A photovoltaic power generation station area power quality optimization method based on a three-phase HDT system

Abstract

The application discloses a photovoltaic power generation substation power quality optimization method based on a three-phase HDT system, and relates to the technical field of power quality optimization of distribution networks.The method comprises the following steps: a three-phase hybrid distribution transformer system composed of a standard transformer, a power electronic converter, a bypass switch and an LC filter is constructed; based on the operation characteristics of the three-phase hybrid distribution transformer system, the voltage amplitude adjustment capability and the harmonic compensation capability of the three-phase hybrid distribution transformer system power supply are simulated and tested by using simulation technology, so that the voltage regulation capability of the three-phase hybrid distribution transformer system is verified; and the voltage regulation capability of the three-phase hybrid distribution transformer system is combined, and the power quality of a photovoltaic power generation substation is optimized by the three-phase hybrid distribution transformer system.The application verifies that the three-phase HDT system has good voltage amplitude and phase compensation capability and harmonic compensation capability, and lays a good foundation for the application of the three-phase HDT system in the power quality optimization of photovoltaic power generation substations.

Description

Technical Field

[0001] This invention relates to the field of power quality optimization technology for distribution networks, and more specifically, to a method for optimizing power quality in photovoltaic power generation areas based on a three-phase HDT system. Background Technology

[0002] With rapid global economic growth, continuously rising energy demand, and the gradual depletion of traditional energy sources, clean and renewable energy has gradually become a focus of attention, aiming to promote sustainable development by transforming the energy structure. As a clean and renewable energy source, solar energy, with its inexhaustible, low-cost, and pollution-free characteristics, demonstrates unparalleled advantages among many new energy sources. In recent years, photovoltaic (PV) power generation has developed rapidly. However, among the many challenges facing PV power generation technology, the impact of grid-connected PV systems on the power grid remains a crucial issue that urgently needs to be addressed.

[0003] Power quality issues caused by distributed photovoltaic (PV) grid connection are gradually emerging, with harmonics, voltage deviations, power system frequency deviations, voltage fluctuations, and flicker becoming increasingly prominent. Harmonic issues: PV inverters contain numerous power electronic components, inevitably generating harmonics during the conversion of direct current (DC) to alternating current (AC), causing harmonic pollution to the power grid. This is particularly pronounced when the inverter is under light load; when the output power is below 20% of the rated value, the total harmonic distortion (THD) of the current may exceed 5%. If multiple harmonic sources exist in the grid, power resonance caused by higher-order harmonics may also occur. Therefore, in addition to ensuring the reliability of the inverter, it is also necessary to reduce the total harmonic content of the current in the line.

[0004] Voltage Issues: The output power of photovoltaic (PV) power generation is susceptible to fluctuations due to factors such as sunlight intensity and weather conditions. These fluctuations can lead to voltage instability, manifesting as frequent voltage swings or flicker. Especially in areas with a high proportion of PV power generation, grid voltage fluctuations can affect the normal operation of user equipment. Furthermore, when a PV system is connected to the grid, sudden changes in sunlight (such as cloud cover or weather changes) can cause a significant drop in PV power generation, resulting in a temporary voltage drop. This voltage dip can impact the grid and user equipment, particularly in situations with a high proportion of PV power generation and low load.

[0005] How to reduce the impact of distributed photovoltaic grid connection on the power quality of the distribution network and improve the distribution network's ability to absorb photovoltaic power generation has become an important research topic for scholars at home and abroad. The current power quality indicators are summarized in Table 1.

[0006] Table 1. Formulas for Calculating Power Quality

[0007]

[0008] In Table 1, U x U is the effective value of the node voltage. N For the rated voltage, U a and U b These represent the adjacent peak and trough voltages on the effective voltage curve, U. y U is the effective value of the fundamental component of the phase voltage. m U is the effective voltage value of the m-th harmonic component, where M is the maximum harmonic order. n U is the effective value of the negative sequence fundamental component of the voltage. p This represents the effective value of the positive sequence fundamental component of the voltage.

[0009] The key indicators of the power quality standards are shown in Table 2.

[0010] Table 2 Power Quality Standards

[0011]

[0012] Total harmonic distortion (THD) refers to the percentage of total harmonic distortion relative to the fundamental frequency. Currently, most solutions to power quality problems caused by distributed photovoltaic grid connection are sought at either the distribution network or power source levels.

[0013] On the distribution network side: (1) Add harmonic elimination equipment to the power grid to reduce the harmonic content in the power grid; (2) Adjusting the transformer tap can change the reactive power distribution in the system and improve the voltage deviation caused by uneven reactive power distribution; (3) Static var compensator (SVC), static synchronous compensator (STATCOM) and other reactive power compensation equipment; (4) Reasonably install distributed photovoltaic and other distributed power sources, which can effectively improve the voltage drop problem caused by excessive power transmission distance.

[0014] On the power supply side: (1) Research grid-connected inverters that improve power quality, such as multi-functional grid-connected inverters that combine grid connection of renewable energy and power quality management functions; (2) Add active filters to reduce the harmonic content in the system by injecting reverse harmonics; (3) Research short-term power prediction methods for distributed photovoltaics to improve prediction accuracy, adjust scheduling plans in a timely and reasonable manner, effectively reduce the adverse effects of distributed photovoltaic grid connection on the power grid, and ensure the safe and stable operation of the power grid.

[0015] Optimizing power quality in photovoltaic (PV) distribution areas primarily involves using a series of technical means and management measures to improve the impact of PV power generation systems on power quality during grid-connected operation, particularly in the distribution area, to ensure grid stability and that power quality meets required standards. The volatility and intermittency of PV power generation can adversely affect power quality, with common issues including voltage fluctuations, frequency fluctuations, and harmonic pollution. Therefore, the main objective of optimizing power quality in PV distribution areas is to mitigate these negative impacts and enhance the stability and reliability of power supply.

[0016] There are currently no effective solutions to the problems in the relevant technologies. Summary of the Invention

[0017] To address the problems in related technologies, this invention proposes a method for optimizing power quality in photovoltaic power generation areas based on a three-phase HDT system, in order to overcome the aforementioned technical problems existing in existing related technologies.

[0018] Therefore, the specific technical solution adopted by the present invention is as follows:

[0019] A method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system, the method comprising:

[0020] Construct a three-phase hybrid distribution transformer system consisting of a standard transformer, a power electronic converter, a bypass switch, and an LC filter;

[0021] Based on the operating characteristics of a three-phase hybrid distribution transformer system, simulation technology is used to simulate and test the voltage amplitude regulation capability and harmonic compensation capability of the power supply of the three-phase hybrid distribution transformer system, so as to verify the voltage regulation capability of the three-phase hybrid distribution transformer system.

