Flywheel medium-voltage dynamic UPS system based on SST

Abstract

The invention provides a flywheel medium-voltage dynamic UPS system based on SST, and relates to the technical field of power supply circuits, and the system comprises a main power supply access which is connected between a medium-voltage input end and a load output end, and is provided with a first input switch, a first static valve group and an output switch; the static bypass path is connected with the main power supply path in parallel, and a second input switch and a second static valve group are arranged on the static bypass path; the alternating current side of the solid-state transformer is connected to the load output end in parallel; and a direct-current bus of the flywheel direct-current energy storage system is connected to the direct-current side of the solid-state transformer, so that the solid-state transformer forms a power electronic conversion interface for electric energy exchange and grid connection between the flywheel direct-current energy storage system and the load output end. According to the invention, the solid-state transformer is used for replacing a traditional conversion device, thereby simplifying the structure, improving the system efficiency, reducing the occupied area, guaranteeing the continuous power supply of a load, and improving the power quality of the load.

Description

Technical Field

[0001] This application relates to the field of power supply circuit technology, and more specifically, to a flywheel medium-voltage dynamic UPS system based on SST. Background Technology

[0002] In traditional flywheel uninterruptible power supply (UPS) systems, the flywheel energy storage component needs to pass through a separate power conversion system (PCS) and a power frequency step-up transformer before it can be connected to the medium-voltage power grid and supply power to the load. This two-stage architecture of "converter plus transformer" faces several prominent drawbacks in practical applications.

[0003] First, the architecture includes two separate large power devices, resulting in a bulky overall system with a significant footprint, which is a major constraint in space-constrained applications. Second, the energy requires two consecutive transformations and transfers, causing additional losses and reducing the overall energy efficiency of the system. Finally, the connections between the converter and transformer, as well as between them and other parts of the system, typically rely on a large number of cables, which not only increases material costs but also complicates the internal wiring, increasing the complexity of installation and maintenance and introducing potential points of failure. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a flywheel medium-voltage dynamic UPS system based on SST to overcome at least one of the above-mentioned defects.

[0005] In a first aspect, embodiments of this application provide a flywheel medium-voltage dynamic UPS system based on SST. The system includes: a main power supply path connected between the medium-voltage input terminal and the load output terminal, wherein the main power supply path is provided with a first input switch, a first static valve group, and an output switch, serving as the main power supply path connecting the medium-voltage input terminal and the load output terminal; a static bypass path connected in parallel with the main power supply path, wherein the static bypass path is provided with a second input switch and a second static valve group, serving as a backup power supply path connecting the medium-voltage input terminal and the load output terminal when the main power supply path or the flywheel DC energy storage system is disconnected; a solid-state transformer, wherein the AC side of the solid-state transformer is connected in parallel to the load output terminal; and a flywheel DC energy storage system, wherein the DC bus of the flywheel DC energy storage system is connected to the DC side of the solid-state transformer, such that the solid-state transformer constitutes a power electronic conversion interface for power exchange and grid connection between the flywheel DC energy storage system and the load output terminal.

[0006] In one optional embodiment of this application, the solid-state transformer includes a first-stage conversion unit and a second-stage conversion unit, wherein the AC side of the first-stage conversion unit constitutes the AC side of the solid-state transformer, the DC side of the first-stage conversion unit is connected to the input terminal of the second-stage conversion unit, and the output terminal of the second-stage conversion unit constitutes the DC side of the solid-state transformer.

[0007] In one optional embodiment of this application, the second-stage conversion unit includes a DC / AC conversion module, a high-frequency isolation transformer, and an AC / DC conversion module connected in sequence.

[0008] In one optional embodiment of this application, the flywheel DC energy storage system includes a machine-side converter and a flywheel body, wherein the DC terminal of the machine-side converter constitutes the DC side of the flywheel DC energy storage system, and the AC terminal of the machine-side converter is connected to the motor of the flywheel body.

[0009] In one optional embodiment of this application, a maintenance bypass is further included, wherein a maintenance switch is provided on the maintenance bypass, and the maintenance bypass is connected between the medium voltage input terminal and the load output terminal.

[0010] In one optional embodiment of this application, a main controller is further included. The main controller is configured to: control the first static valve group of the main power supply path to shut down and control the solid-state transformer to enter off-grid mode when the power supply at the medium-voltage input terminal is abnormal, so that the flywheel DC energy storage system supplies power to the load output terminal through the solid-state transformer; send a start command to the backup power supply; and after the backup power supply starts, control the solid-state transformer to lock phase with the backup power supply and control the first static valve group of the main power supply path to open, so as to transfer the load from the flywheel DC energy storage system to the backup power supply.

[0011] In one optional embodiment of this application, the main controller is further configured to: after the medium-voltage input power is restored, control the first static valve group of the main power supply path to shut down and control the solid-state transformer to enter off-grid mode; control the solid-state transformer to lock phase with the restored medium-voltage input power and control the first static valve group of the main power supply path to open, so as to switch the load back to the medium-voltage input power supply.

[0012] In one optional embodiment of this application, the flywheel DC energy storage system is configured to: absorb electrical energy from the load output terminal with a constant voltage and adjustable current in a charging state; and output electrical energy to the load output terminal with a constant voltage through the solid-state transformer in a discharging state.

[0013] In one alternative embodiment of this application, the solid-state transformer is further configured to suppress voltage and / or current harmonics at the load output.

[0014] In one optional embodiment of this application, a reactor is further provided on the main power supply path, and the reactor is connected in series between the first static valve group and the output switch.

