Power distribution network voltage double-layer optimization method and device

Abstract

The invention discloses a power distribution network voltage double-layer optimization method and device, and belongs to the technical field of power system control. A plurality of nodes of the power distribution network system are connected with a photovoltaic power generation system or a capacitor bank. The method comprises the following steps: acquiring input data of the plurality of nodes in the power distribution network system; optimizing the mechanical tap gear of the transformer and the switching group number of the capacitor group by taking the minimum line loss as the target and taking the condition that the voltage of the power distribution network system is not out of limit as the constraint; according to the mechanical tap gear and the switching group number of the capacitor bank, with the highest new energy consumption rate, the minimum operation cost and the minimum line loss as targets, the compensation capacity, the energy storage charging and discharging power and the compensation transformation ratio of the power electronic converter of the STATCOM are optimized; and configuring the power distribution network system under the condition that the voltage of the power distribution network system does not exceed the limit. According to the method, the voltage out-of-limit problem caused by photovoltaic backward flow is solved, and the voltage quality of the power distribution network is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of power system control, and in particular, relates to a method and device for double-layer optimization of distribution network voltage. Background Art

[0002] Photovoltaic power generation is green, environmentally friendly and highly sustainable. As an important form of renewable energy, distributed photovoltaics have developed rapidly around the world and have achieved significant applications in power distribution systems.

[0003] With the vigorous development of new power systems, the large-scale access to renewable energy sources such as wind power and photovoltaic power generation, and the continuous growth of fluctuating loads, voltage fluctuations are becoming more and more frequent, posing new challenges to the grid's ability to maintain voltage stability. When photovoltaic systems are connected to power systems on a large scale, especially in distribution systems, the randomness and volatility of photovoltaic output will cause system voltage fluctuations, making it difficult to maintain voltage stability. In addition, the access of a high proportion of photovoltaics will cause photovoltaic backflow, causing the power flow of the distribution line to flow backward to the upper power grid and generate serious overvoltage in the system.

[0004] These problems have a great impact on the stable operation and economy of the power system. When considering the voltage optimization of the distribution network, combining optimization with the transformer is often an effective method. The on-load tap-changing transformer plays the role of regulating voltage and maintaining voltage stability in the power grid. On this basis, how to configure the parameters of the distribution network connected to the photovoltaic system to improve the voltage quality of the distribution network is an urgent problem to be solved. Summary of the invention

[0005] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a distribution network voltage double-layer optimization method and device, which solves the voltage over-limit problem caused by photovoltaic backflow and improves the voltage quality of the distribution network.

[0006] In a first aspect, the present application provides a double-layer optimization method for distribution network voltage, which is applied to a distribution network system having multiple nodes, wherein the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, and the distribution network system is provided with a target transformer, wherein the target transformer is a hybrid on-load tap-changing transformer, and the target transformer is provided with a power electronic converter, and the method comprises: Acquire input data of a plurality of nodes in the power distribution network system, wherein the input data includes node voltage parameters and transformer parameters; Taking the minimum line loss as the goal and the voltage of the distribution network system not exceeding the limit as the constraint, the mechanical tap position of the target transformer and the number of capacitor bank switching groups are optimized to obtain a first optimization scheme; According to the mechanical tap position of the target transformer and the number of switched capacitor groups in the first optimization scheme, the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter are optimized with the goal of maximizing the new energy consumption rate, minimizing the operating cost, and minimizing the line loss, thereby obtaining the second optimization scheme; When it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit, the distribution network system is configured using the second optimization scheme.

[0007] According to one embodiment of the present application, the hybrid on-load tap-changing transformer comprises: a primary circuit on the primary side, a magnetic conductor and a secondary circuit on the secondary side; The primary circuit includes a stepped winding and a power electronic converter, and the power electronic converter is connected to the magnetic conductor via a compensation winding; The input end of the power electronic converter is connected to a plurality of corresponding tapped windings via a plurality of parallel mechanical taps.

[0008] According to one embodiment of the present application, the power electronic converter is a single-output AC-AC converter; The input inductor L connected in sequence in , the first half bridge, the second half bridge, the input capacitor C in , the third half-bridge, output inductor L out and output capacitor C out , output capacitor C out Connected in parallel with the compensation winding; The first group of half bridges includes two half bridge modules connected in series, and the half bridge modules include a switch tube and a freewheeling diode connected in parallel. The switch tube is an IGBT. The first group of half bridges, the second group of half bridges and the third group of half bridges have the same structure.

[0009] According to an embodiment of the present application, the first group of half-bridges includes a half-bridge module in which a switch tube Q1 and a freewheeling diode D1 are connected in parallel, and a half-bridge module in which a switch tube Q2 and a switch tube D2 are connected in parallel; The second half-bridge group includes a half-bridge module in which the switch tube Q3 and the freewheeling diode D3 are connected in parallel, and a half-bridge module in which the switch tube Q4 and the switch tube D4 are connected in parallel; The third half-bridge group includes a half-bridge module in which the switch tube Q5 and the freewheeling diode D5 are connected in parallel, and a half-bridge module in which the switch tube Q6 and the switch tube D6 are connected in parallel.

[0010] According to one embodiment of the present application, through the first group of half bridges, the second group of half bridges, the input inductor L in And the input capacitor C in The boost module of the power electronic converter is composed of the third half-bridge and the output capacitor C outBuck modules that make up the power electronic converter; The working state of the boost module is a first state and a second state; In the first state, the switch tubes Q2 and Q4 are turned on, the switch tubes Q1 and Q3 are turned off, and the current flows through the switch tube Q2 and the freewheeling diode D4 of the switch tube Q4 to form a loop. The input voltage of the power electronic converter is the input inductor L in Charge; In the second state, the switch tubes Q1 and Q4 are turned on, the switch tubes Q2 and Q3 are turned off, and the current flows through the freewheeling diode D1 of the switch tube Q1 and the input capacitor C in , and the freewheeling diode D4 of Q4 form a loop, the input voltage of the power electronic converter and the input inductor L in At the same time, the input capacitor C in Charge; The working states of the step-down module are a third state, a fourth state and a fifth state; In the third state and the fourth state, the switch tubes Q4 and Q5 are turned on, the switch tubes Q3 and Q6 are turned off, the switch tube Q1 in the boost module is turned on, the switch tube Q2 is turned off, and the current flows through the input capacitor C in , switch tube Q5, output inductor L out , load winding, and switch tube Q4 form a loop, input capacitor C in is the output inductor L out and load winding power supply; In the fifth state, Q4 and Q6 are turned on, Q3 and Q5 are turned off, and the current flows through the output inductor L out , load winding, Q4, and Q6's freewheeling diode D6 form a loop. In this state, the output inductor L out Continue current to provide energy to the load winding.

[0011] According to one embodiment of the present application, the relationship between the output voltage and the input voltage of the power electronic converter is:

[0012] in, is the input voltage of the power electronic converter, is the output voltage of the power electronic converter, is the conduction duty cycle of the switch tube Q5, is the conduction duty cycle of the switch tube Q2; Output voltage of power electronic converter Converted to the secondary voltage for:

[0013] Among them, k2 is the transformation ratio of the compensation winding, Input voltage and input voltage The amplitude ratio of is the amplitude of the grid-side input sinusoidal voltage, is the voltage amplitude at the input side of the power electronic converter, is the angular frequency of the input sine wave; The output voltage of the target transformer is :

[0014] in, The voltage on the step winding is converted to the voltage on the secondary side. is the input voltage of the target transformer.

[0015] According to an embodiment of the present application, the optimization of the mechanical tap position of the target transformer and the number of capacitor bank switching groups to obtain a first optimization scheme includes: Based on the learning factor and annealing speed, the fitness and particle position of each particle are calculated based on the initial particle position and velocity; The initial annealing temperature is obtained based on the optimal fitness; Based on the annealing initial temperature, calculating the annealing algorithm fitness of each particle; Based on the fitness of the annealing algorithm, the global optimum is replaced by individual random selection to update the position and speed of each particle and the optimal position of the population, and the fitness value is calculated to perform an annealing operation until the set annealing temperature is reached to obtain a first optimization solution.

