Lithium iron phosphate and super capacitor hybrid energy storage uninterruptible power supply system and control method

Abstract

The present application relates to the technical field of uninterrupted power supply, and discloses a lithium iron phosphate and super capacitor hybrid energy storage uninterrupted power supply system and a control method, the system comprising a rectifying module, an inverting module, a lithium iron phosphate energy storage module, a super capacitor energy storage module, a bidirectional step-up / down DC conversion module and a main control module, the lithium iron phosphate energy storage module being directly connected in parallel with a DC bus, and the super capacitor energy storage module being connected to the DC bus through the bidirectional step-up / down DC conversion module; the control method divides system operation into normal power supply, power supply interruption transient, long-time backup and load sudden increase stages, the main control module controls the bidirectional step-up / down DC conversion module, the DC bus voltage is raised during the transient state to form voltage clamping for the lithium iron phosphate energy storage module, and the super capacitor energy storage module bears transient impact power. The present application reduces steady-state operation loss, realizes smooth power transfer and dynamic health degree derating constraint of the system, and improves overall operation safety.

Description

Technical Field

[0001] This invention relates to the field of uninterruptible power supply technology, specifically to a hybrid energy storage uninterruptible power supply system and control method using lithium iron phosphate and supercapacitors. Background Technology

[0002] Uninterruptible power supplies (UPS) provide continuous power support to loads when external mains power is interrupted or abnormal. Conventional UPS use a single battery as the energy storage medium. However, with the increasing transient impact characteristics of external loads, a single energy storage medium is difficult to simultaneously meet the requirements of long-term energy backup and transient high-power response. Therefore, hybrid energy storage systems composed of lithium iron phosphate batteries and supercapacitors have been applied.

[0003] In existing hybrid energy storage uninterruptible power supply systems, different energy storage media are connected to the DC bus through their own independent DC-DC converters. This structure increases the number of hardware components, resulting in higher power loss during steady-state operation. If the hardware is simplified and the battery pack is directly connected in parallel to the DC bus, the voltage difference between the open-circuit voltage of the battery and the no-load DC bus will cause surge current at the moment the system cold-start closed loop is closed, affecting the safety of the hardware circuit.

[0004] Furthermore, existing hybrid energy storage control logic is relatively rigid and difficult to adapt to complex operating conditions. When lithium iron phosphate batteries face transient drops in mains power or sudden load impacts, directly outputting large currents will lead to accelerated cell life decay. High-rate discharge in low-temperature environments can also cause internal lithium plating failures. Existing bidirectional converters mostly use fixed switching frequencies and duty cycles, resulting in low energy conversion efficiency under transient compensation conditions. During long-term backup phases caused by continuous mains power interruptions, the handover process between supercapacitor power outage and battery power takeover lacks smooth guidance of DC bus voltage, causing bus voltage fluctuations. At the same time, conventional systems rely on fixed setpoints for discharge current limiting control without dynamically adjusting based on battery cycle count, historical charge / discharge depth, and real-time operating temperature. This leads to the risk of thermal runaway or accelerated damage to aging batteries under overload conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a hybrid energy storage uninterruptible power supply system and control method for lithium iron phosphate and supercapacitors, which solves the problems of high steady-state loss, large cold start impact, battery damage and large energy transfer fluctuations in existing hybrid energy storage systems under complex operating conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In the first aspect, a hybrid energy storage uninterruptible power supply system combining lithium iron phosphate and supercapacitors is provided. The system includes: a rectifier module, wherein the AC input terminal of the rectifier module is connected to an external mains power supply, and the DC output terminal of the rectifier module is connected to a DC bus. The inverter module has its DC input terminal connected to the DC bus and its AC output terminal connected to an external load. Lithium iron phosphate energy storage module, the lithium iron phosphate energy storage module is directly connected in parallel to the DC bus; The supercapacitor energy storage module is connected to the DC bus via a bidirectional buck-boost DC-DC converter module. A bidirectional buck-boost DC-DC converter module, with its low-voltage side connected to a supercapacitor energy storage module and its high-voltage side connected to a DC bus. The main control module is connected to the lithium iron phosphate energy storage module, the supercapacitor energy storage module, and the bidirectional buck-boost DC-DC converter module.

[0007] The hardware topology of this invention combines lithium iron phosphate batteries with supercapacitors. The passive direct connection bus of the lithium iron phosphate energy storage module simplifies the system hardware structure and reduces steady-state losses. The supercapacitor energy storage module provides transient power throughput through an isolated access via an active converter, forming a physical complementarity between energy-type and power-type energy storage media.

[0008] Furthermore, the main control module has a pre-stored three-dimensional mapping matrix of the conversion efficiency of the bidirectional buck-boost DC-DC converter module; The main control module is configured to acquire the equivalent power demand on the DC side of the inverter module input and the real-time terminal voltage of the supercapacitor energy storage module, and dynamically adjust the switching frequency and duty cycle of the bidirectional buck-boost DC-DC converter module according to the objective function. The objective function is jointly determined by the high-frequency conversion efficiency of the bidirectional buck-boost DC-DC converter module under transient compensation, the transient high-frequency demand component in the external load power, the real-time operating voltage of the DC bus, and the real-time terminal voltage of the supercapacitor energy storage module.

[0009] This invention establishes a mathematical correlation between multidimensional operating parameters and hardware conversion efficiency, and optimizes the switching frequency and duty cycle in real time during dynamic compensation, avoiding the additional switching losses caused by conventional fixed switching parameters, and improving the power conversion efficiency of the bidirectional buck-boost DC-DC converter module under transient conditions.

[0010] Furthermore, during the initial stage of system cold start, the main control module is configured to delay the connection of the lithium iron phosphate energy storage module and control the rectifier module to establish the base voltage of the DC bus according to a preset constant voltage ramp-up slope. When the voltage difference between the open-circuit terminal voltage of the lithium iron phosphate energy storage module and the operating voltage of the DC bus is less than the preset allowable voltage difference threshold, the main control module outputs a signal to close the circuit where the lithium iron phosphate energy storage module is located, so that the lithium iron phosphate energy storage module is connected to the DC bus.

[0011] This invention utilizes a rectifier module to actively establish the DC bus voltage. Once the DC bus voltage is equal to the terminal voltage of the lithium iron phosphate energy storage module, the grid connection circuit is closed. This startup mechanism eliminates the surge current caused by voltage difference when the energy storage battery pack is directly connected to the unloaded bus, ensuring the startup safety of the hardware circuit.

[0012] Preferably, when the actual ambient temperature is determined to be lower than the set low temperature protection safety threshold, the main control module is configured to restrict the lithium iron phosphate energy storage module from outputting high-power pulses to the DC bus; The main control module outputs a high-frequency alternating duty cycle sequence to the bidirectional buck-boost DC-DC converter module, which controls the bidirectional buck-boost DC-DC converter module to perform high-frequency reciprocating micro-amplitude charging and discharging actions on the supercapacitor energy storage module. The Joule heat generated by the equivalent series internal resistance of the supercapacitor energy storage module when the alternating current passes through it is used to compensate for the ambient heat. The main control module is configured to calculate the heat generated based on the instantaneous value of the high-frequency compensated AC current, the equivalent series internal resistance of the supercapacitor energy storage module, and the duration of the high-frequency action.

[0013] This invention limits the high-power output of lithium iron phosphate energy storage modules in low-temperature environments. By controlling the supercapacitor energy storage module to generate high-frequency micro-amplitude charging and discharging, the equivalent series internal resistance of the device is stimulated to generate physical heat. This invention forms an internal self-heating compensation mechanism without external heating devices, preventing lithium plating damage caused by high-rate discharge of lithium iron phosphate batteries at low temperatures.

[0014] Furthermore, the main control module is configured to collect the AC input voltage at the front end of the rectifier module in real time, and perform dual judgment logic by combining the lower limit of the effective voltage value and the instantaneous rate of change of the voltage. When the effective value of the current AC input voltage is less than the set undervoltage protection lower limit, and the absolute value of the instantaneous rate of change of the AC input voltage is greater than or equal to the set rate of change trigger threshold, the main control module determines that a substantial interruption of the mains power has occurred and triggers the feedforward takeover procedure of the active power branch.