[0015] The flywheel medium-voltage dynamic UPS system based on SST provided in this application includes: a medium-voltage input terminal for connecting to a medium-voltage AC power supply; a main power supply path connected between the medium-voltage input terminal and the load output terminal, wherein the main power supply path is provided with a first input switch, a first static valve group, and an output switch; a static bypass path connected in parallel with the main power supply path, wherein the static bypass path is provided with a second input switch and a second static valve group; a solid-state transformer, wherein the AC side of the solid-state transformer is connected in parallel to the load output terminal; and a flywheel DC energy storage system, wherein the DC bus of the flywheel DC energy storage system is connected to the DC side of the solid-state transformer, so that the solid-state transformer constitutes a power electronic conversion interface for power exchange and grid connection between the flywheel DC energy storage system and the load output terminal. Through this application, replacing the traditional conversion device with a solid-state transformer simplifies the structure and ensures continuous power supply to the load.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 One of the schematic diagrams of a flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application; Figure 2 This is a schematic diagram of the flywheel DC energy storage system provided in the embodiments of this application; Figure 3 This is a schematic diagram of the solid-state transformer provided in an embodiment of this application; Figure 4 A second schematic diagram of a flywheel medium-voltage dynamic UPS system based on SST provided in an embodiment of this application; Figure 5 This is one of the flowcharts for the flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application; Figure 6 This is the second flowchart of the flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. Based on the embodiments of this application, every other embodiment obtained by those skilled in the art without inventive effort falls within the scope of protection of this application.

[0020] First, the applicable scenarios for this application will be introduced. This application can be applied to the field of power supply circuit technology.

[0021] Research has revealed that traditional flywheel medium-voltage dynamic UPS systems consist of a flywheel DC energy storage system, a power circuit converter (PCS), a power frequency step-up transformer, static valve groups, and switchgear. The flywheel DC energy storage system is connected in parallel to the 10kV load side via the PCS and the step-up transformer. This "PCS + power frequency step-up transformer" topology is widely used, but it suffers from drawbacks such as large footprint, high copper consumption, low efficiency, and complex cabling. These drawbacks directly limit the overall grid connection efficiency and harmonic mitigation capabilities of the flywheel medium-voltage UPS system, while also significantly restricting site space and cabling arrangements. With the rapid development of data centers, especially intelligent computing centers, more stringent requirements are being placed on the footprint, efficiency, and harmonic mitigation capabilities of traditional flywheel medium-voltage UPS systems, necessitating the accelerated development of new technological approaches.

[0022] Traditional flywheel medium-voltage dynamic UPS systems can only be connected to the grid via a power frequency step-up transformer, resulting in low efficiency, large footprint, and complex wiring.

[0023] Based on this, this application provides a flywheel medium-voltage dynamic UPS system based on SST, aiming to simplify the system structure and improve energy efficiency and power density. Specifically, this application uses a solid-state transformer as the sole power electronic conversion and grid connection interface between the flywheel DC energy storage system and the medium-voltage load side, replacing the series combination of "energy storage converter" and "power frequency step-up transformer" in the traditional architecture, thereby achieving device integration and simplification at the hardware topology level.

[0024] With the rise and development of solid-state transformer (SST) technology, a new topology architecture that uses power electronic equipment to replace power frequency transformers has emerged. This system uses a flywheel DC energy storage system to directly connect to the 10kV load side through the SST, without the need for an additional power frequency step-up transformer. This can significantly reduce the system footprint, improve grid connection efficiency, and directly use busbars to reduce cable usage and wiring complexity. At the same time, it can perform online management of voltage and current harmonics on the load side and input side, greatly improving the grid-connected power quality.

[0025] Please see Figure 1 , Figure 1 This is one of the schematic diagrams of a flywheel medium-voltage dynamic UPS system based on SST provided in an embodiment of this application. Figure 1 As shown in the figure, the flywheel medium-voltage dynamic UPS system based on SST provided in this application embodiment includes: main power supply path 1, static bypass path 4, solid-state transformer 5, and flywheel DC energy storage system 6.

[0026] The main power supply path 1 is connected between the medium voltage input terminal 2 and the load output terminal 3. The main power supply path 1 is equipped with a first input switch K21, a first static valve group SW1 and an output switch K22, which are used as the main power supply path connecting the medium voltage input terminal 2 and the load output terminal 3.

[0027] Among them, the medium voltage input terminal 2 is used to connect to a medium voltage AC power supply.

[0028] Here, the medium-voltage input terminal 2 serves as the main power input of the system and is connected to an external medium-voltage AC power source (such as a 10kV mains power grid, backup power supply, diesel generator, or new energy power generation system).

[0029] The output of medium-voltage input terminal 2 is simultaneously connected to the beginning of the main power supply path 1, the beginning of the static bypass path 4, and the beginning of the maintenance bypass path 7, enabling power access and distribution. This introduces medium-voltage AC power to the entire UPS system and distributes it to multiple power supply paths, including the main path and bypass paths. It establishes a standard interface between the system and various external power sources, ensuring the diversity and reliability of power supply sources.

[0030] Here, a UPS system is a power protection device that contains an energy storage device, uses an inverter as the main unit, and outputs stable voltage and frequency.

[0031] Among them, the main power supply path 1 serves as the main path, connecting the medium voltage input terminal 2 and the load output terminal 3.

[0032] Furthermore, a reactor is also provided on the main power supply path 1, and the reactor is connected in series between the first static valve group SW1 and the output switch K22.

