Partial energy storage embedded medium-voltage optical storage integrated system and control method thereof

Abstract

The invention relates to a partial energy storage embedded medium-voltage optical storage integrated system and a control method thereof, the integrated system comprises at least one photovoltaic sub-module and at least one energy storage embedded sub-module, and the photovoltaic sub-modules and the energy storage embedded sub-modules are in cascade connection; the control method adopts hierarchical control and comprises system-level power control, inter-phase and intra-phase power balance control and module-level power control in each sub-module, the system-level power control is used for carrying out active / reactive power control according to sampled voltage and current of a power grid, and the module-level power control is used for carrying out inter-phase and intra-phase power balance control. The inter-phase and intra-phase power balance control is used for carrying out inter-phase and intra-phase power distribution based on the energy storage SOC of each energy storage embedded sub-module so as to realize inter-phase balance and intra-phase balance, and the module-level power control in each sub-module is used for controlling the photovoltaic unit to output the maximum power and enabling each sub-module to output stable direct-current voltage. Compared with the prior art, the system has the advantages of high energy efficiency, low cost, high reliability and the like.

Description

Technical Field

[0001] The present invention belongs to the field of power electronic converter topology and control, and relates to an energy storage system for medium-voltage AC distribution networks (10kV and above), and in particular to a partially stored energy embedded medium-voltage photovoltaic storage integrated system and a control method thereof. Background Art

[0002] As the global energy transition progresses, the proportion of renewable energy, particularly photovoltaic and wind power, in distribution networks is gradually increasing. However, the randomness and volatility of renewable energy generation, as well as the mismatch between its output and load variations, have brought unprecedented challenges to power system scheduling and stable operation.

[0003] Energy storage, a key technology for balancing supply and demand and improving grid stability, is widely recognized as an effective means of addressing the challenges of renewable energy consumption. However, current energy storage technologies are primarily applied to low-voltage distribution networks. These low-voltage energy storage converters are characterized by small individual capacity and large numbers, resulting in complex integrated access structures for energy storage power stations and increased difficulty in coordinated control. With the continued growth in renewable energy penetration, the demand for large-capacity, megawatt-class energy storage systems has also increased significantly.

[0004] Furthermore, current medium-voltage direct-mounted solar-to-storage integrated systems face numerous technical challenges in practical application, such as optimizing the system architecture and circuit topology, and designing and optimizing control strategies. Developing a highly energy-efficient and cost-effective system architecture and circuit topology, and ensuring efficient operation of medium-voltage solar-to-storage integrated systems, remain pressing challenges in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-efficiency, low-cost, high-reliability partially stored energy embedded medium-voltage photovoltaic storage integrated system and its control method, so as to realize photovoltaic storage access under the medium-voltage power grid, respond to the grid demand in real time, and flexibly adjust the photovoltaic storage power.

[0006] The purpose of the present invention can be achieved by the following technical solutions: A partially energy storage embedded medium-voltage photovoltaic storage integrated system includes at least one photovoltaic submodule and at least one energy storage embedded submodule, wherein the photovoltaic submodule and the energy storage embedded submodule are cascade-connected. The photovoltaic submodule includes a photovoltaic unit and a first converter connected to each other. The energy storage embedded submodule includes a bidirectional circuit consisting of a photovoltaic unit and an energy storage unit and a second converter connected to the bidirectional circuit.

[0007] Furthermore, the first converter is an isolated DC converter, and the second converter is a photovoltaic-storage integrated three-port DC converter, and the photovoltaic-storage integrated three-port DC converter includes a bidirectional DC converter and an isolated converter connected to each other.

[0008] The present invention also provides a power control method for the partially energy-storage embedded medium-voltage photovoltaic storage integrated system as described above. The power control method adopts hierarchical control, including system-level power control, power balancing control between phases and within phases, and module-level power control within each submodule, wherein: The system-level power control is used to perform active / reactive power control based on the sampled grid voltage and current; The inter-phase and intra-phase power balancing control is used to distribute power between phases and within phases based on the energy storage SOC of each energy storage embedded submodule to achieve inter-phase balance and intra-phase balance; The module-level power control within each submodule is used to control the photovoltaic unit to output the maximum power and enable each submodule to output a stable DC voltage.

[0009] Furthermore, in the inter-phase and intra-phase power balancing control, the mean SOC of the inter-phase energy storage unit is obtained, the zero-sequence component that needs to be injected into the modulation signal is calculated, and the initial three-phase modulation signal is generated based on the zero-sequence component through power decoupling control to achieve inter-phase balancing control.

[0010] Furthermore, the zero-sequence component is generated by a PI controller.

