Method for coordinating UPQC with photovoltaic inverter to govern over-limit of substation voltage

Abstract

The application discloses a method for coordinating UPQC and photovoltaic inverters to govern the over-limit of substation voltage, which comprises the following steps: obtaining substation electrical parameters, and calculating the real-time voltage deviation of the substation based on the substation electrical parameters; setting different working condition thresholds of the real-time voltage deviation of the substation in advance, determining the current working condition of the substation based on the relationship between the real-time voltage deviation of the substation and the working condition thresholds; determining the photovoltaic compensation weight of the photovoltaic inverter according to the current working condition of the substation; adjusting the reactive power output of the photovoltaic inverter according to the photovoltaic compensation weight, and adjusting the active power output based on the real-time voltage deviation of the substation; and driving the UPQC device to reduce or increase the voltage at the load end based on the current measured voltage deviation of the substation, so as to eliminate the over-limit of the substation voltage.

Description

Technical Field

[0001] This invention relates to the field of transformer area voltage over-limit control technology, and in particular to a method for coordinating UPQC and photovoltaic inverters to manage transformer area voltage over-limit. Background Technology

[0002] High-penetration distribution areas refer to low-voltage distribution areas where the total installed capacity of distributed photovoltaic (PV) exceeds 50% of the total distribution transformer capacity. Long-distance distribution areas mainly refer to areas with an operating range of 1 kilometer or more. These types of distribution areas are numerous and objectively exist in urban-rural fringe areas or relatively remote areas. With the large-scale popularization of household PV, these areas exhibit multiple power quality problems, such as high PV power generation and backfeeding during the day, voltage exceeding the upper limit; low voltage or even below the lower limit during peak nighttime loads; severe three-phase imbalance; and large reactive power fluctuations. Moreover, due to the long distances involved, these distribution areas are complex to manage, and the effects are often not very obvious.

[0003] Currently, there are four main types of solutions for mitigating voltage exceedances in photovoltaic (PV) distribution areas. The first type is the series-based solution, represented by on-load tap changers (OTCs). This solution directly adjusts the load voltage amplitude to achieve voltage regulation, but its response time is on the order of seconds, lagging behind the rate of PV power fluctuations. Furthermore, its windings generate additional reactive power voltage drops, resulting in significant operating losses and making it unsuitable for the rapid voltage fluctuations in long-distance, high-permeability PV distribution areas. The second type is the parallel compensation solution, represented by parallel capacitors and static var generators (SVAs). This solution can offset some of the reactive power voltage drop by adjusting reactive power. However, to balance the active power voltage drop, a reverse reactive component needs to be injected, which increases the reactive current and line losses, failing to fundamentally solve the voltage exceedance problem caused by active power flow. The third type is the UPQC (Power Response Quality Control) scheme combining series and parallel connections. Parallel modules address reactive power, harmonics, and three-phase imbalance, while series modules compensate for voltage deviations. Compared to single series or parallel schemes, this approach offers more comprehensive coverage and lower operating losses. However, in long-distance, high-penetration photovoltaic (PV) areas, its voltage regulation coverage is limited by the device's capacity and installation location, resulting in insufficient effectiveness in addressing voltage exceedances at remote PV grid connection points. It typically only resolves about 70% of voltage exceedance issues in these areas. The fourth type directly restricts PV output. When series and parallel devices cannot meet voltage regulation requirements, the active power output of the PV system is forcibly reduced to alleviate voltage exceedances. This method results in significant losses of PV power generation, substantially reducing PV operating revenue, which contradicts the development goal of maximizing the absorption of distributed PV power.

[0004] Current methods for managing voltage exceedances in transformer substations have significant technical shortcomings: relying solely on photovoltaic inverters for voltage regulation has limited reactive power regulation capacity, making it unable to completely correct severe voltage exceedances, and excessive active power curtailment leads to substantial curtailment and reduced power generation revenue; using UPQC (Upgraded Voltage Control Center) for independent management results in issues such as voltage regulation lag, low management accuracy, and poor adaptability to various operating conditions, failing to achieve precise management of voltage exceedances across all operating conditions. There is an urgent need for a voltage exceedance management solution with a quantitative control model and hierarchical coordination to accurately address both overvoltage and undervoltage issues in transformer substations. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a method for UPQC and photovoltaic inverter to jointly manage the voltage exceeding the limit in the transformer area, which mainly solves the technical problems existing in the background art.