[0022] By combining the voltage regulation capability of the three-phase hybrid distribution transformer system, the power quality of the photovoltaic power generation area can be optimized through the three-phase hybrid distribution transformer system.

[0023] Preferably, based on the operating characteristics of the three-phase hybrid distribution transformer system, simulation technology is used to simulate and test the voltage amplitude regulation capability and harmonic compensation capability of the power supply of the three-phase hybrid distribution transformer system, in order to verify the voltage regulation capability of the three-phase hybrid distribution transformer system, including:

[0024] The operating characteristics of a three-phase hybrid distribution transformer system are analyzed, including its working principle and voltage regulation characteristics.

[0025] A simulation model of a three-phase hybrid distribution transformer system was built using simulation software. Simulation parameters were set, and simulation scenarios for voltage fluctuation, voltage phase change, and voltage odd harmonics were constructed based on the operating characteristics of the three-phase hybrid distribution transformer system.

[0026] The voltage amplitude regulation capability and harmonic compensation capability of the three-phase hybrid distribution transformer system were simulated and tested in the simulation scenario using a simulation model to verify the voltage regulation capability of the three-phase hybrid distribution transformer system.

[0027] Preferably, the analysis of the operating characteristics of a three-phase hybrid distribution transformer system includes:

[0028] Calculate the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and analyze the voltage fluctuation of the power supply of the three-phase hybrid distribution transformer system based on the voltage difference;

[0029] Compensation for voltage fluctuations in a three-phase hybrid distribution transformer system is achieved through a power electronic converter, specifically including:

[0030] The voltage amplitude and voltage phase of the power supply of the three-phase hybrid distribution transformer system are dually regulated by a power electronic converter; the secondary load voltage of the three-phase hybrid distribution transformer system is regulated based on the duty cycle of the power electronic converter.

[0031] Preferably, calculating the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and analyzing the voltage fluctuation of the power supply of the three-phase hybrid distribution transformer system based on the voltage difference, includes:

[0032] A three-phase hybrid distribution transformer system is used to regulate the power flow of a photovoltaic power generation area containing k nodes, and photovoltaic power is injected into node j.

[0033] Based on the voltage of node n before node j of the three-phase hybrid distribution transformer system and the voltage of node n before node j where distributed photovoltaic power is not connected, calculate the voltage difference between node j and adjacent node j-1 in the three-phase hybrid distribution transformer system.

[0034] When the voltage difference is greater than zero, it means that the active power consumed by the load is greater than the active power injected by the distributed photovoltaic system; when the voltage difference is less than zero, it means that the active power consumed by the load is less than the active power injected by the distributed photovoltaic system.

[0035] Preferably, the dual regulation of voltage amplitude and voltage phase of the power supply of the three-phase hybrid distribution transformer system via a power electronic converter includes:

[0036] Based on the voltage relationship measured by the power supply of a three-phase hybrid distribution transformer system, the compensation voltage of the power electronic converter under voltage fluctuation conditions is analyzed.

[0037] Based on the voltage fluctuation of one phase, the duty cycle status of the power electronic converters of the other two phases is determined. When the duty cycles of the power electronic converters of the other two phases are the same, the three-phase hybrid distribution transformer system performs voltage amplitude regulation. When the duty cycles of the power electronic converters of the other two phases are different, the three-phase hybrid distribution transformer system performs dual regulation of voltage amplitude and voltage phase.

[0038] Based on the phase difference between each phase in a three-phase hybrid distribution transformer system, the relationship between the flexible transformation ratio and voltage phase of the three-phase hybrid distribution transformer system is constructed to meet the requirements of load flexible regulation.

[0039] Preferably, voltage amplitude regulation is performed through a three-phase hybrid distribution transformer system, including:

[0040] When the voltage on the power supply side of the three-phase hybrid distribution transformer system fluctuates, the actual value of the primary winding voltage of the three-phase HDT system is obtained.

[0041] The effective value of the primary winding voltage of the three-phase hybrid distribution transformer system is calculated based on the actual value, and the error between the effective value and the preset reference value is compensated by a proportional-integral controller.

[0042] The drive signal of the proportional-integral controller is transmitted to the power electronic converter, and after being regulated by the power electronic converter, it is transmitted to the power supply side to achieve voltage regulation.

[0043] Preferably, before setting the simulation parameters, the simulation model of the three-phase hybrid distribution transformer system is built using simulation software, the following steps are also included:

[0044] The thermal analysis characteristics of a three-phase hybrid distribution transformer system are obtained, and a balance parameter combination between the operating characteristics and the thermal analysis characteristics is constructed.

[0045] Taking the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, the combination of balance parameters is used as the input of a pre-constructed electro-thermal balance coupling model. The electro-thermal balance coupling model is solved to obtain the optimal balance parameters.

[0046] Using the optimal balance parameter as a pre-regulation factor, the simulation parameters are dynamically adjusted through the pre-regulation factor after the simulation model of the three-phase hybrid distribution transformer system is built.

[0047] Preferably, taking the optimal voltage regulation capability of the three-phase hybrid distribution transformer system under thermal response as the optimization objective, the combination of balance parameters is used as the input to a pre-constructed electro-thermal balance coupling model. Solving the electro-thermal balance coupling model yields the optimal balance parameters, including:

[0048] With the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, an electro-thermal coupling constraint condition is constructed.

[0049] We introduce the dual problem of the electro-thermal equilibrium coupling model using Lagrange multipliers, and decompose the dual problem into a voltage regulation subproblem and a thermal response subproblem.

[0050] The voltage regulation subproblem and the thermal response subproblem are solved iteratively using local algorithms and heuristic search algorithms respectively, and the optimal solutions are integrated to obtain the optimal equilibrium parameters.

[0051] Preferably, solving the heat response subproblem using a heuristic search algorithm includes:

[0052] Construct a neighborhood structure for heuristic search, perform thermal allocation on nodes with excessive heat in the electro-thermal balance coupling model, and generate several candidate solutions;

[0053] A scoring function is constructed with the goal of achieving the optimal thermal response, and the scoring function is used to calculate the score of each candidate solution in the neighborhood structure in each iteration.

[0054] If the score of the new solution is greater than or equal to the score of the current solution, the new solution is taken as the current best solution. If the score of the new solution is less than the score of the current solution, the inferior solution is updated with a preset probability to obtain the updated current best solution.

