating data. The three-phase imbalance is calculated using the substation operating data, satisfying the following relationship:

[0016]

[0017] In the formula,

[0018] △ε U2 This refers to the three-phase voltage imbalance.

[0019] U1 and U2 represent the root mean square values ​​of the positive and negative sequence components of the three-phase voltage, respectively.

[0020] Step 2.2: Based on the three-phase unbalance, using the rated voltage of each phase and the impedance based on the transformer equivalent model, the reactive power output of the capacitor bank is obtained, satisfying the following relationship:

[0021]

[0022] In the formula, △Q C For the reactive power output of the capacitor bank, x T The impedance ΔQ represents the equivalent model of the transformer. C U represents the capacitance of the capacitor bank. i (i = A, B, C) represents the rated voltage of each phase.

[0023] Step 2.3: Based on the three-phase imbalance, using the rated voltage of each phase and the resistance and reactance based on the equivalent line model, the reactive power output of the distributed photovoltaic equipment is obtained, satisfying the following relationship:

[0024]

[0025] In the formula, R and X are the resistance and reactance of the equivalent model of the line between the three-phase line common coupling point and the photovoltaic grid connection point, respectively; ΔQ is the reactive power change value of the photovoltaic inverter output.

[0026] Preferably, in step 3, the historical longitudinal data includes: the output data of distributed photovoltaic equipment and the user load data of July and August within the past three years; through data filtering and comparison, the maximum value of distributed photovoltaic equipment output, the minimum value of distributed photovoltaic equipment output, the maximum value of user load and the minimum value of user load are extracted from the historical longitudinal data.

[0027] When the distributed photovoltaic equipment in the distribution network stops outputting power, reaching its minimum output, and the user load reaches its maximum, the three-phase imbalance in the distribution area will reach its maximum value, i.e., the upper limit of the three-phase imbalance.

[0028] Preferably, step 4 includes:

[0029] Step 4.1: Determine the reactive power output of the first group of distributed photovoltaic devices based on the upper limit of the three-phase imbalance.

[0030] Step 4.2: Calculate the current three-phase imbalance based on the reactive power output of the first group of distributed photovoltaic devices;

[0031] Step 4.3: Determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance.

[0032] Step 4.4: Correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulation equipment and the first group of distributed photovoltaic equipment in the transformer area;

[0033] Step 4.5: If the corrected current three-phase imbalance is greater than the limit, then use the corrected current three-phase imbalance to determine the reactive power output of the second group of distributed photovoltaic equipment and repeat steps 4.2 to 4.4 until the three-phase imbalance is less than or equal to the limit.

[0034] The limit value is no greater than 2%.

[0035] In step 4, if the goal of the governance is to reduce the voltage at the point of common coupling, the reactive power output of the distributed photovoltaic equipment will be negative, i.e., it will absorb reactive power; if the goal of the governance is to increase the voltage at the point of common coupling, the reactive power output of the distributed photovoltaic equipment will be positive, i.e., it will generate reactive power.

[0036] The reactive power regulation equipment includes SVG and capacitor banks; the reactive power output of the reactive power regulation equipment is determined based on the current three-phase imbalance, including the reactive power output of the capacitor banks and the reactive power output of the SVG; when the distributed photovoltaic equipment has not yet reached its maximum resource, that is, when there are still distributed photovoltaic equipment with unregulated reactive power output, the reactive power output of the SVG is not required, and the reactive power output of the capacitor banks is used in conjunction with the reactive power output of the distributed photovoltaic equipment;

[0037] When all the reactive power output of n sets of distributed photovoltaic equipment is utilized, the reactive power output gap or margin in the distribution area is met by the reactive power output of the SVG.

[0038] In another aspect, the present invention proposes a three-phase imbalance management system for distributed photovoltaic and adjustable resources in the transformer area, comprising: a data acquisition module, a reactive power output calculation module for distributed photovoltaic equipment, a reactive power output calculation module for reactive power regulation equipment, a three-phase imbalance calculation module, and a reactive power output allocation module.