[0006] To achieve the above objectives, the technical solution of this invention is implemented as follows: This invention discloses a method for coordinating UPQC and photovoltaic inverters to manage voltage exceedance in transformer substations, the method comprising the following steps: Obtain the electrical parameters of the transformer substation and calculate the real-time voltage deviation of the substation based on the electrical parameters; Different operating condition thresholds for the real-time voltage deviation of the transformer area are preset, and the current operating condition of the transformer area is determined based on the different relationships between the real-time voltage deviation of the transformer area and the operating condition thresholds. The photovoltaic compensation weight of the photovoltaic inverter is determined based on the current operating conditions of the transformer substation. The photovoltaic inverter adjusts the reactive power output according to the photovoltaic compensation weight and adjusts the active power output based on the real-time voltage deviation of the distribution area. Based on the current measured voltage deviation in the transformer area, the UPQC device is driven to reduce or increase the load-side voltage to eliminate voltage exceeding the limit in the transformer area.

[0007] Optionally, the real-time value of the load voltage of the transformer area is obtained, and the real-time voltage deviation of the transformer area is calculated based on the difference between the real-time value of the load voltage of the transformer area and the rated voltage of the transformer area.

[0008] Optionally, a first threshold and a second threshold are set. When the absolute value of the real-time voltage deviation of the transformer area is less than or equal to the first threshold, it is determined to be a normal operating condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the first threshold and less than or equal to the second threshold, it is determined to be a slight over-limit condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the second threshold, it is determined to be a serious over-limit condition.

[0009] Optionally, when the transformer area is in a slightly over-limit operating condition, the photovoltaic compensation weight is zero, the photovoltaic inverter does not participate in voltage regulation and does not limit active power output, and the load voltage is adjusted by the UPQC device. Specifically, the compensation voltage is calculated, and if the compensation voltage is positive, the UPQC device increases the load terminal voltage; if the compensation voltage is negative, the UPQC device decreases the load terminal voltage.

[0010] Optionally, when the transformer area is in a severe over-limit operating condition, the UPQC compensation weight is determined based on the real-time voltage deviation of the transformer area, and the photovoltaic compensation weight is determined based on the UPQC compensation weight. The reactive power regulation of the photovoltaic inverter is calculated based on the photovoltaic compensation weight, and the active power output of the photovoltaic inverter is calculated based on the real-time voltage deviation of the transformer area.

[0011] Optionally, the photovoltaic compensation weight is calculated based on the UPQC compensation weight, and the calculation formula is as follows:

[0012] in, For photovoltaic compensation weight, UPQC compensation weights; The UPQC compensation weight is calculated using the following formula:

[0013] in, This represents the real-time voltage deviation of the transformer substation.

[0014] Optionally, the reactive power regulation of the photovoltaic inverter can be calculated using the following formula:

[0015] in, This refers to the reactive power regulation of the photovoltaic inverter. This is the reactive power voltage regulation proportional coefficient. The rated apparent power of the photovoltaic inverter.

[0016] Optionally, the active power reduction of the photovoltaic inverter is calculated based on the real-time voltage deviation of the distribution area, and the calculation formula is as follows:

[0017] In the formula, The active power regulation coefficient, The amount was reduced to reflect the positive results. The rated active power of the photovoltaic inverter; The target active power output is obtained by subtracting the active power reduction from the current active power output of the photovoltaic inverter. The calculation formula is as follows:

[0018] in, Contribute to photovoltaic inverters Provides real-time active power output for photovoltaic inverters.

[0019] Optionally, after the photovoltaic inverter completes reactive power regulation and active power regulation, it re-acquires the true value of the transformer area voltage and, based on the current measured voltage deviation of the transformer area, drives the UPQC device to reduce or increase the load-side voltage to eliminate the transformer area voltage exceeding the limit.

