Low-voltage transformer area distributed photovoltaic aggregation network construction method supported by energy storage flexible transformer

Abstract

After a high-proportion distributed photovoltaic is connected into a transformer area, voltage out-of-limit of a tail end line and heavy overload of a transformer are easily caused by volatility and randomness, but a traditional power grid cannot directly regulate and control the distributed photovoltaic, and reverse heavy overload of a plurality of photovoltaic transformer areas may cause reduction of active regulation capability of the power grid and increase of instability risk. The invention provides a photovoltaic court aggregation network construction method supported by an energy storage flexible transformer. According to the method, through flexible interaction of the energy storage flexible transformer and the distributed photovoltaic, the grid construction characteristics of the grid-connected points of the transformer area are transformed, and the functions of inertia simulation, one-time adjustment and the like of the micro-grid of the transformer area are achieved. And the power grid only needs to carry out communication and regulation on the energy storage flexible transformer, so that the management and control difficulty is greatly reduced. Meanwhile, through flexible charging and discharging of an embedded energy storage unit of the energy storage flexible transformer and series voltage control, the functions of power fluctuation suppression in the transformer area, voltage stabilization on the low-voltage side and the like can be achieved at the same time, and efficient decoupling of active support of an external power grid and stable adjustment of internal voltage is achieved.

Description

Technical Field

[0001] This invention relates to the field of grid connection of low-voltage distribution area photovoltaic-storage microgrids. In response to the grid construction support and dispatch response requirements of microgrids under high photovoltaic penetration conditions, it integrates energy storage collaborative control and virtual synchronous generator (VSG) grid construction mechanism to realize coordinated output of photovoltaic and energy storage, stable voltage / frequency support and flexible response to upper-level dispatch commands, forming a distribution area-level photovoltaic-storage microgrid system with active support capabilities. Background Technology

[0002] In recent years, the integration of high-proportion distributed photovoltaic (PV) power into low-voltage distribution areas has become an important trend in energy transformation. These distribution areas, by integrating local loads and supporting equipment, have gradually formed distribution area-level PV microgrids. The construction of such microgrids is not only an exploration of the efficient utilization of distributed energy resources, but also provides a new form for the flexible operation of the terminal power system. However, regional photovoltaic microgrids face significant challenges in operation. On the one hand, the inherent volatility and randomness of photovoltaic power generation can easily lead to voltage and power flow exceeding limits in both directions on the microgrid distribution lines. On the other hand, as the photovoltaic penetration rate within the microgrid area continues to increase, the inertia of the regional power grid decreases, its proactive regulation capability weakens, and the risk of system instability increases significantly. More importantly, traditional grid control models cannot communicate directly with distributed photovoltaic inverters, lacking efficient scheduling methods for such distributed resources, making it difficult to effectively solve the above problems. Against this backdrop, existing technologies are insufficient to meet the demands for stable and efficient operation of regional photovoltaic microgrids, necessitating an innovative technical solution to overcome these bottlenecks. This invention addresses this practical dilemma by proposing a photovoltaic microgrid aggregation method supported by a flexible energy storage transformer, aiming to resolve numerous current challenges through technological innovation. Summary of the Invention

[0003] This invention proposes the following technical solution: Constant voltage control is adopted on the series side of the energy storage flexible transformer to ensure the stability of the voltage reference in the distribution area; on the parallel side, the charging and discharging power constraints of the energy storage battery are prioritized, and then combined with the upper-level dispatch instructions, the net power of the distribution area, and the maximum apparent capacity of the parallel converter to generate the active and reactive power references for its VSG network; the grid-side POC node voltage reference is generated through VSG network control, and then generated through a voltage loop. I poc Reference, subtract load current I load To avoid the parallel converter carrying high power, the current loop control is ultimately used to generate a voltage reference command to drive the parallel converter.

[0004] This invention enables stable grid connection of net power in distribution areas, enhances the absorption and dispatch capabilities of distributed energy, ensures the safe and efficient operation of energy storage batteries, avoids overload of parallel equipment, and strengthens the coordinated response capability between distribution areas and the main power grid. It is suitable for AC / DC hybrid distribution areas that include photovoltaics and energy storage and require hierarchical dispatch response, providing strong support for the friendly grid connection and flexible control of distributed energy in new power systems.