[0016] According to one embodiment of the present application, after obtaining the second optimization solution, the method further includes: When it is determined that the voltage of the distribution network system in the second optimization scheme exceeds the limit, the mechanical tap position of the target transformer and the number of capacitor group switching groups are re-optimized according to the input data until the voltage of the distribution network system in the second optimization scheme does not exceed the limit, and the distribution network system is configured according to the second optimization scheme.

[0017] According to one embodiment of the present application, the power distribution network system includes nodes 1 to 33; Nodes 1 to 18 are connected in sequence, a power electronic embedded hybrid on-load tap-changing transformer is connected between 2 and 3, node 10 is connected to a first photovoltaic power generation system, node 14 is connected to a first capacitor bank, and node 18 is connected to a second photovoltaic power generation system and an energy storage device. Node 2 is also connected to nodes 19 to 22 connected in sequence, node 20 is connected to a third photovoltaic power generation system, and node 20 is connected to a second capacitor bank; Node 3 is also connected to nodes 23 to 25 which are connected in sequence; The node 6 is also connected to the nodes 26 to 33 which are connected in sequence, the node 32 is connected to the fourth photovoltaic power generation system, and the node 33 is connected to the third capacitor group.

[0018] In a second aspect, the present application provides a distribution network voltage double-layer optimization device, which is applied to a distribution network system having multiple nodes, wherein the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, and the distribution network system is provided with a target transformer, wherein the target transformer is a hybrid on-load tap-changing transformer, and the target transformer is provided with a power electronic converter, wherein the device comprises: An acquisition module, used to acquire input data of multiple nodes in the distribution network system, wherein the input data includes node voltage parameters and transformer parameters; The first processing module is used to optimize the mechanical tap position of the target transformer and the number of capacitor bank switching groups with the goal of minimizing line loss and the constraint that the voltage of the distribution network system does not exceed the limit, so as to obtain a first optimization scheme; The second processing module is used to optimize the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter according to the mechanical tap position of the target transformer and the number of switched groups of the capacitor bank in the first optimization scheme, with the highest new energy consumption rate, the lowest operating cost, and the lowest line loss as the goal, to obtain a second optimization scheme; The third processing module is used to configure the distribution network system through the second optimization scheme when it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit.

[0019] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application.

[0020] The present invention provides a method and device for optimizing the voltage of a distribution network, which has the following advantages over the prior art: (1) Through a multi-level and multi-objective optimization strategy, the mechanical taps, capacitor banks, STATCOM, energy storage systems, and converters are gradually optimized and adjusted to minimize line losses, reduce operating costs, and increase the new energy consumption rate. In the case of voltage fluctuations or photovoltaic backflow, the voltage can be ensured not to exceed the limit. By adjusting the working status of equipment such as transformers, energy storage, and capacitor banks, the operating efficiency and stability of the distribution network system are ensured, the energy utilization rate and voltage quality of the distribution network system are improved, and the losses are reduced.

[0021] (2) By integrating the traditional on-load tap-changing transformer with the power electronic converter, the power electronic converter is used for continuous ratio compensation to achieve fast and stepless voltage regulation, thereby enhancing the flexibility and accuracy of system voltage regulation. In this two-layer optimization method, the discrete layer uses the mechanical tap position and the number of capacitor groups switched at each moment as decision variables, and the continuous layer uses the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter at each moment as decision variables. A comprehensive optimization mathematical model is established with the clean energy consumption rate, operating cost, and line loss as objective functions to meet the constraints of each node voltage. The simulated annealing algorithm is used to improve the particle swarm algorithm to solve the clean energy output strategy, reactive compensation device output strategy, and transformer voltage regulation strategy. It can jump out of the local optimal solution with a certain probability and search in the global range, avoiding falling into the local optimal solution and realizing the optimized operation of the entire power grid distribution system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 It is one of the flow charts of the double-layer optimization method for distribution network voltage provided in the embodiment of the present application; Figure 2 It is a single-phase topology diagram of a hybrid on-load tap-changing transformer provided in an embodiment of the present application; Figure 3 This is the second flow chart of the double-layer optimization method for distribution network voltage provided in the embodiment of the present application; Figure 4 This is the third flow chart of the double-layer optimization method for distribution network voltage provided in the embodiment of the present application; Figure 5 is a structural schematic diagram of a power distribution network system provided in an embodiment of the present application; Figure 6 is a node voltage distribution diagram before optimization provided by an embodiment of the present application; Figure 7 It is a node voltage distribution diagram of method 1 provided in an embodiment of the present application; Figure 8 It is a node voltage distribution diagram of method 2 provided in an embodiment of the present application; Fig. 9 It is a node voltage distribution diagram of method 3 provided in an embodiment of the present application; Fig.10 It is a mechanical tap change diagram of method 1 provided in an embodiment of the present application; Fig.11 It is a mechanical tap change diagram of method 2 provided in an embodiment of the present application; Fig.12It is a mechanical tap change diagram of method 3 provided in an embodiment of the present application; Fig.13 This is a diagram showing the change in the transformer equivalent total transformation ratio after compensation according to method 3 provided in an embodiment of the present application; Fig.14 It is a structural schematic diagram of a double-layer optimization device for distribution network voltage provided in an embodiment of the present application. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0024] The distribution network voltage double-layer optimization method and the distribution network voltage double-layer optimization device provided in the embodiments of the present application are described in detail below with reference to the accompanying drawings through specific embodiments and their application scenarios.

[0025] Among them, the double-layer optimization method of distribution network voltage is applied to a distribution network system with multiple nodes, the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, the distribution network system is provided with a target transformer, the target transformer is a hybrid on-load tap-changing transformer, and the target transformer is provided with a power electronic converter.

[0026] like Figure 1 As shown, the distribution network voltage double-layer optimization method includes: Step 110: acquiring input data of a plurality of nodes in the distribution network system, wherein the input data includes node voltage parameters and transformer parameters; Step 120, with the minimum line loss as the goal and the voltage of the distribution network system not exceeding the limit as the constraint, the mechanical tap position of the target transformer and the number of capacitor bank switching groups are optimized to obtain a first optimization scheme; Step 130: According to the mechanical tap position of the target transformer and the number of switched capacitor groups in the first optimization scheme, the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter are optimized with the goal of maximizing the new energy consumption rate, minimizing the operating cost, and minimizing the line loss, so as to obtain a second optimization scheme; Step 140: When it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit, configure the distribution network system through the second optimization scheme.

[0027] The capacitor bank may be a static synchronous compensator (STATCOM).

[0028] First, in step 110, input data of each node in the power distribution network system is collected. The input data is the basis of optimization and can affect the power distribution and voltage regulation of the power grid.

[0029] The node voltage parameters are used to characterize the voltage condition of each node and reflect the voltage distribution in the distribution network system.

[0030] Transformer parameters include the transformer's rated power, transformation ratio, mechanical tap position range, load conditions, etc.

[0031] Input data can be provided by monitoring and measuring equipment (such as SCADA system) of the distribution network system, and the accuracy of the distribution network system dispatching decision can be ensured through real-time or periodic collection.

[0032] In step 120 , the goal is to minimize line losses while ensuring that the voltage in the distribution network system does not exceed a specified range.

[0033] The mechanical tap position of the transformer determines the voltage adjustment range in the distribution network system. By adjusting the mechanical tap position, the node voltage can be flexibly controlled, thereby affecting the line loss.

[0034] Capacitor banks are used to provide reactive power compensation and improve the voltage quality of the power grid. By adjusting the switching of capacitors, the reactive power loss on the line can be effectively reduced and the voltage can be stabilized.

[0035] Through constraints, the voltage in the power grid is ensured to be within the specified safety range to avoid overvoltage or undervoltage.

[0036] A preliminary first optimization plan is obtained to ensure that the power grid can minimize line losses while ensuring voltage safety.

[0037] In step 130, based on the first optimization scheme, the configuration of the capacitor bank and the energy storage system is further optimized, that is, the compensation capacity of the STATCOM of the capacitor bank and the energy storage charging and discharging power are optimized. According to the mechanical tap position and the number of switching groups of the capacitor bank in the first optimization scheme, the charging and discharging strategy of the energy storage system is further adjusted to improve the utilization efficiency of energy and avoid losses caused by overvoltage or overload as much as possible.