[0015] This invention combines a dual determination mechanism of the effective value and instantaneous rate of change of AC input voltage, which identifies abnormal trends in the mains power ahead of conventional drop algorithms that rely solely on the effective value. This triggers the feedforward power support of the supercapacitor energy storage module in advance, shortens the bus voltage drop window during energy source switching, and maintains the continuity of the output voltage.

[0016] Furthermore, during the transient period of mains power outage and energy source switching or during sudden load impact, the main control module is configured to instantaneously increase the output reference voltage of the bidirectional buck-boost DC-DC converter module, so that the instantaneous operating voltage of the DC bus is raised to the level equal to or higher than the current open-circuit voltage of the lithium iron phosphate energy storage module. The potential difference between the two ends of the branch where the lithium iron phosphate energy storage module is located is controlled to zero or to present a negative voltage, thereby limiting the transient output current of the lithium iron phosphate energy storage module to a set safe level.

[0017] This invention utilizes the rapid response of the bidirectional buck-boost DC-DC converter module to instantaneously boost the DC bus voltage, thereby clamping or suppressing the voltage of the main battery. Under these conditions, the lithium iron phosphate energy storage module cannot physically output a large current due to zero or negative voltage difference. The transient impact power of the system is forced to be borne by the supercapacitor energy storage module, thus achieving hardware-level current limiting protection for the lithium iron phosphate energy storage module.

[0018] Furthermore, during the long-term backup phase of continuous mains power interruption, when the terminal voltage of the supercapacitor energy storage module is detected to drop to the set discharge lower limit threshold, the main control module is configured to introduce a ramp decay function that decreases with time to dynamically lower the output current reference value of the bidirectional buck-boost DC-DC converter module, so that the voltage on the DC bus will break free from clamping and drop back. When the DC bus voltage drops to the current open-circuit voltage of the lithium iron phosphate energy storage module, a forward conduction voltage difference is established in the branch where the lithium iron phosphate energy storage module is located, smoothly filling the power gap caused by the withdrawal of the supercapacitor energy storage module.

[0019] This invention introduces a ramp decay function that decreases over time to smoothly adjust the output command of the bidirectional buck-boost DC-DC converter module, so that the DC bus voltage is actively and slowly pulled down to the open circuit voltage point of the lithium iron phosphate energy storage module. The above process avoids the power surge at the handover point between the supercapacitor energy storage module's power supply withdrawal and the lithium iron phosphate energy storage module's power supply takeover, and realizes a smooth energy handover between the two different energy storage media under long-term power outage conditions.

[0020] Furthermore, the main control module is configured to acquire the battery cycle count, historical average charge / discharge depth, and current real-time cell operating temperature of the lithium iron phosphate energy storage module, and to execute a dynamic current limiting strategy in conjunction with the battery management system configured in the lithium iron phosphate energy storage module. The main control module is configured to multiply the rated current limiting reference value by a temperature derating factor related to the current cell operating temperature, and then multiply it by a health derating factor related to the number of battery cycles and the historical average charge and discharge depth, to calculate the dynamic discharge current limiting threshold and to drate the output capacity of the lithium iron phosphate energy storage module.

[0021] This invention incorporates the cell operating temperature and the battery's historical degradation state into the calculation of the discharge current limit. It dynamically adjusts the output boundary based on the actual physical health state of the lithium iron phosphate energy storage module to prevent the battery from accelerating degradation or thermal runaway under overload conditions due to aging or extreme temperatures.

[0022] Furthermore, the main control module is configured to acquire instantaneous current data from the DC input side of the inverter module and use a digital high-pass filtering algorithm combined with discrete differential operation to separate the transient high-frequency components in the load current. The main control module is configured to calculate the time derivative of the transient high-frequency component and compare it with the set impact current identification threshold. If the time derivative of the transient high-frequency component is greater than or equal to the set impact current identification threshold, it is determined that an impact load has occurred. The main control module is also configured to calculate the short-term limit support time based on the current equivalent capacity and operating voltage of the supercapacitor energy storage module and send a graded power outage warning signal to the outside when the lithium iron phosphate energy storage module experiences a hardware abnormality and encounters a mains power outage.

[0023] This invention utilizes a digital high-pass filtering algorithm and discrete differential operation to strip away the background steady-state current and lock the load mutation point; at the same time, it establishes a degradation operation mechanism under extreme faults, and calculates and provides deterministic redundant support time based on the current state of the supercapacitor energy storage module when the lithium iron phosphate energy storage module fails, thereby improving the overall safety early warning capability of the system.

[0024] Secondly, the present invention also provides a method for controlling a hybrid energy storage uninterruptible power supply combining lithium iron phosphate and supercapacitors, the method comprising the following steps: During the normal operation of the mains power, the rectifier module converts AC power to DC power to stabilize the DC bus voltage. The lithium iron phosphate energy storage module is connected in parallel to the DC bus to maintain floating charge. The main control module controls the bidirectional buck-boost DC-DC converter module to operate at a reduced voltage and charge the supercapacitor energy storage module to a full charge. During the momentary interruption of mains power, the main control module detects the drop in AC input voltage and controls the bidirectional buck-boost DC-DC converter module to start boost output. The DC bus voltage is supported solely by the supercapacitor energy storage module. The main control module limits the discharge rate of the lithium iron phosphate energy storage module so that the supercapacitor energy storage module can provide instantaneous power. During the long-term backup phase of continuous mains power outage, when the voltage of the supercapacitor energy storage module drops to a set threshold, the main control module controls the bidirectional buck-boost DC-DC converter to reduce output or shut down, and the system switches to the lithium iron phosphate energy storage module to discharge to the DC bus to maintain power supply. During the load surge compensation phase, when an inrush current is detected from an external load, the main control module adjusts the bidirectional buck-boost DC-DC converter to output peak power instantaneously. The supercapacitor energy storage module bears the inrush current, while the lithium iron phosphate energy storage module maintains its original discharge state. During the mains power restoration phase, the rectifier module re-establishes the DC bus voltage, and the main control module prioritizes controlling the bidirectional buck-boost DC-DC converter to recharge the supercapacitor energy storage module. After determining that the supercapacitor energy storage module is fully charged, the control system then charges the lithium iron phosphate energy storage module.

[0025] The control method of this invention relies on a hybrid energy storage hardware topology. Based on the changing states of the external mains power and load, the collaborative operation of the system is decomposed into five independent and continuous operating intervals in time sequence. This invention achieves decoupled control of steady-state energy storage and transient power response and closed-loop management of system operation by scheduling the power flow of the basic support energy source and transient compensation energy source at different operating stages.

[0026] This invention provides a hybrid energy storage uninterruptible power supply system and control method combining lithium iron phosphate and supercapacitors. It offers the following advantages: 1. This invention directly connects the lithium iron phosphate energy storage module in parallel to the DC bus and isolates the supercapacitor energy storage module to the DC bus via a bidirectional buck-boost DC-DC converter module. This eliminates the power conversion stage of the main energy storage branch, reducing hardware losses during steady-state operation. At the same time, during the cold start phase, the rectifier module actively establishes the DC bus base voltage. Once the DC bus voltage is equal to the open-circuit voltage of the lithium iron phosphate energy storage module, the circuit is closed, eliminating the surge current generated when the main battery pack is directly connected to the grid, thus improving the hardware safety during the system startup phase.

[0027] 2. This invention utilizes the rapid response of a bidirectional buck-boost DC-DC converter module to instantaneously boost the DC bus voltage during transient periods of load impact or mains power interruption. This creates a zero or negative voltage difference across the lithium iron phosphate energy storage module, forcing the supercapacitor energy storage module to handle transient high power and preventing damage to the lithium iron phosphate energy storage module from high-rate discharge. Furthermore, it controls the supercapacitor energy storage module to perform high-frequency micro-amplitude charging and discharging in low-temperature environments, using the heating effect of the equivalent series internal resistance of the device to compensate for environmental heat, thus solving the problem of lithium plating failure caused by direct high-current discharge of conventional batteries at low temperatures.