[0055] Stop when the iteration is satisfied, and take the final solution as the optimal solution to the heat response subproblem.

[0056] Preferably, the expression for the flexible turns ratio of a three-phase hybrid distribution transformer system is:

[0057]

[0058] In the formula, n TR n is the turns ratio of the main winding of a three-phase hybrid distribution transformer system. aux n is the turns ratio of the auxiliary winding in a three-phase hybrid distribution transformer system. HDT-A n HDT-B and n HDT-C These represent the flexible transformation ratios of each phase in a three-phase hybrid distribution transformer system, D. a D b and D c These represent the duty cycle per phase of the power electronic converter, e -j120° This indicates that the included angle between two phases of a three-phase hybrid distribution transformer system is -120°, e j120° This indicates that the angle between two phases in a three-phase hybrid distribution transformer system is 120°.

[0059] The beneficial effects of this invention are as follows: This invention constructs a three-phase hybrid distribution transformer system composed of a traditional transformer and a power electronic converter, analyzes its working principle and voltage regulation capability, and conducts simulation tests on the three-phase HDT system, verifying that the three-phase HDT system has good voltage amplitude and phase compensation capability as well as harmonic compensation capability, laying a good foundation for its application in power quality optimization in photovoltaic power generation areas, and thus contributing to the improvement of power quality in the distribution network. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a flowchart of a photovoltaic power generation area power quality optimization method based on a three-phase HDT system according to an embodiment of the present invention;

[0062] Figure 2 This is an injection network diagram of a photovoltaic power generation system in a photovoltaic power generation area power quality optimization method based on a three-phase HDT system according to an embodiment of the present invention.

[0063] Figure 3 This is a topology diagram of a three-phase HDT system for photovoltaic power generation areas in an embodiment of the present invention.

[0064] Figure 4 This is a control strategy diagram of a three-phase HDT system for photovoltaic power generation systems in a photovoltaic power generation area power quality optimization method based on a three-phase HDT system according to an embodiment of the present invention.

[0065] Figure 5 This is a voltage waveform diagram of a three-phase HDT system under voltage dip-surge conditions in a power quality optimization method for a photovoltaic power generation area based on a three-phase HDT system according to an embodiment of the present invention.

[0066] Figure 6 This is a voltage waveform diagram of a three-phase HDT system under voltage surge-dip conditions in a power quality optimization method for a photovoltaic power generation area based on a three-phase HDT system according to an embodiment of the present invention.

[0067] Figure 7 This is a voltage waveform diagram of a three-phase HDT system under voltage phase change in a photovoltaic power generation area power quality optimization method based on a three-phase HDT system according to an embodiment of the present invention.

[0068] Figure 8 This is a voltage waveform diagram of a three-phase HDT system under odd harmonic conditions in a power quality optimization method for photovoltaic power generation areas based on a three-phase HDT system according to an embodiment of the present invention.

[0069] Figure 9 This is a diagram of the IEEE 33-node photovoltaic power generation system in a photovoltaic power generation area power quality optimization method based on a three-phase HDT system according to an embodiment of the present invention.

[0070] Figure 10 This is a diagram showing the maximum and minimum voltage distribution under different control devices in a photovoltaic power generation system, according to an embodiment of the present invention, in a photovoltaic power generation area power quality optimization method based on a three-phase HDT system. Detailed Implementation

[0071] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention.

[0072] According to an embodiment of the present invention, a method for optimizing power quality in photovoltaic power generation areas based on a three-phase HDT system is provided.

[0073] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1 As shown, according to an embodiment of the present invention, a photovoltaic power generation area power quality optimization method based on a three-phase HDT system includes:

[0074] S1. Construct a three-phase hybrid distribution transformer system consisting of a standard transformer, a power electronic converter, a bypass switch, and an LC filter.

[0075] It should be noted that the power quality optimization of photovoltaic power generation areas in this invention is based on the analysis of a three-phase HDT (Hybrid distribution transformer) system. The three-phase HDT system has the characteristics of both a traditional transformer (equivalent to a standard transformer) and a power electronic converter. This system has voltage amplitude and phase adjustment capabilities and harmonic compensation capabilities.

[0076] The three-phase HDT system structure consists of a traditional transformer, a PEC module, a bypass switch, and input / output LC filters. The PEC module is used to compensate for voltage fluctuations on the power supply side of the HDT system.

[0077] Specifically, the three-phase HDT system is a two-phase supported and controlled HDT system. Its PEC module (power electronic converter) has bipolar compensation capability for voltage amplitude and phase, and harmonic compensation capability. That is, taking phase A as an example, when the voltage U on the power supply side of phase A... Sa When fluctuations occur, the PEC modules of phases B and C on the secondary side provide compensation voltage ΔU. bc Adjust the voltage of phase A of the HDT system; additionally, when U Sa When odd harmonics occur, the load-side PEC module can compensate for the harmonics in real time, greatly reducing THD and improving the load-side voltage waveform.

[0078] S2. Based on the operating characteristics of the three-phase hybrid distribution transformer system, simulation technology is used to simulate and test the voltage amplitude regulation capability and harmonic compensation capability of the power supply of the three-phase hybrid distribution transformer system, so as to verify the voltage regulation capability of the three-phase hybrid distribution transformer system.

[0079] It should be noted that the voltage amplitude and phase regulation capability and harmonic compensation capability of the three-phase HDT system were simulated and tested. By conducting voltage surge-drop, voltage drop-surge, voltage phase fluctuation and odd harmonic simulation tests on the power supply side voltage of the system, the results show that the load side voltage waveform of the three-phase HDT system remains basically unchanged under the simulation scenario. This verifies that the three-phase HDT system has good voltage amplitude and phase regulation capability and harmonic compensation capability.

[0080] Based on the operating characteristics of a three-phase hybrid distribution transformer system, simulation technology is used to test the voltage amplitude regulation capability and harmonic compensation capability of the power supply of the three-phase hybrid distribution transformer system, in order to verify the voltage regulation capability of the three-phase hybrid distribution transformer system, including:

[0081] The operating characteristics of a three-phase hybrid distribution transformer system are analyzed, including its working principle and voltage regulation characteristics.

[0082] The analysis of the operating characteristics of a three-phase hybrid distribution transformer system includes:

[0083] Calculate the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and analyze the voltage fluctuation of the power supply of the three-phase hybrid distribution transformer system based on the voltage difference.

[0084] The calculation of the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and the analysis of voltage fluctuations in the power supply of the three-phase hybrid distribution transformer system based on the voltage difference, include:

[0085] A three-phase hybrid distribution transformer system is used to regulate the power flow of a photovoltaic power generation area containing k nodes, and photovoltaic power is injected into node j.