[0020] The beneficial effects of this invention are as follows: Through the control logic of operating condition classification and dynamic weight matching, the governance strategy can be adaptively adjusted according to the actual severity of voltage exceedance in the distribution area. Under minor exceedance conditions, UPQC independent voltage regulation is prioritized without restricting photovoltaic active power output. Under severe exceedance conditions, multiple devices are activated to collaboratively share the voltage regulation task, resulting in stronger adaptability across all operating conditions and effectively reducing photovoltaic curtailment rate. The step-by-step governance logic of coarse photovoltaic regulation followed by fine UPQC regulation leverages the distributed layout characteristics of photovoltaic inverters to cover voltage deviations at the far end of the distribution area, compensating for the voltage regulation coverage shortcomings of centralized UPQC devices. UPQC then performs precise correction of residual voltage deviations, simultaneously achieving harmonic suppression, three-phase imbalance governance, and reactive power compensation, comprehensively improving the power quality of the distribution area. The overall solution significantly reduces the configuration capacity of UPQC devices, reduces hardware investment costs for distribution area voltage governance, and has a fast control response speed, adapting to dynamic fluctuations in photovoltaic output and load, avoiding secondary voltage fluctuations during voltage regulation, and effectively improving the voltage qualification rate and operational stability of the distribution area. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the component architecture of a long-distance, high-penetration photovoltaic power station in an embodiment of this application; Figure 2 This is a flowchart illustrating a method for collaboratively managing voltage exceedance in a distribution area using UPQC and a photovoltaic inverter, as described in this application. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. In the following description, the expression "some embodiments" refers to a subset of all possible embodiments; however, it should be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0024] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0025] It should be understood that the present invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Furthermore, the terminology used herein is intended only to describe particular embodiments and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “compose” and / or “comprising,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0026] It should also be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "inner," "outer," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0027] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Optional embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0028] Please refer to the attached document. Figure 1 This application provides a method for coordinating UPQC and photovoltaic inverters to manage voltage overruns in a distribution area. It is applied to a 400V long-distance, high-penetration photovoltaic distribution area, which typically contains a distribution transformer, multiple distributed photovoltaic inverters, and a UPQC device. The coordinating controller undertakes data acquisition and coordinating control functions and establishes data transmission links with each photovoltaic inverter and UPQC device.

[0029] The UPQC device has a capacity of 30kVA and adopts a back-to-back topology. Its components include a series-side converter, a parallel-side converter, a series injection transformer, a coupling transformer, and a DC bus capacitor. The series-side converter is connected in series with the low-voltage bus between the distribution transformer's low-voltage outlet and the load via the series injection transformer. The parallel-side converter is connected in parallel with the low-voltage bus via the coupling transformer. The series-side converter and the parallel-side converter are connected via the DC bus capacitor.

[0030] See Figure 2 The method includes the following steps: S1. Obtain the electrical parameters of the transformer area and calculate the real-time voltage deviation of the transformer area based on the electrical parameters of the transformer area; S2. Pre-set different operating condition thresholds for the real-time voltage deviation of the transformer area, and determine the current operating condition of the transformer area based on the different relationships between the real-time voltage deviation of the transformer area and the operating condition thresholds. S3. Determine the photovoltaic compensation weight of the photovoltaic inverter based on the current operating conditions of the transformer area; S4. The photovoltaic inverter adjusts the reactive power output according to the photovoltaic compensation weight and adjusts the active power output based on the real-time voltage deviation of the transformer area. S5. Based on the current measured voltage deviation in the transformer area, drive the UPQC device to reduce or increase the load terminal voltage to eliminate the transformer area voltage exceeding the limit.

[0031] The implementation of each step described above is explained in detail below with reference to specific embodiments. The collaborative controller acquires the electrical parameters of each key node in the distribution area, selects the node with the most representative voltage deviation as the voltage regulation reference node, and calculates the real-time voltage deviation of the distribution area based on the real-time voltage of the reference node and the rated voltage of the distribution area. The collaborative controller has pre-set operating condition thresholds corresponding to different voltage states in the distribution area. The calculated real-time voltage deviation of the distribution area is compared with the preset operating condition thresholds, and the current operating condition of the distribution area is determined based on the comparison results. Based on the determined current operating condition of the distribution area, the collaborative controller determines the photovoltaic compensation weight corresponding to the photovoltaic inverter, so that the proportion of voltage regulation tasks undertaken by the photovoltaic inverter dynamically adapts to the severity of the operating condition. After receiving the control command, each photovoltaic inverter in the distribution area adjusts its reactive power output according to the determined photovoltaic compensation weight, and simultaneously adjusts its active power output according to the magnitude of the real-time voltage deviation of the distribution area. Through the coordinated adjustment of reactive power output and active power output, the voltage deviation of the distribution area is initially offset. After the photovoltaic inverter completes the output regulation, the co-controller collects the current measured voltage deviation at the load end of the distribution area, outputs the corresponding control command to the UPQC device, drives the UPQC device to reduce or increase the voltage amplitude at the load end accordingly, compensates for the remaining voltage deviation, and finally eliminates the problem of voltage exceeding the limit in the distribution area.

