Bidirectional uninterruptible power supply system and control method thereof

Abstract

The invention relates to the technical field of power supply, and discloses a bidirectional uninterruptible power supply system and a control method thereof.The bidirectional uninterruptible power supply system comprises a static bypass unit with a first end connected to an external power grid and a second end serving as a power grid output end; the first end of the power conversion unit is connected with the energy storage device, and the second end is connected with the power grid output end of the static bypass unit to form an alternating-current connecting end to be connected with a load; the controller is configured to control the static bypass unit and the power conversion unit, when an external power grid is in a normal state, the static bypass unit is controlled to be conducted, the external power grid supplies power to a load, and meanwhile the power conversion unit is configured to be in a rectification charging mode and / or an electric energy quality compensation mode; and when the external power grid is in an abnormal state, the static bypass unit is controlled to be switched off, and the power conversion unit is controlled to enter an inversion discharge mode. The application has the effects of simplifying the topological structure and optimizing the power supply quality, and can meet the power demand of industrial and commercial scenes.

Description

Technical Field

[0001] This application relates to next-generation information technology, especially in the field of power supply technology, and in particular to a bidirectional uninterruptible power supply system and its control method. Background Technology

[0002] Uninterruptible power supplies (UPS) are the primary devices for ensuring continuous power supply to loads and are widely used in scenarios with stringent power stability requirements, such as industrial control and data centers. Traditional UPS systems often employ an architecture of "rectifier + inverter + static bypass + DC / DC converter," and also require an independent DC power supply to charge the energy storage battery, resulting in a cumbersome system structure, a large number of components, and high costs.

[0003] Existing traditional UPS systems have significant limitations: The energy conversion process during mode switching involves multiple steps; when the mains power is normal, it requires two conversions—rectification and inversion—to supply power to the load, resulting in lower system efficiency. The overall system architecture is complex; the use of numerous components not only increases the probability of failure but also requires a separate DC power supply to charge the energy storage battery, further increasing equipment size and raising maintenance costs and complexity. In bypass mode, it can only output mains power and cannot compensate for voltage fluctuations and harmonics in the mains power, making it difficult to ensure a stable and reliable power supply to the load. In battery mode, it requires two energy conversions—a DC / DC converter and an inverter—resulting in significant energy loss and affecting the battery's endurance, failing to meet long-term emergency power supply needs.

[0004] Regarding the aforementioned technologies, existing UPS systems are complex in architecture, high in cost, low in efficiency, and inconvenient to maintain, failing to meet the high reliability requirements of industrial and commercial scenarios. There is an urgent need for an uninterruptible power supply solution that simplifies the topology and balances power quality and charging functions. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a bidirectional uninterruptible power supply system and its control method.

[0006] In the first aspect, this application provides a bidirectional uninterruptible power supply system, which adopts the following technical solution: A bidirectional uninterruptible power supply (UPS) system includes: a static bypass unit, with a first end for connecting to an external power grid and a second end serving as a power grid output; a power conversion unit, with a first end for connecting to an energy storage device and a second end connected to the power grid output of the static bypass unit to form an AC connection terminal for connecting a load; and a controller connected to the power conversion unit and the static bypass unit, configured to control the static bypass unit and the power conversion unit. When the external power grid is in a normal state, the controller controls the static bypass unit to conduct, allowing the external power grid to supply power to the load. Simultaneously, the controller configures the power conversion unit to operate in rectification charging mode and / or power quality compensation mode. The rectification charging mode is used to convert the AC power from the external power grid into DC power adapted to the energy storage device, and the power quality compensation mode is used to dynamically compensate for the power quality of the AC connection terminal. When the external power grid is in an abnormal state, the controller controls the static bypass unit to turn off and controls the power conversion unit to enter inverter discharge mode, converting the DC power from the energy storage device into AC power adapted to the load.

[0007] By adopting the above technical solution, a simple architecture of static bypass + dynamic compensation is constructed. When the external power supply is normal, the static bypass is used as the main power supply path to reduce conversion losses. The power conversion unit simultaneously completes energy storage charging and dynamic compensation for external power interference (such as voltage fluctuations and harmonic correction), which improves the problem of lack of power quality optimization in the traditional bypass mode. Multifunctionality is integrated with a minimalist topology, eliminating the need for separate rectifiers and charging power supplies in traditional UPS. The power conversion unit integrates the three core functions of inversion, rectification and charging through bidirectional mode, reducing the number of components, reducing costs, improving efficiency, and shrinking size while reducing fault nodes. It achieves working condition switching. When the external power supply is abnormal, the mode can be quickly switched to ensure uninterrupted power supply. It can also be expanded to an external power supply-battery joint power supply mode to adapt to diverse needs such as peak shaving and valley filling, which is especially suitable for high-power application scenarios.

[0008] Optionally, the power conversion unit includes a bidirectional DC / AC module, a DC bus, and a bidirectional DC / AC module. The first end of the bidirectional DC / AC module is used to connect to the energy storage device, and the second end is connected to the DC bus. The DC side of the bidirectional DC / AC module is connected to the DC bus, and the AC side is connected to the AC connection terminal. Under normal external grid conditions, the bidirectional DC / AC module converts AC power into DC bus voltage and transmits electrical energy to the energy storage device through the bidirectional DC / AC module. Under abnormal external grid conditions, the bidirectional DC / AC module establishes DC bus voltage and performs inverter discharge through the bidirectional DC / AC module to transmit electrical energy to the load.

[0009] By adopting the above technical solution and modular design, the DC bus serves as the core of energy transfer, enabling bidirectional flow of electrical energy. The bidirectional DC / AC module is responsible for AC / DC conversion. The bidirectional DC / DC module adapts to the voltage difference between the energy storage device and the bus, ensuring efficient and stable energy transmission under different operating conditions and further optimizing system performance.

[0010] Optionally, the DC bus has a positive bus, a negative bus, and a bus midpoint; the bidirectional DC / AC module has a three-level topology and is configured to selectively connect the AC connection terminal to the positive bus, the negative bus, or the bus midpoint by controlling the on / off state of the internal switching devices, so that the voltage of the AC connection terminal switches between positive level, zero level, and negative level.

[0011] By adopting the above technical solutions, the three-level topology makes the output voltage waveform closer to a sine wave, reduces harmonic distortion rate, and optimizes power supply quality; by switching connection nodes to achieve multi-level output, it reduces voltage stress on switching devices, adapts to high-power application scenarios, and improves circuit operation stability and efficiency.

[0012] Optionally, the bidirectional DC / AC module has a T-type three-level topology, including a bridge arm switch branch and a bidirectional switch auxiliary branch; the vertical bridge arm switch branch is connected between the positive bus and the negative bus, and the midpoint of the bridge arm serves as the AC phase line output terminal; the bidirectional switch auxiliary branch is connected between the AC phase line output terminal and the midpoint of the bus; the controller is configured to control the bidirectional DC / AC module to perform power factor correction rectification in rectification charging mode and to control the bidirectional DC / AC module to perform three-level inversion in inverter discharge mode.

[0013] By adopting the above technical solutions, the coordinated design of the bridge arm switch branch and the bidirectional switch auxiliary branch in the T-type three-level topology can not only improve the power quality on the grid side and reduce interference to the external grid in the rectification charging mode with power factor correction rectification, but also ensure the stability and reliability of AC output through flexible switching logic switching in the inverter discharge mode, achieving a smooth connection between rectification and inverter modes. At the same time, the T-type topology itself simplifies the switch control logic, and the coordinated action of the two branches can further reduce switching losses, adapting to the application requirements of high power and high efficiency.

[0014] Optionally, the bidirectional DC / DC module adopts a Buck-Boost bidirectional topology, including a first inductor, a first switching transistor, and a second switching transistor. The first and second switching transistors are connected in series between the positive and negative buses of the DC bus. The first end of the first inductor is used to connect to the positive terminal of the energy storage device, and the second end is connected to the common connection node of the first and second switching transistors. The end of the second switching transistor away from the common connection node is used to connect to the negative terminal of the energy storage device and connect to the negative bus. The bidirectional DC / DC module is configured to have a Buck buck mode and a Boost boost mode. The Buck buck mode is adapted to the normal state of the external power grid, and the Boost boost mode is adapted to the abnormal state of the external power grid.