[0005] The grid-side output current is measured based on the current sensor. i g Output current of series converter i se Output current of parallel converter i sh The load current i load For the turns ratio of series coupled transformers and i sh The product of these factors reduces the capacity requirement of the current sensor. The voltage at the point of common coupling is measured using the voltage sensor. v poc voltage at the common grid connection point v pcc ; The controller is used to receive grid power dispatch information, net power of distribution areas, and grid-connected power of medium-voltage nodes. Grid dispatch signals. disp This includes power dispatch instructions and inertia coefficients. The net power of the distribution area refers to the power of a high-proportion photovoltaic power generation cluster that can be fed into the grid after meeting local consumption requirements. P pcc , Q pcc The controller prioritizes the charging and discharging power constraints of the energy storage battery to determine the maximum and minimum charging and discharging power of the energy storage battery. P bat，max , P bat，min This allows for the generation of active power dispatch response commands for the parallel converter that meet energy storage power limits. ΔP sh Secondly, by combining the maximum apparent capacity of the parallel converter, a power reference for responding to grid reactive power dispatch is generated. ΔQ sh .

[0006] The controller performs VSG network control based on the generated parallel converter power reference and the net power of the transformer area, thereby obtaining the common grid connection point voltage amplitude reference of the parallel controllers. E poc，ref and phase reference θ refBased on this, dual closed-loop control of voltage and current is implemented for series and parallel converters; at the same time, power fluctuations are smoothed through energy storage charging and discharging to respond to dispatching needs and support the stable grid connection of net power in the distribution area.

[0007] The controller uses the node voltage amplitude reference generated by the common point of connection (POC) based on VSG control. E poc,ref Phase reference θ ref And the actual voltage feedback of POC, generating POC node current reference through voltage loop control. i g,ref ; The controller will obtain i g,ref Subtract the load current measured in real time i load Generate the output current reference of the parallel converter i sh,ref To avoid it carrying excessive power; The controller is based on the output current reference of the parallel converter. i sh,ref Through the inverter-side current of the actual parallel converter I sh,dq Perform current closed-loop control to generate a modulation wave reference for the parallel converter, which also serves as the voltage reference for the POC node. v poc,abc ref ; The controller is based on the obtained voltage amplitude reference of the POC node. E poc,ref Phase reference θ ref and control reference for PCC nodes E m The output current reference of the series converter is generated through voltage loop control. i se,ref ; The controller is based on the output current reference of the series converter. i se,ref Through the inverter side current of the actual series converter i se,dq To perform current closed-loop control, a modulation wave reference for the series converter is generated after coordinate transformation. v se,abc ref ; Based on the obtained modulation signals of the series converter and parallel converter, the controller obtains the drive signals of the series and parallel converters through the sinusoidal pulse width modulator.

[0008] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: 1. Simplified system connection and communication architecture: By using the energy storage flexible transformer as an intermediary, distributed photovoltaics do not need to be directly connected to the dispatch center, reducing the direct interaction links between distributed resources and the dispatch center, lowering the system communication complexity and connection cost, and improving the convenience and integration efficiency of distributed photovoltaic grid connection.

[0009] 2. Reduced energy storage capacity requirements and improved economic efficiency: Only a small capacity of energy storage is needed to achieve grid construction. Compared with the large capacity energy storage solutions that may be required in existing technologies, it significantly reduces the investment cost of energy storage equipment, installation space requirements and operation and maintenance costs, and enhances the economic efficiency and practicality of the technical solution.

[0010] 3. Enhanced voltage stability and disturbance rejection capability: Even when there are external voltage disturbances, the voltage balance on the power supply side can still be guaranteed, which effectively improves the system's anti-interference capability and voltage stability. This solves the problem in the existing technology that external disturbances may cause voltage imbalance on the power supply side and affect the power supply quality, thus ensuring the reliable operation of the power system.