[0028] 3. This invention introduces a ramp decay function that decreases over time during the long-term backup phase of continuous mains power interruption. This smoothly reduces the output current command of the bidirectional buck-boost DC-DC converter module, guiding the DC bus voltage to actively fall back to the open-circuit voltage point of the lithium iron phosphate energy storage module. This achieves a stable power handover between the supercapacitor energy storage module and the lithium iron phosphate energy storage module, preventing sudden changes in the bus voltage. By combining the cell operating temperature, battery cycle count, and historical average charge-discharge depth to calculate the dynamic discharge current limiting threshold, this invention applies derating constraints to lithium iron phosphate energy storage modules at different aging stages, thus slowing down the overall energy storage medium degradation rate of the system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the system architecture of the present invention; Figure 2 This is a schematic diagram of the method flow of the present invention; Figure 3 This is a schematic diagram of the control flow during the normal operation phase of the mains power supply according to the present invention; Figure 4 This is a schematic diagram of the control flow during the instantaneous phase of mains power interruption according to the present invention; Figure 5 This is a schematic diagram of the control process for the long-term backup phase of continuous mains power interruption according to the present invention. Figure 6 This is a schematic diagram of the control flow for the load surge compensation stage of the present invention; Figure 7 This is a schematic diagram of the control process during the mains power restoration phase of the present invention; Figure 8 This is a comparison chart of the physical current limiting effect of the battery under different control schemes of the present invention.

[0030] Among them, 10 is the rectifier module; 20 is the inverter module; 30 is the DC bus; 40 is the main control module; 50 is the lithium iron phosphate energy storage module; 51 is the battery management system; 60 is the supercapacitor energy storage module; and 70 is the bidirectional buck-boost DC-DC converter module. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] See attached document Figure 1 The present invention provides a control system for a hybrid energy storage uninterruptible power supply consisting of lithium iron phosphate and supercapacitor. The system includes: a rectifier module 10, an inverter module 20, a DC bus 30, a main control module 40, a lithium iron phosphate energy storage module 50, a supercapacitor energy storage module 60, and a bidirectional buck-boost DC-DC converter module 70.

[0033] The rectifier module 10 has its AC input terminal connected to external AC power and its DC output terminal connected to the DC bus 30. The rectifier module 10 converts the input AC power into DC power to maintain the voltage of the DC bus 30. The inverter module 20 has its DC input terminal connected to the DC bus 30 and its AC output terminal connected to an external load. The inverter module 20 converts the DC power on the DC bus 30 into AC power to supply power to the external load.

[0034] The lithium iron phosphate energy storage module 50 is directly connected in parallel to the DC bus 30, forming a passive energy branch to provide long-term backup energy. The lithium iron phosphate energy storage module 50 adopts an 8-cell configuration and is adapted to a float charge voltage of 27.6V to 28.0V. In this embodiment, the rated float charge voltage of the DC bus 30 is configured to be 27.8V. The lithium iron phosphate energy storage module 50 does not go through any DC / DC converter, but is directly connected in parallel to the DC bus 30 through a contact switch controlled by the main control module 40. The lithium iron phosphate energy storage module 50 is equipped with a BMS51.

[0035] The supercapacitor energy storage module 60 is connected to the DC bus 30 via the bidirectional buck-boost DC-DC converter module 70, forming an active power branch that provides instantaneous power support and load impact compensation. The supercapacitor energy storage module 60 is composed of 10 series 3V-level cells. The hardware rated full charge voltage is 30V. To extend its service life and adapt to the system's buck charging logic, the actual operating voltage range is configured to be 15V to 27.8V. The low-voltage side of the bidirectional buck-boost DC-DC converter module 70 is connected to the supercapacitor energy storage module 60, and the high-voltage side is connected to the DC bus 30. The supercapacitor energy storage module 60 is equipped with a CMS61.

[0036] In the active power branch, the supercapacitor energy storage module 60 performs voltage conversion through the bidirectional buck-boost DC-DC converter module 70, thereby releasing the voltage binding with the DC bus 30 and realizing independent power dispatch.

[0037] The main control module 40 is connected to the BMS51 of the lithium iron phosphate energy storage module 50, the CMS61 of the supercapacitor energy storage module 60, and the bidirectional buck-boost DC-DC converter module 70. The main control module 40 collects AC input voltage, DC bus 30 voltage, load current and ambient temperature. The main control module 40 obtains voltage, current, temperature and SOC data fed back by BMS51, and obtains voltage and operating parameters fed back by CMS61.

[0038] The main control module 40 executes joint decision-making and control strategies based on the collected data, generates control commands, outputs PWM signals to the bidirectional buck-boost DC-DC converter module 70, adjusts the duty cycle of the bidirectional buck-boost DC-DC converter module 70, and controls the start-up, shutdown, and power closed-loop of the bidirectional buck-boost DC-DC converter module 70.

[0039] The hybrid energy storage uninterruptible power supply system 100 adopts an integrated compact structure design. The lithium iron phosphate energy storage module 50, the supercapacitor energy storage module 60, and the bidirectional buck-boost DC-DC converter module 70 are all integrated inside the UPS chassis, with no external energy storage units.

[0040] See attached document Figure 2 This invention provides a control method for a hybrid energy storage uninterruptible power supply combining lithium iron phosphate and supercapacitors, the method comprising the following steps: S10, during normal mains power operation, the rectifier module 10 converts external AC power into DC power, stabilizing the voltage of the DC bus 30 at 27.8V; the lithium iron phosphate energy storage module 50 is directly connected in parallel to the DC bus 30 and is in a floating charge state; the main control module 40 controls the bidirectional buck-boost DC-DC converter module 70 to operate in buck mode, performing constant voltage charging on the supercapacitor energy storage module 60, so that the supercapacitor energy storage module 60 reaches and maintains a full charge state of 27.8V; S20, during the momentary interruption of mains power, the main control module 40 detects a drop in AC input voltage and controls the bidirectional buck-boost DC-DC converter module 70 to instantly start boost output; the system then switches to supercapacitor energy storage module 60 supporting the voltage of DC bus 30 independently via bidirectional buck-boost DC-DC converter module 70; the main control module 40 limits the discharge rate of lithium iron phosphate energy storage module 50 so that it does not output large current during this stage, and the supercapacitor energy storage module 60 provides instantaneous power; S30, during the long-term backup phase of continuous mains power interruption, the voltage of the supercapacitor energy storage module 60 decreases as it discharges. When the voltage drops to the set threshold, the main control module 40 sends a command to the bidirectional buck-boost DC-DC converter module 70 to reduce the output power or shut down. The system then switches to the lithium iron phosphate energy storage module 50 to take over the power supply and discharge smoothly to the DC bus 30 to maintain the system's backup power supply. S40, during the load surge compensation phase, the main control module 40 monitors the load-side current changes in real time. When it detects that the external load generates inrush current or surge demand, it adjusts the closed-loop parameters of the bidirectional buck-boost DC-DC converter module 70 to make it output peak power instantaneously. The surge current is borne by the branch where the supercapacitor energy storage module 60 is located, while the branch where the lithium iron phosphate energy storage module 50 is located maintains the original discharge state. S50, during the mains power restoration phase, the mains power input is restored, and the rectifier module 10 re-establishes a stable DC bus 30 voltage; the main control module 40 executes charging priority scheduling, prioritizing the operation of the bidirectional buck-boost DC-DC converter module 70 to quickly recharge the supercapacitor energy storage module 60; when it is determined that the supercapacitor energy storage module 60 is fully charged, the system switches to slow charging and subsequent float charging of the lithium iron phosphate energy storage module 50.

[0041] See attached document Figure 3 In specific implementations, step S10 provided by the present invention may include the following steps: S101, cold start voltage build-up timing control of the whole machine: In the initial stage of cold start of the uninterruptible power supply system 100, if the bus circuit where the lithium iron phosphate energy storage module 50 is located is directly connected, a transient inrush current will be triggered due to the initial voltage difference and the capacitive load devices on the DC bus 30 side. The main control module 40 delays the connection of the lithium iron phosphate energy storage module 50 and prioritizes the start-up and operation of the rectifier module 10.

