Control method based on common direct current side bus of solid-state transformer

Abstract

The invention provides a control method based on a common DC side bus of a solid-state transformer, which belongs to the technical field of photovoltaic charging and comprises the following steps: the solid-state transformer is respectively connected with a photovoltaic unit, an energy storage unit and a DC load unit of an optical storage and charging system, and a unified DC bus is constructed; acquiring operation parameters of each port of the solid-state transformer, and calculating the power change rate of the unified direct-current bus; determining an energy flow direction according to the unified direct current bus, and determining a time sequence control stage of the optical storage and charging system and a corresponding priority power distribution strategy in combination with the power change rate to obtain a cooperative control instruction; and adjusting the power of each port of the solid-state transformer according to the cooperative control instruction to complete the control of the common DC side bus of the solid-state transformer. The problems that an existing optical storage and charging system is low in energy efficiency due to lengthy energy links and dispersed control, and bus power fluctuation cannot be effectively restrained and dynamic response is slow due to lack of a control strategy matched with a solid-state transformer and a bus are solved.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic charging technology, and in particular relates to a control method based on a common DC bus of a solid-state transformer. Background Technology

[0002] With the rapid development of distributed photovoltaic (PV), DC load, and energy storage systems, integrated PV-storage-charging systems have become an important direction for new energy utilization. In scenarios such as industrial parks, public charging stations, and commercial complexes, PV power generation, energy storage systems, and DC load charging loads exhibit significant high volatility and uncertainty. Existing PV-storage-charging systems generally employ a parallel operation of multiple independent devices, such as a power frequency transformer, PV inverter, energy storage PCS, and DC load, leading to problems such as dispersed energy flow, slow response, and inconsistent control. Currently, solid-state transformers (SSTs) are gradually replacing power frequency transformers in scenarios such as AC power grid distribution, DC loads, power routing, and micro-AC grids.

[0003] In traditional photovoltaic-storage-charging (PV-SGC) systems, photovoltaic power is converted multiple times (DC→AC→DC) before supplying power to energy storage or DC loads, and energy storage discharges via DC→AC→DC to reach the DC load. This results in long conversion links, low efficiency, and high losses. Secondly, in traditional PV-SGC architectures, the ports do not share a unified bus, failing to provide a high-power, stable interface for DC fast charging, hindering the implementation of multi-source hybrid power supply from PV, ESS, and grid, and resulting in low system integration. This makes it difficult for PV-SGC systems to achieve true fusion, enabling rapid and unified power adjustment and failing to meet the rapidly growing demand for large-scale new energy and high-power charging. Furthermore, when SST (Single-Stage Transmission) systems are applied, their control strategies often follow traditional approaches or simply integrate local control at each port, failing to fully leverage the potential of SST as a global energy hub. When facing multi-stage energy conversion, existing systems still incur significant losses. Fluctuations in PV power cannot be proactively suppressed in the early stages of disturbances through coordinated power output across ports, leading to potentially large fluctuations in the DC bus voltage and reducing the performance of the PV-SGC system. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, this invention provides a control method based on a solid-state transformer's common DC-side bus. This method solves the problems of low overall efficiency in existing photovoltaic-storage-charging systems due to lengthy energy links and decentralized control, as well as the inability to effectively suppress bus power fluctuations and slow dynamic response when applying solid-state transformers to photovoltaic-storage-charging systems due to the lack of matching control strategies.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a control method based on the common DC side bus of a solid-state transformer, comprising the following steps: The operating parameters of each port of the solid-state transformer are obtained; the solid-state transformer is connected to the photovoltaic unit, energy storage unit and DC load unit of the photovoltaic-energy storage-charging system respectively, and the photovoltaic unit, energy storage unit and DC load unit are coupled through the solid-state transformer to form a unified DC bus; Calculate the power change rate of the unified DC bus based on the operating parameters; Based on the unified DC bus, the energy flow direction is determined, and combined with the power change rate, the timing control stage of the photovoltaic energy storage and charging system and the corresponding priority power allocation strategy are determined to obtain the coordinated control command. According to the coordinated control command, the power of each port of the solid-state transformer is adjusted to complete the control of the common DC bus of the solid-state transformer.