[0086] Based on the voltage of node n before node j of the three-phase hybrid distribution transformer system and the voltage of node n before node j where distributed photovoltaic power is not connected, calculate the voltage difference between node j and adjacent node j-1 in the three-phase hybrid distribution transformer system.

[0087] When the voltage difference is greater than zero, it means that the active power consumed by the load is greater than the active power injected by the distributed photovoltaic system; when the voltage difference is less than zero, it means that the active power consumed by the load is less than the active power injected by the distributed photovoltaic system.

[0088] Compensation for voltage fluctuations in a three-phase hybrid distribution transformer system is achieved through a power electronic converter, specifically including:

[0089] The voltage amplitude and voltage phase of the power supply of the three-phase hybrid distribution transformer system are dually regulated by a power electronic converter; the secondary load voltage of the three-phase hybrid distribution transformer system is regulated based on the duty cycle of the power electronic converter.

[0090] Among them, the dual regulation of voltage amplitude and voltage phase of the power supply of the three-phase hybrid distribution transformer system through the power electronic converter includes:

[0091] Based on the voltage relationship measured by the power supply of a three-phase hybrid distribution transformer system, the compensation voltage of the power electronic converter under voltage fluctuation conditions is analyzed.

[0092] Based on the voltage fluctuation of one phase, the duty cycle status of the power electronic converters of the other two phases is determined. When the duty cycles of the power electronic converters of the other two phases are the same, the three-phase hybrid distribution transformer system performs voltage amplitude regulation. When the duty cycles of the power electronic converters of the other two phases are different, the three-phase hybrid distribution transformer system performs dual regulation of voltage amplitude and voltage phase.

[0093] Among them, voltage amplitude regulation through a three-phase hybrid distribution transformer system includes:

[0094] When the voltage on the power supply side of the three-phase hybrid distribution transformer system fluctuates, the actual value of the primary winding voltage of the three-phase HDT system is obtained.

[0095] The effective value of the primary winding voltage of the three-phase hybrid distribution transformer system is calculated based on the actual value, and the error between the effective value and the preset reference value is compensated by a proportional-integral controller.

[0096] The drive signal of the proportional-integral controller is transmitted to the power electronic converter, and after being regulated by the power electronic converter, it is transmitted to the power supply side to achieve voltage regulation.

[0097] Based on the phase difference between each phase in a three-phase hybrid distribution transformer system, the relationship between the flexible transformation ratio and voltage phase of the three-phase hybrid distribution transformer system is constructed to meet the requirements of load flexible regulation.

[0098] It should be noted that this invention proposes the following for photovoltaic power generation systems: Figure 2 The diagram shows a photovoltaic (PV) power generation system network. On the left side of the diagram is the power source, which uses a three-phase HDT system to regulate the power flow of the distribution system. There are a total of k nodes, with PV power S injected into node j. PV ,Depend on Figure 2 As can be seen, the specific formula in this system network is as follows (1):

[0099]

[0100] In the formula, S i P represents the apparent power of node i in a three-phase HDT system. i With Q i These represent the active and reactive power of the i-node in a three-phase HDT system, S. j To control the apparent power of node j, P j With Q j The active and reactive power of node j are respectively, S PV For the apparent photovoltaic power injected into node j, P PV With Q PV Z represents the photovoltaic active power and reactive power injected into node j, respectively. i R is the impedance of node i. i Let X be the resistance of node i. i Z is the reactance of node i. j R is the impedance at node j. j Let X be the resistance at node j. j Let J be the reactance of node j.

[0101] U n1 U is the voltage of node n preceding node j in a three-phase HDT system with distributed photovoltaic access. n2 Let n be the voltage of the node n preceding node j in the three-phase HDT system where the distributed photovoltaic system is not connected to node j. The specific expression is shown in (2):

[0102]

[0103] In the formula, U j U is the voltage at node j of the three-phase HDT system. j-1U is the voltage at node j-1, k is the total number of nodes, where U j with U j-1 The voltage difference between them is shown in equation (3):

[0104]

[0105] As shown in equation (3), ΔU is mainly related to the active power of the node. ΔU can be greater than zero or less than zero. When the active power consumed by the load is greater than the active power injected by the distributed photovoltaic system, ΔU is greater than zero; when the active power consumed by the load is less than the active power injected by the distributed photovoltaic system, ΔU is less than zero.

[0106] The power electronic converter topology and modulation strategy used in the three-phase HDT system of this invention are as follows: Figure 3 As shown, the specific voltage relationship formulas are as follows (4) to (7):

[0107]

[0108]

[0109] In the formula, These refer to the three-phase power supply side voltages of a three-phase HDT system. These are the voltages of the photovoltaic power generation station areas on the three-phase load side; These are the voltages of the three-phase main windings on the secondary side, respectively. These are the compensation voltages for the three-phase power electronic converter; D a D b D c These represent the duty cycles of the three-phase power electronic converter; n Ta1 n Tb1 n Tc1 n Ta2 n Tb2 n Tc2 n Ta3 n Tb3 n Tc3 These are the turns ratios of the three-phase main winding and auxiliary winding on the secondary side, respectively; W A W B W C These are the three-phase main windings on the power supply side; W a1 W b1 W c1 These are the secondary side three-phase main windings; W a2 W b2 W c2 These are the secondary side three-phase auxiliary windings; Z LA-PV Z LB-PV Z LC-PVThese are the three-phase impedances on the load side; This is the output voltage of the secondary side of a traditional transformer.

[0110] Equation (8) can be obtained from equations (4) to (7):

[0111]

[0112] Power electronic converter compensation voltage under voltage fluctuation conditions Considering the other two phases: the power electronic converters of phase B and phase C, we can obtain equation (9):

[0113]

[0114] In the formula, To consider the power electronic converter compensation voltage for phases B and C, taking phase A voltage as an example, when D... b =D c At that time, the three-phase HDT system can only perform voltage amplitude regulation. b ≠D c At that time, the three-phase HDT system can perform both voltage amplitude regulation and voltage phase regulation. b The numerical range is [-1, 1], so the system can be adjusted for both positive and negative polarity.