[0038] In order to maximize the new energy consumption rate, the compensation capacity of STATCOM and the charging and discharging power of energy storage can be optimized to absorb as much new energy as possible while ensuring the stability of the power grid.

[0039] To minimize operating costs, the configuration of capacitor banks and energy storage systems can be optimized to reduce dependence on traditional energy sources, thereby reducing operating costs.

[0040] In order to minimize line losses, line losses caused by power loss can be reduced through flexible energy storage scheduling and adjustment of STATCOM's compensation capacity.

[0041] In step 140, based on the second optimization scheme, the voltage of the distribution network system is ensured not to exceed the limit, the distribution network system is configured through the second optimization scheme, the mechanical tap position of the transformer and the number of capacitor groups switched on and off are adjusted to achieve optimal voltage control and loss optimization, and the energy storage system is configured.

[0042] When renewable energy generation fluctuates, energy storage systems can help balance electricity demand, optimize electricity flows, and ensure stable operation of the power grid.

[0043] The configured distribution network can achieve the effects of minimizing line losses, minimizing operating costs, maximizing new energy consumption, and ensuring voltage stability without exceeding limits under multi-objective optimization.

[0044] According to the double-layer optimization method for distribution network voltage provided in the embodiment of the present application, through a multi-level and multi-objective optimization strategy, the mechanical taps, capacitor banks, STATCOM, energy storage systems and converters are gradually optimized and adjusted to minimize line losses, reduce operating costs, and increase the new energy consumption rate. In the case of voltage fluctuations or photovoltaic backflow, it can ensure that the voltage does not exceed the limit. By adjusting the working conditions of equipment such as transformers, energy storage and capacitor banks, the operating efficiency and stability of the distribution network system are ensured, the energy utilization rate and the voltage quality of the distribution network system are improved, and the losses are reduced.

[0045] In the related art, traditional on-load tap-changing transformers often use mechanical taps (mechanical taps). This type of tap-changing switch has a complex structure and is prone to arcing during the switching process, which can burn out the contacts. The switching action time is long and it is difficult to determine the exact time. Mechanical switches are mostly oil-immersed, and overvoltage and arc suppression are prevented by introducing transition resistors during the tap switching process. A mechanical vacuum arc-extinguishing on-load tap-changing switch is used, and the tap switching is completed in a vacuum tube, so there is no problem of insulating oil deterioration and pollution caused by switching arcs. Although the mechanical vacuum arc-extinguishing on-load tap-changing switch has a simple structure and high reliability, if a vacuum leak occurs in the vacuum tube, the arc may not be extinguished or vacuum electrical breakdown may occur under the action of overvoltage, resulting in an inter-stage short-circuit accident. If safety protection backup measures are added, the number of transition resistors and vacuum tubes needs to be increased, which increases the cost. With the development of power electronics technology, on-load voltage regulators include two routes. One is the full power electronic switch, which replaces all mechanical switches with power electronic switches, and uses the arc-free current-breaking characteristics of power electronic devices to improve the voltage regulation switching process of the on-load voltage regulator transformer. The other is the power electronic hybrid switch, which uses the short-time cut-in of power electronic devices during the switching process to cancel the traditional transition resistance branch to prevent the generation of arcs. The full power electronic switch on-load voltage regulator device, its voltage regulating tap mostly uses two reverse parallel thyristors as tap switches, and its voltage regulating coil is set on the primary side of the transformer, which includes the main winding, the primary side voltage regulating winding and two groups of power electronic switches. The low-voltage side of the transformer is connected to the load, and the power electronic switch is turned on and off by controlling the thyristor trigger pulse, thereby realizing the input and cut of the voltage regulating winding. For circuits where the thyristor conduction time is not easy to accurately determine, transition resistors can also be added to limit the overcurrent that may occur during the switching process; in order to reduce the number of power electronic tap switches and achieve the purpose of cost saving, the power electronic switches can also be coded and managed according to the voltage regulation requirements. Through the combination of multiple switch states, a small number of voltage regulating windings are combined into multiple voltage regulating states, thereby reducing the number of taps of the graded voltage regulating windings and simplifying the system structure. The composite on-load tap-changing switch is a mechanical and power electronic hybrid voltage regulation technology formed by mechanical switches and power electronic switches, which can form the technical advantages of small conduction loss and arc-free and impact-free switching. Its characteristics are that mechanical switches are used in most of the operating time, and power electronic switches are only put into use when switching taps, thus combining the advantages of high reliability of mechanical switches and arc-free and impact-free switching of power electronic switches. The traditional composite on-load tap-changing transformers in the power system are mainly regulated by combined, star-shaped neutral point, and double transition resistor on-load tap-changing switches. Generally, arc-free on-load tap-changing switches with thyristors combined with mechanical switches cannot reliably extinguish arcs, and have complex electrical structures.In recent years, some improvement schemes have been proposed. For example, the on-load tap changer is composed of three single-phase structures, each phase is independent of each other. During the switching process, the power electronic switch first cuts off the current, and then the mechanical switch is performed to achieve arc-free switching of the tap. In addition, the load current is continuous during the whole process. Although there will be a circulating current during the switching process, it is limited by the current limiting resistor. Although there are certain disadvantages in the voltage regulation time, some scholars have proposed a topological scheme using a composite switch cascade H-bridge module as a new type of on-load tap changer. The composite switch contains fast mechanical switches, power electronic switches, metal oxide varistors and other core components. The main branch is composed of a fast mechanical switch to conduct stable transformer load current; the transfer branch is composed of two back-to-back series IGBTs to realize current transfer during the transformer voltage regulation switching process, and the auxiliary mechanical switch realizes arc-free breaking. The composite switch is used to form a cascade H-bridge module to realize the coding voltage regulation of the voltage regulation winding, which improves the response speed of the voltage regulation and realizes its fast, wide and arc-free on-load voltage regulation. In general, the basic idea of ​​the above switch-type on-load voltage-regulating transformers is to adjust the load voltage by controlling the switch states of various types and switching on or off the transformer voltage-regulating windings. This type of voltage regulation method is a step-by-step regulation method for the load voltage and cannot achieve stepless voltage regulation. As the structure and control of future power grids become more and more complex, it is urgent to improve the voltage optimization method of the distribution network and seek more effective voltage optimization methods.

[0046] Traditional on-load voltage-regulating transformers can only regulate voltage according to certain discrete steps, and cannot achieve stepless voltage regulation. Frequent adjustment of transformer taps will also cause equipment wear and reduce service life. In addition, the response speed is slow when dealing with high-frequency photoelectric fluctuations and rapidly changing loads. In order to better deal with the problem of voltage fluctuations, various devices for dealing with voltage fluctuations have emerged, including dynamic voltage restorers, power electronic transformers and other devices. The dynamic voltage restorer device has good dynamic characteristics. However, the device requires an additional large low-frequency transformer or capacitor bank, resulting in high costs. The power electronic transformer can achieve controllable voltage and current. At the same time, it can also connect to AC and DC power grids, and has flexible reliability. Although its advantages are obvious, it is expensive and has not been widely used.

[0047] AC-AC converters, as links of AC energy, can be divided into direct and indirect types. Indirect AC-AC technology is essentially AC-DC-AC technology, which consists of a rectifier module, a DC energy storage unit, and an inverter module. The indirect converter can simultaneously control the amplitude, phase, and frequency of AC power, and has a flexible control method. However, due to the existence of a DC energy storage unit, the indirect converter has a short service life, a large footprint, and high operating and maintenance costs. Direct AC-AC technology does not have a DC energy storage unit, and the AC energy passes directly through the converter without conversion. This gives the direct AC-AC converter the advantages of simple structure, small size, high efficiency, and low operating and maintenance costs.

[0048] Direct AC-AC converters also have shortcomings. For example, most topologies are difficult to control the AC voltage amplitude and phase simultaneously. With the development of science and technology, domestic and foreign researchers have combined the advantages of traditional transformers and power electronic transformers, and proposed the concept of hybrid transformers, also called flexible voltage regulators. It combines the stability and high efficiency of traditional transformers with the functions of power electronic transformers to improve power quality and flow control. Compared with traditional transformers, it has more complete functions, can face more complex situations and more precise control, and has higher conversion efficiency and lower cost than power electronic transformers.