[0006] Traditional photovoltaic-storage-charging systems employ a decentralized structure with power frequency transformers and multiple independent converters, resulting in numerous cascaded energy conversions, low energy transmission efficiency, slow response, and poor coordination among control devices. This invention introduces a solid-state transformer (SST) and designs a corresponding control strategy to address the problem of insufficient bus voltage stability caused by photovoltaic power fluctuations and DC load impacts. This invention uses a SST as the core to construct the connection structure, forming a unified DC bus, and proposes a corresponding control strategy. By collecting parameters from each port and calculating the power change rate of the unified DC bus, the power fluctuations of the photovoltaic-storage-charging system are quantified, reducing response delay. Combining the power change rate and energy flow direction, different timing control stages and corresponding priority power allocation strategies are defined. This enables coordinated control in complex scenarios with rapid voltage changes from multiple energy sources and multiple loads, maintaining DC bus voltage stability and achieving fast and precise control. This invention solves the problem of independent photovoltaic, energy storage, and DC load components in traditional photovoltaic-storage-charging systems, which cannot be uniformly scheduled. It achieves centralized energy flow management and rapid system response, improving overall system energy efficiency, dynamic response speed, and DC bus voltage stability, meeting the integrated application requirements of photovoltaic-energy storage-DC load.

[0007] Furthermore, the operating parameters of each port of the solid-state transformer include: the power generation of the photovoltaic unit, the current and voltage of the energy storage unit, the charging demand and power of the DC load unit, the voltage of the unified DC bus, the AC grid power, and equipment status information. The power generation of the photovoltaic unit is used to characterize the real-time power generation capability of the photovoltaic array and is the basis for maximum power point tracking and energy dispatch. The current and voltage of the energy storage unit are used to characterize the real-time charging and discharging power and state of charge of the energy storage system. The charging requirements and power of the DC load unit are used to characterize the real-time power demand of the DC load. The voltage of the unified DC bus is used to influence the voltage stability control strategy. The AC grid power is used to characterize the energy transmission status of the photovoltaic-storage-charging system and the AC grid; The device status information is used to characterize the start / stop, fault, and temperature of each port.

[0008] The further beneficial effects mentioned above are as follows: In traditional photovoltaic-storage-charging systems, the parameters of each device are collected independently, resulting in isolated information and delays and deviations in system-level control. This invention connects each unit with a solid-state transformer and, by collecting the operating parameters of each port of the solid-state transformer, achieves rapid calculation of the power change rate, thereby improving the system's dynamic response speed, control accuracy, and overall operational stability.

[0009] Furthermore, the expression for the power change rate is as follows:

[0010] in, To standardize the power change of the DC bus between two adjacent sampling times, To standardize the power change of the DC bus between two adjacent sampling times, For a moment Unified DC bus power, For a moment Unified DC bus power, This represents the time interval between two adjacent sampling times.

[0011] Furthermore: the energy flow direction includes: The photovoltaic unit is connected to the unified DC bus through the photovoltaic DC terminal of the solid-state transformer via the photovoltaic inverter, thus obtaining the energy flow from the photovoltaic unit to the unified DC bus; The surplus electrical energy of the photovoltaic unit is directly input into the energy storage unit through a unified DC bus to charge the energy storage unit ESS, reducing the number of energy conversions and obtaining the energy flow from the photovoltaic unit to the energy storage unit; The energy storage unit is directly input to the DC load unit through a unified DC bus, resulting in the energy flow from the energy storage unit to the DC load unit; During the high-output phase, the photovoltaic unit can directly supply energy to the DC load unit from the unified DC bus, realizing photovoltaic DC fast charging and obtaining the energy flow from the photovoltaic unit to the DC load unit. When the photovoltaic unit's photovoltaic power is insufficient and the energy storage unit's power is insufficient, the solid-state transformer's AC / DC module inputs the energy from the AC grid into the unified DC bus, resulting in an energy flow from the AC grid to the unified DC bus. When the photovoltaic unit generates excess power and the energy storage unit is fully charged, the photovoltaic-storage-charging system feeds energy back to the AC grid, resulting in an energy flow from the DC bus to the AC grid.