[0115] Based on the derivation of equation (9) above, the flexible transformer ratio n of the three-phase HDT system is... HDT Specifically, as shown in equation (10):

[0116]

[0117] In the formula, n TR n is the turns ratio of the main winding of a three-phase HDT system. aux n is the turns ratio of the auxiliary winding in a three-phase HDT system. HDT-A n HDT-B and n HDT-C This refers to the flexible transformation ratio of each phase in a three-phase HDT system. Since phases A, B, and C differ by 120°, they are differentiated here, and e is added to each phase. -j120° With e j120° Let's explain the phasors of the three phases, where e -j120° This refers to a phase angle of -120°, e j120° This refers to an angle of 120 degrees between the two phases.

[0118] Taking phase A as an example, it can be seen from formula (10) that n HDT-A The influencing factors are mainly divided into four categories: B-phase power electronic converter D b The duty cycle D of the C-phase power electronic converter c Main winding ratio nTR and auxiliary winding ratio n aux .

[0119] The three-phase system proposed in this invention is a two-phase supported and regulated HDT system. This system consists of a traditional transformer and a power electronic converter. The three-phase HDT system has the ability to support and regulate the voltage of the current phase based on the voltage of the other two phases. Through the regulation of the power electronic converters of the other two phases, dual regulation of the voltage amplitude or phase of the current phase can be achieved, which can meet the requirements for flexible load regulation. By changing the duty cycle of the power electronic converter, the secondary load voltage of the three-phase HDT system can be regulated to maintain its voltage stability. This is the biggest feature of the three-phase HDT system proposed in this invention. At the same time, the operating mode of the three-phase HDT system can be switched according to the bypass switch, so that it operates in traditional transformer mode or HDT mode. It combines the advantages of traditional transformers and power electronic converters, and can be better applied to distribution networks.

[0120] The voltage control of a three-phase HDT system mainly focuses on the voltage amplitude on the power supply side, and its specific control strategy is as follows: Figure 4 As shown in the figure. U L-ref U L and U error These represent the reference value, the actual value, and the difference between the two for the primary winding voltage of a three-phase HDT system. When the power supply voltage fluctuates, U... L The measurement data will be regulated using a proportional-integral (PI) controller to improve accuracy. Next, the drive signal will be transmitted to the power electronic converter, regulated by the converter, and then sent to the power supply side for voltage adjustment. Figure 4 The dashed line in the diagram illustrates the principle of AC voltage RMS detection. This principle calculates the collected RMS value of the power frequency AC voltage through a control strategy and regulates the voltage on the power supply side. After processing by a power electronic converter, U is obtained through a 90° phase shifter. L The cosine value of (t) can be obtained by square rooting the squares of the sine and cosine values ​​respectively. L The effective value. Then, the calculated effective value is compared with the system's reference value U. L-ref The difference between the two values ​​is used to obtain the error U. error Error compensation is achieved through a proportional-integral (PI) controller.

[0121] Combination Figure 3 The three-phase HDT topology is analyzed, taking phase A as an example. When the power supply side voltage U S When fluctuations occur, the bypass switch S bp2 and S bp3 Closed, and S bp-aWhen disconnected, the three-phase HDT system simultaneously operates the conventional transformer and the power electronic converter; when the three-phase HDT system voltage is running normally, the bypass switch S... bp2 and S bp3 Disconnect, and S bp-a When the circuit is closed, the power electronic converter stops operating, and the three-phase HDT system relies solely on the conventional transformer to maintain a stable state. If the power electronic converter malfunctions, the bypass switch S... bp2 and S bp3 Disconnect. At this time, the bypass checker will start to perform fault detection on the three-phase HDT system. The situation of the other two phases is similar to the above steps, and will not be described in detail here.

[0122] A simulation model of a three-phase hybrid distribution transformer system was built using simulation software. Simulation parameters were set, and simulation scenarios for voltage fluctuation, voltage phase change, and voltage odd harmonics were constructed based on the operating characteristics of the three-phase hybrid distribution transformer system.

[0123] The process of building a simulation model of a three-phase hybrid distribution transformer system using simulation software, and setting the simulation parameters, includes the following:

[0124] The thermal analysis characteristics of a three-phase hybrid distribution transformer system are obtained, and a balance parameter combination between the operating characteristics and the thermal analysis characteristics is constructed.

[0125] It should be noted that by modeling the operating environment, electrical load, and heat conduction characteristics of the three-phase hybrid distribution transformer system, the system's thermal response characteristics, including temperature distribution, heat load, and heat dissipation efficiency, are obtained.

[0126] Taking the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, the combination of balance parameters is used as the input of a pre-constructed electro-thermal balance coupling model. The electro-thermal balance coupling model is solved to obtain the optimal balance parameters.

[0127] Among them, the optimal voltage regulation capability of the three-phase hybrid distribution transformer system under thermal response is taken as the optimization objective. The combination of balance parameters is used as the input of the pre-constructed electro-thermal balance coupling model. The electro-thermal balance coupling model is solved to obtain the optimal balance parameters, including:

[0128] With the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, an electro-thermal coupling constraint condition is constructed.

[0129] We introduce the dual problem of the electro-thermal equilibrium coupling model using Lagrange multipliers, and decompose the dual problem into a voltage regulation subproblem and a thermal response subproblem.

[0130] It should be noted that the architecture of the electro-thermal balance coupling model mainly consists of an electrical model, a thermal model, and a coupling mechanism. The electrical model describes the operating characteristics of key components in a three-phase hybrid distribution transformer system, while the thermal model depicts the conduction, convection, and heat dissipation processes of heat generated by electrical losses within the equipment. The two are coupled through the relationship between power loss and temperature rise. The model principle is based on the laws of energy conservation and heat conduction. Given an electrical input, the node heating power is calculated, and then the node temperature is calculated through the heat conduction model. This, in turn, constrains the electrical operation, thus forming a closed loop. For example, end-to-end modeling can be performed using a finite element method (FEM)-based electro-thermal coupling simulation model, a machine learning-based thermal state prediction model, or a physical information neural network (PINN).

[0131] The voltage regulation subproblem and the thermal response subproblem are solved iteratively using local algorithms and heuristic search algorithms respectively, and the optimal solutions are integrated to obtain the optimal equilibrium parameters.

[0132] It should be noted that in the coupled electro-thermal equilibrium model, when iteratively solving the voltage regulation subproblem and the thermal response subproblem using local algorithms and heuristic search algorithms, the local algorithms and heuristic search algorithms respectively include:

[0133] Local algorithms (for the voltage regulation subproblem): Local algorithms are a class of methods that perform local optimization based on the current solution. They are often used to fine-tune the objective function and gradually find a local optimum. In the voltage regulation subproblem, local algorithms are used to regulate the voltage so that the power system voltage meets the constraints and maximizes the voltage regulation capability. Specifically, they include:

[0134] Calculate the adjustment cost (such as power loss, current, efficiency, etc.) under the current voltage configuration; select a suitable local direction (e.g., the negative gradient direction in gradient descent) based on the voltage adjustment target and system state; make small adjustments in the selected direction, update the voltage configuration, and compare the cost of the new configuration with the change in the previous state. If the cost after voltage configuration adjustment does not change significantly (i.e., the objective function converges), stop adjusting; if the convergence condition is not met, continue adjusting. When the convergence condition is met, output the optimal voltage configuration.