[0011] 4. Strong compatibility, reducing the cost of transformation and promotion: It does not require changing the grid-connected operation control mode of traditional photovoltaic inverters, and can be directly compatible with existing equipment. It avoids the transformation or replacement of existing photovoltaic inverters, significantly reducing the cost and implementation difficulty of system upgrades, and making it easy to promote and apply in the existing power grid architecture. Attached Figure Description

[0012] Figure 1 A simplified electrical connection diagram of a photovoltaic grid aggregation device supported by an energy storage flexible transformer, provided in an embodiment of the present invention; Figure 2 This is an electrical topology diagram of a photovoltaic grid aggregation device supported by an energy storage flexible transformer, provided in an embodiment of the present invention. Figure 3 A schematic diagram illustrating the internal and external characteristics of a photovoltaic grid aggregation device supported by a flexible energy storage transformer, provided in an embodiment of the present invention; Figure 4 This is a controller block diagram of a photovoltaic grid aggregation method supported by an energy storage flexible transformer provided in an embodiment of the present invention; Figure 5 A chart illustrating the charging and discharging power constraints of the energy storage battery in a photovoltaic grid aggregation method supported by a flexible energy storage transformer, provided in an embodiment of the present invention. Figure 6 This is a schematic diagram illustrating the implementation process of a photovoltaic power grid aggregation method supported by an energy storage flexible transformer, as provided in an embodiment of the present invention. Figure 7The curves of the active, reactive, and apparent power response of the photovoltaic power grid aggregation method supported by a flexible energy storage transformer, measured at the grid-side common grid connection point, are the curves of the net power of the photovoltaic power grid and the energy storage power aggregation network after a step command. Figure 8 The curves of the active, reactive, and apparent power response after a step command are obtained at the grid-side common grid connection point of a photovoltaic power grid supported by a flexible energy storage transformer, which is provided in an embodiment of the present invention. Figure 9 The present invention provides a power curve diagram showing how energy storage supplements maintain constant grid-side power when the net power of the photovoltaic distribution area fluctuates at the grid-side common grid connection point, based on a photovoltaic distribution area aggregation grid construction method supported by an energy storage flexible transformer. Figure 10 This is a step curve measured at the common grid connection point of a photovoltaic grid aggregation method supported by an energy storage flexible transformer provided in an embodiment of the present invention, reflecting the relationship between the active and reactive power response on the grid side and the apparent capacity constraint of the parallel converter. Figure 11 This is the Pf grid sag characteristic curve measured at the common grid connection point of a photovoltaic grid aggregation method supported by an energy storage flexible transformer provided in an embodiment of the present invention. Figure 12 This is the QU grid sag characteristic curve measured at the common grid connection point of a photovoltaic grid aggregation method supported by an energy storage flexible transformer provided in an embodiment of the present invention. Figure 13 This is a schematic diagram of a module of an embodiment of a photovoltaic grid aggregation method supported by an energy storage flexible transformer provided by the present invention; Figure 14 This is a schematic diagram of a photovoltaic grid aggregation device supported by a flexible energy storage transformer, provided in an embodiment of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this application, "multiple" can also be understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order. The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0014] The present invention proposes a method for photovoltaic power grid aggregation supported by a flexible energy storage transformer, comprising the following steps: Please refer to Figure 1 A photovoltaic power grid aggregation device supported by a flexible energy storage transformer, characterized by comprising a controller, a series converter, a parallel converter, an energy storage battery, a passive transformer, and a series isolation transformer (with a turns ratio of...). N se (e.g., current sensors, voltage sensors, etc.)

[0015] The parallel converter is connected to a storage battery on its DC side and to an inductor on its AC side. L sh A second current sensor is connected to the common grid connection point formed by the secondary side of the passive transformer; the primary side of the passive transformer is connected to the 10kV power grid via a resistor; a first voltage sensor is installed at the common grid connection point, and a first current sensor is installed on the grid-side incoming line of the primary side; the AC side of the series converter is connected via an inductor... L se 、 The third current sensor is connected to the primary side of the series isolation transformer, and its secondary side is connected to the load-side bus. The load-side bus is connected to the resistive-inductive load and the photovoltaic cluster, and a second voltage sensor is installed at the bus. The controller signal input terminal is connected to each sensor and the energy storage status detection terminal, and the output terminal is connected to the control terminal of the series and parallel converters, thereby controlling the power output of the series and parallel converters.

[0016] Please refer to Figure 2 :exist Figure 1Based on this, the topology of the energy storage flexible transformer is further refined to clarify the topological structure and functional boundaries of its series and parallel sides.