[0012] The further beneficial effects mentioned above are as follows: In existing photovoltaic-storage-charging systems, the energy transmission of photovoltaic units and load units requires multiple DC and AC conversions, resulting in high path losses and difficulty in tracking energy flow. This invention constructs a unified DC bus using a solid-state transformer. By sharing a unified DC bus, unnecessary AC / DC conversion links and energy conversion cascades are reduced, improving the overall energy efficiency of the system. Furthermore, it provides a physical path judgment basis for the control strategy, enabling the timing stage division and power allocation to be mapped one-to-one to specific equipment units, achieving precise and rapid scheduling of energy flow, and enhancing the controllability and stability of the photovoltaic-storage-charging system.

[0013] Furthermore: the determination of the timing control stage of the optical energy storage and charging system and the corresponding priority power allocation strategy specifically includes: Determine the dominant energy path based on the direction of energy flow; By combining the power change rate and the dominant energy path, the basis for stage division can be obtained; The phase division criteria are matched with the preset timing control phase trigger conditions to determine the timing control phase of the optical storage and charging system, and the corresponding priority power allocation strategy is invoked.

[0014] The further beneficial effects mentioned above are as follows: Traditional bus control methods often use a single, fixed response logic when facing dynamic changes in photovoltaic energy storage and charging systems. This makes it difficult to distinguish the source and characteristics of bus power fluctuations, resulting in weak targeting and low efficiency of power regulation. This invention achieves a comprehensive judgment of power fluctuations by combining dynamic power change rate with static energy path. It can judge both the degree and trend of fluctuations, as well as their source, which facilitates targeted adjustment, improves management efficiency, and enhances the performance control accuracy and overall energy transmission efficiency of the system in various scenarios.

[0015] Furthermore: the preset timing control stage triggering conditions include: When the dominant energy path is that the photovoltaic unit flows to the unified DC bus, and the power change rate is greater than the first positive threshold, it is judged to be the photovoltaic rising stage; When the dominant energy path is photovoltaic units flowing to a unified DC bus, and the power change rate is less than the first negative threshold, it is judged to be in the photovoltaic decline phase. The dominant energy path is from the unified DC bus to the DC load unit, and the power change rate of the DC load unit is greater than the second positive threshold, which is judged to be the load impact stage.

[0016] The further beneficial effects mentioned above are as follows: Existing dynamic control strategies often suffer from inaccurate identification of the state of photovoltaic-storage-charging systems due to their reliance on a single criterion, such as the difficulty in determining whether power fluctuations originate from photovoltaics or the load. This invention, by determining the dominant energy path based on the energy flow direction and combining it with the power change rate to divide the control stages, ensures the accuracy of the control stage division. Furthermore, it invokes control strategies matched to the control stages, achieving targeted adjustment for specific disturbance types and improving the stability of the unified DC bus and its power fluctuation suppression capability.

[0017] Furthermore: the corresponding priority power allocation strategy includes: Priority power allocation strategy during the photovoltaic upswing phase: Photovoltaic units operate in maximum power point tracking mode, while energy storage units increase charging power; Priority power allocation strategy during the photovoltaic decline phase: As the output power of photovoltaic units decreases, energy storage units are put into standby mode; Priority power allocation strategy during load surge phase: As the power demand of DC load units increases, energy storage units increase their discharge power to support the unified DC bus.

[0018] The further beneficial effects are as follows: Traditional photovoltaic-storage-charging systems employ general or lagging power regulation methods when dealing with different operating conditions, leading to reduced photovoltaic utilization and large fluctuations in bus power. This invention assigns a priority power allocation strategy to each control stage, ensuring the storage of surplus power during the photovoltaic rise phase; putting the energy storage unit into standby mode during the photovoltaic decline phase, preparing for capacity output; and enabling the energy storage unit to provide the main energy supply during load surges. This invention achieves rapid and precise coordinated control of the DC bus voltage, improving the dynamic response capability and overall operational stability of the photovoltaic-storage-charging system.

[0019] The beneficial effects of this invention are: By constructing a unified DC bus using solid-state transformers, energy conversion stages can be reduced and energy efficiency improved. Photovoltaics, energy storage, and DC loads are all directly interconnected on the DC side, significantly reducing losses compared to the traditional multi-stage energy conversion of DC→AC→DC. By unifying the DC bus, the energy path from the photovoltaic unit to the energy storage unit and from the photovoltaic unit to the DC load unit becomes more transparent and reliable, avoiding the problem of indistinguishable energy mixing in traditional solutions, and enabling accurate metering of energy such as photovoltaic input into energy storage. Solid-state transformers have millisecond-level bus voltage regulation capabilities. Combined with control strategies, they can quickly stabilize and unify the power fluctuations of the DC bus, improving the charging experience and system stability.