[0033] The reactor plays the following main roles in the system: First, it filters out high-frequency harmonic currents generated by the solid-state transformer 5 and the nonlinear equipment at the load output terminal 3, reducing the impact on the power quality of the grid and reducing the additional losses and heat generation caused by harmonics; Second, it limits the amplitude and rise rate of fault current and inrush current during short-circuit faults or power switching, protecting downstream equipment such as the first static valve group SW1 and output switch K22; Third, it stabilizes the system impedance by providing inductive impedance, suppresses voltage fluctuations, enhances transient stability during load changes or mode switching, and assists the solid-state transformer 5 in achieving smoother power regulation.

[0034] The specific path is as follows: medium voltage input terminal 2 - first input switch K21 - first static valve group SW1 - (optional reactor) - output switch K22 - load output terminal 3.

[0035] Main power supply path 1 serves as the main channel for normal operation. When the external power supply (mains power) is normal, this is the main path for powering the load.

[0036] It can also achieve rapid switching of execution channels. By controlling the rapid on / off of the first static valve group SW1, it can achieve millisecond-level seamless switching between mains power and backup power, providing a high-quality, low-impedance main power supply path.

[0037] The first static valve group SW1 in the main power supply path 1 is a key component for realizing the "zero interruption" switching function of the system.

[0038] The static bypass circuit 4 is connected in parallel with the main power supply circuit 1. The static bypass circuit 4 is equipped with a second input switch K11 and a second static valve group SW2.

[0039] It serves as a bypass and is connected in parallel with the main power supply path 1. The specific path is: medium voltage input terminal 2 - second input switch K11 - second static valve group SW2 - bypass output switch K12 - load output terminal 3.

[0040] Preferably, the static bypass path 4 can serve as a backup power supply channel. When the main power supply path 1 needs to be shut down due to planned maintenance, failure, or testing, this path serves as a backup power supply channel to ensure that the power supply to the load is not interrupted.

[0041] Furthermore, the static bypass path 4 can also serve as a maintenance transition channel, acting as a temporary power supply bridge during system startup initialization or switching to maintenance mode. This greatly improves system availability and allows the load to continue to receive power even when the main circuit or core energy storage system is not working, providing the infrastructure for realizing "online maintenance" of the system.

[0042] Solid-state transformer 5, the AC side of solid-state transformer 5 is connected in parallel to the load output terminal 3.

[0043] Here, the AC side of the solid-state transformer 5 is directly connected in parallel to the bus of the load output terminal 3, and the DC side of the solid-state transformer 5 is directly connected to the DC side of the flywheel DC energy storage system 6 through the DC bus.

[0044] Preferably, the solid-state transformer 5 can serve as an integrated energy interface, acting as the sole integrated power electronic conversion interface between the flywheel (low-voltage DC) and the medium-voltage AC grid / load. It replaces the two separate devices, the "energy storage converter (PCS)" and the "power frequency step-up transformer," in the traditional architecture.

[0045] Solid-state transformer 5 can operate in multiple modes, as detailed below: 1) PQ mode (grid-connected): Power is drawn from the load-side bus to charge the flywheel or to regulate reactive power and harmonics.

[0046] 2) VF mode (off-grid): As an independent voltage source, it uses flywheel energy storage to output a stable and high-quality sinusoidal voltage to the load.

[0047] Furthermore, the solid-state transformer 5 can also actively mitigate harmonics, and its built-in control algorithm can actively suppress voltage and current harmonics on the load side and the grid side.

[0048] The solid-state transformer 5 is also configured to suppress voltage and / or current harmonics at the load output terminal 3.

[0049] This application integrates two sets of equipment into one, reducing the system size, weight, and floor space; moreover, the efficiency of power electronic conversion is higher than that of power frequency transformer, reducing system operating losses; it not only ensures uninterrupted power supply but also purifies electrical energy, actively improving the power quality on both the load side and the grid side.

[0050] The flywheel DC energy storage system 6 has its DC bus connected to the DC side of the solid-state transformer 5, making the solid-state transformer 5 a power electronic conversion interface for energy exchange and grid connection between the flywheel DC energy storage system 6 and the load output terminal 3.

[0051] In the first embodiment, at the system level, the DC bus side of the flywheel DC energy storage system 6 is directly connected to the DC side of the solid-state transformer (SST). This is the key connection of this solution, abandoning the traditional "flywheel-PCS-transformer" connection method.

[0052] In the second embodiment, at the internal configuration level, the flywheel DC energy storage system 6 includes a machine-side converter and a flywheel body, wherein the DC end of the machine-side converter constitutes the DC side of the flywheel DC energy storage system, and the AC end of the machine-side converter is connected to the motor of the flywheel body.

[0053] For further details, please refer to Figure 2 , Figure 2This is a schematic diagram of the flywheel DC energy storage system provided in an embodiment of this application. Figure 2 As shown, the flywheel DC energy storage system includes: a generator-side converter 31, a flywheel management subsystem 32, an auxiliary monitoring subsystem 33, a generator 34, a flywheel rotor 35, and a magnetic bearing controller 36.

[0054] The generator-side converter 31 serves as the core power electronic interface of the system, connecting the DC bus at one end and the generator 34 at the other, enabling bidirectional conversion between DC and AC power. During charging, it converts the electrical energy from the DC bus into controllable AC power to drive the generator 34 as a motor, thereby accelerating the flywheel rotor 35. During discharging, it converts the AC power generated by the generator 34 into stable DC power and feeds it back to the DC bus.

[0055] The Flywheel Management System (FMS) 32 communicates and controls with the generator-side converter 31, magnetic bearing controller 36, auxiliary monitoring subsystem 33, etc., and is responsible for the coordinated control and energy management of the entire energy storage system, including receiving and executing charging and discharging power commands, monitoring and optimizing system operating status (such as speed and state of charge), and communicating with the upper-level grid control system.