[0017] Please refer to Figure 3 A schematic diagram illustrating the internal and external characteristics of a photovoltaic power grid aggregation device supported by a flexible energy storage transformer, characterized in that: The photovoltaic grid aggregation device supported by the energy storage flexible transformer exhibits generator inertial support characteristics on the outside, and can respond to the primary regulation and dispatch commands of the power grid. ， The power grid only needs to communicate with and regulate the flexible energy storage transformer, which greatly reduces the difficulty of management and control.

[0018] The photovoltaic grid aggregation method supported by the energy storage flexible transformer can simultaneously achieve functions such as suppressing photovoltaic power fluctuations and stabilizing low-voltage side voltage by flexibly charging and discharging energy storage units embedded in the energy storage flexible transformer and controlling series voltage.

[0019] Please refer to Figure 4 A control strategy for a photovoltaic power grid aggregation method supported by a flexible energy storage transformer, characterized by: The controller collects grid dispatch commands, net power of distribution areas, and grid-connected power of medium-voltage nodes. It then calculates active power references based on energy storage battery charging / discharging power constraints and apparent capacity constraints of parallel converters. P ref With reactive power reference Q ref Subsequently, VSG network control is performed to obtain the reference voltage amplitude at the common grid connection point. E poc，ref and phase reference θ ref Subsequently, dual closed-loop control of voltage and current for both series and parallel converters is implemented, ultimately generating voltage reference commands to drive the series and parallel converters. The specific details are as follows: The energy storage battery's charge and discharge power is constrained by its state of charge (SOC) range, based on its rated power. P rated When the SOC is between 20% and 80%, the maximum charge / discharge power is... P bat,max With minimum charge and discharge power P bat,min The absolute values ​​are all 0.8 P rated It exhibits constant power charge and discharge characteristics; when the SOC is between 0% and 20%, P bat,max The absolute value remains at 0.8 P rated ,but P bat,minWhen the SOC drops to 0, the charging and discharging power decreases linearly with increasing SOC; when the SOC is between 80% and 95%, P bat,max The absolute value remains 0.8 P rated , P bat,min Similarly, the charging and discharging power decreases linearly with increasing SOC, even when it is 0.

[0020] The controller is based on the obtained V pcc,d and I g,d , I g,q The active and reactive power on the grid side were calculated. P g , Q g After low-pass filtering, it looks like the following formula: (1) The controller is based on the obtained V pcc,d and I se,d , I se,q The calculated net power of the transformer substation uploaded to the load side is as follows: P pcc , Q pcc As shown in the following formula: (2) The controller is based on the power grid active power dispatch command. ΔP mg,ref Net power of the Taiwan area P pcc The active power output of the parallel converter is obtained by constraining the charging and discharging power of the energy storage battery. ΔP sh Compare it with the net power of the transformer area P pcc Superimposed, the active power reference of the VSG network of the parallel converter is obtained. P ref Based on this, combined with the maximum apparent capacity of the parallel converter... S sh,max Its reactive power output was calculated. ΔQ sh In terms of net power of the distribution area Q pcc After superposition, the reactive power reference of the VSG network of the parallel converter is obtained. Q refThe parallel converter exhibits apparent capacity constraints, as detailed below, which demonstrates the principle of prioritizing active power over reactive power: (3) The parallel controller is based on the obtained grid-connected power reference of the medium-voltage node in the parallel converter. P ref , Q ref Simultaneously, VSG network control is performed by combining the primary regulation coefficient, inertia regulation coefficient, and damping coefficient issued by the power grid dispatch center, thereby obtaining the reference voltage amplitude of the common grid connection point of the parallel controller. E poc，ref and phase reference θ ref As shown in the following formula: (4) Based on the reference common grid connection point voltage amplitude obtained by the controller E poc，ref and phase reference θ ref In the dq coordinate system, a dual closed-loop control of voltage and current is performed on the parallel converter. First, based on the actual voltage feedback of the POC, the POC node current reference is generated through voltage loop control. I g,d ref , I g,q ref As shown in the following formula: (5) The controller will obtain I g,ref Subtract the load current measured in real time I load Generate the output current reference of the parallel converter I sh,ref To avoid it carrying excessive power, as shown in the following formula: (6) The controller is based on the output current reference of the parallel converter. I sh,ref Through the inverter-side current of the actual parallel converter I sh,dq Perform current closed-loop control and add voltage feedforward to generate a modulation wave reference in the dq coordinate system of the parallel converter. V sh,d ref , V sh,q ref As shown in the following formula: (7) After obtaining the reference modulation signals for each converter, the drive signals for the series and parallel converters are obtained by coordinate transformation and sinusoidal pulse width modulation.