[0020] By implementing control strategies, photovoltaic power is prioritized for supplying the load, then charged for energy storage, and finally fed into the grid, thereby reducing curtailment and improving economic efficiency and the utilization rate of solar power. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a control method based on a common DC bus of a solid-state transformer; Figure 2 This is an energy flow diagram of the photovoltaic energy storage and charging system based on a unified DC bus, as described in this invention. Detailed Implementation

[0022] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] Example 1 like Figure 1 As shown, this invention provides a control method based on a common DC bus of a solid-state transformer, comprising the following steps: The operating parameters of each port of the solid-state transformer are obtained; the solid-state transformer is connected to the photovoltaic unit, energy storage unit and DC load unit of the photovoltaic-energy storage-charging system respectively, and the photovoltaic unit, energy storage unit and DC load unit are coupled through the solid-state transformer to form a unified DC bus; Calculate the power change rate of the unified DC bus based on the operating parameters; Based on the unified DC bus, the energy flow direction is determined, and combined with the power change rate, the timing control stage of the photovoltaic energy storage and charging system and the corresponding priority power allocation strategy are determined to obtain the coordinated control command. According to the coordinated control command, the power of each port of the solid-state transformer is adjusted to complete the control of the common DC bus of the solid-state transformer.

[0024] To address the problem that existing bus control strategies for solid-state transformers in photovoltaic-storage-charging systems are insufficient to meet the energy flow management requirements of the system, this invention provides a control method based on a common DC bus of a solid-state transformer. This method establishes a shared DC bus, or unified DC bus, connecting multiple energy sources and loads in the photovoltaic-storage-charging system, including photovoltaic units, energy storage units, and DC load units. All energy sources and loads in the system are connected to this DC bus via solid-state transformers, achieving unified energy management and optimization. By monitoring and calculating the power change rate of the unified DC bus, the power fluctuation trend of the photovoltaic-storage-charging system can be reflected, helping to determine the voltage fluctuation of the bus, the direction of energy flow, and the charging and discharging operations of the system, as well as whether external AC grid energy supplementation is needed. Based on the power change rate of the unified DC bus, the system is divided into time-series control stages, and a preset priority power allocation strategy is matched to each stage. Finally, a coordinated control command is generated. By executing this command, the power ports of the solid-state transformer are coordinated and adjusted, achieving precise and rapid control of the DC bus voltage. This invention solves the problems of overall energy transmission efficiency caused by the lengthy energy bus links and decentralized bus control in existing photovoltaic-storage-charging systems, as well as the problems of slow response and difficulty in effectively suppressing photovoltaic power fluctuations due to the lack of corresponding control strategies for the bus. It reduces the losses caused by multi-stage energy conversion, improves the overall system efficiency, and can quickly adjust to AC grid fluctuations or sudden load increases to ensure stable power output.

[0025] In one embodiment of the present invention, a solid-state transformer connects the photovoltaic unit, energy storage unit, and DC load unit of the photovoltaic-energy storage-charging system, respectively, and couples the photovoltaic unit, energy storage unit, and DC load unit through the solid-state transformer to construct a unified DC bus. High-frequency isolation, AC / DC, and DC / DC conversion modules within the solid-state transformer enable efficient and rapid energy transmission and scheduling. The photovoltaic-energy storage-charging system constructed using the solid-state transformer of the present invention shares a single DC bus, i.e., a unified DC bus, which is directly and stably provided by the DC stage of the solid-state transformer. The photovoltaic unit, energy storage unit, and DC load unit are all connected to this unified DC bus. The AC port is connected to the AC power grid through the solid-state transformer, realizing an integrated AC / DC / DC multi-port structure. By establishing a topology based on the unified DC bus of the solid-state transformer, any energy source or energy load within the photovoltaic-energy storage-charging system can efficiently exchange power on the DC side, improving the overall system conversion efficiency and significantly simplifying the number of system devices and wiring layout. Simultaneously, to maintain the energy efficiency and stable power output of the photovoltaic-energy storage-charging system, the operating parameters of each port of the solid-state transformer are obtained.

