A multi-feeder area-oriented light storage charging-UPQC global cooperative control and power quality treatment method and system

Abstract

The application discloses a multi-feeder area-oriented optical storage charging-UPQC global cooperative control and power quality treatment method and system, and belongs to the field of power quality treatment. In view of the problems of multi-source disturbance of power quality of a multi-feeder area, cross-feeder propagation and lack of cooperative treatment, the system comprises a multi-feeder unified power quality conditioner (UPQC) device, a public direct-current bus and an area-level cooperative controller. A series compensation unit is connected in series to each feeder, a public parallel compensation unit (P0) is connected to a low-voltage public bus, a photovoltaic array, a hybrid energy storage unit and a charging pile are connected to the public direct-current bus through respective transformers. The method constructs an area global state vector and calculates a power quality index, and when the index is out of limit, compensation and power instructions are solved through multi-objective optimization, and are executed. Feedback updating is achieved to realize rolling optimization. The application is suitable for power quality treatment of a low-voltage multi-feeder area containing distributed photovoltaic, energy storage and charging loads.

Description

Technical Field

[0001] This invention relates to the field of power quality management technology, specifically to a method and system for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer areas. Background Technology

[0002] With the advancement of the construction of new power systems, distributed photovoltaic, energy storage devices, electric vehicle charging piles and a large number of power electronic loads are connected to low-voltage distribution transformer areas. The operation of the transformer area has changed from traditional unidirectional power supply to multi-source coupling operation of source, grid, load, storage and charging. In multi-feeder transformer areas, multiple feeders share the distribution transformer and low-voltage bus. The photovoltaic output, charging load and nonlinear load on different feeders have randomness and fluctuation, which can easily cause voltage dips, dips, harmonic distortion, insufficient reactive power, reduced power factor and three-phase imbalance. Among them, power quality indicators such as harmonic distortion have been limited by national recommended standards, as recorded in reference [1]. Since each feeder is coupled to the other through the common connection point, the reactive power fluctuation, harmonic injection or charging load change of a certain feeder may affect other feeders through the common bus, so that the power quality problem presents the characteristics of multi-source disturbance, multi-target coupling and cross-feeder propagation.

[0003] Existing power quality management equipment mainly includes passive filters, active power filters, dynamic voltage restorers, static var generators, and unified power quality regulators (UPQC), as described in reference [2]. Among them, passive filters have a fixed compensation spectrum and are easily affected by system impedance, resulting in poor adaptability; active power filters are mainly used to manage harmonics and reactive power; dynamic voltage restorers focus on voltage sag compensation; and static var generators are mainly used for reactive power regulation. The functions of the above devices are different. If they are configured independently for different power quality problems, not only will the investment and operation and maintenance costs be high, but compensation conflicts are also likely to occur due to the lack of coordinated control.

[0004] The UPQC consists of a series compensation unit, a parallel compensation unit, and a common DC bus. It has functions such as voltage compensation, harmonic control, reactive power compensation, and DC bus stabilization. The basic circuit structure and series-parallel compensation control method have been disclosed in prior patent literature, as described in reference [3]. However, existing technologies mostly focus on a single UPQC or a single common connection point as the target of governance, emphasizing local voltage or current quality governance. It is difficult to adapt to the power, voltage, harmonic, and energy coupling relationship between photovoltaic, energy storage, charging piles, nonlinear loads, and UPQC in multi-feeder areas. Moreover, under conditions that require continuous active power support, such as deep voltage sags, its compensation capability is limited by the DC side energy storage capacity.

[0005] To enhance the new energy consumption and active power support capabilities of UPQC, existing technologies connect photovoltaic power generation units or energy storage devices to the DC side of UPQC, as described in reference [4]. However, such schemes are mostly simple superpositions of grid connection and power quality management functions, and photovoltaic inverters, energy storage converters, charging piles and UPQC usually adopt relatively independent local control methods, lacking a unified substation-level coordinated control and multi-objective optimization allocation mechanism, making it difficult to simultaneously take into account voltage stability, harmonic suppression, reactive power compensation, three-phase imbalance management, DC bus voltage stability and energy storage state of charge constraints. Therefore, it is urgent to propose a global collaborative control and multi-objective power quality management method for photovoltaic-storage-charging-UPQC in multi-feeder substations.

[0006] References: Reference [1]: State Bureau of Technical Supervision. GB / T 14549—1993 Power Quality - Harmonics in Public Power Grids [S]. Beijing: China Standards Press, 1993. Reference [2]: Wang Zhaoan, Yang Jun, Liu Jinjun, et al. Harmonic suppression and reactive power compensation [M]. 2nd ed. Beijing: China Machine Press, 2005. Literature[3]:Fujita H, Akagi H. The unified power quality conditioner: theintegration of series- and shunt-active filters[J]. IEEE Transactions onPower Electronics, 1998, 13(2): 315-322. Literature[4]:Jindal AK, Ghosh A, Joshi A. Interline unified power qualityconditioner[J]. IEEE Transactions on Power Delivery, 2007, 22(1): 364-372. Summary of the Invention To address the shortcomings of existing power quality management methods, which primarily rely on local compensation for single feeders and single devices and are ill-suited for the coupled operation of power generation, grid, load, energy storage, and charging in multi-feeder distribution areas, this invention provides a global collaborative control and power quality management method and system for photovoltaic-energy storage-charging-UPQC systems in multi-feeder distribution areas. Centered on a multi-feeder UPQC device, it couples photovoltaic, battery-supercapacitor hybrid energy storage, and charging piles via a common DC bus. A distribution area-level hierarchical collaborative control architecture is employed to uniformly solve compensation and power allocation commands, achieving multi-objective global collaborative management of voltage, harmonics, reactive power, three-phase imbalance, and DC bus voltage.

[0007] The technical solution adopted in this invention is as follows: A method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC in multi-feeder transformer areas includes the following steps: S1: Collect the voltage and current of each feeder, the voltage of the common DC bus, photovoltaic output, charging load power, and the state of charge of the hybrid energy storage unit to construct the global state vector of the transformer area; S2: Calculate various power quality indicators based on the global state vector of the transformer area. The power quality indicators include voltage deviation, total harmonic distortion rate of current and three-phase voltage imbalance of each feeder, as well as reactive power, DC bus voltage deviation and energy storage state of charge. S3: Compare each of the power quality indicators with the corresponding set limits to determine whether any limit has been exceeded; if none of the limits have been exceeded, maintain the current operating state and return to S1; S4: If any of the power quality indicators exceeds the limit, a multi-objective optimization model is established with each of the power quality indicators as the optimization objective, and the multi-objective optimization model is solved under the constraints to obtain the series compensation voltage command of each series compensation unit, the compensation current command of the common parallel compensation unit, the photovoltaic power command, the hybrid energy storage power command, and the charging load adjustment command. S5: Send each instruction to the corresponding series compensation unit, common parallel compensation unit, and the converters of the photovoltaic array, hybrid energy storage unit and charging pile for execution, so that each series compensation unit injects compensation voltage into the corresponding feeder, the common parallel compensation unit injects compensation current into the low-voltage common bus, and the hybrid energy storage unit releases or absorbs power through the common DC bus. S6: Collect the running status feedback after execution, update the global status vector of the transformer area, and return to S1 to enter the next control cycle to realize rolling optimization control.

[0008] In step S1, the hybrid energy storage unit includes battery energy storage and a supercapacitor, and the battery energy storage and the supercapacitor are respectively connected to a common DC bus via their respective bidirectional DC / DC converters; step S1 includes: S1.1: In the k-th control cycle, the voltage of the three feeders is synchronously acquired. , , and current , , Total harmonic distortion of current in the three feeders , , and three-phase voltage imbalance And collect the voltage of the common DC bus. Photovoltaic power output Charging load power The state of charge (SOC) of the battery energy storage. and the state of charge of the supercapacitor ; S1.2: Using the state variables collected in S1.1 as elements, construct the global state vector of the transformer area in a fixed arrangement order: ; In the formula, Let be the global state vector of the transformer area in the k-th control cycle. , , These represent the voltages of the three feeders. , , These represent the currents of the three feeders. , , These are the total harmonic distortion rates of the currents of the three feeders. This refers to the three-phase voltage imbalance. The voltage of the common DC bus. Contribute to photovoltaic power For charging load power, , These represent the state of charge of battery energy storage and supercapacitors, respectively.