[0056] The Automated Driving System (ADS) 33 is connected to the flywheel management subsystem 32 and collects signals from various system components (such as vacuum, vibration, and temperature sensors) in real time. It is responsible for controlling system auxiliary equipment (such as vacuum pumps and cooling devices) and for real-time monitoring and safety protection of key physical quantities of the system (such as vacuum level, vibration, and temperature) to ensure that the system operates within a safe range.

[0057] The generator 34 is rigidly connected to the flywheel rotor 35 on the same axis. Its electrical port is connected to the machine-side converter 31. During the charging phase, it operates as a motor, converting electrical energy into the mechanical kinetic energy of the flywheel rotor. During the discharging phase, it operates as a generator, converting the mechanical kinetic energy of the flywheel rotor back into electrical energy.

[0058] The flywheel rotor 35 is directly connected to the generator 34 via a shaft and is supported by a magnetic bearing, storing energy in the form of kinetic energy from high-speed rotation. The stored energy is proportional to the square of the rotational speed, making it the system's direct energy storage unit.

[0059] The Active Magnetic Bearing (AMB) controller 36 is connected to the flywheel management subsystem 32 and drives the magnetic bearing (not shown in the figure) to work. The magnetic bearing acts on the shaft of the flywheel rotor 35. By actively controlling the electromagnetic force, the flywheel rotor 35 is kept stably suspended during operation, eliminating mechanical friction and wear, which is the key to achieving high-speed and high-efficiency operation.

[0060] The flywheel management subsystem 32 coordinates the entire system according to instructions. During charging, the machine-side converter 31 drives the generator 34 (acting as a motor), which in turn drives the flywheel rotor 35 to accelerate its rotation, converting electrical energy into kinetic energy for storage. During discharging, the high-speed rotating flywheel rotor 35 drives the generator 34 to generate electricity, and the machine-side converter 31 converts the generated electrical energy and sends it out. Throughout the entire process, the magnetic bearing controller 36 ensures stable rotor levitation, and the auxiliary monitoring subsystem 33 ensures a safe operating environment.

[0061] The flywheel DC energy storage system also ensures uninterrupted power supply to the load during the brief switching between mains power and backup power, which is the core value of the UPS system; compared with batteries, it is more suitable for scenarios with frequent charging and discharging and high power support.

[0062] Through the innovative connection and functional definition of the above devices, this system achieves: Extremely simple architecture: SST serves as the core interface, simplifying the system from the traditional three-stage energy conversion (flywheel-PCS-transformer-grid) to a two-stage (flywheel-SST-grid), significantly reducing the number of devices, connection points, cable usage, and floor space.

[0063] Functional integration and enhancement: In addition to achieving uninterrupted power supply, it also integrates active harmonic mitigation function, combining "power protection" and "clean power" into one.

[0064] Highly reliable and intelligent operation: The triple path design of "main path + bypass + maintenance bypass", combined with the precise scheduling of SST working mode and static valve group by the main controller, ensures continuous, stable and high-quality power supply to the load under all expected failure scenarios and maintenance scenarios.

[0065] In this embodiment, the flywheel DC energy storage system 6 is configured to: absorb electrical energy from the load output terminal 3 with a constant voltage and adjustable current in the charging state; and output electrical energy to the load output terminal 3 with a constant voltage through the solid-state transformer 5 in the discharging state.

[0066] In the first embodiment of this application, when the flywheel DC energy storage system 6 is in a charging state, its machine-side converter 31 is configured to absorb electrical energy from the load output terminal 3 in a constant voltage and adjustable current mode. Specifically, the machine-side converter 31 acts as a regulator of the DC bus voltage, precisely stabilizing the DC bus voltage at a preset rated value; at the same time, the system can set and adjust the magnitude of the charging current according to the operating requirements, so that the machine-side converter 31 absorbs electrical energy from the DC bus with a controlled current and converts it into kinetic energy storage for the flywheel rotor 35.

[0067] The purpose of this charging control strategy is to efficiently and reliably replenish the flywheel energy storage unit when the system is in normal mains power online mode, maintaining it in an optimal state of charge and ensuring it is always ready for emergency discharge. Constant voltage control helps maintain the stability of the DC bus voltage, providing a foundation for the stable operation of the upstream solid-state transformer 5 and the local converter itself; while adjustable charging current gives the system charging power flexibility, allowing for flexible adjustment of the charging speed according to grid conditions or dispatch requirements, and enabling optimized management and lifespan protection of the flywheel energy storage unit under different operating conditions.

[0068] Through the above methods, the flywheel DC energy storage system 6 can ensure the sufficiency and consistency of energy reserves during the charging process, and also provides key support for the high reliability and high efficiency coordination of the entire power supply system in different operating modes.

[0069] In the second embodiment of this application, when the flywheel DC energy storage system 6 is in discharge mode, its generator-side converter 31 is configured to operate in constant voltage mode and output electrical energy to the load output terminal 3 through the solid-state transformer 5. Specifically, when the system detects an abnormality in the mains power and the solid-state transformer receives an off-grid mode command, the generator-side converter 31 switches to voltage source operating mode, dynamically adjusting and stabilizing the DC bus voltage at a preset discharge voltage value; simultaneously, the kinetic energy stored in the flywheel is converted into electrical energy and output to the DC bus under the control of the generator-side converter 31, and then converted into stable AC power that meets the load requirements by the solid-state transformer 5.

[0070] The purpose of this discharge control strategy is to provide the load with an independent AC power supply that meets the required voltage and frequency during mains power outages, thereby ensuring the continuity and reliability of power supply. By maintaining a constant DC bus voltage, stable input conditions are provided for the solid-state transformer 5 to generate high-quality AC power in off-grid mode, thus ensuring the accuracy and purity of the output voltage.