[0011] Furthermore, in the inter-phase and intra-phase power balancing control, the average SOC of each energy storage unit in each phase is obtained, a correction coefficient is added, and the modulation signal is distributed proportionally to achieve intra-phase balancing control.

[0012] Furthermore, the system-level control performs real-time data exchange and command transmission with the module-level control of each submodule through a communication interface.

[0013] Furthermore, during the control process, each submodule stores and uploads submodule information, where the submodule information includes whether the submodule operates normally, the battery SOC status, and the photovoltaic status.

[0014] The present invention also provides a computer-readable storage medium comprising one or more programs for execution by one or more processors of an electronic device, wherein the one or more programs include instructions for executing the power control method as described above.

[0015] The present invention also provides an electronic device, comprising one or more processors, a memory, and one or more programs stored in the memory, wherein the one or more programs include instructions for executing the power control method as described above.

[0016] The present invention provides a partially stored embedded medium-voltage photovoltaic-storage integrated system and its control method suitable for medium-voltage power grids. This system aims to address the technical issues currently existing in medium-voltage photovoltaic-storage integrated systems in terms of energy efficiency, cost, and power regulation. Its implementation will bring the following beneficial effects: 1. The system architecture is conducive to improving system energy efficiency and reducing costs: The present invention sets up an energy storage embedded sub-module, and connects the energy storage unit in the form of an energy storage embedded sub-module, so as not to add additional energy storage sub-modules, thereby realizing a high-efficiency, low-cost system composition architecture and circuit topology, which can not only realize the integration of light and storage, flexible configuration, but also meet the actual needs of voltage resistance, current resistance, isolation, etc. The integrated sub-module can simultaneously realize the isolation of light, storage and medium-voltage AC power grid, with good safety and high reliability. It can simultaneously realize the connection of photovoltaic and energy storage to the medium-voltage AC power grid, replacing the traditional two independent medium-voltage photovoltaic and medium-voltage energy storage devices, thereby simplifying the power supply architecture, improving system energy efficiency and reducing costs.

[0017] 2. Realize flexible power regulation of photovoltaic, energy storage and medium-voltage AC power grid: The control strategy of the present invention adopts a multi-layer power control method of system-level power control, inter-phase and intra-phase power balancing control and module-level power control to achieve flexible and efficient power scheduling between photovoltaic, energy storage and network. System-level control can exchange data and transmit commands in real time with the module-level control of each sub-module through the communication interface to ensure the coordinated operation of each module in the system and achieve SOC balance of all sub-modules. Hierarchical control enables the system to dynamically adjust the energy storage SOC balance, respond to power fluctuations of photovoltaic or grid-side loads, and ensure stable and efficient operation of the system under different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The overall topology and control diagram of the system of the present invention; Figure 2 This is an example of the topology of the photovoltaic submodule and the energy storage embedded submodule in the embodiment of the present invention; Figure 3 This is a cascade topology diagram of each submodule in an embodiment of the present invention; Figure 4 This is an example of power balancing control in an embodiment of the present invention; Figure 5 This is a Simulink simulation topology diagram in an embodiment of the present invention; Figure 6 Grid-side voltage and current waveforms of the cascaded system in a 3.15kV medium-voltage power grid according to an embodiment of the present invention; Figure 7 Schematic diagram of the change of module power when the irradiation value changes in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0020] This embodiment provides a partially energy storage embedded medium-voltage photovoltaic storage integrated system and its control method. By constructing an efficient, stable and reliable medium-voltage photovoltaic storage integrated power supply system, it can achieve efficient coordination of photovoltaic power generation and energy storage, ensure the stable operation of the system, improve the reliability of the system, and at the same time design a control strategy for the medium-voltage photovoltaic storage integrated system.

[0021] In this embodiment, first, the topology of a medium-voltage photovoltaic-storage integrated power supply system is constructed. The medium-voltage photovoltaic-storage integrated system adopts a cascade structure of some energy storage embedded sub-modules, and connects the energy storage unit to some photovoltaic sub-modules through the energy storage embedded sub-modules, wherein each sub-module outputs a stable DC voltage after passing through an isolated DC / DC converter. Although the output voltage of a single sub-module is low, the energy storage embedded sub-module and the photovoltaic sub-module are cascaded to effectively increase the output voltage of the entire system to the voltage level required by the medium and high voltage power grid, thereby connecting to the medium and high voltage power grid. When constructing this system architecture, it is necessary to consider multiple factors such as energy storage configuration requirements, system voltage level requirements, and overall economic efficiency to determine the parameters and quantity of photovoltaic sub-modules and energy storage embedded sub-modules.