[0009] S2 includes: 2.1: Perform fundamental and harmonic decomposition on the voltage and current of each feeder in the global state vector of the transformer area, and perform symmetrical component decomposition on the fundamental voltage obtained by decomposition to obtain the effective value of the fundamental voltage, the effective value of the fundamental current, the effective value of each harmonic current, as well as the positive sequence voltage component and the negative sequence voltage component of each feeder. 2.2: Based on the fundamental voltage RMS value obtained in 2.1, calculate the voltage deviation index of each feeder: ; In the formula, For the first Voltage deviation index of the feeder line For the first The fundamental voltage RMS value of the feeder line. Rated voltage, Here are the feeder numbers, i = 1, 2, 3; 2.3: Based on the RMS value of the fundamental current and the RMS values ​​of each harmonic current obtained in 2.1, calculate the total harmonic distortion rate of the current in each feeder: ; In the formula, For the first Total harmonic distortion of current in a feeder line. For the first The fundamental current RMS value of the feeder For the first The effective value of the h-th harmonic current of the feeder, where H is the highest harmonic order involved in the calculation; S2.4: Based on the positive-sequence and negative-sequence voltage components obtained in 2.1, calculate the three-phase voltage imbalance: ; In the formula, It is the positive sequence voltage component. It is the negative sequence voltage component.

[0010] S3 includes: S3.1: The voltage deviation index of each feeder calculated in S2 Total harmonic distortion of current Three-phase voltage imbalance And reactive power and DC bus voltage deviation are compared with their respective set limits; S3.2: If none of the comparison results exceed the limit, the power quality of the transformer area is determined to be normal, the current operating status is maintained, and the process returns to S1 to continue status monitoring. S3.3: If any comparison result exceeds the limit, it is determined that a power quality exceeding the limit event has occurred, and the multi-objective optimization model established in S4 is entered for solution.

[0011] S4 includes: S4.1: Based on the power quality indicators calculated in S2, construct voltage deviation index items respectively. Harmonic distortion index Reactive power compensation index item Three-phase imbalance index item DC bus voltage deviation index item and energy storage state of charge deviation index ; S4.2: Assign corresponding weights to each indicator item constructed in S4.1 and perform a weighted summation to construct a multi-objective optimization objective function: ; In the formula, J is the comprehensive objective function. ~ These are the weighting coefficients for each indicator item; S4.3: Using the minimization of the comprehensive objective function J constructed in S4.2 as the optimization objective, the various instructions described in S4 are obtained by solving the problem.

[0012] In step S4.3, the constraints for solving the multi-objective optimization model include: (1) UPQC capacity constraint: The compensation power output by each series compensation unit and the common parallel compensation unit shall not exceed their respective rated capacity; (2) Photovoltaic output constraint: The photovoltaic power command shall not exceed the current maximum power output of the photovoltaic array; (3) Energy storage state of charge constraints: ,and In the formula, , These are the lower and upper limits of the battery's state of charge, respectively. , These are the lower and upper limits of the state of charge of a supercapacitor, respectively. (4) Charge and discharge power constraints: ,and ; In the formula, , These represent the actual charge and discharge power of battery energy storage and supercapacitors, respectively. , These are the maximum charging and discharging power of battery energy storage and supercapacitors, respectively. (5) Charging load adjustment constraint: The adjustment amount corresponding to the charging load adjustment command shall not exceed the adjustable power range of the charging pile. (6) DC bus voltage constraint: ; In the formula, , These are the lower and upper limits of the allowable voltage for the common DC bus, respectively.

[0013] S5 includes: S5.1: Based on the series compensation voltage command for each feeder, generate the compensation voltage reference value for each series compensation unit. , , , , , These are the compensation voltage reference values ​​for the series compensation units corresponding to the three feeders. The deviation between each compensation voltage reference value and the actual voltage of the corresponding feeder is controlled by voltage outer loop proportional resonance (PR) and then pulse width modulation (PWM) is performed to generate the drive signal for each series compensation unit, which drives each series compensation unit to inject series compensation voltage into the corresponding feeder. S5.2: Generate compensation reference values ​​for harmonic current, reactive current and unbalanced current of the common parallel compensation unit according to the compensation current command. After controlling the current outer loop proportional resonance (PR) with the deviation between the compensation reference value and the actual output current of the common parallel compensation unit, pulse width modulation (PWM) is performed to generate the drive signal of the common parallel compensation unit, which drives the common parallel compensation unit to inject compensation current into the low voltage common bus. S5.3: Based on the active power required for the series compensation in S5.1 and the parallel compensation in S5.2, as well as the photovoltaic power command, synthesize the power demand of the common DC bus, and control the hybrid energy storage unit to release or absorb power through the common DC bus to maintain the voltage stability of the common DC bus.

[0014] S5.3 includes: S5.3.1: The reference value of the common DC bus voltage Compared with actual value The deviation between them is controlled by proportional-integral (PI) control and combined with the active power required for series compensation in S5.1 and parallel compensation in S5.2, as well as the feedforward component of the photovoltaic power command, to obtain the power demand of the common DC bus. ; S5.3.2: Power requirements for the common DC bus obtained from S5.3.1 Perform low-pass filtering and use the low-frequency continuous power component as the power command for battery energy storage: ; In the formula, For battery energy storage power command, This indicates a low-pass filter stage. The superscript "*" indicates a command value, used to distinguish it from the actual value. S5.3.3: The power requirement Power command for battery energy storage The difference serves as the power command for the supercapacitor, enabling the battery energy storage to handle the low-frequency continuous power component and the supercapacitor to handle the high-frequency instantaneous power component. ; In the formula, For supercapacitor power commands; The above two equations satisfy: ; S5.3.4: Based on the battery's state of charge State of charge of supercapacitors and the charge / discharge power limit for the battery energy storage power command Supercapacitor Power Command Constraint corrections are performed, and the corrected power commands are converted into the duty cycles of the bidirectional DC / DC converters on the battery storage side. Duty cycle of the bidirectional DC / DC converter on the supercapacitor side This drives the corresponding bidirectional DC / DC converter to work.

[0015] S6 includes: S6.1: After the execution of the instructions in S5, re-collect the operating status of each feeder, multi-feeder UPQC device, photovoltaic array, hybrid energy storage unit and charging pile; S6.2: Update the global status vector of the transformer area based on the operating status re-collected in S6.1, and obtain the updated global status vector of the transformer area. ,in, This is the global state vector of the transformer area during the (k+1)th control cycle; S6.3: The global state vector of the transformer area in the (k+1)th control cycle Returning to S1 as the initial state for the next control cycle, S1~S6 are executed cyclically to achieve rolling optimization control with continuous monitoring and dynamic correction.

[0016] A global collaborative control and power quality management system for photovoltaic, energy storage, charging, and UPQC in multi-feeder transformer areas, comprising: Multi-feeder unified power quality conditioner (UPQC) device, common DC bus, photovoltaic array, hybrid energy storage unit, charging pile, and substation-level collaborative controller; among which: The multi-feeder unified power quality conditioner (UPQC) device includes multiple series compensation units connected in series in each feeder of the multi-feeder area, and a common parallel compensation unit connected in parallel to the low-voltage common bus of the multi-feeder area. The DC side of each series compensation unit and the common parallel compensation unit are connected to the common DC bus. The photovoltaic array is connected to the common DC bus via a DC / DC converter, the hybrid energy storage unit is connected to the common DC bus via a bidirectional DC / DC converter, and the charging pile is connected to the common DC bus via a DC / DC converter. The district-level collaborative controller includes: The state perception module is used to collect the voltage and current of each feeder, the voltage of the common DC bus, photovoltaic output, charging load power and energy storage charge status to construct a global state vector of the transformer area. The indicator evaluation module is used to calculate various power quality indicators based on the global state vector of the transformer area. The power quality indicators include voltage deviation, total harmonic distortion rate of current and three-phase voltage imbalance of each feeder, as well as reactive power, DC bus voltage deviation and energy storage state of charge. The limit-breaking judgment module is used to compare each power quality indicator with the corresponding set limit value to determine whether a limit-breaking has occurred. If no limit-breaking has occurred, the current operating state is maintained. The collaborative optimization module is used to establish a multi-objective optimization model with each power quality index as the optimization objective when any power quality index exceeds the limit, and solve the multi-objective optimization model under constraints to obtain the series compensation voltage command of each series compensation unit, the compensation current command of the common parallel compensation unit, the photovoltaic power command, the hybrid energy storage power command, and the charging load adjustment command. The instruction distribution module is used to send each instruction to the corresponding series compensation unit, the common parallel compensation unit, and the converters of the photovoltaic array, the hybrid energy storage unit and the charging pile for execution, so that each series compensation unit injects compensation voltage into the corresponding feeder, the common parallel compensation unit injects compensation current into the low-voltage common bus, and the hybrid energy storage unit releases or absorbs power through the common DC bus. The feedback update module is used to collect the running status feedback after execution, update the global state vector of the transformer area, and trigger the state perception module to enter the next control cycle to realize rolling optimization control.