[0071] Therefore, the flywheel DC energy storage system 6 can achieve millisecond-level response and seamless switching during discharge, effectively supporting the system to maintain continuous and stable power supply to the load throughout the entire process of power failure and recovery, and can maintain stable output voltage when the load power fluctuates, thus ensuring power quality.

[0072] This charging and discharging configuration is not isolated; it works in deep collaboration with the solid-state transformer 5 (SST) and the main controller. In the charging state, the solid-state transformer 5 operates in grid-connected mode and provides power to the flywheel. In the discharging state, the flywheel acts as an energy support for the solid-state transformer to switch to off-grid mode. The two are tightly coupled through the DC bus, and the matching of their voltage levels reflects the collaborative design. At the same time, the start and stop of the charging and discharging process, the switching of operating modes, and the setting of voltage and current are all uniformly scheduled and coordinated by the main controller according to the real-time status of the system.

[0073] For preferred options, please refer to [link / reference]. Figure 3 , Figure 3 This is a schematic diagram of the solid-state transformer provided in an embodiment of this application. Figure 3 As shown, the solid-state transformer includes a first-stage conversion unit 21 and a second-stage conversion unit 22.

[0074] In this system, the AC side of the first-stage conversion unit 21 constitutes the AC side of the solid-state transformer 5, and its DC side is connected to the input terminal of the second-stage conversion unit 22. The core function of the first-stage conversion unit 21 is to perform AC / DC conversion, converting the medium-voltage AC voltage (V1) from the load output side 3 into a stable first-stage DC voltage (V2). Specifically, its input terminal (AC side) is directly connected in parallel to the medium-voltage AC bus (e.g., 10kV AC) on the load side, serving as the port for energy interaction between the SST and the power grid.

[0075] When energy flows from the grid to the flywheel DC energy storage system 6 (charging or phase adjustment), it rectifies the AC voltage (V1) into a controllable first-stage DC voltage (V2). When energy is fed back to the grid from the flywheel (discharging), it acts as an active inverter, converting the first-stage DC voltage (V2) into an AC voltage (V1) synchronized with the grid. The first-stage conversion unit 21 replaces the traditional power frequency transformer, realizing a direct and controllable interface with the medium-voltage grid and providing a stable intermediate DC energy platform for subsequent stages.

[0076] The input of the second-stage conversion unit 22 receives the first-stage DC voltage (V2) from the first-stage conversion unit 21, and its output forms the DC side of the solid-state transformer 5, used to connect to the DC bus of the flywheel DC energy storage system 6. This unit mainly consists of three sub-modules connected in sequence: a DC / AC conversion module, a high-frequency isolation transformer 221, and an AC / DC conversion module, which together complete the DC / DC isolation conversion. The DC / AC conversion module inverts the first-stage DC voltage (V2) into high-frequency AC power, which is key to achieving device miniaturization. The high-frequency isolation transformer 221 operates at high frequency, achieving electrical isolation between the input and output, and its size and weight are significantly reduced compared to a power frequency transformer. The AC / DC conversion module rectifies and filters the high-frequency AC power, converting it into a second-stage DC voltage (V3, e.g., 1100V DC) matching the voltage level of the flywheel system. The voltage stabilizing capacitors C1 and C2 shown in the figure are used to stabilize the first-stage DC voltage V2 and the second-stage DC voltage V3, respectively. The second-stage conversion unit 22 achieves voltage matching and electrical isolation through high-frequency technology, allowing energy to flow flexibly and bidirectionally between the first-stage DC voltage (V2) on the grid side and the second-stage DC voltage (V3) on the flywheel side.

[0077] Based on the close coupling and collaborative operation of the first-stage conversion unit 21 and the second-stage conversion unit 22, the solid-state transformer 5, as a highly integrated whole, achieves the following comprehensive technical effects: Firstly, in terms of structure, it integrates AC / DC conversion (AC to DC), electrical isolation, and DC / DC conversion (DC to DC) functions into a single device, directly replacing the traditional independent energy storage converter and power frequency step-up transformer, thus reducing the number of devices, internal connections, and floor space.

[0078] Secondly, in terms of performance, the adoption of fully electronic high-frequency conversion technology reduces the iron and copper losses of traditional transformers, thereby improving the overall energy efficiency and power density of the system.

[0079] In addition, in terms of control and function, through software programmable control, it can flexibly and quickly achieve seamless switching between grid-connected and off-grid modes. Relying on its rapid response capability, it has built-in real-time harmonic suppression and reactive power compensation functions, thereby ensuring power supply continuity while actively improving power quality.

[0080] In summary, the solid-state transformer 5, with its first-stage conversion unit 21 and second-stage conversion unit 22 (including a high-frequency isolation transformer 221, etc.) as its core architecture, constitutes a highly integrated, intelligent, and controllable power electronic conversion device that integrates voltage conversion, electrical isolation, bidirectional power flow, voltage stabilization, and power quality management.

[0081] For further details, please refer to Figure 4 , Figure 4 This is a second schematic diagram of the flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application, as shown below. Figure 4 As shown, it also includes a maintenance bypass 7, an automatic transfer switch 8, a main power supply 9, and a backup power supply 10. The maintenance bypass 7 is equipped with a maintenance switch K1 and is connected between the medium voltage input terminal 2 and the load output terminal 3.

[0082] The maintenance bypass 7 is a direct path completely independent of the main power supply path 1, the static bypass path 4, and the energy loop containing the solid-state transformer 5 and the flywheel DC energy storage system 6. It is equipped with a maintenance switch K1, whose two ends are directly connected between the medium-voltage input terminal 2 and the load output terminal 3. When the power electronic equipment in the system (such as the first static valve group SW1 and the solid-state transformer 5) or the flywheel DC energy storage system 6 needs to be completely de-energized for isolated maintenance, the maintenance switch K1 can be closed to provide power to the load through this simplified path, thereby achieving uninterrupted power supply maintenance for the entire system.