[0015] By adopting the above technical solution, the Buck-Boost topology achieves bidirectional voltage conversion. The buck mode meets the energy storage and charging requirements, while the boost mode ensures stable bus voltage, adapting to different operating conditions without the need for additional components. The simple topology reduces losses, and combined with inductive energy storage and freewheeling, ensures continuous and efficient energy transfer.

[0016] Optionally, the first switching transistor, the second switching transistor, and the switching devices inside the bidirectional DC / AC module are all fully controllable power semiconductor devices, selected from at least one of the following groups: insulated gate bipolar transistor, metal oxide semiconductor field-effect transistor, silicon carbide metal oxide semiconductor field-effect transistor, and gallium nitride high electron mobility transistor.

[0017] By adopting the above technical solutions, fully controllable power semiconductor devices possess the characteristics of fast switching response and low conduction loss. Their built-in parasitic diodes can naturally conduct under conditions such as rectification charging and mode switching. In conjunction with the switching logic of the switching devices, they can realize current freewheeling or bidirectional conduction functions, ensuring the continuity and stability of the power conversion process. In particular, wide bandgap devices such as silicon carbide (SiC) and gallium nitride (GaN) not only inherit the core advantages of fully controllable devices, but also adapt to high temperature and high frequency conditions, effectively improving the system power density and long-term operating efficiency. At the same time, the selection range of multiple types of devices can be flexibly adjusted according to the power level and cost budget of the actual application scenario, significantly enhancing the engineering adaptability of the solution.

[0018] Optionally, it also includes a status detection unit, which is connected to the external power grid, the controller, the energy storage device and the AC connection terminal respectively, and is configured to collect the operating status parameters of the external power grid, the energy storage device and the load respectively; the controller is configured to trigger the switching of the working mode of the static bypass unit and the power conversion unit based on the operating status parameters of the status detection unit.

[0019] By adopting the above technical solution, the status detection unit captures the operating parameters of each key node in real time, providing the controller with accurate decision-making basis; the controller quickly judges the grid status based on the parameters, triggers mode switching, ensures uninterrupted power supply, and improves the system's adaptability and reliability to complex operating conditions.

[0020] Secondly, the control method for a bidirectional uninterruptible power supply system provided in this application adopts the following technical solution: A control method for a bidirectional uninterruptible power supply system, applied to any of the bidirectional uninterruptible power supply systems described in the first aspect above, includes the following steps: S1. The controller collects operating status parameters of the external power grid, energy storage device, and AC connection terminal through the status detection unit. S2. The controller determines whether the external power grid is in a normal state based on the operating status parameters. S3. If the external power grid is determined to be in a normal state, the controller controls the static bypass unit to conduct to establish the main power supply path to the load. Simultaneously, the controller controls the power conversion unit to connect in parallel with the main power supply path and performs at least one of the following operations based on the operating status parameters: draws power from the external power grid for rectification and charges the energy storage device; dynamically compensates for the power quality at the AC connection terminal. S4. If the external power grid is determined to be in an abnormal state, the controller controls the static bypass unit to turn off and controls the power conversion unit to enter inverter discharge mode, allowing the energy storage device to supply power to the load.

[0021] By adopting the above technical solutions, the system can switch to bypass main power supply mode when the power grid is normal, which improves the continuous double conversion loss of traditional online UPS and enhances operating efficiency; at the same time, the power conversion units can be connected in parallel to carry out power quality compensation, which improves the problem that the traditional bypass mode cannot manage harmonics and reactive power, and enhances the adaptability of the power grid.

[0022] Optionally, step S3 includes: S31, when the status detection unit detects that the power quality parameters of the AC connection terminal exceed the preset compensation threshold, controlling the bidirectional DC / AC module 41 to inject compensation current into the AC connection terminal to perform dynamic power quality compensation; S32, when the status detection unit detects that the charging status of the energy storage device is lower than the preset charging threshold, controlling the bidirectional DC / AC module 41 to rectify the AC power of the external power grid into the DC bus voltage, controlling the bidirectional DC / DC module to work in Buck step-down mode, and converting the DC bus voltage into a DC voltage suitable for the energy storage device.

[0023] By adopting the above technical solution, differentiated control logic is triggered according to operating parameters. When the power quality exceeds the standard, the bidirectional DC / AC module 41 accurately injects compensation current to quickly improve the power supply waveform and reduce harmonics. When the energy storage capacity is insufficient, the rectification and charging process is automatically started to achieve the coordinated operation of charging and power supply, which not only ensures sufficient power of the energy storage device, but also ensures stable power quality at the load end.

[0024] Optionally, step S4 includes: S41, controlling the bidirectional DC / DC module to operate in Boost mode to convert the DC voltage of the energy storage device into the DC bus voltage; S42, the bidirectional DC / AC module 41 inverts the DC bus voltage into AC power adapted to the load; S43, supplying power to the load based on the inverted AC power.

[0025] By adopting the above technical solution, the inverter discharge process is executed in steps. First, the bidirectional DC / DC module boosts the voltage to establish a stable DC bus voltage, and then the bidirectional DC / AC module 41 completes the inverter conversion, ensuring that the load end obtains AC power with stable waveform and qualified parameters. At the same time, it ensures the speed and smoothness of mode switching when the power grid is abnormal, and prevents power outages or voltage fluctuations from affecting the load.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. By adopting the above technical solution, a simple architecture of static bypass + dynamic compensation is constructed. When the external power supply is normal, the static bypass is used as the main power supply path to reduce conversion losses. The power conversion unit simultaneously completes energy storage charging and dynamic compensation for external power interference (such as voltage fluctuation and harmonic correction), which improves the problem of lack of power quality optimization in the traditional bypass mode. It integrates multiple functions with a simplified topology, eliminating the need for separate rectifiers and charging power supplies in traditional UPS. The power conversion unit integrates the three core functions of inversion, rectification and charging through bidirectional mode, which greatly reduces the number of components. This reduces costs, improves efficiency and shrinks size while reducing fault nodes. It achieves working condition switching. When the external power supply is abnormal, it can quickly complete the mode switching to ensure uninterrupted power supply. It can also be expanded to an external power supply-battery joint power supply mode to adapt to diverse needs such as peak shaving and valley filling, which is especially suitable for high-power application scenarios. 2. The coordinated design of the bridge arm switch branch and the bidirectional switch auxiliary branch in the T-type three-level topology not only improves the power quality on the grid side and reduces interference to the external grid by cooperating with power factor correction rectification in rectifier charging mode, but also ensures the stability and reliability of AC output through flexible switching logic switching in inverter discharge mode, achieving a smooth transition between rectification and inverter modes. At the same time, the T-type topology itself simplifies the switch control logic, and the coordinated action of the two branches can further reduce switching losses, adapting to the application requirements of high power and high efficiency. 3. The status detection unit captures the operating parameters of each key node in real time, providing the controller with accurate decision-making basis; the controller quickly judges the grid status based on the parameters, triggers mode switching, ensures uninterrupted power supply, and improves the system's adaptability and reliability to complex operating conditions. Attached Figure Description

[0027] Figure 1 This is a structural diagram of an uninterruptible power supply system provided by related technologies; Figure 2 This is a structural diagram of the bidirectional uninterruptible power supply system provided in the embodiments of this application; Figure 3 This is a structural diagram of another bidirectional uninterruptible power supply system provided in an embodiment of this application; Figure 4 This is a circuit structure diagram of the power conversion unit provided in the embodiments of this application; Figure 5 This is a schematic diagram of the current path of the bidirectional DC / AC module in the positive half-cycle inductor energy storage stage of the rectifier charging mode provided in the embodiments of this application; Figure 6 This is a schematic diagram of the current path of the bidirectional DC / AC module provided in this application embodiment during the positive half-cycle charging stage to the positive bus in rectifier charging mode; Figure 7 This is a schematic diagram of the current path of the bidirectional DC / AC module in the negative half-cycle inductor energy storage stage of the rectifier charging mode provided in the embodiments of this application; Figure 8 This is a schematic diagram of the current path of the bidirectional DC / AC module provided in this application embodiment during the negative half-cycle charging stage to the negative bus in rectifier charging mode; Figure 9 This is a schematic diagram of the current path of the bidirectional DC / AC module provided in this application when it outputs a positive level in inverter discharge mode; Figure 10 This is a schematic diagram of the current path of the bidirectional DC / AC module provided in this application embodiment when the freewheeling current reaches zero level during the positive half-cycle in inverter discharge mode; Figure 11 This is a schematic diagram of the current path when the bidirectional DC / AC module provided in this application outputs a negative level in inverter discharge mode; Figure 12 This is a schematic diagram of the current path of the bidirectional DC / AC module provided in this application embodiment when the freewheeling current reaches zero level during the negative half-cycle in inverter discharge mode; Figure 13 This is a circuit diagram of another power conversion unit provided in an embodiment of this application; Figure 14 This is a flowchart of the control method for a bidirectional uninterruptible power supply system provided in an embodiment of this application.

