Solid state transformer system with integrated energy storage unit and control method thereof

Abstract

The application discloses a kind of integrated energy storage unit's solid state transformer system and its control method, system includes solid state transformer, energy storage unit, load port and controller, solid state transformer includes several power modules, power module includes several power sub-modules, the input end between several power sub-modules is cascaded connection, forms the alternating current input end of solid state transformer, and internal DC bus is formed in each power sub-module, and the output end of several power sub-modules is as the DC output end of solid state transformer;Energy storage unit is respectively connected on the internal DC bus of each power sub-module;Load port is connected to the several DC output ends of solid state transformer;The controller is electrically connected with each power sub-module and each energy storage unit, and is configured as: according to the output power demand of each load port and the state of charge of each energy storage unit, determine the power instruction corresponding to each power sub-module, and according to power instruction control corresponding energy storage unit carries out charge-discharge power regulation.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a solid-state transformer system with integrated energy storage unit and its control method. Background Technology

[0002] Solid State Transformer (SST) is a new type of power conversion device based on power electronic conversion technology. Compared with traditional power frequency transformers, SST has advantages such as small size, DC port availability, and bidirectional power controllability. It has broad application prospects in fields such as electric vehicle charging, new energy consumption, and AC / DC hybrid distribution networks.

[0003] Currently, energy storage power supply architectures typically employ cascaded H-bridge solid-state transformers for power conversion, such as... Figure 1 As shown, AC power is transformed into a unified DC bus LV by a solid-state transformer using a cascaded H-bridge scheme. Then, an isolated DC-DC converter distributes the power on the DC bus LV to different loads (such as electric vehicle charging stations). Simultaneously, to provide instantaneous power support and renewable energy absorption capacity, energy storage units such as lithium batteries are typically connected centrally to the DC bus LV, and their charging and discharging are controlled by a non-isolated DC-DC converter. In this architecture, the energy of the energy storage units must undergo multiple stages of transformation by a complete solid-state transformer and its own non-isolated DC-DC converter, resulting in a lengthy energy transmission path, redundant power processing, and significant overall energy transmission losses. Summary of the Invention

[0004] This invention provides a solid-state transformer system with integrated energy storage unit and its control method to solve the technical problems of long energy transmission path, redundant power processing links, and large overall energy transmission loss in the existing energy storage power supply architecture.

[0005] In a first aspect, the present invention provides a solid-state transformer system with an integrated energy storage unit, comprising: A solid-state transformer includes several power modules, each power module including several power sub-modules. The input terminals of the power sub-modules are cascaded to form the AC input terminal of the solid-state transformer for connecting to AC power. Each power sub-module has an internal DC bus. The output terminals of the power sub-modules serve as the DC output terminal of the solid-state transformer. Several energy storage units are connected one-to-one to the internal DC bus of each power submodule; Several load ports are respectively connected to several DC output terminals of the solid-state transformer; The controller is electrically connected to each of the power submodules and each of the energy storage units, and the controller is configured to: determine the power command corresponding to each of the power submodules according to the output power requirements of the loads connected to each of the load ports and the state of charge of each of the energy storage units, and control the corresponding energy storage units to adjust the charging and discharging power according to the power command, so as to achieve power balance of each power submodule.

[0006] Secondly, a control method for a solid-state transformer system with an integrated energy storage unit is provided, applied to the aforementioned solid-state transformer system with an integrated energy storage unit, the control method comprising: Obtain the load demand of each load port and the state of charge of multiple energy storage units; Based on the load requirements and the state of charge of each energy storage unit, calculate the power command corresponding to each power submodule; According to the power commands, the energy storage unit corresponding to the power submodule is controlled to adjust the charging and discharging power so as to maintain power balance among the power submodules.

[0007] Compared with existing technologies, the solid-state transformer system integrating energy storage units in this invention connects each energy storage unit to an internal DC bus formed within each power submodule of the solid-state transformer. This allows each power submodule to perform energy buffering and power compensation locally through its corresponding energy storage unit. On the one hand, the energy storage unit absorbs or releases the power difference between branches nearby, eliminating the need to connect all power submodules in parallel to a unified common DC bus before outputting through a subsequent isolated DC-DC converter. This reduces the number of power conversion processing stages and shortens the energy transmission path from the energy storage unit / grid to the load, thereby reducing conduction losses and improving power conversion efficiency. On the other hand, the energy storage unit itself acts as a large-capacity buffer element connected across the internal DC bus, effectively suppressing twice the power frequency ripple power on the bus. This significantly reduces or even eliminates the large-capacity support capacitor on the intermediate bus, reducing system size and material costs. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the existing energy storage power supply architecture.