[0049] As the adjustable range increases, the capacity and cost of power electronic modules will also increase accordingly, and the operating efficiency, power density and manufacturing cost of hybrid transformers will gradually become prominent. At the same time, in the current distribution network voltage optimization, most of them are single-stage optimization solutions. The single-layer optimization method integrates all decision variables and objective functions in a unified framework for optimization. The model is simple and the solution speed is fast, but it may not fully tap the system potential, resulting in a local optimal solution. In addition, the single-layer optimization lacks flexibility and is difficult to adapt to rapidly changing grid conditions and needs.

[0050] In order to cope with a series of problems such as voltage fluctuations caused by a high proportion of photovoltaic access to the distribution system, a power electronic embedded hybrid on-load tap-changing transformer is used in the voltage optimization of the distribution network. The embodiment of the present application provides a distribution network voltage discrete-continuous layer optimization method of a hybrid on-load tap-changing transformer, which aims to solve the voltage over-limit problem caused by photovoltaic backflow and optimize the voltage within a more reasonable range. At the same time, it can improve the absorption rate of new energy photovoltaics, reduce the number of switching times of the transformer mechanical taps, the operating costs and losses of the system, and achieve economic and stable operation of the system. Through this method, intelligent management of power grid operation can be achieved, the stability and reliability of the system can be enhanced, it is helpful to balance the supply and demand of electricity, promote the development of the power grid system towards intelligence and flexibility, and promote the continuous integration of renewable energy in the power resource system and its application in a wider range.

[0051] In some embodiments, Figure 2 As shown, the hybrid on-load tap-changing transformer comprises: a primary circuit on the primary side, a magnetic conductor and a secondary circuit on the secondary side; The primary circuit includes a stepped winding and a power electronic converter, and the power electronic converter is connected to the magnetic conductor via a compensation winding; The input end of the power electronic converter is connected to a plurality of corresponding tapped windings via a plurality of parallel mechanical taps.

[0052] The stepped winding includes a main winding and a plurality of tap windings connected in sequence, and each tap winding is respectively connected to a mechanical tap.

[0053] The mechanical taps include K1, K2, K3, and K4.

[0054] As an important device for regulating voltage and maintaining voltage stability in the power grid, the on-load voltage-regulating transformer has also put forward higher and higher requirements for its voltage regulation capability. Existing on-load voltage-regulating transformers can only regulate voltage according to certain discrete steps, and cannot achieve stepless voltage regulation; the action speed is slow, and the switch action life is short; it cannot regulate reactive power, and a reactive power compensation device needs to be configured to solve the reactive power shortage. Although all-solid-state power electronic transformers can achieve the above functions, they need to have 100% power regulation capability and are expensive. The embodiment of the present application integrates a single-output AC-AC converter at the mechanical tap of the adjustable winding of a traditional transformer to form a new power electronic embedded hybrid voltage-regulating transformer, which can achieve fast stepless voltage regulation through a small part of the voltage control.

[0055] In some embodiments, the power electronic converter is a single output AC-AC converter; The input inductor L connected in sequence in , the first half bridge, the second half bridge, the input capacitor C in , the third half-bridge, output inductor L out and output capacitor C out , output capacitor C out Connected in parallel with the compensation winding; The first group of half bridges includes two half bridge modules connected in series, and the half bridge modules include a switch tube and a freewheeling diode connected in parallel. The switch tube is an IGBT. The first group of half bridges, the second group of half bridges and the third group of half bridges have the same structure.

[0056] In some embodiments, the first group of half-bridges includes a half-bridge module in which a switch tube Q1 and a freewheeling diode D1 are connected in parallel, and a half-bridge module in which a switch tube Q2 and a switch tube D2 are connected in parallel; The second half-bridge group includes a half-bridge module in which the switch tube Q3 and the freewheeling diode D3 are connected in parallel, and a half-bridge module in which the switch tube Q4 and the switch tube D4 are connected in parallel; The third half-bridge group includes a half-bridge module in which the switch tube Q5 and the freewheeling diode D5 are connected in parallel, and a half-bridge module in which the switch tube Q6 and the switch tube D6 are connected in parallel.

[0057] In some embodiments, the first half-bridge, the second half-bridge, and the input inductor L in And the input capacitor C in The boost module of the power electronic converter is composed of the third half-bridge and the output capacitor C out Buck modules that make up the power electronic converter; The working state of the boost module is a first state and a second state; In the first state, the switch tubes Q2 and Q4 are turned on, the switch tubes Q1 and Q3 are turned off, and the current flows through the switch tube Q2 and the freewheeling diode D4 of the switch tube Q4 to form a loop. The input voltage of the power electronic converter is the input inductor L in Charge; In the second state, the switch tubes Q1 and Q4 are turned on, the switch tubes Q2 and Q3 are turned off, and the current flows through the freewheeling diode D1 of the switch tube Q1 and the input capacitor C in , and the freewheeling diode D4 of Q4 form a loop, the input voltage of the power electronic converter and the input inductor L in At the same time, the input capacitor C in Charge; The working states of the step-down module are a third state, a fourth state and a fifth state; In the third state and the fourth state, the switch tubes Q4 and Q5 are turned on, the switch tubes Q3 and Q6 are turned off, the switch tube Q1 in the boost module is turned on, the switch tube Q2 is turned off, and the current flows through the input capacitor C in , switch tube Q5, output inductor L out , load winding, and switch tube Q4 form a loop, input capacitor C in is the output inductor L out and load winding power supply; In the fifth state, Q4 and Q6 are turned on, Q3 and Q5 are turned off, and the current flows through the output inductor L out , load winding, Q4, and Q6's freewheeling diode D6 form a loop. In this state, the output inductor L out Continue current to provide energy to the load winding.

[0058] The double-layer optimization method for distribution network voltage provided by the present application combines the primary side of the traditional on-load voltage-regulating transformer with the power electronic converter by setting the target transformer. The access of the primary winding can be realized by controlling the mechanical tap, thereby changing the main transformation ratio of the transformer. The power electronic converter is connected in series with the primary winding. The total voltage of the primary side can be adjusted by controlling the output compensation voltage of the power electronic converter, and finally the transformation ratio of the entire transformer is changed equivalently, so as to achieve stable regulation of the system voltage. The mechanical switch can realize the disconnection and closing operation in the no-load state, and no arc will be generated in this process. The voltage regulation in this process belongs to step voltage regulation. In addition, the necessary series compensation can be realized by connecting the power electronic converter in series on the primary side to stabilize the voltage at both ends of the load. Specifically, under normal circumstances, the system only closes one of the mechanical switches. When voltage fluctuations occur, the system can change the state of each mechanical switch to put in or cut off part of the step winding, change the transformation ratio of the transformer to achieve step voltage regulation; and can also realize stepless voltage regulation by applying a control strategy to the power electronic converter so that it can output a compensation voltage with controllable amplitude, so as to finally stabilize the voltage at both ends of the load.

[0059] like Figure 3 As shown, in the two-layer optimization method for distribution network voltage, the two-layer optimization can be completed through discrete layer and continuous layer; The discrete layer has a discrete layer model built in, and the input data is input into the discrete layer model to obtain the mechanical tap position of the target transformer and the number of capacitor group switching groups output by the discrete layer model; The continuous layer has a built-in continuous layer model. The mechanical tap position and the number of capacitor group switching groups are input into the continuous layer model to obtain the compensation capacity of STATCOM, energy storage charging and discharging power and power electronic converter compensation ratio output by the continuous layer model. The voltage distribution of the distribution network system is determined based on the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter. It can be judged whether the voltage exceeds the limit based on the voltage distribution. When it is determined that the voltage does not exceed the limit, a second optimization scheme including the optimal configuration is obtained.

[0060] Among them, in the discrete layer, the discrete layer model takes the minimum line loss as the goal, and optimizes the mechanical tap position and the number of capacitor groups switched on and off while ensuring that the voltage does not exceed the limit. The continuous layer takes the new energy consumption rate, operating costs and line losses as the goals, and optimizes the compensation capacity of STATCOM, the energy storage charging and discharging power and the compensation changes of the power electronic converter to meet the smaller voltage deviation. The discrete layer and continuous layer models interact to form the final optimization solution.