[0021] Please refer to Figure 5 A method for constructing a photovoltaic power grid supported by a flexible energy storage transformer includes a power constraint chart for the charging and discharging power of energy storage batteries. Based on the state of charge (SOC) of the energy storage batteries, the maximum and minimum charging and discharging power are determined. P bat,max , P bat,min And determine its charge and discharge characteristics to indicate the power output limit threshold of the parallel converter.

[0022] Please refer to Figure 6 A schematic diagram illustrating the implementation process of a photovoltaic power grid aggregation method supported by a flexible energy storage transformer, including: Step S601: The controller collects and calculates power grid dispatch instructions. P mg,ref , Q mg,ref Net power of the transformer area P pcc , Q pcc and actual operating power on the grid side P g , Q g .

[0023] Step S602: The controller is combined P g , Q g ,and Figure 4 The energy storage battery charging and discharging power constraint and the maximum apparent capacity of the parallel converter S sh,max Net power of the transformer area P pcc , Q pcc Generate active and reactive power references for VSG control of parallel converters. P ref , Q ref .

[0024] Step S603: The controller is based on the calculated... P ref , Q ref Perform VSG network control to generate a common grid connection point voltage amplitude reference. E poc，ref and phase reference θ ref .

[0025] Step S604: The controller is based on E poc，ref and θ ref The series and parallel converters are subjected to dual closed-loop voltage and current control, and the modulation signals for the parallel and series converters are generated through coordinate transformation. v poc,abc ref , v se,abc ref .

[0026] Step S605: After obtaining the reference modulation signals of each converter, the drive signals of the series and parallel converters are obtained by sinusoidal pulse width modulation.

[0027] Please refer to Figure 7 , Figure 7 The paper presents curves showing the full response of the net power of the photovoltaic power distribution area and the energy storage power aggregation network after a step command, measured at the grid-side common grid connection point, using a photovoltaic power distribution area aggregation network supported by a flexible energy storage transformer.

[0028] Please refer to Figure 8 , Figure 8 This paper presents curves of the active, reactive, and apparent power responses after a step command in a photovoltaic power distribution network aggregation method supported by a flexible energy storage transformer, measured at the grid-side common grid connection point. These curves illustrate the impact of energy storage capacity constraints and parallel converter apparent capacity constraints on grid dispatch commands.

[0029] Please refer to Figure 9 , Figure 9 The paper presents a power curve showing how energy storage supplements maintain constant grid-side power when the net power of a photovoltaic distribution area fluctuates, as measured at the grid-side common grid connection point, using a photovoltaic distribution area aggregation grid construction method supported by an energy storage flexible transformer.

[0030] Please refer to Figure 10 , Figure 10 This paper presents a step curve at the common grid connection point of a photovoltaic (PV) grid aggregation method supported by a flexible energy storage transformer, reflecting the relationship between the grid-side active and reactive power response and the apparent capacity constraint of the parallel converter. As shown in the figure, when the apparent capacity of the parallel converter is sufficient, both the active and reactive power dispatch curves on the grid side can fully respond. When the apparent capacity of the parallel converter is insufficient to support full response to both active and reactive power dispatch, active power should be prioritized, followed by reactive power. In extreme cases, the parallel converter can even completely refrain from generating reactive power to respond to active power dispatch as much as possible.

[0031] Please refer to Figure 11 , Figure 11 This paper presents the Pf grid sag characteristic curves measured at the common grid connection point of a photovoltaic (PV) grid aggregation method supported by a flexible energy storage transformer. Figure 11 As shown, when the frequency on the external network side drops, the parallel converter generates active power due to the VSG network characteristics of the system.

[0032] Please refer to Figure 12 , Figure 12 This paper presents the QU grid sag characteristic curves of a photovoltaic (PV) grid aggregation method supported by a flexible energy storage transformer, measured at the common grid connection point. (See figure below.) Figure 12 As shown, when the voltage amplitude on the external grid side drops, the parallel converter generates reactive power due to the VSG network characteristics of the system.