[0032] As one implementation method, the real-time value of the load voltage of the transformer substation is obtained, and the real-time voltage deviation of the transformer substation is calculated based on the difference between the real-time value of the load voltage of the transformer substation and the rated voltage of the transformer substation.

[0033] Specifically, the collaborative controller directly acquires the real-time load voltage value at the load end by connecting to the voltage sampling circuit on the load bus side of the distribution area. Using the actual operating voltage at the load end as the reference parameter for voltage regulation calculation, it directly reflects the true voltage level borne by the load without needing to convert the line voltage drop. Furthermore, the acquired real-time load voltage value is compared with the rated phase voltage of the distribution area, and then the difference is compared with the rated voltage of the distribution area and converted into a percentage to obtain the real-time voltage deviation of the distribution area. This fully reflects the degree of deviation of the load-end voltage relative to the rated voltage. The calculation formula is as follows:

[0034] In the formula, This is the reference value for the transformer substation voltage. This is the real-time value of the load voltage.

[0035] As one implementation method, a first threshold and a second threshold are set. When the absolute value of the real-time voltage deviation of the transformer area is less than or equal to the first threshold, it is determined to be a normal operating condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the first threshold and less than or equal to the second threshold, it is determined to be a slight over-limit condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the second threshold, it is determined to be a serious over-limit condition.

[0036] Specifically, in some embodiments, the first threshold is set to 7%, and the second threshold is set to 10%. Under normal operating conditions, the voltage in the transformer substation is within the acceptable operating range, and there is no need to initiate voltage regulation. In cases of minor over-limit operation, voltage adjustment correction can be completed using a single device. or This is a severe over-limit operating condition. At this time, the voltage deviation is large, and it is necessary to activate the multi-device coordinated voltage regulation mode to ensure that the voltage quickly returns to the qualified range.

[0037] As a preferred approach, the operating condition determination adopts a multi-cycle continuous confirmation mechanism. Only when the voltage deviation calculation results of three consecutive sampling cycles all fall within the same operating condition range will the current operating condition be finally locked and the corresponding voltage regulation strategy be executed. This avoids incorrect switching of operating conditions caused by instantaneous voltage fluctuations and transient disturbances in the power grid, and improves the anti-interference capability and operational stability of the control logic.

[0038] In certain application scenarios of this application, the specific values ​​of the first threshold and the second threshold can be adaptively adjusted according to the actual power supply radius, photovoltaic penetration rate, and line impedance parameters of the distribution area. For long-distance, high-penetration, heavily loaded distribution areas, the threshold values ​​can be appropriately lowered to trigger the coordinated voltage regulation mechanism in advance, prevent the risk of voltage exceeding the limit from further expanding, and adapt to the differentiated governance needs of different distribution areas.

[0039] As one implementation method, when the transformer area is in a slightly over-limit operating condition, the photovoltaic compensation weight is zero, the photovoltaic inverter does not participate in voltage regulation and does not limit active power output, and the load voltage is regulated by the UPQC device.

[0040] Specifically, the target compensation voltage of the UPQC device is calculated based on the voltage reference value of the distribution area and the real-time voltage value on the load side. The calculation formula is as follows:

[0041] In the formula, The target compensation voltage for the UPQC series unit. This is the reference value for the transformer substation voltage. The calculated compensation voltage is the real-time voltage value on the load side. If the calculated compensation voltage is positive, the UPQC device injects a positive compensation voltage into the line through a series injection unit to increase the load-side voltage. If the calculated compensation voltage is negative, the UPQC device injects a negative compensation voltage into the line to decrease the load-side voltage, thereby correcting the load-side voltage to the acceptable operating range.