[0061] The input voltage of the entire transformer is V in The voltage on the stepped winding and the input voltage of the power electronic converter Composition. That is: (Formula 1) When the mechanical tap K is in a specific position, the output voltage of the step-by-step voltage regulation part is fixed. Assume that the input voltage of each part is: (Formula 2) (Formula 3) In the formula, is the amplitude of the grid-side input sinusoidal voltage, is the voltage amplitude at the input side of the power electronic converter; is the angular frequency of the input sine wave; a is the amplitude ratio of the two input voltages.

[0062] The voltage on the step winding is converted to the voltage on the secondary side: (Formula 4) In the formula, k1 is the transformation ratio of the stepped winding, and the calculation formula is: (Formula 5) In the formula, k0 is the rated transformation ratio of the transformer, g is the gear position of the mechanical tap at the current moment, and g max is the maximum value of the mechanical tap position, and Δk is the adjustment step.

[0063] Voltage stability is one of the key factors to ensure the safe and stable operation of the power system. As the main equipment responsible for voltage level conversion in the power grid, the core function of the on-load tap-changing transformer is to change the number of turns of the connected winding by adjusting the switch state of the mechanical tap. This adjustment process aims to achieve stable operation of the load voltage within a specific working range and ensure reliable power supply of the power grid. Traditional on-load tap-changing transformers often use mechanical switches. However, the structure of this switch is quite complex. When switching, it is easy to cause arcing, which in turn damages the contacts. The action time of the switch is long, and it is difficult to accurately control the specific time point of its switching. In addition, the traditional on-load tap-changing transformer also has the following weak links: the mechanical tap is fixed, the voltage regulation can only be in a certain step length, and it is difficult to smoothly steplessly regulate the voltage; the action response is slow, and it is difficult to adapt to occasions with fast dynamic changes. The continuous progress of power electronics technology has made it possible for on-load tap-changing switches to switch without arcing. By using the full power electronic switch topology to replace all traditional mechanical switches with AC-AC converters, the arc-free current interruption characteristics of power electronic devices are used to optimize the voltage regulation switching process. However, the full power electronic transformer has high cost and complex control strategy. Although it has rich functions, it has poor stability. Alternatively, through the hybrid AC-AC converter topology, only some mechanical switches are replaced with power electronic switches, which reduces the cost and improves the stability while preventing arc generation. The power electronic link of the hybrid transformer is a direct AC-AC converter. The hybrid transformer integrates the advantages of traditional transformers and full power electronic transformers and has high application value.

[0064] like Figure 2 As shown in the figure, the dotted box part shows a single output AC-AC converter, Q represents an NPN type IGBT, D represents a freewheeling diode, Q1, D1 and Q2, D2 form the first half bridge, and the input inductor L in Q3, D3 and Q4, D4 form the second half-bridge, Q5, D5 and Q6, D6 form the third half-bridge, and the output inductor L out The first half bridge, the second half bridge, and the input inductor L in And the input capacitor C in The boost module of the power electronic converter, the third half-bridge and the output inductor L out It constitutes the step-down module of the power electronic converter.

[0065] In the boost module modulation scheme, the inductor has two stages of charging and discharging. According to this idea, it should be prioritized to make sure that Q3 and Q4 are turned on at the industrial frequency, and then determine whether Q3 or Q4 is turned on first, to find the stage that can charge or discharge the inductor.

[0066] If Q3 is turned on first, no matter what working state Q1 and Q2 are in, in the positive half cycle, the current only flows from the power supply through the input inductor L in The circuit is formed, but the inductor discharge stage is missing. Therefore, this solution is obviously not advisable. When Q3 and Q4 are turned on at the industrial frequency, Q4 must be turned on first. Then the conduction mode of Q1 and Q2 is determined. The analysis method is the same as that of Q3 and Q4. Q1 and Q2 can be turned on at high frequency or low frequency. In one switching cycle, there are two conduction states for each switch. The buck module is mainly composed of switches Q5, Q6 and output inductor L out In order to achieve the step-down function, a period of time is required in a switching cycle to rely on the input capacitor C in power supply, and for a period of time the capacitor cannot participate in the power supply, relying only on the output inductor L out According to this idea, and combined with the control strategy of switches Q1 to Q4 in the boost module modulation, there are three conduction states of each switch in a switching cycle.

[0067] Next, the current flow path and the energy conversion relationship between inductors, capacitors and other components under various working conditions are as follows: If Q1 and Q2 are turned on at high frequency, and the on-duty ratios of Q2 and Q5 are D Q2 , D Q5 , the switching cycle is T, taking the positive half cycle of the input AC as an example, the working state of the boost module can be divided into [0-D Q2 T] and [D Q2 TT]. In [0-D Q2 In the T] stage, Q2 and Q4 are turned on, Q1 and Q3 are turned off, and the current flows through Q2 and the freewheeling diode D4 of Q4 to form a loop. In this state, the input voltage of the power electronic converter is the input inductor L in Charging. Q2 In the TT phase, Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the current flows through the freewheeling diode D1 of Q1 and the input capacitor C in , and the freewheeling diode D4 of Q4 form a loop. In this state, the input voltage of the power electronic converter and the input inductor L in At the same time, the input capacitor C in Charge.

[0068] The working state of the buck module can be divided into [0-D Q2 T]、[D Q2 TD Q5 T], and [D Q5 TT]. In [0-D Q2 T] and [D Q2 TD Q5T] stage, Q4 and Q5 are turned on, Q3 and Q6 are turned off, the difference is that in [0-D Q2 In the [D Q2 TD Q5 In the T] stage, Q1 in the boost module is turned on and Q2 is turned off. At this time, the current flows through the input capacitor C in , Q5, output inductor L out , load winding, and Q4 form a loop. In this state, the input capacitor C in Equivalent to the power supply, which is the output inductor L out and load windings. Q5 In the TT phase, Q4 and Q6 are turned on, Q3 and Q5 are turned off, and the current flows through the output inductor L out , load winding, Q4, and Q6's freewheeling diode D6 form a loop. In this state, the output inductor L out The continuous current provides energy for the load winding. When the input AC power is in the negative half cycle, it is only necessary to make the modulation strategy centrally symmetrical, and the specific modulation strategy will not be described in detail.

[0069] In some embodiments, the relationship between the output voltage and the input voltage of the power electronic converter is: (Formula 6) in, is the input voltage of the power electronic converter, is the output voltage of the power electronic converter, is the conduction duty cycle of the switch tube Q5, is the conduction duty cycle of the switch tube Q2; Output voltage of power electronic converter Converted to the secondary voltage for: (Formula 7) Among them, k2 is the transformation ratio of the compensation winding, Input voltage and input voltage The amplitude ratio of is the amplitude of the grid-side input sinusoidal voltage, is the voltage amplitude at the input side of the power electronic converter, is the angular frequency of the input sine wave; The output voltage of the target transformer is : (Formula 8) in, The voltage on the step winding is converted to the voltage on the secondary side. is the input voltage of the target transformer.

[0070] Therefore, by controlling the position of the mechanical tap and the duty cycle of each switch of the power electronic converter, the equivalent total transformation ratio of the entire transformer can be accurately adjusted, thereby achieving system voltage stability.

[0071] According to the voltage optimization problem of the distribution network system of the target transformer, the highest clean energy consumption rate, the lowest active power loss of the distribution network system and the lowest operating cost are selected as the objective function as the optimization mathematical model here; at the same time, considering the range allowed by the constraints, the optimal value is solved by the simulated annealing particle swarm fusion algorithm.