[0017] This invention provides a global collaborative control and power quality management method and system for photovoltaic-storage-charging-UPQC in multi-feeder transformer substations, with the following technical advantages: 1) In multi-feeder transformer substations, where feeders are coupled via a common busbar, disturbances propagate across feeders. Existing UPQC (Upgraded Voltage Quality Control) systems, often based on single units or common connection points, are ill-suited for multi-feeder coupling scenarios. This invention addresses this by employing a multi-feeder UPQC structure: multiple series compensation units connected in series to each feeder, plus a common parallel compensation unit connected in parallel to the low-voltage common busbar and the common DC busbar, along with a unified global state vector sensing mechanism for the entire substation. This allows each series compensation unit to inject compensation voltage locally based on its feeder voltage state, achieving distributed voltage management with "one compensation per feeder." The common parallel compensation unit uniformly manages the current quality on the common busbar side. Both systems achieve power mutual support via the common DC busbar, preventing disturbances from any feeder from propagating unconstrainedly through the common busbar. Compared to existing single-point management technologies, this invention extends voltage compensation capability from a "single connection point" to the "whole multi-feeder domain."

[0018] 2) Since each of the PPF, APF, DVR, and SVG functions has its own focus, configuring them independently not only results in high investment and maintenance costs but also easily leads to compensation conflicts due to a lack of coordination and control. This invention employs a multi-objective optimization model to achieve harmonic suppression, reactive power compensation, and imbalance management simultaneously within a unified optimization framework using a single multi-feeder UPQC device. This fundamentally eliminates compensation conflicts between multiple devices and significantly reduces redundant equipment investment.

[0019] 3) Existing UPQCs are limited by DC-side energy storage capacity, resulting in limited compensation capabilities under conditions requiring continuous active power support, such as deep voltage sags. Furthermore, sudden changes in charging load and photovoltaic fluctuations directly impact the DC bus. This invention addresses this by implementing a hybrid energy storage unit connected to a common DC bus via a bidirectional DC / DC converter, along with a power frequency division and allocation mechanism. The supercapacitor, with a millisecond-level response, prioritizes smoothing instantaneous power surges such as charging load jumps and nonlinear load impacts. The battery storage then provides continuous power support on a time scale, from seconds to minutes. This time-scale relay ensures that the active power required for compensation no longer depends on instantaneous exchange on the AC side.

[0020] 4) Existing photovoltaic (PV) grid-connected UPQC systems are simply a combination of grid connection and power management functions, lacking energy storage buffering and global coordination between PV intermittency and compensation needs; each device operates independently and locally, posing risks of overcharging and over-discharging of energy storage. This invention describes a structure where PV arrays and charging piles are connected to a common DC bus via their respective converters to participate in power coordination; energy storage state of charge constraints and charging / discharging power constraints; and SOC constraints and power limiting correction mechanisms. This ensures that in Mode B, when PV output increases, priority is given to supporting the DC bus and load demand; when charging power suddenly increases or PV output decreases, supercapacitors and battery energy storage sequentially compensate; the state of charge of battery energy storage and supercapacitors did not exceed limits throughout the simulation. Compared to existing technologies, this application transforms PV from a "simple power source to be consumed" and charging piles from "simple objects to be managed" into resources that can participate in regional power coordination, with energy storage operating within a safe range throughout.

[0021] 5) The photovoltaic inverter, energy storage converter, charging pile, and UPQC each employ independent local control, lacking a unified state awareness and multi-objective optimization allocation mechanism at the distribution area level, making it unable to adapt to the random and variable operating conditions. This invention addresses this by implementing an over-limit judgment triggering mechanism and a "execution feedback → state vector update" mechanism. →The next cycle" rolling optimization mechanism; the corresponding status perception, limit judgment, and feedback update modules on the system side. This ensures that the system maintains normal operation when all indicators are within limits, avoiding continuous full-load operation of the optimization controller; if any indicator exceeds the limit, multi-objective optimization is triggered; after the instruction is executed, the status is re-collected and rolled over for correction, forming a closed loop of "monitoring-judgment-optimization-execution-feedback", so that the control strategy can be dynamically adjusted according to time-varying operating conditions such as photovoltaic fluctuations and charging load jumps. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and examples; Figure 1 This is the overall topology diagram of the UPQC (Optical Storage-Charging-UPQC) system for multi-feeder substations.

[0023] Figure 2 This is a topology diagram of a T-NPC three-level converter.

[0024] Figure 3 This is a structural diagram of a battery-supercapacitor hybrid energy storage unit.

[0025] Figure 4 Diagram of the hierarchical collaborative control architecture for photovoltaic, energy storage, charging, and UPQC at the substation level.

[0026] Figure 5 Flowchart for multi-objective optimization control of power quality in multi-feeder transformer areas.

[0027] Figure 6 Block diagram of the photovoltaic-storage-charging-UPQC collaborative control strategy.

[0028] Figure 7 This is a diagram showing the effect of voltage sag compensation for feeder F1.

[0029] Figure 8 The diagram shows the effect of PCC current THD control.

[0030] Figure 9 This diagram illustrates the effect of stable control of the common DC bus voltage.

[0031] Figure 10 A diagram illustrating the effect of UPQC power coordination control for photovoltaic energy storage and charging. Detailed Implementation

[0032] (I) Example 1: A global collaborative control and power quality management system for photovoltaic, energy storage, and charging systems in multi-feeder transformer areas, including: 1. System overall topology: like Figure 1 As shown, the system in this embodiment is applied to a low-voltage distribution substation containing distributed photovoltaics, hybrid energy storage, electric vehicle charging piles, sensitive and important loads, nonlinear loads and unbalanced loads. It includes the upstream power grid, 10kV / 0.4kV distribution transformers, low-voltage common bus, multi-feeder unified power quality conditioner (UPQC) device, common DC bus, photovoltaic array, hybrid energy storage unit and charging pile.

[0033] The upstream power grid is connected to the low-voltage common bus via a 10kV / 0.4kV distribution transformer. The low-voltage common bus supplies power to feeders 1, 2, and 3. The three feeders connect to loads of different characteristics: feeder 1 connects to sensitive and critical loads, feeder 2 connects to nonlinear / unbalanced loads, and feeder 3 connects to charging / pulsating loads. Because the load characteristics of different feeders are different, harmonic currents, reactive power fluctuations, or impulse power generated by one feeder can affect other feeders through the low-voltage common bus. Therefore, this embodiment sets up a unified multi-feeder UPQC device on the multi-feeder side.

[0034] The multi-feeder UPQC device includes a common parallel compensation unit P0 and series compensation units SE1, SE2, and SE3 connected in series in feeders 1, 2, and 3, respectively. Series compensation units SE1, SE2, and SE3 inject series compensation voltage into the corresponding feeders to manage voltage dips, voltage swells, and three-phase imbalances in each feeder. The common parallel compensation unit P0 is connected to the low-voltage common bus to compensate for harmonic currents, reactive currents, and unbalanced currents on the low-voltage common bus side, and to maintain voltage stability on the common DC bus.

[0035] The multi-feeder UPQC device adopts a common DC bus structure, with two buses on the DC side: DC+ and DC-. The photovoltaic array is connected to the common DC bus via a DC / DC converter to provide renewable energy power support to the UPQC DC side. Battery energy storage and supercapacitors are connected to the common DC bus via bidirectional DC / DC converters, forming a hybrid energy storage unit. Charging piles are connected to the common DC bus via DC / DC converters, allowing the charging load to not only be managed but also participate in power coordination under certain conditions. Through this structure, multi-feeder power quality compensation, photovoltaic power absorption, energy storage support, and charging load regulation can be unified and coordinated under the same common DC bus.