[0042] Furthermore, when a transformer substation is in a severe over-limit condition, the UPQC compensation weight is first determined based on the real-time voltage deviation of the substation, and the corresponding photovoltaic compensation weight is determined based on the UPQC compensation weight. Then, the reactive power regulation of the photovoltaic inverter is calculated based on the photovoltaic compensation weight, and the target active power output of the photovoltaic inverter is calculated based on the real-time voltage deviation of the substation. Through the hierarchical collaboration between the photovoltaic inverter and the UPQC device, the precise management of voltage over-limit is achieved.

[0043] Specifically, the UPQC compensation weight is calculated using the following formula:

[0044] The photovoltaic compensation weight satisfies the following formula:

[0045] In the above formula, As compensation weight for UPQC, As the photovoltaic compensation weight increases, the greater the voltage exceeds the limit and the higher the absolute value of the real-time voltage deviation, the greater the corresponding photovoltaic compensation weight. This allows the photovoltaic inverter to assume more voltage regulation responsibility, alleviating the capacity pressure on the UPQC device.

[0046] When calculating the reactive power regulation of a photovoltaic inverter, the reactive power voltage regulation quantification formula is used:

[0047] During the listing process, This is the reactive power voltage regulation proportional coefficient, and its value can be selected from 0.8 to 1.2. The total installed capacity of photovoltaic power in the area is set at the rated power. The total reactive power regulation of the photovoltaic system in the distribution area is calculated. After the total reactive power regulation is obtained, it can be allocated to each photovoltaic inverter according to the rated capacity ratio of each photovoltaic inverter. Under overvoltage conditions, the photovoltaic inverter is controlled to output inductive reactive power, and under undervoltage conditions, the photovoltaic inverter is controlled to output capacitive reactive power. The voltage drop of the line is initially offset by the regulation of reactive power output, and the coarse voltage regulation is completed.

[0048] Meanwhile, based on the real-time voltage deviation of the distribution area, the target active power output of the photovoltaic inverter is calculated, and a gradual active power limiting strategy is adopted. The formula for calculating the target active power output is as follows:

[0049] The active power reduction amount satisfies the following formula:

[0050] In the formula, Contribute to the goal of photovoltaic inverters. To provide real-time active power output for photovoltaic inverters, This refers to the amount of active power reduction in a single instance. The rated active power of the photovoltaic inverter. This indicates that the single active power adjustment range does not exceed 3% of the rated output. It is the active power regulation coefficient, with a value range of 0.5 to 0.9. While assisting in voltage regulation, it maximizes the retention of photovoltaic active power output, suppresses secondary voltage fluctuations caused by power surges, and balances voltage regulation effect with photovoltaic power generation revenue.

[0051] In one implementation, after the photovoltaic inverter completes reactive power regulation and active power regulation, it re-acquires the true value of the transformer area voltage and, based on the current measured voltage deviation of the transformer area, drives the UPQC device to reduce or increase the load-side voltage to eliminate the transformer area voltage exceeding the limit.

[0052] Specifically, the collaborative controller calculates the target compensation voltage on the UPQC series side based on the transformer substation voltage reference value, the actual load voltage after photovoltaic voltage regulation, and the residual voltage deviation. The calculation formula is as follows:

[0053] In the formula, The target compensation voltage for the UPQC series unit. This is the reference value for the transformer substation voltage. This is the actual load voltage value of the transformer substation re-collected after photovoltaic voltage regulation. This represents the residual voltage deviation after photovoltaic voltage regulation.

[0054] When the distribution area is under overvoltage conditions, the target compensation voltage is negative. The UPQC device injects negative compensation voltage into the line through a series-connected transformer to reduce the load-side voltage. When the distribution area is undervoltage conditions, the target compensation voltage is positive. The UPQC device injects positive compensation voltage to increase the load-side voltage, thereby correcting the remaining voltage deviation after the photovoltaic coarse adjustment.

[0055] Furthermore, the voltage regulation process employs a PI closed-loop iterative correction mechanism, with the iterative formula as follows:

[0056] In the formula, This represents the voltage deviation value in the k-th iteration. This is the proportional adjustment coefficient. The integral coefficient is used as the adjustment coefficient. The collaborative controller completes an iterative update of the voltage sampling and compensation command every 20ms. The proportional coefficient is 0.8 and the integral coefficient is 0.2. Through closed-loop iteration, the voltage deviation is gradually converged to achieve error-free and stable regulation of the transformer area voltage.