[0026] The operating parameters of each port of the solid-state transformer include: the power generation of the photovoltaic unit, the current and voltage of the energy storage unit, the charging demand and power of the DC load unit, the voltage of the unified DC bus, the AC grid power, and equipment status information. The sampling period can be set to 10-20ms. The power generation of the photovoltaic unit represents the real-time power generation capability of the photovoltaic array and is the basis for maximum power point tracking and energy dispatch. The current and voltage of the energy storage unit represent the real-time charging and discharging power and state of charge of the energy storage system, and are used for energy storage dispatch and battery protection. The charging demand and power of the DC load unit represent the real-time power demand of the DC load, and are used for load balancing and power distribution. The voltage of the unified DC bus is the core indicator of the photovoltaic-energy storage-charging system of this invention and affects the voltage stability control strategy. The AC grid power reflects the energy transmission status between the photovoltaic-energy storage-charging system and the AC grid. Equipment status information includes the start-up, shutdown, fault, and temperature status of each port.

[0027] In one embodiment of the present invention, the real-time power and operating status of the photovoltaic-storage-charging system can be determined by the operating parameters of each port of the solid-state transformer, but the rapid change trend of the load or power generation of the photovoltaic-storage-charging system cannot be determined. The present invention calculates the power change rate of the unified DC bus based on the operating parameters. The expression for the power change rate is as follows:

[0028] in, To standardize the power change of the DC bus between two adjacent sampling times, To standardize the power change of the DC bus between two adjacent sampling times, For a moment Unified DC bus power, For a moment Unified DC bus power, This represents the time interval between two adjacent sampling times.

[0029] By using the power change rate, the energy flow trend can be determined, and the trends of photovoltaic unit fluctuations, DC loads, pulse loads, and the photovoltaic-storage-charging system can be identified. This allows for the determination of whether the energy storage system needs charging and discharging operations, and whether energy replenishment through the AC grid is required. Although the power change rate can quantify the magnitude and speed of power changes on the DC bus, and its value can reflect the severity of voltage fluctuations or the intensity of load impacts, it is difficult to accurately control the photovoltaic-storage-charging system by using the power change rate because it cannot identify the specific source and path of the change. To solve this problem, this invention introduces the energy flow direction.

[0030] In one embodiment of the present invention, the power change rate is used to quantify the severity and trend of power fluctuations in the photovoltaic energy storage and charging system. However, it is not possible to accurately determine which unit has changed or how the energy flows. The present invention determines the direction of energy flow based on a unified DC bus. Specifically, the present invention connects multiple energy sources and loads in the photovoltaic energy storage and charging system through a unified DC bus.

[0031] like Figure 2 The diagram shown is an energy flow diagram of the photovoltaic energy storage and charging system constructed based on a unified DC bus according to the present invention. The energy flow includes: The photovoltaic unit (PV) is connected to the unified DC bus (DC Bus) through the photovoltaic inverter and the photovoltaic DC terminal of the solid-state transformer, thus obtaining the energy flow from the photovoltaic unit to the unified DC bus; The surplus electrical energy of the photovoltaic unit (PV) is directly input into the energy storage unit (ESS) through the unified DC bus to charge the energy storage unit (ESS), reducing the number of energy conversions and obtaining the energy flow from the photovoltaic unit to the energy storage unit. The energy storage unit (ESS) is directly input to the DC load unit through a unified DC bus, thus obtaining the energy flow from the energy storage unit to the DC load unit. During the high-output phase, the photovoltaic unit (PV) can directly supply energy to the DC load unit from the unified DC bus, realizing photovoltaic DC fast charging and obtaining the energy flow from the photovoltaic unit to the DC load unit. When the photovoltaic (PV) unit is insufficient and the energy storage unit (ESS) is insufficient, the solid-state transformer's AC / DC module inputs the energy from the AC grid into the unified DC bus, thus obtaining the energy flow from the AC grid to the unified DC bus. When the photovoltaic (PV) unit generates excess power and the energy storage unit (ESS) is fully charged, the PV-storage-charging system feeds energy back to the AC grid, resulting in an energy flow from a unified DC bus to the AC grid.