[0083] The input terminals of the automatic transfer switch 8 are connected to the main power supply 9 (AC power) and the backup power supply 10, respectively, while its output terminal is connected to the medium-voltage input terminal 2 of the system. The automatic transfer switch 8 is responsible for automatically or manually switching between the two AC power supplies, providing upstream power redundancy for the entire power supply system and further improving power supply reliability.

[0084] In conclusion, Figure 4 The system shown employs a multi-architecture design consisting of main power supply path 1 (including K21, SW1, K22), static bypass path 4 (including SW2), solid-state transformer 5, flywheel DC energy storage system 6, and maintenance bypass path 7 (including K1). It also relies on automatic transfer switch 8 to manage the switching between main power supply 9 and backup power supply 10, thus constructing a highly reliable power supply network with millisecond-level dynamic protection, continuous voltage support, and uninterrupted maintenance capabilities.

[0085] Furthermore, this application also includes a central controller; please refer to [link to relevant documentation]. Figure 5 , Figure 5 This is one of the flowcharts of the flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application, such as... Figure 5 As shown, the main controller is configured as follows: S101. When the power supply at the medium voltage input terminal 2 is abnormal, the first static valve group SW1 of the main power supply path 1 is shut off, and the solid-state transformer 5 is controlled to enter the off-grid mode, so that the flywheel DC energy storage system 6 supplies power to the load output terminal 3 through the solid-state transformer 5.

[0086] Here, the main controller monitors the voltage at medium voltage input terminal 2 in real time. When a mains power outage, a severe voltage drop, or an abnormal frequency is detected, it is immediately identified as a "power supply abnormality" and the switching contingency plan is activated.

[0087] The first static valve group SW1 is shut off. This is equivalent to instantly shutting off the main power supply from the faulty mains, isolating the load from the abnormal power grid, and preventing the fault from escalating.

[0088] The solid-state transformer (SST) is controlled to enter off-grid mode (VF mode). This command instantly switches the SST from its previous "grid-connected charging" state to "independent power generation" state. The SST immediately utilizes the energy released by the flywheel DC energy storage system to generate a stable, pure sinusoidal voltage, which is directly applied to the load output terminal bus 3.

[0089] Within milliseconds of a mains power failure, fault isolation and the establishment of a new, stable power source can be completed, achieving a "zero-interruption" switch from mains power to flywheel power. The load equipment will not experience any voltage drops or power outages, and business operations will remain unaffected.

[0090] S102, Send a start command to the backup power supply 10.

[0091] Almost simultaneously or shortly after issuing the command, the main controller sends a start command to the backup power source (usually a diesel generator).

[0092] The long-term backup power supply requires a relatively long start-up time (usually tens of seconds) to stabilize its output; this is a parallel operation. While the flywheel instantly takes over the load and ensures business continuity, it buys valuable preparation time for the slower-starting generator. The flywheel's energy storage is sufficient to support these tens of seconds, ensuring continuous power supply to the load.

[0093] S103. After the backup power supply 10 is started, control the solid-state transformer 5 to lock phase with the backup power supply 10, and control the first static valve group SW1 of the main power supply path 1 to open, so as to transfer the load from the flywheel DC energy storage system 6 to the backup power supply 10.

[0094] The main controller waits and confirms that backup power supply 10 has been successfully started and that the output voltage is stable.

[0095] The solid-state transformer 5 (SST) is phase-locked with the backup power supply 10. This is one of the most critical technical aspects. The controller adjusts the voltage waveform output of the SST (VF mode) to achieve complete synchronization with the output of the backup power supply 10 in terms of frequency, phase, and amplitude.

[0096] After confirming that the phase-locked loop is complete, the first static valve group SW1 of the main power supply path 1 is reopened. At this time, since the voltages on both sides are completely synchronized, closing the switch will not generate any inrush current.

[0097] At the instant SW1 is closed and the two power supplies are connected in parallel, the controller instructs the flywheel DC energy storage system 6 to gradually reduce its output at a set slope, while the backup power supply increases its output synchronously, thereby smoothly and without disturbance transferring the load current from the flywheel-SST system to the backup power supply.

[0098] The purpose of this application is to safely and smoothly transfer power supply responsibility from a short-term emergency flywheel to a long-term backup power source without interrupting the load power supply; achieving a "seamless" switch from flywheel power supply to backup power supply. Phase-locked loop (PLL) technology avoids the huge circulating currents and mechanical shocks that may occur when power supplies are connected in parallel, protecting all equipment; the smooth load transfer ensures that there are no fluctuations in power quality (voltage, frequency).

[0099] For further details, please refer to Figure 6 , Figure 6 This is the second flowchart of the flywheel medium-voltage dynamic UPS system based on SST provided in the embodiments of this application, as follows: Figure 6 As shown, the main controller is also configured as follows: S201. After the power supply at the medium voltage input terminal 2 is restored, the first static valve group SW1 of the main power supply path 1 is shut off, and the solid-state transformer 5 is controlled to enter the off-grid mode.

[0100] First, the main controller continuously monitors and confirms that the mains voltage at the medium voltage input terminal 2 has returned to a stable level and meets the standard for reconnection.

[0101] Then, the first static valve group SW1 of the main power supply path 1 is shut off. This action cuts off the direct connection between the load and the currently supplying backup power source 10. At this point, the load loses its main power supply.