[0036] 2. Converter Topology: like Figure 2 As shown, in this embodiment, the series compensation units SE1, SE2, SE3 and the common parallel compensation unit P0 all adopt the T-NPC three-level converter topology. This topology consists of DC-side split capacitors C1 and C2, a neutral point O, and three-phase bridge arm power switches, capable of outputting multi-level compensation voltage or compensation current. The controller controls the on / off state of each power switch according to the compensation voltage or compensation current command, enabling the converter to output positive, zero, and negative levels, thereby achieving more precise voltage and current compensation. Compared to traditional two-level converters, the T-NPC three-level topology can reduce voltage stress on switching devices, decrease output voltage harmonics and current ripple, and improve the accuracy of series voltage compensation and parallel current compensation. It is suitable for comprehensive management of voltage sags, voltage swells, harmonic distortion, and three-phase imbalance in multi-feeder transformer areas.

[0037] 3. Hybrid energy storage unit: like Figure 3 As shown, the hybrid energy storage unit consists of battery energy storage, a supercapacitor, a battery-side bidirectional DC / DC converter, a supercapacitor-side bidirectional DC / DC converter, and a hybrid energy storage coordination controller. Battery energy storage primarily provides energy support at the second to minute level, maintaining power balance, supporting voltage sags, and improving photovoltaic absorption capacity. The supercapacitor primarily provides millisecond-level instantaneous power buffering, suppressing sudden changes in charging load, nonlinear load impacts, and rapid voltage fluctuations on the common DC bus caused by UPQC compensation.

[0038] The hybrid energy storage coordination controller is based on the voltage of the common DC bus. State of charge of battery energy storage State of charge of supercapacitors The power demand of the common DC bus is processed through steps such as DC bus voltage outer loop, power demand decomposition and time scale allocation, energy storage state of charge constraint and power limiting, to generate battery energy storage power commands. and duty cycle Supercapacitor Power Command and duty cycle Among them, the state of charge of battery energy storage State of charge of supercapacitors Collectively referred to as energy storage state of charge.

[0039] When there are sudden changes in charging load, fluctuations in photovoltaic output, or rapid changes in UPQC compensation power, the supercapacitor prioritizes responding to instantaneous power demands, while battery energy storage provides continuous power support, thereby suppressing voltage fluctuations on the common DC bus. The hybrid energy storage power allocation relationship is expressed as follows: ; ; ; In the formula, For the power requirements of the common DC bus, For battery energy storage power command, This is a power command for supercapacitors. This indicates a low-pass filter stage. The superscript "*" represents a command value, used to distinguish it from the actual value. Battery energy storage handles low-frequency, continuous power components, while supercapacitors handle high-frequency, instantaneous power components. When the voltage of the common DC bus is lower than its reference value... When the battery energy storage and supercapacitor release power to the common DC bus; when the voltage of the common DC bus is higher than the reference value... At that time, battery energy storage and supercapacitors absorb excess power, where... This is a reference value for the common DC bus voltage. The controller simultaneously considers energy storage state-of-charge constraints and power limiting to prevent overcharging or over-discharging of battery energy storage or excessive consumption of supercapacitors. In this embodiment, For example, if 700V is chosen, the cutoff frequency of the low-pass filter stage can be set to 0.1Hz to 1Hz, which is between the power response time scale of battery energy storage and supercapacitor.

[0040] 4. Hierarchical collaborative control architecture: like Figure 4As shown, this embodiment adopts a hierarchical collaborative control architecture consisting of a distribution area-level decision-making layer, a collaborative optimization layer, and an equipment execution layer. The distribution area-level decision-making layer includes a distribution area-level collaborative controller and a data acquisition / communication module, used to collect operating data such as multi-feeder voltage, current, total harmonic distortion of current, three-phase voltage imbalance, voltage of the common DC bus, photovoltaic output, energy storage state of charge, and charging load power. The equipment execution layer includes series compensation units SE1, SE2, and SE3, a common parallel compensation unit P0, a DC / DC converter for the photovoltaic array, a hybrid energy storage unit, and a DC / DC converter for the charging pile, used to execute voltage compensation, current compensation, and power regulation commands issued from the upper layer.

[0041] The transformer substation-level collaborative controller includes a state perception module, an index evaluation module, a limit violation judgment module, a collaborative optimization module, an instruction allocation module, and a feedback update module. The state perception module collects the voltage and current of each feeder, the voltage of the common DC bus, photovoltaic output, charging load power, and energy storage state of charge to construct a global state vector for the transformer substation. The index evaluation module calculates various power quality indices based on the global state vector. The limit violation judgment module compares each power quality index with its corresponding set limit and determines whether a limit violation has occurred. The collaborative optimization module establishes a multi-objective optimization model and solves for various instructions under constraints when any power quality index exceeds its limit. The instruction allocation module distributes the instructions to the corresponding units in the equipment execution layer for execution. The feedback update module collects operational status feedback after execution, updates the global state vector of the transformer substation, and triggers the state perception module to enter the next control cycle, achieving rolling optimization control. The data interaction between these modules constitutes the multi-feeder state perception, power quality index evaluation, multi-objective optimization, compensation, and power instruction allocation functions of the collaborative optimization layer.

[0042] (II) Example 2: A global collaborative control method for photovoltaic-storage-charging-UPQC in multi-feeder substations, such as... Figure 5 As shown, the method of this embodiment cyclically executes the following steps S1 to S6 in each control cycle.

[0043] S1: Status Acquisition and Global Status Vector Construction for Transit Area: S1.1: In the k-th control cycle, the voltage of the three feeders is synchronously acquired by the data acquisition / communication module. , , and current , , Total harmonic distortion of current in the three feeders , , and three-phase voltage imbalance And collect the voltage of the common DC bus. Photovoltaic power output Charging load power State of charge of battery energy storage and the state of charge of supercapacitors ; S1.2: Using the state variables collected in S1.1 as elements, construct the global state vector of the transformer area in a fixed arrangement order: ; In the formula, Let be the global state vector of the transformer area in the k-th control cycle. , , These represent the voltages of the three feeders. , , These represent the currents of the three feeders. , , These are the total harmonic distortion rates of the currents of the three feeders. This refers to the three-phase voltage imbalance. The voltage of the common DC bus. Contribute to photovoltaic power For charging load power, , These represent the states of charge of battery storage and supercapacitors, respectively. This state vector unifies the electrical states of multiple feeders, the energy states of the DC side, and the states of source-load-storage equipment into a single data structure, providing complete state input for regional-level global coordinated control.

[0044] S2: Calculation of power quality indicators: S2.1: Perform fundamental and harmonic decomposition on the voltage and current of each feeder in the global state vector of the transformer area, and perform symmetrical component decomposition on the fundamental voltage obtained by decomposition to obtain the effective value of the fundamental voltage, the effective value of the fundamental current, the effective value of each harmonic current, as well as the positive sequence voltage component and the negative sequence voltage component of each feeder. S2.2: Calculate the voltage deviation index of each feeder: ; In the formula, The voltage deviation index of the i-th feeder. Let be the effective value of the fundamental voltage of the i-th feeder. The rated voltage is used, and i is the feeder number, i=1,2,3; in this embodiment, the rated phase voltage is used. For example, 230V; S2.3: Calculate the total harmonic distortion (THD) of the current in each feeder: ; In the formula, Let be the total harmonic distortion of the current in the i-th feeder. Let be the effective value of the fundamental current of the i-th feeder. Here is the effective value of the h-th harmonic current of the i-th feeder, and H is the highest harmonic order involved in the calculation. In this embodiment, H is, for example, 25. S2.4: Calculate the three-phase voltage imbalance: ; In the formula, It is the positive sequence voltage component. This represents the negative sequence voltage component. In addition, reactive power, DC bus voltage deviation, and energy storage state of charge are also calculated, collectively forming various power quality indicators.

[0045] S3: Limit Exceedance Detection: S3.1: The voltage deviation index of each feeder calculated in S2 Total harmonic distortion of current Three-phase voltage imbalance And reactive power and DC bus voltage deviation are compared with their respective set limits; S3.2: If none of the comparison results exceed the limit, the power quality of the distribution area is determined to be normal, the system maintains the current operating state, and returns to S1 to continue status monitoring; S3.3: If any comparison result exceeds the limit, such as voltage exceeding the limit, harmonic exceedance, reactive power deficiency, three-phase imbalance, or DC bus voltage exceeding the limit, then a power quality exceeding the limit event is determined to have occurred, and proceed to S4.