[0009] Figure 2 This is a schematic diagram of the structure of the first embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0010] Figure 3 yes Figure 2 The diagram shows a detailed circuit diagram of the solid-state transformer system with integrated energy storage unit.

[0011] Figure 4 This is a schematic diagram of the structure of a second embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0012] Figure 5 This is a structural schematic diagram of the third embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0013] Figure 6 This is a structural schematic diagram of the fourth embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0014] Figure 7 This is a circuit structure diagram of the fifth embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0015] Figure 8 This is a schematic diagram of the structure of the sixth embodiment of the solid-state transformer system with integrated energy storage unit of the present invention.

[0016] Figure 9 This is a flowchart illustrating a specific embodiment of the control method for the solid-state transformer system with integrated energy storage unit of the present invention. Detailed Implementation

[0017] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below with reference to the schematic diagram, but it is not limited thereto.

[0018] Reference Figure 2 , Figure 2 This is a schematic structural block diagram of a first embodiment of the solid-state transformer system integrating energy storage units according to the present invention. In the embodiment shown in the figure, the solid-state transformer system integrating energy storage units according to the present invention includes a solid-state transformer, several energy storage units 20, and several load ports 30. The solid-state transformer includes several power modules 10, each power module 10 including several power sub-modules 11. The input sides of the several power sub-modules 11 are cascaded to form the AC input terminal of the solid-state transformer for connecting to AC power (such as a medium-voltage distribution network). Each power sub-module 11 has an internal DC bus, and the output terminals of the several power sub-modules 11 serve as the DC output terminals of the solid-state transformer. Several energy storage units 20 are also included. Each energy storage unit 20 is connected to the internal DC bus of each power submodule 11, and the load port 30 is connected to the DC output terminal of the solid-state transformer. The controller can be electrically connected to each power submodule 11 and each energy storage unit 20, and the controller is configured to: determine the power command corresponding to each power submodule 11 according to the output power demand of the load connected to each load port 30 and the state of charge of each energy storage unit 20, and control the corresponding energy storage unit 20 to adjust the charging and discharging power according to the power command, so as to achieve power balance of each power submodule 11.

[0019] In this invention, each power module 10 has several power sub-modules 11 connected to an energy storage unit 20 on their internal DC bus. This forms a distributed structure of "one sub-module, one energy storage unit" within the power module 10. This allows each power sub-module 11 to buffer energy locally through its corresponding energy storage unit 20. Furthermore, when there is power imbalance at each load port 30, the energy storage unit 20 can absorb or release the power difference corresponding to the power sub-module 11, maintaining power balance among the power sub-modules 11. This also allows each power sub-module 11 to directly provide independent DC output without... All power submodules 11 need to be connected in parallel to a unified common DC bus before being output through a subsequent isolated DC-DC converter. This reduces the number of power conversion processing stages and shortens the energy transmission path from the energy storage unit 20 / grid to the load, thereby reducing conduction losses and improving power conversion efficiency. On the other hand, the energy storage unit 20 itself is also equivalent to a large-capacity buffer element connected across the internal DC bus, which can effectively suppress twice the power frequency ripple power on the internal DC bus. Therefore, the large-capacity support capacitor of the intermediate bus can be significantly reduced or even omitted, reducing system size and material costs.