[0022] Next, the overall power control strategy is configured to ensure coordinated operation between the modules within the system, so that photovoltaic power generation and energy storage output can work together efficiently and maintain stable operation of the entire system.

[0023] Finally, based on the system model and the proposed power control strategy, the control parameters are optimized and designed.

[0024] Specifically: The system architecture and control strategy of the medium voltage photovoltaic storage integrated system based on partially embedded energy storage submodules are as follows: Figure 1 As shown in the figure, the general structure of the system architecture described in this embodiment in a three-phase system is shown. Each phase can be composed of multiple cascaded sub-modules. The specific topology of the sub-module can be selected according to actual needs. The system adopts a hierarchical control method, including system-level power control, power balancing control between phases and within phases, and module-level power control within each sub-module.

[0025] for Figure 1The topology of the medium-voltage integrated photovoltaic and energy storage system utilizes a cascaded structure with embedded energy storage submodules, comprising several photovoltaic submodules and embedded energy storage submodules. For each phase of a single-phase or three-phase system, (NM) photovoltaic submodules and M embedded energy storage integrated submodules are used to form the photovoltaic and energy storage cascade power electronic conversion system architecture. Unlike traditional cascaded photovoltaic and energy storage systems, this embodiment integrates energy storage units as embedded energy storage submodules, eliminating the need for additional energy storage submodules. Furthermore, the system is not limited to embedding energy storage units within all photovoltaic submodules; instead, the configuration can be flexibly optimized based on actual needs. For example, in a cascaded structure with N submodules, energy storage units can be integrated into M photovoltaic submodules to form embedded energy storage submodules. These M embedded energy storage submodules and (NM) photovoltaic submodules are then cascaded and connected to the medium-voltage AC grid.

[0026] In a specific embodiment, the photovoltaic submodule includes a connected photovoltaic unit and a first converter, and the embedded energy storage submodule includes a bidirectional circuit formed by the photovoltaic unit and the energy storage unit, and a second converter connected to the bidirectional circuit. Specifically, the first converter can be an isolated DC converter, and the second converter can be a photovoltaic-storage integrated three-port DC converter, which includes a connected bidirectional DC converter and an isolated converter.

[0027] Figure 2 The topological structures of the photovoltaic submodule and the embedded energy storage submodule are shown in Figure 2. (a) shows the photovoltaic submodule, and (b) shows the embedded energy storage submodule. Both use a dual active bridge (DAB) circuit as the topology for the DC conversion portion of the submodule's front-end. The embedded energy storage submodule, on the other hand, builds on the isolated converter by adding an energy storage port and a bidirectional DC converter connecting the energy storage and photovoltaic devices.

[0028] Take a single-phase system as an example, Figure 3 As shown in the figure, N submodules all output corresponding DC voltages, among which M energy storage embedded submodules and (NM) photovoltaic submodules are cascaded on the output side and connected to the medium-voltage power grid. The formed cascade system can reach the voltage level required for direct access to the medium- and high-voltage power grids.

[0029] The hierarchical control adopted by the system includes system-level power control, inter-phase and intra-phase power balancing control, and module-level control of sub-modules. For overall power control, the first step is to receive information uploaded by the sub-module, including key information such as whether the sub-module is operating normally, battery SOC status, and photovoltaic status. After that, grid phase tracking is performed, and the phase angle and frequency of the grid voltage and current are tracked through a phase-locked loop for the subsequent generation of voltage modulation signals. Power control is then carried out, and the d-axis current and q-axis current that each sub-module needs to provide are calculated based on the given target output power. Inter-phase power balancing control is used to ensure the SOC balance of the battery cluster in the three-phase module. After averaging the total SOC of the battery cells of each phase, the SOC of each phase is subtracted from the average SOC between the phases, and the zero-sequence component is generated through the PI controller. , inject the zero sequence component into the dq axis component of the modulation wave and then perform Park inverse transform to generate the initial three-phase modulation voltage 、 and . The intra-phase power balancing control is to distribute the power that each energy storage embedded sub-module needs to provide according to the battery SOC in the sub-module. After averaging the SOC of each energy storage unit in each phase, it calculates the proportion k of the SOC of each sub-module energy storage unit as a correction coefficient, and distributes it proportionally to the three-phase modulation wave of each sub-module in each phase through the correction coefficient k. The module-level power control of the sub-module is the MPPT control of the photovoltaic unit and the output voltage control of the DC / DC converter, where the DC / DC converter controls the DC voltage through the voltage loop. In addition, it is necessary to upload the SOC status, photovoltaic working status and battery working status to the upper-level control. For pure photovoltaic sub-modules, it is necessary to meet the maximum power point operation through the voltage control of the DC / DC converter, and it is also necessary to upload its photovoltaic working status to the upper-level control. The above steps of power control and SOC balancing control can be expressed as follows Figure 4 shown.