[0072] In this embodiment, the advantages of high overload capacity and low conduction loss of the mechanical switch of the voltage regulating device of the traditional on-load tap-changing transformer are combined, and the power electronic converter is integrated into the tap-changing switch part of the on-load tap-changing transformer to form a new hybrid on-load tap-changing transformer to realize the voltage step-by-step and stepless regulation functions of the transformer. When the step-by-step and stepless voltage regulation are coordinated, the transformation ratio of the on-load tap-changing transformer is first changed by the mechanical switch to adjust to cope with a wide range of voltage fluctuations, and then the power electronic converter connected in series on the primary side can output an accurate and effective compensation voltage, and the fast stepless voltage regulation can be achieved through the compensation voltage control. It is a low-cost new power grid equipment that can solve the voltage limit problem caused by "photovoltaic backflow" and optimize the voltage within a more reasonable range. At the same time, through the hierarchical optimization of discrete layers and continuous layers, and the coordinated control of the output results of on-load tap-changing transformers, capacitor banks, STATCOM, energy storage devices and other devices, it is possible to achieve voltage optimization that takes into account multiple objective functions, and can also greatly improve the grid's ability to absorb renewable energy, reduce the number of switching times of the transformer's mechanical taps, the system's operating costs and losses, improve the grid's power factor, improve transmission efficiency, and achieve economical and stable operation of the system, which has broad application prospects.

[0073] In the discrete layer optimization model, the objective function of the discrete layer is based on the line loss Minimum target ： (Formula 9) Where N is the total number of nodes in the distribution network system; is the conductance between nodes i and j; , are the voltages at nodes i and j respectively; is the voltage phase angle difference between nodes i and j.

[0074] Leave The constraints of the discrete layer include: voltage constraint, mechanical tap position constraint, mechanical tap adjustment times constraint The voltage constraint is ： (Formula 10) Where: and are the maximum and minimum values ​​of the voltage at node i, respectively.

[0075] Mechanical tap position constraints ： (Formula 11) Where: Tap t is the gear position of the tap at time t; min 、Tap max They are the minimum and maximum values ​​of the tap position respectively.

[0076] Mechanical tap adjustment times constraints ： (Formula 12) Where: Tap t+1 is the position of the tap at time t+1; Tmax is the maximum number of times the tap can be adjusted.

[0077] Constraints on the number of capacitor banks switched on and off: (Formula 13) Where: N t N is the number of capacitors switched on and off at time t; max The maximum number of capacitor groups that can be switched on and off.

[0078] In the continuous layer objective function of the continuous layer optimization model ， Operating costs include the photovoltaic system investment cost C p , Cost of purchasing electricity from the power grid C g , Mechanical tapping action cost C t , capacitor bank switching cost C c and the energy storage device cost C b The objective function expression is as follows: (Formula 14) in: (Formula 15) (Formula 16) (Formula 17) (Formula 18) (Formula 19) In the formula, C pv is the unit power cost of photovoltaic power generation; P pv,tis the photovoltaic power generation power of the system at time t; C gird,t is the grid electricity price at time t; P gird,t is the amount of electricity purchased and sold at time t; C oltc is the cost of a single mechanical tap action; T oltc,t is the number of times the mechanical tap is adjusted at time t; C cb is the unit switching cost of the capacitor bank; T cb,t is the number of capacitor groups switched at time t; C bess P is the unit power cost of charging and discharging the energy storage device; bess,t is the charging and discharging power of the energy storage device at time t.

[0079] Regarding the new energy consumption rate ， The solution of the maximum photovoltaic absorption rate is transformed into the solution of the minimum photovoltaic abandonment rate to facilitate the unified solution of the objective function. The objective function expression is as follows: (Formula 20) Where: P av,t is the total photovoltaic power consumption of the system at time t.

[0080] Continuous layer constraints include voltage constraints 、 Photovoltaic system output constraints, energy storage device constraints, STATCOM output constraints and power electronic transformer regulation constraints.

[0081] Voltage Constraints: The continuous layer voltage is constrained to a more reasonable scope Therefore, the voltage constraint is modified to: (Formula 21) Where: , are the maximum and minimum values ​​of the voltage at node i after double-layer optimization.

[0082] Photovoltaic system output constraints: (Formula 22) (Formula 23) Where: P pv,max , P pv,min are the maximum and minimum values ​​of active power injected into the photovoltaic system respectively; Q pv,max , Q pv,min They are the maximum and minimum values ​​of reactive power injected into the photovoltaic system respectively.

[0083] Energy storage device constraints: (Formula 24) (Formula 25) (Formula 26) Where: SOC bess,t+1 , SOC bess,t are the charge states of the energy storage device at time t+1 and time t respectively; η c , η d are the charging and discharging efficiency of the energy storage device respectively; , are the charging and discharging power of the energy storage device at time t; ΔT is the unit time length; E bess is the capacity of the energy storage device. bess,max , P bess,min are the maximum and minimum values ​​of the charging and discharging power of the energy storage device connected to node i; SOC bess,i SOC is the state of charge of the energy storage device connected to node i; bess,max , SOC bess,min Node The maximum and minimum state of charge of the connected energy storage device.

[0084] STATCOM output constraints: (Formula 27) Where: Q statcom,i is the reactive power compensation power of node i connected to STATCOM; Q statcom,max , Q statcom,min are the maximum and minimum values ​​of reactive power compensated by STATCOM respectively.

[0085] Power Electronic Transformer Regulation Constraints: (Formula 28) Where: K compensate is the compensation transformation ratio of the power electronic transformer; K compensate,max , K compensate,min They are respectively the maximum and minimum values ​​that the power electronic transformer regulation ratio can continuously compensate.

[0086] In some embodiments, Figure 2 As shown, through the first half bridge, the second half bridge, and the input inductor L in And the input capacitor C in The boost module of the power electronic converter is composed of the third half-bridge and the output capacitor C out Buck modules that make up the power electronic converter; The working state of the boost module is a first state and a second state; In the first state, the switch tubes Q2 and Q4 are turned on, the switch tubes Q1 and Q3 are turned off, and the current flows through the switch tube Q2 and the freewheeling diode D4 of the switch tube Q4 to form a loop. The input voltage of the power electronic converter is the input inductor Lin Charge; In the second state, the switch tubes Q1 and Q4 are turned on, the switch tubes Q2 and Q3 are turned off, and the current flows through the freewheeling diode D1 of the switch tube Q1 and the input capacitor C in , and the freewheeling diode D4 of Q4 form a loop, the input voltage of the power electronic converter and the input inductor L in At the same time, the input capacitor C in Charge; The working states of the step-down module are a third state, a fourth state and a fifth state; In the third state and the fourth state, the switch tubes Q4 and Q5 are turned on, the switch tubes Q3 and Q6 are turned off, the switch tube Q1 in the boost module is turned on, the switch tube Q2 is turned off, and the current flows through the input capacitor C in , switch tube Q5, output inductor L out , load winding, and switch tube Q4 form a loop, input capacitor C in is the output inductor L out and load winding power supply; In the fifth state, Q4 and Q6 are turned on, Q3 and Q5 are turned off, and the current flows through the output inductor L out , load winding, Q4, and Q6's freewheeling diode D6 form a loop. In this state, the output inductor L out Continue current to provide energy to the load winding.

[0087] In some embodiments ， like Figure 4 As shown, considering the range allowed by the constraints, the optimal value is solved by simulated annealing particle swarm fusion algorithm 。

[0088] The voltage regulation problem of the distribution network system covers complex factors such as photovoltaic power generation and energy storage systems. At the same time, the multidimensional complexity of its objective function and constraint conditions makes it difficult for traditional analytical methods to obtain accurate solutions. The simulated annealing algorithm has a strong global search capability. When encountering a poor solution, there is a certain probability of jumping out of the local optimal solution, but it requires a very high annealing temperature, so its convergence speed is slow; the particle swarm algorithm has a faster optimization speed, but it is easy to fall into the local optimal solution.

[0089] Therefore, this method integrates the simulated annealing algorithm and the particle swarm algorithm, introduces the idea of ​​simulated annealing probability jump, overcomes the premature defect of the particle swarm algorithm, accelerates the convergence speed of the simulated annealing algorithm, and improves the performance of the algorithm as a whole.

[0090] Initialize the simulated annealing temperature T, generate a random solution x0, randomly perturb the initial solution to generate a new feasible solution x1, calculate the difference Δf of the objective function corresponding to the two solutions, and decide whether to accept the new solution with a specific probability. The probability calculation formula is: (Formula 29) Among them, the random solution x0 and the feasible solution x1 can be various decision variables, such as mechanical tap gear, the number of capacitor groups, the compensation capacity of STATCOM, the energy storage power, the compensation ratio of the power electronic converter, etc.