[0046] S4: Establishment and solution of multi-objective optimization model: Based on the power quality indicators obtained from S2 calculations, voltage deviation index items are constructed respectively. Harmonic distortion index Reactive power compensation index item Three-phase imbalance index item DC bus voltage deviation index item and energy storage state of charge deviation index ; By assigning appropriate weights to each indicator and performing a weighted summation, a multi-objective optimization objective function is constructed: ; In the formula, J is the comprehensive objective function. to These are the weighting coefficients for each indicator item; the weighting coefficients are set according to the priority of transformer area management. For example, when the sensitive and important loads connected to feeder 1 have high voltage quality requirements, the weighting coefficient is increased. Prioritize optimizing voltage deviation indicators; With the goal of minimizing the comprehensive objective function J, the solution is obtained under constraints, yielding the series compensation voltage command for each series compensation unit, the compensation current command for the common parallel compensation unit, the photovoltaic power command, the hybrid energy storage power command, and the charging load adjustment command.

[0047] The constraints include: (1) UPQC capacity constraint: The compensation power output by each series compensation unit and the common parallel compensation unit shall not exceed their respective rated capacity; (2) Photovoltaic output constraint: The photovoltaic power command shall not exceed the current maximum power output of the photovoltaic array; (3) Energy storage state of charge constraints: and In the formula , These are the lower and upper limits of the battery's state of charge, respectively. , These are the lower and upper limits of the state of charge of a supercapacitor, respectively, for example... Limited to 20%–90%, Limited to 10%–95%; (4): Charge and discharge power constraints: and In the formula, , These represent the actual charge and discharge power of battery energy storage and supercapacitors, respectively. , The maximum charging and discharging power of the battery storage and the supercapacitor are respectively; (5) Charging load adjustment constraint: the adjustment amount corresponding to the charging load adjustment command shall not exceed the adjustable power range of the charging pile; (6) DC bus voltage constraint: In the formula, , These are the lower and upper limits of the allowable voltage for the common DC bus, respectively.

[0048] S5: Instruction Assignment and Execution The commands obtained from S4 are sent to the device execution layer for execution: each series compensation unit SE1, SE2, and SE3 injects series compensation voltage into the corresponding feeder; the common parallel compensation unit P0 injects compensation current into the low-voltage common bus; the converters of the photovoltaic array, hybrid energy storage unit, and charging pile execute the corresponding power commands, so that the hybrid energy storage unit releases or absorbs power through the common DC bus. See Example 3 for the specific control process.

[0049] S6: Feedback Updates and Scrolling Optimizations S6.1: After the execution of the instructions in S5, re-collect the operating status of each feeder, multi-feeder UPQC device, photovoltaic array, hybrid energy storage unit and charging pile; S6.2: Update the global state vector of the transformer area with the newly acquired operating status to obtain the updated global state vector of the transformer area. In the formula This is the global state vector of the transformer area during the (k+1)th control cycle; S6.3: with Returning to S1 as the initial state for the next control cycle, S1~S6 are executed cyclically to achieve continuous monitoring, dynamic correction, and rolling optimization control.

[0050] (III) Photovoltaic-Storage-Charging-UPQC Coordinated Control Strategy: like Figure 6 As shown, the collaborative control strategy in this embodiment includes three control regions: UPQC series compensation control, UPQC parallel compensation control, and hybrid energy storage common DC bus support control.

[0051] (1) UPQC series compensation control: The series compensation control area generates a compensation voltage reference value based on the series compensation voltage command of each feeder. , , In the formula , , These are the compensation voltage reference values ​​for the series compensation units corresponding to the three feeders. The deviation between each compensation voltage reference value and the actual voltage of the corresponding feeder is controlled by a voltage outer loop proportional resonance (PR) and then pulse width modulation (PWM) is applied to generate drive signals for the series compensation units SE1, SE2, and SE3, respectively, to compensate for voltage sags, voltage swells, and three-phase imbalances in each feeder. Using proportional resonance control, infinite gain can be obtained at the fundamental frequency, achieving zero steady-state error tracking of the power frequency compensation voltage.

[0052] (2) UPQC Parallel Compensation Control: The parallel compensation control area generates compensation reference values ​​for harmonic current, reactive current and unbalanced current of the common parallel compensation unit P0 according to the compensation current command. The deviation between the compensation reference value and the actual output current of the common parallel compensation unit P0 is pulse width modulated (PWM) after being controlled by the current outer loop proportional resonance (PR) to generate the drive signal of the common parallel compensation unit P0, which is used to compensate for the harmonic current, reactive current and zero-sequence / negative-sequence unbalanced current on the low-voltage common bus side.

[0053] (3) Hybrid energy storage common DC bus support control: The hybrid energy storage control area will use the reference value of the common DC bus voltage. Compared with actual value The deviation between them is controlled by proportional-integral (PI) and combined with the active power required for series compensation, parallel compensation, and the feedforward component of the photovoltaic power command to obtain the power demand of the common DC bus. Subsequently, power demand decomposition and time-scale allocation are performed according to the hybrid energy storage power allocation relationship described in Part 3 of Example 1. After energy storage state of charge constraint and power limiting correction, the duty cycle of the bidirectional DC / DC converter on the battery energy storage side is generated respectively. Duty cycle of the bidirectional DC / DC converter on the supercapacitor side This drives the corresponding bidirectional DC / DC converter to operate, thereby achieving voltage stability and instantaneous power support for the common DC bus.

[0054] (4) Theory of multi-feeder compensation and common DC bus power balance: For the A feeder line, with series compensation units superimposing compensation voltages to ensure the load-side voltage tracks the rated positive-sequence fundamental reference value; a common parallel compensation unit injects compensation current to ensure the upstream grid-side current retains only the positive-sequence fundamental component required for active power transmission. Its basic compensation relationship is expressed as: ; ; ; In the formula, This represents the instantaneous value of the power supply side voltage of the j-th feeder; This represents the instantaneous value of the series compensation voltage of the j-th feeder; This represents the instantaneous value of the load-side voltage of the j-th feeder; This indicates the commanded value for series compensation voltage; This indicates the rated positive sequence fundamental reference value of the load-side voltage; This represents the instantaneous value of the current on the upstream power grid side; This represents the instantaneous value of the low-voltage common bus load current; This indicates the instantaneous value of the common parallel compensation current; Indicates the command value of the common parallel compensation current; This represents the desired reference value for the positive-sequence fundamental current on the upstream power grid side; As can be seen from the above relationship, the series unit mainly manages the feeder voltage quality, while the common parallel unit mainly manages the common bus current quality. The two types of compensation units exchange active power through the common DC bus.

[0055] The common DC bus is equivalent to a capacitor. Its energy storage is: ; In the formula, This represents the energy stored in the equivalent capacitance of the common DC bus. This represents the equivalent capacitance of the common DC bus. This represents the actual value of the common DC bus voltage; Assuming that the power injected into the common DC bus by photovoltaic, battery energy storage, and supercapacitors is positive, and the power absorbed from the common DC bus by charging loads, series compensation units, and common parallel compensation units is positive, then the instantaneous power balance equation of the common DC bus is: ; In the formula, N represents the number of feeders; This represents the rate of change of the DC bus voltage with respect to time. This indicates the power injected by the photovoltaic unit into the DC bus; This indicates the power exchanged between the battery energy storage and the DC bus; This indicates the power exchanged between the supercapacitor and the DC bus; This indicates the power absorbed by the charging load from the DC bus; Indicates the first The active power exchanged between the feeder series compensation unit and the DC bus; This indicates the active power exchanged between the common parallel compensation unit and the DC bus; This indicates the power loss of each converter and line.

[0056] When the right-hand side of the equation is positive, the DC bus voltage increases; when the right-hand side is negative, the DC bus voltage decreases. Therefore, the essence of stabilizing the common DC bus voltage is to make the algebraic sum of the power at each port approach zero. Hybrid energy storage handles both rapid and sustained power deficits, while the common parallel compensation unit P0 adjusts its active current component according to the remaining power deviation. The two coordinate according to the principle of "hybrid energy storage priority, P0 surplus balance," avoiding simultaneous competition among multiple DC voltage control loops.