[0135] Heuristic search algorithms (for the heat response subproblem): Heuristic search algorithms are a class of optimization algorithms that guide the search process through heuristic rules or empirical judgments. They are typically used for global searches or to handle complex optimization problems. In the heat response subproblem, heuristic search algorithms are used to optimize temperature distribution and heat dissipation strategies to ensure that temperature rise constraints are met. Specifically, they include:

[0136] The temperature field is initialized based on the current voltage configuration, and an initial heat dissipation strategy is set. Based on the current thermal state, a set of candidate solutions is generated, specifically including:

[0137] Increase heat dissipation at nodes that exceed temperature limits;

[0138] Transfer the heat dissipation resources of the low-temperature node to the high-temperature node;

[0139] Optimize the cooling solution by changing the cooler layout or radiator size.

[0140] Candidate solutions are evaluated based on a heuristic scoring function, which may include maximum temperature, heat dissipation energy consumption, and constraint violation penalties.

[0141] Select the candidate solution with the best score as the update scheme for the current solution.

[0142] If the new solution scores poorly, it can be accepted with a certain probability, using simulated annealing to avoid getting trapped in local optima. The acceptance probability is usually determined by a temperature decay function; as the temperature gradually decreases, the acceptance probability of inferior solutions decreases.

[0143] Update the current thermal response state (new temperature field and heat dissipation strategy) based on the selected optimal candidate solution.

[0144] If the change in temperature field is less than a preset threshold, or if the maximum number of iterations is reached, the search stops. When the convergence condition is met, the optimal temperature field and the corresponding heat dissipation strategy are output.

[0145] It should be noted that, with the goal of achieving the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response, an electro-thermal balance coupled model is constructed, incorporating both voltage regulation requirements and temperature rise limitations into the optimization framework.

[0146] By introducing Lagrange multipliers, this coupled optimization problem is transformed into its dual form, and its dual function is decomposed into two subproblems: a voltage regulation subproblem and a thermal response subproblem. The voltage regulation subproblem is solved using a local algorithm to obtain the optimal voltage configuration under the current thermal state, while the thermal response subproblem is handled using a heuristic search algorithm to optimize the system's thermal response by adjusting heat dissipation resources and the temperature field, and then feeding this optimization back to the electrical model.

[0147] In each iteration, the two subproblems serve as input and output to each other. Voltage configuration affects the node's heating power, while temperature state, in turn, constrains the feasible solution space for voltage regulation. By iteratively solving the two subproblems and updating the Lagrange multipliers after each round to correct the degree of violation of coupling constraints, until the optimal gap or convergence criterion is met, the optimal parameter combination that balances the system's electrical performance and thermal stability can be obtained.

[0148] The key to integrating the two types of optimal solutions lies in coordinating the shared variables. Specifically, the voltage configuration should meet the heat dissipation capacity under the corresponding thermal state, and the temperature response should be based on the heat source distribution under the current electrical conditions. The final balanced parameter combination not only ensures the system has good voltage regulation capability but also effectively controls the risk of overheating, improving system safety and operating efficiency.

[0149] The solution to the heat response subproblem using a heuristic search algorithm includes:

[0150] Construct a neighborhood structure for heuristic search, perform thermal allocation on nodes with excessive heat in the electro-thermal balance coupling model, and generate several candidate solutions;

[0151] A scoring function is constructed with the goal of achieving the optimal thermal response, and the scoring function is used to calculate the score of each candidate solution in the neighborhood structure in each iteration.

[0152] If the score of the new solution is greater than or equal to the score of the current solution, the new solution is taken as the current best solution. If the score of the new solution is less than the score of the current solution, the inferior solution is updated with a preset probability to obtain the updated current best solution.

[0153] Stop when the iteration is satisfied, and take the final solution as the optimal solution to the heat response subproblem.

[0154] Using the optimal balance parameter as a pre-regulation factor, the simulation parameters are dynamically adjusted through the pre-regulation factor after the simulation model of the three-phase hybrid distribution transformer system is built.

[0155] The voltage amplitude regulation capability and harmonic compensation capability of the three-phase hybrid distribution transformer system were simulated and tested in the simulation scenario using a simulation model to verify the voltage regulation capability of the three-phase hybrid distribution transformer system.

[0156] It should be noted that, to verify the voltage quality optimization capability of the three-phase HDT system in a photovoltaic power generation area, a simulation model of the three-phase HDT system was built on PSIM simulation software to verify its voltage regulation and harmonic compensation capabilities. Specific simulation parameters are as follows: primary side voltage 10kV, secondary side voltage 400V, load side impedance 100 + j0.2Ω, LC input and output side filter inductance 0.5mH, and capacitance 20μF. Three simulation scenarios are then listed: voltage dip-voltage surge, voltage surge-voltage dip, voltage phase change, and voltage odd harmonics. See [link to simulation details] for more information. Figures 6-9 .

[0157] Figure 5 and Figure 6 In the process, from 0.04s to 0.12s, the voltage (u) on the power supply side of phase A of the three-phase HDT system was measured. SA u SB uSC Add voltage fluctuations (voltage spikes / drops) through the load voltage waveform (u) LA u LB u LC As can be seen, as the power supply voltage fluctuates between 0.04s and 0.12s, the load voltage waveform remains basically unchanged. The three-phase HDT system compensates for the load voltage amplitude during the fluctuation of the power supply voltage amplitude, thus verifying the voltage amplitude compensation capability of the three-phase HDT system.

[0158] Figure 7 At 0.04s, the phase of the power supply voltage on both phase A and phase B of the three-phase HDT system shifted by 30°. It can be seen that the waveform of the load-side voltage remains basically unchanged under this condition, and the phase of the load-side voltage does not shift with the phase fluctuation of the power supply voltage. The three-phase HDT system compensates for the phase of the load-side voltage during the phase fluctuation of the power supply voltage, thus verifying the voltage phase compensation capability of the three-phase HDT system.