[0091] By repeating the perturbation at a certain temperature, the annealing temperature controls the solution process towards the optimal method, and there is also a certain probability of accepting a worse solution to escape the local optimal value.

[0092] The particle swarm algorithm with convergence factor can ensure that the solution is not limited by boundaries and speed. When the algorithm iterates to the mth generation, assuming that the optimal solution of the individual is P best , the global optimal solution is G best , the corresponding particle velocity and position update formula is: (Formula 30) (Formula 31) (Formula 32) Where: v m+1 、v m are the velocities of the m+1th and mth generation particles respectively; x m+1 、x m are the positions of the m+1th and mth generation particles respectively; μ is the convergence factor; c1 is the individual learning coefficient; c2 is the global learning coefficient; r1 and r2 are both random numbers between 0 and 1.

[0093] In order to prevent the global optimal value from being in the local optimal value, causing all particles to seek the optimal value, making the search ability worse, a random one of the individual optimal values ​​is Replace the global optimal value G best : (Formula 33) Calculate the speed and position of each particle according to the updated formula, and then calculate its fitness to perform annealing operation to determine whether the set annealing temperature T is reached. s That is, the termination condition is met until the optimal result is output.

[0094] In some embodiments, after obtaining the second optimization solution, the method further includes: When it is determined that the voltage of the distribution network system in the second optimization scheme exceeds the limit, the gear of the mechanical tap of the target transformer and the number of capacitor groups switched on and off are re-optimized according to the input data until the voltage of the distribution network system in the second optimization scheme does not exceed the limit, and the distribution network system is configured according to the second optimization scheme.

[0095] In some embodiments, Figure 5 As shown, the power distribution network system includes nodes 1 to 33; Nodes 1 to 18 are connected in sequence, a power electronic embedded hybrid on-load tap-changing transformer (target transformer) is connected between 2 and 3, node 10 is connected to the first photovoltaic power generation system, node 14 is connected to the first capacitor bank (STATCOM), and node 18 is connected to the second photovoltaic power generation system and the energy storage device; Node 2 is also connected to nodes 19 to 22 connected in sequence, node 20 is connected to a third photovoltaic power generation system, and node 20 is connected to a second capacitor bank (STATCOM); Node 3 is also connected to nodes 23 to 25 which are connected in sequence; The node 6 is also connected to the nodes 26 to 33 which are connected in sequence, the node 32 is connected to the fourth photovoltaic power generation system, and the node 33 is connected to the third capacitor group (STATCOM).

[0096] Taking the improved IEEE33-node distribution network system as an example, the effectiveness of the double-layer optimization method for distribution network voltage in this application is verified. On the basis of the original standard IEEE33-node system, a transformer is connected between nodes 2 and 3, the adjustment step is 1%, the power electronic mechanical tap position compensation range is 0.9-1.1, and a capacitor group with a rated number of 10 groups is connected at nodes 14 and 28, and the rated capacity of a single group is 0.1Mvar. A photovoltaic system with a rated capacity of 8MVA is connected at nodes 10 and 20, a STATCOM with a rated capacity of 1MVar is connected at nodes 15 and 30, and an energy storage device with a rated capacity of 8MVA is connected at node 20.

[0097] Three different methods are used for comparative analysis. Method 1 is a common on-load voltage-regulating transformer, while Method 2 is a power electronic embedded hybrid transformer used in this scheme. Both methods are common single-stage solutions. The comparison can reflect the advantages of power electronic embedded hybrid transformers in optimizing the voltage of distribution networks. Method 3 uses a power electronic embedded hybrid transformer and adopts the proposed discrete-continuous layer optimization method. Compared with Method 2, Method 3 can reflect the advantages of the proposed discrete-continuous double-layer optimization method.

[0098] like Figure 6-9The following are the node voltage distribution diagrams before optimization and after optimization using three different methods. It can be seen that the voltage effect of method 1 has improved compared with that before optimization, but the voltage deviation of some nodes is still large, with the maximum node voltage exceeding 1.08pu and the minimum below 0.92pu. Compared with method 1, method 2 has better node voltage optimization effect, with the maximum node voltage not exceeding 1.08pu and the minimum above 0.92pu. Method 3 has the best optimization effect, which can be stabilized between 1.04-0.92pu and has a smaller fluctuation.

[0099] like Figure 10-12 The following are the changes of the mechanical tap position of the transformer in three different methods. The number of mechanical tap actions in method 1 is 13 times, and the number of mechanical tap actions in methods 2 and 3 is 2 times.

[0100] like Fig.13 The figure shows the equivalent total transformation ratio after transformer compensation in method 3. When the mechanical tap is operated only twice, the power electronic transformer continuously outputs the compensation voltage, which can achieve accurate regulation of the system voltage.

[0101] Table 1 below shows the comparison of parameters under different optimization methods. Before optimization, the total voltage deviation was 41.989pu, the new energy consumption rate was 87.800%, the operating cost was 313890.961 yuan, and the network loss was 7.581MW; the total voltage deviation of method 1 was 12.555pu, the number of capacitor switching groups was 280 groups, the new energy consumption rate was 93.934%, the operating cost was 298461.417 yuan, and the network loss was 5.404MW; the total voltage deviation of method 2 was 10.659pu, the number of capacitor switching groups was 240 groups, the new energy consumption rate was 95.712%, the operating cost was 293408.055 yuan, and the network loss was 5.175MW; the total voltage deviation of method 3 was 6.863pu, the number of capacitor switching groups was 180 groups, the new energy consumption rate was 97.079%, the operating cost was 289582.912 yuan, and the network loss was 4.864MW. After comparison, it was found that method 3 has better optimization effect on various parameter indicators than other methods, which proves the effectiveness of the proposed optimization method.

[0102] Table 1 Summary of optimization results of different methods

[0103] In this embodiment, by integrating the traditional on-load tap-changing transformer with the power electronic converter, the power electronic converter is used for continuous ratio compensation to achieve fast and stepless voltage regulation, thereby enhancing the flexibility and accuracy of system voltage regulation. In this two-layer optimization method, the discrete layer uses the mechanical tap position and the number of capacitor group switching groups at each moment as decision variables, and the continuous layer uses the compensation capacity of STATCOM at each moment, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter as decision variables. A comprehensive optimization mathematical model is established with the clean energy consumption rate, operating cost, and line loss as the objective function to meet the voltage of each node within the constraint range. The simulated annealing algorithm is used to improve the particle swarm algorithm to solve the clean energy output strategy, the reactive compensation device output strategy, and the transformer voltage regulation strategy. It can jump out of the local optimal solution with a certain probability and search in the global range, avoiding falling into the local optimal solution and realizing the optimized operation of the entire power grid distribution system.

[0104] The present application also provides a distribution network voltage double-layer optimization device, which is applied to a distribution network system with multiple nodes, wherein the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, and the distribution network system is provided with a target transformer, wherein the target transformer is a hybrid on-load tap-changing transformer, and the target transformer is provided with a power electronic converter.

[0105] like Fig.14 As shown, the device comprises: An acquisition module 1410 is used to acquire input data of multiple nodes in the power distribution network system, wherein the input data includes node voltage parameters and transformer parameters; The first processing module 1420 is used to optimize the mechanical tap position of the target transformer and the number of capacitor bank switching groups with the goal of minimizing line loss and the constraint that the voltage of the distribution network system does not exceed the limit, so as to obtain a first optimization scheme; The second processing module 1430 is used to optimize the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter according to the mechanical tap position of the target transformer and the number of switched groups of the capacitor bank in the first optimization scheme, with the goal of maximizing the new energy consumption rate, minimizing the operating cost, and minimizing the line loss, so as to obtain a second optimization scheme; The third processing module 1440 is used to configure the distribution network system through the second optimization scheme when it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit.

[0106] The distribution network voltage double-layer optimization device provided in the embodiment of the present application can achieve the same technical effect as the distribution network voltage double-layer optimization method in the above embodiment, and will not be repeated here.