[0032] The power change rate quantifies the severity and trend of power fluctuations in a photovoltaic-storage-charging system, while the energy flow direction clarifies whether the power disturbance originates from photovoltaic output fluctuations, sudden changes in load demand, or alternating changes in the AC grid. The combination of power change rate and energy flow direction not only determines the power fluctuation trend but also accurately identifies which unit is experiencing the fluctuation and the start and end points of the voltage fluctuation. This provides a direct decision-making basis for subsequent precise division of timing control stages and for matching targeted multi-port priority power allocation strategies to each stage. This invention quantifies power fluctuation trends and locates disturbance sources through power change rate and energy flow direction, enabling the suppression of photovoltaic fluctuations and load power impacts, coordinated allocation of multi-port power, and stable control of the unified DC bus voltage, thereby improving the overall operating efficiency and economy of the photovoltaic-storage-charging system.

[0033] In one embodiment of the present invention, existing photovoltaic-storage-charging systems utilize solid-state transformers as integration platforms. While this enables multi-port physical connections and basic energy transmission at the hardware level, its control strategies often rely on traditional steady-state scheduling or hysteresis feedback based on bus voltage deviation. This makes it difficult to accurately identify trends and coordinate interventions in scenarios with rapidly changing power, resulting in sluggish system dynamic response and difficulty in handling rapid photovoltaic fluctuations and the impact of DC loads. Therefore, the present invention determines the energy flow direction in real time based on a unified DC bus and, combined with the power change rate characterizing the trend, dynamically divides the photovoltaic-storage-charging system into timing control stages and matches a corresponding priority power allocation strategy for each stage, generating predictive coordinated control commands. The preset timing control stage triggering conditions include: When the dominant energy path is that the photovoltaic unit flows to the unified DC bus and the power change rate is greater than the first positive threshold, it is judged to be the photovoltaic rising stage; the corresponding priority power allocation strategy is: the photovoltaic unit operates in the maximum power point tracking mode to obtain the maximum available power, and the energy storage unit prioritizes to increase the charging power to absorb incremental power and stabilize the bus voltage under the premise of meeting the photovoltaic-storage-charging system and charging constraints. When the dominant energy path is that the photovoltaic unit flows to the unified DC bus, and the power change rate is less than the first negative threshold, it is judged to be in the photovoltaic decline stage; the corresponding priority power allocation strategy is: the output power of the photovoltaic unit decreases, and the energy storage unit is put into standby mode. The dominant energy path is from the unified DC bus to the DC load unit, and the power change rate of the DC load unit is greater than the second positive threshold, which is judged as the load impact stage; the corresponding priority power allocation strategy is: when the power demand of the DC load unit increases, the energy storage unit increases the discharge power to support the unified DC bus.

[0034] In a specific embodiment of the present invention, the present invention obtains the operating parameters of each port of the solid-state transformer and executes a control strategy, including: based on the DC load demand power, prioritizing the use of photovoltaic units and other renewable energy sources to supply the DC load unit; when there is surplus power from photovoltaic units and other renewable energy sources, prioritizing the increase of the charging power of the energy storage unit to absorb the surplus power, provided that the upper limit of the photovoltaic-energy storage-charging system and the charging power is allowed; when there is still surplus power after the energy storage reaches the charging limit, energy feedback is performed between the solid-state transformer and the AC grid; when the renewable power is insufficient and the photovoltaic-energy storage-charging system or the discharge power is limited, energy is supplemented from the AC grid through the solid-state transformer to meet the DC bus power balance and voltage stability.

[0035] In a specific embodiment of the present invention, the power change rate can also be compared with a preset threshold to perform a basic power allocation strategy: When the power change rate is greater than 0, it is determined that the power is rising rapidly. At this time, the power output of the photovoltaic unit and other renewable energy sources in the photovoltaic-storage-charging system increases, or the power demand of the DC load unit decreases. Priority is given to increasing the charging absorption increment of the energy storage unit. When the energy storage unit is limited by the charging power, the surplus power is sent to the AC grid. In order to avoid the power change rate from fluctuating around 0 due to power fluctuations, a positive threshold greater than 0 can be set appropriately. When the power change rate is less than 0, it is determined that the power is rapidly decreasing. At this time, the power output of the photovoltaic unit and other renewable energy sources in the photovoltaic-storage-charging system decreases, or the power demand of the DC load unit increases. The power gap is compensated by the energy storage unit first. When the energy storage unit is limited by the discharge power, the energy is supplemented by the AC grid. In order to avoid the power change rate from fluctuating around 0 due to power fluctuations, a negative threshold less than 0 can be set appropriately. When the rate of change of power falls within the set threshold dead zone, it is determined to be a slow power change. The current power allocation strategy is maintained, and only minor adjustments are made to the power commands of the energy storage unit and the AC grid to stabilize the voltage of the unified DC bus.