[0033] This invention is not limited to the embodiments described above. The above description of specific embodiments is intended to illustrate and explain the technical solutions of this invention. The specific embodiments described above are merely illustrative and not restrictive. Without departing from the spirit and scope of the claims, those skilled in the art can make many specific modifications based on the teachings of this invention, and these modifications all fall within the scope of protection of this invention.

[0034] Example module Figure 13 As shown, a method for aggregating photovoltaic grids in a photovoltaic substation supported by an energy storage flexible transformer includes: The first acquisition module 1301, the controller, collects and calculates power grid dispatch instructions. P mg,ref , Q mg,ref Net power of the transformer area P pcc , Q pcc and grid-connected power of medium-voltage nodes P g , Q g ; The first determining module 1302, the controller, combines the power calculated above, and... Figure 5 The energy storage battery charging and discharging power constraint and the maximum apparent capacity of the parallel converter S sh,max Net power of the transformer area P pcc , Q pcc Generate active and reactive power references for VSG control of parallel converters. P ref , Q ref .

[0035] The second determining module 1303, the controller is based on the calculated... P ref , Q ref Simultaneously, VSG network control is performed by combining the primary regulation coefficient, inertial regulation coefficient, and damping coefficient issued by the power grid dispatch center, generating a reference voltage amplitude at the common grid connection point. E poc，ref and phase reference θ ref ; The third determining module 1304, the controller is based on E poc，ref and θ ref The series and parallel converters are subjected to dual closed-loop voltage and current control, and the modulation signals for the parallel and series converters are generated through coordinate transformation. v poc,abc ref , v se,abc ref 。

[0036] The second obtaining module 1305 is used to obtain the switching signals of each power converter by sinusoidal pulse width modulation based on the modulation signal determined by the third determining module 1304.

[0037] A schematic diagram of the device is shown below. Figure 14 As shown, Figure 14 This is a schematic diagram of a photovoltaic grid aggregation device supported by a flexible energy storage transformer, provided in an embodiment of the present invention.

[0038] The schematic diagram of the photovoltaic grid aggregation device based on the energy storage flexible transformer is shown below. Figure 14 As shown, it includes: converters 1401 and 1402, a controller 1403, a memory 1405, and a computer program 1304 stored in the memory and executable on the controller. When the controller executes the computer program, it implements the steps in the above-described power flow transfer method embodiments. Alternatively, when the controller executes the computer program, it implements the power of each module / unit in the above embodiments, for example... Figure 13 The functions of modules 1301 to 1305 are shown.

[0039] For example, the computer program can be divided into one or more modules / units, which are stored in the memory and executed by the controller to complete the embodiments of the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, which describe the execution process of the computer program in the low-voltage zone flexible power flow transfer device of the energy storage flexible transformer. For example, the computer program can be divided into a first obtaining module, a first determining module, a second determining module, a third determining module, and a second obtaining module, with the functions of each module as follows: The first acquisition module is used to collect and calculate power grid dispatch instructions. P mg,ref , Q mg,ref Net power of the transformer area P pcc , Q pcc and grid-connected power of medium-voltage nodes P g , Q g ; The first determining module is used to combine the calculated power above with... Figure 4 The energy storage battery charging and discharging power constraint and the maximum apparent capacity of the parallel converter S sh,max Net power of the transformer area P pcc , Q pcc Generate active and reactive power references for VSG control of parallel converters. P ref , Q ref .

[0040] The second determining module is used to determine the result based on the calculated value. P ref , Q ref Simultaneously, VSG network control is performed by combining the primary regulation coefficient, inertial regulation coefficient, and damping coefficient issued by the power grid dispatch center, generating a reference voltage amplitude at the common grid connection point. E poc，ref and phase reference θ ref ; The third determining module is used to determine based on E poc，ref and θ ref The series and parallel converters are subjected to dual closed-loop voltage and current control, and the modulation signals for the parallel and series converters are generated through coordinate transformation. vpoc,abc ref , v se,abc ref 。 The second obtaining module is used to obtain the switching signals of each power converter by sinusoidal pulse width modulation based on the modulation wave voltage determined by the third determining module.

[0041] The photovoltaic grid aggregation device supported by the energy storage flexible transformer may include, but is not limited to, converters, controllers, and memory. Those skilled in the art will understand that... Figure 14 This is merely an example of a photovoltaic power grid aggregation device supported by a flexible energy storage transformer, and does not constitute a limitation on such devices. It may include more or fewer components than shown in the figure, or combine certain components, or different components. For example, the life assessment terminal equipment for the power transformer may also include input / output devices, network access devices, buses, etc.