[0039] The data acquisition module is used to acquire the operating data of the distribution area based on the equivalent models of the lines, transformers, and reactive power regulation equipment within the distribution area; and to extract the maximum and minimum output values ​​of distributed photovoltaic equipment and the maximum and minimum user load values ​​from the historical longitudinal data of the distribution area.

[0040] The three-phase imbalance calculation module is used to calculate the three-phase imbalance based on the operating data of the distribution area, and to determine the upper limit of the three-phase imbalance based on the minimum output of the distributed photovoltaic equipment and the maximum user load.

[0041] The reactive power output calculation module for distributed photovoltaic equipment is used to determine the reactive power output of distributed photovoltaic equipment based on the three-phase imbalance.

[0042] The reactive power output calculation module for reactive power regulation equipment is used to determine the reactive power output of reactive power regulation equipment using three-phase imbalance.

[0043] The reactive power output allocation module is used to call the reactive power output calculation module of the distributed photovoltaic equipment to determine the reactive power output of the first group of distributed photovoltaic equipment based on the upper limit of the three-phase imbalance. Based on the reactive power output of the first group of distributed photovoltaic equipment, it calls the three-phase imbalance calculation module to calculate the current three-phase imbalance. It then calls the reactive power output calculation module of the reactive power regulating equipment to determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Next, it calls the three-phase imbalance calculation module to correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulating equipment and the first group of distributed photovoltaic equipment in the distribution area. If the corrected current three-phase imbalance is greater than the limit, it adjusts the reactive power output of the second group of distributed photovoltaic equipment and the reactive power regulating equipment until the three-phase imbalance is less than or equal to the limit. After the reactive power output of all n groups of distributed photovoltaic equipment has been called, it adjusts the reactive power output of the SVG to meet the reactive power output gap or margin in the distribution area.

[0044] The beneficial effects of this invention are as follows: Compared with the prior art, this invention takes into account the reactive power regulation capability of distributed photovoltaic (PV) systems, and directly applies the characteristic that changes in the output power of distributed PV systems can alter the voltage at the beginning of the line to address the three-phase voltage imbalance of the line. At the same time, it fully utilizes the reactive power regulation capabilities of various adjustable resources (SVG, capacitor banks) within the distribution area, and considers the order and capacity of each device's regulation when coordinating control with distributed PV systems. Under the premise of ensuring the safe, economical, and effective operation of the distribution area, it adjusts the power values ​​of each device, thus efficiently addressing the three-phase imbalance problem caused by distributed PV systems integrated into the power distribution system. Attached Figure Description

[0045] Figure 1 This is a three-phase line topology network diagram of a 380V transformer substation in an embodiment of the present invention;

[0046] Figure 2 This is a flowchart of a three-phase imbalance management method for distributed photovoltaic and adjustable resources in a transformer substation proposed in this invention;

[0047] Figure 3 This is a schematic diagram of the equivalent calculation model of the distribution line and transformer used in the example of this invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0049] like Figure 1 The 380V three-phase line topology network shown has a starting node 10 connected to one side of transformer 20, and the other side of transformer 20 connected to the common coupling point on the line via fuse 30. n sets of distributed photovoltaic devices are connected to phase A of the line, as shown in Figure 1, 2, ..., n. The connection of the distributed photovoltaic devices changes the load symmetry in the line, causing a three-phase voltage imbalance at the common coupling point.

[0050] This invention proposes a method for managing the three-phase imbalance of distributed photovoltaic power and adjustable resources in transformer substations, such as... Figure 2 As shown, it includes:

[0051] Step 1: Establish equivalent models of lines, transformers, and reactive power regulation equipment within the distribution area; based on these models, obtain the distribution area's operational data.

[0052] Figure 1 The distribution network shown has symmetrical three-phase line parameters but asymmetrical loads. The line voltage of the distribution area is 380V, and the power lines between nodes are overhead lines or cable lines with a length not exceeding 1000m. The influence of ground admittance in the lines can be ignored, so the equivalent model of the lines chooses to ignore the ground admittance of the π-type circuit. The transformers in the distribution area are three-phase double-winding transformers, and the equivalent model of the transformers adopts the Γ-type circuit model of the distribution transformer to reduce the number of nodes in the power flow calculation. Figure 3 This is a schematic diagram of the equivalent line model and the equivalent transformer model used in the examples of this invention.