[0042] The rectifier module 10 introduces external AC power and establishes the base voltage of the DC bus 30 according to a preset constant voltage ramp rate. The preset constant voltage ramp rate ranges from 5V / s to 15V / s. The main control module 40 collects the operating voltage of the DC bus 30 and the open-circuit voltage of the lithium iron phosphate energy storage module 50 in real time. When the voltage difference between the open-circuit voltage of the lithium iron phosphate energy storage module 50 and the operating voltage of the DC bus 30 is less than a preset differential voltage allowable threshold, the preset differential voltage allowable threshold ranges from 0.5V to 1.0V, and the main control module 40 outputs a closed signal. The contact switch of the lithium iron phosphate energy storage module 50 allows the lithium iron phosphate energy storage module 50 to be connected to the DC bus 30 with almost no potential difference, avoiding internal circulating current caused by voltage surges, thereby reducing the risk of damage to components from large surge currents. To prevent control program deadlock due to voltage build-up failure, the main control module 40 is equipped with a start-up timeout timer. If the voltage difference between the open-circuit voltage of the lithium iron phosphate energy storage module 50 and the operating voltage of the DC bus 30 is still not met after the set maximum voltage build-up time is exceeded, the maximum voltage build-up time ranges from 2s to 5s, and a system fault alarm is triggered.

[0043] S102, System steady-state float charging control: After the DC bus 30 voltage is established and stabilized, the rectifier module 10 undertakes the external load power transmitted by the inverter module 20 and stabilizes the DC bus 30 voltage in a closed loop at the preset rated float charging voltage. Since the lithium iron phosphate energy storage module 50 is directly physically connected in parallel with the DC bus 30, the lithium iron phosphate energy storage module 50 passively follows the operating voltage of the DC bus 30, enters and maintains a micro-current float charging state. At the same time, the main control module 40 sends a buck mode command and a target voltage reference to the bidirectional buck-boost DC-DC converter module 70. The bidirectional buck-boost DC-DC converter module 70 performs buck chopping processing on the DC bus 30 voltage on the high-voltage side and charges the supercapacitor energy storage module 60 on the low-voltage side with a constant current.

[0044] For the specific current and voltage dual closed-loop pulse width modulation regulation process inside the bidirectional buck-boost DC-DC converter module 70, it is carried out according to the existing conventional control methods of power converters. When the voltage at the terminal of the supercapacitor energy storage module 60 reaches the rated full charge voltage set by the system, the main control module 40 adjusts the duty cycle to switch to constant voltage compensation mode to compensate for the self-discharge leakage current of the supercapacitor and maintain the energy ready state of the active power branch.

[0045] S103, Efficiency Optimization and Duty Cycle Adaptive Adjustment: Under light load or no-load conditions, due to the fixed switching frequency of power devices, switching losses account for a relatively high proportion of overall power consumption. To reduce the static power loss of the equipment, the main control module 40 pre-stores a three-dimensional mapping matrix of the conversion efficiency of the bidirectional buck-boost DC-DC converter module 70 in its internal non-volatile memory. This three-dimensional mapping matrix is ​​obtained through full-condition power scan calibration before the equipment leaves the factory. The main control module 40 obtains the equivalent DC-side power demand input from the inverter module 20 in real time. Combined with the real-time terminal voltage of the supercapacitor energy storage module 60, and under the premise of maintaining the DC bus 30 operating voltage strictly equal to the battery float charge voltage, the asymmetric modulation mode is activated. The main control module 40 dynamically corrects the switching frequency and duty cycle of the bidirectional buck-boost DC-DC converter module 70 according to the objective function. The formula for the objective function is: ; In the formula, For transient power compensation coefficient of active branch; The high-frequency conversion efficiency of the bidirectional buck-boost DC-DC converter module 70 under transient compensation state; This refers to the transient high-frequency demand component in the external load power; This is the real-time operating voltage of DC bus 30; This is the real-time terminal voltage of the supercapacitor energy storage module 60.

[0046] The main control module 40 calculates and tracks the optimal duty cycle operating point that maximizes the power conversion efficiency, and changes the charging and discharging time ratio of the internal inductor to dynamically reduce the internal switching losses during system standby operation.

[0047] S104, self-heating closed-loop control in low-temperature environments: Due to the slow internal chemical reaction of lithium iron phosphate batteries in extremely cold environments, there is a risk of lithium plating during high-current discharge. Supercapacitors, on the other hand, have excellent wide-temperature range operating characteristics. The main control module 40 reads the ambient temperature data fed back by the battery management system 51 and the capacitor management system in real time through the communication network. When it is determined that the actual ambient temperature is lower than the set low-temperature protection safety threshold, the set low-temperature protection safety threshold is set according to the battery cell specifications. The set low-temperature protection safety threshold ranges from 0℃ to 5℃. The main control module 40 modifies the underlying control logic to lock the high-rate discharge permission of the lithium iron phosphate energy storage module 50 and restricts the output of high-power pulses from the lithium iron phosphate energy storage module 50 to the DC bus 30 through instructions.

[0048] During this period, the main control module 40 outputs a high-frequency alternating duty cycle sequence to the bidirectional buck-boost DC-DC converter module 70, controlling the bidirectional buck-boost DC-DC converter module 70 to perform high-frequency reciprocating micro-amplitude charge and discharge operations on the supercapacitor energy storage module 60. This process utilizes the Joule heat generated by the inherent equivalent series internal resistance of the supercapacitor energy storage module 60 when alternating current passes through it to compensate for ambient heat within the sealed integrated casing. The main control module 40 accumulates and calculates the heat generated by the self-heating mechanism according to Joule's law. The formula for calculating the accumulated heat generated by the self-heating mechanism is as follows: ; In the formula, This refers to the Joule heat generated by the supercapacitor energy storage module 60 during impact load compensation. This is the upper limit of the duration of the transient high-frequency compensation action; This refers to the instantaneous value of the high-frequency compensated AC current output by the supercapacitor energy storage module 60. For the time variable in the transient compensation process; The equivalent series internal resistance of the supercapacitor energy storage module 60; Let be the differential of the time variable.

[0049] When the ambient temperature rises again and reaches the set normal temperature recovery threshold (the set normal temperature recovery threshold ranges from 10℃ to 15℃), the main control module 40 cancels the alternating duty cycle sequence command and restores the system's standard energy storage backup logic.

[0050] See attached document Figure 4 In specific implementations, step S20 provided by the present invention may include the following steps: S201 performs mains power drop prediction and identification. In traditional power grid failure detection, the response is triggered only after a deep voltage drop occurs on the DC bus 30, resulting in a power interruption blind zone. The main control module 40 collects the AC input voltage at the front end of the rectifier module 10 in real time through an external sampling network at a set sampling rate. The set sampling rate ranges from 5kHz to 20kHz. In order to achieve a fast feedforward response and reduce the probability of misjudgment caused by normal harmonic disturbances in the power grid, the main control module 40 executes a dual judgment logic that combines the lower limit of the effective voltage value and the instantaneous rate of change of voltage.

[0051] The main control module 40 calculates the voltage change rate within a discrete time window in real time. When the current effective value of the AC input voltage is less than the set undervoltage protection lower limit (the set undervoltage protection lower limit ranges from 180V to 200V), and the absolute value of the instantaneous change rate of the AC input voltage is greater than or equal to the set change rate trigger threshold (the set change rate trigger threshold ranges from 50V / ms to 100V / ms), a substantial interruption of the mains power is determined, and the feedforward takeover procedure of the active power branch is triggered. The logic condition formula for determining the mains power drop is as follows: ; In the formula, The calculated effective value of the current AC input voltage; The set lower limit threshold for power grid undervoltage protection; For the current number The instantaneous sampled value of the AC input voltage for each sampling period; This is the index number of the discrete sampling time of the AC voltage; For the preceding number The instantaneous sampled value of the AC input voltage for each sampling period; Number of sampling points for the time window to prevent false judgments during AC voltage dips; This refers to the single sampling period time of the AC voltage analog-to-digital conversion; The preset AC voltage sag rate trigger threshold is set to a value greater than the maximum normal voltage fluctuation rate generated during normal load switching of the power grid.

[0052] S202, the active branch instantaneous boost power supply is executed. After the main control module 40 confirms the mains power interruption, it sends a working mode switching command to the bidirectional buck-boost DC-DC converter module 70. The bidirectional buck-boost DC-DC converter module 70 quickly closes the buck charging path and opens the boost discharging path. For transient conditions, the proportional-integral closed-loop control parameters corresponding to the heavy load transient response inside the main control module 40 are increased to improve the dynamic response speed of the system by increasing the proportional gain coefficient. The supercapacitor energy storage module 60 releases the stored electrical energy. Through the high-frequency chopping boost effect of the bidirectional buck-boost DC-DC converter module 70, peak current is injected into the DC bus 30 to compensate for the power gap caused by the mains power failure in the rectifier module 10.