[0020] In some embodiments, each power submodule 11 may include an AC-DC converter unit 111 and an isolated DC-DC converter unit 112 connected in sequence. The input terminal of the AC-DC converter unit 111 and the output terminal of the isolated DC-DC converter unit 112 serve as the input terminal and output terminal of the power submodule 11, respectively. The internal DC bus is formed at the output terminal of the AC-DC converter unit 111. In this embodiment, the output terminals of the power submodules 11 in the same cascade level of the plurality of power modules 10 are interconnected to form a DC output terminal. Each load port 30 is directly connected to each DC output terminal. As can be seen, in this embodiment, the AC sides of each AC-DC conversion unit 111 in the same power module 10 are cascaded and connected as the AC input side of the solid-state transformer, which can be connected to the AC power grid to convert AC voltage into DC voltage. The isolated DC-DC conversion unit 112 is used to adjust the DC voltage to a stable output voltage. The secondary sides of the isolated DC-DC conversion units 112 in the same cascaded level in each power module 10 are interconnected to form an independent DC output port, which can directly transmit electrical energy to the load through the load port 30. Based on the above design, multiple power submodules 11 are connected in series on the AC side to share the AC voltage. Each power submodule 11 rectifies the AC voltage it shares into DC through its AC-DC conversion unit 111, forming an internal DC bus (i.e., intermediate bus) at the output of the AC-DC conversion unit 111. Multiple energy storage units 20 are distributedly connected to the internal DC bus of each power submodule 11 to buffer the energy of each power submodule branch. The electrical energy can be directly supplied to the load port 30 after being converted by each power submodule 11 through the DC output terminal. This eliminates the need for a centralized common DC bus and a subsequent isolated DC-DC converter. Furthermore, the energy storage units 20 can absorb or release the power difference of each power submodule branch under the control of the controller, making the structure more streamlined.

[0021] Combination Figure 3In this embodiment, the AC input terminal of the solid-state transformer is connected to a three-phase AC power grid. The solid-state transformer contains three power modules 10, each of which includes multiple power sub-modules 11. The number of energy storage units 20 is the same as the total number of power sub-modules 11 in the three power modules 10. Preferably, each energy storage unit 20 is connected to an internal DC bus formed by the output terminal of the AC-DC conversion unit 111 in the power sub-module 11 via a DC-DC converter 40, to facilitate power balance control. The DC-DC converter 40 can be a buck converter. Both the AC-DC conversion unit 111 and the isolated DC-DC conversion unit 112 can be mainly composed of H-bridge converters. The isolated DC-DC conversion unit 112 also uses a high-frequency transformer to achieve electrical isolation between the primary and secondary sides. In use, the controller can adjust the pulse width modulation duty cycle of the switching transistors in the DC-DC converter 40 to change the direction and magnitude of the charging and discharging current of the energy storage unit 20; at the same time, it can also adjust the phase shift angle between the primary and secondary switching transistors of the isolated DC-DC converter unit 112 to adjust the power output of each power submodule 11 to the load port 30.

[0022] As shown in the figure, the DC output sides of the power sub-modules 11 in the same cascade level of the three power modules 10 are connected in parallel to form a DC output terminal. That is, each DC output terminal is formed by connecting the output terminals of the three power sub-modules 11 in the same cascade level of the three different power modules 10. In this embodiment, the number of DC output terminals of the solid-state transformer is the same as the number of power sub-modules 11 in each power module 10. For example, each power module 10 may include three power submodules: power submodule A, power submodule B, and power submodule C. The number of energy storage units 20 is set to nine. The AC input sides of power submodules A, B, and C in each power module 10 are cascaded to form three AC input terminals, which are respectively connected to phases A, B, and C of the three-phase AC power grid. The output terminals of the AC-DC conversion units 111 in power submodules A, B, and C are all connected to the energy storage units 20 through DC-DC converters 40. It can be understood that the same cascade level can be the same series in the three power modules 10. In the corresponding cascading levels, such as in this example, if the three power sub-modules A in the three power modules 10 are at the same cascading level, their output terminals are interconnected to form a DC output terminal; and if the three power sub-modules B in the three power modules 10 are at the same cascading level, their output terminals are interconnected to form a DC output terminal; the output terminals of the power sub-module C in the three power modules 10 are also interconnected to form a DC output terminal, so that the solid-state transformer has a total of three DC output terminals. The load port 30 can also be set to three, namely, load port A, load port B and load port C, and the three load ports 30 are respectively connected to the three DC output terminals.