[0042] The controller can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0043] The memory can be an internal storage unit of the photovoltaic power grid aggregation device 14 supported by the flexible energy storage transformer, or an external memory circuit of the system device 14. Examples include plug-in hard drives, smart media cards (SMC), secure digital cards (SD), and flash cards equipped on the photovoltaic power grid aggregation device 14 supported by the flexible energy storage transformer. Furthermore, the memory can include both internal storage units of the system device 14 and external storage devices. The memory is used to store the computer program and other programs and data required by the photovoltaic power grid aggregation device supported by the flexible energy storage transformer. The memory can be used to temporarily store data that has been output or will be output.

[0044] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0045] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0046] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0047] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / terminal device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0048] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some units can be selected to achieve the purpose of this embodiment according to actual needs.

[0049] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0050] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0051] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A photovoltaic subterritorial polymeric networked device supported by an energy- storing flexible transformer, characterized by The controller, series converter, parallel converter, energy storage battery, passive transformer, series isolation transformer (transformer ratio N se ), current sensor, voltage sensor, etc. The parallel converter DC side connects the energy storage battery, and the AC side connects the public grid connection point formed by the secondary side of the inductance L sh , second current sensor, and passive transformer secondary side; the primary side of the passive transformer connects the 10kV power grid through resistance impedance, the public grid connection point is provided with a first voltage sensor, and the primary side grid side incoming line is provided with a first current sensor; the AC side of the series converter connects the primary side of the series isolation transformer through the inductance L se , third current sensor, and the secondary side connects the load side bus; the load side bus connects the resistance and inductance load and photovoltaic cluster, and the bus is provided with a second voltage sensor; the controller signal input end connects each sensor and energy storage state detection end, and the output end connects the series and parallel converter control end, thereby controlling the power output of the series and parallel converter.

2. A method of photovoltaic district aggregation networking supported by energy storage flexible transformer, characterized in that, Comprise: According to the current sensor, the grid-side output current i g , the output current of the series converter i se , the output current of the parallel converter i sh , wherein the load current i load is the product of the series coupling transformer ratio N se and i sh ; according to the voltage sensor, the common connection point voltage v poc and the common grid connection point voltage v pcc are measured. The controller is used for receiving power grid power scheduling information, transformer area net power information, and grid side real-time power information. The power grid scheduling signal disp The power scheduling instruction is combined with the inertia coefficient. The transformer area net power signal refers to the power of a high proportion of photovoltaic power generation clusters on the grid after meeting local consumption P pcc 、 Q pcc The controller prioritizes the energy storage battery charging and discharging power constraint to determine the maximum and minimum charging and discharging power of the energy storage battery P bat，max 、 P bat，min , so as to obtain the parallel converter active scheduling response instruction that satisfies the energy storage power limit Delta P sh ; secondly, combined with the maximum apparent capacity of the parallel converter, a power reference responding to the power grid reactive scheduling is generated Delta Q sh ; The controller performs VSG grid connection control based on the generated parallel converter power reference and the net power of the transformer area, and then obtains a common grid connection point voltage amplitude reference of the parallel controller E poc，ref and phase reference Theta ref Based on this, the voltage and current double-loop control of the series and parallel converters is performed; meanwhile, the power fluctuation is smoothed through energy storage charging and discharging to respond to the scheduling demand and support the stable grid connection of the net power of the transformer area; The controller generates a node voltage magnitude reference for the common point of common coupling (PCC) based on the VSG control E poc,ref , a phase reference Theta ref and an actual voltage feedback of the PCC v poc , generates a PCC node current reference by voltage loop control i g,ref ; The controller will obtain i g,ref , subtract the real-time measured load current i load , generate the output current reference of the parallel converter i sh,ref , avoid its carrying too much power; The controller is based on the output current reference of the parallel converter i sh,ref By comparing with the actual parallel converter inverter side current I sh,dq Do current closed-loop control, after coordinate transformation, generate the modulation wave reference of the parallel converter, which is also the POC node voltage reference v poc,abc ; The controller generates an output current reference for the series current converter based on the obtained voltage amplitude reference of the PCC node E pcc,ref , actual voltage feedback of the PCC node v pcc , by a voltage loop control i se,ref ; The controller is based on the output current reference of the series converter i se,ref , by the actual series converter inverter side current I se,dq Do current closed-loop control, after the coordinate transformation to generate the series converter modulation wave reference v se,abc ; The controller obtains the control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series and parallel converters.