[0053] Through the aforementioned closed-loop response process, the supercapacitor energy storage module 60 independently undertakes the load demand transmitted by the inverter module 20, clamps and maintains the voltage of the DC bus 30 near the rated float charge voltage, and provides continuous power supply to the load side. When the voltage fluctuation rate of the DC bus 30 recovers to the set stable band, the set stable band value range is ±1% to ±3%. The main control module 40 switches the closed-loop control parameters back to the steady-state parameters to avoid continuous high-frequency oscillations in the system. For the switching transistor turn-on and turn-off logic of the boost converter inside the bidirectional buck-boost DC-DC converter module 70, it is based on the existing bidirectional DC-DC converter pulse width modulation method.

[0054] S203 executes high-rate discharge lockout control during the transient phase. During the transient period of mains power interruption and energy source switching, there is transient oscillation caused by power reconstruction in the system network. Since the lithium iron phosphate energy storage module 50 is connected in parallel to the DC bus 30 instead of in series with the converter, if the voltage of the DC bus 30 drops slightly, the lithium iron phosphate cell with low internal resistance will output a transient impact current to the DC bus 30. This instantaneous high-frequency large current will affect the internal electrode structure of the cell, accelerate battery aging, and pose a risk of triggering the hardware overcurrent protection of the battery management system 51. In order to isolate the transient impact, the main control module 40 adjusts the reference reference of the active branch through software feedforward adjustment, and instantaneously increases the output reference voltage of the bidirectional buck-boost DC-DC converter module 70.

[0055] The bidirectional buck-boost DC-DC converter module 70 outputs a large current based on the reference voltage, raising the instantaneous voltage of the DC bus 30 to a level equal to or slightly higher than the current open-circuit voltage of the lithium iron phosphate energy storage module 50. Based on Kirchhoff's voltage law, the potential difference across the passive branch where the lithium iron phosphate energy storage module 50 is located is controlled to zero or exhibits a slight negative voltage. Therefore, the lithium iron phosphate energy storage module 50 is subject to physical current limiting suppression during this transient phase, and the output current of the lithium iron phosphate energy storage module 50 is limited to a low level. The transient impact at the moment of sudden change is mainly absorbed and borne by the branch where the supercapacitor energy storage module 60 is located.

[0056] See attached document Figure 5 In specific implementations, step S30 provided by the present invention may include the following steps: S301 executes dual-source discharge power smooth handover control. During the transient support process at the initial stage of mains power interruption, as the supercapacitor energy storage module 60 discharges at constant power to the DC bus 30, its terminal voltage shows a downward trend. The main control module 40 monitors the terminal voltage of the supercapacitor energy storage module 60 in real time. When it detects that the terminal voltage of the supercapacitor energy storage module 60 drops to the set lower discharge threshold, it triggers the smooth handover procedure between the two energy storage media. The set lower discharge threshold is established based on the minimum allowable operating voltage of the bidirectional buck-boost DC-DC converter module 70 to maintain the rated boost output. The set lower discharge threshold value is 15V, which is half of the rated full charge voltage of the supercapacitor energy storage module 60, in order to balance energy utilization and conversion efficiency.

[0057] After the power transfer is triggered, the main control module 40 introduces a ramp attenuation function that decreases over time through an internal algorithm to dynamically lower the reference value of the output current of the bidirectional buck-boost DC-DC converter module 70. To ensure a safe power transfer before the supercapacitor is depleted, the main control module 40 calculates and sets the attenuation slope of the ramp attenuation function in real time based on the equivalent power demand of the current external load and the current remaining available energy of the supercapacitor energy storage module 60. As the output power of the bidirectional buck-boost DC-DC converter module 70 slowly decreases, the voltage on the DC bus 30 is released from the active clamping state and drops slightly.

[0058] Based on the physical characteristics of parallel circuits, when the DC bus voltage drops to the current open-circuit voltage of the lithium iron phosphate energy storage module 50, a forward conduction voltage difference is established in the branch where the lithium iron phosphate energy storage module 50 is located. The output current of the lithium iron phosphate energy storage module 50 increases accordingly as the voltage difference increases, thereby smoothly filling the power gap caused by the withdrawal of the supercapacitor energy storage module 60. This process avoids a deep drop in bus voltage caused by the instantaneous shutdown of the converter.

[0059] S302 executes long-term steady-state discharge control of lithium iron phosphate. When the output current reference value of the bidirectional buck-boost DC-DC converter module 70 decays to zero, the smooth handover process is completed. The main control module 40 sends a standby shutdown command to the bidirectional buck-boost DC-DC converter module 70, the supercapacitor energy storage module 60 stops outputting, and the system switches to the lithium iron phosphate energy storage module 50 to independently undertake all the steady-state load requirements transmitted by the inverter module 20. During this long-term backup power supply period, since the lithium iron phosphate energy storage module 50 is directly connected without going through the converter, the voltage of the DC bus 30 directly follows the discharge characteristic curve of the lithium iron phosphate energy storage module 50 and decreases. The main control module 40 continuously obtains the real-time terminal voltage and remaining power status fed back by the battery management system 51 through the communication bus.

[0060] Considering the voltage drop effect caused by the increased internal resistance at the discharge end of the lithium iron phosphate battery, the main control module 40 compensates for the preset base shutdown voltage based on the current real-time discharge current value. The preset base shutdown voltage ranges from 21.6V to 22.4V. The dynamic shutdown protection lower limit is calculated. When the main control module 40 detects that the terminal voltage of the lithium iron phosphate energy storage module 50 reaches the calculated dynamic shutdown protection lower limit, it determines that the battery energy is exhausted. It then sends a shutdown command to the inverter module 20 and cuts off the power supply to the external load to prevent the cell from being deeply over-discharged. The real-time estimation of the remaining power in the lithium iron phosphate energy storage module 50 is based on the existing method of combining ampere-hour integration and open-circuit voltage.

[0061] S303, implements adaptive current limiting protection based on multi-parameter fusion for battery health. To prevent overcurrent failure caused by aging due to prolonged discharge in the later stages of the lithium iron phosphate energy storage module 50's life cycle, the main control module 40, in conjunction with the battery management system 51, executes a dynamic current limiting strategy. Conventional fixed overcurrent protection thresholds are difficult to fully adapt to the objective law of increasing cell internal resistance with aging. The main control module 40 obtains the battery cycle count, historical average charge / discharge depth, and current real-time cell operating temperature stored in the battery management system 51 in real time. The main control module 40 performs fusion calculations on the above operating parameters and calculates the adaptive discharge current limiting threshold in real time, dynamically derating the output capacity of the lithium iron phosphate energy storage module 50. The method for calculating the adaptive discharge current limiting threshold is as follows: multiply the rated current limiting benchmark value of the lithium iron phosphate energy storage module 50 by a temperature derating factor related to the current cell operating temperature, and then multiply by a health derating factor related to the battery cycle count and historical average charge / discharge depth. The logical formula for calculating the adaptive discharge current limiting threshold is as follows: ; In the formula, The dynamic discharge current limiting threshold of the lithium iron phosphate energy storage module 50 is calculated by the main control module 40. The rated current limit reference value set for the lithium iron phosphate energy storage module 50 under factory standard operating conditions; This is a function of the temperature derating factor; This represents the current real-time operating temperature of the battery cell. A function for the health deduction coefficient; The number of historical usage cycles recorded internally by the battery; The average depth of charge and discharge during the battery's historical operation.

[0062] The data for temperature derating coefficient and health derating coefficient are obtained from actual measurements and calibrations conducted in an environmental chamber and aging test platform before the equipment leaves the factory. The data is then stored in the storage unit of the main control module 40 in the form of a two-dimensional lookup table. The main control module 40 compares the real-time passive branch discharge current with the calculated dynamic discharge current limiting threshold. If the actual discharge current continues to exceed the calculated dynamic discharge current limiting threshold, the main control module 40 immediately triggers the local overcurrent degradation logic and sends a load reduction command to the external power distribution equipment through the communication interface. This indirectly reduces the total load demand of the DC bus 30, forcing the actual discharge current of the lithium iron phosphate energy storage module 50 to fall back to within the current limiting threshold, thereby maintaining the safe operation of the core power supply circuit.