[0028] Explanation of reference numerals in the attached figures: 1. External power grid; 2. Static bypass unit; 3. Load; 4. Power conversion unit; 41. Bidirectional DC / AC module; 411. Bridge arm switch branch; 412. Bidirectional switch auxiliary branch; 42. DC bus; 43. Bidirectional DC / DC module; 5. Energy storage device; 6. Controller; 7. Status detection unit. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1-14 This application will be described in further detail.

[0030] like Figure 1 As shown, a traditional uninterruptible power supply (UPS) system provided by related technologies has a structure with two power inputs: one power signal is connected to a static bypass, and the other power signal is connected sequentially to an AC / DC rectifier and a DC / AC inverter before being connected to the load. Simultaneously, the DC side of the AC / DC rectifier is also connected to a DC / DC converter, which transmits the power signal to the battery pack. The signal output of the static bypass is connected to the signal output of the DC / AC inverter before being connected to the load. In this traditional structure, the power needs to undergo multiple conversions to complete power supply and charging. The superposition of conversion stages leads to high system losses, making it difficult to improve operating efficiency. Furthermore, the complex system structure increases the number of potential failure points and costs. Additionally, the static bypass only serves an emergency switching function and cannot collaboratively optimize power quality under normal operating conditions. The flexibility of mode switching is insufficient, making it difficult to adapt to diverse actual power supply needs such as peak shaving and valley filling.

[0031] To address the shortcomings of the aforementioned technologies, such as Figure 2 and Figure 3 As shown, this application provides a simplified, more efficient, and more adaptable bidirectional uninterruptible power supply system. The bidirectional uninterruptible power supply system includes a static bypass unit 2, whose first end is used to connect to an external power grid 1, and its second end serves as a power grid output terminal; a power conversion unit 4, whose first end is used to connect to an energy storage device 5, and its second end is connected to the power grid output terminal of the static bypass unit 2 to form an AC connection terminal for connecting a load 3; and a controller 6, configured to control the static bypass unit 2 and the power conversion unit 4. When the external power grid 1 is in a normal state, the controller turns on the static bypass unit 2, allowing the external power grid to connect. Power grid 1 supplies power to load 3, while simultaneously controlling power conversion unit 4 to operate in rectification charging mode, converting AC power from external power grid 1 into DC power suitable for energy storage device 5, or controlling power conversion unit 4 to operate in power quality compensation mode. In this case, the main power supply circuit composed of power conversion unit 4 and static bypass unit 2 is connected in parallel to perform dynamic power quality compensation for AC connection terminals. When external power grid 1 is in an abnormal state, static bypass unit 2 is turned off, and power conversion unit 4 is controlled to enter inverter discharge mode, converting DC power from energy storage device 5 into AC power suitable for load 3.

[0032] Specifically, in one embodiment, the static bypass unit 2 can employ power switching devices with on / off control functions, such as contactors, relays, or thyristors, to achieve rapid switching of the power grid supply path; the power conversion unit 4 can be composed of a bidirectional DC / AC converter (such as a two-level full-bridge topology, a three-level T-type topology, etc.) (e.g. Figure 3As shown), it can also be constructed by combining bidirectional DC / DC converters (such as Buck-Boost topology, isolated LLC topology, etc.) with bidirectional DC / AC converters (such as two-level full-bridge topology, three-level T-type topology, etc.) (e.g. Figure 2 As shown in the diagram, it can adapt to different power levels and voltage conversion requirements. For example, in scenarios where there is a large difference between the battery pack voltage and the AC voltage of load 3, a combination circuit of "isolated LLC topology bidirectional DC / DC converter + three-level T-type topology bidirectional DC / AC converter" can be used. The bidirectional DC / DC converter completes the isolated voltage conversion between the battery pack and the DC bus, and the bidirectional DC / AC converter realizes the AC / DC bidirectional conversion between the DC bus and load 3. The energy storage device 5 can be a lithium battery pack, lead-acid battery pack, or supercapacitor, etc., with charging and discharging functions. The controller 6 can be a processing device with data operation and signal control functions, such as MCU (microcontroller unit), DSP (digital signal processor), or FPGA (field programmable gate array), to realize state detection, mode judgment, and drive control of switching devices. The external power supply can be mains power (such as 220V single-phase AC or 380V three-phase AC), and can also be adapted to distributed power sources such as photovoltaic and wind power.

[0033] Specifically, such as Figure 2 As shown, in one embodiment, a simplified bidirectional uninterruptible power supply system includes: an external power grid 1, a static bypass unit 2, a load 3, a power conversion unit 4 integrating a DC / DC converter and a DC / AC inverter, an energy storage device 5 (battery pack), a controller 6, and a status detection unit 7; the first end of the static bypass unit 2 is connected to the external power grid 1, and the second end is connected to the output end of the power conversion unit 4 and then connected to the load 3; the input end of the power conversion unit 4 is connected to the battery pack, and the controller 6 is communicatively connected to the status detection unit 7, the static bypass unit 2, and the power conversion unit 4 respectively; under this architecture, the power conversion unit 4 also has a dynamic compensation function: when there are voltage fluctuations, harmonics, or other interferences in the external power supply, the controller 6 will control the power conversion unit 4 to output compensation energy, which is superimposed with the mains power transmitted by the static bypass and supplied to the load 3 to optimize power quality.

[0034] like Figure 3As shown, in another embodiment, a different minimalist bidirectional uninterruptible power supply system is provided. Unlike the previous embodiment, it eliminates the need for a separate DC / DC converter and directly uses a bidirectional DC / AC inverter as the power conversion unit 4. One end of the inverter is connected to the energy storage device 5 (battery pack), and the other end is connected to the output of the static bypass unit 2 and then connected to the load 3. This architecture directly completes the bidirectional conversion of AC and DC power through the bidirectional topology characteristics of the DC / AC inverter, which is suitable for scenarios where the battery voltage and the load 3 voltage have a high degree of matching. At the same time, the bidirectional DC / AC inverter in this architecture also integrates dynamic compensation function: when the external power supply is normal, the status detection unit 7 can detect the voltage and current distortion on the load 3 side in real time, and output compensation signal through the bidirectional DC / AC inverter to correct the harmonics and fluctuations of the mains power, ensuring that the load 3 obtains high-quality power.

[0035] Understandably, this application constructs a simplified architecture of static bypass + dynamic compensation. When the external power supply is normal, the static bypass is used as the main power supply path to reduce conversion losses. The power conversion unit 4 simultaneously completes energy storage charging and dynamic compensation for external power supply interference (such as voltage fluctuations and harmonic correction), which improves the problem of lack of power quality optimization in the traditional bypass mode. It integrates multiple functions with a simplified topology, eliminating the need for separate rectifiers and charging power supplies in traditional UPS systems. The power conversion unit 4 integrates three major functions—inversion, rectification, and charging—through bidirectional mode, reducing the number of components, thereby reducing costs, improving efficiency, and shrinking size while reducing fault nodes. It achieves working condition switching, and can quickly complete mode switching when the external power supply is abnormal to ensure uninterrupted power supply.