[0023] In some embodiments, the controller is specifically configured to: when the state of charge of any energy storage unit 20 reaches a preset upper limit, using the power of the load port 30 with the smallest actual required output power as a reference, control the output power of the power submodules 11 corresponding to the remaining load ports 30 to be consistent with the reference, and control the energy storage units 20 connected to them to discharge, so as to compensate for the power difference between the actual required output power of the load port 30 and the reference, thereby avoiding overcharging of the fully charged energy storage unit 20 and maintaining the system power balance. For example, when the energy storage unit 20 connected to the internal DC bus in the power submodule C reaches the preset upper limit (i.e., fully charged), since the energy storage unit 20 can no longer absorb additional electrical energy, the controller will use the power of the load port 30 with the smallest actual required output power as a reference (assuming that the actual required output power of the load connected to port C is the smallest), and control the transmission power (i.e., output power) of all power submodules 11 to be uniformly equal to the reference power. For load port C, the power input from the AC grid is just enough to meet its own load demand, so its energy storage unit 20 does not need to perform power compensation; while for other ports whose actual required output power is greater than the benchmark (such as load ports A and B), in order to keep their AC side input power unchanged, their respective energy storage units 20 will discharge to provide the differential power to meet their load demand that is higher than the benchmark.

[0024] In some embodiments, the controller may be further configured to: when the required output power of multiple load ports 30 is unbalanced, control the energy storage unit 20 corresponding to the load port 30 with a larger required output power to discharge, and / or control the energy storage unit 20 corresponding to the load port 30 with a smaller required output power to charge. For example, when the actual required output power of load ports A and B is equal, while the actual required output power of load port C is smaller, since the AC sides of each power submodule 11 are cascaded and connected to the same AC power grid, the controller can control the energy storage units 20 corresponding to load ports A and B to discharge, and / or control the energy storage unit 20 corresponding to load port C to charge, so that each power submodule 11 maintains the same transmission power, thereby ensuring that the AC side voltage of each power submodule 11 is equalized.

[0025] Furthermore, in some embodiments, the controller can also be configured to: control the energy storage unit 20 to output ripple power that is complementary to the double power frequency ripple power generated on the internal DC bus of the corresponding power submodule 11, so as to at least partially cancel the double power frequency ripple power, thereby further reducing the capacitance value of the DC support capacitor required for the internal DC bus. Based on this design, the controller can also superimpose a ripple cancellation control component on the basis of power balance control. Specifically, the controller detects the double power frequency ripple power on the internal DC bus of each power submodule 11 and controls the corresponding energy storage unit 20 to output ripple power that is opposite in phase and matches the amplitude of the ripple power. When the energy storage unit 20 discharges, its output ripple power partially replaces the ripple power originally absorbed or released by the DC support capacitor on the internal DC bus; the same applies when the energy storage unit 20 is charging. As a result, the capacitance value of the large-capacity DC support capacitor required on the internal DC bus can be further reduced significantly, and even only a small-capacity filter capacitor (such as...) for filtering high-frequency switching ripple can be retained. Figure 3 As shown in C1), this reduces system size and cost.

[0026] In some embodiments, the solid-state transformer system with integrated energy storage unit also possesses black-start capability. The energy storage unit 20 is further configured to provide operating power to the controller when the connected AC power is interrupted, thereby achieving the black-start function. Based on this design, when the power grid is interrupted, the energy storage unit 20, connected to the power submodule 11, can provide operating power to the controller and other components through its connected DC-DC converter 40. After the controller is powered on, it performs various hardware status self-checks. Only after all self-check processes pass and no faults are confirmed can the controller connect the system to the external power grid or output electrical energy. This black-start function greatly improves the safety and reliability of system startup, eliminating the need for additional external auxiliary power supply configuration.

[0027] As can be seen from the above, in the solid-state transformer system integrating energy storage units in this embodiment, the energy storage units 20 are distributedly connected to the internal DC buses of each power submodule 11 in the solid-state transformer. When the power of each load port 30 is unbalanced, the charging and discharging of the energy storage units 20 can be controlled to compensate for the power difference, so that the power submodules 11 maintain power balance. This eliminates the need for a centralized common DC bus in traditional solutions, reduces the transmission path and power conversion stages from the AC side to the energy storage units 20 and the load, reduces energy transmission losses, improves the power conversion efficiency from the grid to the DC load, and also improves the system's adaptability and operational reliability to different load conditions. At the same time, since the energy storage units 20 themselves can buffer power frequency ripple power and can also output ripple power for ripple cancellation under the control of the controller, the large-capacity support capacitor on the internal DC bus can be reduced or even eliminated, reducing system size and material costs. In addition, since each power submodule 11 is equipped with an energy storage unit 20, the energy storage unit 20 can provide emergency power to the controller when the power grid fails, thereby realizing the black start function of the system and greatly improving the overall operational reliability and intelligence level of the power supply system.