[0159] Figure 8 In the experiment, between 0.04s and 0.12s, a 25% third harmonic and a 15% fifth harmonic were added to the power supply side voltage of phase A of the three-phase HDT system. At this time, the THD was 29.2%. During the period when the harmonics were added, it can be seen that the voltage of phase A power supply side was distorted, while the voltage waveform of the load side remained basically unchanged and was not affected by the odd harmonics. At this time, the THD was only 1.7%, which means that the three-phase HDT system compensated for the odd harmonics of the load side voltage during this period. This verifies that the three-phase HDT system has the ability to compensate for harmonics.

[0160] S3. Combining the voltage regulation capability of the three-phase hybrid distribution transformer system, the power quality of the photovoltaic power generation area is optimized through the three-phase hybrid distribution transformer system.

[0161] It should be noted that, after verifying the power quality compensation capability of the three-phase HDT system, the specific application of the system in photovoltaic power generation areas is analyzed. Taking the IEEE 33-bus system as an example, the power quality optimization problem of the three-phase HDT system in photovoltaic power generation areas is analyzed and compared. Through the voltage distribution scenario of the voltage regulation device in the IEEE 33-bus system, it can be seen that the three-phase HDT system can optimize and regulate the power flow of the grid, and the node voltage is within the allowable voltage deviation range. Moreover, compared with other voltage regulation devices, the three-phase HDT system has better power quality optimization capability.

[0162] This invention primarily addresses the voltage quality issues arising from the increased penetration rate of photovoltaic (PV) power generation in PV power generation areas. Therefore, it uses the IEEE 33-bus system as the PV power generation area system for analysis and explanation. For details on the IEEE 33-bus system, please refer to [link to IEEE 33-bus system documentation]. Figure 9 .

[0163] Depend on Figure 9 As can be seen, the IEEE 33-node system example includes six distributed photovoltaic (PV) power stations located at nodes 7, 10, 13, 24, 27, and 30. Additionally, four scenarios are defined for the IEEE 33-node system, illustrated by incorporating control equipment: on-load tap changers (OLTCs), existing capacitor banks (CBs) in the distribution network, and high-voltage transformers (HDTs). Specific scenarios are shown in Table 3.

[0164] Table 3 IEEE 33-node system scenario table

[0165] Scene Scene setting I Initial running scenario II OLTC and CBs regulation scenarios III HDT independent control scenario IV HDT and CBS Joint Control Scenarios

[0166] To deeply analyze the specific impact of different scenarios on the voltage of photovoltaic power generation systems, and to visually observe the voltage fluctuation amplitude and the contribution of control methods to voltage regulation under four scenarios, this paper presents a comparison chart of the maximum and minimum voltage values ​​at each node under different voltage control devices in the four scenarios. Details can be found in [the relevant section]. Figure 10 .

[0167] Scenario I represents the initial operational state, i.e., the state before adjustment by control devices such as OLTC, CBs, and HDT. From Figure 10 It can be seen that in Scenario I, due to factors such as network topology and electrical distance, the maximum voltage U of nodes 13-18 in the IEEE 33-node system is... max With minimum voltage U min Voltage over-limit phenomena occurred in all cases, with U at nodes 29-33. min Voltage over-limit phenomenon also occurred, that is, when the network is not regulated, the voltage of each node in the system generally exceeds the voltage limit range [0.97, 1.03].

[0168] Scenario II adds control devices, namely OLTC and CBs, to Scenario I. Observing the voltage curve in Scenario II, it can be clearly seen that by installing OLTC and CBs, most of the voltage over-limit nodes in Scenario I are eliminated, voltage fluctuations are significantly reduced, and the voltage quality of network nodes is significantly improved. However, the voltage of some nodes (such as nodes 13-18 and 31-33) still does not enter the expected voltage range. Although most of the node voltages when OLTC participates in the regulation are within the specified voltage limit range [0.97, 1.03], the overall level is low, and a small number of node voltages have per-unit values ​​below 0.97.

[0169] In Scenario III, the voltage curve was further improved by adding a three-phase HDT system. The voltage regulation effect of the three-phase HDT system further improved the voltage quality of the network nodes, and the voltage of all nodes operated within the expected voltage range. It can be seen that the three-phase HDT system has better voltage regulation capability than OLTC and CBs.

[0170] Scenario IV adds CBs to the Scenario III: Three-phase HDT system. As can be seen from the voltage curve, the U of the network node in Scenario IV... max with U min Compared to Scenario III, further optimization and improvement have been achieved, resulting in improved overall voltage fluctuations and more voltage nodes trending towards the stable specified voltage limits [0.97, 1.03]. After power flow optimization and regulation by the three-phase HDT system, all node voltages are within the specified voltage deviation range, demonstrating the improvement effect of the three-phase HDT system on the voltage of each node. In summary, the three-phase HDT system has the ability to improve the overall voltage level and optimize power quality in photovoltaic power generation systems. Combined with other control equipment such as CBS, it can better achieve voltage compensation effects.

[0171] This invention discloses a power quality optimization method for photovoltaic power generation areas based on a three-phase HDT system. Addressing power quality issues in photovoltaic power generation areas, such as voltage deviation, harmonics, and power system frequency deviation, a three-phase HDT system composed of a traditional transformer and a power electronic converter is proposed. The working principle and voltage regulation capability of this three-phase HDT system are analyzed in detail. Simulation tests were then conducted on the proposed three-phase HDT system. The system was validated by setting different scenarios for the power supply side voltage: voltage surge-dip, voltage dip-surge, voltage phase fluctuation, and odd harmonic simulation tests. The results show that the load-side voltage waveform remains essentially unchanged, unaffected by power supply side voltage fluctuations. The study also examined the impact of harmonics, thus verifying that the three-phase HDT system possesses excellent voltage amplitude and phase compensation capabilities, as well as harmonic compensation capabilities. Subsequently, the power quality optimization of the three-phase HDT system in photovoltaic power generation areas was analyzed and compared. Through the voltage distribution in its IEEE 33-node system, it was found that it can optimize and regulate power flow in the grid. Furthermore, the three-phase HDT system has a compensation effect on the voltage of each node, with all node voltages within the allowable voltage deviation range. Compared to other voltage regulation devices, the three-phase HDT system has superior power quality optimization capabilities, thereby improving the power quality problem in photovoltaic power generation areas and showing broad application potential in the future.