[0057] In some embodiments, the collaborative controller can identify the equivalent line impedance of the transformer area in real time, calculate the line voltage drop in real time by combining the effective voltage difference formula of the transformer area, and dynamically correct the voltage deviation calculation results and UPQC compensation commands through impedance calibration to offset the voltage regulation error caused by time-varying line impedance and random fluctuations in power flow, thereby further improving the accuracy of voltage compensation and ensuring that the problem of voltage exceeding the limit in the transformer area can still be stably eliminated under complex operating conditions such as photovoltaic power output fluctuations and dynamic load changes.

[0058] To verify the effectiveness of this invention, an actual operation test was conducted in a typical long-distance, high-penetration, low-voltage photovoltaic power distribution area. This area is equipped with a 100kVA, 0.4kV three-phase four-wire distribution transformer, and the total installed capacity of residential photovoltaic power in the area is 120kW, with three photovoltaic inverters with a rated capacity of 50kW each. The area is also equipped with a UPQC device with a rated capacity of 30kVA. The collaborative controller adopts industrial-grade PLC hardware and is equipped with a model predictive control algorithm. It establishes a real-time communication link with each photovoltaic inverter and UPQC device to perform all-time collaborative voltage regulation control.

[0059] During peak solar power generation periods (10:00–16:00), the active power output of the photovoltaic system in the distribution area reaches 100–120kW. Backflow of power causes the voltage at the load end of the distribution area to rise to 245–255V, exceeding the upper limit of acceptable voltage. The co-controller collects the electrical parameters of the distribution area during this period and calculates the real-time voltage deviation. After comparing with preset thresholds, it determines that the distribution area is in a severely over-limit condition. Correspondingly, it calculates the UPQC compensation weight and the photovoltaic compensation weight, and issues voltage regulation commands to each photovoltaic inverter. The photovoltaic inverters, according to the commands, limit the total active power output to 80kW, while simultaneously outputting 20kvar of inductive reactive power. By reducing active power and injecting inductive reactive power to increase the line voltage drop, the voltage in the distribution area is initially reduced to 235–240V. Afterwards, the co-controller re-acquires the measured voltage of the transformer area and drives the UPQC series side to output a compensation voltage of -5 to -10V based on the residual voltage deviation, further stabilizing the load voltage within the range of 228±2V; at the same time, the UPQC parallel side synchronously performs harmonic mitigation and three-phase imbalance compensation, reducing the total harmonic distortion (THD) of the transformer area voltage from 15% to 4% and the three-phase voltage imbalance from 12% to 1.5%.

[0060] During peak nighttime load periods (18:00–22:00), photovoltaic output drops to zero, while the load in the distribution area reaches 80–90kW. This heavy load causes a significant increase in line voltage drop, resulting in the load-side voltage dropping to 190–200V, below the acceptable lower limit. The co-controller calculates the real-time voltage deviation and determines it to be a severe over-limit condition. It then issues a voltage regulation command to the photovoltaic inverters, controlling each inverter to maximize capacitive reactive power output. The total capacitive reactive power output reaches 30kvar, which compensates for part of the line voltage drop, allowing the distribution area voltage to initially recover to 215–220V. Subsequently, based on the residual voltage deviation, the co-controller drives the UPQC series side to output a positive compensation voltage of +5 to +10V, stabilizing the load-side voltage within the 225±2V range. Simultaneously, the UPQC parallel side compensates for the remaining 10kvar of reactive power, maintaining the distribution area power factor at 0.98.

[0061] During the transition period when the output fluctuates between morning and evening, the collaborative controller performs rolling optimization control through the MPC algorithm, dynamically allocating the active and reactive power compensation tasks of the photovoltaic inverter and the UPQC device. The overall system response time reaches 3-5ms, which can smoothly track voltage fluctuations and avoid significant voltage fluctuations during the transition process.

[0062] Actual operation verification shows that after adopting the collaborative governance scheme of this embodiment, the voltage qualification rate of the distribution area increased to 99.95%, compared to only 82% before the governance; the three-phase voltage imbalance was reduced to less than 1.8%, far better than the 10%–15% level before the governance; the total harmonic distortion rate of voltage was controlled to less than 4.2%, compared to 12%–18% before the governance; and the photovoltaic curtailment rate was reduced to 0.8%, a significant reduction compared to the 15%–20% curtailment rate of traditional voltage regulation schemes. At the same time, this collaborative scheme only requires a 30kVA UPQC device to achieve the same governance goals, compared to the 50kVA capacity required by the traditional single UPQC governance scheme, saving 40% of the device capacity and significantly reducing the hardware cost of power quality governance in the distribution area.