[0036] To avoid misjudgment, threshold triggering requires several consecutive sampling periods to switch stages, and a hysteresis exit condition is used to prevent frequent switching.

[0037] In a specific embodiment of the present invention, the photovoltaic-storage-charging system based on a solid-state transformer can optimize energy scheduling according to real-time parameters such as sunlight, wind speed, and load demand, ensuring maximum energy utilization efficiency and avoiding power waste. When optimizing energy scheduling on a slower timescale, the photovoltaic-storage-charging system acquires real-time information such as renewable energy output corresponding to sunlight / wind speed, load demand, state of charge and charging / discharging capacity of energy storage units, and AC grid switching capacity. It can predict short-term power surplus or deficit by combining recent trends. When a renewable energy surplus is predicted, the charging power of the energy storage is prioritized to absorb the surplus energy; if the energy storage still has surplus due to state of charge or charging power limitations, it is transmitted to the AC grid through the solid-state transformer to avoid energy curtailment and waste. When a renewable energy shortage is predicted or the load increases, the energy storage discharge is prioritized to compensate for the power deficit; if the energy storage is limited by state of charge or discharge power limitations, the AC grid provides supplementary energy. The dispatch results are issued in the form of "target power for energy storage charging and discharging / target state of charge range / upper limit of AC grid exchange power," and are executed by the aforementioned priority power allocation strategy in the fast-track phase to achieve efficient energy utilization and DC bus stability. For example, at noon, sunlight intensifies, and it is predicted that photovoltaic output will increase significantly in the next 10 minutes, while the DC load remains relatively stable; at this time, the energy storage SOC is at a moderate level and has charging margin. The system determines that there will be surplus power, and the dispatch command prioritizes increasing the energy storage charging power to absorb the incremental power; if the energy storage still has surplus power even after reaching the charging limit, the remaining power is transmitted to the AC grid via a solid-state transformer, achieving a waste-free dispatch of "prioritizing self-use and energy storage, followed by external transmission." Subsequently, if cloud cover causes a rapid decline in photovoltaic power, the system switches to a strategy of "prioritizing energy storage discharge support, and supplementing energy to the AC grid when necessary," to maintain bus voltage and power supply continuity while avoiding unnecessary energy waste.

[0038] The beneficial effects of this invention are as follows: This invention constructs a unified DC bus using a solid-state transformer, enabling direct interconnection of photovoltaic (PV) systems, energy storage, and DC loads on the DC side. This reduces the need for multi-stage DC→AC→DC energy conversion steps required in traditional architectures, lowering system losses and improving overall energy efficiency. Furthermore, the unified DC bus makes the energy transmission paths from PV units to energy storage units and from PV units to DC load units clear and controllable, avoiding the difficulty in distinguishing energy mixing in traditional AC coupling energy transmission schemes, and facilitating the determination and calculation of PV power flow. Simultaneously, leveraging the rapid bus voltage regulation capability of the solid-state transformer, combined with the timing-coordinated control strategy proposed in this invention, it can suppress power fluctuations caused by PV fluctuations and load impacts, quickly stabilizing the DC bus voltage, improving charging quality and system operational reliability, reducing curtailment, and increasing PV self-consumption rate and overall system economy.

Claims

1. A control method based on a common DC bus of a solid-state transformer, characterized in that, Includes the following steps: The operating parameters of each port of the solid-state transformer are obtained; the solid-state transformer is connected to the photovoltaic unit, energy storage unit and DC load unit of the photovoltaic-energy storage-charging system respectively, and the photovoltaic unit, energy storage unit and DC load unit are coupled through the solid-state transformer to form a unified DC bus; Calculate the power change rate of the unified DC bus based on the operating parameters; Based on the unified DC bus, the energy flow direction is determined, and combined with the power change rate, the timing control stage of the photovoltaic energy storage and charging system and the corresponding priority power allocation strategy are determined to obtain the coordinated control command. According to the coordinated control command, the power of each port of the solid-state transformer is adjusted to complete the control of the common DC bus of the solid-state transformer.