[0030] The core of voltage balancing control is the SOC state of each battery in each phase. Intra-phase balancing control is determined by the SOC state of each battery in each phase and the average intra-phase SOC. Inter-phase balancing control is determined by the average SOC of each phase and the average inter-phase SOC. Inter-phase SOC balancing is achieved by offsetting the neutral point. The three-phase current remains symmetrical. By offsetting the neutral point position while maintaining the output line voltage, the phase voltage of each phase can be adjusted, thereby adjusting the three-phase output power and achieving inter-phase energy storage SOC balance. Intra-phase SOC balancing is achieved by changing the module output voltage. Since the sub-modules are connected in cascade, that is, the current flowing through them is consistent, the output power ratio of each module in the cascade can be adjusted by changing the output voltage of each module, thereby adjusting the energy storage SOC balance of each sub-module in the cascade.

[0031] In order to verify the effectiveness of the photovoltaic storage integrated system architecture of the partially energy storage embedded submodule described in the present invention, a specific example will be given. Figure 5 The simulation topology is shown in Figure 1. The system is a three-phase system, with each phase consisting of a cascade of one photovoltaic submodule and two energy storage embedded submodules. Its main parameters are shown in Tables 1-3.

[0032] Figure 6 The figure shows the voltage and current under normal operation of all modules. After the converter is started, it reaches a steady state within one cycle, outputting a sinusoidal current with the same frequency and phase as the voltage waveform, and the output power reaches the set 1MW.

[0033] Table 1 Overall design example parameters <![CDATA[Medium voltage grid line voltage V G > 3.15kV Grid frequency 50Hz Rated power of the whole machine 1MW <![CDATA[Filter inductor L f > 1mH Number of photovoltaic sub-modules 3 Number of energy storage embedded sub-modules 6 Table 2 PV submodule design example parameters <![CDATA[Switching frequency f s > 1kHz Modulation method Carrier phase shift modulation Photovoltaic rated voltage 1450V DAB output voltage 1400V Table 3 Parameters of the energy storage embedded submodule design example <![CDATA[Switching frequency f s > 1kHz Modulation method Carrier phase shift modulation Photovoltaic rated voltage 1450V DAB output voltage 1400V Battery rated voltage 1200V Figure 7 The ambient radiation value is shown as 1000W / m at t=5s. 2 Change to 800W / m 2 The power of each module in one of the three phases changes when the system is powered. To meet the overall system power requirement of 1MW, taking into account some losses, the output power per phase is close to 340kW. Each phase of the system contains two energy storage embedded submodules and one photovoltaic submodule. The maximum power that each photovoltaic module can provide before the change is approximately 140kW. The total power provided by the energy storage embedded submodule is approximately 102kW, of which the battery unit absorbs approximately 38kW of power to balance the excess power of the photovoltaic module. The photovoltaic submodule outputs all the power. After the change in sunlight, the maximum power that the photovoltaic module can provide drops to approximately 113kW. At this time, the total power required by the system cannot be maintained by photovoltaic power alone. At this time, energy storage batteries are required to provide 4kW of power to meet the system requirements. The simulation results demonstrate the feasibility of a photovoltaic-storage integrated system based on some energy storage embedded submodules.

[0034] The present invention, through the design and improvement of the above-mentioned medium-voltage photovoltaic-storage integrated system and its control method, can solve the following technical problems faced by current medium-voltage direct-mounted photovoltaic-storage integrated systems in practical applications: 1. Optimization of system architecture and circuit topology: In high-voltage, high-capacity applications (voltage levels of 10kV or above, megawatt-level and above), the key technical challenge is to develop a highly energy-efficient and cost-effective system architecture and circuit topology that enables photovoltaic and energy storage integration, flexible configuration, and meets practical requirements such as voltage resistance, current tolerance, and isolation. The medium-voltage photovoltaic and energy storage integrated system of this invention enables efficient and cost-effective integration of photovoltaic and energy storage into the medium-voltage grid.

[0035] 2. Control Strategy Design and Optimization: Developing a flexible power regulation strategy is key to ensuring efficient operation of integrated PV-storage systems. This control strategy, designed in this paper, responds to grid demand in real time and flexibly adjusts PV-storage power. It includes system-level active and reactive power control, module-level PV-storage power balance, and optimized energy storage charging and discharging strategies. It also considers the impact of PV MPPT and energy storage SOC, ensuring reliable operation in practical applications.