3. A method of photovoltaic district aggregation networking supported by an energy storage flexible transformer according to claim 2, characterized in that, Controller to control the phase reference obtained by VSG Theta ref Coordinate transformation for reference to obtain grid side voltage v poc , load point of common connection voltage v pcc Grid side current i g Parallel converter output current i sh Series converter output current i se D-axis and q-axis components of V poc,d , V poc,q , V pcc,d , V pcc,q , I g,d , I g,q , I sh,d , I sh,q , I se,d , I se,q ; The energy storage battery's charge and discharge power is constrained by its state of charge (SOC) range, based on its rated power. P rated When the SOC is between 20% and 80%, the maximum charge / discharge power is... P bat,max With minimum charge and discharge power P bat,min The absolute values ​​are all 0.8 P rated It exhibits constant power charge and discharge characteristics; when the SOC is between 0% and 20%, P bat,max The absolute value remains at 0.8 P rated ,but P bat,min When the SOC drops to 0, the charging and discharging power decreases linearly with increasing SOC; when the SOC is between 80% and 95%, P bat,max The absolute value remains 0.8 P rated , P bat,min Similarly, the charging and discharging power decreases linearly with increasing SOC, even when it is 0. The controller calculates the power of the grid-connected node in the grid according to the obtained V pcc,d and I g,d , I g,q The power of the grid-connected node in the grid is calculated as follows: P g , Q g After low-pass filtering, as shown in the following formula: （1） The controller calculates the net power of the transformer substation according to the obtained V pcc,d and I se,d , I se,q The net power of the transformer substation is calculated as follows P pcc , Q pcc as shown in the following formula: （2） The controller is based on grid active scheduling instruction Delta P mg,ref And the net power of the transformer area P pcc , through the energy storage battery charge and discharge power constraint to get the active output of the parallel converter Delta P sh , superimposed with the net power of the transformer area P pcc , get the VSG network active power reference of the parallel converter P ref ; on this basis, combined with the maximum apparent capacity of the parallel converter S sh,max , the reactive output is calculated Delta Q sh , after superimposed with the net power of the transformer area Q pcc , get the VSG network reactive power reference of the parallel converter Q ref , the apparent capacity constraint of the parallel converter, as shown below, can reflect the characteristics of active priority and reactive second: （3）。 4. The energy storage flexible transformer supported photovoltaic subzone polymer network method according to claim 2, wherein, The parallel controller is configured to obtain a grid-connected power reference of a voltage node of the parallel converter P ref 、 Q ref The VSG network control is performed in combination with a primary regulation coefficient, an inertia regulation coefficient and a damping coefficient issued by the power grid dispatching, and then a common grid-connected point voltage amplitude reference of the parallel controller is obtained E poc，ref and a phase reference Theta ref as shown in the following formula: （4）。 5. The energy storage flexible transformer supported photovoltaic subterritorial polymer networked method according to claim 2, wherein, a common point of common coupling voltage amplitude reference obtained by the controller E poc，ref and phase reference Theta ref In the dq coordinate system, a voltage and current double closed loop control is performed on the parallel converter, and a POC node current reference is generated by the voltage loop control according to the actual voltage feedback of the POC I g,d ref 、 I g,q ref as shown in the following formula: （5） The controller will obtain I g,ref , subtract the real-time measured load current I load , generate the output current reference of the parallel converter I sh,ref , avoid its carrying too much power, as follows: （6） The controller is based on the output current reference of the parallel converter I sh,ref , by the actual parallel converter inverter side current I sh,dq Do current closed-loop control, and add voltage feedforward, generate the modulation wave reference of the parallel converter in dq coordinate system V sh,d ref 、 V sh,q ref As shown in the following formula: （7）。 6. The energy-storing flexible transformer supported photovoltaic local area polymer network method of claim 2, wherein, After obtaining the reference modulation signals of the converters, the driving signals of the series and parallel converters are obtained through coordinate transformation and sinusoidal pulse width modulation.

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