[0063] See attached document Figure 6 In specific implementations, step S40 provided by the present invention may include the following steps: S401, performs surge load identification based on current change rate. During the operation of the uninterruptible power supply system, nonlinear loads such as inductive devices or motors are connected to the external load circuit at the back end of the inverter module 20. These nonlinear loads generate surge currents when starting up or when the operating conditions change abruptly. The main control module 40 obtains the instantaneous current data of the DC input side of the inverter module 20 through a current sampling network, and performs frequency domain analysis on the current signal using an internal digital signal processing algorithm. The main control module 40 uses a digital high-pass filter algorithm combined with discrete differential operation to separate the steady-state low-frequency components and transient high-frequency components in the load current. The cutoff frequency of the digital high-pass filter algorithm is set to be greater than the maximum load fluctuation frequency during normal steady-state operation of the system to filter out normal low-frequency power adjustments. The main control module 40 calculates the time derivative of the transient high-frequency components and compares it with the set surge current identification threshold. The set surge current identification threshold ranges from 20A / ms to 50A / ms. The logical condition formula for determining the occurrence of a surge load is as follows: ; In the formula, For the current number The instantaneous current sampled value on the load side for each sampling period; This is the index number of the discrete sampling time of the load current; For the preceding number The instantaneous current sampled value on the load side for each sampling period; The number of sampling intervals selected is used to calculate the rate of change of the impact current; The time interval for a single cycle of load current sampling; The preset threshold for triggering the rate of change of the impact current.

[0064] When the above conditions are met, the main control module 40 confirms that a sudden surge has occurred in the external load and triggers the transient compensation program of the active power branch.

[0065] S402, perform high-frequency transient power compensation for the active branch. After confirming the occurrence of the impact load, the main control module 40 detects whether the current terminal voltage of the supercapacitor energy storage module 60 is higher than its minimum allowable operating voltage threshold to confirm that the active branch has compensation capability. If the main control module 40 detects that the current terminal voltage of the supercapacitor energy storage module 60 is lower than the minimum allowable operating voltage threshold, it determines that the active branch cannot complete the compensation independently. The main control module 40 exits the transient compensation program, and the rectifier module 10 or the lithium iron phosphate energy storage module 50 shares the sudden load according to the conventional overcurrent protection logic, and simultaneously reports the system energy limitation alarm. Under the premise that the energy determination is passed, the main control module 40 adjusts the closed-loop parameters in the internal control logic of the bidirectional buck-boost DC-DC converter module 70, and improves the dynamic tracking response speed of the converter by increasing the proportional gain coefficient of the current loop in the proportional-integral regulator.

[0066] Since the supercapacitor energy storage module 60 uses the double-layer electrostatic adsorption principle to store energy, it has a power density far higher than that of chemical batteries and an extremely low equivalent series internal resistance. The bidirectional buck-boost DC-DC converter module 70 enters the peak power output state. The supercapacitor energy storage module 60 releases its internal energy and injects high-frequency compensation current into the DC bus 30 through chopper conversion. The injected high-frequency compensation current responds to the peak load demand generated by the external load. During the compensation period, the main control module 40 continuously monitors the time derivative of the current. When the current change rate falls back and is lower than the set exit threshold for several consecutive sampling cycles, the set exit threshold ranges from 2A / ms to 5A / ms. It is determined that the external load start-up process has ended, and the main control module 40 reverts the closed-loop control parameters to the original steady-state operating parameters. The specific duty cycle generation process of the bidirectional buck-boost DC-DC converter module 70 during the peak output period is based on the existing digital current closed-loop pulse width modulation method.

[0067] In S403, the low-frequency steady-state lockout control of the passive branch is executed. During the transient period of a sudden inrush current from the external load, if the voltage of the DC bus 30 is not intervened, the instantaneous increase in load will cause the voltage of the DC bus 30 to drop. The lithium iron phosphate energy storage module 50 directly connected to it will passively output a high-frequency pulsed current due to the increased voltage difference. This high-frequency pulsed discharge behavior not only generates excessive Joule heat, but also causes the active material inside the cell to fall off, affecting its service life. Based on the high-frequency transient power compensation in step S402 of the active branch, the bidirectional buck-boost DC-DC converter module 70 injects a large current into the DC bus 30 while forming an active clamping effect on the node voltage of the DC bus 30.

[0068] The main control module 40 adjusts the control reference to keep the real-time operating voltage of the DC bus 30 at a level equal to or slightly higher than the open-circuit voltage of the lithium iron phosphate energy storage module 50. By suppressing the voltage difference space of the forward conduction of the lithium iron phosphate energy storage module 50, the physical output path of the lithium iron phosphate energy storage module 50 is blocked. Therefore, during sudden load impacts, the lithium iron phosphate energy storage module 50 is maintained in the low-frequency steady-state output operating range, responding to the stable power supply requirements of the system foundation and reducing the loss of cell life due to high-frequency peak current.

[0069] See attached document Figure 7 In specific implementations, step S50 provided by the present invention may include the following steps: S501 executes priority-based energy quick-readiness control. After the mains power is restored to normal, the rectifier module 10 restarts and establishes the working voltage of the DC bus 30. The main control module 40 obtains the rated maximum output power of the rectifier module 10 and the current DC-side load demand power of the inverter module 20 in real time, calculates the difference between the two to obtain the system's surplus power. In order to cope with the situation where the mains power is interrupted again in a short period of time, the main control module 40 allocates the calculated surplus power to the active power branch first. Considering the hardware current carrying capacity, the main control module 40 compares the calculated surplus power with the maximum allowable charging power of the bidirectional buck-boost DC-DC converter module 70 and takes the smaller value of the two as the target charging power.

[0070] Subsequently, the main control module 40 converts the target charging power into a charging current reference value for the bidirectional buck-boost DC-DC converter module 70, and controls the bidirectional buck-boost DC-DC converter module 70 to enter the buck charging mode, injecting current into the supercapacitor energy storage module 60. Since the supercapacitor energy storage module 60 has extremely low physical internal resistance, it can accept a large current input rate. The supercapacitor energy storage module 60 can quickly recover to a fully charged standby state in a short time. During this stage, the main control module 40 adjusts the rectifier module 10 to limit the operating voltage of the DC bus 30 to a level that dynamically tracks and is equal to the current open-circuit voltage of the lithium iron phosphate energy storage module 50, so that the potential difference between the two ends of the passive branch approaches zero, preventing the lithium iron phosphate energy storage module 50 from prematurely absorbing charging current or discharging to the DC bus 30.

[0071] S502, a graded slow-charge control to avoid heat accumulation is implemented. The main control module 40 monitors the terminal voltage of the supercapacitor energy storage module 60 in real time through the capacitor management system. When the terminal voltage of the supercapacitor energy storage module 60 reaches the set rated full-charge threshold (the set rated full-charge threshold ranges from 27.5V to 27.8V), the main control module 40 determines that the active branch energy reserve is ready and controls the bidirectional buck-boost DC-DC converter module 70 to switch to micro-current float charging state. Subsequently, the main control module 40 raises the output voltage reference of the rectifier module 10, so that the voltage of the DC bus 30 rises to the charging voltage platform corresponding to the lithium iron phosphate energy storage module 50. As the voltage of the DC bus 30 rises, the branch where the lithium iron phosphate energy storage module 50 is located is forward-biased and enters the charging stage. The main control module 40 controls the rectifier module 10 to output a limited constant current to perform small-current slow charging of the lithium iron phosphate energy storage module 50.

[0072] The tiered charging sequence staggers the high-power charging demands of the active and passive branches, reducing the risk of heat accumulation and excessive temperature rise caused by dual-source synchronous high-current charging inside the closed physical casing of the system. At the end of constant voltage charging, the main control module 40 monitors the charging absorption current of the lithium iron phosphate energy storage module 50 in real time. When the charging absorption current of the lithium iron phosphate energy storage module 50 decreases and remains below the preset cutoff current threshold (set according to the specifications provided by the battery manufacturer, with a value of 5% of the nominal capacity of the lithium iron phosphate energy storage module 50), it is determined that the lithium iron phosphate energy storage module 50 is fully charged, and the main control module 40 then restores the operating voltage of the DC bus 30 to the rated float charge voltage.