[0063] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for collaborative governance of substation voltage out-of-limit by UPQC and photovoltaic inverter, characterized in that, The method includes the following steps: Obtain the electrical parameters of the transformer substation and calculate the real-time voltage deviation of the substation based on the electrical parameters; Different operating condition thresholds for the real-time voltage deviation of the transformer area are preset, and the current operating condition of the transformer area is determined based on the different relationships between the real-time voltage deviation of the transformer area and the operating condition thresholds. The photovoltaic compensation weight of the photovoltaic inverter is determined based on the current operating conditions of the transformer substation. The photovoltaic inverter adjusts the reactive power output according to the photovoltaic compensation weight and adjusts the active power output based on the real-time voltage deviation of the distribution area. Based on the current measured voltage deviation in the transformer area, the UPQC device is driven to reduce or increase the load-side voltage to eliminate voltage exceeding the limit in the transformer area.

2. The method of claim 1, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. Obtain the real-time value of the load voltage in the transformer substation, and calculate the real-time voltage deviation of the transformer substation based on the difference between the real-time value of the load voltage in the transformer substation and the rated voltage of the transformer substation.

3. The method of claim 2, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. A first threshold and a second threshold are set. When the absolute value of the real-time voltage deviation of the transformer area is less than or equal to the first threshold, it is determined to be a normal operating condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the first threshold and less than or equal to the second threshold, it is determined to be a slight over-limit condition. When the absolute value of the real-time voltage deviation of the transformer area is greater than the second threshold, it is determined to be a serious over-limit condition.

4. The method of claim 3, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. When the transformer area is in a slightly over-limit operating condition, the photovoltaic compensation weight is zero, the photovoltaic inverter does not participate in voltage regulation and does not limit active power output, and the load voltage is adjusted by the UPQC device. Specifically, the compensation voltage is calculated. If the compensation voltage is positive, the UPQC device increases the load terminal voltage. If the compensation voltage is negative, the UPQC device decreases the load terminal voltage.

5. The method of claim 4, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. When a transformer substation is in a severely over-limit operating condition, the UPQC compensation weight is determined based on the real-time voltage deviation of the substation, and the photovoltaic compensation weight is determined based on the UPQC compensation weight. The reactive power regulation of the photovoltaic inverter is calculated based on the photovoltaic compensation weight, and the active power output of the photovoltaic inverter is calculated based on the real-time voltage deviation of the substation.

6. The method of claim 5, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. The photovoltaic compensation weight is calculated based on the UPQC compensation weight, and the calculation formula is as follows: wherein, is a photovoltaic compensation weight, is a UPQC compensation weight; The UPQC compensation weight is calculated using the following formula: wherein, is the real-time voltage deviation for the transformer area.

7. The method of claim 6, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. The reactive power regulation of the photovoltaic inverter is calculated using the following formula: wherein, is the reactive power regulation amount for the photovoltaic inverter, is the reactive voltage regulation proportionality coefficient, is the photovoltaic inverter rated apparent power.

8. The method of claim 7, wherein the UPQC is used in conjunction with a photovoltaic inverter to manage voltage excursions in a distribution area. The active power reduction of the photovoltaic inverter is calculated based on the real-time voltage deviation of the transformer area, and the calculation formula is as follows: wherein is the active regulation coefficient, is the active down-regulation amount, is the photovoltaic inverter rated active power; The target active power output is obtained by subtracting the active power reduction from the current active power output of the photovoltaic inverter. The calculation formula is as follows: in, Contribute to photovoltaic inverters Provides real-time active power output for photovoltaic inverters.

9. The method for coordinating UPQC and photovoltaic inverter in managing voltage exceedance in a distribution area according to claim 1, characterized in that, After the photovoltaic inverter completes reactive power regulation and active power regulation, it re-acquires the true value of the transformer area voltage and, based on the current measured voltage deviation of the transformer area, drives the UPQC device to reduce or increase the load-side voltage to eliminate the transformer area voltage exceeding the limit.

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