[0028] It should be noted that the application scenarios of this invention are not limited to electric vehicle charging, but are also applicable to the power supply and energy management of other DC loads.

[0029] Reference Figure 4 , Figure 4This is a schematic block diagram of a second embodiment of the solid-state transformer system integrating an energy storage unit according to the present invention. The difference between this embodiment and the first embodiment is that the energy storage unit 20 is directly mounted on the internal DC bus of the power submodule 11; the remaining structures are the same or similar. In this embodiment, the energy storage unit 20 is directly connected to the internal DC bus of the power submodule 11 without a DC-DC converter. This "direct connection" means that the charging and discharging current of the energy storage unit 20 is determined by the voltage difference between the internal DC bus voltage and the voltage of the energy storage unit 20 itself, which limits the adjustment flexibility. However, in scenarios where the voltage of the energy storage unit 20 itself matches the bus voltage and the system allows the absorption of power difference in a passive response manner, it is still possible to reduce the energy transmission path and the number of power conversion processing stages, improve the power conversion efficiency from the grid to the DC load, and achieve a certain purpose of energy storage power compensation and energy balance according to the difference in the required output power of each load port 30. It also has the advantages of no switching device delay, extremely fast instantaneous response, effective simplification of system structure and further reduction of material costs. It is suitable for stable operating conditions where the voltage of the energy storage unit 20 is naturally matched with the voltage of the internal DC bus and the load fluctuation amplitude is small. For example, when the load of the charging pile connected to a certain power submodule 11 suddenly increases, the DC bus inside it will experience a slight voltage drop due to instantaneous power intake. At this time, the terminal voltage of the energy storage unit 20 will generate a positive voltage difference relative to the bus, thereby spontaneously discharging to the bus to compensate for the power difference. Conversely, if the load decreases and there is excess power on the bus, the bus voltage will rise slightly, and the energy storage unit 20 will spontaneously absorb power to charge.

[0030] Reference Figure 5 , Figure 5 This is a schematic structural block diagram of a third embodiment of the solid-state transformer system integrating an energy storage unit according to the present invention. The difference between this embodiment and the first embodiment is that the solid-state transformer system integrating the energy storage unit in this embodiment further includes a power distribution unit 50; the rest of the structure is the same or similar. In this embodiment, the power distribution unit 50 is connected between each DC output terminal of the solid-state transformer and each load port 30. Specifically, multiple input terminals of the power distribution unit 50 are respectively connected to multiple DC output terminals of the solid-state transformer, and multiple output ports of the power distribution unit 50 are respectively connected to each load port 30. Furthermore, the power distribution unit 50 is communicatively connected to the controller and is configured to distribute and schedule the electrical energy output by each power submodule 11 according to the power command generated by the controller, so as to adjust the power obtained by each load port 30 in real time.

[0031] As shown in the figure, in this embodiment, the power distribution unit 50 can be used to connect different load ports 30 in parallel to flexibly distribute power. Simultaneously, the energy between each energy storage unit 20 can also be indirectly scheduled through energy coupling between the power distribution unit 50 and each power submodule 11. That is, the electrical energy distributed by the power distribution unit 50 includes both the electrical energy output from the AC grid after conversion by the solid-state transformer and the electrical energy released by the energy storage unit 20 through the corresponding power submodule 11 (when the energy storage unit 20 supplies power to the load). Therefore, this embodiment of the solid-state transformer system integrating energy storage units, through the cooperation of the energy storage unit 20 and multiple power submodules 11 in the solid-state transformer, combined with the controller and power distribution unit 50, reduces the number of power conversion processing stages and improves the energy conversion efficiency from the energy storage unit 20 and the grid to the DC load. Furthermore, it can flexibly schedule energy storage for power compensation and energy balancing based on the required output power differences of each load port 30, and can also perform flexible power distribution and scheduling based on the load access status of each load port 30, further improving the system's adaptability to different load conditions and operational reliability.