[0073] S503 executes asymmetric equipment fault redundancy and degradation switching control. Those skilled in the art will understand that during the entire system lifecycle, the main control module 40 monitors the hardware health status of each energy storage unit and conversion unit in real time. When the capacitor management system reports a hardware failure in the supercapacitor energy storage module 60 or the bidirectional buck-boost DC-DC converter module 70, the main control module 40 shuts off the drive signal of the active power branch, and the system degrades to a pure lithium iron phosphate backup mode, with the lithium iron phosphate energy storage module 50 taking over the system's backup response function. When the battery management system 51 reports a hardware abnormality or grid disconnection in the lithium iron phosphate energy storage module 50, the main control module 40 initiates cross-backup logic. If a mains power interruption occurs during the failure of the lithium iron phosphate energy storage module 50, the main control module 40 controls the bidirectional buck-boost DC-DC converter module 70 to operate at full power, relying on the supercapacitor energy storage module 60 to provide short-term power support. The main control module 40 calculates in real time the short-term limit support time that the supercapacitor energy storage module 60 can provide. The calculation formula for the short-term limit support time that the supercapacitor energy storage module 60 can provide is as follows: ; In the formula, This refers to the calculated short-time limit support time of the supercapacitor. For the physical energy calculation formula, there is a constant coefficient; The actual equivalent capacitance of the supercapacitor is adjusted based on the current health status assessment; This is the initial terminal voltage sample value of the supercapacitor energy storage module 60 when the fault occurs; This is the lowest permissible discharge operating voltage for the bidirectional buck-boost DC-DC converter module 70; The current average load demand power transmitted to inverter module 20; The average conversion efficiency of the bidirectional buck-boost DC-DC converter module 70 under discharge support conditions.

[0074] Based on the support time calculated above, the main control module 40 sends a graded power outage warning signal to the load-side terminal through the external communication interface. It uses the time window of the short-term limit support time to assist the load-side in writing critical data into non-volatile storage media, thereby reducing the risk of data loss.

[0075] To aid in understanding the technical solution of this invention, an application example of an uninterruptible power supply system for edge computing nodes is provided below.

[0076] In this application embodiment, the hybrid energy storage uninterruptible power supply system is configured with an external rated load of 3000W. When an external inductive load is connected and started, the transient peak power generated by the system is 5000W, and the impact duration is 0.5s. The rated float charge voltage of the internal DC bus 30 is configured to be 27.8V. The lithium iron phosphate energy storage module 50 adopts an 8-series 50Ah cell combination. When fully charged and at rest, the open circuit voltage is 26.8V. The equivalent series internal resistance of the battery pack is calibrated to be 5.2mΩ. The supercapacitor energy storage module 60 is composed of 10 series 500F / 3V single capacitors, and the equivalent total capacitance is set to 50F. The minimum allowable discharge operating voltage of the bidirectional buck-boost DC-DC converter module 70 is set to 15V.

[0077] The system's operating parameters under normal mains power outage conditions are as follows: After detecting a mains power outage, the main control module 40 controls the bidirectional buck-boost DC-DC converter module 70 to switch to boost mode. The main control module 40 sets the output reference voltage of the bidirectional buck-boost DC-DC converter module 70 to 27.5V, which is higher than the current open-circuit voltage of the lithium iron phosphate energy storage module 50 (26.8V). At this time, the 3000W load power is entirely provided by the supercapacitor energy storage module 60, with a corresponding output current of 109A. Since the initial voltage of the supercapacitor energy storage module 60 is 27.8V and its operating cutoff voltage is 15V, it can be used... The calculated energy value is 13696J. Under this load condition, the supercapacitor energy storage module 60 independently supports the system for about 3.42 seconds. When the discharge time reaches the lower discharge threshold, the main control module 40 executes the ramp attenuation algorithm, the output current of the bidirectional buck-boost DC-DC converter module 70 decreases, and the voltage of the DC bus 30 drops accordingly. When the voltage of the DC bus 30 drops to 26.8V or below, a forward conduction voltage difference is formed in the branch where the lithium iron phosphate energy storage module 50 is located, and the output current begins. After a smooth handover, the lithium iron phosphate energy storage module 50 finally takes over the entire load with a constant current of 112A.

[0078] Under the impact condition of sudden load increase, the operating parameters are as follows: the basic load is maintained at 3000W, and the additional impact power demand of 2000W generates a transient current of 72A. The main control module 40 identifies the impact load through high-pass filtering and controls the bidirectional buck-boost DC-DC converter module 70 to inject high-frequency compensation current into the DC bus 30. During the compensation period, the voltage of the DC bus 30 is higher than the open-circuit voltage of the lithium iron phosphate energy storage module 50. The output current of the lithium iron phosphate energy storage module 50 is maintained at around 112A. The sudden impact current of 72A is borne by the branch where the supercapacitor energy storage module 60 is located.

[0079] The operating parameters under the energy recovery charging condition after the mains power is restored are as follows: The rated maximum output power of the rectifier module 10 is set to 4000W. After deducting the basic load of 3000W, the system has a surplus power of 1000W. The main control module 40 allocates the 1000W surplus power to the active power branch. The bidirectional buck-boost DC-DC converter module 70 charges the supercapacitor energy storage module 60 with this power. After the voltage at the terminal of the supercapacitor energy storage module 60 reaches 27.8V, the main control module 40 controls the rectifier module 10 to raise the voltage of the DC bus 30 and slowly charge the lithium iron phosphate energy storage module 50 with a small current of 2.5A.

[0080] The following provides experimental data obtained from multiple comparative tests of the traditional control scheme and the control scheme of the present invention under the above parameter configuration.

[0081] Table 1: Comparison of Test Data for Uninterruptible Power Supply Systems under Multiple Operating Conditions

[0082] According to Table 1 and Figure 8 Compared with traditional control schemes, the control method for hybrid energy storage uninterruptible power supply (UPS) of lithium iron phosphate and supercapacitor provided by this invention differs in voltage stability, battery physical current limiting, and system thermal management indicators. During the mains power interruption switching phase, the traditional scheme relies solely on the chemical response speed of the parallel battery pack to fill the power gap, resulting in a sudden deep drop in bus voltage of 2.75V to 2.91V. This scheme uses AC voltage feedforward judgment and instantaneous voltage boosting by the supercapacitor to take over. The measured maximum drop in bus voltage is maintained within the range of 0.38V to 0.45V, indicating that the high-frequency compensation action of the active branch suppresses voltage surges and ensures the continuity of power supply to the DC bus 30 side.

[0083] Under transient conditions of sudden external load surges, data shows that in traditional solutions, the battery pack directly bears all load changes, with its peak output current reaching 179.6A to 185.1A, far exceeding the steady-state output level of the system. At this time, the internal resistance voltage drop causes the bus voltage fluctuation to approach 1.5V. After implementing the control method of this invention, based on the real-time identification of the load-side surge current change rate, the supercapacitor outputs compensation current through the DC / DC converter module. Test results show that, due to the clamping of the DC bus 30 voltage, the peak output current of the lithium iron phosphate battery pack decreases and stabilizes at 112.8A to 115.3A, eliminating the large current pulse caused by high-rate discharge. At this time, the DC bus 30 voltage fluctuation amplitude is reduced to 0.15V to 0.22V. This indicates that through the combination of hardware structure and control logic, the system achieves current diversion and isolation of surge current, avoiding the risk of fatigue damage to the cell structure caused by high-frequency peak current.

[0084] After the system's long-term discharge ends and the mains power is restored, the internal thermal data reflects the impact of the charging strategy on the ambient temperature rise. In the traditional solution, under the multi-medium synchronous high-current charging mode, the highest temperature rise rate inside the chassis is 2.41℃ / min to 2.55℃ / min, which may cause local heat accumulation in the compact chassis. This invention adopts a priority-based energy scheduling algorithm, which prioritizes high-power recharge to the low-internal-resistance supercapacitor, and then performs low-current slow charging on the lithium iron phosphate battery. The test results show that after implementing the hierarchical timing staggered control, the highest temperature rise rate of the system decreases to 1.35℃ / min to 1.42℃ / min. The decrease in the ambient temperature rise value indicates that the hierarchical slow charging logic disperses the charging heat power along the time axis, reduces the difficulty of the equipment relying on passive heat dissipation to maintain the operating temperature, and extends the high-temperature service life of the system's core components.