[0053] The equivalent model of the line includes resistance R and reactance X, and the line impedance satisfies Z = R + jX; the equivalent model of the transformer includes resistance R. T and reactance X T Conductivity G T and susceptance B T The impedance satisfies Z T =R T +jX T Admittance satisfies Y T =G T -jB T .

[0054] The operating data of the transformer area includes, but is not limited to: active power, reactive power, voltage, and other data of users or equipment.

[0055] Step 2: Calculate the three-phase imbalance based on the transformer area operation data; use the three-phase imbalance to determine the reactive power output of the reactive power regulation equipment and the reactive power output of the distributed photovoltaic equipment.

[0056] The connection of distributed photovoltaic (PV) equipment alters the load symmetry in the power line. Changes in its active and reactive power output change the power distribution along the line, altering the voltage drop between the PV grid connection point and the beginning of the phase, thus changing the voltage at the beginning of that phase. This causes a three-phase voltage imbalance at the point of common coupling (PCC). In other words, changes in the output power of distributed PV can change the voltage at the beginning of the line. Therefore, not only can reactive power regulation equipment change the three-phase voltage imbalance at the beginning of the line, but distributed PV equipment can also simultaneously change the three-phase voltage imbalance at the beginning of the line, thereby achieving the management of three-phase imbalance in the distribution network area. Therefore, as... Figure 1 As shown, phase A is also equipped with a Static Var Generator (SVG) and a capacitor bank C. The reactive power regulation equipment (SVG and capacitor bank) is installed at the beginning of the line connected to the distributed photovoltaic equipment as a supplement to the output of the distributed photovoltaic equipment.

[0057] Step 2 includes:

[0058] Step 2.1, when addressing three-phase imbalance by adjusting the reactive power output of the reactive power regulation equipment and distributed photovoltaic equipment within the transformer substation, the adjustment of reactive power output needs to be based on the substation operating data. The three-phase imbalance is calculated using the substation operating data, satisfying the following relationship:

[0059]

[0060] In the formula,

[0061] △ε U2 This refers to the three-phase voltage imbalance.

[0062] U1 and U2 represent the root mean square values ​​of the positive and negative sequence components of the three-phase voltage, respectively.

[0063] Step 2.2: Based on the three-phase unbalance, using the rated voltage of each phase and the impedance based on the transformer equivalent model, the reactive power output of the capacitor bank is obtained, satisfying the following relationship:

[0064]

[0065] In the formula, △Q C For the reactive power output of the capacitor bank, x T The impedance ΔQ represents the equivalent model of the transformer. C U represents the capacitance of the capacitor bank. i (i = A, B, C) represents the rated voltage of each phase.

[0066] Step 2.3: Based on the three-phase imbalance, using the rated voltage of each phase and the resistance and reactance based on the equivalent line model, the reactive power output of the distributed photovoltaic equipment is obtained, satisfying the following relationship:

[0067]

[0068] In the formula, R and X are the resistance and reactance of the equivalent model of the line between the three-phase line common coupling point and the photovoltaic grid connection point, respectively; ΔQ is the reactive power change value of the photovoltaic inverter output.

[0069] By utilizing the three-phase voltage imbalance, reactive power output can be allocated on demand between reactive power regulation equipment and distributed photovoltaic (PV) equipment. Considering that distributed PV itself has reactive power regulation capabilities, the characteristic that changes in the output power of distributed PV can alter the voltage at the beginning of the line can be directly applied to address the three-phase voltage imbalance of the line.

[0070] Step 3: Extract the maximum and minimum values ​​of active power output of distributed photovoltaic equipment and the maximum and minimum values ​​of user load from the historical longitudinal data of the transformer area; determine the upper limit of three-phase imbalance based on the minimum value of distributed photovoltaic equipment output and the maximum value of user load.