[0036] In one embodiment, the bidirectional uninterruptible power supply system of this application can also be extended to an external power supply-battery joint power supply mode to adapt to diverse needs such as peak shaving and valley filling. In this mode, the static bypass unit 2 remains connected to the power grid, and the controller 6 dynamically adjusts the power ratio of the power grid supply and the battery supply according to the parameters such as the power grid load and the SOC of the energy storage device collected by the state detection unit 7. When the power grid is in a peak electricity consumption period and the load rate exceeds the preset threshold, the controller 6 instructs the power conversion unit 4 to work, and the energy storage device 5 releases energy and inverts it into AC power to supply power to the load 3 together with the power grid supply, sharing the power grid supply pressure and realizing "peak shaving". When the power grid is in a low electricity consumption period, the load rate is low and the SOC (state of charge) of the energy storage device is lower than the preset value, the controller 6 controls the power conversion unit 4 to enter the rectification mode, and uses the power energy during the low period to charge the energy storage device 5 to complete "valley filling". Even in the face of high power load or load change scenarios, the power supply stability can be ensured by the dynamic allocation of power between the power grid and the battery, while responding to the peak shaving needs of the power grid and improving energy utilization efficiency.

[0037] like Figure 4As shown, in one embodiment, the power conversion unit 4 includes a bidirectional DC / DC module 43, a DC bus 42, and a bidirectional DC / AC module 41. The first end of the bidirectional DC / DC module 43 is connected to the energy storage device 5, and the second end is connected to the DC bus 42. The DC side of the bidirectional DC / AC module 41 is connected to the DC bus 42, and the AC side is connected to the AC connection terminal. Under normal conditions of the external power grid 1, the bidirectional DC / AC module 41 converts AC power into DC bus voltage and transmits electrical energy to the energy storage device 5 through the bidirectional DC / DC module 43. Under abnormal conditions of the external power grid 1, the bidirectional DC / DC module 43 establishes DC bus voltage and performs inverter discharge through the bidirectional DC / AC module 41 to transmit electrical energy to the load 3.

[0038] Specifically, in one embodiment, the DC bus 42 includes a series circuit consisting of at least two capacitors. One end of capacitor C3 is connected to the positive bus (BUS+) and the other end is connected to the bus midpoint (N). One end of capacitor C4 is connected to the bus midpoint (N) and the other end is connected to the negative bus (BUS-). The capacitors provide a midpoint potential reference for the three-level topology through voltage division. In one embodiment, the bidirectional DC / AC module 41 employs a three-level topology. This structure, by adding an intermediate level (typically the DC bus midpoint level) to the traditional two-level topology, makes the output stepped voltage waveform closer to an ideal sine wave, thereby reducing harmonic distortion (THD), decreasing the size and cost of the output filter (inductor, capacitor), and reducing the voltage stress on the switching devices (referring to the maximum peak voltage across the device when the switch is off, typically half the DC bus voltage).

[0039] Specifically, this invention can be implemented using various three-level topologies, such as a T-type neutral point clamping (T-type) topology (e.g.) Figure 4 (as shown) or diode neutral point clamp (NPC type) topology (such as Figure 13 (As shown). Regardless of the topology used, this module includes three independent bridge circuits: phase A, phase B, and phase C. Each bridge circuit is connected to the corresponding inductors (L3-L5) and capacitors (C6-C8) to form a complete three-phase inverter system.

[0040] In one embodiment, when a T-type three-level topology is used ( Figure 4Taking the A-phase bridge circuit as an example, its structural features are as follows: The bridge arm switch branch 411 consists of two switching transistors (e.g., Q7 and Q8) connected in series to form a half-bridge arm, which is connected between the DC bus BUS+ and BUS-. The common connection point of these two switching transistors constitutes the A-phase output terminal. The bidirectional switch auxiliary branch 412 consists of two switching transistors (e.g., Q13 and Q14) arranged in a common-source / common-drain back-to-back configuration to form a bidirectional switch. This bidirectional switch is connected between the A-phase output terminal and the DC bus midpoint N. By controlling these two branches, the A-phase output terminal can be selectively connected to the positive bus (BUS+), negative bus (BUS-), or bus midpoint (N), thereby achieving three-level output. This structure has high conversion efficiency due to its short conduction path at 0-level output.

[0041] In yet another embodiment, when a diode neutral-point clamped three-level topology is used ( Figure 13 Taking phase A of the bridge as an example, its structural characteristics are: The bridge arm switch branch consists of four switching transistors with the same rated voltage connected in series (e.g., Q19-Q22), and the clamping diode branch consists of two high-speed clamping diodes connected together. One diode is connected between the upper switching transistor (e.g., Q19) and the bus midpoint (N); the other diode is connected between the lower switching transistor (e.g., Q22) and the bus midpoint (N). Through a specific switch combination, the A-phase output terminal can be clamped to the bus midpoint (N) by the clamping diodes, thereby achieving three-level output.

[0042] Understandably, a three-level topology can make the output voltage waveform closer to a sine wave, reduce harmonic distortion, and optimize power supply quality; by switching connection nodes to achieve multi-level output, it reduces voltage stress on switching devices, adapts to high-power application scenarios, and improves circuit stability and efficiency.

[0043] Furthermore, in this embodiment, the bidirectional DC / AC module 41 adopts a T-type three-level topology, which includes three independent bridge circuits: phase A, phase B, and phase C. Each bridge circuit includes a bridge arm switch branch 411, a bidirectional switch auxiliary branch 412, a capacitor, and an inductor. Specifically, the bridge arm switch branch 411 corresponding to phase A is composed of switching transistors Q11 and Q12, and the corresponding bidirectional switch auxiliary branch 412 is composed of switching transistors Q13 and Q14, along with a capacitor C6 and an inductor L3. The bridge arm switch branch 411 corresponding to phase B is composed of switching transistors Q9 and Q10, and the corresponding bidirectional switch auxiliary branch 412 is composed of a capacitor C6 and an inductor L3. Circuit 412 is composed of switching transistors Q15 and Q16, with corresponding capacitor C7 and inductor L4. The corresponding bridge arm switch branch 411 is composed of switching transistors Q7 and Q8, and the corresponding bidirectional switch auxiliary branch 412 is composed of switching transistors Q17 and Q18, with corresponding capacitor C8 and inductor L5. Taking its A-phase bridge circuit as an example, this bridge circuit includes a vertical bridge arm switch branch 411 and a bidirectional switch auxiliary branch 412. The vertical bridge arm switch branch 411 is composed of switching transistors Q11 and Q12 connected in series and connected between the positive bus BUS+ and the negative bus BUS- of the DC bus 42. The common connection point (midpoint of the bridge arm) of switching transistors Q11 and Q12 constitutes the A-phase output terminal. The bidirectional switch auxiliary branch 412 is composed of switching transistors Q13 and Q14 connected back-to-back in a common-source manner to form a bidirectional conduction unit. One end of the bidirectional conduction unit is connected to the A-phase output terminal, and the other end is connected to the bus midpoint (N) of DC bus 42, thus constructing a complete three-level bridge circuit capable of selectively connecting the A-phase output terminal to the positive bus (BUS+), negative bus (BUS-), or bus midpoint (N). The working principle of this bridge circuit is detailed below: First, in rectified charging mode, this T-type three-level topology is equivalent to a Vienna rectifier circuit, used to achieve power factor correction (PFC) and rectification. Through correction, the input current and voltage phases tend to be aligned, reducing reactive power loss and harmonic pollution in the power grid and improving energy utilization. In this mode, controller 6 controls the switches Q11 and Q12 in the vertical bridge arm switch branch 411 to be in the off state, utilizing only the parasitic body diodes inside the switches as rectifier diodes. Simultaneously, high-frequency pulse width modulation (PWM) is applied to the switches Q13 and Q14 in the bidirectional switch auxiliary branch 412. The specific workflow is as follows: like Figure 5 As shown, when the AC input voltage is in the positive half-cycle: controller 6 turns on switch Q14, while switches Q11, Q12, and Q13 remain off. The AC power supply forms a loop through inductor L3 and the turned-on Q14, storing energy in inductor L3. Figure 6As shown, when controller 6 turns off Q14, the energy stored in inductor L3 is superimposed with the mains voltage and charges capacitor C3 on the positive bus side through the body diode of switch Q11.