[0085] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hybrid energy storage uninterruptible power supply system combining lithium iron phosphate and supercapacitors, characterized in that, The system includes: A rectifier module, wherein the AC input terminal of the rectifier module is connected to an external mains power supply, and the DC output terminal of the rectifier module is connected to a DC bus; An inverter module, wherein the DC input terminal of the inverter module is connected to the DC bus, and the AC output terminal of the inverter module is connected to an external load; A lithium iron phosphate energy storage module, wherein the lithium iron phosphate energy storage module is directly connected in parallel to the DC bus; A supercapacitor energy storage module, wherein the supercapacitor energy storage module is connected to the DC bus via a bidirectional buck-boost DC-DC converter module; A bidirectional buck-boost DC-DC converter module, wherein the low-voltage side of the bidirectional buck-boost DC-DC converter module is connected to the supercapacitor energy storage module, and the high-voltage side of the bidirectional buck-boost DC-DC converter module is connected to the DC bus; The main control module is connected to the lithium iron phosphate energy storage module, the supercapacitor energy storage module and the bidirectional buck-boost DC-DC converter module respectively.

2. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, The main control module has a three-dimensional mapping matrix pre-stored inside regarding the conversion efficiency of the bidirectional buck-boost DC-DC converter module; The main control module is configured to acquire the equivalent DC-side power demand input of the inverter module and the real-time terminal voltage of the supercapacitor energy storage module, and dynamically correct the switching frequency and duty cycle of the bidirectional buck-boost DC-DC converter module according to the objective function. The objective function is jointly determined by the high-frequency conversion efficiency of the bidirectional buck-boost DC-DC converter module in transient compensation state, the transient high-frequency demand component in the external load power, the real-time operating voltage of the DC bus, and the real-time terminal voltage of the supercapacitor energy storage module.

3. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, During the initial cold start phase of the system, the main control module is configured to delay the connection of the lithium iron phosphate energy storage module and control the rectifier module to establish the base voltage of the DC bus according to a preset constant voltage ramp rate. When the voltage difference between the open-circuit voltage of the lithium iron phosphate energy storage module and the operating voltage of the DC bus is less than a preset voltage difference allowable threshold, the main control module outputs a signal to close the circuit where the lithium iron phosphate energy storage module is located, so that the lithium iron phosphate energy storage module is connected to the DC bus.

4. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, When the actual ambient temperature is determined to be lower than the set low temperature protection safety threshold, the main control module is configured to restrict the lithium iron phosphate energy storage module from outputting high-power pulses to the DC bus; The main control module outputs a high-frequency alternating duty cycle sequence to the bidirectional buck-boost DC-DC converter module, and controls the bidirectional buck-boost DC-DC converter module to perform high-frequency reciprocating micro-amplitude charging and discharging actions on the supercapacitor energy storage module. The Joule heat generated by the equivalent series internal resistance of the supercapacitor energy storage module when the alternating current passes through it is used to compensate for environmental heat. The main control module is configured to calculate the heat generated based on the instantaneous value of the high-frequency compensated AC current, the equivalent series internal resistance of the supercapacitor energy storage module, and the cumulative duration of the high-frequency action.

5. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, The main control module is configured to collect the AC input voltage at the front end of the rectifier module in real time, and perform dual judgment logic by combining the lower limit of the effective voltage value and the instantaneous rate of change of the voltage. When the effective value of the current AC input voltage is less than the set undervoltage protection lower limit, and the absolute value of the instantaneous rate of change of the AC input voltage is greater than or equal to the set rate of change trigger threshold, the main control module determines that a substantial interruption of the mains power has occurred and triggers the feedforward takeover procedure of the active power branch.

6. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, During the transient period of mains power outage and energy source switching or during sudden load impact, the main control module is configured to instantaneously increase the output reference voltage of the bidirectional buck-boost DC-DC converter module, so that the instantaneous operating voltage of the DC bus is raised to the level equal to or higher than the current open-circuit voltage of the lithium iron phosphate energy storage module. The potential difference between the two ends of the branch where the lithium iron phosphate energy storage module is located is controlled to be zero or to be negative, thereby limiting the transient output current of the lithium iron phosphate energy storage module to a set safe level.

7. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, During the long-term backup phase of continuous mains power interruption, when the terminal voltage of the supercapacitor energy storage module is detected to drop to the set discharge lower limit threshold, the main control module is configured to introduce a ramp decay function that decreases with time to dynamically lower the output current reference value of the bidirectional buck-boost DC-DC converter module, so that the voltage on the DC bus will break free from clamping and drop back. When the DC bus voltage drops to the current open-circuit voltage of the lithium iron phosphate energy storage module, a forward conduction voltage difference is established in the branch where the lithium iron phosphate energy storage module is located, smoothly filling the power gap caused by the withdrawal of the supercapacitor energy storage module.

8. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, The main control module is configured to acquire the battery cycle count, historical average charge / discharge depth, and current real-time cell operating temperature of the lithium iron phosphate energy storage module, and to execute a dynamic current limiting strategy in conjunction with the battery management system configured in the lithium iron phosphate energy storage module. The main control module is configured to multiply the rated current limiting reference value by a temperature derating factor related to the current cell operating temperature, and then multiply it by a health derating factor related to the number of battery cycles and the historical average charge and discharge depth, to calculate the dynamic discharge current limiting threshold, thereby derating the output capacity of the lithium iron phosphate energy storage module.

9. The lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to claim 1, characterized in that, The main control module is configured to acquire instantaneous current data on the DC input side of the inverter module and use a digital high-pass filtering algorithm combined with discrete differential operation to separate the transient high-frequency components in the load current. The main control module is configured to calculate the time derivative of the transient high-frequency component and compare it with the set impact current identification threshold. If the time derivative of the transient high-frequency component is greater than or equal to the set impact current identification threshold, it is determined that an impact load has occurred. The main control module is also configured to calculate the short-term limit support time based on the current equivalent capacity and operating voltage of the supercapacitor energy storage module and send a graded power outage warning signal to the outside when the lithium iron phosphate energy storage module experiences a hardware abnormality and encounters a mains power outage.

10. A control method for a hybrid energy storage uninterruptible power supply combining lithium iron phosphate and supercapacitors, characterized in that, The method using the lithium iron phosphate and supercapacitor hybrid energy storage uninterruptible power supply system according to any one of claims 1 to 9 includes the following steps: During normal mains power operation, the rectifier module converts AC power to DC power to stabilize the DC bus voltage. The lithium iron phosphate energy storage module is connected in parallel to the DC bus to maintain floating charge. The main control module controls the bidirectional buck-boost DC-DC converter module to operate at a reduced voltage to charge the supercapacitor energy storage module to full charge. During the momentary interruption of mains power, the main control module detects the drop in AC input voltage and controls the bidirectional buck-boost DC-DC converter module to start boost output. The DC bus voltage is supported solely by the supercapacitor energy storage module. The main control module limits the discharge rate of the lithium iron phosphate energy storage module so that the supercapacitor energy storage module can provide instantaneous power. During the long-term backup phase of continuous mains power outage, when the voltage of the supercapacitor energy storage module drops to a set threshold, the main control module controls the bidirectional buck-boost DC-DC converter module to reduce its output or shut down, and the system switches to the lithium iron phosphate energy storage module to discharge to the DC bus to maintain power supply. During the load surge compensation phase, when an inrush current is detected from an external load, the main control module adjusts the bidirectional buck-boost DC-DC converter module to output peak power instantaneously, and the supercapacitor energy storage module bears the inrush current, while the lithium iron phosphate energy storage module maintains its original discharge state. During the mains power restoration phase, the rectifier module re-establishes the DC bus voltage, and the main control module prioritizes controlling the bidirectional buck-boost DC-DC converter to recharge the supercapacitor energy storage module. After determining that the supercapacitor energy storage module is fully charged, the control system then charges the lithium iron phosphate energy storage module.

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