[0102] At this moment, almost simultaneously, the solid-state transformer 5 (SST) enters off-grid mode (VF mode). The SST restarts its "independent power generation" function, using the energy stored in the flywheel to instantly establish a stable voltage for the load output bus 3. Therefore, the power supply to the load is not interrupted; the power source simply switches instantly from the backup power supply back to the flywheel-SST system.

[0103] The purpose of this application is to safely "disconnect" the load from the backup power supply 10, creating a clean, conflict-free starting point for switching back to the main power supply 9 (mains power). This is a key prerequisite for achieving seamless switching between any two power supplies.

[0104] This step avoids directly connecting the backup power supply 10 and the mains power supply, which are two independent power sources. If this step is skipped and the switching is performed directly, the parallel connection of the two asynchronous power systems will generate a huge circulating current, which may damage the equipment or cause the switching to fail.

[0105] S202, control the solid-state transformer 5 to lock the power supply of the restored medium-voltage input terminal 2, and control the first static valve group SW1 of the main power supply path 1 to open, so as to switch the load back to the power supply of the medium-voltage input terminal 2.

[0106] First, a synchronization check (phase-locked loop) is performed, controlling the solid-state transformer 5 (SST) to lock phase with the restored mains power. The main controller adjusts the voltage waveform output by the SST (VF mode) to make it completely synchronized with the newly restored mains power in terms of frequency, phase, and amplitude.

[0107] Then, after closing the connection and confirming that the phase-locking is accurate, the first static valve group SW1 of the main power supply path 1 is reopened. Since the voltage output by SST is completely consistent with the mains power, closing SW1 will not cause any inrush current.

[0108] Finally, to transfer the load and restore normal operation, the flywheel-SST system connects to the mains power supply in parallel the instant SW1 closes. The controller then instructs the flywheel to reduce its output, while the mains power supply synchronously increases its output, smoothly and undisturbedly returning the load to the mains power supply. Once the switch is complete, the controller instructs the SST to exit VF mode and return to PQ (grid-connected) mode to recharge the flywheel and potentially restore its grid-connected functions, such as harmonic mitigation. Simultaneously, the backup power supply is instructed to shut down safely.

[0109] The purpose of this application is to smoothly and safely transfer power supply responsibility from the transitional flywheel system to the restored mains power without interrupting the load's power supply, thus restoring the system to its standard online operating state. Through the above steps, a seamless restoration from backup power to mains power is achieved. Phase-locked loop (PLL) ensures electrical stability during switching, with no fluctuations in load voltage and frequency. The system state is then safely reset.

[0110] In summary, the specific operation and control methods of this application include the following core processes: 1) System startup process The system achieves safe power-on from shutdown to online operation through two seamless switching processes. First, basic power supply is established by closing the maintenance bypass switch. Then, relevant contactors are sequentially engaged, triggering the static bypass valve group. After the static bypass stabilizes, the maintenance bypass is disconnected, completing the initial switching. Next, the system detects and closes the main circuit switch, triggering the main static valve group while blocking the static bypass trigger, thus seamlessly switching to the online mode directly powered by the main circuit. Finally, the solid-state transformer is started to enter the grid-connected charging state.

[0111] 2) Procedure for switching to backup power in case of mains power failure When the main grid power fails, the system utilizes flywheel energy storage as a transition unit to continuously supply power to the backup power source. At the moment of switching, the system immediately locks the main static valve group and instructs the solid-state transformer to switch to off-grid mode, with the flywheel independently supporting the load, while simultaneously starting the backup power source. Once the backup power source is ready, the system controls the solid-state transformer to perform phase-locked synchronization with it, subsequently triggering the main static valve group to smoothly transfer the load to the backup power source at a preset slope, ultimately completing the power supply switch and restoring the flywheel to charging mode.

[0112] 3) Switching back to mains power after mains power is restored After the mains power is restored, the system performs a switchback operation from the backup power source. First, the system re-takes over the load using the flywheel, i.e., it locks the main static valve group and puts the solid-state transformer into off-grid mode. Next, it controls the solid-state transformer to synchronize with the restored mains power, and then triggers the main static valve group to seamlessly transfer the load from the flywheel back to the mains power supply. After the switchover is complete, the system restores the flywheel to grid-connected charging and controls the backup power source to shut down after a delay.

[0113] 4) Switching from online mode to maintenance bypass process When core system equipment requires maintenance, it can be switched to maintenance bypass to achieve uninterrupted maintenance. First, the system closes the main static valve group and simultaneously triggers the static bypass valve group, achieving a seamless switch from online mode to static bypass mode. Then, the main circuit switch is disconnected. Next, the maintenance bypass switch is closed, and after it stabilizes, the static bypass valve group is closed, completing the switch to maintenance bypass mode. At this point, equipment such as flywheel energy storage can be safely isolated and maintained.

[0114] 5) Flywheel DC energy storage system charge and discharge control mode The flywheel DC energy storage system has clearly defined charging and discharging operating parameters. In charging mode, the charging voltage is fixed at V_charge, and the charging current can be adjusted between I_charge_min and I_charge_max (default I_charge_default), with a corresponding charging time of approximately T_charge_min to T_charge_max. The steady-state accuracy of the DC bus voltage is better than η_charge. In discharging mode, the discharging voltage is fixed at V_discharge, with a voltage steady-state accuracy better than η_discharge. The maximum system discharge power is P_discharge_max (corresponding to a current of approximately I_discharge_max), and the typical duration of full-power discharge is T_discharge_full.