[0071] Historical longitudinal data includes distributed photovoltaic (PV) equipment output data and user load data from July and August of the past three years. Through data filtering and comparison, the maximum and minimum output values ​​of distributed PV equipment, as well as the maximum and minimum user load values, are extracted from the historical longitudinal data.

[0072] When the distributed photovoltaic equipment in the distribution network stops outputting power, reaching its minimum output, and the user load reaches its maximum, the three-phase imbalance in the distribution area will reach its maximum value, i.e., the upper limit of the three-phase imbalance.

[0073] Step 4: First, determine the reactive power output of the first group of distributed photovoltaic (PV) devices based on the upper limit of the three-phase imbalance. Calculate the current three-phase imbalance based on the reactive power output of the first group of PV devices. Determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulating equipment in the transformer area and the reactive power output of the first group of PV devices. If the corrected current three-phase imbalance is greater than the limit, repeat the above steps to determine the reactive power output of the second group of PV devices and the reactive power regulating equipment, until the three-phase imbalance is less than or equal to the limit.

[0074] The limit value is set at no more than 2%.

[0075] In step 4, since the single-phase voltage at the beginning of the line increases when the distributed photovoltaic equipment reaches its maximum output and the user load reaches its minimum, the reactive power output of the distributed photovoltaic equipment is adjusted first to timely and accurately address the three-phase voltage imbalance at the beginning of the line.

[0076] When coordinating and controlling the adjustable reactive power resources within the distribution area, the three-phase imbalance is corrected by calling upon the reactive power output of distributed photovoltaic equipment. Furthermore, when allocating the reactive power output of reactive power regulation equipment, the number of distributed photovoltaic equipment and the order of their outputs need to be comprehensively considered.

[0077] Specifically, the current three-phase imbalance is first corrected by adjusting the reactive power output of the distributed photovoltaic (PV) devices, for example, by adjusting the devices connected to phase A first. Based on the relationship between the three-phase imbalance and the change in distributed PV output according to the present invention, the target reactive power value that needs to be adjusted to correct the current imbalance is calculated. Taking an example transformer area as an example, the adjustment sequence is as follows: First, adjust the reactive power output of the first group of distributed PV devices on phase A. The current three-phase imbalance is calculated based on the reactive power output of the first group of distributed PV devices. The reactive power output of the reactive power adjustment device is determined based on the current three-phase imbalance. The current three-phase imbalance is corrected based on the sum of the reactive power output of the reactive power adjustment device and the first group of distributed PV devices in the transformer area. It is then determined whether the corrected current three-phase imbalance meets the limit requirements. If it does, the adjustment of reactive power resources ends. If it does not meet the limit requirements, i.e., the treatment effect is not achieved, then the adjustment of the second group of distributed PV devices on phase A is prioritized, and so on until the nth group of distributed PV devices on phase A is adjusted.

[0078] Furthermore, since both increases and decreases in line load can lead to three-phase voltage imbalance, the relationship between the three-phase imbalance and the reactive power output of distributed photovoltaic (PV) equipment proposed in this invention can generally yield two reactive power values. Therefore, if the goal is to reduce the voltage at the point of common coupling (PCC), the reactive power output of the distributed PV equipment should actually be negative, i.e., it absorbs reactive power; if the goal is to increase the PCC, the reactive power output of the distributed PV equipment should actually be positive, i.e., it generates reactive power.

[0079] Reactive power regulation equipment includes SVG (Static Var Generator) and capacitor banks. The reactive power output of the reactive power regulation equipment, determined based on the current three-phase imbalance, includes the reactive power output of the capacitor banks and the reactive power output of the SVG. When distributed photovoltaic (PV) equipment has not yet reached its maximum resource capacity (i.e., there are still distributed PV devices on phase A with unregulated reactive power output), the reactive power output of the SVG is not required; instead, the reactive power output of the capacitor banks is used in conjunction with the reactive power output of the distributed PV devices. However, once the reactive power output of all n distributed PV devices is utilized, the reactive power output gap or margin within the distribution area is met by the reactive power output of the SVG.