[0036] The description of this application is based on the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products of the embodiments. It should be emphasized that the computer program instructions can be designed to implement each process and / or block in the flowchart and / or block diagram, as well as combinations of processes and / or blocks in the flowchart and / or block diagram. These computer program instructions can be run on a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device, thereby generating a machine that implements the functions of one or more processes and / or blocks specified in the flowchart and / or block diagram by executing the instructions of the processor of the computer or other programmable data processing device.

[0037] In addition, these computer program instructions can also be stored in a computer-readable memory, so that when these instructions are executed on a computer or other programmable data processing device, they can direct these devices to operate in a specific manner. In this way, the instructions stored in the memory generate an article of manufacture containing instruction means, and this instruction means implements the functions of one or more processes and / or blocks specified in the flowchart and / or block diagram.

[0038] These computer program instructions can also be loaded onto a computer or other programmable data processing device to execute a series of operating steps on the device to generate a computer-implemented process. In this way, the instructions executed on the computer or other programmable device can provide steps to implement the functions of one or more processes and / or blocks specified in the flowchart and / or block diagram.

[0039] In this document, terms such as "comprises," "includes," and the like are used solely to distinguish one entity or operation from another, and do not necessarily imply any actual relationship or order between such entities or operations. Furthermore, the use of the terms "comprises," "includes," or variations thereof is intended to encompass non-exclusive inclusion, i.e., inclusion not only of the listed elements but also of other elements not expressly listed, or of elements inherent to the process, method, article, or apparatus. In the absence of other qualifications, the use of the phrase "comprises a ..." to define an element does not preclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

Claims

1. A partially energy storage embedded medium-voltage photovoltaic energy storage integrated system, characterized in that: It includes at least one photovoltaic submodule and at least one energy storage embedded submodule, each of the photovoltaic submodule and the energy storage embedded submodule is cascade connected, wherein: The photovoltaic submodule includes a photovoltaic unit and a first converter connected to each other. The energy storage embedded submodule includes a bidirectional circuit formed by a photovoltaic unit and an energy storage unit and a second converter connected to the bidirectional circuit.

2. The partially energy storage embedded medium-voltage photovoltaic energy storage integrated system according to claim 1, characterized in that: The first converter is an isolated DC converter, and the second converter is a photovoltaic-storage integrated three-port DC converter. The photovoltaic-storage integrated three-port DC converter includes a bidirectional DC converter and an isolated converter connected to each other.

3. A power control method for a partially energy storage embedded medium-voltage photovoltaic storage integrated system as claimed in any one of claims 1-2, characterized in that: The power control method adopts hierarchical control, including system-level power control, power balance control between phases and within phases, and module-level power control within each submodule, wherein: The system-level power control is used to perform active / reactive power control according to the sampled grid voltage and current; The inter-phase and intra-phase power balancing control is used to distribute power between phases and within phases based on the energy storage SOC of each energy storage embedded submodule to achieve inter-phase balance and intra-phase balance; The module-level power control inside each submodule is used to control the photovoltaic unit to output the maximum power and make each submodule output a stable DC voltage.

4. The power control method according to claim 3, characterized in that: In the inter-phase and intra-phase power balancing control, the mean SOC of the inter-phase energy storage unit is obtained, the zero-sequence component that needs to be injected into the modulation signal is calculated, and the initial three-phase modulation signal is generated based on the zero-sequence component through power decoupling control to achieve inter-phase balancing control.

5. The power control method according to claim 4, characterized in that: The zero-sequence component is generated by a PI controller.

6. The power control method according to claim 3, characterized in that: In the inter-phase and intra-phase power balancing control, the average SOC of each energy storage unit in each phase is obtained, a correction coefficient is added, and the modulation signal is distributed proportionally to achieve intra-phase balancing control.

7. The power control method according to claim 3, characterized in that: The system-level control performs real-time data exchange and command transmission with the module-level control of each submodule through a communication interface.

8. The power control method according to claim 3, characterized in that: During the control process, each submodule stores and uploads submodule information, which includes whether the submodule operates normally, the battery SOC status and the photovoltaic status.

9. A computer-readable storage medium, characterized in that: The method comprises one or more programs for execution by one or more processors of an electronic device, wherein the one or more programs comprise instructions for executing the power control method according to any one of claims 3 to 8.

10. An electronic device, characterized in that: The system comprises one or more processors, a memory and one or more programs stored in the memory, wherein the one or more programs include instructions for executing the power control method according to any one of claims 3 to 8.

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