[0032] It should be noted that the physical form of the controller can be implemented in various ways in different embodiments of the present invention. In one embodiment, the controller can be an independent external controller, such as a microcontroller, digital signal processor, or field-programmable gate array chip. In another embodiment, the controller can also be directly integrated into the power distribution unit 50, for example, the controller function can be implemented using the main control microcontroller built into the power distribution unit 50.

[0033] Reference Figure 6 , Figure 6This is a schematic structural block diagram of a fourth embodiment of the solid-state transformer system integrating an energy storage unit according to the present invention. The difference between this embodiment and the first embodiment is that a centralized DC bus LV can be provided at the DC output terminal of the solid-state transformer system integrating the energy storage unit in this embodiment; the rest of the structure is the same or similar. In this embodiment, the output terminals of each power submodule 11 are connected in parallel to the centralized DC bus LV, which is connected to each load port 30 for power supply. As shown in the figure, in this embodiment, part of the DC output terminal of the solid-state transformer is connected to the centralized DC bus LV, which is then connected to the load port 30 through a subsequent isolated DC-DC converter; while the other part of the DC output terminal is directly connected to the load port 30. Each energy storage unit 20 is connected to the internal DC bus formed in each power submodule 11 of the solid-state transformer. The energy storage unit 20 can absorb or release the power difference of each branch nearby, without having to connect all the power submodules 11 in parallel to the centralized DC bus LV and then output through the subsequent isolated DC-DC converter. This can reduce the overall conduction loss of the system and improve the overall conversion efficiency. At the same time, it can also realize the purpose of scheduling energy storage for power compensation and energy balancing according to the difference in the required output power of each load port 30, as well as reducing the system size and material cost.

[0034] Reference Figure 7 , Figure 7This is a circuit diagram of a fifth embodiment of the solid-state transformer system integrating an energy storage unit according to the present invention. The difference between this embodiment and the first embodiment is that the AC input terminal of the solid-state transformer system integrating the energy storage unit in this embodiment is connected to a single-phase AC power grid, and the number of power modules 10 in the solid-state transformer is different, while the rest of the structure is the same or similar. In this embodiment, the solid-state transformer includes one power module 10, wherein the output terminal of each power submodule 11 in the power module 10 respectively forms a DC output terminal. In this embodiment, when the system input is a single-phase AC input, the solid-state transformer is configured with only one power module 10. The output terminals of each power submodule 11 in the power module 10 directly serve as multiple DC output terminals of the solid-state transformer, connected to the load port 30. Each energy storage unit 20 is connected to the internal DC bus of each power submodule 11. This also reduces the number of power conversion processing stages in the system and shortens the energy transmission path from the grid to the load, thereby reducing conduction losses and improving the power conversion efficiency from the grid to the DC load. At the same time, it can also dynamically compensate for the power differences of each load port 30 at the power submodule 11 level, maintaining power balance among multiple power submodules 11, thereby ensuring the balanced and stable AC voltage of each submodule, thus improving the system's adaptability to different load conditions and operational reliability. Understandably, in some other embodiments, a power distribution unit 50 or similar unit can be added based on this fifth embodiment to achieve flexible power distribution and scheduling according to the load access status of each load port 30.

[0035] Reference Figure 8 , Figure 8 This is a schematic structural block diagram of the sixth embodiment of the solid-state transformer system integrating energy storage units according to the present invention. The difference between this embodiment and the second embodiment lies in the specific connection of the output side of the power submodule 11; the rest of the structure is the same or similar. In this embodiment, the DC output side of each power submodule 11 in the same cascade level of the three power modules 10 independently serves as a DC output terminal of the solid-state transformer, correspondingly connected to one of the load ports 30. That is, in this embodiment, the number of energy storage units 20 is the same as the total number of all power submodules 11 in the three power modules 10, and the DC output side of each power submodule 11 is directly and individually used as a DC output terminal, which can be directly connected to a load port 30 for output. It can be seen that in this embodiment, by connecting the energy storage units 20 to the internal DC bus of the power submodule 11, the number of power conversion processing stages of the system can also be reduced, the energy transmission path from the grid to the load end can be shortened, and the power differences of each load port 30 can be dynamically compensated at the power submodule 11 level, maintaining power balance among multiple power submodules 11. Understandably, in some other embodiments, a power distribution unit 50 or similar unit may be added to the sixth embodiment to flexibly perform power distribution and scheduling.