[0080] Furthermore, based on the line data recorded by the fusion terminal, the SVG continuously adjusts the reactive power output to achieve the effect of controlling three-phase imbalance.

[0081] This invention fully leverages the reactive power adjustment capabilities of various adjustable reactive resources (SVG, capacitor banks) within the distribution area. When coordinating control with distributed photovoltaic equipment, it considers the order and capacity of adjustment of each reactive power device. Under the premise of ensuring the safe, economical, and effective operation of the distribution area, it adjusts the power value of each reactive power device, effectively addressing the three-phase imbalance problem when distributed photovoltaic equipment is integrated into the power distribution system.

[0082] In another aspect, the present invention proposes a three-phase imbalance management system for distributed photovoltaic and adjustable resources in the transformer area, comprising: a data acquisition module, a reactive power output calculation module for distributed photovoltaic equipment, a reactive power output calculation module for reactive power regulation equipment, a three-phase imbalance calculation module, and a reactive power output allocation module.

[0083] The data acquisition module is used to acquire the operating data of the distribution area based on the equivalent models of the lines, transformers, and reactive power regulation equipment within the distribution area; and to extract the maximum and minimum output values ​​of distributed photovoltaic equipment and the maximum and minimum user load values ​​from the historical longitudinal data of the distribution area.

[0084] The three-phase imbalance calculation module is used to calculate the three-phase imbalance based on the operating data of the distribution area, and to determine the upper limit of the three-phase imbalance based on the minimum output of the distributed photovoltaic equipment and the maximum user load.

[0085] The reactive power output calculation module for distributed photovoltaic equipment is used to determine the reactive power output of distributed photovoltaic equipment based on the three-phase imbalance.

[0086] The reactive power output calculation module for reactive power regulation equipment is used to determine the reactive power output of reactive power regulation equipment using three-phase imbalance.

[0087] The reactive power output allocation module is used to call the reactive power output calculation module of the distributed photovoltaic equipment to determine the reactive power output of the first group of distributed photovoltaic equipment based on the upper limit of the three-phase imbalance. Based on the reactive power output of the first group of distributed photovoltaic equipment, it calls the three-phase imbalance calculation module to calculate the current three-phase imbalance. It then calls the reactive power output calculation module of the reactive power regulating equipment to determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Next, it calls the three-phase imbalance calculation module to correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulating equipment and the first group of distributed photovoltaic equipment in the distribution area. If the corrected current three-phase imbalance is greater than the limit, it adjusts the reactive power output of the second group of distributed photovoltaic equipment and the reactive power regulating equipment until the three-phase imbalance is less than or equal to the limit. After the reactive power output of all n groups of distributed photovoltaic equipment has been called, it adjusts the reactive power output of the SVG to meet the reactive power output gap or margin in the distribution area.