2. The control method based on the common DC bus of a solid-state transformer according to claim 1, characterized in that, The operating parameters of each port of the solid-state transformer include: the power generation of the photovoltaic unit, the current and voltage of the energy storage unit, the charging demand and power of the DC load unit, the voltage of the unified DC bus, the power of the AC grid, and equipment status information. The power generation of the photovoltaic unit is used to characterize the real-time power generation capability of the photovoltaic array and is the basis for maximum power point tracking and energy dispatch. The current and voltage of the energy storage unit are used to characterize the real-time charging and discharging power and state of charge of the energy storage system. The charging requirements and power of the DC load unit are used to characterize the real-time power demand of the DC load. The voltage of the unified DC bus is used to influence the voltage stability control strategy. The AC grid power is used to characterize the energy transmission status of the photovoltaic-storage-charging system and the AC grid; The device status information is used to characterize the start / stop, fault, and temperature of each port.

3. The control method based on the common DC bus of a solid-state transformer according to claim 1, characterized in that, The expression for the power change rate is as follows: in, To standardize the power change of the DC bus between two adjacent sampling times, To standardize the power change of the DC bus between two adjacent sampling times, For a moment Unified DC bus power, For a moment Unified DC bus power, This represents the time interval between two adjacent sampling times.

4. The control method based on the common DC bus of a solid-state transformer according to claim 1, characterized in that, The energy flow direction includes: The photovoltaic unit is connected to the unified DC bus through the photovoltaic DC terminal of the solid-state transformer via the photovoltaic inverter, thus obtaining the energy flow from the photovoltaic unit to the unified DC bus; The surplus electrical energy of the photovoltaic unit is directly input into the energy storage unit through a unified DC bus to charge the energy storage unit ESS, reducing the number of energy conversions and obtaining the energy flow from the photovoltaic unit to the energy storage unit; The energy storage unit is directly input to the DC load unit through a unified DC bus, resulting in the energy flow from the energy storage unit to the DC load unit; During the high-output phase, the photovoltaic unit can directly supply energy to the DC load unit from the unified DC bus, realizing photovoltaic DC fast charging and obtaining the energy flow from the photovoltaic unit to the DC load unit. When the photovoltaic unit's photovoltaic power is insufficient and the energy storage unit's power is insufficient, the solid-state transformer's AC / DC module inputs the energy from the AC grid into the unified DC bus, resulting in an energy flow from the AC grid to the unified DC bus. When the photovoltaic unit generates excess power and the energy storage unit is fully charged, the photovoltaic-storage-charging system feeds energy back to the AC grid, resulting in an energy flow from the DC bus to the AC grid.

5. The control method based on the common DC bus of a solid-state transformer according to claim 1, characterized in that, The determination of the timing control stage of the optical energy storage and charging system and the corresponding priority power allocation strategy specifically includes: Determine the dominant energy path based on the direction of energy flow; By combining the power change rate and the dominant energy path, the basis for stage division can be obtained; The phase division criteria are matched with the preset timing control phase trigger conditions to determine the timing control phase of the optical storage and charging system, and the corresponding priority power allocation strategy is invoked.

6. The control method based on the common DC bus of a solid-state transformer according to claim 5, characterized in that, The preset timing control phase triggering conditions include: When the dominant energy path is that the photovoltaic unit flows to the unified DC bus, and the power change rate is greater than the first positive threshold, it is judged to be the photovoltaic rising stage; When the dominant energy path is photovoltaic units flowing to a unified DC bus, and the power change rate is less than the first negative threshold, it is judged to be in the photovoltaic decline phase. The dominant energy path is from the unified DC bus to the DC load unit, and the power change rate of the DC load unit is greater than the second positive threshold, which is judged to be the load impact stage.

7. The control method based on the common DC side bus of a solid-state transformer according to claim 6, characterized in that, The corresponding priority power allocation strategy includes: Priority power allocation strategy during the photovoltaic upswing phase: Photovoltaic units operate in maximum power point tracking mode, while energy storage units increase charging power; Priority power allocation strategy during the photovoltaic decline phase: As the output power of photovoltaic units decreases, energy storage units are put into standby mode; Priority power allocation strategy during load surge phase: As the power demand of DC load units increases, energy storage units increase their discharge power to support the unified DC bus.

Images