[0172] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system, characterized in that the method includes: Construct a three-phase hybrid distribution transformer system consisting of a standard transformer, a power electronic converter, a bypass switch, and an LC filter; The operating characteristics of a three-phase hybrid distribution transformer system are analyzed, including the working principle and voltage regulation characteristics of the three-phase hybrid distribution transformer system. A simulation model of a three-phase hybrid distribution transformer system was built using simulation software. Simulation parameters were set, and simulation scenarios for voltage fluctuation, voltage phase change, and voltage odd harmonics were constructed based on the operating characteristics of the three-phase hybrid distribution transformer system. The voltage amplitude regulation capability and harmonic compensation capability of the three-phase hybrid distribution transformer system were simulated and tested in the simulation scenario using a simulation model to verify the voltage regulation capability of the three-phase hybrid distribution transformer system. By leveraging the voltage regulation capability of a three-phase hybrid distribution transformer system, the power quality of the photovoltaic power generation area can be optimized. The process of building a simulation model of a three-phase hybrid distribution transformer system using simulation software and setting simulation parameters includes, before: The thermal analysis characteristics of a three-phase hybrid distribution transformer system are obtained, and a balance parameter combination between the operating characteristics and the thermal analysis characteristics is constructed. Taking the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, the combination of balance parameters is used as the input of a pre-constructed electro-thermal balance coupling model. The electro-thermal balance coupling model is solved to obtain the optimal balance parameters. Using the optimal balance parameter as a pre-regulation factor, the simulation parameters are dynamically adjusted through the pre-regulation factor after the simulation model of the three-phase hybrid distribution transformer system is built.

2. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 1, characterized in that, The analysis of the operating characteristics of the three-phase hybrid distribution transformer system includes: Calculate the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and analyze the voltage fluctuation of the power supply of the three-phase hybrid distribution transformer system based on the voltage difference; Compensation for voltage fluctuations in a three-phase hybrid distribution transformer system is achieved through a power electronic converter, specifically including: The voltage amplitude and voltage phase of the power supply of the three-phase hybrid distribution transformer system are dually regulated by a power electronic converter; the secondary load voltage of the three-phase hybrid distribution transformer system is regulated based on the duty cycle of the power electronic converter.

3. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 2, characterized in that, The calculation of the voltage difference between the three-phase hybrid distribution transformer system connected to and not connected to distributed photovoltaic power, and the analysis of voltage fluctuations in the power supply of the three-phase hybrid distribution transformer system based on the voltage difference, includes: A three-phase hybrid distribution transformer system is used to regulate the power flow of a photovoltaic power generation area containing k nodes, and photovoltaic power is injected into node j. Based on the voltage of node n before node j of the three-phase hybrid distribution transformer system and the voltage of node n before node j where distributed photovoltaic power is not connected, calculate the voltage difference between node j and adjacent node j-1 in the three-phase hybrid distribution transformer system. When the voltage difference is greater than zero, it means that the active power consumed by the load is greater than the active power injected by the distributed photovoltaic system; when the voltage difference is less than zero, it means that the active power consumed by the load is less than the active power injected by the distributed photovoltaic system.

4. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 2, characterized in that, The dual regulation of voltage amplitude and voltage phase of the three-phase hybrid distribution transformer system power supply via a power electronic converter includes: Based on the voltage relationship measured by the power supply of a three-phase hybrid distribution transformer system, the compensation voltage of the power electronic converter under voltage fluctuation conditions is analyzed. Based on the voltage fluctuation of one phase, the duty cycle status of the power electronic converters of the other two phases is determined. When the duty cycles of the power electronic converters of the other two phases are the same, the three-phase hybrid distribution transformer system performs voltage amplitude regulation. When the duty cycles of the power electronic converters of the other two phases are different, the three-phase hybrid distribution transformer system performs dual regulation of voltage amplitude and voltage phase. Based on the phase difference between each phase in a three-phase hybrid distribution transformer system, the relationship between the flexible transformation ratio and voltage phase of the three-phase hybrid distribution transformer system is constructed to meet the requirements of load flexible regulation.

5. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 4, characterized in that, Voltage amplitude regulation via the three-phase hybrid distribution transformer system includes: When the voltage on the power supply side of the three-phase hybrid distribution transformer system fluctuates, the actual value of the primary winding voltage of the three-phase HDT system is obtained. The effective value of the primary winding voltage of the three-phase hybrid distribution transformer system is calculated based on the actual value, and the error between the effective value and the preset reference value is compensated by a proportional-integral controller. The drive signal of the proportional-integral controller is transmitted to the power electronic converter, and after being regulated by the power electronic converter, it is transmitted to the power supply side to achieve voltage regulation.

6. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 1, characterized in that, The optimization objective is to achieve the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response. The optimal balance parameters are obtained by using the combination of balance parameters as input to a pre-constructed electro-thermal balance coupling model and solving the model. These optimal balance parameters include: With the optimal voltage regulation capability of a three-phase hybrid distribution transformer system under thermal response as the optimization objective, an electro-thermal coupling constraint condition is constructed. We introduce the dual problem of the electro-thermal equilibrium coupling model using Lagrange multipliers, and decompose the dual problem into a voltage regulation subproblem and a thermal response subproblem. The voltage regulation subproblem and the thermal response subproblem are solved iteratively using local algorithms and heuristic search algorithms respectively, and the optimal solutions are integrated to obtain the optimal equilibrium parameters.

7. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 6, characterized in that, Solving the heat response subproblem using a heuristic search algorithm includes: Construct a neighborhood structure for heuristic search, perform thermal allocation on nodes with excessive heat in the electro-thermal balance coupling model, and generate several candidate solutions; A scoring function is constructed with the goal of achieving the optimal thermal response, and the scoring function is used to calculate the score of each candidate solution in the neighborhood structure in each iteration. If the score of the new solution is greater than or equal to the score of the current solution, the new solution is taken as the current best solution. If the score of the new solution is less than the score of the current solution, the inferior solution is updated with a preset probability to obtain the updated current best solution. Stop when the iteration is satisfied, and take the final solution as the optimal solution to the heat response subproblem.

8. The method for optimizing power quality in a photovoltaic power generation area based on a three-phase HDT system according to claim 4, characterized in that, The expression for the flexible turns ratio of the three-phase hybrid distribution transformer system is: ； In the formula, n TR n is the turns ratio of the main winding of a three-phase hybrid distribution transformer system. aux n is the turns ratio of the auxiliary winding in a three-phase hybrid distribution transformer system. HDT-A n HDT-B and n HDT-C These represent the flexible transformation ratios of each phase in a three-phase hybrid distribution transformer system, D. a D b and D c These represent the duty cycle per phase of the power electronic converter, e -j120° This indicates that the included angle between two phases of a three-phase hybrid distribution transformer system is -120°, e j120° This indicates that the angle between two phases in a three-phase hybrid distribution transformer system is 120°.

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