[0036] Reference Figure 9 , Figure 9 This is a flowchart illustrating a specific embodiment of the control method for a solid-state transformer system with integrated energy storage unit according to the present invention. The control method can be applied to the solid-state transformer system with integrated energy storage unit described in any of the above embodiments. In this embodiment, taking the solid-state transformer system with integrated energy storage unit described in the third embodiment as an example, the control method includes the following steps: S1. Obtain the load demand of each load port and the state of charge of multiple energy storage units.

[0037] S2. Calculate the power command corresponding to each power submodule based on the load requirements and the state of charge of each energy storage unit.

[0038] In this step, the actual required output power (i.e., load demand) of each load port and the current state of charge of each energy storage unit are acquired in real time. Under normal power balancing conditions, the system of this invention sets the AC input power of each power submodule to be consistent, i.e., unified as the target reference power, based on the premise of maintaining the AC voltage balance of each power submodule. Then, the difference between the target reference power and the load demand of each load port is calculated to determine the charging and discharging compensation power required by the energy storage unit corresponding to each power submodule, and power commands corresponding to each power submodule are generated. In this embodiment, the power command can be a control command that includes the charging or discharging direction and power magnitude.

[0039] S3. According to each of the power commands, control the energy storage unit corresponding to the power submodule to adjust the charging and discharging power so as to maintain power balance among the power submodules.

[0040] Specifically, in this step, when the state of charge of any of the energy storage units reaches a preset upper limit, the output power of the power submodules corresponding to the other load ports is controlled to be consistent with the benchmark, using the power of the load port with the lowest actual required output power as a reference. Simultaneously, the energy storage units corresponding to the other load ports are controlled to discharge to compensate for the power difference between the actual required output power of that load port and the benchmark. Through this control, overcharging of fully charged energy storage units can be avoided, and equal transmission power can be maintained among the power submodules, thereby maintaining equal AC voltage across all power submodules.

[0041] Furthermore, this step may also include: when the required output power of multiple load ports is unbalanced, controlling the energy storage unit corresponding to the load port with a larger required output power to discharge, and / or controlling the energy storage unit corresponding to the load port with a smaller required output power to charge, so as to balance the power difference between each power sub-module. That is, the corresponding energy storage unit can be controlled to absorb the power difference between adjacent power sub-modules, so that each power sub-module maintains equal transmission power, thereby achieving voltage equalization of the AC side voltage of each power sub-module.

[0042] In summary, in this invention, each power submodule can be buffered by an energy storage unit. When the power is unbalanced at each load port, the energy storage unit can absorb or release the power difference corresponding to the power submodule, thus maintaining power balance among the power submodules. On the one hand, this allows the power submodules to directly provide independent DC output without connecting all power submodules in parallel to a unified common DC bus and then outputting through a subsequent isolated DC-DC converter. This reduces the number of power conversion processing stages and shortens the energy transmission path from the energy storage unit / grid to the load, thereby reducing conduction losses and improving power conversion efficiency. On the other hand, the energy storage unit itself also acts as a large-capacity buffer element connected across the internal DC bus. It can not only effectively suppress the double power frequency ripple power on the bus, but also output ripple power for ripple cancellation under the control of the controller. This can reduce or even eliminate the large-capacity support capacitor on the internal DC bus, reducing system size and material costs. Furthermore, since each power submodule is equipped with an energy storage unit, the energy storage unit can provide emergency power to the controller when the power grid fails, realizing the black start function under power grid failure, which greatly improves the overall operational reliability and intelligence level of the power supply system. At the same time, the controller, in conjunction with the power distribution unit, can also perform flexible power distribution and scheduling according to the load access status of each load port, thereby further improving the system's adaptability to different load conditions and operational reliability.