[0044] like Figure 7 As shown, when the AC input voltage is in the negative half-cycle: controller 6 turns on switch Q13, while switches Q11, Q12, and Q14 remain off. The AC power supply forms a circuit through the turned-on Q13 and inductor L3, storing energy in inductor L3. Figure 8 As shown, when controller 6 turns off Q13, the energy stored in inductor L3 is superimposed with the mains voltage and charges capacitor C4 on the negative bus side through the body diode of switch Q12.

[0045] Secondly, in inverter discharge (i.e., battery powered) mode, the circuit operates as a standard T-type three-level inverter. In this mode, controller 6 coordinates pulse width modulation (PWM) on switches Q11 and Q12 in the vertical bridge arm switch branch 411 and switches Q13 and Q14 in the bidirectional switch auxiliary branch 412 to synthesize the required three-level AC voltage at the A-phase output. The specific workflow is as follows: like Figure 9 As shown, when a positive voltage level is required (during the positive half-cycle): Controller 6 turns on switches Q11 and Q13, while simultaneously turning off Q12 and Q14. Current flows out from the positive bus BUS+, through the turned-on Q11, the A-phase output terminal, inductor L3, and capacitor C6 (C6 acts as a filter capacitor, and L3 as a filter inductor), and finally returns to the bus midpoint N, thus generating a positive voltage level at the A-phase output terminal that is at the same potential as the positive bus.

[0046] like Figure 10 As shown, when a zero voltage level is required for output: During the positive half-cycle of the output, if it is necessary to switch to the zero level, controller 6 will turn off Q11. At this time, since the current of inductor L3 cannot change abruptly, the current continues to flow through capacitor C6 to the bus midpoint N, through the conducting switch Q13, and then through the body diode of switch Q14 for freewheeling, returning to the A-phase output terminal, thereby clamping the A-phase output terminal to a zero level (same potential as N) that is at the same potential as the bus midpoint.

[0047] like Figure 11 As shown, when a negative voltage level is required (during the negative half-cycle): Controller 6 turns on switches Q12 and Q14, while simultaneously turning off Q11 and Q13. Current flows out from the bus midpoint N, through capacitor C6, inductor L3, the A-phase output terminal, and the turned-on Q12, finally returning to the negative bus BUS-, thus generating a negative voltage level at the A-phase output terminal that is at the same potential as the negative bus; as Figure 12As shown, when Q12 is turned off, since the current of inductor L3 cannot change abruptly, the current freewheels back to point N through the body diodes of the conducting Q14 and Q13.

[0048] Similarly, the topology of the B-phase and C-phase bridge circuits is completely consistent with that of the A-phase, both including the corresponding vertical bridge arm switch branch 411, bidirectional switch auxiliary branch 412, and external inductor and capacitor elements. In the rectification and charging mode, the B and C phases, respectively, perform energy storage, rectification, and bus capacitor charging actions according to the same logic as the A-phase, based on the AC input voltage of their respective phases, and work together to achieve power factor correction and rectification of the three-phase AC power. In the inverter discharge mode, under the synchronous pulse width modulation control of the controller 6, the B and C phases respectively output three-level AC voltages with a phase difference of 120° from the A-phase voltage. The three voltages are combined to provide a stable three-phase AC power to the load 3.

[0049] Understandably, the coordinated design of the bridge arm switch branch 411 and the bidirectional switch auxiliary branch 412 in the T-type three-level topology not only improves the power quality on the grid side and reduces interference to the external grid 1 by cooperating with power factor correction rectification in the rectifier charging mode, but also ensures the stability and reliability of the AC output through flexible switching logic switching in the inverter discharge mode, achieving a smooth transition between rectification and inverter modes. At the same time, the T-type topology itself simplifies the switch control logic, and the coordinated action of the two branches can further reduce switching losses, adapting to the application requirements of high power and high efficiency.

[0050] In one embodiment, the bidirectional DC / DC module 43 is used to realize bidirectional energy exchange and voltage level matching between the energy storage device 5 and the DC bus 42. This module can employ various topologies, such as a two-level half-bridge bidirectional Buck-Boost topology (e.g., Figure 4 (as shown) or a three-level bidirectional DC / DC topology (such as...) Figure 13 (As shown). Regardless of the topology used, its function is to flexibly operate in two core modes by coordinating pulse width modulation (PWM) control of the switching transistors: buck charging mode (Buck mode) which steps down the DC bus voltage to charge the energy storage device, and boost discharging mode (Boost mode) which steps up the energy storage device voltage to support the DC bus.

[0051] like Figure 4 As shown, in one embodiment, taking a two-level topology as an example, its specific working principle is as follows: The bidirectional DC / DC module 43 includes a Buck-Boost topology, comprising an inductor L1, a first switch Q1, and a second switch Q2. One end of the inductor L1 is connected to the energy storage device 5 (battery), and the other end is connected to the common connection node of the first switch Q1 and the second switch Q2. Q1 is connected to the positive bus, and Q2 is connected to the negative bus. By coordinating pulse width modulation (PWM) control of the switches Q1 and Q2, this module can flexibly operate in two core modes: buck charging mode (Buck mode) and boost discharging mode (Boost mode). The specific working principle is as follows: Buck charging mode is typically activated when the external power grid 1 is supplying power normally. It is used to step down the higher voltage of the DC bus 42 to charge the energy storage device 5. Controller 6 performs PWM modulation on the first switch Q1, and the second switch Q2 works as a freewheeling switch. When the first switch Q1 is on, the second switch Q2 is off. Current flows out from the positive bus, passing sequentially through the on-state Q1, the common connection node, and the inductor L1, charging the energy storage device 5 and storing energy in the inductor L1, whose current increases linearly. When the first switch Q1 is off, since the inductor current cannot change abruptly, the energy stored in L1 needs to be released. At this time, controller 6 turns on the second switch Q2 (or uses its body diode), and L1, through the energy storage device 5 and the on-state Q2, forms a freewheeling loop to continue charging the energy storage device 5. During this period, the inductor current decreases linearly. By periodically repeating the above process, precise control of the charging current is achieved. The boost discharge mode is typically activated when the external power grid 1 is abnormal or when the battery needs to supply power to the load 3 (power quality compensation mode). It is used to boost the lower voltage of the energy storage device 5 to stabilize the DC bus voltage. The controller 6 performs PWM modulation on the second switch Q2, with the first switch Q1 acting as a freewheeling switch. When the second switch Q2 is on, the first switch Q1 is off. The energy storage device 5 forms a circuit through the inductor L1 and the on-state Q2, storing energy in the inductor L1, and its current increases linearly. At this time, the support capacitor on the DC bus 42 side (such as...) Figure 4 C1 and C2 in the diagram are distinct from the voltage divider capacitors C3 and C4. The DC bus may also include bus support capacitors C1 and C2 connected in parallel between the positive and negative buses. These support capacitors are used to stabilize the DC bus voltage and suppress bus ripple (powering subsequent circuits). When the second switch Q2 is turned off, because the inductor current cannot change abruptly, a reverse induced electromotive force (EMF) is generated across inductor L1, with the left side positive and the right side negative. This induced voltage is superimposed on the voltage of the energy storage device 5, forming a potential higher than the positive bus voltage. This forces current to flow through the body diode of the first switch Q1 to the positive bus, charging the support capacitors C1 and C2 of the DC bus 42 and supplying power to subsequent circuits. By periodically repeating this process, energy transfer and voltage boosting from the energy storage device 5 to the DC bus 42 are achieved.