[0115] The above-mentioned V_charge, I_charge_min, I_charge_max, I_charge_default, T_charge_min, T_charge_max, η_charge, V_discharge, η_discharge, P_discharge_max, I_discharge_max, and T_discharge_full are all variable parameters of the flywheel DC energy storage system. Their specific values ​​can be configured and set according to the actual system design specifications, load requirements, and application scenarios, and are not limited to a specific value.

[0116] Compared with existing power supply solutions that rely on traditional power frequency transformers and distributed energy storage interfaces, the flywheel medium-voltage dynamic UPS system based on SST provided in this application deeply integrates a high-frequency isolated solid-state transformer (SST) with a flywheel DC energy storage system and constructs a multi-redundancy architecture that includes a main power supply path, static bypass, and maintenance bypass. This solves the problems of traditional systems being bulky, inefficient, slow in dynamic response, and requiring power interruption during maintenance. It achieves a comprehensive effect of high equipment integration, proactive power quality management, seamless switching of millisecond-level faults, and online uninterrupted maintenance, significantly improving the power supply continuity and power quality of critical loads in medium-voltage power distribution scenarios.

[0117] The flywheel medium-voltage dynamic UPS system based on SST provided in this application mainly achieves two technical effects: First, a complete system electrical topology and architecture is proposed, which integrates key components such as 10kV medium voltage input, main power supply path, static bypass, maintenance bypass, solid-state transformer (SST), flywheel DC energy storage system and load output. Energy interaction between the flywheel system and the AC side is realized through SST, which ensures load-side voltage stability and power quality improvement.

[0118] Secondly, a complete system control mode and logic were designed, covering system startup, mains power failure and recovery switching, bypass operation, and specific charging and discharging control of flywheel energy storage, thereby ensuring reliable and stable online operation of the system under various working conditions.

[0119] The key technological contribution of this application is as follows: First, it is the first time that a complete system topology and structure covering medium-voltage input, multiple redundant power supplies, SST interface and flywheel energy storage has been constructed. This design is comprehensive and reasonable and is not available in existing technologies.

[0120] Second, it pioneered a complete set of system control modes and flywheel control strategies to match this topology, including various switching processes and operating logic, which is the core innovation of this application.

[0121] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0122] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the shown or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0123] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0124] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0125] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a processor-executable, non-volatile, computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0126] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The scope of protection of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A flywheel medium-voltage dynamic UPS system based on SST, characterized in that, include: The main power supply path is connected between the medium voltage input terminal and the load output terminal. The main power supply path is equipped with a first input switch, a first static valve group and an output switch, which are used as the main power supply path connecting the medium voltage input terminal and the load output terminal. A static bypass path is connected in parallel with the main power supply path. The static bypass path is equipped with a second input switch and a second static valve group, which is used as a backup power supply path connecting the medium voltage input terminal and the load output terminal when the main power supply path or the flywheel DC energy storage system is disconnected. A solid-state transformer, wherein the AC side of the solid-state transformer is connected in parallel to the load output terminal; A flywheel DC energy storage system, wherein the DC bus of the flywheel DC energy storage system is connected to the DC side of the solid-state transformer, so that the solid-state transformer constitutes a power electronic conversion interface for energy exchange and grid connection between the flywheel DC energy storage system and the load output terminal.

2. The system according to claim 1, characterized in that, The solid-state transformer includes a first-stage conversion unit and a second-stage conversion unit. The AC side of the first-stage conversion unit constitutes the AC side of the solid-state transformer, and the DC side of the first-stage conversion unit is connected to the input terminal of the second-stage conversion unit. The output of the second-stage conversion unit constitutes the DC side of the solid-state transformer.

3. The system according to claim 2, characterized in that, The second-stage conversion unit includes a DC / AC conversion module, a high-frequency isolation transformer, and an AC / DC conversion module connected in sequence.

4. The system according to claim 1, characterized in that, The flywheel DC energy storage system includes a machine-side converter and a flywheel body. The DC terminal of the machine-side converter constitutes the DC side of the flywheel DC energy storage system, and the AC terminal of the machine-side converter is connected to the motor of the flywheel body.

5. The system according to claim 1, characterized in that, It also includes maintenance bypass, The maintenance bypass is equipped with a maintenance switch, and the maintenance bypass is connected between the medium voltage input terminal and the load output terminal.

6. The system according to claim 1, characterized in that, It also includes a central controller, which is configured to: When the power supply at the medium voltage input terminal is abnormal, the first static valve group of the main power supply path is shut off, and the solid-state transformer is controlled to enter off-grid mode, so that the flywheel DC energy storage system supplies power to the load output terminal through the solid-state transformer; Send a start command to the backup power supply; After the backup power supply is started, the solid-state transformer is controlled to lock phase with the backup power supply, and the first static valve group of the main power supply path is controlled to open, so as to transfer the load from the flywheel DC energy storage system to the backup power supply.

7. The system according to claim 6, characterized in that, The main controller is also configured to: After the power supply at the medium voltage input terminal is restored, the first static valve group of the main power supply path is shut off, and the solid-state transformer is controlled to enter the off-grid mode. The solid-state transformer is controlled to lock phase with the restored medium-voltage input power supply, and the first static valve group of the main power supply path is controlled to open, so as to switch the load back to the medium-voltage input power supply.

8. The system according to claim 1, characterized in that, The flywheel DC energy storage system is configured as follows: In the charging state, electrical energy is absorbed from the load output terminal with a constant voltage and adjustable current; in the discharging state, electrical energy is output to the load output terminal with a constant voltage through the solid-state transformer.

9. The system according to claim 1, characterized in that, The solid-state transformer is also configured to suppress voltage and / or current harmonics at the load output.

10. The system according to claim 1, characterized in that, A reactor is also provided on the main power supply path, and the reactor is connected in series between the first static valve group and the output switch.

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