[0043] The above 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 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 solid-state transformer system with integrated energy storage unit, characterized in that, include: A solid-state transformer includes several power modules, each power module including several power sub-modules. The input terminals of the power sub-modules are cascaded to form the AC input terminal of the solid-state transformer for connecting to AC power. Each power sub-module has an internal DC bus. The output terminals of the power sub-modules serve as the DC output terminal of the solid-state transformer. Several energy storage units are connected one-to-one to the internal DC bus of each power submodule; Several load ports are respectively connected to several DC output terminals of the solid-state transformer; The controller is electrically connected to each of the power submodules and each of the energy storage units, and the controller is configured to: determine the power command corresponding to each of the power submodules according to the output power requirements of the loads connected to each of the load ports and the state of charge of each of the energy storage units, and control the corresponding energy storage units to adjust the charging and discharging power according to the power command, so as to achieve power balance of each power submodule.

2. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, The energy storage unit is directly mounted on the internal DC bus of the power submodule, or each energy storage unit is connected to the internal DC bus of the power submodule through a DC-DC converter.

3. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, Each power submodule includes an AC-DC converter unit and an isolated DC-DC converter unit connected in sequence. The input terminal of the AC-DC converter unit and the output terminal of the isolated DC-DC converter unit serve as the input terminal and output terminal of the power submodule, respectively. The internal DC bus is formed at the output terminal of the AC-DC converter unit, and the output terminals of each power submodule are connected in parallel to a centralized DC bus. The centralized DC bus is connected to each load port for power supply.

4. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, Each power submodule includes an AC-DC converter and an isolated DC-DC converter connected in sequence. The input terminal of the AC-DC converter and the output terminal of the isolated DC-DC converter serve as the input terminal and output terminal of the power submodule, respectively. The internal DC bus is formed at the output terminal of the AC-DC converter. The DC output sides of the power submodules in the same cascade level in the power modules are interconnected to form a DC output terminal. Each load port is directly connected to each DC output terminal.

5. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, Each power submodule includes an AC-DC converter unit and an isolated DC-DC converter unit connected in sequence. The input terminal of the AC-DC converter unit and the output terminal of the isolated DC-DC converter unit serve as the input terminal and output terminal of the power submodule, respectively. The internal DC bus is formed at the output terminal of the AC-DC converter unit. The DC output side of each power submodule in the same cascaded level in the plurality of power modules independently serves as a DC output terminal of the solid-state transformer. Each load port is directly connected to each DC output terminal.

6. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, The solid-state transformer system of the integrated energy storage unit also includes a power distribution unit. The power distribution unit is connected between each DC output terminal of the solid-state transformer and each load port. The power distribution unit is communicatively connected to the controller and is configured to distribute and schedule the electrical energy output by each power submodule according to the power command generated by the controller.

7. The solid-state transformer system with integrated energy storage unit as described in claim 1 or 6, characterized in that, The controller is specifically configured to: when the state of charge of any of the energy storage units reaches a preset upper limit, using the power of the load port with the lowest actual required output power as a reference, control the output power of the power submodules corresponding to the remaining load ports to be consistent with the reference, and control the energy storage units connected to them to discharge, so as to compensate for the power difference between the actual required output power of the load port and the reference; and / or, When the required output power of multiple load ports is unbalanced, the energy storage unit corresponding to the load port with the larger required output power is controlled to discharge, and / or the energy storage unit corresponding to the load port with the smaller required output power is controlled to charge.

8. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, The controller is further configured to: control the energy storage unit to output ripple power that is complementary to the double power frequency ripple power generated on the internal DC bus of the corresponding power submodule, so as to at least partially offset the double power frequency ripple power; and the energy storage unit is further configured to: provide working power to the controller when the connected AC power is disconnected, so as to realize the black start function.

9. The solid-state transformer system with integrated energy storage unit as described in claim 1, characterized in that, The solid-state transformer has a single-phase AC input terminal or a three-phase AC input terminal.

10. A control method for a solid-state transformer system applied to an integrated energy storage unit as described in any one of claims 1-9, characterized in that, include: Obtain the load demand of each load port and the state of charge of multiple energy storage units; Based on the load requirements and the state of charge of each energy storage unit, calculate the power command corresponding to each power submodule; According to the power commands, the energy storage unit corresponding to the power submodule is controlled to adjust the charging and discharging power so as to maintain power balance among the power submodules.

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