[0052] Understandably, the Buck-Boost topology adopted by the bidirectional DC / DC module 43 has the core advantage of enabling bidirectional energy flow and bidirectional voltage conversion within the same hardware circuit. In buck mode, it efficiently meets the charging needs of the energy storage device 5; in boost mode, it serves as a crucial voltage support, ensuring voltage stability of the DC bus 42 under various operating conditions. This design adapts to different operating conditions without adding or removing any additional components. Its simple topology not only reduces system cost and size but also effectively reduces power loss. Combined with the energy storage and freewheeling functions of the inductor, it ensures the continuity and efficiency of energy transfer between the energy storage device 5 and the DC bus 42.

[0053] like Figure 13 As shown, in another embodiment, the bidirectional DC / DC module 43 can employ a three-level topology. This structure further reduces the voltage stress on the switching transistors and decreases the current ripple on the inductor L1 by increasing the number of switching devices and levels. Specifically, this topology consists of four switching transistors (Q3-Q6) and one capacitor (C0). Through specific switching timing control, the connection point of the inductor L1 can switch between the positive and negative terminals of the DC bus and an intermediate level (provided by the capacitor C0 in the circuit). Compared to a two-level topology, the three-level structure can output a smoother current waveform, reduce electromagnetic interference (EMI), and allow the use of a smaller filter inductor, thereby improving the overall system efficiency and power density in higher power or higher voltage applications. This three-level topology also supports the aforementioned buck charging and boost discharging bidirectional operating modes.

[0054] It should be noted that the above description of specific embodiments of the bidirectional DC / DC module 43 and the bidirectional DC / AC module 41 is merely illustrative and not intended to limit the scope of protection of this application. Those skilled in the art will understand that... Figure 4 The two-level DC / DC topology shown Figure 13 The three-level DC / DC topology shown is similar to... Figure 4 The T-type three-level DC / AC topology shown Figure 13 The NPC three-level DC / AC topologies shown can be arbitrarily combined according to actual application requirements. For example, the system can adopt... Figure 3 DC / DC module pairing Figure 13 DC / AC modules, or using Figure 13 DC / DC module pairing Figure 4 DC / AC modules. All equivalent substitutions or combinations based on the same inventive concept should fall within the protection scope of this application.

[0055] In one embodiment, the first switching transistor, the second switching transistor, and the switching devices inside the bidirectional DC / AC module 41 in the above embodiments are all fully controllable power semiconductor devices, selected from at least one of the following groups: insulated gate bipolar transistor, metal oxide semiconductor field-effect transistor, silicon carbide metal oxide semiconductor field-effect transistor, and gallium nitride high electron mobility transistor, preferably silicon carbide metal oxide semiconductor field-effect transistor. Compared with traditional silicon-based power devices, this type of device has a wider bandgap, higher breakdown electric field strength, and lower on-resistance. It can operate stably at higher switching frequencies and operating temperatures, effectively reducing the energy loss of the device itself and reducing the size of the device.

[0056] By adopting the above technical solutions, fully controllable power semiconductor devices possess the characteristics of fast switching response and low conduction loss. Their built-in parasitic diodes can naturally conduct under conditions such as rectification charging and mode switching. In conjunction with the switching logic of the switching devices, they can realize current freewheeling or bidirectional conduction functions, ensuring the continuity and stability of the power conversion process. In particular, wide bandgap devices such as silicon carbide (SiC) and gallium nitride (GaN) not only inherit the core advantages of fully controllable devices, but also adapt to high temperature and high frequency conditions, effectively improving the system power density and long-term operating efficiency. At the same time, the selection range of multiple types of devices can be flexibly adjusted according to the power level and cost budget of the actual application scenario, significantly enhancing the engineering adaptability of the solution.

[0057] Reference Figure 2 and Figure 3 In one embodiment, the system further includes a status detection unit 7, which is connected to the external power grid 1, the energy storage device 5 and the AC connection terminal, and is configured to collect the operating status parameters of the external power grid 1, the energy storage device 5 and the load 3, respectively. The controller 6 is configured to trigger the switching of the working modes of the static bypass unit 2 and the power conversion unit 4 based on the operating status parameters of the status detection unit 7.

[0058] Specifically, the status detection unit 7 can be composed of multiple sensors, signal conditioning circuits, and analog-to-digital converters (ADCs) in hardware. In one embodiment, for the detection of the external power grid 1, the status detection unit 7 includes voltage transformers and current transformers, respectively coupled to the input terminals of the external power grid 1, to proportionally reduce the voltage and current signals of the power grid. The reduced analog signals are filtered and amplified by a signal conditioning circuit composed of operational amplifiers, and then sent to the ADC port of the controller 6 to be converted into digital quantities. The controller 6 performs real-time calculations on these digital signals (such as calculating the effective value, frequency, phase, etc.) to determine whether the external power grid 1 has abnormal states such as overvoltage, undervoltage, frequency deviation, or power outage. In another embodiment, for the detection of the energy storage device 5, the status detection unit 7 includes a high-precision voltage divider resistor network and a Hall current sensor. The voltage divider resistor network is connected across the two ends of the energy storage device 5 to measure its terminal voltage; the Hall current sensor is connected in series in the circuit of the energy storage device 5 to measure its charging and discharging current non-contactly. These signals, after being adjusted, are sent to the ADC of the controller 6, enabling the controller 6 to monitor the state of charge (SOC), state of health (SOH), and charge / discharge rate of the energy storage device 5 in real time. In another embodiment, the status detection unit 7 detects the operating status of the load 3 by monitoring the output voltage and current at the AC connection terminal. Its detection method is similar to that of the external power grid 1, utilizing voltage and current transformers to acquire signals, allowing the controller 6 to determine whether the load 3 is overloaded or short-circuited, and providing a basis for dynamically adjusting the output.

[0059] In one embodiment, the controller 6 internally presets multi-level operating mode switching thresholds and logic, making decisions based on parameters collected by the state detection unit 7, such as switching from mains power supply mode to battery inverter mode: when the state detection unit 7 detects that the effective voltage value of the external power grid 1 is lower than a preset undervoltage threshold (e.g., lower than 85% of the nominal voltage) or the power grid frequency is outside the normal range (e.g., ±0.5Hz), and this continues for a very short preset time (e.g., 10ms), the controller 6 determines that there is a power grid fault. At this time, the controller 6 controls the static bypass unit 2 to disconnect from the external power grid 1, and simultaneously instructs the bidirectional DC / DC module 43 in the power conversion unit 4 to enter the Boost mode to stabilize the DC bus 42, and instructs the bidirectional DC / AC module 41 to enter the inverter mode, so that the energy storage device 5 seamlessly takes over the power supply to the load 3. The entire switching process is completed in milliseconds, ensuring uninterrupted power supply to the load 3; or, when the device is in battery inverter mode, the state detection unit 7 continues to monitor the state of the external power grid 1. Once the grid voltage and frequency are detected to have returned to normal and remain stable for a preset recovery time (e.g., 1 second), the controller 6 will activate the phase-locked loop (PLL) circuit to synchronize the output of the bidirectional DC / AC module 41 with the grid voltage in terms of frequency, phase, and amplitude. After synchronization is complete, the controller 6 instructs the static bypass unit 2 to close, smoothly switching the load 3 back to being powered by the external grid 1. Subsequently, the controller 6 will determine whether to activate the buck charging mode to replenish the energy storage device 5 based on the SOC state of the energy storage device 5 and the user settings. In addition, the controller 6 also supports a power quality compensation mode. When the status detection unit 7 detects power quality problems such as voltage fluctuations and excessive harmonics in the external power grid, the controller 6 will instruct the bidirectional DC / AC module 41 of the power conversion unit 4 to enter the compensation mode. By adjusting the output voltage amplitude, phase and harmonic components in real time, it dynamically compensates for external power interference, realizes voltage fluctuation suppression and harmonic correction, and ensures that the load receives stable and high-quality power. At the same time, in order to adapt to diverse needs such as peak shaving and valley filling, especially suitable for high-power application scenarios, the controller 6 can start the external power supply-battery joint power supply mode. In this mode, the static bypass unit 2 remains connected to the power grid. The controller 6 dynamically adjusts the power ratio of the power grid supply and the battery supply according to the grid load, energy storage device SOC and other parameters collected by the status detection unit 7. During peak power consumption, the energy storage device provides power to share the grid pressure and achieve "peak shaving". During off-peak power consumption, if the energy storage SOC is insufficient, it uses low-priced electricity to charge it and achieve "valley filling", ensuring the stable operation of high-power loads while responding to the grid peak shaving needs.