[0057] (5) Hybrid energy storage state evolution and multi-timescale power allocation The positive direction of power is defined as the discharge of energy from battery storage and supercapacitors to the common DC bus. ; In the formula, Indicates energy storage unit The power exchanged with the DC bus is in the positive direction of discharge; It represents the discharge power component, which is always non-negative, and is greater than zero only during discharge; It represents the charging power component, which is always non-negative, and is greater than zero only when charging; Considering charging and discharging efficiency, the state-of-charge evolution relationship within the discrete control period is as follows: ; ; In the formula, , They represent the first , No. Control cycle battery energy storage state of charge; , They represent the first , No. Controlling the state of charge of the supercapacitor during the control cycle; Indicates the duration of the discrete control cycle; , These represent the rated available energy of battery storage and supercapacitors, respectively. , They represent the first The discharge power components of cyclic batteries and supercapacitors; , They represent the first The charging power components of cycle batteries and supercapacitors; , These represent the discharge efficiency of the battery and the supercapacitor, respectively. , These represent the charging efficiency of the battery and the supercapacitor, respectively.

[0058] The aforementioned state equation is used to predict the state of charge in the next cycle during optimization, and together with the upper and lower limits of the state of charge, it helps prevent overcharging and over-discharging.

[0059] To enable battery storage to handle low-frequency continuous power and supercapacitors to handle high-frequency instantaneous power, the low-pass filter stage is explicitly represented as: ; ; In the formula, Indicates the power distribution cutoff angular frequency. The selection should be lower than the main response frequency band of the supercapacitor and higher than the allowable slow power conversion frequency band of the battery, and should be adjusted in combination with the battery power ramp rate, the remaining energy of the supercapacitor and the state of charge margin. This represents the transfer function of a first-order low-pass filter. Represents the complex frequency variable of the Laplace transform; This indicates a power deficit command for the common DC bus. This indicates the power command allocated to battery energy storage; This indicates the power command allocated to the supercapacitor; This represents an equivalent high-pass filter stage, which extracts high-frequency power components. This reduces the number of times the battery needs to track high-frequency power fluctuations, thus reducing battery current surges.

[0060] (6) Normalized multi-objective optimization, constraints and rolling solution mechanism To avoid scale imbalance caused by directly weighting indices with different dimensions such as voltage, harmonics, reactive power, three-phase imbalance, DC bus voltage, and state of charge, this embodiment uses limit values ​​or allowable deviations for normalization. Each index item can be expressed as: ; ; ; ; ; In the formula, The voltage deviation index item is the normalized sum of squares of the voltage deviation of each feeder. Indicates the first The deviation of the load-side voltage of a feeder from its rated value; Indicates the voltage tolerance limit Harmonic distortion index; Indicates the first Total harmonic distortion of the feeder; This indicates the permissible limit for total harmonic distortion (THD). This indicates the reactive power indicator item; This indicates the reactive power / reactive power deficit of the common bus (upstream power grid side); Indicates the permissible limit for reactive power; This indicates the three-phase imbalance index item; Indicates the degree of three-phase voltage imbalance; This indicates the permissible limit for voltage unbalance. This indicates the DC bus voltage deviation index item; This indicates the reference value for the DC bus voltage; Indicates the allowable deviation limit of DC bus voltage; The indicator representing the state of charge retention is the normalized sum of squares of the deviation of the battery and supercapacitor's SOC from the reference value. , These represent the permissible deviations in the state of charge of batteries and supercapacitors, respectively. , The decision vectors are composed of the battery and supercapacitor state of charge reference values, common parallel compensation current, photovoltaic power, battery power, supercapacitor power, and charging load regulation, respectively. ; In the formula, Indicates the first Decision vector of the control cycle, superscript Indicates vector transpose; This indicates a series compensation voltage command, covering... Voltage command for the series compensation unit of the feeder line; Indicates a command for common parallel compensation current; Indicates photovoltaic power command; Indicates battery energy storage power command; Indicates the supercapacitor power command; This indicates a charging load adjustment command, which is the schedulable power increment relative to the original charging demand. In one implementation, to suppress sudden changes in instructions between adjacent control cycles, an instruction change rate penalty term is added to the original synthesis objective function, resulting in: ; In the formula, Represent the overall objective function; Indicates the index item number, Corresponding in sequence , , , , , ; Indicates the first The weight coefficients of the indicators satisfy the following conditions: and The priority is set according to factors such as voltage quality, harmonic control, and energy storage safety. Indicates the instruction smoothing coefficient. Adjust the strength of the penalty term for the rate of change of the instruction; The vector 2 norm (Euclidean norm); It represents the difference between decision vectors of adjacent control cycles, and its squared term is used to suppress instruction abrupt changes; The weights are set according to priorities such as voltage quality of sensitive loads, harmonic control of common busbars, and energy storage safety. After adopting normalized indicators, the weights can reflect the relative importance of each control objective, and are no longer mainly affected by the physical dimensions.

[0061] In addition to the aforementioned constraints on photovoltaic output, energy storage state of charge, charging and discharging power, charging load regulation, and DC bus voltage, the capacity constraints of the series compensation unit and the common parallel compensation unit can be further written as: ; ; In the formula, , They represent the first The active and reactive power output of the feeder series compensation unit; Indicates the first Rated capacity of the feeder series compensation unit; , These represent the active and reactive power outputs of the common parallel compensation unit, respectively. This indicates the apparent power output of the common parallel compensation unit; This indicates the rated capacity of the common parallel compensation unit.

[0062] Meanwhile, the power balance equation of the common DC bus and the energy storage state of charge evolution equation are used as equality constraints to ensure that the optimized power command simultaneously meets power quality requirements and energy feasibility. If an energy storage unit reaches its state of charge or power boundary, the unallocated power will be taken over by another energy storage unit, the common parallel compensation unit, or the adjustable capacity of the charging load according to the remaining margin.

[0063] In the k-th control cycle, the collaborative optimization module takes the current state x(k) and the disturbance d(k) as inputs, and obtains the optimal command within the feasible region Ω. The feedback update module then obtains the state for the next cycle. The rolling solution relationship is as follows: ; ; In the formula, Indicates the first The optimal decision vector obtained from the control cycle; This indicates that the objective function The value of the decision variable that achieves its minimum; The optimal feasible region is composed of inequality constraints such as photovoltaic output, SOC, charging and discharging power, load regulation, and DC bus voltage, as well as equation constraints such as DC bus power balance equation and SOC evolution equation. , They represent the first , No. The system state vector of the period (a collection of state variables such as feeder voltage and current, DC bus voltage, and energy storage SOC); The system state evolution mapping is represented by the state transition relationship consisting of the DC bus power balance equation and the energy storage charging state evolution equation. Indicates the first The periodic disturbance vector includes uncontrollable external inputs such as photovoltaic power output fluctuations, charging load steps, and feeder disturbances.

[0064] The above process is re-solved in each control cycle, enabling the commands to be dynamically corrected according to photovoltaic fluctuations, charging load steps, and feeder disturbances. The equipment execution layer uses a non-ideal proportional resonant controller to achieve finite gain tracking of the fundamental and selected harmonics, and its transfer function can be expressed as: ; In the formula, This represents the transfer function of a non-ideal (finite bandwidth) proportional resonant controller, used for tracking control of the fundamental wave and selected harmonics; This represents the scaling factor, which determines the fundamental gain and control response speed across the entire frequency band; It represents the resonance coefficient, which determines the magnitude of the gain at the resonance peak at the target frequency; Indicates the resonant bandwidth; This indicates the target angular frequency, corresponding to the fundamental frequency or selected harmonic angular frequency to be tracked. .

[0065] The finite bandwidth form can avoid the infinite gain of the ideal proportional resonant controller at the target frequency and improve the system's adaptability to frequency offset and parameter errors.

[0066] For the stability of the common DC bus voltage, let Choose an energy-type function: ; Near the rated operating point, when the power regulation loop ensures that the net power deviation on the DC side meets the following requirements:

[0067] At that time, from the power balance equation of the common DC bus, we can obtain: ; In the above formula, The selected energy-type (Lyapunov) function represents the "error energy" stored in the voltage error and is always non-negative; This represents the DC bus voltage error, i.e., the actual voltage. Compared with reference value difference; This represents the net power deviation on the DC side, which is the corrected power generated by the power regulation loop according to the error ratio. Indicates the gain coefficient of the power regulation loop ( The convergence rate of the error is determined by the convergence rate of the error. This represents the time derivative of the energy function; This indicates that the error energy is monotonically non-increasing.