[0088] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0089] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0090] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0091] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for managing three-phase imbalance in distributed photovoltaic and adjustable resources in a transformer substation, characterized in that, The method includes: Step 1: Establish equivalent models of lines, transformers, and reactive power regulation equipment within the distribution area; based on these models, obtain the distribution area's operational data. Step 2: Calculate the three-phase imbalance based on the transformer area operation data; use the three-phase imbalance to determine the reactive power output of the reactive power regulation equipment and the reactive power output of the distributed photovoltaic equipment respectively; Step 2 includes: Based on the three-phase imbalance, using the rated voltage of each phase and the impedance based on the transformer equivalent model, the reactive power output of the capacitor bank is obtained, satisfying the following relationship: wherein is the reactive power output of the capacitor bank, is the impedance of the transformer equivalent model, is the capacitance of the capacitor bank, is the rated voltage of each phase, is the three-phase voltage unbalance degree; Based on the three-phase unbalance, and using the rated voltage of each phase and the resistance and reactance based on the equivalent line model, the reactive power output of the distributed photovoltaic system is obtained, satisfying the following relationship: In the formula, , These represent the resistance and reactance of the equivalent model of the line between the three-phase line common coupling point and the photovoltaic grid connection point; This represents the change in reactive power output from the photovoltaic inverter. Step 3: Extract the maximum and minimum values ​​of active power output of distributed photovoltaic equipment and the maximum and minimum values ​​of user load from the historical longitudinal data of the transformer area; determine the upper limit of three-phase imbalance based on the minimum value of distributed photovoltaic equipment output and the maximum value of user load. Step 4: First, determine the reactive power output of the first group of distributed photovoltaic (PV) devices based on the upper limit of the three-phase imbalance. Calculate the current three-phase imbalance based on the reactive power output of the first group of PV devices. Determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulating equipment in the transformer area and the reactive power output of the first group of PV devices. If the corrected current three-phase imbalance is greater than the limit, repeat the above steps to determine the reactive power output of the second group of PV devices and the reactive power regulating equipment, until the three-phase imbalance is less than or equal to the limit. The reactive power regulation equipment includes SVG and capacitor banks; the reactive power output of the reactive power regulation equipment is determined based on the current three-phase imbalance, including the reactive power output of the capacitor banks and the reactive power output of the SVG; when the distributed photovoltaic equipment has not yet reached its maximum resource, that is, when there are still distributed photovoltaic equipment with unregulated reactive power output, the reactive power output of the SVG is not required, and the reactive power output of the capacitor banks is used in conjunction with the reactive power output of the distributed photovoltaic equipment; When all the reactive power output of n sets of distributed photovoltaic equipment is utilized, the reactive power output gap or margin in the distribution area is met by the reactive power output of the SVG.

2. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 1, characterized in that, In step 1, the equivalent model of the line will be selected. The ground admittance of the circuit is negligible, and the equivalent model of the transformer adopts the distribution transformer. Type circuit model.

3. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 2, characterized in that, The operating data of the transformer area includes, but is not limited to: active power, reactive power, voltage, and other data of users or equipment.

4. The three-phase imbalance mitigation method for distributed photovoltaic and adjustable resources in transformer substations according to claim 3, characterized in that, Step 2 also includes: Step 2.1, when addressing three-phase imbalance by adjusting the reactive power output of the reactive power regulation equipment and distributed photovoltaic equipment within the transformer substation, the adjustment of reactive power output needs to be based on the substation operating data. The three-phase imbalance is calculated using the substation operating data, satisfying the following relationship: In the formula, This refers to the three-phase voltage imbalance. , These represent the root mean square values ​​of the positive and negative sequence components of the three-phase voltage, respectively.

5. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 1, characterized in that, In step 3, the historical longitudinal data includes: the output data of distributed photovoltaic equipment and the user load data of July and August within the past three years; through data filtering and comparison, the maximum value of distributed photovoltaic equipment output, the minimum value of distributed photovoltaic equipment output, the maximum value of user load and the minimum value of user load are extracted from the historical longitudinal data.

6. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 5, characterized in that, When the distributed photovoltaic equipment in the distribution network stops outputting power, reaching its minimum output, and the user load reaches its maximum, the three-phase imbalance in the distribution area will reach its maximum value, i.e., the upper limit of the three-phase imbalance.

7. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 1, characterized in that, Step 4 includes: Step 4.1: Determine the reactive power output of the first group of distributed photovoltaic devices based on the upper limit of the three-phase imbalance. Step 4.2: Calculate the current three-phase imbalance based on the reactive power output of the first group of distributed photovoltaic devices; Step 4.3: Determine the reactive power output of the reactive power regulating equipment based on the current three-phase imbalance. Step 4.4: Correct the current three-phase imbalance based on the sum of the reactive power output of the reactive power regulation equipment and the first group of distributed photovoltaic equipment in the transformer area; Step 4.5: If the corrected current three-phase imbalance is greater than the limit, then use the corrected current three-phase imbalance to determine the reactive power output of the second group of distributed photovoltaic equipment and repeat steps 4.2 to 4.4 until the three-phase imbalance is less than or equal to the limit.

8. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 7, characterized in that, The limit value is no greater than 2%.

9. The method for managing three-phase imbalance of distributed photovoltaic and adjustable resources in transformer substations according to claim 1, characterized in that, In step 4, if the goal of the governance is to reduce the voltage at the point of common coupling, the reactive power output of the distributed photovoltaic equipment will be negative, i.e., it will absorb reactive power; if the goal of the governance is to increase the voltage at the point of common coupling, the reactive power output of the distributed photovoltaic equipment will be positive, i.e., it will generate reactive power.

10. A three-phase imbalance control system for distributed photovoltaic and adjustable transformer resources utilizing the method described in any one of claims 1-9, characterized in that, The system includes: a data acquisition module, a distributed photovoltaic equipment reactive power output calculation module, a reactive power regulation equipment reactive power output calculation module, a three-phase imbalance calculation module, and a reactive power output distribution module. The data acquisition module is used to acquire the operating data of the distribution area based on the equivalent models of the lines, transformers, and reactive power regulation equipment within the distribution area; and to extract the maximum and minimum output values ​​of distributed photovoltaic equipment and the maximum and minimum user load values ​​from the historical longitudinal data of the distribution area. The three-phase imbalance calculation module is used to calculate the three-phase imbalance based on the operating data of the distribution area, and to determine the upper limit of the three-phase imbalance based on the minimum output of the distributed photovoltaic equipment and the maximum user load. The reactive power output calculation module for distributed photovoltaic (PV) equipment is used to determine the reactive power output of distributed PV equipment based on three-phase imbalance. This includes: based on the three-phase imbalance, using the rated voltage of each phase and the impedance based on the transformer equivalent model, obtaining the reactive power output of the capacitor bank, satisfying the following relationship: In the formula, To provide reactive power output for the capacitor bank This represents the impedance of the transformer equivalent model. Indicates the capacitance of the capacitor bank. The rated voltage of each phase, This refers to the three-phase voltage imbalance. Based on the three-phase unbalance, and using the rated voltage of each phase and the resistance and reactance based on the equivalent line model, the reactive power output of the distributed photovoltaic system is obtained, satisfying the following relationship: In the formula, , These represent the resistance and reactance of the equivalent model of the line between the three-phase line common coupling point and the photovoltaic grid connection point; This represents the change in reactive power output from the photovoltaic inverter. The reactive power output calculation module for reactive power regulation equipment is used to determine the reactive power output of reactive power regulation equipment using three-phase imbalance. The reactive power output allocation module calls the distributed photovoltaic (PV) equipment reactive power output calculation module to first determine the reactive power output of the first group of distributed PV equipment based on the upper limit of the three-phase imbalance. Based on the reactive power output of the first group of distributed PV equipment, it calls the three-phase imbalance calculation module to calculate the current three-phase imbalance. It then calls the reactive power regulation equipment reactive power output calculation module to determine the reactive power output of the reactive power regulation equipment based on the current three-phase imbalance. Finally, it calls the three-phase imbalance calculation module to correct the current three-phase imbalance based on the sum of the reactive power outputs of the reactive power regulation equipment and the first group of distributed PV equipment within the transformer area. If the corrected current three-phase imbalance is greater than the limit, it adjusts the reactive power output of the second group of distributed PV equipment. Reactive power output and reactive power regulation equipment are used until the three-phase imbalance is less than or equal to the limit. Reactive power regulation equipment includes SVG and capacitor banks. The reactive power output of the reactive power regulation equipment is determined based on the current three-phase imbalance, including the reactive power output of the capacitor banks and the reactive power output of the SVG. When the distributed photovoltaic equipment has not reached its maximum resource, i.e., when there are still distributed photovoltaic equipment with unregulated reactive power output, the reactive power output of the SVG is not required, and the reactive power output of the capacitor banks is used in conjunction with the reactive power output of the distributed photovoltaic equipment. When the reactive power output of all n groups of distributed photovoltaic equipment is utilized, the reactive power output of the SVG is adjusted to meet the reactive power output gap or margin in the distribution area.

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