[0060] Understandably, the status detection unit 7 captures the operating parameters of each key node in real time, providing a basis for decision-making for the controller 6; the controller 6 quickly judges the grid status based on the parameters, triggers mode switching, ensures uninterrupted power supply, and improves the system's adaptability and reliability to complex operating conditions.

[0061] like Figure 14 As shown in the embodiments, this application also discloses a control method for a bidirectional uninterruptible power supply system, applied to the bidirectional uninterruptible power supply system in any of the above embodiments, including the following steps: S1. Collect the operating status parameters of the external power grid 1, energy storage device 5 and AC connection terminal through the status detection unit 7; S2, Controller 6 determines whether the status of external power grid 1 is normal based on the operating status parameters; Specifically, to ensure the accuracy of the judgment, in steps S1 and S2, the controller 6 continuously analyzes key parameters such as the effective value and frequency of the grid voltage, the terminal voltage and charging status of the energy storage device 5, and the current harmonics and voltage fluctuations at the AC connection terminal, which are collected in real time by the state detection unit 7. To prevent erroneous switching due to instantaneous disturbances, the controller 6 integrates judgment logic with hysteresis characteristics. For example, it is only determined to be an "abnormal state" when the grid voltage or frequency exceeds the preset normal range (e.g., nominal voltage ±10%, nominal frequency ±0.5Hz) for a preset time (e.g., 10ms), thereby ensuring the stability and reliability of state switching.

[0062] S3. If the external power grid 1 is determined to be in a normal state, control the static bypass unit 2 to conduct to establish the main power supply path to the load 3; at the same time, control the power conversion unit 4 to be connected in parallel with the main power supply path, and perform at least one of the following operations as needed according to the operating status parameters: The external power grid 1 draws electrical energy for rectification and charges the energy storage device 5. Dynamic compensation for power quality at AC connection terminals; In this step, when the external power grid 1 is determined to be normal, the system enters a flexible combined operating mode of bypass main supply + parallel dynamic adjustment. In this mode, the static bypass undertakes the main power supply task to maximize energy efficiency, while the power conversion unit 4 acts as a parallel power quality manager and smart charger, intervening according to real-time demand. The specific implementation of this step is as follows: First, controller 6 controls the closing of the static bypass unit 2, establishing a power supply path from the external power grid 1 to the load 3, thus achieving mains power supply. Simultaneously, controller 6 activates the power conversion unit 4, and through the following steps, performs charging operations on the energy storage device 5 and dynamic power quality compensation operations: S31. Dynamic power quality compensation operation: When the status detection unit 7 detects that the power quality parameters at the AC connection end exceed the preset compensation threshold, it controls the bidirectional DC / AC module 41 to inject compensation current into the AC connection end for dynamic power quality compensation. In a specific embodiment, assuming the load 3 is a data center server (containing a large number of switching power supplies), the status detection unit 7 detects that the grid-side current harmonic distortion rate (THD) has risen to 8% (exceeding the preset threshold of 5%) due to its nonlinear characteristics. At this time, the controller 6 triggers the compensation function. The bidirectional DC / AC module 41, acting as an active power filter (APF), injects a compensation current of equal magnitude and opposite phase to the harmonic into the AC line through high-frequency PWM modulation, suppressing the grid-side THD to below 3%. This improves the problem that traditional bypass modes cannot address harmonic pollution.

[0063] S32. During the charging operation of the energy storage device 5, when the status detection unit 7 detects that the charging status of the energy storage device 5 is lower than the preset charging threshold, it controls the bidirectional DC / AC module 41 to rectify the AC power from the external power grid 1 into a DC bus voltage, and further controls the bidirectional DC / DC module 43 to operate in Buck mode to convert the DC bus voltage into a DC voltage suitable for the energy storage device 5. In a specific embodiment, the charging process is triggered when the SOC of the energy storage device 5 is lower than a preset value (e.g., 95%). The bidirectional DC / AC module 41 draws the required active power from the external power grid 1 and utilizes its power factor correction (PFC) capability to efficiently rectify the AC power into a stable DC bus voltage while ensuring that the input power factor is close to 1 (e.g., >0.99); then, the stable DC bus voltage is sent to the bidirectional DC / DC module 43. The controller 6 enables it to operate precisely in Buck mode. Based on the real-time status of the energy storage device 5, it employs a multi-stage intelligent charging strategy, including constant current, constant voltage, and float charging, to safely convert the DC bus voltage into a suitable charging voltage to charge the energy storage device 5.

[0064] It is worth noting that the triggering conditions for the charging operation of the energy storage device 5 and the dynamic power quality compensation operation are independent of each other. The system can flexibly perform composite tasks such as charging only, compensating only, or performing power quality compensation while charging the energy storage device 5, according to actual needs.

[0065] S4. If the external power grid 1 is determined to be in an abnormal state, the static bypass unit 2 is turned off and the power conversion unit 4 is put into inverter discharge mode, and the energy storage device 5 supplies power to the load 3. When the external power grid 1 experiences a power outage, voltage / frequency deviation or other abnormalities, the controller 6 performs switching and inverter power supply operations to ensure the continuity of power supply to the load 3.

[0066] In one specific embodiment, firstly, the controller 6 rapidly shuts down the static bypass unit 2 within microseconds, electrically isolating the load 3 from the abnormal external power grid 1. Simultaneously, the controller 6 triggers the power conversion unit 4 to quickly switch to inverter discharge mode. The specific implementation steps of this mode are as follows: S41. Control the bidirectional DC / DC module 43 to operate in Boost mode, converting the DC voltage of the energy storage device 5 into the DC bus voltage.

[0067] Specifically, the bidirectional DC / DC module 43 draws energy from the energy storage device 5 and stably raises its lower DC voltage (such as battery voltage) to the high DC bus voltage required by the subsequent inverter, providing a stable and reliable energy platform for the inverter.

[0068] S42, The bidirectional DC / AC module 41 inverts the DC bus voltage into AC power to adapt to the load 3.

[0069] Specifically, the bidirectional DC / AC module 41 efficiently inverts the stable DC bus voltage into a sinusoidal AC current that meets the requirements of load 3. To ensure the quality of the output power, the controller 6 preferably adopts a dual closed-loop feedback control strategy of voltage and current. The outer voltage loop is responsible for stabilizing the effective value of the output voltage, while the inner current loop is responsible for quickly tracking the sinusoidal reference waveform and suppressing disturbances in load 3.

[0070] S43. Power is supplied to load 3 based on the AC power after inversion. Finally, the AC power generated by the inverter supplies power to load 3 through the output port, ensuring that even under nonlinear load 3 or sudden load 3, the output voltage waveform remains smooth and the distortion is low, thereby ensuring that the critical load 3 obtains a stable and uninterrupted power supply.

[0071] In one embodiment, to adapt to diverse needs such as peak shaving and valley filling, and especially to high-power application scenarios, the method further includes activating an external power supply-battery combined power supply mode. In this mode, the static bypass unit 2 remains connected to the power grid, and the controller 6 dynamically adjusts the power ratio of the power grid supply and the battery supply based on parameters such as the power grid load and the SOC of the energy storage device collected by the state detection unit 7. When the power grid is at its peak and the load factor exceeds a preset threshold, the controller 6 instructs the bidirectional DC / DC module 43 and the bidirectional DC / AC module 41 to work together, with the energy storage device 5 releasing energy and converting it into AC power. Together with the grid, it supplies power to load 3, sharing the grid's power supply pressure and achieving "peak shaving". When the grid is in a low-demand period, the load rate is low, and the SOC of the energy storage device is lower than the preset value, the controller 6 controls the bidirectional DC / AC module 41 to enter the rectification mode and the bidirectional DC / DC module 43 to enter the buck mode, using the power during the low-demand period to charge the energy storage device 5, completing "valley filling". In this mode, even when facing high-power loads or sudden load changes, the power dynamic allocation between the grid and the battery can ensure power supply stability, while responding to the grid's peak shaving needs and improving energy utilization efficiency.