[0107] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A two-layer optimization method for distribution network voltage, characterized in that: Applied to a distribution network system having multiple nodes, the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, the distribution network system is provided with a target transformer, the target transformer is a hybrid on-load tap-changing transformer, and the target transformer is provided with a power electronic converter, the method comprises: Acquire input data of a plurality of nodes in the power distribution network system, wherein the input data includes node voltage parameters and transformer parameters; Taking the minimum line loss as the goal and the voltage of the distribution network system not exceeding the limit as the constraint, the mechanical tap position of the target transformer and the number of capacitor bank switching groups are optimized to obtain a first optimization scheme; According to the mechanical tap position of the target transformer and the number of switched capacitor groups in the first optimization scheme, the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter are optimized with the goal of maximizing the new energy consumption rate, minimizing the operating cost, and minimizing the line loss, thereby obtaining the second optimization scheme; When it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit, the distribution network system is configured using the second optimization scheme.

2. The double-layer optimization method for distribution network voltage according to claim 1 is characterized in that: The hybrid on-load tap-changing transformer comprises: a primary circuit on the primary side, a magnetic conductor and a secondary circuit on the secondary side; The primary circuit includes a stepped winding and a power electronic converter, and the power electronic converter is connected to the magnetic conductor via a compensation winding; The input end of the power electronic converter is connected to a plurality of corresponding tapped windings via a plurality of parallel mechanical taps.

3. The double-layer optimization method for distribution network voltage according to claim 2 is characterized in that: The power electronic converter is a single-output AC-AC converter; The input inductor L connected in sequence in , the first half bridge, the second half bridge, the input capacitor C in , the third half-bridge, output inductor L out and output capacitor C out , output capacitor C out Connected in parallel with the compensation winding; The first group of half bridges includes two half bridge modules connected in series, and the half bridge modules include a switch tube and a freewheeling diode connected in parallel. The switch tube is an IGBT. The first group of half bridges, the second group of half bridges and the third group of half bridges have the same structure.

4. The double-layer optimization method for distribution network voltage according to claim 3 is characterized in that: The first half-bridge group includes a half-bridge module in which a switch tube Q1 and a freewheeling diode D1 are connected in parallel, and a half-bridge module in which a switch tube Q2 and a switch tube D2 are connected in parallel; The second half-bridge group includes a half-bridge module in which the switch tube Q3 and the freewheeling diode D3 are connected in parallel, and a half-bridge module in which the switch tube Q4 and the switch tube D4 are connected in parallel; The third half-bridge group includes a half-bridge module in which the switch tube Q5 and the freewheeling diode D5 are connected in parallel, and a half-bridge module in which the switch tube Q6 and the switch tube D6 are connected in parallel.

5. The double-layer optimization method for distribution network voltage according to claim 4 is characterized in that: Through the first half bridge, the second half bridge, and the input inductor L in And the input capacitor C in The boost module of the power electronic converter is composed of the third half-bridge and the output capacitor C out Buck modules that make up the power electronic converter; The working state of the boost module is a first state and a second state; In the first state, the switch tubes Q2 and Q4 are turned on, the switch tubes Q1 and Q3 are turned off, and the current flows through the switch tube Q2 and the freewheeling diode D4 of the switch tube Q4 to form a loop. The input voltage of the power electronic converter is the input inductor L in Charge; In the second state, the switch tubes Q1 and Q4 are turned on, the switch tubes Q2 and Q3 are turned off, and the current flows through the freewheeling diode D1 of the switch tube Q1 and the input capacitor C in , and the freewheeling diode D4 of Q4 form a loop, the input voltage of the power electronic converter and the input inductor L in At the same time, the input capacitor C in Charge; The working states of the step-down module are a third state, a fourth state and a fifth state; In the third state and the fourth state, the switch tubes Q4 and Q5 are turned on, the switch tubes Q3 and Q6 are turned off, the switch tube Q1 in the boost module is turned on, the switch tube Q2 is turned off, and the current flows through the input capacitor C in , switch tube Q5, output inductor L out , load winding, and switch tube Q4 form a loop, input capacitor C in is the output inductor L out and load winding power supply; In the fifth state, Q4 and Q6 are turned on, Q3 and Q5 are turned off, and the current flows through the output inductor L out , load winding, Q4, and Q6's freewheeling diode D6 form a loop. In this state, the output inductor L out Continue current to provide energy to the load winding.

6. According to one embodiment of the present application, the relationship between the output voltage and the input voltage of the power electronic converter is: ； in, is the input voltage of the power electronic converter, is the output voltage of the power electronic converter, is the conduction duty cycle of the switch tube Q5, is the conduction duty cycle of the switch tube Q2; Output voltage of power electronic converter Converted to the secondary voltage for: ； Where k2 is the transformation ratio of the compensation winding, Input voltage and input voltage The amplitude ratio of is the amplitude of the grid-side input sinusoidal voltage, is the voltage amplitude at the input side of the power electronic converter, is the angular frequency of the input sine wave; The output voltage of the target transformer is : ； in, The voltage on the step winding is converted to the voltage on the secondary side. is the input voltage of the target transformer.

7. The double-layer optimization method for distribution network voltage according to claim 1, characterized in that: The step of optimizing the mechanical tap position of the target transformer and the number of capacitor bank switching groups to obtain a first optimization scheme includes: Based on the learning factor and annealing speed, the fitness and particle position of each particle are calculated based on the initial particle position and velocity; The initial annealing temperature is obtained based on the optimal fitness; Based on the annealing initial temperature, calculating the annealing algorithm fitness of each particle; Based on the fitness of the annealing algorithm, the global optimum is replaced by individual random selection to update the position and speed of each particle and the optimal position of the population, and the fitness value is calculated to perform an annealing operation until the set annealing temperature is reached to obtain a first optimization solution.

8. The double-layer optimization method for distribution network voltage according to claim 1, characterized in that: After obtaining the second optimization solution, the method further includes: When it is determined that the voltage of the distribution network system in the second optimization scheme exceeds the limit, the mechanical tap position of the target transformer and the number of capacitor group switching groups are re-optimized according to the input data until the voltage of the distribution network system in the second optimization scheme does not exceed the limit, and the distribution network system is configured according to the second optimization scheme.

9. The double-layer optimization method for distribution network voltage according to claim 1, characterized in that: The power distribution network system includes nodes 1 to 33; Nodes 1 to 18 are connected in sequence, a power electronic embedded hybrid on-load tap-changing transformer is connected between 2 and 3, node 10 is connected to a first photovoltaic power generation system, node 14 is connected to a first capacitor bank, and node 18 is connected to a second photovoltaic power generation system and an energy storage device. Node 2 is also connected to nodes 19 to 22 connected in sequence, node 20 is connected to a third photovoltaic power generation system, and node 20 is connected to a second capacitor bank; Node 3 is also connected to nodes 23 to 25 which are connected in sequence; The node 6 is also connected to the nodes 26 to 33 which are connected in sequence, the node 32 is connected to the fourth photovoltaic power generation system, and the node 33 is connected to the third capacitor group.

10. A double-layer optimization device for distribution network voltage, characterized in that: Applied to a distribution network system having multiple nodes, the multiple nodes are connected to a photovoltaic power generation system or a capacitor bank, the distribution network system is provided with a target transformer, the target transformer is a hybrid on-load tap-changing transformer, the target transformer is provided with a power electronic converter, the device comprises: An acquisition module, used to acquire input data of multiple nodes in the distribution network system, wherein the input data includes node voltage parameters and transformer parameters; The first processing module is used to optimize the mechanical tap position of the target transformer and the number of capacitor bank switching groups with the goal of minimizing line loss and the constraint that the voltage of the distribution network system does not exceed the limit, so as to obtain a first optimization scheme; The second processing module is used to optimize the compensation capacity of STATCOM, the energy storage charging and discharging power, and the compensation ratio of the power electronic converter according to the mechanical tap position of the target transformer and the number of switched groups of the capacitor bank in the first optimization scheme, with the highest new energy consumption rate, the lowest operating cost, and the lowest line loss as the goal, to obtain a second optimization scheme; The third processing module is used to configure the distribution network system through the second optimization scheme when it is determined that the voltage of the distribution network system in the second optimization scheme does not exceed the limit.

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