[0068] Therefore, in the local operating region where the energy storage power, converter capacity, and state of charge constraints are not saturated, the common DC bus voltage error can converge to zero; when the constraints reach the boundary, the system maintains bounded operation through the redistribution of remaining power and rolling correction in the next control cycle.

[0069] (iv) Simulation experiments and effect verification: To verify the effectiveness of this invention, a quasi-circuit-level average value simulation model of a low-voltage multi-feeder transformer area with photovoltaic-storage-charging-UPQC was established. The model includes the upstream power grid, a 10kV / 0.4kV distribution transformer, a low-voltage common bus, three low-voltage feeders, a series compensation unit, a common parallel compensation unit, a photovoltaic unit, a hybrid energy storage unit, and an electric vehicle charging load. Two operating modes were compared in the simulation: Mode A was the no-cooperative-control mode, where series compensation, parallel compensation, and photovoltaic-storage-charging cooperative control were not activated; Mode B was the photovoltaic-storage-charging-UPQC cooperative control mode with this invention enabled. The simulation conditions were set as follows: Feeder 1 experienced a 20% voltage dip between 0.20s and 0.35s; Feeder 2 was connected to a nonlinear load containing 5th, 7th, and 11th harmonics, and a three-phase unbalanced load was set; Feeder 3 was connected to an electric vehicle charging load, with step changes in charging power at 0.40s and 0.70s; photovoltaic output fluctuated at 0.30s and 0.60s; the simulation time was 1s. Simulation results are as follows Figures 7-10 As shown: 1) Voltage sag compensation effect: In mode A, the minimum voltage on the load side of feeder 1 drops to 184.75V, and there is a significant risk of undervoltage for sensitive and important loads; in mode B, the load side voltage recovers to 230.94V, which is close to the rated phase voltage.

[0070] 2) Harmonic mitigation effect: The average total harmonic distortion rate of the low-voltage common bus is 15.26% under mode A; under mode B, it decreases to 1.22%, of which the 5th harmonic decreases from 12.00% to 0.96%, the 7th harmonic decreases from 8.00% to 0.64%, and the 11th harmonic decreases from 5.00% to 0.40%.

[0071] 3) Effect of three-phase imbalance treatment: The three-phase voltage imbalance was reduced from 5.70% in Mode A to 0.68% in Mode B.

[0072] 4) Reactive power compensation effect: The power factor of the low-voltage common bus is improved from 0.957 in mode A to 0.998 in mode B.

[0073] 5) Stabilization effect of common DC bus voltage: The maximum voltage deviation of the common DC bus decreased from 77.46V in mode A to 2.00V in mode B, and the peak-to-peak voltage of the common DC bus decreased from 34.30V to 2.21V during the charging surge.

[0074] 6) Power Coordination and Energy Storage Safety: In Mode B, when the photovoltaic output increases, it prioritizes supporting the common DC bus and load demand. When the charging load power suddenly increases or the photovoltaic output decreases, the supercapacitor quickly releases power and the battery energy storage then takes on continuous support. Throughout the simulation, the state of charge of the battery energy storage and the supercapacitor did not exceed the limit.

[0075] 7) Overall optimization effect: The overall objective function J decreased from 0.3735 in mode A to 0.0445 in mode B, indicating that the system has been significantly improved in multiple objectives such as voltage quality, harmonic control, reactive power compensation, three-phase imbalance control, voltage stability of the common DC bus and coordinated operation of energy storage.

[0076] (v) Extended and alternative implementation methods: a: The above embodiment takes three feeders as an example, but the present invention is also applicable to transformer areas with two, four or more feeders. It only requires the addition of series compensation units connected in series to each feeder and the expansion of the dimension of the transformer area's global state vector. b: In addition to T-NPC three-level converter topology, diode-clamped three-level converter topology or traditional two-level converter topology can also be used, with only the compensation accuracy being different; c: The proportional resonant control of the voltage outer loop and the current outer loop can be replaced by proportional integral control or repetitive control; d: The area-level collaborative controller can be implemented using control hardware composed of digital signal processors (DSPs) and field programmable gate arrays (FPGAs). The data acquisition / communication module can use CAN bus or industrial Ethernet to realize the transmission of status variables and commands of each unit. e: The solution of the multi-objective optimization model can be achieved by quadratic programming, model predictive control or intelligent optimization algorithm, all of which are within the scope of protection of this invention.

Claims

1. A method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC in multi-feeder transformer areas, characterized in that... Includes the following steps: S1: Collect the voltage and current of each feeder, the voltage of the common DC bus, photovoltaic output, charging load power, and the state of charge of the hybrid energy storage unit to construct the global state vector of the transformer area; S2: Calculate various power quality indicators based on the global state vector of the transformer area. The power quality indicators include voltage deviation, total harmonic distortion rate of current and three-phase voltage imbalance of each feeder, as well as reactive power, DC bus voltage deviation and energy storage state of charge. S3: Compare each of the power quality indicators with the corresponding set limits to determine whether any limit has been exceeded; if none of the limits have been exceeded, maintain the current operating state and return to S1; S4: If any of the power quality indicators exceeds the limit, a multi-objective optimization model is established with each of the power quality indicators as the optimization objective, and the multi-objective optimization model is solved under the constraints to obtain the series compensation voltage command of each series compensation unit, the compensation current command of the common parallel compensation unit, the photovoltaic power command, the hybrid energy storage power command, and the charging load adjustment command. S5: Send each instruction to the corresponding series compensation unit, common parallel compensation unit, and the converters of the photovoltaic array, hybrid energy storage unit and charging pile for execution, so that each series compensation unit injects compensation voltage into the corresponding feeder, the common parallel compensation unit injects compensation current into the low-voltage common bus, and the hybrid energy storage unit releases or absorbs power through the common DC bus. S6: Collect the running status feedback after execution, update the global status vector of the transformer area, and return to S1 to enter the next control cycle to realize rolling optimization control.

2. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 1, characterized in that: In step S1, the hybrid energy storage unit includes battery energy storage and a supercapacitor, and the battery energy storage and the supercapacitor are respectively connected to a common DC bus via their respective bidirectional DC / DC converters; step S1 includes: S1.1: In the k-th control cycle, the voltage of the three feeders is synchronously acquired. , , and current , , Total harmonic distortion of current in the three feeders , , and three-phase voltage imbalance And collect the voltage of the common DC bus. Photovoltaic power output Charging load power The state of charge (SOC) of the battery energy storage. and the state of charge of the supercapacitor ; S1.2: Using the state variables collected in S1.1 as elements, construct the global state vector of the transformer area in a fixed arrangement order: ； In the formula, Let be the global state vector of the transformer area in the k-th control cycle. , , These represent the voltages of the three feeders. , , These represent the currents of the three feeders. , , These are the total harmonic distortion rates of the currents of the three feeders. This refers to the three-phase voltage imbalance. The voltage of the common DC bus. Contribute to photovoltaic power For charging load power, , These represent the state of charge of battery energy storage and supercapacitors, respectively.

3. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 2, characterized in that: S2 includes: 2.1: Perform fundamental and harmonic decomposition on the voltage and current of each feeder in the global state vector of the transformer area, and perform symmetrical component decomposition on the fundamental voltage obtained by decomposition to obtain the effective value of the fundamental voltage, the effective value of the fundamental current, the effective value of each harmonic current, as well as the positive sequence voltage component and the negative sequence voltage component of each feeder. 2.2: Based on the fundamental voltage RMS value obtained in 2.1, calculate the voltage deviation index of each feeder: ； In the formula, For the first Voltage deviation index of the feeder line For the first The fundamental voltage RMS value of the feeder. Rated voltage, Here are the feeder numbers, i = 1, 2, 3; 2.3: Based on the RMS value of the fundamental current and the RMS values ​​of each harmonic current obtained in 2.1, calculate the total harmonic distortion rate of the current in each feeder: ； In the formula, For the first Total harmonic distortion of current in a feeder line. For the first The fundamental current RMS value of the feeder For the first The effective value of the h-th harmonic current of the feeder, where H is the highest harmonic order involved in the calculation; S2.4: Based on the positive-sequence and negative-sequence voltage components obtained in 2.1, calculate the three-phase voltage imbalance: ； In the formula, It is the positive sequence voltage component. It is the negative sequence voltage component.

4. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 3, characterized in that: S3 includes: S3.1: The voltage deviation index of each feeder calculated in S2 Total harmonic distortion of current Three-phase voltage imbalance And reactive power and DC bus voltage deviation are compared with their respective set limits; S3.2: If none of the comparison results exceed the limit, the power quality of the transformer area is determined to be normal, the current operating status is maintained, and the process returns to S1 to continue status monitoring. S3.3: If any comparison result exceeds the limit, it is determined that a power quality exceeding the limit event has occurred, and the multi-objective optimization model established in S4 is entered for solution.

5. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 4, characterized in that: S4 includes: S4.1: Based on the power quality indicators calculated in S2, construct voltage deviation index items respectively. Harmonic distortion index Reactive power compensation index item Three-phase imbalance index item DC bus voltage deviation index item and energy storage state of charge deviation index ; S4.2: Assign corresponding weights to each indicator item constructed in S4.1 and perform a weighted summation to construct a multi-objective optimization objective function: ； In the formula, J is the comprehensive objective function. ~ These are the weighting coefficients for each indicator item; S4.3: Using the minimization of the comprehensive objective function J constructed in S4.2 as the optimization objective, the various instructions described in S4 are obtained by solving the problem.

6. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 5, characterized in that: In step S4.3, the constraints for solving the multi-objective optimization model include: (1) UPQC capacity constraint: The compensation power output by each series compensation unit and the common parallel compensation unit shall not exceed their respective rated capacity; (2) Photovoltaic output constraint: The photovoltaic power command shall not exceed the current maximum power output of the photovoltaic array; (3) Energy storage state of charge constraints: ,and In the formula, , These are the lower and upper limits of the battery's state of charge, respectively. , These are the lower and upper limits of the state of charge of a supercapacitor, respectively. (4) Charge and discharge power constraints: ,and ; In the formula, , These represent the actual charge and discharge power of battery energy storage and supercapacitors, respectively. , These are the maximum charging and discharging power of battery energy storage and supercapacitors, respectively. (5) Charging load adjustment constraint: The adjustment amount corresponding to the charging load adjustment command shall not exceed the adjustable power range of the charging pile. (6) DC bus voltage constraint: ; In the formula, , These are the lower and upper limits of the allowable voltage for the common DC bus, respectively.

7. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 6, characterized in that: S5 includes: S5.1: Based on the series compensation voltage command for each feeder, generate the compensation voltage reference value for each series compensation unit. , , , , , These are the compensation voltage reference values ​​for the series compensation units corresponding to the three feeders. The deviation between each compensation voltage reference value and the actual voltage of the corresponding feeder is controlled by voltage outer loop proportional resonance (PR) and then pulse width modulation (PWM) is performed to generate the drive signal for each series compensation unit, which drives each series compensation unit to inject series compensation voltage into the corresponding feeder. S5.2: Generate compensation reference values ​​for harmonic current, reactive current and unbalanced current of the common parallel compensation unit according to the compensation current command. After controlling the current outer loop proportional resonance (PR) with the deviation between the compensation reference value and the actual output current of the common parallel compensation unit, pulse width modulation (PWM) is performed to generate the drive signal of the common parallel compensation unit, which drives the common parallel compensation unit to inject compensation current into the low voltage common bus. S5.3: Based on the active power required for the series compensation in S5.1 and the parallel compensation in S5.2, as well as the photovoltaic power command, synthesize the power demand of the common DC bus, and control the hybrid energy storage unit to release or absorb power through the common DC bus to maintain the voltage stability of the common DC bus.

8. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 7, characterized in that: S5.3 includes: S5.3.1: The reference value of the common DC bus voltage Compared with actual value The deviation between them is controlled by proportional-integral (PI) control and combined with the active power required for series compensation in S5.1 and parallel compensation in S5.2, as well as the feedforward component of the photovoltaic power command, to obtain the power demand of the common DC bus. ; S5.3.2: Power requirements for the common DC bus obtained from S5.3.1 Perform low-pass filtering and use the low-frequency continuous power component as the power command for battery energy storage: ； In the formula, For battery energy storage power command, This indicates a low-pass filter stage. The superscript "*" indicates a command value, used to distinguish it from the actual value. S5.3.3: The power requirement Power command for battery energy storage The difference serves as the power command for the supercapacitor, enabling the battery energy storage to handle the low-frequency continuous power component and the supercapacitor to handle the high-frequency instantaneous power component. ； In the formula, For supercapacitor power commands; The above two equations satisfy: ； S5.3.4: Based on the battery's state of charge State of charge of supercapacitors and the charge / discharge power limit for the battery energy storage power command Supercapacitor Power Command Constraint corrections are performed, and the corrected power commands are converted into the duty cycles of the bidirectional DC / DC converters on the battery storage side. Duty cycle of the bidirectional DC / DC converter on the supercapacitor side This drives the corresponding bidirectional DC / DC converter to work.

9. The method for global collaborative control and power quality management of photovoltaic-storage-charging-UPQC for multi-feeder transformer substations according to claim 8, characterized in that: S6 includes: S6.1: After the execution of each instruction in S5, re-collect the operating status of each feeder, multi-feeder UPQC device, photovoltaic array, hybrid energy storage unit and charging pile; S6.2: Update the global status vector of the transformer area based on the operating status re-collected in S6.1, and obtain the updated global status vector of the transformer area. ,in, This is the global state vector of the transformer area during the (k+1)th control cycle; S6.3: The global state vector of the transformer area in the (k+1)th control cycle Returning to S1 as the initial state for the next control cycle, S1~S6 are executed cyclically to achieve rolling optimization control with continuous monitoring and dynamic correction.

10. A global collaborative control and power quality management system for photovoltaic-storage-charging-UPQC in multi-feeder transformer areas, characterized in that... The system includes: Multi-feeder unified power quality conditioner (UPQC) device, common DC bus, photovoltaic array, hybrid energy storage unit, charging pile, and substation-level collaborative controller; among which: The multi-feeder unified power quality conditioner (UPQC) device includes multiple series compensation units connected in series in each feeder of the multi-feeder area, and a common parallel compensation unit connected in parallel to the low-voltage common bus of the multi-feeder area. The DC side of each series compensation unit and the common parallel compensation unit are connected to the common DC bus. The photovoltaic array is connected to the common DC bus via a DC / DC converter, the hybrid energy storage unit is connected to the common DC bus via a bidirectional DC / DC converter, and the charging pile is connected to the common DC bus via a DC / DC converter. The district-level collaborative controller includes: The state perception module is used to collect the voltage and current of each feeder, the voltage of the common DC bus, photovoltaic output, charging load power and energy storage charge status to construct a global state vector of the transformer area. The indicator evaluation module is used to calculate various power quality indicators based on the global state vector of the transformer area. The power quality indicators include voltage deviation, total harmonic distortion rate of current and three-phase voltage imbalance of each feeder, as well as reactive power, DC bus voltage deviation and energy storage state of charge. The limit-breaking detection module is used to compare each power quality indicator with the corresponding set limit value to determine whether a limit-breaking has occurred. If no limit-breaking has occurred, the current operating state is maintained. The collaborative optimization module is used to establish a multi-objective optimization model with each power quality index as the optimization objective when any power quality index exceeds the limit, and solve the multi-objective optimization model under constraints to obtain the series compensation voltage command of each series compensation unit, the compensation current command of the common parallel compensation unit, the photovoltaic power command, the hybrid energy storage power command, and the charging load adjustment command. The instruction distribution module is used to send each instruction to the corresponding series compensation unit, the common parallel compensation unit, and the converters of the photovoltaic array, the hybrid energy storage unit and the charging pile for execution, so that each series compensation unit injects compensation voltage into the corresponding feeder, the common parallel compensation unit injects compensation current into the low-voltage common bus, and the hybrid energy storage unit releases or absorbs power through the common DC bus. The feedback update module is used to collect the running status feedback after execution, update the global state vector of the transformer area, and trigger the state perception module to enter the next control cycle to realize rolling optimization control.

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