[0072] By adopting the above technical solution, under normal grid conditions, the system can switch to bypass main power supply mode, which reduces energy loss and improves operating efficiency compared to traditional online UPS continuous double conversion. At the same time, the power conversion unit 4 works in parallel in bypass mode, which can actively compensate for power quality problems such as harmonics and reactive power, and realize the grid adaptability improvement that traditional bypass mode does not have. This method decouples the charging and compensation functions, and can trigger corresponding functions on demand based on real-time status parameters. It can not only ensure the backup power needs of energy storage device 5, but also optimize the power consumption environment and realize refined energy management. When the grid is abnormal, the system can quickly isolate the faulty grid and the energy storage device 5 takes over the power supply. Relying on the coordinated boost and inverter operation of the bidirectional power module, it provides high-quality uninterrupted power supply to load 3, ensuring the safe and stable operation of core equipment.

[0073] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A bi-directional uninterruptible power supply system, characterized by, The application relates to a static bypass unit (2) having a first end for connecting to an external power grid (1) and a second end as a power grid output end; a power conversion unit (4) having a first end for connecting to an energy storage device (5) and a second end connected to the power grid output end of the static bypass unit (2) to form an AC connection end for connecting to a load (3); and a controller (6) connected to the power conversion unit (4) and the static bypass unit (2) and configured to control the static bypass unit (2) and the power conversion unit (4) to control the static bypass unit (2) to be turned on and the load (3) to be powered by the external power grid (1) in a normal state of the external power grid (1), and to configure the power conversion unit (4) to work in a rectification charging mode and / or an electric energy quality compensation mode, the rectification charging mode being used for converting AC electric energy of the external power grid (1) into DC electric energy suitable for the energy storage device (5), and the electric energy quality compensation mode being used for performing dynamic compensation on the AC connection end; and to control the static bypass unit (2) to be turned off and the power conversion unit (4) to enter an inversion discharging mode to convert DC electric energy of the energy storage device (5) into AC electric energy suitable for the load (3) in an abnormal state of the external power grid (1). The power conversion unit (4) comprises a bidirectional DC / DC module (43), a DC bus (42) and a bidirectional DC / AC module (41), the first end of the bidirectional DC / DC module (43) is used for connecting to the energy storage device (5), the second end is connected to the DC bus (42), the DC side of the bidirectional DC / AC module (41) is connected to the DC bus (42), and the AC side is connected to the AC connection end. In the normal state of the external power grid (1), the bidirectional DC / AC module (41) converts AC power into DC bus voltage, and the bidirectional DC / DC module (43) transmits electric energy to the energy storage device (5). In the abnormal state of the external power grid (1), the bidirectional DC / DC module (43) establishes DC bus voltage, and the bidirectional DC / AC module (41) performs inversion discharging to transmit electric energy to the load (3). The DC bus (42) has a positive bus, a negative bus and a bus midpoint, the bidirectional DC / AC module (41) is a three-level topology structure, and the bidirectional DC / AC module (41) is configured to selectively connect the AC connection end to the positive bus, the negative bus or the bus midpoint by controlling the on-off state of internal switching devices, so that the voltage of the AC connection end is switched between a positive level, a zero level and a negative level.

2. The bidirectional uninterruptible power supply system of claim 1, wherein, ​ ​ ​ 3. The bidirectional uninterruptible power supply system of claim 2, wherein, ​ 4. The bidirectional uninterruptible power supply system of claim 3, wherein, The bidirectional DC / AC module (41) is a T-type three-level topology structure, comprising a bridge arm switch branch (411) and a bidirectional switch auxiliary branch (412), the bridge arm switch branch (411) is connected between the positive bus and the negative bus, and the bridge arm midpoint is used as an AC phase line output end; the bidirectional switch auxiliary branch (412) is connected between the AC phase line output end and the bus midpoint; the controller (6) is configured to control the bidirectional DC / AC module (41) to perform power factor correction rectification in the rectification charging mode and to perform three-level inversion in the inversion discharging mode.

5. The bidirectional uninterruptible power supply system of claim 3, wherein, The bidirectional DC / DC module (43) is a Buck-Boost bidirectional topology structure, comprising a first inductor, a first switch tube and a second switch tube; The first switch tube and the second switch tube are connected in series between the positive bus and the negative bus of the DC bus (42), a first end of the first inductor is used for connecting the positive electrode of the energy storage device (5), a second end is connected to a common connection node of the first switch tube and the second switch tube, and an end of the second switch tube away from the common connection node is used for connecting the negative electrode of the energy storage device (5) and accessing the negative bus; The bidirectional DC / DC module (43) is configured to have a Buck step-down mode and a Boost step-up mode, the Buck step-down mode is adapted to a normal state of the external power grid (1), and the Boost step-up mode is adapted to an abnormal state of the external power grid (1).

6. The bidirectional uninterruptible power supply system of claim 5, wherein, The first switch tube, the second switch tube and the switching devices inside the bidirectional DC / AC module (41) are all fully controlled power semiconductor devices, and are selected from at least one of the following groups: Insulated gate bipolar transistors, metal oxide semiconductor field effect transistors, silicon carbide metal oxide semiconductor field effect transistors and gallium nitride high electron mobility transistors.

7. The bidirectional uninterruptible power supply system of claim 1, wherein, Further comprising a state detection unit (7), the state detection unit (7) is connected with the controller (6), the external power grid (1), the energy storage device (5) and the AC connection end respectively, and is configured to collect the operating state parameters of the external power grid (1), the energy storage device (5) and the load (3) respectively; the controller (6) is configured to trigger the working mode switching of the static bypass unit (2) and the power conversion unit (4) based on the operating state parameters of the state detection unit (7).

8. A control method of a bidirectional uninterruptible power supply system, characterized by, The method comprises the following steps: S1, collecting the operating state parameters of the external power grid (1), the energy storage device (5) and the AC connection end through the state detection unit (7); S2, the controller (6) determines whether the state of the external power grid (1) is normal based on the operating state parameters; S3, if the external power grid (1) is in a normal state, control the static bypass unit (2) to conduct to build a main power supply path to the load (3); at the same time, control the power conversion unit (4) to be connected in parallel with the main power supply path, and perform at least one of the following operations according to the operating state parameter: draw power from the external power grid (1) for rectification, and charge the energy storage device (5); dynamically compensate the power quality of the AC connection end; S4, if the external power grid (1) is in an abnormal state, control the static bypass unit (2) to be turned off, control the power conversion unit (4) to enter an inverter discharge mode, and supply power to the load (3) by the energy storage device (5).

9. The control method of a bidirectional uninterruptible power supply system according to claim 8, characterized by, The power conversion unit (4) includes a bidirectional DC / AC module (41) and a bidirectional DC / DC module (43), and step S3 includes: S31, when the state detection unit (7) detects that the power quality parameter of the AC connection end exceeds the preset compensation threshold, control the bidirectional DC / AC module (41) to inject a compensation current into the AC connection end, and perform dynamic power quality compensation; S32, when the state detection unit (7) detects that the charge state of the energy storage device (5) is lower than the preset charge threshold, control the bidirectional DC / AC module (41) to rectify the AC power of the external power grid (1) into a DC bus voltage, and control the bidirectional DC / DC module (43) to work in a Buck step-down mode to convert the DC bus voltage into a DC voltage suitable for the energy storage device (5).

10. The control method of a bidirectional uninterruptible power supply system according to claim 9, characterized by, Step S4 includes: S41, control the bidirectional DC / DC module (43) to work in a Boost step-up mode to convert the DC voltage of the energy storage device (5) into a DC bus voltage; S42, convert the DC bus voltage into AC power suitable for the load (3) by the bidirectional DC / AC module (41); S43, supply power to the load (3) based on the converted AC power.

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